WO2021117829A1 - Corps fritté à base de nitrure de silicium de type plaque et son procédé de fabrication - Google Patents

Corps fritté à base de nitrure de silicium de type plaque et son procédé de fabrication Download PDF

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WO2021117829A1
WO2021117829A1 PCT/JP2020/046124 JP2020046124W WO2021117829A1 WO 2021117829 A1 WO2021117829 A1 WO 2021117829A1 JP 2020046124 W JP2020046124 W JP 2020046124W WO 2021117829 A1 WO2021117829 A1 WO 2021117829A1
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silicon nitride
sintered body
less
weight
earth metal
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Japanese (ja)
Inventor
猛 藤永
あき 猪野
道夫 本田
昌孝 藤永
耕司 柴田
山田　哲夫
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Ube Corp
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Ube Industries Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
    • C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • C04B35/587—Fine ceramics
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • C04B35/593—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride obtained by pressure sintering
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/03—Use of materials for the substrate

Definitions

  • the present invention relates to a plate-shaped silicon nitride sintered body containing ⁇ -type silicon nitride as a main component, which has particularly high thermal conductivity, high mechanical strength and toughness, and is suitable for use as an insulating substrate and a circuit board.
  • the present invention relates to a silicon nitride sintered body in the form of a silicon nitride and a method for producing the same.
  • Silicon nitride sintered bodies are used for various mechanical parts and wear-resistant parts because they have excellent mechanical strength, toughness, and thermal shock resistance, and they are also electrically insulated by utilizing high electrical insulation and excellent thermal conductivity. It is also applied to materials.
  • As conventional electrically insulating ceramics aluminum oxide, aluminum nitride and the like are known. Since aluminum oxide has a low thermal conductivity, there is a problem that heat dissipation is insufficient for application to power semiconductors and the like.
  • aluminum nitride has high thermal conductivity and excellent heat dissipation, but has low mechanical strength and fracture toughness, so that there is a problem that cracks occur in the module assembly process.
  • Patent Document 1 states that Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb are found in the grain boundary phase composed of oxide or oxynitride. It contains 0.5% by weight or more and 10% by weight or less of one or more metal elements selected from among them, the Al atom content in the grain boundary phase is 1% by weight or less, and the pore ratio is 5%.
  • a high thermal conductivity silicon nitride sintered body in which the proportion of ⁇ -type silicon nitride grains having a minor axis diameter of 5 ⁇ m or more is 10% by volume or more and 60% by volume or less.
  • this sintered body is manufactured under extremely harsh high temperature and high pressure conditions of a firing gas pressure of 100 to 300 atm and a firing temperature of 2000 ° C., and an expensive sintering furnace that can be used under high temperature and high pressure is required. Therefore, there is a problem that it leads to an increase in cost. Therefore, it is required to manufacture a silicon nitride sintered substrate at a lower atmospheric pressure.
  • a sintered body obtained from a CIP molded body having a thickness of 4 mm or a thickness of 6 mm is ground to form a plate-like product having a thickness of about 1 mm.
  • the chemical composition and microstructure of the silicon nitride sintered body are significantly different between the surface layer and the inside, the physical characteristics (heat) of the sintered body finished into a plate-like material having a thickness of about 1 mm by grinding. (Conductivity and mechanical properties) cannot be used as a substitute for the physical property values (thermal conductivity and mechanical properties) of a silicon nitride sintered substrate for mass production.
  • D 10 , D 50 and D 90 have particle size distributions of 0.5 to 0.8 ⁇ m, 2.5 to 4.5 ⁇ m and 7.5 to 10.0 ⁇ m, respectively, and contain oxygen.
  • Silicon nitride powder having an amount of 0.01 to 0.5 wt% and having a proportion of ⁇ -type silicon nitride particles present in particles having an average particle size (D 50 ) or more of 1 to 50% has good sheet formability. It is described to provide a sintered body having excellent, high strength, high toughness, and excellent heat dissipation.
  • the D 50 of the silicon nitride powder has a large value of 2.5 to 4.5 ⁇ m, and the aspect ratio of the ⁇ -type silicon nitride particles present therein is 7.0 or more, and MgO / Y 2 O 3
  • the bending strength is 790 MPa or less and the breaking toughness value is 7.5 MPa ⁇ m or less, probably because the weight ratio is as large as 3.0.
  • the thermal conductivity of the sample having a bending strength of 790 MPa is 85 W / (m ⁇ K) or less.
  • the number of columnar ⁇ -type silicon nitride particles having a major axis length of more than 10 ⁇ m is 20,000 per 1 mm 2.
  • a silicon nitride substrate made of a body is disclosed.
  • the examples and MgO / Y 2 O 3 weight ratio calculated from the sintering aid composition described in Table 1 showing a comparative example is 0.055 ⁇ 0.194 (wt / wt) , The blending ratio of MgO is small. Probably because of this, although the obtained silicon nitride substrate has excellent electrical characteristics, the thermal conductivity is 90 W / (m ⁇ K) or less, and the bending strength is 750 MPa or less, which are low values.
  • Patent Document 5 discloses a silicon nitride substrate in which the orientation ratio of silicon nitride particles in a plane perpendicular to the thickness direction is defined.
  • the amount of MgO added is as large as 3 wt% or more
  • the degree of orientation determined from the ratio of the X-ray diffraction line intensity is as large as 0.28 to 0.33 on the surface and 0.18 to 0.29 on the inside.
  • the thermal conductivity of the examples is 93 W / (m ⁇ K) or less.
  • the three-point bending strength of the obtained silicon nitride sintered body is 864 MPa or less, and the fracture toughness value is 6.8 MPa ⁇ m or less.
  • the grain boundary phase is an amorphous phase and a MgSiN 2 crystal phase
  • the silicon nitride board with improved thermal conductivity by containing no crystalline phase is disclosed that includes a rare earth element and (RE) Has been done.
  • RE rare earth element
  • characteristic values of a silicon nitride sintered body using a silicon nitride powder having a specific surface area of 5 to 30 m 2 / g produced by rotary kiln firing as a raw material are disclosed.
  • Tables 3 and 4 show the bending of the silicon nitride sintered body obtained by adding yttrium oxide and aluminum oxide as sintering aids and sintering at 1780 ° C. for 2 hours in a nitrogen gas atmosphere, respectively.
  • the bending strength and thermal conductivity of the silicon nitride sintered body obtained by adding yttrium oxide and magnesium oxide as sintering aids and sintering at 1900 ° C. for 22 hours under pressurized nitrogen gas can be obtained.
  • the bending strength of the silicon nitride sintered body obtained by sintering at 1780 ° C. for 2 hours in a nitrogen gas atmosphere is 1020 to 1220 MPa. It is a common general knowledge of those skilled in the art that a silicon nitride sintered body to which aluminum oxide is added exhibits a remarkably low thermal conductivity. On the other hand, according to Table 4, the silicon nitride sintered body to which yttrium oxide and magnesium oxide are added shows a high thermal conductivity of 130 to 142 W / mK, but at a high temperature of 1900 ° C. to 22 hours for a long time.
  • Patent Document 8 discloses silicon nitride ceramics in which the c-axis of ⁇ -silicon nitride particles is oriented in the thickness direction of the substrate.
  • the raw material slurry is placed in a molding mold, and the slurry is dried in a rotating magnetic field about a central axis along the thickness direction of the mold to form a molded product made of raw material powder. Since it is a special molding method, it has not reached the mass production stage.
  • the c-axis of the ⁇ silicon nitride particles is the thickness direction of the substrate. Since it is oriented in the direction of, the bending strength of the sintered substrate is remarkably lowered, which causes a problem in terms of strength characteristics.
  • Patent Document 9 has particles having a minor axis diameter of 2 ⁇ m or more, and controls the total amount of impurities of oxygen, Al, Ca, and Fe in the silicon nitride granules to 1500 ppm or less, thereby achieving thermal conductivity and machinery.
  • a silicon nitride sintered body having improved properties and a method for producing the same are described.
  • a large amount of sintering aid is added in which the total amount of yttrium and / or lanthanoid elements is 8 to 15% by weight in terms of oxide, and the total amount of yttrium and / or lanthanoid elements is 8% by weight in terms of oxide.
  • the room temperature strength remains at 338 to 638 MPa (803 MPa only in Example 24), and the fracture toughness value remains at 6.9 MPa ⁇ m or less. Further, neither the average particle size nor the specific surface area of the silicon nitride powder is described, and the high levels of Al, Ca and Fe contents of the powders A to M of 190 ppm to 2220 ppm also cause a decrease in strength.
  • Non-Patent Document 1 it is reported that the theoretical thermal conductivity of ⁇ -type silicon nitride calculated from MD simulation is 170 W / m ⁇ K in the a-axis direction and 450 W / m ⁇ K in the c-axis direction. Therefore, it is unclear what it means to define the minor axis diameter (particle size in the a-axis direction) by ignoring the particle size in the long axis (c axis) direction, which has high thermal conductivity.
  • a columnar silicon nitride whisker is added to the raw material powder in advance and formed, and a microstructure in which grains are selectively grown with the whisker as a core in the sintering process is constructed to construct a microstructure, thereby providing thermal conductivity.
  • a method for producing a silicon nitride sintered body in which the above is improved is described.
  • the aspect ratio (ratio of average length to average diameter) of the whiskers is as large as 10 or more, not only is molding difficult, but densification in the sintering process is significantly hindered. Therefore, the whiskers are hydroheat-treated in advance to oxidize the surface and promote sinterability.
  • the hydrothermal treatment is not only a complicated process of 96 hours at 120 ° C., but also increases the oxygen content of the obtained sintered body, so that it is difficult to obtain a sintered body having high thermal conductivity.
  • the CIP molded body is sintered, the bending strength is 830 MPa or less, and the fracture toughness value is 8 MPa ⁇ m or less.
  • Patent Document 11 states that the ⁇ fraction is 30 to 100%, the amount of oxygen is less than 0.5 wt%, the average particle size is 0.2 to 10 ⁇ m, the aspect ratio is 10 or less, and the particles.
  • the oxygen content of the raw material Si 3 N 4 powder is extremely low, the average particle size is large and the aspect ratio is 4 or more, and the impurity Fe content and Al content are high, and MgO / RExOy as an auxiliary component is used.
  • the bending strength is 850 MPa or less, probably because the weight ratio is 1.5 or more, and the breaking toughness value has not been measured.
  • the scanning electron microscope of the silicon nitride powder shown in FIG. 1 also shows that the particles are very coarse.
  • a silicon nitride material having a ⁇ fraction of 30 to 100%, an oxygen content of 0.5 wt% or less, an average particle size of 0.2 to 10 ⁇ m, and an aspect ratio of 10 or less.
  • the silicon nitride particles obtained by blending a sintering aid containing the above elements and holding the mixture at 1800 ° C. to 1950 ° C. for 5 to 40 hours in a nitrogen atmosphere of 0.5 MPa for sintering.
  • a silicon nitride sintered body in which 5 particles / ⁇ m 2 or more are present is disclosed.
  • the silicon nitride powder having a ⁇ fraction of 30 to 100%, an average particle size of 0.2 to 10 ⁇ m, and an aspect ratio of 10 or less is obtained by firing ⁇ -type silicon nitride powder at a high temperature.
  • the coarse and low oxygen content is described (the same synthetic conditions as those of the silicon nitride powder disclosed in Patent Document 11 are described).
  • Patent Document 14 describes a silicon nitride sintered body in which at least one rare earth element selected from rare earth elements (RE) containing Mg, Lu and Y is added as a sintering aid, and is a grain boundary phase. At least (RE, Lu) 4 Si 2 O 7 N 2 crystals are precipitated in the silicon nitride particles, and fine particles having a particle size of 100 nm or less containing Mg or Lu and an O element are present in the silicon nitride particles.
  • RE rare earth elements
  • Lu 2 O 3 is an expensive substance called 200 times the Y 2 O 3 (Y 2 O 3 is Lu 2 O 3 is 671 US dollars against 3.35 US dollars (China F.o.B.Export It is not practical to use prices 09-Mar-2018 (USD / kg)) as a sintering aid, as will be apparent from Tables 1, 2 and 3 showing the results of Examples 1-3. Most of the samples are prepared under the harsh conditions of holding at 1950 ° C. for 20 hours, and the oxygen volatility ⁇ O in the sintering process is a very large value of 53.5% to 96.2%.
  • the obtained sintered body Under harsh sintering conditions such as those in which the oxygen volatilization rate is large, the obtained sintered body has significant color unevenness, and the composition and structure inside the sintered body fluctuate greatly, so that a uniform sintered body can be obtained. Therefore, the bending strength is reduced to 799 MPa or less.
  • the sample obtained under relatively mild sintering conditions of 1900 ° C. or less has an oxygen volatility ⁇ O of 10.7% to 22.7%. Because it is too small, the MgO content in the composition in the sintered body is high (1.30 mol%, 3.20 mol%, 5.00 mol% and 8.00 mol%, respectively), and the appropriate MgO content. There is no sample with a large amount.
  • Patent Document 3 in order to achieve both high thermal conductivity and high mechanical strength, a high atmospheric pressure of 40 atm (4 MPa) or more is required, so a sintering furnace that can be used under high pressure is required. .. As can be seen from the examples, at 9 atm (0.9 MPa), the characteristics are significantly insufficient in terms of both thermal conductivity and mechanical strength.
  • the present invention is a plate-shaped silicon nitride baked material having both high thermal conductivity and excellent mechanical properties at a lower pressure without increasing the atmospheric pressure at the time of sintering as in Patent Document 3.
  • the purpose is to provide a unity.
  • the present invention provides the following aspects.
  • various aspects of the present invention will be described as a method for producing a plate-shaped silicon nitride sintered body, a blend of silicon nitride powder for producing a plate-shaped silicon nitride sintered body, and the like. It is effective in each side of a powder formulation for producing a plate-shaped silicon nitride sintered body, a plate-shaped silicon nitride sintered body, and a silicon nitride sintered body substrate, and is particularly effective in that side surface.
  • the present invention (I) a) The ⁇ fraction is 10% or less, the oxygen content is 0.75% by weight or more and 2.2% by weight or less, and the specific surface area by the BET method is 7.0 m 2 / g or more and 13.0 m 2 / g or less. 40 to 94 parts by weight of the ⁇ -type first silicon nitride powder having an average particle size of 0.55 ⁇ m or more and 1.5 ⁇ m or less in the volume-based particle size distribution measured by the laser diffraction / scattering method.
  • the ⁇ fraction is 60% or more and 100% or less, the oxygen content is 0.55% by weight or more and 2.0% by weight or less, and the specific surface area by the BET method is 2.5 m 2 / g or more and 10.0 m 2 /.
  • the value is less than g and smaller than the specific surface area of the first silicon nitride powder, and the average particle size in the volume-based particle size distribution measured by the laser diffraction scattering method is 0.7 ⁇ m or more and less than 2.0 ⁇ m.
  • a compounding ratio such that the weight ratio of the alkaline earth metal oxide to the rare earth metal oxide satisfies 0.40 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.4.
  • a starting composition containing 3.2 to 7.0% by weight of an alkaline earth metal oxide and a rare earth metal oxide having an effective ion radius of 87 pm or more based on the total weight of the silicon nitride raw material and the sintering aid.
  • a green sheet is prepared from the starting composition by a sheet forming process.
  • (III) Solvent the green sheet, and then (IV) By sintering while maintaining the maximum holding temperature in the temperature range of 1790 ° C.
  • Non-Patent Document 2 Shannon et. Al.
  • Dy 107 pm (6 coordinates), Er (erbium) 89 pm (6 coordinates), Ho (holmium) 90.1 pm (6 coordinates), La (lantern) 103.2 pm (6 coordinates), Lu (yttrium) 86.1 pm (6 coordinates), Nd (neodymium) 98.3 pm (6 coordinates) ), Sc (scandium) 74.5 pm (6 coordinates), Y (yttrium) 90 pm (6 coordinates), Yb (ittelbium) 102 pm (6 coordinates).
  • the ratio of the measured alkaline earth metal content to the measured rare earth metal content as the sintered body is determined by the oxide standard of the alkaline earth metal oxide and the rare earth metal oxide in the sintered body.
  • the alkaline earth metal is magnesium and the rare earth metal is erbium, 0.07 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.23, and the alkaline earth metal is magnesium.
  • the rare earth metal is yttrium, 0.06 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.11.
  • One aspect of the present invention is characterized in that a plate-shaped silicon nitride sintered body having an actually measured oxygen content of 1.3% by weight or more and 2.8% by weight or less is produced. To do.
  • the silicon nitride sintered body has a plate-like shape having a thickness of 1.5 mm or less and a thickness / area ratio of 0.015 (1 / mm) or less.
  • a method for producing a silicon nitride sintered body is provided.
  • the plate-shaped silicon nitride sintered body preferably has a plate surface surface layer portion perpendicular to the thickness direction of 0.03 mm or less per side by grinding or polishing.
  • a plate-shaped silicon nitride sintered body is produced by using a starting composition having a 95% diameter of 10.0 ⁇ m or less in the cumulative particle size distribution curve of the second silicon nitride powder. It is characterized by that.
  • the aluminum content and iron content of the second silicon nitride powder are 100 ppm or less, respectively, and the chromium content, nickel content, tungsten content, copper content and manganese content are high. It is characterized in that a plate-shaped silicon nitride sintered body is produced by using a starting composition of 30 ppm or less each.
  • the sintering aid contains silicon dioxide powder in addition to the alkaline earth metal oxide and the rare earth metal oxide, and silicon dioxide is based on the total weight of the silicon nitride raw material and the sintering aid.
  • a plate-shaped silicon nitride sintered body is produced by using a starting composition having a content of 0.1% by weight or more and 2.5% by weight or less.
  • the total content of the measured alkaline earth metal and the measured rare earth metal as a sintered body is 1.5, which is the metal element content derived from the sintering aid excluding silicon. It is characterized in that the above-mentioned plate-shaped silicon nitride sintered body having a weight of% by weight or more and 4.5% by weight or less is produced.
  • the measured content of the total of the alkaline earth metal and the rare earth metal as the sintered body is measured, and the alkaline earth metal oxide and the rare earth metal oxide in the sintered body are determined based on the oxide.
  • the total content it is 2.1% by weight or more and 6.2% by weight or less.
  • the alkaline earth metal oxide is magnesium oxide
  • the rare earth metal oxide having an effective ion radius of 87 pm or more is at least one oxide selected from yttrium oxide, elbium oxide and itterbium oxide. It is characterized in that the plate-shaped silicon nitride sintered body is produced.
  • sintering such as atmospheric gas pressure, maximum holding temperature, and holding time at maximum holding temperature so that the weight loss rate before and after sintering is 2.5% by weight to 8.0% by weight.
  • the nitride obtained when the surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less is irradiated with X-rays.
  • a plane obtained by grinding from a surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less to the inside by 0.08 mm or more is irradiated with X-rays.
  • the ratio ⁇ I (200) + I (210) ⁇ / ⁇ 2 ⁇ I (101) ⁇ of / 2 to the diffraction intensity I (101) of the (101) plane is 1.10 or more and 1.40 or less.
  • the number of particles having a major axis diameter of more than 10 ⁇ m among the columnar ⁇ -type silicon nitride particles is 1200 or more per 1 mm 2 of the cut surface.
  • the major axis diameter of the columnar ⁇ -type silicon nitride particles is based on the area of the total silicon nitride particles. It is characterized in that a plate-shaped silicon nitride sintered body having an area fraction of 3 ⁇ m or more and an area fraction of 45% or more and 87% or less is produced.
  • the cumulative particle size distribution of the major axis diameter represented by the area% of the columnar ⁇ -type silicon nitride particles is observed. It is characterized by producing a plate-shaped silicon nitride sintered body in which the 50% diameter D 50 on the curve is 2.8 ⁇ m or more and 6.8 ⁇ m or less, and the 80% diameter D 80 is 8.1 ⁇ m or more and 12.5 ⁇ m or less. And.
  • the area division of the grain boundary phase is based on the total area of the total silicon nitride particles and the grain boundary phase. As a result, a plate-shaped silicon nitride sintered body having an area% of 20 area or less is produced.
  • magnesium oxide has an effective ion radius of 87 pm with a blending ratio such that the weight ratio of magnesium oxide and rare earth metal oxide satisfies 0.42 ⁇ magnesium oxide / rare earth metal oxide ⁇ 1.1.
  • the above rare earth metal oxides and silicon dioxide are added, and the amount of the sintering aid added is 4.0 to 6.5% by weight based on the total weight of the silicon nitride powder and the sintering aid.
  • the plate-shaped molded body (green sheet) produced by the sheet molding process is degreased, and then the maximum holding temperature is 1820 ° C. or higher and 1910 ° C.
  • the ratio of the measured magnesium content to the measured rare earth metal content was 0.07 ⁇ measured magnesium content / measured rare earth metal content ⁇ 0.75.
  • the total content of the measured magnesium and the above-mentioned measured rare earth metal content, the metal element content derived from the sintering aid excluding silicon is 1.6% by weight or more and 4.0% by weight or less, and the measured oxygen content is contained.
  • the amount is 1.6% by weight or more and 2.6% by weight or less, and the relative density is 98% or more. It is characterized by that.
  • the maximum holding temperature may be in the temperature range of 1790 ° C. or higher and 1910 ° C. or lower.
  • the first silicon nitride powder and the second silicon nitride powder specified in "Method A" (paragraph 0020) described above. It contains silicon nitride powder, ⁇ fraction is 7% or more and 64% or less, oxygen content is 0.74% by weight or more and 1.95% by weight or less, and specific surface area by BET method is 6.3 m2 / g or more and 12.8 m2.
  • the average particle size in the particle size distribution is 0.66 ⁇ m or more and 1.5 ⁇ m or less
  • the obtained frequency distribution curve has two peaks, and the peak top of the peak is 0.5 to 1.2 ⁇ m. Within the range (first peak) and the range of 1.1 to 3.8 ⁇ m (second peak), the second peak is 0.5 to 3.0 ⁇ m larger than the first peak.
  • a silicon nitride powder for producing a plate-shaped silicon nitride sintered body can also have the same aspects and characteristics as those described above as a modification of "Method A" as long as it can be applied to the silicon nitride powder formulation.
  • Raw material powder composition for producing a plate-shaped silicon nitride sintered body the first silicon nitride powder having the characteristics specified in the above-mentioned "Method A" (paragraph 0020) and the first silicon nitride powder.
  • a raw material powder composition for producing a plate-shaped silicon nitride sintered body containing a second silicon nitride powder and a sintering aid is provided.
  • This raw material powder composition can also have the same aspects and characteristics as those described above as a modification of "Method A" as long as it can be applied to the raw material powder composition.
  • the plate-shaped silicon nitride sintered body of the present invention has an actually measured alkaline earth metal content and an actually measured rare earth metal content (the effective ionic radius of the rare earth metal is 87 pm).
  • the ratio with (the above) is 0.05 ⁇ measured alkaline earth metal content / measured rare earth metal content ⁇ 0.85.
  • the measured value of the metal element content derived from the sintering aid excluding silicon, which is the sum of the measured alkaline earth metal content and the measured rare earth metal content, is 1.5% by weight or more and 4.5% by weight or less.
  • the relative density is 98% or more.
  • This plate-shaped silicon nitride sintered body can be produced by sintering a plate-shaped molded body produced by a sheet molding process at an atmospheric gas pressure of 3 MPa or less.
  • this plate-shaped silicon nitride sintered body is obtained by grinding from a surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less to the inside by 0.08 mm or more.
  • the ratio of (210) ⁇ / 2 to the diffraction intensity I (101) on the (101) plane ⁇ I (200) + I (210) ⁇ / ⁇ 2 ⁇ I (101) ⁇ is 1.10 or more and 1.40 or less. is there.
  • the ratio of / 2 to the diffraction intensity I (101) of the (101) plane ⁇ I (200) + I (210) ⁇ / ⁇ 2 ⁇ I (101) ⁇ is expressed as “diffraction intensity ratio related to c-axis orientation”. ..
  • the measured content of the total of the alkaline earth metal and the rare earth metal as the sintered body is measured, and the alkaline earth metal oxide and the rare earth metal oxide in the sintered body are determined based on the oxide.
  • the alkaline earth metal is magnesium and the rare earth metal is ittrium, it is 2.1% by weight or more and 6.2% by weight or less.
  • the plate-shaped silicon nitride sintered body has an actually measured oxygen content of 1.3% by weight or more and 2.8% by weight or less as a sintered body.
  • the number of particles having a major axis diameter of more than 10 ⁇ m was 1200 or more and 10,000 or less per 1 mm 2 of the cut surface. It is characterized by being a plate-shaped silicon nitride sintered body.
  • the plate-shaped silicon nitride sintered body is characterized in that the thickness is 1.5 mm or less and the thickness / area ratio is 0.015 (1 / mm) or less.
  • the plate-shaped silicon nitride sintered body preferably has a plate surface surface layer portion perpendicular to the thickness direction of 0.03 mm or less per side by grinding or polishing.
  • the plate-shaped silicon nitride sintered body is obtained when a surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less is irradiated with X-rays.
  • the above-mentioned "diffraction intensity ratio related to c-axis orientation" is 1.10 or more and 1.50 or less.
  • the present invention in the X-ray diffraction pattern of ⁇ -type silicon nitride obtained when the surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less is irradiated with X-rays, grain boundaries.
  • the main peak ((22-1)) of the J phase (RE 4 Si 2 O 7 N 2 ) which does not substantially contain the crystal phase of the Mg compound composed of MgSiN 2 or the like and constitutes the grain boundary phase.
  • the sum of the diffraction intensity of the surface) and the diffraction intensity of the main peak ((211) surface) of the N-merylite phase (RE 2 Si 3 O 3 N 4) is the sum of the diffraction intensity of the ⁇ -type silicon nitride in the silicon nitride sintered body (200). ) Is a plate-shaped silicon nitride sintered body having a surface diffraction intensity of less than 0.07 (including zero).
  • the silicon nitride sintered body is a plate-shaped silicon nitride sintered body in which color tone unevenness is suppressed.
  • the alkaline earth metal oxide is magnesium oxide
  • the rare earth metal oxide having an effective ion radius of 87 pm or more is at least one oxide selected from yttrium oxide, erbium oxide and ytterbium oxide. It is characterized by that.
  • the plate-shaped silicon nitride sintered body has a measured magnesium content as a sintered body and the measured rare earth metal content (rare earth metal has an effective ion radius of 87 pm or more). ) Is 0.07 ⁇ measured magnesium content / measured rare earth metal content ⁇ 0.75, and the above-mentioned measured magnesium content and the above-mentioned measured rare earth metal content are summed, and sintered excluding silicon.
  • the content of the metal element derived from the auxiliary agent is 1.6% by weight or more and 4.0% by weight or less.
  • the major axis diameter of the columnar ⁇ -type silicon nitride particles is based on the area of the total silicon nitride particles.
  • Plate-shaped silicon nitride sintering having an area fraction of 3 ⁇ m or more particles of 45% or more and 87% or less and an area fraction of particles having a major axis diameter of more than 10 ⁇ m of 6.5% or more and 39% or less. It is characterized by being a body.
  • the cumulative particle size distribution of the major axis diameter represented by the area% of the columnar ⁇ -type silicon nitride particles is observed.
  • a plate-shaped silicon nitride sintered body composed of particles having a 50% diameter D 50 of 2.8 ⁇ m or more and 6.8 ⁇ m or less and an 80% diameter D 80 of 8.1 ⁇ m or more and 12.5 ⁇ m or less in the curve. It is characterized by being.
  • the area division of the grain boundary phase is based on the total area of the total silicon nitride particles and the grain boundary phase. It is characterized by being a plate-shaped silicon nitride sintered body having an area of 20 area% or less.
  • One aspect of the present invention is characterized in that the measured oxygen content of the sintered body is 1.6% by weight or more and 2.6% by weight or less.
  • the ratio of the measured magnesium content as a sintered body to the measured rare earth metal content is 0.09 ⁇ measured magnesium.
  • the content / measured rare earth metal content ⁇ 0.65, and the total of the measured magnesium content and the measured rare earth metal content, the metal element content derived from the sintering aid excluding silicon is 1. It is characterized in that it is 7% by weight or more and 3.5% by weight or less.
  • the measured aluminum content and the measured iron content of the plate-shaped silicon nitride sintered body are 60 ppm or less, respectively, and the measured chromium content, the measured nickel content, the measured tungsten content, and the measured iron are measured.
  • the copper content and the measured manganese content are each 18 ppm or less.
  • One aspect of the present invention is characterized in that the measured oxygen content of the sintered body is 1.9% by weight or more and 2.46% by weight or less.
  • the present invention it is obtained when a plane obtained by grinding from a surface polished to an arithmetic mean roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less to the inside by 0.08 mm or more is irradiated with X-rays.
  • the "diffraction intensity ratio related to the c-axis orientation" is 1.20 or more and 1.40 or less.
  • the cumulative particle size distribution of the major axis diameter represented by the area% of the columnar ⁇ -type silicon nitride particles is observed.
  • a plate-shaped silicon nitride sintered body composed of particles having a 50% diameter D 50 of 5.5 ⁇ m or more and 6.8 ⁇ m or less and an 80% diameter D 80 of 9.5 ⁇ m or more and 12 ⁇ m or less in the curve. It is characterized by that.
  • the thermal conductivity is 110 W / (m ⁇ K) or more at room temperature
  • the four-point bending strength is 900 MPa or more at room temperature
  • the K IC is 8.0 MPa ⁇ m or more.
  • silicon Nitride Sintered Substrate In one aspect of the present invention, a substrate using the plate-shaped silicon nitride sintered body described in each of the above paragraphs is provided. These silicon nitride sintered substrates obtained by the present invention are suitable for insulating substrates or circuit boards because they are excellent in insulating properties and thermal conductivity.
  • a plate-shaped silicon nitride sintered body having both high thermal conductivity and excellent mechanical properties is provided, and the plate-shaped silicon nitride sintered body is still available. It can be manufactured without increasing the atmospheric pressure at the time of sintering.
  • the present invention is one aspect of the present invention.
  • the ⁇ fraction is 60% or more and 100% or less, the oxygen content is 0.55% by weight or more and 2.0% by weight or less, and the specific surface area by the BET method is 2.5 m 2 / g or more and 10.0 m 2 / g.
  • the value is less than or equal to the specific surface area of the first silicon nitride powder, and the average particle size in the volume-based particle size distribution measured by the laser diffraction scattering method is 0.7 ⁇ m or more and less than 2.0 ⁇ m.
  • a compounding ratio such that the weight ratio of the alkaline earth metal oxide to the rare earth metal oxide satisfies 0.40 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.4.
  • a starting composition containing 3.2 to 7.0% by weight of an alkaline earth metal oxide and a rare earth metal oxide having an effective ion radius of 87 pm or more based on the total weight of the silicon nitride raw material and the sintering aid.
  • the silicon nitride sintered body In the silicon nitride sintered body, heat is transferred by lattice vibration (phonon). Therefore, phonon scattering by different ions causes a decrease in thermal conductivity. Further, the silicon nitride sintered body is composed of a silicon nitride particle phase and a grain boundary phase thereof. Since the thermal conductivity of the grain boundary phase is low, the thermal conductivity decreases as the amount of grain boundary phase increases. Further, since the pores remaining in the silicon nitride sintered body significantly reduce the thermal conductivity, it is necessary to be a dense sintered body.
  • the selection of silicon nitride powder as a starting material is extremely important. It is important and it is necessary to highly control the properties of the raw material powder. That is, in the present invention, the ⁇ -type first silicon nitride powder having a specific specific surface area and oxygen content and the ⁇ fraction having a smaller specific surface area and a larger average particle size than the first silicon nitride powder.
  • a raw material powder containing a second silicon nitride powder of 60 or more and 100% or less is used.
  • the first silicon nitride powder 10% ⁇ fraction less, an oxygen content of 0.75 wt% to 2.2 wt% or less, the specific surface area by BET method of 7.0 m 2 / g or more 13.0m 2 It is an ⁇ -type silicon nitride powder having an average particle size of 0.55 ⁇ m or more and 1.5 ⁇ m or less in a volume-based particle size distribution measured by a laser diffraction / scattering method of / g or less.
  • the first silicon nitride powder is an ⁇ -type silicon nitride powder and has a ⁇ fraction of 10% or less, but a more preferable range is 56% or less, and a further preferable range is 3% or less.
  • the ⁇ -type silicon nitride powder has a high dissolution rate in the melt phase consisting of an alkaline earth metal oxide-rare earth metal oxide-silica-based auxiliary component produced in the sintering process, and can be dissolved in the melt phase. Denseification proceeds through precipitation accompanied by a phase transition to ⁇ -type silicon nitride.
  • the presence of oxygen contained in the silicon nitride powder is essential, and if the oxygen content is less than 0.75% by weight, a sufficient amount of melt phase is formed. Instead, densification is hindered, the open porosity increases, and the maximum opening diameter increases.
  • the oxygen content exceeds 2.2% by weight, the volume of the melt phase is too large and remains as a grain boundary phase after sintering, so that both thermal conductivity and mechanical properties (strength, fracture toughness) To reduce. In particular, the decrease in thermal conductivity is remarkable.
  • the oxygen content is 0.75% by weight or more and 2.2% by weight or less, a more preferable range is 1.0% by weight or more and 2.0% by weight or less, and a more preferable range is 1.2% by weight or more and 1.8% by weight. % Or less.
  • the specific surface area is an important powder property that governs densification through the above-mentioned dissolution and precipitation process, and when the specific surface area by the BET method is less than 7.0 m 2 / g, the driving force for sintering decreases. Unless the amount of the sintering aid added exceeds 7.0% by weight, a high-density silicon nitride sintered body cannot be obtained. On the other hand, if the amount of the sintering aid added exceeds 7.0% by weight, the thermal conductivity decreases, which is not preferable.
  • the equivalent sphere diameter of the silicon nitride powder having a specific surface area of 7.0 m 2 / g by the BET method is 0.27 ⁇ m and the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method exceeds 1.5 ⁇ m.
  • the agglomeration index ratio of the average particle size to the equivalent sphere calculated from the specific surface area
  • the agglomeration is too strong, and the fine structure of the obtained silicon nitride sintered body becomes non-uniform. Therefore, it is not preferable.
  • the specific surface area by the BET method is 7.0 m 2 / g or more and 13.0 m 2 / g or less, and a more preferable range is 9.5 m 2 / g or more and 12.0 m 2 / g or less.
  • the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method is less than 0.55 ⁇ m, the particles agglomerate in the process of preparing the coating slurry, which also makes it difficult to form a green sheet.
  • the thermal conductivity of the obtained silicon nitride sintered body tends to decrease.
  • a more preferable range of the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method is 0.7 ⁇ m or more and 1.1 ⁇ m or less.
  • ⁇ -type silicon nitride powder has the advantage that it is easier to obtain high-purity (very low metal impurity content) and fine-grained (high specific surface area and small average particle size) powder.
  • the first silicon nitride powder can be of very high purity, for example, aluminum content is 10 ppm or less, iron content is 12 ppm or less, chromium content is 2 ppm or less, nickel content is 3 ppm or less.
  • Silicon nitride powder having a tungsten content, a copper content and a manganese content of 1 ppm or less can be used.
  • the particle size is increased.
  • Two types of silicon nitride powders having different specific surface areas or oxygen contents may be mixed in order to control the distribution. For example, a silicon nitride powder having a specific surface area of 7.0 m 2 / g or less and an oxygen content of less than 0.75% by weight according to the BET method and a silicon nitride powder having a specific surface area of 13.0 m 2 / g or more and an oxygen content of 2 by the BET method. .
  • the specific surface area of the mixed silicon nitride raw material by the BET method is 7.0 m 2 / g or more and 13.0 m 2 / g or less, and the oxygen content. Is 0.75% by weight or more and 2.2% by weight or less, and if the specific surface area is larger than that of the second silicon nitride powder and the average particle size is smaller, the first silicon nitride powder can be used.
  • the second silicon nitride powder has a ⁇ fraction of 60% or more and 100% or less, an oxygen content of 0.55% by weight or more and 2.0% by weight or less, and a specific surface area of 2 by the BET method. .5m 2 / a g or more 10.0 m 2 / g or less is smaller than the specific surface area of the first silicon nitride powder, an average particle diameter in volume-based particle size distribution measured by laser diffraction scattering method It is 0.7 ⁇ m or more and less than 2.0 ⁇ m, which is a value larger than the average particle size of the first silicon nitride powder, and has an aspect ratio of 3 or less.
  • the second silicon nitride powder has a ⁇ fraction of 60% or more and 100% or less, but a preferable range of ⁇ fraction is 80% or more and 100% or less, and a more preferable range is 90% or more and 100% or less.
  • the silicon nitride powder having a ⁇ content of 60% or more and 100% or less is a nucleus in which columnar ⁇ -type silicon nitride particles grow from the alkali metal oxide-rare earth metal oxide-based silicate melt phase in the sintering process. Therefore, rapid phase transition and grain growth such as ⁇ -type silicon nitride powder are suppressed, which helps to homogenize the fine structure of the sintered body made of ⁇ -type silicon nitride. Even in the silicon nitride powder mainly composed of ⁇ particles, if the oxygen content is less than 0.55% by weight, densification is hindered because a sufficient amount of melt phase is not generated, the porosity is increased, and the maximum opening diameter is increased. growing.
  • the oxygen content exceeds 2.0% by weight, the volume of the melt phase is too large and remains as a grain boundary phase after sintering, so that both thermal conductivity and mechanical strength are lowered.
  • the oxygen content is 0.55% by weight or more and 2.0% by weight or less, and a more preferable range is 0.9% by weight or more and 1.7% by weight or less.
  • the silicon nitride powder mainly composed of ⁇ particles has a smaller specific surface area and a larger average particle diameter than the ⁇ -type silicon nitride powder. Is preferable.
  • the specific surface area by the BET method exceeds 10 m 2 / g, the dissolution proceeds in the silicate melt phase in the same manner as the ⁇ -type silicon nitride powder, which is not preferable from the viewpoint of microstructural homogenization by controlling the microstructure. ..
  • the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method is less than 0.7 ⁇ m, the particles are aggregated in the coating slurry preparation step, and the obtained silicon nitride sintered body is fine.
  • the structure tends to be non-uniform and the thermal conductivity tends to decrease.
  • the specific surface area by the BET method is less than 2.5 m 2 / g, the sintering rate becomes slow, it becomes difficult to densify, and the porosity increases.
  • the specific surface area by the BET method is 2.5 m 2 / g or more and 10.0 m 2 / g or less, and a more preferable range is 3.05 m 2 / g or more and 8.5 m 2 / g or less.
  • the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method exceeds 2.0 ⁇ m, not only the sintering rate becomes slow, but also coarse particles further grown after the sintering step remain. , It is not preferable because it adversely affects the mechanical properties of the obtained silicon nitride sintered body.
  • the 95% diameter is preferably 10.0 ⁇ m or less, more preferably 8.0 ⁇ m or less, and particularly preferably 6.4 ⁇ m or less.
  • the 100% diameter is 10.0 ⁇ m or less.
  • the average particle size in the volume-based particle size distribution measured by the laser diffraction / scattering method is 0.7 ⁇ m or more and less than 2.0 ⁇ m, and a more preferable range is 0.9 ⁇ m or more and less than 1.5 ⁇ m.
  • aspect ratios are less than 2.5.
  • the second silicon nitride powder was obtained by pulverizing a mass of silicon nitride particles having a ⁇ fraction of 60% or more and 100% or less.
  • the second silicon nitride powder has an aluminum content and an iron content of 100 ppm or less, respectively, and a chromium content, a nickel content, a tungsten content, a copper content, and a manganese content of 30 ppm or less, respectively. It is preferable to use silicon nitride powder.
  • These metal impurities are accumulated in the grain boundary phase of the silicon nitride sintered body and cause a decrease in thermal conductivity.
  • the thermal conductivity decreases. There is a fear. If the chromium content, nickel content, tungsten content, copper content, and manganese content each exceed 30 ppm, the total metal impurities will be unacceptable, and the thermal conductivity may decrease. .. In particular, since aluminum dissolves inside ⁇ -type silicon nitride particles after sintering, it is known that the dissolved aluminum ions scatter phonons, which are the main players in heat transfer, resulting in a significant decrease in thermal conductivity. There is. It is more preferable that the aluminum content and the iron content are each less than 60 ppm, and the chromium content, the nickel content, the tungsten content, the copper content and the manganese content are each 15 ppm or less.
  • the second silicon nitride powder is a ⁇ -type silicon nitride powder synthesized by a combustion synthesis method utilizing the self-heating and propagation phenomenon associated with the combustion reaction disclosed in Patent Document 15, and is powder X-ray.
  • crystallite diameter D C that is calculated using the Williamson-Hall type from the diffraction pattern is at 120nm or more, beta-type silicon nitride powder crystal effective strain is 1.5 ⁇ 10 -4 or less can be preferably used.
  • the blending ratio of the first silicon nitride powder and the second silicon nitride powder is 40 parts by weight to 94 parts by weight for the first silicon nitride powder and 60 parts by weight to 6 parts by weight for the second silicon nitride powder. If the blending ratio of the second silicon nitride powder is less than 6 parts by weight, the effect of adding the silicon nitride powder mainly composed of ⁇ -type particles is ineffective, and the action of homogenizing the fine structure of the sintered body is reduced. Alternatively, although the mechanical properties are good, the thermal conductivity is lowered, which is not preferable.
  • the blending ratio of the second silicon nitride powder exceeds 40 parts by weight, the effect of blending the first silicon nitride powder and the second silicon nitride powder cannot be seen, and the sintering rate decreases. Further, even if a high-density silicon nitride sintered body is obtained, the thermal conductivity does not decrease so much, but the bending strength and the fracture toughness value decrease, and the mechanical properties deteriorate, which is not preferable. Therefore, the blending ratio of the second silicon nitride powder is preferably 60 parts by weight to 6 parts by weight, more preferably 50 parts by weight to 10 parts by weight, and further 45 parts by weight to 15 parts by weight. Is particularly preferable.
  • the present inventors have found that when the blending ratio of the second silicon nitride powder having a ⁇ content of 60% or more and 100% or less is appropriate, the silicon nitride material is formed. It has been found that the silicon nitride particles constituting the sintered body become coarser and the above-mentioned "diffraction intensity ratio related to c-axis orientation" becomes smaller.
  • the present invention is a first silicon nitride powder containing 40 parts by weight to 94 parts by weight of the first silicon nitride powder and 60 parts by weight to 6 parts by weight of the second silicon nitride powder.
  • the average particle size in the particle size distribution is 0.66 ⁇ m or more and 1.5 ⁇ m or less
  • the obtained frequency distribution curve has two peaks, and the peak top of the peak is It is in the range of 0.5 to 1.2 ⁇ m (first peak) and 1.1 to 3.8 ⁇ m (second peak), and the second peak is 0.5 to 0.5 to more than the first peak.
  • a powder formulation having a large value of 3.0 ⁇ m.
  • a combination of the first silicon nitride powder and the second silicon nitride powder having such characteristics is suitably used as a raw material powder for producing a plate-shaped silicon nitride sintered body.
  • the frequency at the peak top of the second peak (coarse grain side) is lower than the frequency at the peak top of the first peak (fine grain side), and the average particle size is the average particle size in the volume-based particle size distribution.
  • the particle size distribution based on the volume measured by the laser diffraction scattering method is used. Two clear peaks appear in the frequency distribution curve of, and the peak top is the first peak in the range of 0.5 to 1.2 ⁇ m (fine grain side) and the second peak in the range of 1.1 to 3.8 ⁇ m (coarse grain). Side) is recognized.
  • the frequency distribution curve in the range of 1.1 to 3.8 ⁇ m is higher. It has a convex curve, and the second peak (coarse grain side) can be identified.
  • the blending ratio of the second silicon nitride powder is small. It may be difficult to identify the second peak (coarse grain side) in the frequency distribution curve of the volume-based particle size distribution.
  • ⁇ fraction> In the sintering of silicon nitride, densification proceeds through dissolution and precipitation of silicon nitride particles in the silicate-based melt phase generated in the sintering process. Since ⁇ -type silicon nitride particles have a faster dissolution rate in the silicate-based melt phase than ⁇ -type silicon nitride particles, the ⁇ fraction in this silicon nitride powder formulation may be 7% or more and 64% or less. desirable. If the ⁇ fraction is less than 7%, it becomes difficult to control the fine structure of the sintered body (distribution of minor axis diameter, major axis diameter, aspect ratio, etc. of columnar ⁇ -type silicon nitride particles). If the ⁇ fraction exceeds 64%, the sintering rate decreases, and it becomes difficult to obtain a high-density silicon nitride sintered body. Also, the porosity increases.
  • ⁇ Oxygen content> In order to form the silicate-based melt phase, the presence of oxygen contained in the silicon nitride powder is essential, and an oxygen content of less than 0.74% by weight in the silicon nitride powder formulation is sufficient. There is a risk that an amount of melt phase will not be generated, densification will be hindered, the open pore ratio will increase, and the maximum opening diameter will increase. On the other hand, when the oxygen content exceeds 1.95% by weight, the volume of the melt phase is too large and remains as a grain boundary phase after sintering, so that both thermal conductivity and mechanical properties (strength, fracture toughness) are obtained. May decrease. In particular, there is a risk that the thermal conductivity will drop significantly. A more preferable range of oxygen content is 0.9% by weight or more and 1.8% by weight or less.
  • the specific surface area by BET method is an important powder properties governing the densification is less than 6.3 m 2 / g or more 12.8m 2 / g. If the specific surface area by the BET method is less than 6.3 m 2 / g, the driving force for sintering decreases. Therefore, high-density silicon nitride unless the amount of the sintering aid added exceeds 7.0% by weight. There is a risk that a silicon sintered body cannot be obtained. On the other hand, if the amount of the sintering aid added exceeds 7.0% by weight, the thermal conductivity decreases, which is not preferable.
  • a more preferable range of the specific surface area by the BET method is 8.5 m 2 / g or more and 12.0 m 2 / g or less.
  • the silicon nitride powder formulation has an average particle size (D 50 ) of 0.66 ⁇ m or more and 1.5 ⁇ m or less in a volume-based particle size distribution measured by a laser diffraction / scattering method.
  • D 50 average particle size
  • the average particle size in the volume-based particle size distribution is less than 0.66 ⁇ m, the particles agglomerate in the process of preparing the coating slurry, which also makes it difficult to form a green sheet and the resulting silicon nitride baking.
  • the thermal conductivity of the body tends to decrease.
  • the spherical equivalent diameter of the silicon nitride powder having a specific surface area of 6.3 m 2 / g by the BET method is 0.30 ⁇ m, and the average particles in the volume-based particle size distribution measured by the laser diffraction scattering method of the silicon nitride powder mixture.
  • the agglomeration index ratio of the average particle size to the equivalent sphere calculated from the specific surface area
  • the agglomeration is too strong, resulting in silicon nitride firing. It is not preferable because the microstructure of the body becomes non-uniform.
  • the average particle size (D 50 ) in the volume-based particle size distribution exceeds 1.5 ⁇ m, not only the sintering rate will be slowed down, but also the mechanical properties of the obtained silicon nitride sintered body will be adversely affected. Not preferred.
  • a more preferable range of the average particle size (D 50 ) in the volume-based particle size distribution is 0.7 ⁇ m or more and 1.2 ⁇ m or less.
  • the coarse particles with abnormal grain growth increase, which adversely affects the mechanical properties.
  • the 95% diameter is preferably 6.5 ⁇ m or less, more preferably 5.8 ⁇ m or less, and particularly preferably 5.0 ⁇ m or less.
  • the 100% diameter (D 100) of the silicon nitride powder formulation is 7.5 ⁇ m or less.
  • the frequency distribution curve obtained from the particle size distribution measurement of the silicon nitride powder formulation has two peaks due to the formulation of the first silicon nitride powder and the second silicon nitride powder, and the peak top of the peak is 0. It is in the range of .5 to 1.2 ⁇ m (first peak) and the range of 1.1 to 3.8 ⁇ m (second peak), and the second peak (coarse grain side) is the first peak (fine grain side). It is a value 0.5 to 3.0 ⁇ m larger than that.
  • the particles agglomerate in the process of preparing the coating slurry, which makes it difficult to form a green sheet and the resulting silicon nitride sintered.
  • the microstructure of the body tends to be non-uniform, and the thermal conductivity of the obtained silicon nitride sintered body tends to decrease.
  • the peak top of the first peak (fine grain side) exceeds 1.2 ⁇ m, the sintering rate becomes slow, the porosity and the maximum opening diameter become large, and the mechanical properties deteriorate, which is not preferable.
  • the peak top of the second peak (coarse grain side) is less than 1.1 ⁇ m, the effect of adding the silicon nitride powder mainly composed of ⁇ -type particles is small, and the effect of homogenizing the fine structure of the sintered body is small. Although the mechanical properties are good because of the decrease, the thermal conductivity is decreased, which is not preferable.
  • the peak top of the first peak (fine grain side) is more preferably in the range of 0.55 to 0.98 ⁇ m.
  • the nitride is nitrided. Since the silicon nitride particles constituting the silicon sintered body become coarse and the "diffraction intensity ratio related to c-axis orientation" becomes small, it has both high thermal conductivity and excellent mechanical properties (strength and fracture toughness). A plate-shaped silicon nitride sintered body can be obtained.
  • the peak top of the second peak is close to the value within 0.49 ⁇ m from the peak top of the first peak (fine grain side) and overlaps the base portion of the first peak (fine grain side).
  • the peak top of the second peak is more preferably 0.7 to 2.8 ⁇ m larger than the peak top of the first peak (fine grain side), and is 0.9 to 2.5 ⁇ m larger. Is more preferable.
  • the frequency at the peak top of the second peak is lower than the frequency at the peak top of the first peak (fine grain side).
  • the frequency at the peak top of the second peak (coarse grain side) is higher than the frequency at the peak top of the first peak (fine grain side)
  • the sintering rate decreases and the mechanical properties deteriorate.
  • an alkaline earth metal oxide is used as a sintering aid in silicon nitride powder.
  • the ratio of the weight to the rare earth metal oxide is 0.40 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.4, and the alkali earth metal oxide and the effective ion radius are 87 pm.
  • the above rare earth metal oxide is added in an amount of 3.2 to 7.0% by weight based on the total weight of the silicon nitride powder and the sintering aid.
  • the ratio of the measured alkaline earth metal content to the measured rare earth metal content as the sintered body is determined by the oxide standard of the alkaline earth metal oxide and the rare earth metal oxide in the sintered body.
  • the alkaline earth metal is magnesium and the rare earth metal is erbium, 0.07 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.23, the alkaline earth metal is magnesium, and the rare earth metal In the case of yttrium, 0.06 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.11.
  • the weight ratio of alkaline earth metal oxide to rare earth metal oxide (alkali earth metal oxide / rare earth metal oxide) in the composition is less than 0.40, the ratio of rare earth metal oxide is too large.
  • the melting temperature of the grain boundary phase rises during the sintering process. Therefore, unless a large amount of silica (SiO 2 ) is added, the relative density of the sintered body decreases, and a dense sintered body cannot be obtained.
  • the alkaline earth metal oxide / rare earth metal oxide representing the weight ratio of the alkaline earth metal oxide and the rare earth metal oxide is less than 0.40 or more than 1.4. It is not preferable because it reduces the mechanical properties (strength and breaking toughness).
  • the weight ratios of alkaline earth metal oxides / rare earth metal oxides in the compounding composition are 0.42 or more, 0.45 or more, 0.48 or more, and 1.1 or less, 0.90 or less, 0.70. It may be:
  • the amount of the alkaline earth metal oxide and the rare earth metal oxide added is less than 3.2% by weight, the amount of the liquid phase generated in the sintering process is insufficient and a high-density sintered body cannot be obtained. Conductivity is reduced and mechanical properties (strength and fracture toughness) are also reduced. Even if the addition amount of the alkaline earth metal oxide and the rare earth metal oxide exceeds 7.0% by weight, the mechanical properties (strength and fracture toughness) are hardly lowered, but the thermal conductivity is lowered, which is not preferable.
  • the amount of the alkaline earth metal oxide and the rare earth metal oxide added is more preferably 4.0% by weight or more and 6.5% by weight or less.
  • the amount of the alkaline earth metal oxide added is more preferably 2.5% by weight or less.
  • the speed of densification can be increased.
  • the amount of silicon dioxide added is 0.1% by weight or more and 2.5% by weight or less based on the total weight of the silicon nitride raw material and the sintering aid. If the addition amount is less than 0.1% by weight, the effect cannot be discerned, and if it exceeds 2.5% by weight, the volume of the grain boundary phase increases after sintering and the thermal conductivity decreases, which is not preferable.
  • a more preferable range of the amount of silicon dioxide added is 0.5% by weight or more and 1.8% by weight or less.
  • the silicon nitride molded product is sintered in a nitrogen atmosphere or a nitrogen-containing inert atmosphere, it is one of the alkaline earth metal oxides and rare earth metal oxides added as sintering aids in the sintering process.
  • the part volatilizes due to evaporation together with the silica component in the silicon nitride raw material. Therefore, the content of the sintering aid mainly contained in the grain boundaries of the silicon nitride sintered body differs from the composition of the starting material.
  • the ratio of the measured alkaline earth metal content to the measured rare earth metal content as a sintered body is 0.05 ⁇ measured alkaline earth metal content / measured rare earth metal content ⁇ 0.85. ..
  • the relative density of the sintered body decreases. Further, even if the measured alkaline earth metal content / measured rare earth metal content is less than 0.05 or more than 0.85, the mechanical properties (strength and fracture toughness) are deteriorated. Not preferable. Furthermore, the weight ratio of the measured alkaline earth metal content / measured rare earth metal content of the sintered body is 0.07 or more, 0.09 or more, 0.10 or more, and 0.75 or less, 0.65 or less. It may be 0.55 or less.
  • the sintering aid component volatilizes, and the content of the sintering aid mainly contained in the grain boundaries of the silicon nitride sintered body differs from the blending composition of the starting material. Therefore, in the present invention.
  • the present inventors investigated in detail the relationship between the weight loss rate before and after sintering and the chemical composition of the obtained silicon nitride sintered body.
  • the sintering aid component but also the silicon nitride itself is partially volatilized, and if the weight reduction rate before and after sintering is not controlled within the above range, the obtained silicon nitride sintered body is actually measured.
  • the alkaline earth metal content, the measured rare earth metal content, and the ratio of both cannot be controlled, and completed the present invention.
  • a more preferable range of the weight loss rate before and after sintering is 3.5% by weight to 7.5% by weight, and a more preferable range is 4.5% by weight to 7.5% by weight.
  • the filling amount and filling method of the green sheet in the setter in addition to controlling the weight loss rate before and after sintering, so that the oxygen volatilization rate before and after sintering is 23% to 50%.
  • sintering conditions such as the degree of sealing of the setter, atmospheric gas pressure, the maximum holding temperature and the holding time at the maximum holding temperature, a plate-shaped silicon nitride sintered body having a desired measured oxygen content can be produced. To do.
  • the measured oxygen content of the silicon nitride sintered body in the present invention is preferably 1.3% by weight or more and 2.8% by weight or less. It is more preferably 1.6% by weight or more and 2.6% by weight or less, further preferably 1.9% by weight or more and 2.6% by weight or less, and particularly preferably 2.35% by weight or more and 2.55% by weight. It is as follows. If the raw material composition and sintering conditions are such that the measured oxygen content is less than 1.3% by weight, the relative density of the sintered body will be less than 98%. Further, the crystal phase is precipitated at the grain boundaries of the plate-shaped silicon nitride sintered body, which causes uneven color tone, which is not preferable.
  • a plate-shaped silicon nitride sintered body having an actually measured oxygen content of more than 2.8% by weight is not preferable because its thermal conductivity is lowered. Further, when directly bonded to a metal plate such as copper or aluminum, voids are generated at the bonding interface and the bonding strength is lowered, which is not preferable.
  • Magnesium oxide is preferably used as the alkaline earth metal oxide, and at least one oxide selected from yttrium oxide, erbium oxide and itterbium oxide is preferably used as the rare earth metal oxide.
  • the weight ratio of magnesium oxide to rare earth metal oxide in the composition is 0.40 ⁇ magnesium oxide / rare earth metal oxide ⁇ 1.4, but 0.42 ⁇ magnesium oxide / rare earth metal oxide ⁇ 1.1. It is preferably 0.45 ⁇ magnesium oxide / rare earth metal oxide ⁇ 0.90. Further, it is particularly preferable that 0.48 ⁇ magnesium oxide / rare earth metal oxide ⁇ 0.70.
  • the ratio of the measured magnesium content to the measured rare earth metal content as a sintered body is preferably 0.07 ⁇ measured magnesium content / measured rare earth metal content ⁇ 0.75, and further 0.09 ⁇ It is more preferable that the measured magnesium content / measured rare earth metal content ⁇ 0.65. Further, it is particularly preferable that 0.10 ⁇ the measured magnesium content / the measured rare earth metal content ⁇ 0.55.
  • Y 2 Si 3 O 3 N 4 N-merylite
  • Y 10 Si 7 O 23 N 4 H phase
  • Y 4 Si 2 O 7 N 2 J phase
  • YSiO 2 N K phase
  • crystalline phase is precipitated, such as producing color unevenness due to the crystal phase deposited on a plate-shaped silicon nitride sintered body was taken out. Since the precipitated crystal phase generally has a higher true density than the amorphous phase, shrinkage causes a dense region of micropores around the precipitated crystal phase. The dense region of micropores becomes the starting point of crack growth due to repeated stress and load due to thermal cycle, and causes fatigue fracture and thermal cycle fracture.
  • the orientation of the growth surface of the precipitated crystal phase and the presence of the micropore dense region cause uneven color tone on the surface of the sintered body.
  • the diffraction intensity of the main peak ((22-1) plane) of the J phase (RE 4 Si 2 O 7 N 2) constituting the grain boundary phase and N-merylite The total diffraction intensity of the main peak ((211) plane) of the phase (RE 2 Si 3 O 3 N 4 ) is 0 with respect to the diffraction intensity of the (200) plane of ⁇ -type silicon nitride in the silicon nitride sintered body.
  • the crystal phase of Mg compounds comprising two like MgSiN the grain boundaries of the plate-shaped silicon nitride sintered body of the present invention, substantially free.
  • the fact that the crystal phase composed of MgSiN 2 is not substantially contained means that the X-ray diffraction peak intensity of (121) of the MgSiN 2 crystal phase constitutes a silicon nitride sintered body. Less than 0.0005 times the sum of the X-ray diffraction peak intensities of the (110), (200), (101), (210), (201), (310), (320) and (002) planes of the crystal particles of Means that
  • the mechanical properties (bending strength and fracture toughness) of the silicon nitride sintered body tend to decrease. It is in.
  • 4-point bending strength is at 900MPa or more at room temperature
  • the IF method fracture toughness value K IC measured by (indentation method) is plate-shaped at least 8.0MPa ⁇ m nitride It is not preferable because it becomes difficult to obtain a siliconized sintered body.
  • magnesium oxide and yttrium oxide are preferably added as sintering aids, and the amount of addition thereof is 4.0% by weight or more and 6.5% by weight or less. It is preferable to add so that the weight ratio satisfies 0.42 ⁇ magnesium oxide / yttrium oxide ⁇ 1.1.
  • a plate-shaped molded body (green sheet) is produced by a sheet molding process.
  • the sheet molding method is also called a tape molding method, and a slurry containing, for example, 8 parts by mass or more of an organic binder or a resin binder is applied to 100 parts by mass of the raw material powder using a device such as a doctor blade or a die coater to form a carrier film.
  • a green sheet is prepared by casting it on top to a predetermined thickness.
  • Green sheet production by an extrusion molding method or an injection molding method is also included in the sheet molding method, but in the present invention, the CIP molding method and the mold press molding method are not included in the sheet molding method.
  • the sheet molding method itself is known, and a known sheet molding method may be used in the present invention.
  • a green sheet forming slurry containing a solvent such as a mixed solvent is prepared, and cast on a carrier film to a predetermined thickness using an apparatus such as a doctor blade or a die coater to prepare a green sheet.
  • a correlation is observed between the coating speed in sheet molding and the orientation of ⁇ -type silicon nitride particles after sintering.
  • the coating speed of the green sheet is related to other manufacturing conditions such as slurry composition and sheet thickness, but generally, for example, 0.02 to 0.5 m / min, and further 0.05 to 0.3 m. It may be / min, 0.1 to 0.2 m / min.
  • the conditions for sheet molding and sintering in producing the plate-shaped silicon nitride sintered body of the present invention are the degree of orientation of ⁇ -type silicon nitride particles and the number of columnar ⁇ -type silicon nitride particles exceeding 10 ⁇ m. Since it is selected so as to be within the predetermined range of the present invention, the specific coating speed of the green sheet is selected in relation to it.
  • the green sheet can be a laminated green sheet in consideration of the thickness after sintering.
  • a green sheet or a laminated green sheet (hereinafter, simply referred to as a green sheet) produced by a sheet molding method is usually cut into a molded product having a predetermined shape.
  • the plate-shaped molded body (green sheet) produced by the sheet molding process is sintered at an atmospheric gas pressure of 3 MPa or less, and the relative density is 98%.
  • the above sintered body can be obtained.
  • a plate-shaped molded body (green sheet) produced by a sheet forming process is sintered by holding it at an atmospheric gas pressure of 0.15 MPa or more and 3 MPa or less and a maximum holding temperature of 1790 ° C. or more and 1910 ° C. or less.
  • the ratio of the measured alkaline earth metal content to the measured rare earth metal content as a body is 0.05 ⁇ measured alkaline earth metal content / measured rare earth metal content ⁇ 0.85, and the relative density is 98% or more.
  • the maximum holding temperature is preferably set in the temperature range of 1820 ° C. or higher and 1910 ° C. or lower.
  • the sintered body is sintered by holding for 6 to 20 hours in a temperature range where the maximum holding temperature is 1820 ° C. or higher and 1910 ° C. or lower under a pressurized atmosphere where the nitrogen-containing gas pressure is 0.15 to 0.9 MPa, and the relative density is 98. % Or more, preferably 99.0% or more of the sintered body may be obtained.
  • the temperature range from 1520 ° C. to the maximum holding temperature at a rate of less than 150 ° C./hr.
  • holding at a constant temperature for a certain period of time in the temperature range from 1520 ° C. to the maximum holding temperature is also effective in reducing residual pores.
  • a green sheet molded product When sintering a green sheet molded product, particularly when producing a thin plate-shaped silicon nitride sintered body having a thickness of 1.5 mm or less and further 1.0 mm or less, warpage of the thin plate is suppressed and damage is prevented.
  • a plurality of green sheet compacts are laminated with a separating material (typically boron nitride powder having a particle size of about 4 to 20 ⁇ m) interposed therebetween. Degreased and sintered.
  • a plurality of green sheet molded bodies are stacked and placed in a container such as boron nitride, heated to 400 to 600 ° C.
  • this degreased body is heat-treated at a high temperature as described later to produce a sintered body. After that, it is cooled to room temperature, and the obtained silicon nitride sintered body is peeled off with a separating material layer to obtain a plate-shaped silicon nitride sintered body.
  • the obtained plate-shaped silicon nitride sintered body is usually blast-polished to obtain a silicon nitride sintered body for a substrate having a desired surface roughness.
  • the thickness removed by the blast polishing process may be, for example, about 20 ⁇ m or less on average. Wrap polishing may be performed after blast polishing or without blast polishing.
  • separating material it is preferable to use a mixed powder of boron nitride powder having a particle size of about 4 to 20 ⁇ m and silicon nitride powder having a particle size of 1 to 5 ⁇ m.
  • a molded product (green sheet) using an organic binder or a resin binder not only is it easy to generate coarse pores in the molded body due to the aggregation of the binder, but also a small amount of carbon remains in the molded body even after degreasing, and residual carbon remains. Affects grain growth in the sintering process, which deteriorates the mechanical properties (bending strength and fracture toughness) of the obtained silicon nitride sintered body. The effect is particularly remarkable in the plate-shaped silicon nitride sintered body. Further, it is known that the silicon nitride sintered body has different microstructures (particle size and aspect ratio, grain boundary phase composition and crystal phase) between the surface and the inside of the sintered body.
  • the bending strength of the test piece obtained by grinding and removing the surface layer portion where defects such as pores and cracks are likely to occur by 0.2 mm or more is higher than the bending strength of the test piece in which the surface layer portion remains.
  • the bending strength of the silicon nitride sintered body changes depending on the amount of the organic binder or resin binder used and the cutting / polishing process at the time of preparing the test piece. Even if the bending strength of the obtained test piece has already been disclosed, it cannot be said that it is equivalent to the bending strength of the plate-shaped silicon nitride sintered body in the present invention, and the equivalent bending strength value has already been obtained. It does not mean that it was disclosed.
  • the atmospheric gas pressure acts isotropically, a sintered body in which columnar ⁇ -type silicon nitride particles are oriented as in the present invention cannot be obtained.
  • the "diffraction intensity ratio related to c-axis orientation" is near 1.0 or a value smaller than 1.0, it is not preferable in terms of the balance between thermal conductivity and mechanical properties.
  • a special sintering furnace that can be used under high pressure is required, and the equipment cost becomes remarkably high, which is not preferable.
  • Patent Document 3 realizes high thermal conductivity and high bending strength at atmospheric gas pressures of 40, 60, 100 and 2000 atm, but the data shown in Table 1 shows bulk CIP with a thickness of 3 mm or more. After sintering the molded body, the characteristics of the test piece obtained by cutting and polishing the obtained silicon nitride sintered body are measured, and it is a sheet molding process in which a large amount of organic binder is added. It is not a characteristic value of the obtained plate-shaped silicon nitride sintered body.
  • MgO addition amount is 0.9-1.0 wt%
  • Y 2 O 3 addition amount of 3.1 to 3.0 wt%
  • the number of ⁇ -type silicon nitride particles is a large value of 15223 to 19022 per 1 mm 2 of the cut surface.
  • the bonded body with the metal preferably has a durability of 2000 cycles or more when the temperature raising / lowering cycle from ⁇ 40 ° C. to 180 ° C. is repeated. Further, even if the desired surface roughness can be achieved by lap polishing or the like, which increases the cost, the open porosity on the polished surface is large, and the maximum opening diameter of the open pores exceeds 1.0 ⁇ m. , Not preferable.
  • the nitrogen-containing gas pressure is less than 0.15 MPa
  • the maximum holding temperature during sintering cannot be raised to 1790 ° C or higher. If the maximum holding temperature is less than 1790 ° C., the progress rate of sintering is slow, and it is difficult to obtain a dense plate-shaped silicon nitride sintered body having a relative density of 98% or more.
  • a dense silicon nitride sintered body is obtained at a maximum holding temperature of less than 1790 ° C., the growth of columnar ⁇ -type silicon nitride particles is insufficient, and the silicon nitride sintered body has a low thermal conductivity.
  • the thermal conductivity of the plate-shaped silicon nitride sintered body is 90 W / (m ⁇ K) or more.
  • the maximum holding temperature exceeds 1910 ° C., the growth of columnar ⁇ -type silicon nitride particles becomes remarkably fast, and although the major axis diameter exceeds 10 ⁇ m, the area fraction exceeds 39 area%, which is not preferable. Further, the maximum holding temperature may be 1820 ° C. or higher, or 1880 ° C. or lower.
  • the plate-shaped silicon nitride sintered body obtained under the sintering conditions of a maximum holding temperature of over 1910 ° C. and a holding time of over 20 hours, in which the growth of columnar ⁇ -type silicon nitride particles is extremely fast has a major axis diameter. Since the 50% diameter D 50 and the 80% diameter D 80 in the cumulative particle size distribution curve are excessively large, the thermal conductivity may be high but the mechanical properties may be significantly inferior. For example, the bending strength is reduced to less than 700 MPa. Furthermore, the holding time in the above temperature range may be 8 hours or more or 14 hours or less.
  • the present invention is a plate-shaped silicon nitride sintered body on one side.
  • the ratio of the measured alkaline earth metal content as a sintered body to the measured rare earth metal content (the effective ionic radius of the rare earth metal is 87 pm or more) is 0.05 ⁇ measured alkaline earth metal content / measured rare earth metal
  • the content is ⁇ 0.85
  • the total content of the measured alkaline earth metal and the measured rare earth metal, the metal element content derived from the sintering aid excluding silicon is 1.5% by weight or more and 4.5% by weight or less.
  • Relative density is 98% or more, (200) of ⁇ -type silicon nitride obtained when a plane obtained by grinding from a surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less to the inside by 0.08 mm or more is irradiated with X-rays.
  • the plate-shaped silicon nitride sintered body in the present invention can be produced by a sheet forming process, but has a thickness of 1.5 mm or less, preferably 1.0 mm or less, and a thickness / area ratio of 0. It means the one which is 015 (1 / mm) or less.
  • the amount of the plate surface surface layer portion perpendicular to the thickness direction by grinding or polishing is preferably 0.02 mm or less per side, and more preferably 0.01 mm or less per side.
  • the thickness obtained by peeling with the separating material layer is preferably 1.5 mm or less, preferably.
  • the amount of the surface layer of the plate surface perpendicular to the direction may be 0.02 mm or less per side.
  • a high thermal conductive silicon nitride substrate for a power module is required to have a thickness of 0.32 ⁇ 0.05 mm.
  • the metal impurity content of the plate-shaped silicon nitride sintered body of the present invention depends on the metal impurity content contained in the second silicon nitride powder, but the actually measured aluminum content and the actually measured iron content are respectively. It is 60 ppm or less, and the measured chromium content, the measured nickel content, the measured tungsten content, the measured copper content, and the measured manganese content can each be 18 ppm or less. More preferably, the measured aluminum content and the measured iron content are each less than 40 ppm, and the measured chromium content, the measured nickel content, the measured tungsten content, the measured copper content and the measured manganese content are 10 ppm or less, respectively.
  • the thermal conductivity may decrease. Further, even if the total amount of the measured chromium content, the measured nickel content, the measured tungsten content, the measured copper content and the measured manganese content exceeds 100 ppm, the thermal conductivity may decrease.
  • the thermal conductivity and bending strength can be increased.
  • ⁇ -type silicon nitride after sintering is obtained by highly controlling the properties and blending ratio of ⁇ -type first silicon nitride powder and second silicon nitride particles containing ⁇ -type silicon nitride, and sintering conditions.
  • the orientation of the particles is controlled. Specifically, the "diffraction intensity ratio related to c-axis orientation" calculated from the X-ray diffraction pattern of the obtained silicon nitride sintered body is controlled.
  • the “diffraction intensity ratio related to c-axis orientation” refers to the diffraction intensities I (200) and (210) of the (200) plane of ⁇ -type silicon nitride.
  • the plate-shaped silicon nitride sintered body of the present invention has an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less, further 0.40 ⁇ m or less, and X-rays on a surface polished to 0.30 ⁇ m or less.
  • the diffraction intensity ratio related to the c-axis orientation is 1.10 or more and 1.50 or less, preferably 1.15 or more and 1.50 or less, and more preferably 1.20 or more and 1.50 or less. It is 50 or less. It may be 1.48 or less.
  • the "diffraction intensity ratio related to the c-axis orientation" is 1.10 or more and 1.40 or less, preferably 1.15 or more and 1.40 or less, and more preferably 1.20 or more and 1.40 or less. It may be 1.38 or less.
  • the "diffraction intensity ratio related to c-axis orientation" of the plate-shaped silicon nitride sintered body is measured by X-ray diffraction measurement of the surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less. Ask. If the arithmetic mean roughness Ra of the surface is not within this range, the “diffraction intensity ratio related to the c-axis orientation” cannot be accurately measured. When the arithmetic mean roughness Ra of the surface of the silicon nitride sintered body is 0.05 ⁇ m or more and 0.5 ⁇ m or less, X-ray diffraction measurement may be performed on the surface of the sintered body.
  • the surface of the sintered body is polished so that the arithmetic average roughness Ra is 0.05 ⁇ m or more and 0.5 ⁇ m or less.
  • X-ray diffraction measurement is performed on the polished surface.
  • the polishing method for reducing the arithmetic average roughness Ra of the surface to 0.05 ⁇ m or more and 0.5 ⁇ m or less is not particularly limited, and the polishing amount may be the minimum necessary to realize the above arithmetic average roughness Ra. Generally, for example, about 10 ⁇ m in the depth direction is sufficient.
  • the intensity of the X-ray diffraction pattern of the (200) plane, the (210) plane, and the (101) plane is measured.
  • a plate-shaped silicon nitride sintered body is composed mainly of coarse ⁇ -type columnar particles, fine ⁇ -type columnar particles, and grain boundary phase, and the degree of orientation of the columnar particles is influenced by the coarse columnar particles. Receive a great deal. The larger the "diffraction intensity ratio related to the c-axis orientation", the more the inclination of the major axis of the columnar particles with respect to the direction parallel to the surface of the plate-shaped silicon nitride sintered body (the direction perpendicular to the thickness direction) is 45. It contains more columnar particles that are within degrees.
  • the fact that the value of the "diffraction intensity ratio related to the c-axis orientation" approaches infinity indicates that the inclination of the major axis of the columnar particles with respect to the direction parallel to the surface is close to 0 degrees. .. Reducing the inclination of the long axis of the columnar particles with respect to the direction parallel to the surface is advantageous for achieving high strength.
  • the plate-shaped silicon nitride sintered body of the present invention has a value of "diffraction intensity ratio related to c-axis orientation" controlled to be 1.10 or more and 1.40 or less, particularly inside the plate-shaped silicon nitride sintered body.
  • the slope of the long axis of the columnar particles with respect to the direction parallel to the surface of the sintered body (direction perpendicular to the thickness direction) is suitable for both excellent mechanical properties (high strength and high fracture toughness) and high thermal conductivity. Therefore, it is suitable for insulating substrate applications.
  • Patent Document 8 discloses silicon nitride ceramics characterized in that the c-axis of columnar ⁇ -silicon nitride particles is oriented in the thickness direction of the substrate. According to the publication, 90% or more of the ⁇ -silicon nitride particles have a c-axis inclination of ⁇ 20 degrees or less with respect to the thickness direction of the substrate, and 50% or more of the ⁇ -silicon nitride particles are the substrate. It is described that the thermal conductivity of the silicon nitride ceramics in which the inclination of the c-axis with respect to the thickness direction is within ⁇ 5 degrees is high.
  • the c-axis of the ⁇ silicon nitride particles is the substrate. Since the sintered substrate is oriented in the thickness direction, the bending strength of the sintered substrate is significantly reduced, which causes a problem in terms of strength characteristics.
  • the ⁇ -type silicon nitride particles are not necessarily aligned and oriented in parallel with the thickness direction, and the above-mentioned “diffraction intensity ratio related to c-axis orientation” is 1. Not only can high thermal conductivity be achieved even if it is larger than .10, but also mechanical properties (bending strength and fracture toughness value) can be achieved by making the "diffraction intensity ratio related to c-axis orientation" larger than 1.10. I learned that it can be enhanced.
  • the mechanical properties bending strength and fracture toughness value
  • the thermal conductivity decreases, which is not preferable.
  • a more preferable range of the “diffraction intensity ratio related to c-axis orientation” is 1.20 to 1.40.
  • the polished surface is a surface obtained by, for example, barrel polishing, honing processing, lapping polishing, polishing polishing and buffing.
  • the microstructure of the plate-shaped silicon nitride sintered body of the present invention contains columnar ⁇ -type silicon nitride particles having a major axis diameter of 3 ⁇ m or more, which is a good thermal conductor, in the matrix.
  • Minor axis diameter and major axis diameter of ⁇ -type silicon nitride grains of the columnar is used as a raw material two kinds the Si 3 N 4 powder properties and proportion and sintering conditions (heating rate, the maximum holding temperature and the maximum retention It can be controlled by adjusting the holding time at temperature).
  • the fine structure of the plate-shaped silicon nitride sintered body of the present invention can be classified into ⁇ -type silicon nitride particles having a major axis diameter of 3.0 ⁇ m or more, fine particles having a major axis diameter of less than 3 ⁇ m, and grain boundary phases. it can.
  • ⁇ -type silicon nitride particles having a major axis diameter of 3.0 ⁇ m or more
  • fine particles having a major axis diameter of less than 3 ⁇ m
  • grain boundary phases grain boundary phases.
  • the number of columnar ⁇ -type silicon nitride particles (coarse ⁇ particles) having a major axis diameter of more than 10 ⁇ m is a small value of 1200 to 10000 per 1 mm 2 of the cut surface. More preferably, the number may be 9000 or less, and a value of 1000 or less is also obtained. Since the number of columnar ⁇ -type silicon nitride particles having a major axis diameter of more than 10 ⁇ m is small as described above, the mechanical properties (strength and fracture toughness value) are improved.
  • the total area of all silicon nitride particles (grain boundary from the observed cut surface).
  • the area fraction of the particles having a major axis diameter of 3 ⁇ m or more is 45 area% or more and 87 area% or less, and the major axis diameter is It is preferable that the area fraction of the particles exceeding 10 ⁇ m is 6.5 area% or more and 39 area% or less.
  • the area fraction of particles having a major axis diameter of 3 ⁇ m or more is 45 area% or more and 87 area% of all silicon nitride particles, and the area fraction of particles having a major axis diameter of more than 10 ⁇ m is 6.5 area% or more and 39 area%.
  • the thermal conductivity is increased and the bending strength and breaking toughness value are significantly increased.
  • the area fraction of the particles having a major axis diameter of 3 ⁇ m or more is more preferably 49 area% or more and 87 area% or less of the total silicon nitride particles, and further 55 area% or more and 86. It is particularly preferable that the area is% or less.
  • the maximum holding temperature at the time of sintering is too high and the area fraction of the particles having a major axis diameter exceeding 10 ⁇ m exceeds 39 area% of the total silicon nitride particles, the coarser particles are produced. Since the coarse particles introduced into the structure, which are growing, act as the starting point of fracture, the fracture toughness is greatly reduced, and the four-point bending strength at room temperature is less than 850 MPa. There is a risk that the characteristics will be insufficient for application to substrate applications.
  • the maximum holding temperature at the time of sintering is too low and the area fraction of the columnar ⁇ -type silicon nitride particles having a major axis diameter of 3 ⁇ m or more is less than 45 area%, not only the thermal conductivity is lowered but also the fracture toughness is reduced. It is not preferable because the value decreases.
  • the area division of the grain boundary phase is more preferably 15 area% or less, and further preferably 13 area% or less, based on the total area of the total silicon nitride particles and the grain boundary phase.
  • the 50% diameter D 50 in the cumulative particle size distribution curve of the major axis diameter is 2.8 ⁇ m or more and 6.8 ⁇ m or less, and the 80% diameter D 80 is 8.1 ⁇ m or more and 12.5 ⁇ m or less. It is more preferable that the 50% diameter D 50 is 5.5 ⁇ m or more and 6.8 ⁇ m or less, and the 80% diameter D 80 is 9.5 ⁇ m or more and 12 ⁇ m or less.
  • the area fraction of the particles having a major axis diameter of 3 ⁇ m or more is 45 area% or more and 87 area% of the total silicon nitride particles, based on the area of the total silicon nitride particles. Since the area fraction of particles having a major axis diameter of more than 10 ⁇ m is 6.5 area% or more and 39 area% or less, X-rays are applied to a plane obtained by grinding 0.08 mm or more inward from the above surface.
  • the surface does not have to be polished, but the surface must be polished, and the arithmetic mean roughness Ra of the surface may be 0.05 ⁇ m or more and 0.5 ⁇ m or less, and further. Is preferably 0.40 ⁇ m or less and 0.30 ⁇ m or less. If the arithmetic average roughness Ra is less than 0.05 ⁇ m, the bending strength of the plate-shaped silicon nitride sintered body decreases due to residual stress during processing and the like.
  • the arithmetic mean roughness Ra exceeds 0.5 ⁇ m, it becomes difficult to join the metal plate for forming a circuit, which is not preferable.
  • DBC method direct joining method
  • the open porosity on the surface polished to have an arithmetic mean roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less is 1.0% or less, and the maximum opening diameter of the open pores is 1.0 ⁇ m or less. Excellent electrical characteristics can be expected when the maximum opening diameter of the open pores on the surface is 1.0 ⁇ m or less. In particular, it is more preferable that the maximum opening diameter of the open pores on the surface is 0.5 ⁇ m or less.
  • Such a plate-shaped silicon nitride sintered body having a high density and few residual pores has excellent insulation resistance and withstand voltage, and is therefore suitable for use in electronic substrates such as insulating substrates and circuit boards.
  • a plate-shaped silicon nitride sintered body having both high thermal conductivity and excellent mechanical properties by a sheet forming process which has conventionally lacked performance in terms of both thermal conductivity and mechanical properties. It is advantageous in terms of manufacturing cost because it can be manufactured. That is, according to the present invention, the thermal conductivity is 110 W / (m ⁇ K) or more at room temperature, the four-point bending strength is 900 MPa or more at room temperature, and the fracture toughness value measured by the IF method (indentation method).
  • K IC is above 8.0MPa ⁇ m, it is possible to produce a high thermal conductivity and excellent mechanical properties and a combining plate-shaped silicon nitride sintered body, thermal conductivity and mechanical properties It can be used as a substrate as a well-balanced plate-shaped silicon nitride sintered body.
  • the substrate include an electronic substrate such as an insulating substrate and a circuit board.
  • the silicon nitride raw material 14 types of silicon nitride powders shown in Table 1 were used. Table 1 shows the ⁇ fraction, composition, properties and amount of metal impurities of these raw material powders.
  • the first silicon nitride powders (A-1 to A-5) are silicon nitride powders produced by the imide decomposition method.
  • B-1 to B-7 are ⁇ -type silicon nitride powders synthesized by a combustion synthesis method utilizing the self-heating and propagation phenomenon associated with the combustion reaction disclosed in Patent Document 15.
  • powder X-ray crystallite size D C calculated using the Williamson-Hall type from the diffraction pattern is not less 120nm or more, the silicon nitride powder crystal effective strain is 1.5 ⁇ 10 -4 or less or necessary,
  • the ⁇ -type silicon nitride powder was additionally pulverized by a vibration mill according to the above.
  • B-8 and B-9 are obtained by pulverizing silicon nitride powder synthesized by the direct nitriding method.
  • magnesium oxide (MgO) powder (specific surface area 3 m 2 / g, manufactured by High Purity Chemical Laboratory), yttrium oxide (Y 2 O 3 ) powder (specific surface area 3 m 2 / g, manufactured by Shin-Etsu Chemical Industry Co., Ltd.) and Silicon dioxide (SiO 2 ) powder (specific surface area 11.5 m 2 / g, manufactured by High Purity Chemical Laboratory) was prepared.
  • MgO magnesium oxide
  • Y 2 O 3 yttrium oxide
  • SiO 2 Silicon dioxide
  • Silicon nitride balls which are the crushing medium, usually contain a few percent of Al 2 O 3 , and the amount of wear during ball milling is large. Therefore, the compounded powder after adjusting the raw materials contains around 20 ppm of Al 2 O 3. It is mixed. Therefore, in this embodiment, the Al 2 O 3 content is about 1.9% by weight, and a silicon nitride ball having particularly excellent wear resistance is used to mix Al 2 O 3 during raw material preparation. The amount was kept to a minimum.
  • Reducing the aluminum content of the silicon nitride powder to less than 60 ppm reduces the aluminum content in the raw material for producing the silicon nitride powder, and also mixes aluminum oxide in the process of manufacturing the silicon nitride powder (for example, mixing from a pulverizing medium). ) Is possible.
  • the specific surface area of the silicon nitride powder of the present invention was determined by measuring with a BET 1-point method by adsorbing nitrogen gas using a Macsorb manufactured by Moontech.
  • the particle size distribution of the silicon nitride powder of the present invention was measured as follows. The powder was put into a 0.2 mass% aqueous solution of sodium hexametaphosphate and dispersed for 6 minutes at an output of 300 W using an ultrasonic homogenizer equipped with a stainless steel center cone having a diameter of 26 mm to prepare a dilute solution. , As a measurement sample. The particle size distribution of the measurement sample was measured using a laser diffraction / scattering type particle size distribution measuring device (Microtrack MT3000 manufactured by Microtrack Bell Co., Ltd.).
  • the frequency (volume%) based on the distribution under the integrated sieve was obtained, and the cumulative particle size distribution curve was obtained.
  • the median diameter (50% diameter) in the cumulative particle size distribution curve is defined as the average particle diameter (D 50 , d 50), and the particle diameter corresponding to the 80% distribution under the integrated sieve is defined as the 80% diameter (D 80 , d 80).
  • the particle diameter corresponding to the distribution of 95% was 95% diameter (D 95, d95).
  • the base of the first peak there is a portion where the frequency distribution curve is a convex curve upward compared to the particle size distribution of the first silicon nitride powder, so that the convex curve is inflectioned.
  • the second peak can be identified as a point. Even in the blending range of 75 parts by weight to 94 parts by weight of the first silicon nitride powder and 25 parts by weight to 4 parts by weight of the second silicon nitride powder, the first peak (fine grain side) and the second peak (coarse grain side) ) Are sufficiently separated, the peak tops of each can be easily identified.
  • the volume-based basis is taken into consideration in consideration of the particle size distribution of the second silicon nitride powder. It may be difficult to identify the second peak on the frequency distribution curve of the particle size distribution. In that case, a Voigt distribution type curve that combines a Gaussian function and a Lorentz function is assumed, and the second peak (coarse grain side) can be identified by peak separation.
  • the second peak when it is difficult to identify the second peak (coarse grain side) (the first silicon nitride powder is 90 parts by weight to 95 parts by weight, the second silicon nitride powder is 10 parts by weight to 5 parts by weight).
  • the peak top of the second peak was confirmed by the peak separation method.
  • the second peak is obtained by measuring the frequency distribution data of the area-based particle size by the scanning electron microscope (SEM) observation method described in the following "Measuring method of aspect ratio of silicon nitride powder" (paragraph 0166). It is also possible to determine the particle size of the peak top (on the coarse grain side).
  • the criteria for displaying the particle size distribution are appropriately used according to the particle size range of interest (whether to focus on fine particles or coarse particles), and the frequency distribution data of the area-based particle size distribution is used. It is easy to convert to a frequency distribution curve of volume-based particle size distribution by calculation. On the contrary, it is easy to convert the volume-based frequency distribution (difference%) into the area-based particle size distribution frequency distribution.
  • Example 1 Silicon nitride (Si 3 N 4 ) powder with a specific surface area of 11.2 m 2 / g, an oxygen content of 1.6% by weight, and a ⁇ -type silicon nitride content of 1.8% by mass (A-1 shown in Table 1). 10 parts by mass of ⁇ -type silicon nitride powder prepared by the combustion synthesis method was added to 90 parts by mass. To 94.8 parts by weight of this formulation, 3.3 parts by weight of the above-mentioned toluene oxide and 1.9 parts by weight of the above-mentioned magnesium oxide were added as sintering aids, and 2 parts of the sorbitan ester-based dispersant was added to the powder.
  • the obtained mixed powder slurry is cast on a carrier film to a predetermined thickness using a doctor blade device.
  • a sheet-molded green sheet was obtained. Further, the obtained green sheet was subjected to laminating and crimping treatment of three sheets at a temperature of 120 ° C. and a predetermined pressure to prepare a laminated molded body sheet having a baked size of about 0.35 mm. The produced laminated molded product sheet was visually inspected to confirm the presence or absence of cracks.
  • this laminated molded product sheet was cut into 60 mm ⁇ 70 mm, and the dimensions, average thickness, and weight were measured to calculate the molded product density.
  • the laminated molded product sheet density in this example was 2.0 g / cm 3 . Further, in order to measure the bulk density and the thermal conductivity of the sintered body, the number of laminated green sheets is increased so that the baked size is 10 mm in diameter and 1.0 mm in thickness for a disk-shaped test piece. The molded body sheet was cut out.
  • the laminated molded sheet was placed in a boron nitride container in layers via a separating material and heated in air at 400 to 600 ° C. for 2 to 5 hours to sufficiently add the organic binder component and the like added in advance.
  • Degreased (removed). The weight after degreasing was measured, and the weight and bulk density of the green sheet degreased body were determined assuming that there was no change in the weight of the separating material.
  • the degreased body is heated to 1520 ° C. under a nitrogen atmosphere of 0.8 MPa, heated to 1850 ° C. at a heating rate of 120 ° C./hr from 1520 ° C. to 1800 ° C., and further heated to 1850 ° C.
  • the cooling rate to 1500 ° C. was set to 350 ° C./hr, and the mixture was cooled to room temperature, and the obtained silicon nitride sintered body was peeled off with a separating material layer to obtain a plate-shaped silicon nitride sintered body. ..
  • the obtained plate-shaped silicon nitride sintered body was weighed, the weight loss rate was recorded, and then blast polishing was performed to obtain a silicon nitride sintered body for a substrate having a desired surface roughness.
  • the average thickness removed by the blast polishing process was 10 ⁇ m or less.
  • a laminated molded product sheet having the same dimensions is prepared, the weight thereof is measured, a separating material is applied and dried, and the weight of each laminated molded product sheet is measured again.
  • the laminated molded product sheets are stacked via the separating material, and the weight before and after degreasing is measured. Since the degreasing rate of each laminated molded body sheet is the same, the weight after degreasing of each laminated molded body sheet can be calculated from the weight after degreasing of the stacked laminated molded body sheets.
  • the weight of the sintered laminated molded body sheet can be measured to know the weight change before and after sintering as a whole (the weight change of the separating material is negligible). I have confirmed that there is). Finally, the separator is carefully peeled off and the dry weight of the resulting sintered body is measured. By precisely measuring the weight in each of these steps, it is possible to know the weight change of each sintered sheet before and after sintering. From the obtained weight data, the weight loss rate before and after sintering, which is one of the constituent factors of the present invention, can be accurately grasped.
  • the bulk density of the obtained plate-shaped silicon nitride sintered body was measured by the Archimedes method for measuring the weight and buoyancy of a test piece suspended from a thin wire.
  • the relative density ratio to the theoretical density based on the compounding composition was obtained from the bulk density.
  • X-ray diffraction measurement of plate-shaped silicon nitride sintered body A RINT-TTRIII type wide-angle X-ray diffractometer manufactured by Rigaku Co., Ltd. was used for measuring the X-ray diffraction pattern of the obtained plate-shaped silicon nitride sintered body.
  • the X-ray source is CuK ⁇ ray, and the peak intensities of each diffraction peak ((200) plane, (101) plane and (210) plane) of ⁇ -type silicon nitride are examined, and the presence or absence of a diffraction peak due to MgSiN 2 is checked. Examined.
  • the surface of the silicon nitride sintered body is not 0.05 ⁇ m or more and 0.5 ⁇ m or less
  • the surface is polished to set the arithmetic average roughness Ra to 0.
  • the size was adjusted to 05 ⁇ m or more and 0.5 ⁇ m or less.
  • the arithmetic mean roughness Ra of the surface of the obtained plate-shaped silicon nitride sintered body was measured according to JIS B 0601-2001 (ISO4287-197). Using a stylus type surface roughness meter, a stylus with a stylus tip radius of 2 ⁇ m was applied to the polished surface of the silicon nitride sintered body, the measurement length was 5 mm, and the scanning speed of the stylus was 0. The surface roughness was measured at 5 mm / sec, and the average value of the five points obtained by this measurement was taken as the value of the arithmetic average roughness Ra.
  • a bending test piece having a width of 4.0 mm, a thickness of 0.35 mm, and a length of 40 mm was used for measuring the bending strength of the obtained plate-shaped silicon nitride sintered body.
  • the room temperature is maintained by a four-point bending test jig with an inner span of 10 mm and an outer span of 30 mm, using a method conforming to JIS R1601, except that the thickness (0.35 mmt) of the test piece is different. The four-point bending strength of was measured.
  • the fracture toughness value of the obtained plate-shaped silicon nitride sintered body was measured by the IF method based on JIS-R1607: 2015.
  • a Vickers indenter is pressed into the mirror-polished surface of the plate-shaped silicon nitride sintered body with a predetermined indenter pressing load (5 kgf (49N)) for 15 seconds, and one diagonal of the Vickers indentation is a plate-shaped silicon nitride sintered body.
  • the length of the diagonal line of the Vickers indentation and the length of the crack generated on the extension of the diagonal line were measured so as to be perpendicular to the thickness direction of the body.
  • the fracture toughness value K IC was calculated from the obtained measurement length.
  • the silicon nitride particles and the grain boundary were binarized by an image analyzer (WinROOF Ver5.6.2 manufactured by Mitani Shoji Co., Ltd.) using the obtained SEM photograph.
  • 3 Observation field / measurement
  • the length of the long side and the length of the short side of all ⁇ -type silicon nitride particles existing in the total area were measured.
  • the frequency distribution of the measured long-side length or short-side length of ⁇ -type silicon nitride particles was expressed as the area fraction of each particle (ratio to the total area of the silicon nitride particles). It has been confirmed by X-ray diffraction measurement that all the silicon nitride particles are ⁇ -type silicon nitride.
  • the length of the long side is defined as the major axis diameter and the length of the short side is determined by the particle shape appearing in the observed cross section.
  • the minor axis diameter the frequency distribution of the major axis diameter and minor axis diameter particles based on the area was measured, and the cumulative particle size distribution curve based on the area was obtained to correspond to each of the major axis diameter and the minor axis diameter. The area fraction was calculated.
  • the area fraction of the particles having a major axis diameter of 3 ⁇ m or more is the area fraction of the particles having a major axis diameter of 3 ⁇ m or more with respect to the total area of the observed ⁇ -type silicon nitride particles, and the particles having a major axis diameter of more than 10 ⁇ m (
  • the area fraction of the coarse ⁇ -type particles) is the area fraction of the particles having a major axis diameter of more than 10 ⁇ m with respect to the total area of the observed ⁇ -type silicon nitride particles.
  • the maximum opening diameter and open porosity on the polished surface were calculated as follows. First, using a scanning electron microscope (SEM), an image of 5 observation fields in a region set to 60 ⁇ m ⁇ 44 ⁇ m per observation field from the polished surface of the silicon nitride sintered body at an observation magnification of 2000 times. Was taken in. The maximum opening diameter was determined by measuring the diameter of the largest open pore in 5 observation fields and total measurement area of 13200 ⁇ m 2 with an image analyzer (WinROOF Ver 5.6.2 manufactured by Mitani Shoji Co., Ltd.).
  • the same image analyzer 400 [mu] m 2 the area of measurement by 1 field in the image, the measurement field number 12, that is, the measured total area as 4800Myuemu 2, was determined area of open pores in the measurement the total area.
  • the area of the open pores was divided by the total measured area, and the ratio of the area of the open pores to the total measured area was taken as the open pore ratio on the surface. This made it possible to calculate the open porosity on the surface.
  • the obtained plate-shaped silicon nitride sintered body was crushed and crushed, and passed through a sieve having a mesh size of 250 ⁇ m.
  • the oxygen content of the pyroclastic material sample was measured by an inert gas melting-carbon dioxide infrared absorption method (manufactured by LECO, TC-136 type) based on the JIS R1603-10 oxygen quantification method.
  • the characteristics of the raw material powder used in the production of the silicon nitride sintered body, the composition of the raw material composition, the outline of the production conditions of the silicon nitride sintered body, and the obtained plate-shaped silicon nitride sintered body are listed.
  • Table 1, Table 2, Table 3 and Table 4 show the measurement results of the above evaluation items regarding the chemical composition and the microstructure and thermal / mechanical properties of the obtained plate-shaped silicon nitride sintered body.
  • Examples 1 to 44 are examples of the present invention
  • Comparative Examples 1 to 22 are comparative examples of the present invention.
  • the bending strength at room temperature is the 4-point bending strength
  • the number of coarse ⁇ particles is the long axis of the ⁇ -type silicon nitride particles observed in the 1 mm 2 region of the cut surface perpendicular to the plate surface of the silicon nitride sintered body. It represents the number of ⁇ -type silicon nitride particles having a diameter (length of the long side) exceeding 10 ⁇ m.
  • the area fraction of coarse ⁇ particles ( ⁇ -type silicon nitride particles having a major axis diameter of more than 10 ⁇ m) appearing in the observation field, the area fraction of ⁇ -type silicon nitride particles having a major axis diameter of more than 3 ⁇ m, and the major axis diameter (length).
  • the 50% area diameter (D 50 ) and the 80% area diameter (D 80 ) of the side length) are also described.
  • Table 8 shows the powder characteristics and particle size distribution of the combination of the first silicon nitride powder and the second silicon nitride powder used in Examples and Comparative Examples.
  • the ⁇ fraction is 7% or more and 64% or less
  • the oxygen content is 0.74% by weight or more and 1.95% by weight or less
  • the specific surface area by the BET method is 6.3 m2 / g or more and 12.8 m2 / g.
  • the average particle size in the particle size distribution measured by the laser diffraction scattering method is 0.66 ⁇ m or more and 1.5 ⁇ m or less, and the above-mentioned “Method for measuring the particle size distribution and peak top of silicon nitride powder” (paragraph 0164).
  • the frequency distribution curve obtained by the method described has two peaks, and the peak tops of the peaks are in the range of 0.5 to 1.2 ⁇ m (first peak) and 1.1 to 3.8 ⁇ m (second peak). In the peak), the second peak is 0.5 to 3.0 ⁇ m larger than the first peak.
  • Example 2 A plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 1 except that the sintering temperature was raised to 1900 ° C.
  • Table 2 shows the compounding composition of the raw material composition
  • Table 3 shows the sintering conditions and the chemical composition of the obtained plate-shaped silicon nitride sintered body
  • Table 3 shows the characteristics of the obtained plate-shaped silicon nitride sintered body. It is shown in Table 4.
  • Example 1 (sintering temperature 1850 ° C.) by changing the type of the ⁇ -type second silicon nitride powder and keeping the blending ratio (90/10) of the first silicon nitride powder and the second silicon nitride powder as it is. And in the same manner as in Example 2 (sintering temperature 1900 ° C.), a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3. Tables 3 and 4 show the chemical composition and various properties of the obtained plate-shaped silicon nitride sintered body.
  • Example 4 since the maximum holding temperature is high, the weight loss rate and oxygen volatilization rate at the time of sintering are large, the diffraction intensity ratio related to the c-axis orientation is in an appropriate range, and the area fraction of the coarse ⁇ particles is also large. Due to its large size, the thermal conductivity increased, and the bending strength and fracture toughness values were also at high levels.
  • Example 1 (sintering temperature 1850 ° C.) by changing the type of the ⁇ -type second silicon nitride powder and keeping the blending ratio (90/10) of the first silicon nitride powder and the second silicon nitride powder as it is. And in the same manner as in Example 2 (sintering temperature 1900 ° C.), a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3. Tables 3 and 4 show the chemical composition and various properties of the obtained plate-shaped silicon nitride sintered body.
  • Example 6 since the maximum holding temperature is high, the weight loss rate and oxygen volatilization rate at the time of sintering are large, the diffraction intensity ratio related to the c-axis orientation is in an appropriate range, and the area fraction of the coarse ⁇ particles is also large. Due to its large size, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value). In Example 7, the high thermal conductivity and excellent performance were achieved even if the holding time at the maximum temperature was slightly short (7 hours), probably because the grain growth was promoted by changing the blending ratio and the addition amount of the sintering aid. The mechanical properties (bending strength and fracture toughness value) were shown.
  • Example 8 to 10 The blending ratio (90/10) of the first silicon nitride powder and the second silicon nitride powder was kept as it was, and 0.5% by weight of the silicon dioxide powder was added to the sintering aid.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 1 (sintering temperature 1850 ° C.) and Example 2 (sintering temperature 1900 ° C.). ..
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 9 since the maximum holding temperature is high, the weight loss rate and oxygen volatilization rate at the time of sintering are large, the diffraction intensity ratio related to the c-axis orientation is in an appropriate range, and the area fraction of the coarse ⁇ particles is also large. Due to its large size, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value). In Example 10, the Mg content was significantly reduced and the weight loss rate was large, but it was high, probably because the mixing ratio and the addition amount of the sintering aid were changed to extend the holding time at the maximum temperature (20 hours). It showed thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value).
  • Examples 11 and 12 Same as in Example 8 (sintering temperature 1850 ° C.) and Example 9 (sintering temperature 1900 ° C.) except that the blending ratio of the first silicon nitride powder and the second silicon nitride powder was changed (75/25). Then, a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 1 to 3. By changing the blending ratio of the silicon nitride raw material, the density of the laminated molded product sheet was slightly increased (2.05 g / cm 3 ). The chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 12 since the maximum holding temperature is high, the weight loss rate and oxygen volatilization rate at the time of sintering are large, the diffraction intensity ratio related to the c-axis orientation is in an appropriate range, and the area fraction of the coarse ⁇ particles is also large. Due to its large size, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value).
  • Example 8 sining temperature 1850 ° C.
  • Example 8 sining temperature 1850 ° C.
  • Example 8 sining temperature 1850 ° C.
  • the blending ratio (50/50 or 40/60) of the first silicon nitride powder and the second silicon nitride powder and the additional amount of the silicon dioxide powder were changed.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 9 (sintering temperature 1900 ° C.).
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 14 since the maximum holding temperature is high, the weight loss rate and oxygen volatilization rate at the time of sintering are large, the diffraction intensity ratio related to the c-axis orientation is in an appropriate range, and the area of the coarse ⁇ particles is equal. Due to its high rate, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness).
  • Example 15 when the holding time at 1800 ° C. was extended to 20 hours, the weight loss rate and the oxygen volatilization rate at the time of sintering increased, and the heat equivalent to that of the 1850 ° C. sintered product (Example 16). The conductivity and mechanical properties (bending strength and fracture toughness value) were shown.
  • Example 18 I changed the combination of the types of the first silicon nitride powder and the second silicon nitride powder.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 8 (sintering temperature 1850 ° C.) with the blending ratio (90/10) unchanged. ..
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 18 when the ratio of magnesium oxide and yttrium oxide was changed, the mechanical properties were deteriorated as compared with Example 8.
  • Example 19 the amount of the auxiliary agent added was reduced to 4.5% by weight, but there was no significant effect.
  • Example 20 the atmospheric pressure was lowered to 0.4 MPa, but there was no particular effect, and a silicon nitride sintered body having almost the same characteristics as the case of 0.8 MPa was obtained even at a gas pressure of 0.4 MPa. It was confirmed that sintering can be performed even if the pressure is lowered to 0.4 MPa.
  • Example 22 and 23 Tables 2 and 3 show that the combination of the types of the first silicon nitride powder and the second silicon nitride powder was changed, and the blending ratio (75/25) was the same as in Example 8 (sintering temperature 1850 ° C.).
  • a plate-shaped silicon nitride sintered body was obtained under the conditions described.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • the holding time at the maximum holding temperature (1880 ° C.) was extended to 18 hours, but the weight loss rate and oxygen volatilization rate at the time of sintering were large, and the diffraction intensity ratio related to the c-axis orientation was appropriate. Since the area fraction of the coarse ⁇ particles is large, it exhibits high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value).
  • Example 24 and 25 Similar to Example 8, plate-like under the conditions described in Tables 2 and 3, except that the rare earth oxide used as the sintering aid was changed to Er 2 O 3 or Yb 2 O 3. A silicon nitride sintered body was obtained. The chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4. By changing the rare earth oxide, grain growth was promoted, and the thermal conductivity and bending strength were slightly increased.
  • Example 26 to 28 The same as in Example 8 except that the first silicon nitride powder was A-3 and the second silicon nitride powder was B-2, and the blending ratio was changed (75/25 or 90/10). , A plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3. The chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 26 since the holding time at 1880 ° C. was extended, the weight loss rate and oxygen volatilization rate at the time of sintering were large, the diffraction intensity ratio related to the c-axis orientation was within an appropriate range, and the area of the coarse ⁇ particles. Due to its high rate, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness).
  • Example 29 and 30 The combination of the first silicon nitride powder and the second silicon nitride powder was the same as in Example 8 (90/10) except that A-2 and B-2 were changed, in the same manner as in the same example.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Example 30 the holding time at 1900 ° C. was shortened, but the weight loss rate and oxygen volatilization rate at the time of sintering were large, the diffraction intensity ratio related to the c-axis orientation was in an appropriate range, and the coarse ⁇ particles. Due to its large area fraction, it exhibited high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness).
  • Example 31 A plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 27 except that the amount of the sintering aid added was reduced.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4. Since the holding time at 1850 ° C. was extended, the weight loss rate and oxygen volatility during sintering were large, the diffraction intensity ratio related to the c-axis orientation was within an appropriate range, and the area fraction of coarse ⁇ particles was also large. It showed high thermal conductivity and excellent mechanical properties (bending strength and fracture toughness value).
  • Examples 32 to 37 A plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3 in the same manner as in Example 1 except that the sintering temperature was lowered to 1800 ° C. and sintering was performed. The chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • the sintering temperature is lowered as compared with Example 1, the weight loss rate and the oxygen volatilization rate are lowered, and the oxygen content of the obtained silicon nitride sintered body is 2.7% by weight to 2.9% by weight.
  • the thermal conductivity and the mechanical properties are slightly deteriorated.
  • Example 38 Except with reduced amount of magnesium oxide is a sintered aid (MgO) and yttrium oxide (Y 2 O 3), the same procedure as in Example 14, the plate with the conditions described in Table 2 and Table 3 A silicon nitride sintered body was obtained. The chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4. Even if the amount of the sintering aid added was reduced, the retention time at 1900 ° C. was extended, so that the ultimate density was not a problem. However, as compared with Example 14, the weight loss rate and the oxygen volatilization rate were remarkably increased by the high temperature and long time sintering, and the measured oxygen content of the sintered body was reduced to 1.3% by weight. Therefore, the grain growth progressed and the thermal conductivity increased, but the mechanical properties (bending strength and fracture toughness value) decreased.
  • MgO sintered aid
  • Y 2 O 3 yttrium oxide
  • Table 2 and Table 2 show that the combination and blending ratio of the first silicon nitride powder and the second silicon nitride powder, and the sintering conditions (the amount of the sintering aid added and the maximum temperature and holding time during sintering) were variously changed.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Table 3.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • the oxygen volatilization rate is insufficient and the oxygen content of the sintered body is high as compared with the corresponding examples (for example, Examples 21 to 23, 26 to 28 and 31).
  • the thermal conductivity (bending strength and fracture toughness value) and mechanical properties of the obtained silicon nitride written sintered body were slightly reduced.
  • the weight ratio of magnesium oxide to the rare earth metal oxide in the compounding composition was set to 0.40 ⁇ magnesium oxide / rare earth metal oxide ⁇ 1.4, and the measured magnesium content as a sintered body was set. It was confirmed that the mass ratio of the amount to the measured yttrium content is 0.05 ⁇ measured magnesium content / measured yttrium content ⁇ 0.85, which is suitable for enhancing the thermal conductivity and mechanical properties. ..
  • the thickness of the plate-shaped silicon nitride sintered body excluding the disk-shaped test piece for measuring the thermal conductivity was 0.33 to 0.48 mm. / area ratio 1.0x10 -4 ⁇ 1.9x10 -4 (1 / mm), the removal amount of the vertical plate surface the surface layer portion in the thickness direction was 0.008 ⁇ 0.03 mm per side.
  • the crystal phase of the Mg compound such as MgSiN 2 was not detected by the X-ray diffraction measurement of the silicon nitride sintered body plate surface. Further, the diffraction intensity of the main peak ((22-1) plane) of the J phase (RE 4 Si 2 O 7 N 2 ) constituting the grain boundary phase and the N-merylite phase (RE 2 Si 3 O 3 N 4 ) A plate in which the total diffraction intensity of the main peak ((211) plane) is less than 0.07 (including zero) of the ratio of the ⁇ -type silicon nitride in the silicon nitride sintered body to the diffraction strength of the (200) plane. It was confirmed that it was a silicon nitride sintered body.
  • the minor axis diameter of the silicon nitride particles is also measured, and the minor axis diameter described in Patent Document 9 is used.
  • the area average diameter of the silicon nitride particles of 2 ⁇ m or more is less than 5.0 ⁇ m in all the examples, and the sintered body of the prior art. It has been confirmed that the particle size distribution is remarkably sharper than that of.
  • Comparative Examples 1 and 2 are examples in which only the first silicon nitride powder (A-1) is used as the silicon nitride raw material.
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4.
  • a silicon nitride raw material having a high ⁇ fraction a plate-shaped silicon nitride sintered body having excellent mechanical properties (bending strength, fracture toughness value, etc.) could be obtained.
  • the particles constituting the silicon nitride sintered body are fine and the grain growth is slow, the result is that the thermal conductivity is slightly low.
  • Comparative Examples 3 and 4 are examples in which a raw material composition in which the second silicon nitride powder (B-1) is mixed with the first silicon nitride powder (A-1) is used.
  • the holding time at the maximum temperature was 10 hours, and the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 were shown in Table 3 as in Example 1. And shown in Table 4.
  • the measured oxygen content of the sintered body decreased from 2.75% by weight to 2.35% by weight as the sintering temperature increased.
  • the diffraction intensity ratio related to the c-axis orientation is small, and the grain growth of the coarse ⁇ -grain ⁇ -type silicon nitride particles is insufficient, and the characteristics are as expected. (Thermal conductivity, bending strength and fracture toughness value) No improvement was observed.
  • Comparative Examples 5 to 7 are also examples in which the raw material composition in which the second silicon nitride powder (B-1) is mixed with the first silicon nitride powder (A-1) is used.
  • the weight ratio of magnesium oxide, which is a sintering aid, and rare earth metal oxides By varying the weight ratio of magnesium oxide, which is a sintering aid, and rare earth metal oxides, a plate-shaped silicon nitride sintered body was formed under the conditions shown in Tables 2 and 3 in the same manner as in Comparative Example 1. I made it.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Comparative Examples 5 and 6 probably because the compounding ratio of the second silicon nitride powder having a low specific surface area was too large, the reaching density was also low, and the characteristics of the sintered body (thermal conductivity, bending strength and fracture toughness value) were significantly deteriorated. did.
  • Comparative Example 7 the weight ratio of magnesium oxide, which is a sintering aid, to rare earth metal oxide is inappropriate (magnesium oxide / rare earth metal oxide is 1.5), and high-temperature baking is performed at 1900 ° C. for 10 hours. The expected improvement in characteristics (thermal conductivity, bending strength and fracture toughness value) was not observed even under the binding conditions, and the thermal conductivity, bending strength and fracture toughness value were low.
  • Comparative Example 10 This is an example in which a raw material composition containing silicon nitride powder (A-5) having a ⁇ fraction of 14% by mass, a low specific surface area, and a low oxygen content is used as the first silicon nitride powder.
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4. Due to the low specific surface area and low oxygen content, the thermal conductivity was high, probably due to the progress of grain growth, but the mechanical properties were significantly deteriorated.
  • Comparative Examples 11 and 12 are examples in which the amount of the sintering aid added is changed, and Comparative Example 13 is an example in which the weight ratio of the alkaline earth metal oxide and the rare earth metal oxide is changed (alkaline earth metal oxide). The weight ratio between and the rare earth metal oxide is too small).
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4.
  • Comparative Examples 13 and 14 are examples in which the second silicon nitride powder having a low specific surface area and a coarse particle size was used. Due to the presence of the coarse ⁇ -type silicon nitride particles, the ultimate density was reduced, and the thermal conductivity and mechanical properties (bending strength and fracture toughness value) were significantly reduced.
  • Comparative Example 15 is an example in which the amount of silicon dioxide added is too large.
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4.
  • the amount of silicon dioxide added was too large, the measured oxygen content of the sintered body was high and the grain growth was insufficient, so that the thermal conductivity was low and the mechanical properties were also low.
  • Comparative Examples 16 to 18 Comparative Examples 16 and 17 are examples in which the maximum temperature at the time of sintering is too low, and Comparative Example 18 is an example in which the holding time at 1850 ° C. is too short.
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4.
  • the sintering is significantly insufficient, and not only the relative density of the silicon nitride sintered body decreases, but also the sintering aid in the sintering process ( Evaporation of silicon dioxide (SiO 2 ) component in silicon oxide (magnesium oxide and rare earth metal oxide) and silicon nitride raw material was suppressed. Therefore, in Comparative Examples 16 and 17, the measured oxygen content of the sintered body was about 2.9% by weight.
  • Comparative Example 18 the number of ⁇ -type silicon nitride particles having a major axis diameter of more than 10 ⁇ m is remarkably large, probably because the oxygen content of the raw material composition itself is low, or because the oxygen volatilization amount is small and the holding time is too short. Diminished. In these comparative examples, both thermal conductivity and mechanical properties (bending strength and fracture toughness value) were reduced.
  • Comparative Example 19 is an example in which the second silicon nitride powder contains coarse particles having a low ⁇ fraction of 50% by mass, a low specific surface area, a high oxygen content, and a large diameter D 95 of 95%.
  • a plate-shaped silicon nitride sintered body was obtained under the conditions shown in Tables 2 and 3.
  • the chemical composition and characteristics of the obtained plate-shaped silicon nitride sintered body are shown in Tables 3 and 4.
  • Comparative Examples 20 and 21 are examples in which grain growth has progressed too much. It can be obtained when a high-density sintered body cannot be obtained unless it is held for 30 hours at a maximum holding temperature of 1850 ° C. or held for 22 hours at a maximum holding temperature of 1900 ° C., which is a high temperature-long-term strict sintering condition.
  • the weight ratio (measured magnesium content / measured rare earth metal content) between the measured magnesium content and the measured rare earth metal content of the silicon nitride sintered body is 0.03 to 0.28, and the measured oxygen content is 1. It was 48% by weight to 1.56% by weight.
  • the number of ⁇ -type silicon nitride particles having a major axis length of more than 10 ⁇ m was significantly increased (10,000 particles / mm 2 or more), and the bending strength and fracture toughness value were low. Further, the open porosity on the polished surface is about 1.5%, and the maximum open pore diameter is about 2.0 ⁇ m, which makes it difficult to apply to an insulating substrate or a circuit board.
  • Comparative Example 22 is an example in which the characteristics of the silicon nitride raw material are inappropriate.
  • the chemical composition and characteristics of the plate-shaped silicon nitride sintered body obtained under the conditions shown in Tables 2 and 3 are shown in Tables 3 and 4.
  • As the first silicon nitride powder a powder having a high ⁇ powder ratio and a low specific surface area and a low oxygen content was used, so that grain growth was suppressed, and as a result, the thermal conductivity was lowered.
  • the mechanical properties (bending strength and fracture toughness value) were also low.
  • the thermal conductivity is remarkably lowered in the comparative examples other than Comparative Examples 9, 19, 20 and 21, and the mechanical properties in the comparative examples other than Comparative Examples 1, 2, 3, 4, 10, 12 and 22. (Bending strength and fracture toughness value) were reduced, and there was no plate-shaped silicon nitride sintered body that had both thermal conductivity and mechanical properties.
  • the ⁇ fraction is 0% or more and 10% or less, and the oxygen content is 0.75% by weight or more and 2.2% by weight or less.
  • the fraction is 60% or more and 100% or less, the oxygen content is 0.55% by weight or more and 2.0% by weight or less, and the specific surface area is 2.5 m 2 / g or more and 10.0 m 2 / g or less.
  • the formulation in which the first silicon nitride powder and the second silicon nitride powder are blended in a predetermined ratio has a ⁇ content of 7% or more and 64% or less and an oxygen content of 0. .74 wt% 1.95 wt% or less, the specific surface area by BET method of 6.3 m 2 / g or more 12.8m 2 / g or less, an average particle diameter in the particle size distribution measured by a laser diffraction scattering method 0.
  • the frequency distribution curve which is 66 ⁇ m or more and 1.5 ⁇ m or less and is obtained by the method described in the above-mentioned “Silicon nitride powder particle size distribution and peak top measurement method” (paragraph 0164), has two peaks.
  • the peak tops are in the range of 0.5 to 1.2 ⁇ m (first peak) and 1.1 to 3.8 ⁇ m (second peak), and the second peak is higher than the first peak. Since it has a large value of 0.5 to 3.0 ⁇ m, it is suitable as a raw material for producing the plate-shaped silicon nitride sintered body of the present invention.
  • the total amount of the alkali earth metal oxide (for example, magnesium oxide) and the rare earth metal oxide (for example, yttrium oxide) added as the sintering aid is 3.2% by weight or more and 7.0% by weight. % Or less, the weight ratio satisfies 0.40 ⁇ alkaline earth metal oxide / rare earth metal oxide ⁇ 1.4.
  • the ratio of the measured alkaline earth metal content to the measured rare earth metal content is 0.05 ⁇ measured alkaline earth metal content / measured rare earth metal content ⁇ 0. It is .85 and the relative density is 98% or more.
  • the ⁇ -type silicon nitride obtained when the plane obtained by grinding from the surface polished to an arithmetic average roughness Ra of 0.05 ⁇ m or more and 0.5 ⁇ m or less to the inside by 0.08 mm or more is irradiated with X-rays.
  • the ratio of ⁇ I (200) + I (210) ⁇ / ⁇ 2 ⁇ I (101) ⁇ is 1.10 or more and 1.40 or less.
  • the measured oxygen content is 1.3% by weight or more and 2.8% by weight or less.
  • the number of columnar ⁇ -type silicon nitride particles having a major axis diameter of more than 10 ⁇ m is 1200 or more per 1 mm 2 of the cut surface. Since the area fraction of particles having a major axis diameter of more than 10 ⁇ m is 6.5% or more and 39% or less based on the area of 10,000 or less silicon nitride particles, the thermal conductivity at room temperature is 110 W.
  • the present invention has the first silicon nitride powder having a ⁇ fraction of 0% or more and 10% or less and having a specific oxygen content, specific surface area and average particle size, and the ⁇ fraction.
  • a green sheet is prepared from the starting composition by a sheet molding process, and the green sheet is subjected to a pressurized atmosphere having a nitrogen-containing gas pressure of 0.15 MPa or more and 3 MPa or less, and a maximum holding temperature of 1790 ° C. or more and 1910 ° C. or less.
  • the plate-shaped silicon nitride sintered body of the present invention has a microstructure in which the length of the long axis of the columnar ⁇ -type silicon nitride particles constituting the sintered body and the orientation state thereof are highly controlled.
  • it has high thermal conductivity. Since it has high thermal conductivity and high mechanical strength and toughness, it can not only suppress the occurrence of cracks in the substrate when used as an insulating substrate or circuit board, but also has remarkable thermal shock resistance and cold thermal cycle resistance. You can expect improvement.

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Abstract

La présente invention concerne un procédé d'obtention d'un corps fritté à base de nitrure de silicium de type plaque qui présente une conductivité thermique élevée et d'excellentes caractéristiques mécaniques (résistance et ténacité à la rupture). Dans la présente invention, un corps fritté à base de nitrure de silicium de type plaque dans lequel la teneur en oxygène et le rapport entre la teneur en métal alcalino-terreux et la teneur en métal des terres rares sont régulés de manière très précise est produit par : l'ajout d'un auxiliaire de frittage à une matière première de nitrure de silicium obtenue par mélange d'une première poudre de nitrure de silicium, qui a une fraction β de 0 à 10 % et a une teneur en oxygène, une surface spécifique et un diamètre moyen de particule spécifiés, et d'une seconde poudre de nitrure de silicium, qui a une fraction β de 60 à 100 % et a une teneur en oxygène, une surface spécifique, un diamètre de particule moyen et un rapport de forme spécifiés, ce qui permet de préparer une composition de matériau de départ ; la production d'une feuille crue à partir de la composition de matériau de départ à l'aide d'un procédé de moulage de feuille ; puis le frittage en maintenant la feuille crue dans une atmosphère sous pression ayant une pression de gaz contenant de l'azote comprise entre 0,15 et 3 MPa dans une région de température dans laquelle la température de maintien maximale est comprise entre 1 790 et 1 910 °C. L'invention concerne également un mélange de poudres de matières premières et un corps fritté à base de nitrure de silicium.
PCT/JP2020/046124 2019-12-11 2020-12-10 Corps fritté à base de nitrure de silicium de type plaque et son procédé de fabrication Ceased WO2021117829A1 (fr)

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EP4628448A1 (fr) * 2024-04-02 2025-10-08 Denka Company Limited Poudre de nitrure de silicium
EP4631911A1 (fr) * 2024-04-02 2025-10-15 Denka Company Limited Poudre de nitrure de silicium
WO2026028772A1 (fr) * 2024-07-29 2026-02-05 日本碍子株式会社 Corps fritté en nitrure de silicium

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WO2026028772A1 (fr) * 2024-07-29 2026-02-05 日本碍子株式会社 Corps fritté en nitrure de silicium

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