JPH0359033B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a silicon carbide sintered body for heat-resistant jigs with excellent dimensional accuracy, and in particular, the present invention relates to heat-resistant jigs for the electronics industry, such as diffusion oxidation treatment of semiconductors, diode The present invention relates to a heat-resistant silicon carbide sintered body for use in jigs, which has excellent dimensional accuracy and is suitable for applications such as bonding, glass sealing, and brazing lead frames of packages. [Prior art] Heat-resistant jigs for the electronics industry are mainly used for handling high-purity products such as semiconductors, and are required to have high purity, no product contamination, excellent wear resistance, and It is important to have excellent dimensional accuracy. The heat-resistant jig for the electronic industry is a recrystallized silicon carbide material manufactured from highly purified silicon carbide powder and high-purity silicon for the electronic industry, or a high-purity graphite material whose surface is made of silicon carbide. It is known to be manufactured from a graphite material coated with silicon carbide. [Problems to be Solved by the Invention] However, the recrystallized silicon carbide material is expensive because it uses high-purity silicon for the electronic industry as a starting material, and it is difficult to compare it with other starting materials. Because it uses coarse-grained silicon carbide, the surface has a large surface roughness, and it has the disadvantage that it is difficult to manufacture heat-resistant jigs that require high dimensional accuracy without special machining. On the other hand, the silicon carbide-coated graphite material is manufactured by reacting the surface of the graphite material with SiO gas to convert it into SiC, and the silicon carbide coating layer is relatively thin and porous, so it has low oxidation resistance. It also had the disadvantage of poor abrasion resistance. [Means for Solving the Problems] The present inventors have developed a material for heat-resistant jigs for the electronic industry, which has improved oxidation resistance, abrasion resistance, and With the aim of providing low-cost materials for heat-resistant jigs for the electronics industry with excellent dimensional accuracy, we have conducted a variety of research to develop silicon carbide fine materials with low impurity components that are used in normal pressureless sintering methods. By using powder as a starting material and sintering it in a specific atmosphere and temperature range, it is possible to produce a high-strength silicon carbide sintered body with high surface precision without causing substantial firing shrinkage. The present invention was completed based on this new discovery. The present invention is a silicon carbide sintered body sintered without substantially shrinking, and has an average bending strength of 7 kg/mm ² or more, and is a heat-resistant cured body with excellent dimensional accuracy. It is a silicon carbide sintered body for tools. The present invention will be explained in detail below. The silicon carbide sintered body of the present invention must be made of a silicon carbide sintered body sintered without substantially shrinking. The reason for this is that silicon carbide sintered bodies produced by the normal standing sintering method, which is shrunk during sintering, are preferable in terms of strength and wear resistance; The dimensions of the sintered body are greatly affected by the density of the formed body and the amount of shrinkage during sintering, so in order to produce a sintered body with excellent dimensional accuracy, the shrinkage during sintering must occur uniformly. By the way, in order to cause the above-mentioned contraction uniformly, it is important to obtain a formed body with a uniform density, but it is extremely difficult to obtain a formed body with such a uniform density, and this study This is because it is difficult to produce a sintered body with extremely excellent dimensional accuracy, which is the object of the invention, by causing firing shrinkage. In addition, it is advantageous that the firing shrinkage rate of the silicon carbide sintered body of the present invention, which is sintered without substantially shrinking, is 2% or less, and more preferably 1% or less. be. The silicon carbide sintered body of the present invention needs to have an average bending strength of 7 Kg/mm ² or more. The reason is that the average bending strength of the silicon carbide sintered body is 7.
This is because if it is smaller than Kg/mm ² , it will easily break or crack during use and will not be able to withstand practical use. The silicon carbide sintered body of the present invention is preferably a silicon carbide sintered body having an average crystal grain size of 0.5 to 10 μm and a density of 1.4 to 2.6 g/cm ³ . The reason why the average grain size of the crystals is preferably within the range of 0.5 to 10 μm is that the average grain size of the crystals is
A sintered body smaller than 0.5 μm has weak bonds between crystal grains, and it is difficult to form a sintered body with an average bending strength of 7 Kgmm ² or more, which is the objective of the present invention.
On the other hand, if it is larger than 10 μm, the surface roughness of the sintered body becomes large and the dimensional accuracy deteriorates. The reason why the density is preferably within the range of 1.4 to 2.6 g/cm ³ is that a sintered body with a density smaller than 1.4 g/cm ³ has few bonding points between silicon carbide particles. This is because it is difficult to produce a sintered body with an average bending strength of 7 kg/cm ² or ^more , which is the aim of Although a green body with a suitable density is required, it is extremely difficult and impractical to obtain a green body with a density greater than 2.6 g/cm ³ . The silicon carbide sintered body of the present invention must have excellent dimensional accuracy, and is a silicon carbide sintered body having a three-dimensional network structure composed of silicon carbide crystals with an average aspect ratio of 5 or less. It is preferable that it is made of the following. Next, a method for manufacturing a heat-resistant silicon carbide sintered body for a jig with excellent dimensional accuracy according to the present invention will be described. The silicon carbide sintered body for heat-resistant jigs of the present invention is obtained by forming silicon carbide powder with an average particle size of 5 μm or less into a green body, and then molding the green body in a non-oxidizing atmosphere within a temperature range of 1700 to 2100°C. It can be manufactured by a method of sintering without substantially shrinking. The reason why silicon carbide powder with an average particle size of 5 μm or less is used is that silicon carbide with a particle size larger than 5 μm is preferable for suppressing firing shrinkage, but it reduces the number of bonding points between grains in the sintered body. This is because not only is it difficult to obtain a silicon carbide sintered body having high strength, that is, an average bending strength of 7 kg/mm ² or more, but also the surface roughness is deteriorated. By the way, the crystal system of silicon carbide has α type and β type.
There are two types: type and amorphous, and any of them or a mixture thereof can be used. Among them, β type is easy to obtain in fine powder form with a diameter of 5 μm or less, and is relatively easy to obtain. It can be advantageously used because a high-strength sintered body can be produced, and in particular, it is advantageous to use silicon carbide powder containing 50% by weight or more of β-type silicon carbide. The silicon carbide powder preferably has a total content of boron, aluminum, and iron of 0.3% by weight or less in terms of elements. The reason for this is that if the total content of boron, aluminum and iron is more than 0.3% by weight in terms of elements, sintering will occur during sintering due to interaction with free carbon contained in silicon carbide powder. This is because it tends to shrink, making it difficult to produce a sintered body without causing substantial shrinkage, which is the objective of the present invention. In addition, when the content of boron, aluminum, and iron in the silicon carbide powder is within the above range, a carbonaceous substance can be added to make the starting material contain 5% by weight or less of free carbon.
The free carbon has the effect of suppressing the coarsening of crystal grains, and by making it present in the starting raw material, it is possible to make the crystal grain size of the sintered body uniform and obtain a sintered body with relatively high strength. can. The reason why the free carbon content is set to 5% by weight or less is that if it is more than 5% by weight, excessive carbon will exist between the silicon carbide powder particles, which will significantly inhibit the bonding between the particles. This is because the strength of the sintered body deteriorates. The carbonaceous material may be any material as long as it allows carbon to be present at the start of sintering, such as various organic materials such as phenol resin, lignin sulfonate, polyvinyl alcohol, cornstarch, saccharide, coatal pitch, alginate, or carbon. Pyrolytic carbon such as black, acetylene black can be used advantageously. The silicon carbide powder has a total content of boron, aluminum, and iron of 0.3 in terms of elements.
When the content of carbonaceous substances and free carbon exceeds 0.6% by weight, it is preferable that the content of carbonaceous substances and free carbon is 0.6% by weight or less in terms of fixed carbon amount. The reason is that boron,
If the total content of aluminum and iron exceeds 0.3% by weight in terms of elements, the content of carbonaceous substances and free carbon in terms of fixed carbon content
As explained earlier, if it is more than 0.6% by weight,
This is because the interaction between boron, aluminum, or iron and carbon tends to cause sintering shrinkage during sintering, making it difficult to obtain a sintered body without causing substantial shrinkage, which is the objective of the present invention. be. In addition, if the content of boron, aluminum, and iron is too high, it will deteriorate the physical properties of the sintered body, so it is desirable that the content be as low as possible, and the total content should be 2% by weight or less in terms of elements. preferable. The resulting body is fired within a temperature range of 1700-2100°C. The reason for this is that if the temperature is lower than 1700°C, it is difficult to sufficiently develop the bonds that connect the grains, making it impossible to obtain a sintered body with high strength, whereas if the temperature is higher than 2100°C, once the Among the nets that have grown, those that are smaller than a certain size become constricted or, in severe cases, disappear, resulting in a decrease in strength, and some particles become coarser, causing the surface to become rougher. This is because the roughness deteriorates. The resulting shaped body is fired in a non-oxidizing atmosphere without substantial shrinkage. The reason for this is that shrinkage during sintering is preferable for improving the strength of the sintered body, but generally speaking, the amount of shrinkage during sintering has a large effect on the density of the formed body, so it is necessary to generate uniform shrinkage. Therefore, it is important to obtain a formed body with uniform density. However, it is extremely difficult to obtain a green body with such uniform density, and therefore it is difficult to produce a sintered body with extremely high dimensional accuracy, which is the object of the present invention, by causing firing shrinkage. It is from. In addition, in order to obtain a sintered body with high dimensional accuracy as described above, the firing shrinkage rate when sintering without substantially shrinking is preferably 2% or less, particularly 1% or less. is more suitable. In addition, the formed body has a gas partial pressure of at least one of CO or N ₂ in the atmosphere of 100 Pa for at least 10 minutes within a temperature range of 1700 to 2100°C.
It is preferable that the firing be performed in an atmosphere maintained above. The reason for this is that by increasing the partial pressure of at least one of CO or _N2 in the atmosphere to 100 Pa or higher for at least 10 minutes within the above temperature range, the growth of the nets can be promoted and the sintering of silicon carbide can be accelerated. This is because shrinkage during firing can be effectively suppressed. It is advantageous for the silicon carbide sintered body for a heat-resistant jig of the present invention to be fired by charging the formed body into a heat-resistant container in which the firing atmosphere can be controlled. The reason why it is advantageous to charge the material into a heat-resistant container and fire it while controlling the firing atmosphere is because it can promote bonding between adjacent silicon carbide crystals and the growth of nets. .
The reason why bonding between adjacent silicon carbide crystals and the growth of nets can be promoted by charging the formed body into a heat-resistant container and firing while controlling the firing atmosphere as described above is because the carbonization This is thought to be because movement of silicon carbide between silicon particles by evaporation-recondensation and/or surface diffusion can be promoted. As the heat-resistant container, materials such as graphite and silicon carbide, and materials having functions equivalent to these materials can be advantageously used. Furthermore, it is advantageous to control the volatilization rate of silicon carbide to 5% by weight or less during firing by charging the formed body into a heat-resistant container in which the firing atmosphere can be controlled and firing it. Advantageously, the formed body for producing the silicon carbide sintered body for the heat-resistant jig has a density of 45 to 80% by volume. The reason for this is that when the density of the formed body is lower than 45% by volume, there are fewer points of contact between the silicon carbide particles, which inevitably leads to fewer bonding points and an average bending strength of 7 Kg/mm ² or more, which is the objective of the present invention. The reason for this is that it is difficult to obtain a sintered body having a sintered body with a volume of more than 80% by volume, while it is difficult to produce a formed body having a volume content higher than 80%. Also, in the temperature increase process up to 1700℃ mentioned above,
By maintaining the total gas partial pressure of CO and N ₂ in the atmosphere at 100 Pa or less at a temperature of 1500°C or higher for at least 30 minutes, it is possible to uniformly generate nets between the silicon carbide particles and form a strong bond. can. Note that, as long as carbides other than silicon carbide have a sintering mechanism similar to that of silicon carbide, it is possible to obtain a sintered body with excellent dimensional accuracy and strength as in the present invention. Next, the present invention will be explained with reference to Examples and Comparative Examples. Example 1 The silicon carbide powder used as a starting material consisted of 94.6% by weight of β-type crystals and the remainder substantially of 2H-type crystals, and contained 0.29% by weight of free carbon, 0.17% by weight of oxygen, and 0.03% by weight of aluminum. It mainly contained boron and had an average particle size of 0.28 μm, and no boron was detected. 5 parts by weight of polyvinyl alcohol and 300 parts by weight of water are blended with 100 parts by weight of the silicon carbide powder,
The mixture was mixed in a ball mill for 5 hours and then dried. An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal mold at a pressure of 3000 kg/cm ² . The dimensions of this generated feature are 250mm x 250mm x 30mm
The density was 2.0 g/cm ³ (62% by volume). The formed body was placed in a graphite crucible and fired in a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. The temperature was raised to 2000°C at a rate of 450°C/hour and held at the maximum temperature of 2000°C for 10 minutes. CO gas partial pressure during sintering is room temperature to 1700℃
is 80Pa or less, 300±50Pa at higher temperatures than 1700℃
The argon gas flow rate was appropriately adjusted and controlled so that it was within the range of . The density of the obtained sintered body was 2.05 g/ ^cm3 , and its crystal structure was observed using a scanning electron microscope and revealed that silicon carbide plate crystals with an average aspect ratio of 2.5 are intricately intertwined in multiple directions. The sintered body had a three-dimensional structure with a linear shrinkage rate of 0.25±0.02% in all directions, and the dimensional accuracy of the sintered body was within ±0.05 mm. Furthermore, the average bending strength of this sintered body was extremely high at 18.5 Kg/mm ² . Example 2 The same operation as in Example 1 was repeated to produce a sintered body. The results are shown in Table 1. As can be seen from the results shown in Table 1, the linear shrinkage rate was approximately 0.253±0.022% at maximum, and Example 1
According to the sintering conditions shown in Figure 2, by setting the linear shrinkage rate to 0.25%, forming the formed body, and performing sintering,
It was confirmed that it is possible to easily produce a sintered body with extremely high dimensional accuracy within ±0.055 mm. Comparative Example 1 Boron carbide powder 1 with a specific surface area of 20.5 m ² /g was added to 100 parts by weight of the silicon carbide powder described in Example 1.
2 parts by weight of carbon black powder having a specific surface area of 128 m ² /g, 0.4 parts by weight of polyoxyethylene nonylphenol ether, and 400 parts by weight of water were mixed in a ball mill for 20 hours and then dried. An appropriate amount of this dry mixture was collected, granulated, and then pre-molded using a metal mold at a pressure of 150 kg/ ^cm3 .
Next, use an isostatic press machine to produce 2000
It was molded at a pressure of Kg/cm ² . The dimensions and density of the resulting green bodies are shown in Table 1. The resulting green body was fired in the same manner as in Example 1 using a Tammann type firing furnace in an atmosphere of mainly argon gas at 1 atm. The heating process is from room temperature to 1650℃: 5
After holding at 1,650°C for 45 minutes at a rate of 1,650°C/min, the temperature was further increased at a rate of 5°C/min, and a maximum temperature of 2,100°C was maintained for 30 minutes. The CO gas partial pressure during sintering is between room temperature and 1650℃.
5KPa or less, 500Pa or less when kept at 1650℃,
The argon gas flow rate was appropriately adjusted and controlled so that the temperature was 5 KPa or less in the high temperature range above 1650°C. The results are shown in Table 1. As can be seen from the results shown in Table 1, the obtained sintered bodies are all dense and have high strength, but the shrinkage rate varies widely, making it difficult to manufacture sintered bodies with particularly high dimensional accuracy without finishing processing. That was difficult. Example 3 A sintered body was produced in the same manner as in Example 1, except that the maximum temperature was 1900° C. and a mixed gas of argon gas and nitrogen gas was used as the atmospheric gas. Nitrogen gas partial pressure during sintering is 20Pa or less at room temperature to 1700℃, 1700℃
It was set at 300Pa in the temperature range higher than ℃. The CO gas partial pressure during sintering was controlled by appropriately adjusting the flow rate of the mixed gas of argon gas and nitrogen gas so that it was always below 50 Pa. The density of the obtained sintered body is 2.08
g/cm ³ , the linear shrinkage rate of the formed body was within the range of 0.261±0.012% in any direction, and the dimensional accuracy of the sintered body was within ±0.030 mm.
Furthermore, the average bending strength of this sintered body was as high as 22.5 Kg/cm ² . Comparative Example 2 Same as Example 1, but as silicon carbide powder
95.7% by weight consists of β-type crystals and the remainder consists essentially of 2H-type crystals, 0.10% by weight of diluted carbon, 0.15% by weight
A sintered body was obtained using silicon carbide powder containing mainly oxygen, 0.02% by weight of iron, and 0.02% by weight of aluminum, and having an average particle size of 8 μm. Note that boron could not be detected from this silicon carbide powder. The density of the obtained sintered body is 1.85g/cm ³
The linear shrinkage rate for the formed shape is 0.248±
There is a relatively large variation of 0.058%, and the dimensional accuracy is ±
It was 0.145mm. Further, the average bending strength of this sintered body was 6.3 Kg/mm ² , which was relatively low. Comparative Example 3 Same as Example 1, but the maximum temperature during firing was changed.
A sintered body was obtained by increasing the temperature to 2200°C. The density of the obtained sintered body was as low as 1.95 g/cm ³ , the linear shrinkage rate with respect to the formed body had a relatively large variation of 0.203±0.11%, and the dimensional accuracy was also significantly reduced to ±0.275 mm. Furthermore, the average bending strength of this sintered body was extremely low at 4.2 Kg/mm ² . Example 4 Same as Example 1, but as silicon carbide powder
92.8% by weight of β-type crystals and the remainder essentially of 2H-type crystals, 0.21% by weight of free carbon, 0.17% by weight
of oxygen, 0.05% by weight of iron, 0.01% by weight of aluminum, 0.2% by weight of boron,
Using silicon carbide powder having an average particle size of 0.27 μm, 0.4 parts of novolak type phenolic resin with a fixed carbon content of 51.6% by weight and 300 parts of benzene were blended with 100 parts by weight of the silicon carbide powder, and the mixture was mixed in a ball mill. A sintered body was obtained using the dry mixture obtained by mixing for 5 hours and drying. The density of the obtained sintered body was 2.05 g/cm ³ , and although the linear shrinkage rate was slightly higher than that of the formed body at 0.52±0.03%, the dimensional accuracy was relatively good at ±0.08 mm. The average bending strength of this sintered body is 32.5
A significantly high value of Kg/mm ² was obtained. Comparative Example 4 A sintered body was obtained in the same manner as in Example 4, except that the amount of novolak phenol resin was changed to 1.6 parts. The density of the obtained sintered body was as high as 2.51 g/cm ³ , and the linear shrinkage rate for the formed body was 4.47±0.023%.
The variation was large, and the dimensional accuracy was significantly reduced to ±0.575mm. The average bending strength of this sintered body was 31.7 Kg/mm ² .

〔Effect of the invention〕

As described above, the silicon carbide sintered body for heat-resistant jigs of the present invention is sintered without substantially shrinking, has excellent dimensional accuracy and strength, and is suitable for use in exceptional machines. It can be supplied at low cost without any processing.

Claims (1)

[Claims] 1. After molding silicon carbide powder with an average particle size of 5 μm or less into a green body, within a temperature range of 1700 to 2100°C,
Silicon carbide crystals with an average aspect ratio of 5 or less are fired without substantially shrinking in an atmosphere where the partial pressure of at least one of CO or _N2 in the atmosphere is maintained at 100 Pa or more for at least 10 minutes. 1. A method for producing a heat-resistant silicon carbide sintered body for a jig with excellent dimensional accuracy, characterized in that the sintered body has a three-dimensional network structure with a density of 1.4 to 2.6 g/cm ² .