JPH11199324A - Aluminum nitride sintered body and method for producing the same - Google Patents

Abstract

(57) [Abstract] (with correction) [PROBLEMS] To obtain an aluminum nitride sintered body having high mechanical strength and good heat conduction. The A AlN powder was added Y ₂ O ₃ powder in the production method of the AlN sintered body is sintered, oxygenation derived from materials other than Y ₂ O ₃ and Y ₂ O ₃ added amount of powder By setting the mass ratio to 1: 3 to 1: 5, Y
A composite oxide of -Al Y ₃ Al ₅ O ₁₂ and YAlO ₃
To form a grain boundary phase consisting of a mixed phase with 150 W /
A substrate having a high thermal conductivity of not less than (m · K) and a high strength of not less than 450 MPa. In a method of manufacturing an AlN sintered body in which YF ₃ powder is added to AlN powder and sintered, the mass ratio between the amount of oxygen added from the raw material and the amount of YF ₃ powder added is 1: 2 to 1: 4. Within this range, a high-strength substrate can be similarly obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride sintered body having good mechanical strength and thermal conductivity, for example, for mounting a semiconductor chip in a power transistor module or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In power modules such as large-capacity transistors and IGBTs (insulated gate bipolar transistors), ceramics are used as an insulating heat dissipation substrate. As ceramics, aluminum oxide (hereinafter referred to as A) has good insulation, high thermal conductivity and high strength.
l ₂ O ₃ ) has been widely used. In recent years, aluminum nitride (hereinafter abbreviated as AlN) has been used as an insulating material having a higher thermal conductivity in order to improve heat dissipation for miniaturization and high performance of power modules.

[0003] Normally, AlN powder alone is densely sintered at normal pressure.
It is difficult to obtain solidification. Yttrium (hereinafter Y
Oxides or fluorides of rare earth elements such as lanthanum (La)
Of alkaline earth elements such as chlorides and calcium (Ca)
Sintering is performed by adding a sintering aid such as a material or a fluoride.
In particular, yttrium oxide (hereinafter referred to as Y_TwoO _Three
Yttrium fluoride (hereinafter referred to as YF)_ThreeWritten)
When used, AlN is dense at a relatively low temperature of about 1800 ° C.
And a sintered body with high thermal conductivity can be obtained.
Are known. This is because Y_TwoO_ThreeAnd YF_ThreeBaked
Oxidation when the binder is present near the surface layer of AlN powder
Reacts with oxides or oxynitrides to produce Y-Al-O
Liquid phase of the composite oxide which is produced at normal pressure by liquid phase sintering.
It is considered that sintering becomes possible. At this time,
For discharging oxygen contained in AlN particles to grain boundaries
It is considered that higher thermal conductivity is obtained. In general,
Among commercially available AlN powders used as raw materials, 0.5 to 1
Contains oxygen by mass.

[0004]

The commercially available AlN sintered body has a four-point bending strength of 300 to 350 MPa.
It is about. In particular, when used as an insulating heat-dissipating substrate for power modules, it can be destroyed by stress when joining metal electrodes, destroyed by stress caused by the difference in thermal expansion with the electrodes during the heat cycle after joining electrodes, or destroyed when tightening screws. And there was a problem with its reliability. Therefore, a high-strength AlN sintered body has been required.

An object of the present invention is to provide an AlN sintered body having high mechanical strength and good thermal conductivity, and a method for producing the same.

[0006]

According to the observation of the fracture surface of the AlN sintered body, when the crystal grain size of AlN is larger than 5 μm, the breakdown is predominantly within the grain. It has been found that when the crystal grains are as small as 5 μm or less, the fracture is dominated by the fracture at the grain boundary.
Therefore, it is considered that the mechanical strength can be improved by reducing the crystal grain size to 5 μm or less and strengthening the grain boundaries.

The relationship between mechanical strength and intergranular phase in the case of intergranular fracture
From the result, Y_FourAl_TwoO₉ Complex oxide exists
Then, it turned out that it becomes low strength. And Y_ThreeAl
_FiveO ₁₂Or YAlO_Three Composite oxide alone at the grain boundary
Compared to the case where_ThreeAl_FiveO₁₂And YAlO_Three When
It was found that the strength was higher when coexisted. Ma
In addition, the change in the composition of the grain boundary phase
Effect is large, but has little effect on thermal conductivity
I understood that.

Under these circumstances, in order to solve the above-mentioned problems, according to the present invention, the crystal grain boundary phase is mainly composed of a mixed phase of Y ₃ Al ₅ O ₁₂ and YAlO ₃ which is a composite oxide of Y—Al. In the AlN sintered body, any one of zirconium, hafnium and boron nitride particles in the grain boundary phase,
It has oxynitride particles. If such nitride particles and oxynitride particles are present in the grain boundary phase, they have the effect of suppressing the growth of crystal grains and preventing the progress of cracks at the grain boundaries, and further increase the strength.

[0009] AlN powder by adding Y ₂ O ₃ powder in the production method of the AlN sintered body sintered, the additive amount of oxygen and Y ₂ O ₃ amount derived from materials other than Y ₂ O ₃ The mass ratio is preferably in the range of 1: 3 to 1: 5. In a method of manufacturing an AlN sintered body in which YF ₃ powder is added to AlN powder and sintered, the amount of added oxygen derived from the raw material and YF ₍₃₎ The mass ratio to the amount of the powder added is preferably in the range of 1: 2 to 1: 4.

With such a range, Y_ThreeAl_FiveO₁₂
And YAlO_Three And a coexisting grain boundary phase, and other Y_FourAl
_TwoO₉ Complex oxide, or Y_ThreeAl_FiveO₁₂Or YA
10 _Three Is stronger than when solely exists at the grain boundaries.
You. The amount of added oxygen is adjusted by grinding the AlN powder.
Can also be adjusted. If crushed, particle size of AlN powder is small
Adsorbed oxygen or moisture
Aluminum oxide (hereinafter referred to as Al)
_TwoO_ThreeWill increase). The Al_TwoO_ThreeAnd Y_TwoO_ThreeOr
Composite oxide Y_ThreeAl_FiveO₁₂, YAlO_Three Is generated. Ma
In this case, since the crystal grain size of the raw material is small,
Sintered. In fine grain sintering, the total amount of grain boundary
Sintering at a relatively low temperature, and the particle size of the sintered body
Sintering and densification without porosity can be achieved while keeping the size small.

Al ₂ O ₃ or zirconium (Zr),
The amount of added oxygen can also be adjusted by adding any oxide of hafnium (Hf) or boron (B) or a plurality of oxides thereof. As an oxygen source,
If an oxide of an element that is more easily reduced than Al is added in the sintering temperature and atmosphere, it is reduced to Y ₃ Al ₅ O ₁₂ and YAlO.
₃ becomes a grain boundary phase coexisting. In particular, in the case of oxides or composite oxides of Zr, Hf, or B, the oxides are reduced to nitrides or oxynitrides, and are present in a highly dispersed state with fine particles at grain boundaries in the AlN sintered body. Inhibits the grain growth of AlN during sintering, so that a sintered body having a small particle size can be obtained. Further, it has the effect of preventing the progress of cracks at grain boundaries.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The results of experiments according to the present invention and examples thereof will be described below. The composition ratios shown below are expressed in terms of% by weight with respect to the AlN powder unless otherwise specified, but the same applies to the mass ratio. [Experiment 1] Thermal of AlN sintered body, in order to evaluate the mechanical properties, approximately every 0.5% between 2.5 to 5% of Y ₂ O ₃ amount as a sintering aid to be added to AlN The ceramic substrate sample added to was prepared.

A commercially available AlN powder having an average particle size of 2.0 μm was prepared. The AlN powder was analyzed by an oxygen nitrogen analyzer, and was found to contain 0.85% oxygen. To the AlN powder, 2.5 to 5% of Y ₂ O ₃ having an average particle diameter of 1 μm is added as a sintering aid, and polyvinyl alcohol (hereinafter abbreviated as PVA) as a binder.
Was mixed in a mortar and mesh-granulated to prepare a mixed powder.

The mixed powder is put in a mold and is
Press forming into a square rod and disk shape with the pressure of a
2 hours in the air at 450-500 ° C using an electric furnace
During this time, the binder was removed from the molded body by calcination. That
After that, put in a box made of boron nitride (hereinafter referred to as BN)
Electric heater using carbon-made setter plate and litter
Sintering at 1780-1820 ° C for 2 hours in a nitrogen atmosphere in a furnace
did. The sintering temperature is Y_TwoO _ThreeDepending on the amount of
The temperature was set to disappear. For example, when the addition amount is 3%, 18
20 ° C. Firing at a higher temperature promotes grain growth.
The crystal grain size became 5 μm or more, and intragranular fracture was remarkably observed.
Will be able to And the strength also decreases.

The obtained 3 × 4 × 40 mm square bar-shaped Al
The N sintered body is chamfered (C0.2) and JIS-R-
A four-point bending strength test was performed in accordance with 1601. On the other hand, a disk-shaped AlN sintered body was processed into a diameter of 10 mm and a thickness of 3 mm, and the thermal conductivity at room temperature was determined by a laser flash method. Scanning electron microscope (hereinafter referred to as SEM)
The presence or absence of vacancies is observed by observation, and powder X-ray diffraction (hereinafter referred to as X
The composition of the second phase was determined by measurement.

Observation samples and the like were prepared for each of these samples according to a conventional method, and observed by a transmission electron microscope (hereinafter abbreviated as TEM), and electron diffraction was performed on the inside and at the grain boundaries. As a result, the inside of the crystal grains is AlN, and the grain boundary phase, which is a phase precipitated at the grain boundaries and triple points, is X
The second phase was determined by RD measurement.

Table 1 summarizes sample compositions and evaluation results.

[0018]

[Table 1] Sample Nos. 1 to 6 were obtained by changing the amount of Y ₂ O ₃ added in the range of 2.5 to 5%. From the results shown in Table 1, Y ₂ O
_As the addition amount of ₃ increases, the flexural strength increases, and reaches 3.5% at a maximum of 490 MPa, and then gradually decreases. During this time, the thermal conductivity has not changed at 180 W / (m · K). That is, if the thermal conductivity is 150 W / (m · K) or more and the bending strength is 450 MPa or more, Y ₂
It is understood that 3 to 4% is suitable as the added amount of O ₃ .
The last column of this range was marked with a circle.

In this range, the grain boundary phase is in the coexistence state of Y ₃ Al ₅ O ₁₂ and YAlO _3, which is considered to be the reason for the high bending strength. The addition amount of ₃ to 4% of Y ₂ O ₃ is based on 0.85% of oxygen content of the raw material AlN.
It corresponds to 5-4.7 times. Experiment 1 Al with a larger particle size
When N powder is used and the amount of Y ₂ O ₃ added is adjusted so that the grain boundary phase becomes a mixed phase of Y ₃ Al ₅ O ₁₂ and YAlO ₃ , the oxygen content is small. The amount of the liquid phase forming the boundary phase was too small, and some pores remained in the sintered body, and the strength was slightly reduced.

[Experiment 2] An experiment was carried out using the commercially available AlN powder having an average particle size of 2.0 μm used in Experiment 1 and further pulverized with a ball mill as a starting material. 200 g of a commercially available AlN powder having an average particle size of 2.0 μm and isopropyl alcohol (IPA) were prepared with a diameter of 10 mm and a purity of 99.9.
% Alumina ball with inner diameter 80mm and capacity 500
The mixture was placed in a polyethylene pot of 100 ml and ground at a rotation speed of 120 rpm for 6 hours or 12 hours.

The particles crushed by a ball mill for 6 to 12 hours were subjected to measurement of a particle size by a laser scattering method and analysis of an oxygen content by an oxygen nitrogen analyzer. As a result, those milled for 6 hours had an average particle size of 1.5 μm and an oxygen content of 1.15%.
In the case of 12 hours, the average particle size was 1.2 μm and the oxygen content was 1.8%. The AlN powder was ground in a ball mill, a Y ₂ O ₃ powder as a sintering aid, 3-6% for those 6 hours, for those 12 hours 4-10
% And mixed at a slow rotation speed of 10 rpm. Dry it and add 5% PVA as binder
The mixture was added, mixed in a mortar, and mesh-granulated to prepare a mixed powder. The subsequent sample preparation method and evaluation method are described in Experiment 1.
The same was done.

Table 2 summarizes sample compositions and evaluation results.

[0023]

[Table 2] Sample No. 1-4 corresponds to the amount 3-6% of Y ₂ O ₃ in the grinding time of 6 hours. From the results shown in Table 2, Y ₂ O
_When the addition amount of ₃ increases, the bending strength increases, and at 5%, a maximum of 5
It drops after reaching 20 MPa. During this period, the thermal conductivity slightly decreased to 175 W / (m · K). Assuming that the thermal conductivity is 150 W / (m · K) or more and the bending strength is 450 MPa or more, the addition amount of Y ₂ O ₃ is 4 to 5%. The last column of this range was marked with a circle.

Sample Nos. 5 to 8 were obtained by grinding for 12 hours with Y
_This corresponds to an addition amount of ₂ O ₃ of 4 to 10%. As the addition amount of Y ₂ O ₃ increases, the bending strength increases, and at 8%, the maximum is 520.
After reaching MPa, it decreases. The thermal conductivity further decreased during this period to 170 W / (m · K),
It is still sufficiently larger than 150 W / (m · K). Thermal conductivity of 150W / (m · K) or more, bending strength of 450MP
Assuming that a is equal to or more than a, it is understood that the addition amount of Y ₂ O ₃ is preferably 6 to 8%. The last column of this range was marked with a circle.

By performing ball milling, the oxygen content of the raw material AlN powder was reduced from 0.85% in Experiment 1 to 1.15%.
%, 1.8%. And experiment 1
It can be seen that an AlN sintered body having a high bending strength and a high thermal conductivity can be obtained in a region where the amount of Y ₂ O ₃ is increased from the optimum range of the above. However, the addition amount of Y ₂ O ₃ is 3.5 to 4.3 times in the case of pulverization for 6 hours and 3.3 to 4.3 in the case of pulverization for 12 hours in terms of the ratio to the oxygen content of the raw material AlN.
4 times, which is almost the same range as in the case of Experiment 1.

That is, by supplying a fixed ratio of oxygen to the amount of Y ₂ O ₃ added, 450 MPa
An AlN sintered body having the above mechanical strength and thermal conductivity of 150 W / (m · K) or more can be obtained, and the proportion thereof is such that the addition amount of Y ₂ O ₃ is 3 to 5 times the amount of oxygen. It can be said that this is the ratio of In all the samples marked with a circle, the grain boundary phase is Y ₃ Al ₅ O ₁₂
And YAlO ₃ coexist. Moreover, the raw material AlN
Since the oxygen content and the addition amount of Y ₂ O ₃ are larger than those in Experiment 1, it is considered that the total amount of the grain boundary phase is increased. This is probably because of the high standard.

Further, since the total amount of the grain boundary phase is increased, densification can be performed at a sintering temperature of 1800 ° C. or less, and the effect of reducing the particle size of the original raw material powder is added.
The sintered body had a small particle size. This is also considered to be one of the reasons why the strength was higher than that of Experiment 1. [Experiment 3] In place of Y ₂ O ₃ in Experiment 1, Y was used as a sintering aid.
The F ₃ work was performed adding 1.5 to 4%. Other sample preparation methods were the same as in Experiment 1. As in the evaluation method, as in Experiment 1, a four-point bending strength test, thermal conductivity measurement by a laser flash method, SEM observation, and composition identification of a grain boundary phase measured by an XRD method were performed.

Table 3 summarizes sample compositions and evaluation results.

[0029]

[Table 3] Sample No. 1-6 corresponds to the amount from 1.5 to 4% of YF _3. From the results shown in Table 3, it can be seen that as the addition amount of YF ₃ increases, the flexural strength increases, reaches 2.5% at a maximum of 490 MPa, and then decreases. The thermal conductivity remains at 180 W / (m · K) during this period. Thermal conductivity 150W /
If the bending strength is not less than (m · K) and the bending strength is not less than 450 MPa, it is understood that the addition amount of YF ₃ is preferably 2 to 3%. The last column of this range was marked with a circle.

In this range, the grain boundary phase was in the coexistence state of Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous two examples. The addition amount of YF ₃ of 2 to 3% corresponds to 2.4 to 3.5 times the oxygen content of the raw material AlN of 0.85%. Also, AlN pulverized by the same ball mill as in Experiment 2 was used.
When an experiment of sintering YF ₃ as a sintering aid using powder was performed, an AlN sintered body obtained by sintering the amount of YF ₃ by 2 to 4 times the amount of oxygen in the AlN powder, The results showed that both the bending strength and the thermal conductivity were good.

That is, by supplying a fixed ratio of oxygen to the amount of YF ₃ added, an AlN sintered body having a mechanical strength of 450 MPa or more and a thermal conductivity of 150 W / (m · K) or more. It can be said that the ratio is such that the addition amount of YF ₃ is in the range of 1: 2 to 1: 4 with respect to the oxygen amount. In this method of further pulverizing the AlN powder to adjust the amount of added oxygen, since the added oxygen is uniformly dispersed, the distribution of the grain boundary phase is also made uniform, and the strength is enhanced as a whole. .

[Experiment 4] Commercially available A having an average particle size of 2.0 μm
To 1N powder, ₃ to 7% of Y ₂ O ₃ is added as a sintering aid, and 0.5 to 4% of zirconium oxide (hereinafter referred to as ZrO ₂ ) having a particle size of 50 to 100 nm is added and sintered. A
The thermal and mechanical properties of the 1N sintered body were evaluated. Other sample preparation methods were the same as in Experiment 1. As in the evaluation method, as in Experiment 1, a four-point bending strength test, thermal conductivity measurement by a laser flash method, SEM observation, and composition identification of a grain boundary phase measured by an XRD method were performed.

The sample was observed with a TEM and subjected to electron beam diffraction. As a result, the inside of the grains was AlN, and a Y-Al-O composite oxide and zirconium nitride were confirmed at the grain boundaries and the triple points. Further, as a result of analysis by an oxygen and nitrogen analyzer, the total amount of oxygen contained in the sintered body was not different from that of the starting material. From this result, it is considered that ZrO ₂ became an oxygen generation source and supplied oxygen to AlN or the Y—Al—O composite oxide.

Also in this case, since the fine ZrO ₂ powder was added, the reaction was performed uniformly and the distribution of the grain boundary phase was uniform. [Experiment 4-1] With the addition amount of Y ₂ O ₃ fixed at 5%, Zr
The O ₂ was added 0.5 to 4% thermal sintering the AlN sintered body, the result of evaluating the mechanical properties shown in Table 4.

[0035]

[Table 4]Sample numbers 1 to 5 are ZrO_Two0.5 to 4%
I am responding. ZrO _TwoOxygen supplied from AlN
Calculated by mass ratio to ZrO_TwoWith 0.5-4%
When added, the supply amount of oxygen is 0.13 to 1.0
It becomes 4%. From the results shown in Table 4, ZrO_TwoAmount of
As it increases, the bending strength increases, and at 2%, up to 600 MPa
After reaching, it has fallen.

This is presumably because the presence of the zirconium nitride particles at the grain boundaries has the effect of inhibiting the progress of cracks at the grain boundaries, and further increases the strength. During this time, the thermal conductivity gradually decreases to 180 to 145 W / (m · K). Assuming that the thermal conductivity is 150 W / (m · K) or more and the bending strength is 450 MPa or more, the addition amount of ZrO ₂ is preferably 1.0 to 3.0%. The last column of this range was marked with a circle.

In this range, the grain boundary phase coexists with Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous example. Amount of 5% Y ₂ O _3, relative to the amount of oxygen derived from the 1.0% to 3.0% addition of AlN powder and ZrO _2, 3.
It corresponds to 2-4.6 times. Since the amount of Y ₂ O ₃ added was large, the total amount of the grain boundary phase was larger than in the case of Experiment 1, and the sintering temperature could be reduced to 1800 ° C. or less. Also, since the zirconium nitride particles hinder the growth of AlN grains during sintering, 2 μm
The sintered body had a small particle size. These are also considered to contribute to high strength.

[Experiment 4-2] ZrO_Two2.0% added amount
And Y_TwoO_ThreeIs added to 3.0 to 7.0% and sintered.
Table also shows the results of evaluating the thermal and mechanical properties of the AlN sintered body
The results are shown in FIG. Sample numbers 6 to 10 are Y_TwoO_ThreeAmount of
It corresponds to 3.0 to 7.0%. Y _TwoO_ThreeAmount of
As it increases, the bending strength increases, and up to 600 MPa at 5%
After reaching, it has fallen. Zirconium nitride particles are grain boundaries
It is considered that the presence of the carbon steel increased the strength. Heat conduction
The rate changed between 170 and 160 W / (mK) during this period.
I don't know. With thermal conductivity of 150W / (mK) or more, music
If the bending strength is 450 MPa or more, Y_TwoO_Threeof
It is understood that the amount of addition is preferably 4.0 to 6.0%. this
A circle was marked in the last column of the range.

In this range, the grain boundary phase was in the coexistence state of Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous example. Amount from 4.0 to 6.0% of Y ₂ O _3, relative to the amount of oxygen derived from the 2.0% addition of AlN powder and ZrO _2,
It corresponds to 3.0 to 4.5 times. That is, by supplying a fixed ratio of oxygen to the added amount of Y ₂ O ₃ , mechanical strength of 450 MPa or more and 150 W / (m ·
K) An AlN sintered body having a thermal conductivity of not less than that can be obtained, and it can be said that the ratio is such that the addition amount of Y ₂ O ₃ is 3 to 5 times the amount of oxygen. In particular, by supplying oxygen by adding ZrO ₂ , zirconium nitride particles are precipitated, and higher strength can be obtained.

[Experiment 5] [Experiment 5-1] To a commercially available AlN powder having an average particle size of 2.0 μm, 5% of Y ₂ O ₃ was added as a sintering aid, and
The thermal and mechanical properties of an AlN sintered body obtained by adding 0.5 to 4% of hafnium oxide (hereinafter referred to as HfO ₂ ) of 0 to 100 nm and sintering were evaluated. Other sample preparation methods were the same as in Experiment 4-1. As in the evaluation method, as in Experiment 1, a four-point bending strength test, thermal conductivity measurement by a laser flash method, SEM observation, and composition identification of a grain boundary phase by an XRD method were performed.

Table 5 shows the results of the evaluation.

[0042]

[Table 5]Sample numbers 1 to 5 are HfO_Two0.5 to 8%
I am responding. HfO _TwoOxygen supplied from AlN
HfO_Two0.5 to 8%
When added, the supply amount of oxygen is 0.08 to 1.2.
2%. From the results shown in Table 5, HfO_TwoAmount of
As it increases, the bending strength increases and the maximum is 580 MPa at 2%.
After reaching, it has fallen. Also in this case, hafnium nitride particles
Presence of cracks at grain boundaries hinders crack propagation at grain boundaries
It is considered that the strength is further improved. Heat conduction
During this period, the rate gradually increased to 170-140 W / (mK)
Is declining. Thermal conductivity is 150W / (m ・ K) or more
If the bending strength is 450 MPa or more, Hf
O_TwoIt is clear that 1.0 to 3.0% is suitable for
You. The last column of this range was marked with a circle.

In this range, the grain boundary phase was in the coexistence state of Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous example. Amount of 5% Y ₂ O _3, relative to the amount of oxygen from 1.0 to 4.0 percent addition of AlN powder and HfO _2, 3.
4 to 5.0 times. [Experiment 5-2] To a commercially available AlN powder having an average particle size of 2.0 μm, 5% of Y ₂ O ₃ was added as a sintering aid, and 0.5 to 5% of fine ZrO ₂ and HfO ₂ were further added. The thermal and mechanical properties of the AlN sintered body added and sintered were evaluated. ZrO ₂
The ratio of the added amounts of HfO ₂ and HfO ₂ was 1: 1.

Table 5 shows the evaluation results of the sintered samples.
It was shown to. Sample numbers 6 to 10 correspond to the addition amounts of ZrO ₂ and HfO ₂ of 0.5 to 5%. When the oxygen supplied from these oxides is calculated as a mass ratio to AlN, when these oxides are added in an amount of 0.5 to 5%,
The supply of oxygen is 0.10 to 0.96%.
From the results shown in Table 5, the bending strength increases as the addition amount of ZrO ₂ and HfO ₂ increases, reaches 2 0% at a maximum of 590 MPa, and then decreases. Also in this case, it is considered that the presence of zirconium nitride and hafnium nitride particles at the grain boundaries has an effect of preventing the progress of cracks at the grain boundaries, and further increases the strength. Thermal conductivity is between 175 and 140 W
/ (M · K). Thermal conductivity 150
If the flexural strength is not less than W / (m · K) and the bending strength is not less than 450 MPa, the added amount of ZrO ₂ and HfO ₂ is 1.0 to
It turns out that 4.0% is suitable. The last column of this range was marked with a circle.

In this range, the grain boundary phase was in the coexistence state of Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous example. Amount of 5% Y ₂ O _3, relative to the amount of oxygen from 1.0 to 4.0 percent addition of AlN powder and ZrO ₂ and HfO _2, which corresponds to 3.1 to 4.8 times. That is, Y ₂ O
By supplying a constant ratio of oxygen to the addition amount of ₃ , the mechanical strength of 450 MPa or more and 150 W /
An AlN sintered body having a thermal conductivity of (m · K) or more can be obtained, and it can be said that the ratio is such that the addition amount of Y ₂ O ₃ is 3 to 5 times the amount of oxygen.

Particularly, oxygen is added to HfO ₂ or ZrO ₂
By supplying by adding ₂ and HfO ₂ , hafnium nitride particles or zirconium nitride particles and hafnium nitride particles are precipitated, and higher strength can be obtained. [Experiment 6] Commercially available AlN powder having an average particle size of 2.0 μm
5% of Y ₂ O ₃ is added as a sintering aid, and 50 to 10
0 nm boron oxide (hereinafter referred to as B ₂ O ₃ )
The thermal and mechanical properties of the aluminum nitride sintered body sintered by adding 1.5% were sintered. Other sample preparation methods were the same as in Experiment 4-1. The evaluation method was the same as in Experiment 4-1.

Table 6 shows the results of the evaluation.

[0048]

[Table 6] Sample Nos. 1 to 6 show the addition amount of B ₂ O ₃ of 0.1 to 1.5%
It corresponds to. Oxygen supplied from B ₂ O _{3 is} converted to AlN
0.1 When calculated as mass ratio, the B ₂ O ₃ with respect to
When 1.5% is added, the supply amount of oxygen is 0.0%.
It becomes 7 to 1.03%. From the results shown in Table 6, B ₂ O ₃
Increases, the flexural strength increases, reaches a maximum of 550 MPa at 0.5%, and then decreases. Also in this case, it is considered that the presence of the boron nitride particles at the grain boundaries has the effect of preventing the progress of cracks at the grain boundaries, and further increases the strength. The thermal conductivity is between 175 and 150 W / (m
K), which is gradually decreasing. Thermal conductivity is 150W / (m
・ K) and above, when the bending strength is 450 MPa or more, it is understood that the addition amount of B ₂ O ₃ is preferably 0.25 to 1.0%. The last column of this range was marked with a circle.

In this range, the grain boundary phase coexists with Y ₃ Al ₅ O ₁₂ and YAlO ₃ , as in the previous example. The added amount of Y ₂ O ₃ of 5% is based on the amount of oxygen derived from the addition of 0.25 to 1.00% of AlN powder and B ₂ O ₃ .
It corresponds to 3.2 to 4.9 times. That is, by supplying a fixed ratio of oxygen to the added amount of Y ₂ O ₃ , mechanical strength of 450 MPa or more and 150 W / (m ·
K) An AlN sintered body having a thermal conductivity of not less than that can be obtained, and it can be said that the ratio is such that the addition amount of Y ₂ O ₃ is 3 to 5 times the amount of oxygen. In particular, by supplying oxygen by adding B ₂ O ₃ , boron nitride particles are precipitated and high strength is obtained.

It is presumed that metal oxides such as ZrO ₂ , HfO ₂ , and B ₂ O ₃ which are reduced at the sintering temperature and atmosphere to become nitrides can be used similarly. [Experiment 7] Commercially available AlN powder having an average particle size of 2.0 μm
5% of Y ₂ O ₃ is added as a sintering aid, and 50 to 10
The thermal and mechanical properties of an AlN sintered body sintered by adding 0.25 to 2.5% of Al ₂ O _{3 of} 0 nm were evaluated. Other sample preparation methods were the same as in Experiment 4-1. The evaluation method was the same as in Experiment 4-1.

Table 7 shows the results of the evaluation.

[0052]

[Table 7] Sample Nos. 1 to 6 have the added amount of Al ₂ O ₃ of 0.25 to 2.
It corresponds to 5%. When oxygen supplied from Al ₂ O ₃ is calculated as a mass ratio to AlN, Al ₂ O ₃
When 0.25 to 2.5% is added, the supply amount of oxygen is 0.12 to 1.18%. From the results shown in Table 7, as the addition amount of Al ₂ O ₃ increases, the bending strength increases,
It drops after reaching a maximum of 520 MPa at 1%. In this case, it is considered that the strength was relatively small because the nitride particles did not exist at the grain boundaries. During this time, the thermal conductivity gradually decreases to 180 to 170 W / (m · K). If the thermal conductivity is 150 W / (m · K) or more and the bending strength is 450 MPa or more, it is understood that the addition amount of Al ₂ O ₃ is preferably 0.5 to 1.5%. The last column of this range was marked with a circle.

In this range, the grain boundary phase coexists with Y ₃ Al ₅ O ₁₂ and YAlO ₃ as in the previous example. Also in this case, the distribution of the grain boundary phase was uniform since the fine Al ₂ O ₃ powder was added. Amount of 5% Y ₂ O ₃ is 0.5% to 1.5% of AlN powder and Al ₂ O ₃
This corresponds to 3.2 to 4.6 times the amount of oxygen derived from the addition.

That is, by supplying a fixed ratio of oxygen to the added amount of Y ₂ O ₃ , 450 MPa
An AlN sintered body having the above mechanical strength and thermal conductivity of 150 W / (m · K) or more can be obtained, and the proportion thereof is such that the addition amount of Y ₂ O ₃ is 3 to 5 times the amount of oxygen. It can be said that this is the ratio of [Example] to AlN powder having an average particle size of 2.0 .mu.m, 5% as a sintering aid Y ₂ O ₃ powder and particle size 50~100n
After adding 2% of ZrO ₂ of m and polyvinyl alcohol of 5% as a binder and mixing them in a mortar, they were mesh-granulated to prepare a mixed powder. The mixed powder is put into a mold, press-molded at a pressure of about 100 MPa, and calcined at 450 to 500 ° C. for 2 hours in the air using an electric furnace to remove the binder in the molded body. Put in a box made of boron (hereinafter referred to as BN)
Sintering at 1800 ° C for 2 hours in a nitrogen atmosphere with a carbon heater electric furnace using
An N substrate (plate thickness: 0.63 mm) was produced.

The AlN substrate thus manufactured is
Thermal conductivity is 175W / (mK) and four-point bending strength is 6
It was 00 MPa, and a transistor module was actually fabricated using the AlN substrate, and it was confirmed that the transistor module could be used practically.

[0056]

As described above, according to the present invention, A
in lN powder by adding Y ₂ O ₃ powder in the production method of the AlN sintered body is sintered, the weight ratio of the added amount of oxygen and Y ₂ O ₃ added amount of powder from a raw material other than Y ₂ O ₃ 1: 3
By setting the range to 主 と し て 1: 5, the crystal grain boundary phase is mainly composed of Y ₃ Al ₅ O ₁₂ and YA, which are composite oxides of Y—Al.
It was shown that a substrate composed of a mixed phase with 10 ₃ and having a high thermal conductivity of 150 W / (m · K) or more and a strength of 450 MPa or more and 30% or more higher than a conventional AlN sintered body could be obtained.

In a method for producing an AlN sintered body in which YF ₃ powder is added to AlN powder and sintered, the mass ratio between the amount of oxygen added from the raw material and the amount of YF ₃ powder added is 1: 2.
If it is in the range of 1: 4, it is 30% higher than the same AlN sintered body.
As described above, a high-strength substrate can be obtained. As a method of adding oxygen other than Y ₂ O ₃ , AlN powder is pulverized to increase the amount of Al ₂ O ₃ on the surface, or ZrO ₂ , HfO ₂ , B ₂
Oxides such as O ₃ and Al ₂ O ₃ may be added. Especially Zr
In the case of O ₂ , HfO ₂ , and B ₂ O ₃ , fine particles of nitride are dispersed in the grain boundary phase, suppressing the grain growth of crystals, preventing the propagation of cracks, and further increasing the strength. is there.

When the sintered body according to the present invention, which has excellent mechanical strength and high thermal conductivity, is used as a substrate for a semiconductor device, for example, it is resistant to a heat cycle and is most suitable for a package of a power device, a radiation fin, and the like. . In particular, by applying the present invention to a substrate such as a power transistor module, miniaturization and cost reduction of a semiconductor device and increase in current capacity can be achieved.

Claims (6)

[Claims] 1. A grain boundary phase mainly yttrium - Y ₃ Al ₅ O ₁₂ is a composite oxide of aluminum and YAlO
_{3. An} aluminum nitride sintered body comprising a mixed phase of ( ₃₎ and ( ₃ ), characterized by having any one of zirconium, hafnium and boron nitride particles and oxynitride particles in a crystal grain boundary phase. 2. A method for manufacturing an aluminum nitride sintered body in which yttrium oxide powder is added to aluminum nitride powder and sintered, the mass of the amount of added oxygen derived from raw materials other than yttrium oxide and the amount of yttrium oxide powder added A method for producing an aluminum nitride sintered body, wherein the ratio is in the range of 1: 3 to 1: 5. 3. A method for producing an aluminum nitride sintered body in which yttrium fluoride powder is added to aluminum nitride powder and sintered, the mass ratio of the amount of oxygen added from the raw material to the amount of yttrium fluoride powder added is determined. A method for producing an aluminum nitride sintered body, which is in a range of 1: 2 to 1: 4. 4. The method for producing an aluminum nitride sintered body according to claim 2, wherein the amount of added oxygen is adjusted by pulverizing the aluminum nitride powder. 5. The method according to claim 5, wherein the aluminum oxide is added.
The method for producing an aluminum nitride sintered body according to claim 2 or 3, wherein the amount of added oxygen is adjusted. 6. The aluminum nitride according to claim 2, wherein the amount of oxygen added is adjusted by adding an oxide of any of zirconium, hafnium and boron or a plurality of oxides thereof. A method for manufacturing a sintered body.