JPH02275765A - Production of sintered aluminum nitride - Google Patents

Abstract

PURPOSE:To produce a sintered AIN having dense texture and high thermal conductivity and electrical resistance and suitable as an insulation substrate, at a low cost, by adding a specific sintering assistant to AIN powder, forming the mixture and calcining in a non-oxidizing atmosphere. CONSTITUTION:The objective sintered AIN is produced by mixing 100 pts.wt. of AIN powder with (A) 0.05-5 pts.wt. (in terms of oxide) of one or more components selected from Y, Sc and lanthanoid and (B) 0.01 to 5 pts.wt. of one or more elements selected from metallic Li, metallic Be, metallic Mg, B, Si, S, P, As and metallic Zn, forming the mixture and calcining at 1400 to 2000 deg.C in a non-oxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an aluminum nitride sintered body, and particularly to a method for producing an aluminum nitride sintered body having high thermal conductivity, which is in high demand in industry.

[Prior Art] High thermal conductivity/IN sintered bodies are specifically used as insulating materials, with semiconductor substrate materials being a typical example.

With the trend toward higher integration, higher speed, and higher output of semiconductors, the following problems have been brought into focus. In other words, ■ How to efficiently release the heat generated by the semiconductor chip to the outside of the system.

■ As operating speeds increase, signal delays on the board or package become a problem.

■ As the chip size increases, the difference in thermal expansion between the chip and the substrate increases, reducing the reliability of the bonding.

■ As the voltages used in high-power chips continue to increase, dielectric breakdown of substrates is becoming a problem.

Ceramics for substrates and packages that can replace conventional alumina and can solve these problems faced by semiconductors include: ■ High thermal conductivity.

■ Excellent electrical insulation.

■ Good high frequency characteristics. (Low dielectric constant, low dielectric loss)■
The coefficient of thermal expansion is close to SL or GaAs.

■ Chemically stable.

■ High mechanical strength.

■ Circuit formation is easy.

■ Can be airtightly sealed.

It is desirable to have the following characteristics.

Al2N is considered to be promising as a material basically having such characteristics.

However, when A42N ceramics is specifically applied, it is necessary to satisfy the following minimum characteristics. That is, (1) The sintered body is uniform and dense. High mechanical strength. It is desirable that the relative density is 95% or more.

(2) Thermal conductivity should be as high as possible.

(3) High volume resistance. 1012Ω・cm or more is required.

(4) The surface of the sintered body is smooth and flat.

Among the above items, item (4) is said to be not essential, but it is essential in terms of manufacturing technology since it means omitting processing and lowering manufacturing costs when manufacturing substrates in mass production. Specifically, the surface roughness is 0.5 in Ra after baking.
It is desirable that the warpage is 0.1 mm/50 mm or less.

In the conventional technology, in order to satisfy the above items (1) and (2), as shown in Japanese Patent Publication No. 46-41003, Y2
O3 is used as a sintering aid, or
As shown in No. 9510, ceramics with a thermal conductivity of about 100 W/m have been obtained using Cab, Bad, SrO, etc. as sintering aids. However, users are demanding sintered bodies with even higher thermal conductivity properties depending on the intended use.

Up to now, methods for obtaining high thermal conductivity AffN sintered bodies include (i) a method in which AI2N powder is heat treated at 1600°C or higher in a non-oxidizing atmosphere to reduce the oxygen content of the powder, and then sintered; Kaisho 6l-201(ii) AρN powder after heat treatment was heated at 1800 to 2300°C in a non-oxidizing atmosphere for 20
A method of hot-pressing under a pressure of 210 W/m or higher (Japanese Unexamined Patent Application Publication No. 1983-1989)
201668).

However, these methods are limited to AI2. Since the thin oxygen film on the N surface layer is removed, the difficulty of sintering of Al2N becomes noticeable, and even if a sintering aid is added, the productivity is low, and the desired sintered body cannot be obtained without expensive hot pressing. It is not suitable for mass production.

In addition, the journal of the Ceramics Industry Association, the 2.5th Ceramics Industry Basics Forum, 1DO
3,3HO3 (January 1988) describes a method of obtaining an Al2N sintered body with high thermal conductivity by sintering an Af2N compact at 1850 to 1950°C for 2 to 96 hours in a reducing atmosphere. This is an AR with excellent thermal conductivity.
A sintered body that can be used as an N substrate cannot be obtained.

On the other hand, in JP-A No. 62-52181, a molded body made of Al2N containing 0.2 to 3.4 parts by weight of carbon and 0.1 to 10 parts by weight of yttrium oxide as sintering aids in Al2N was disclosed.
Al2 characterized by being sintered at 600-2100°C
A method for manufacturing a N sintered body is disclosed. However, this invention does not address the following points at all, and due to the following problems, it could not be said to be a satisfactory method for manufacturing an AβN substrate. That is, (1) The density of the sintered body is low.

(2) Electrical insulation properties cannot be obtained.

(3) Uneven coloring and sintering occur.

Also, JP-A-61-127667, 61-21976
No. 3 discloses a technique in which Al2N, Y203, and C are added as auxiliaries;
Not suitable for N-group treatment. Also, JP-A No. 63-2367
The same applies to 65.

[Problem to be solved by the invention] In the sintered body produced by the above conventional method, (a) Thermal conductivity is insufficient.

(b) Sintering can only be done in a furnace with high equipment costs and low productivity, such as a hot press.

(c) No electrical insulation.

(d) Stable quality cannot be obtained.

There were some problems. As described above, it is difficult to say that the previous inventions satisfy all of the four items (a) to (d) above.

Therefore, in order to improve these points, it has been desired to develop a new method for producing a 12N sintered body with high thermal conductivity.

The object of the present invention is to provide a method for increasing the thermal conductivity of an Al2N sintered body that satisfies all of the four problems (a) to (d) above. That is, the object of the present invention is to provide a method for producing an inexpensive ARN sintered body that is dense, has high thermal conductivity and electrical resistance, and has properties suitable as a material typified by electrically insulating substrates.

[Means for Solving the Problems 1] In view of the problems of the prior art described above, the present inventors have conducted research to improve the thermal conductivity of an aluminum nitride sintered body and provide it with the characteristics necessary as a substrate. As a result of repeated research, the following novel matters were discovered, leading to the present invention.

That is, REM and metallic lithium, metallic beryllium, metallic magnesium, boron, silicon, sulfur,
When a sheet molded body to which one or more elements selected from the group of phosphorus, arsenic, and metal zinc were added was sintered in a non-oxidizing atmosphere, a ceramic sintered body with high thermal conductivity was obtained. .

REM here refers to yttrium, scandium, and lanthanoids.

The above-mentioned sintered body is the above-mentioned (a) required as the insulating substrate.
All of the requirements of (d) to (d) were satisfied.

Based on this fact, the present invention was completed as a result of extensive studies regarding the optimal addition range, other elements, and compounds that meet the above requirements. If the additive element or its compound and its addition range are selected in a limited manner, the relative density is 95% or more, the thermal conductivity is 160 W/m or more, the baked surface roughness is Ra 0.5. um or less, volume resistance is 1
0.012 Ω·cm or more, a highly thermally conductive and electrically insulating sintered body of aluminum nitride with no uneven firing can be obtained.

The method for manufacturing the above sintered body is as follows.

That is, the following (
Add a sintering aid consisting of a combination of components selected from the group of (a) to (e), mold this, and mold the obtained molded product in a non-oxidizing atmosphere at a temperature range of 1400 to 2000°C. This can be achieved by firing. The groups of these ingredients are:

(a) 0.05 to 5 parts by volume of one or more selected from the group of oxides of yttrium, scandium, and ranknoids (b) Metallic lithium, metal beryllium, metal magnesium , 111111 element, silicon, sulfur, phosphorus, arsenic, and metal zinc.
01 to 5 parts by weight (c) Alkali metal oxides and alkali metal compounds that become oxides when heated at 2000°C or less, and oxides of boron, silicon, germanium, arsenic, and phosphorus, and 2
0.01 to 5 parts by weight in terms of oxide of one or more selected from the group of compounds that become these oxides when heated at 000°C or less (d) Metal boride, metal nitride, 1f of compounds selected from the group of compounds selected from the group of metal phosphides, metal sulfides, metal silicides, and metal hydrides! or 0.01 to 5 parts by weight of two or more (e) Oxides of aluminum, gallium, indium, tungsten, bismuth, lead, antimony, cadmium, and zinc, and compounds that become these oxides when heated at 2000°C or less 0.01 to 2 parts by weight in terms of oxide of one or more of the above.The combinations of the above component groups are as follows.

■ (a) + (b) ■ (a) + (b) + (c) ■ C a) + (b) + (d) ■ (a + (b) + (c) + (d) ■ (a) + (B) + (E) ■ (A +0) + (Bo) + (C) ■ (A + (B) + (E) + (D) ■ (A + (B) + (E) + ( c) + (d) [Effect 1 The mechanism by which the combined addition of these sintering aids is effective has not been fully elucidated, but is thought to be as follows.

On the surface layer of Al2N, there is at least some type of heb oxide, which is not a complete Aβ203. Assuming that this oxide is AJ2203, a liquid phase xAj220a ・, Y
Generate Y20a. Next, component (b) metal lithium, metal beryllium, metal magnesium, boron, silicon, sulfur, phosphorus, arsenic, and metal zinc are all strong reducing agents and react with impurity oxygen in aluminum nitride. Remove this. That is, at the stage from liquid phase generation to grain growth, step 9. Oxygen on the N surface is reduced by the above component (b) and purifies the Al2N grains while reducing the amount.

The resulting sintered body is considered to be ideal as a highly thermally conductive and electrically insulating sintered body for substrates.

If the amount of the component (a) added is less than 0.05 parts by weight per 100 parts by weight of AgN, the thermal conductivity will not increase and the requirements will not be met. When the amount is more than 5 parts by weight, the amount of grain boundary phase increases, resulting in a decrease in thermal conductivity.

In addition, the amount of the above component (b), that is, the reducing agent component, is as follows:
If the amount is less than 0.01 part by weight per 100 parts by weight of A42N, the distribution of the grain boundary phase will become non-uniform, resulting in a striped pattern. If the amount is more than 2 parts by weight, YN will remain, causing partial coloring and poor appearance. Furthermore, if the amount added is increased, the shrinkage rate upon temperature rise will be slow and the grain boundary phase will volatilize, resulting in poor sintering.

Next, when component (C) is added to components (A) and (B) above, component (C) is an alkali metal oxide or a glass former element oxide, which forms a liquid phase at a lower temperature. Therefore, the grain boundary liquid phase contributes to the promotion of sintering, removes surface oxides of AgN, and homogenizes the grain boundaries by glass formation.
and suppresses abnormal growth of A42N crystal grains due to infiltration. Therefore, it is possible to obtain a sintered body with uniform particle size, high thermal conductivity, high density, high insulation resistance, and little variation in metallization properties.

If the amount of component (c) added is less than 0.01 part by weight, uneven baking is likely to occur due to non-uniform distribution of the remaining grain boundary phase.

If the amount is more than 5 parts by weight, abnormal grain growth will occur during sintering, resulting in lower mechanical strength.

Furthermore, when component (2), that is, a metal boride, metal nitride, metal phosphide, metal sulfide, metal silicide, or metal hydride, is added to the components (a) and (b), these components It also easily combines with oxygen and easily reacts with the impurity oxygen in the AffN crystal to remove it, and at the same time, the reaction product becomes a liquid phase and penetrates into the grain boundaries, exerting the effect of promoting sintering.

Component (a) added at the same time turns into a liquid phase at high temperatures and significantly accelerates sintering. In addition, due to the strong reducing action of the component (b), it combines with oxygen during the grain growth process and volatilizes it.
Furthermore, the thermal conductivity of AgN can be increased.

The amount of the component (d) added is 0.01 to 5 parts by weight per 100 parts by weight of A42N. If it is less than 0.01 parts by weight, the effect of removing impurity oxygen is poor, and if it is added in excess of 5% by weight, there is no improvement in the effect of addition.

Furthermore, when component (C) and component (D) are added in combination to component (A) and component (B), the synergistic effect of the oxygen reduction effect and the liquid phase formation temperature reduction effect results in high thermal conductivity. A9. N substrates can be obtained. In this case, the amount of component (c) and component (d) added may be 0.01 to 5 parts by weight, respectively, per 100 parts by weight of A42N.

Instead of these components (c) and (d), the components (e), namely amphoteric oxides such as aluminum, gallium, indium, tungsten, are added to the components (a) and (b).
Al2N with high thermal conductivity can be obtained by adding oxides of bismuth, lead, antimony, cadmium, and zinc. (e) The effects of the components can be considered as follows.

The compound of component (e) reacts with impurities such as Fe and Ti present in AffN during the sintering process to form compounds at grain boundaries and trap them. Fe present in AfiN
, Ti, etc. impede heat conduction, and when they are removed, the thermal conductivity improves.

The amount of component (e) added is 0.01 to 5 parts by weight per 100 parts by weight of A42N. F if less than 0.01 part by weight
It has a poor effect of reacting with e, Ti, etc. to generate compounds,
Even if it is added in an amount exceeding 5% by weight, there is no improvement in the effect of addition.

Also effective are quaternary or ternary sintering aids in which the above-mentioned components (a), (b), and (e) are further added with components (c) and/or (d). In this case, the characteristics of each component are exhibited, and due to their synergistic effect, Al
2N thermal conductivity is improved.

Next, a specific example of the method for manufacturing the product of the present invention will be described using Y2O3 as the component (a) and metal Zn as the component (b).

0.5 to 5 parts by weight of Y2O3 and 0.0 parts by weight of metal Zn to 100 parts by weight of aluminum nitride powder with an average particle size of 0.1 to 3 μm.
Add in a range of 1 to 0.5 parts by weight, mix and disperse,
A binder is added to create a molded body. As a molding method,
Well-known methods for -M, such as a doctor blade method, press molding method, cast molding method, and extrusion molding method, can be used. The molded body thus obtained is fired at 1400 to 2000°C in a non-oxidizing atmosphere.

In order to obtain an AffN sintered body with high thermal conductivity, it is desirable that the impurity oxygen content of Af2N is as low as possible, but it is sufficient that it is about 1 part by weight or less.

Firing is performed in a /IN crucible, and the firing temperature is 1400°C.
Below, sintering is stopped midway, and microbores are generated due to sublimation of Af2N grains, reducing thermal conductivity.

When fired in an atmosphere with an oxygen concentration of 500 ppm or more, Al2
Oxidation of N occurs, and a sintered body with high thermal conductivity cannot be obtained.

[Effects of the Invention] According to the present invention, an aluminum nitride sintered body having a thermal conductivity of 160 W/m or more and an electric insulator using the same as a base material can be provided, and can be used as a substrate for hybrid ICs, substrates for cer-deep circuits, and power transistors. Industrial applications such as heat sinks for , power diodes, and laser diodes are possible.

[Example] Example 1 To 100 parts by weight of Af2N powder with an average particle size of 1 μm, Y2O3 powder with an average particle size of 1 μm and Mg powder with an average particle size of 6 μm in the amounts shown in Table 1 were added together with a toluene-ethanol mixed solvent. Ag
A N slurry was prepared. Using this, a green sheet was created by a doctor blade method and punched into a 65 x 65 mm square to obtain a green molded body.

After degreasing these in N2 at 700°C, they were fired at 1800°C for 3 hours under normal pressure in N2 atmosphere to obtain an AffN plate.

Properties generally required for an insulating substrate, such as appearance, relative density, thermal conductivity, insulation resistance, and surface roughness, of the obtained Al2N board were measured. The results are shown in Table 1.

Among the characteristics, the relative density was determined by calculating the density of the sintered body using the Archimedes method, divided by the true density, and expressed as a percentage.

Thermal conductivity was measured using the laser flash method. Insulation resistivity was measured using an insulation meter. The surface roughness (Ra) was measured using a stylus type surface roughness meter.

Example 2 An AffN plate was prepared in the same manner as in Example 1, except that various elements shown in Table 2 were used instead of Mg powder among the raw materials, and its appearance, relative density, thermal conductivity, Insulation resistance and surface roughness were measured and the results are shown in Table 2.

Example 3 Aff was produced in the same manner as in Example 1, except that various rare earth oxides shown in Table 3 were used instead of Y203 among the raw materials.
N plates were prepared, and their appearance, relative density, thermal conductivity, insulation resistance, and surface roughness were measured, and the results are shown in Table 3.

Example 4 To 100 parts by weight of /IN powder with an average particle size of 1 μm, Y2 oa powder with an average particle size of 1 μm in the amounts shown in Table 4, B with an average particle size of 3 μm, and various oxidations shown in Table 4 were added. The mixture was added with a toluene-ethanol mixed solvent, sufficiently mixed and crushed in a ball mill, and then polyvinyl butyral resin was added as a binder to prepare an AρN slurry. Using this, a green sheet was created by a doctor blade method and punched into a 65 x 65 mm square to obtain a green molded body.

After degreasing these in N2 at 700°C, they were fired at 1800°C for 3 hours under normal pressure in N2 atmosphere to obtain an AffN plate.

The obtained AJ2N board was measured for characteristics generally required as an insulating substrate, such as appearance, relative density, thermal conductivity, insulation resistance, and surface roughness. The results are shown in Table 4.

Among the characteristics, the relative density was determined by calculating the density of the sintered body using the Archimedes method, divided by the true density, and expressed as a percentage.

Thermal conductivity was measured using the laser flash method. Insulation resistivity was measured using an insulation meter. The surface roughness (Ra) was measured using a stylus type surface roughness meter.

Example 5 To 100 parts by weight of Al2N powder with an average particle size ILLm, a fifth
After adding the amounts of Y2O3 powder with an average particle size of 1 μm shown in the table, B with an average particle size of 3 μm, and various compounds shown in Table 5 together with a toluene-ethanol mixed solvent, thoroughly mixing and crushing in a ball mill, Adding polyvinyl butyral resin as a binder, AI;! , N slurry was prepared. Using this, a green sheet was created by a doctor blade method and punched into a 65 x 65 mm square to obtain a green molded body.

After degreasing these in N2 at 700°C, they were fired at 1800°C for 3 hours under normal pressure in N2 atmosphere to obtain an AgN plate.

Properties generally required for an insulating substrate, such as appearance, relative density, thermal conductivity, insulation resistance, and surface roughness, of the obtained AβNi were measured. The results are shown in Table 5.

Among the characteristics, the relative density was determined by using the Archimedes method to determine the density of the sintered body, divided by the true density, and expressed as a percentage.

Thermal conductivity was measured using the laser flash method. Insulation resistivity was measured using an insulation meter. The surface roughness (Ra) was measured using a stylus type surface roughness meter.

Example 6 An AffN plate was prepared in the same manner as in Example 5 except that Y2O3, B, and various compounds shown in Table 6 were used as raw materials, and its appearance, relative density, thermal conductivity, and insulation were The resistance and surface roughness were measured and the results are shown in Table 6.

Example 7 An AβN plate was prepared in the same manner as in Example 5 except that Y203, B, and various compounds shown in Table 7 were used as raw materials, and its appearance, relative density, thermal conductivity, and insulation were The resistance and surface roughness were measured and the results are shown in Table 7.

Example 8 Af was produced in the same manner as in Example 5, except that Y2O3, Zn powder, and various compounds shown in Table 8 were used as raw materials.
N plates were prepared, and their appearance, relative density, thermal conductivity, insulation resistance, and surface roughness were measured, and the results are shown in Table 8.

Example 9 Af was produced in the same manner as in Example 5, except that Y203, metal Li, and various compounds shown in Table 9 were used as raw materials.
N plates were prepared, and their appearance, relative density, thermal conductivity, insulation resistance, and surface roughness were measured, and the results are shown in Table 9.

Example 10 An ARN board was prepared in the same manner as in Example 5, except that Y2O3, B, and various compounds shown in Table 10 were used as raw materials, and its appearance, relative density, thermal conductivity, and insulation were The resistance and surface roughness were measured and the results are shown in Table 10.

Claims (1)

[Claims] 1. 100 parts by weight of aluminum nitride powder, as a sintering aid, (a) one or more selected from the group of oxides of yttrium, scandium, and lanthanoids, calculated as 0 .05 to 5 parts by weight (b) One or two elements selected from the group of metallic lithium, metallic beryllium, metallic magnesium, boron, silicon, sulfur, phosphorus, arsenic, and metallic zinc.
Add 0.01 to 5 parts by weight of seeds or more, mold the mixed powder, and heat it in a non-oxidizing atmosphere.
A method for producing an aluminum nitride sintered body, the method comprising firing in a temperature range of 400°C to 2000°C. 2. 100 parts by weight of aluminum nitride powder and as a sintering aid, (c) an alkali metal oxide and an alkali metal compound that becomes an oxide when heated at 2000°C or less, and boron;
Oxides of silicon, germanium, arsenic and phosphorus and 20
Claim 1, characterized in that 0.01 to 5 parts by weight of one or more compounds selected from the group of compounds that become oxides when heated at 00°C or below is added in terms of oxides. The method for producing the aluminum nitride sintered body described above. 3. 100 parts by weight of aluminum nitride powder, further added as a sintering aid, (d) a group of compounds selected from the group of metal borides, metal nitrides, metal phosphides, metal sulfides, metal silicides, and metal hydrides. One or more of the selected compounds from 0.01 to
2. The method for producing an aluminum nitride sintered body according to claim 1, wherein 5 parts by weight are added. 4 100 parts by weight of aluminum nitride powder, further added as a sintering aid, (d) a group of compounds selected from the group of metal borides, metal nitrides, metal phosphides, metal sulfides, metal silicides, and metal hydrides. One or more of the selected compounds from 0.01 to
3. The method for producing an aluminum nitride sintered body according to claim 2, wherein 5 parts by weight are added. 5 Add to 100 parts by weight of aluminum nitride powder as a sintering aid; (e) oxides of aluminum, gallium, indium, tungsten, bismuth, lead, antimony, cadmium, and zinc; 0.01 to 0.01 in terms of oxide of one or more compounds
2. The method for producing an aluminum nitride sintered body according to claim 1, wherein 2 parts by weight of the aluminum nitride sintered body is added. 6. 100 parts by weight of aluminum nitride powder and as a sintering aid, (c) an alkali metal oxide and an alkali metal compound that becomes an oxide when heated at 2000°C or less, and boron;
Oxides of silicon, germanium, arsenic and phosphorus and 20
Claim 5, characterized in that 0.01 to 5 parts by weight of one or more selected from the group of compounds that become oxides when heated at 00° C. or lower, calculated as oxides, is added. The method for producing the aluminum nitride sintered body described above. 7 100 parts by weight of aluminum nitride powder, and further added as a sintering aid, (d) a group of compounds selected from the group of metal borides, metal nitrides, metal phosphides, metal sulfides, metal silicides, and metal hydrides. One or more selected compounds from 0.01 to
The method for producing an aluminum nitride sintered body according to claim 5, characterized in that 5 parts by weight of the aluminum nitride sintered body is added. 8. 100 parts by weight of aluminum nitride powder, and as a sintering aid, (d) a group of compounds selected from the group of metal borides, metal nitrides, metal phosphides, metal sulfides, metal silicides, and metal hydrides. One or more selected compounds from 0.01 to
7. The method for producing an aluminum nitride sintered body according to claim 6, wherein 5 parts by weight of the aluminum nitride sintered body is added.