JPH0640772A - Production of aluminum nitride sintered compact and aluminum nitride sintered compact - Google Patents

Abstract

PURPOSE:To provide an aluminum nitride sintered compact excellent in heat conductivity and insulating property and low thermal expansion coefficient free from a layer different from the other part and having uniform characteristics. CONSTITUTION:When an aluminum nitride sintered compact is produced by sintering, operation for destroying the equilibrium state of a reaction on the surface of a compact to be sintered is carried out during sintering so as to prevent the stop of progress of sintering due to an apparent equilibrium state attained by the confrontation between the partial pressure of gaseous N2 in the sintering atmosphere and that of gaseous CO generated by reduction. Since the reaction can be allowed to proceed further, the compact to be sintered reacts sufficiently and difference in characteristics between the interior and surface part of the compact is not produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum nitride sintered body and an aluminum nitride sintered body, and in particular, aluminum nitride is a main component used for a semiconductor heat-radiating substrate and the like, and has a uniform high thermal conductivity. The present invention relates to a method for producing an aluminum nitride sintered body having a specific ratio and an aluminum nitride sintered body.

[0002]

2. Description of the Related Art Utilization of aluminum nitride (AlN) as a heat-radiating substrate is being considered due to its properties such as high electrical insulation, thermal expansion coefficient close to that of Si, and high thermal conductivity. In particular, by studying the AlN raw material powder and the sintering method, researches for improving the thermal conductivity, which is very important as the characteristics of AlN, are actively conducted in various fields.

Generally, an AlN sintered body contains AlN powder and a sintering aid such as a compound of alkaline earth or rare earth element,
It is manufactured by a method of mixing, granulating, molding and obtaining a sintered body by pressureless sintering. These sintering aids such as compounds of alkaline earth or rare earth elements are
By reacting with oxygen that is inevitably mixed in the powder to generate a liquid phase composed of a composite oxide of alumina and a sintering aid, densification in the sintering process is possible.
In addition, the formation of this composite oxide eventually fixes the impurity oxygen at the grain boundary and suppresses the solid solution of oxygen in the grain, thus contributing to the improvement of the thermal conductivity. . However, finally, when the complex oxide remains in the sintered body, the thermal conductivity of the obtained AlN sintered body is limited,
Its thermal conductivity was 170 W / mK or less.

At present, as the capacity of semiconductors is being increased, materials having higher thermal conductivity are required for circuit boards for mounting semiconductors, heat dissipation boards, etc. In order to meet such needs, nitriding is required. When aluminum is applied, it is necessary to solve the problems such as the presence of oxygen and other impurities and the presence of a grain boundary phase formed at grain boundaries as a result of the addition of a sintering aid.

From this point of view, Japanese Patent Laid-Open No. 63-277573 discloses adding an yttrium and / or calcium compound as a sintering aid to an AlN powder for the purpose of providing an aluminum nitride sintered body having excellent thermal conductivity. And is baked in a reducing atmosphere containing nitrogen gas to obtain a Y-Al-O compound and / or Ca-Al-O.
Compared with the conventional aluminum nitride sintered body, the amount of the grain boundary phase such as a system compound phase is reduced, and
By carrying out sintering consisting of a multi-step program of sintering in multiple stages, various optimum conditions for obtaining an aluminum nitride sintered body having a high thermal conductivity are studied, and an aluminum nitride manufacturing method based on such a study is performed. Proposed. The reaction mechanism of the sintering process in the method for producing aluminum nitride described in JP-A-63-277573 is as follows.
When the complex oxide on the outermost surface is removed by the reduction nitriding reaction, a concentration gradient of the complex oxide is generated, which acts as a driving force, and the complex oxide inside moves to the surface. The body is made.

[0006]

However, the above-mentioned Japanese Patent Laid-Open No.
The method for manufacturing aluminum nitride described in 63-277573 has the following problems. That is,
The sintered body obtained by the method for producing aluminum nitride described in 63-277573 has a frame-shaped layer of a color different from the inside when the cross section of a thin piece obtained by observing it in detail is observed, Such a different color layer shows non-uniform reduction in the sintering process, which causes doubt about the uniformity of the characteristics and causes a problem that the characteristics of the central portion are particularly low.
Therefore, in the past, when the difference in color was particularly clear, it was actually rejected in product inspection.
The treatment for removing such a different color layer is performed, which is one of the factors that impair the productivity of aluminum nitride. There is also a problem of processing cost for removing the different color layer. Further, as the capacity of semiconductors has been increased at present, it has been necessary to achieve higher thermal conductivity and insulation and a lower thermal expansion coefficient.

The present invention has been made in view of the above problems in the prior art, and is excellent in thermal conductivity and insulation.
It is an object of the present invention to provide a method for manufacturing an aluminum nitride sintered body having a low coefficient of thermal expansion, which does not form a partially different color layer, and which has uniform properties, and an apparatus therefor, and an aluminum nitride sintered body.

[0008]

The present inventor has conducted various experiments and studies in order to achieve the object of the present invention. In the sintering process for producing an aluminum nitride sintered body, the sintering atmosphere and the reduction reaction cause it. In view of the fact that the gas and the gas locally antagonize and apparently reach an equilibrium state, and then sintering does not proceed, it was found that the object of the present invention is achieved by means of breaking such an equilibrium state, and the present invention is created. Came to do.

That is, the method for producing an aluminum nitride sintered body of the present invention is an aluminum nitride in which aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent such as carbon or an organic binder carbide are mixed and molded and sintered. In the method for producing a sintered body, the operation of breaking the equilibrium state of the surface reaction of the body to be sintered is performed in the sintering process.

As an operation of breaking the equilibrium state of the surface of the sintered body according to the present invention, there is an operation of repeatedly raising and lowering the temperature during the sintering process. By repeating the temperature increase / decrease in this way, the equilibrium gas partial pressure on the surface of the body to be sintered changes, the equilibrium state on the surface of the body to be sintered is broken, and sintering can proceed. Therefore, the properties of the thus obtained sintered body are uniform up to the surface portion, and no frame-shaped different color layer is formed on the cut surface. In addition, as an operation of breaking the equilibrium state of the surface portion of the body to be sintered, there is an operation of adjusting the pressure of the sintering atmosphere gas. That is, the equilibrium gas partial pressure on the surface of the body to be sintered is also changed by means of temporarily reducing the pressure of the sintering atmosphere during the sintering process or means of temporarily reducing the temperature of the sintering atmosphere. It is possible to break the equilibrium state in the surface portion and proceed with the sintering.

The aluminum nitride raw material powder used in the present invention contains 1.5% by weight or less of oxygen, and practically 0.01%.
It is preferable that the content is from about 1.0% by weight. The average particle size is 0.5 when considering sinterability and thermal conductivity.
It is preferably about 5 μm. The additive added as a sintering aid in the present invention is a rare earth element compound and / or an alkaline earth element compound, and the additive added as a high thermal conductivity agent is carbon, an organic binder, a carbide or the like. Is a reducing agent.

Examples of compounds of rare earth elements and alkaline earth elements include oxides, nitrides, fluorides, oxyfluorides, oxynitrides of rare earth elements and alkaline earth elements, and substances which become these compounds by firing. To be For example,
Substances which become these oxides by firing include carbonates, nitrates, oxalates, hydroxides of rare earth elements and alkaline earth elements.

The amount of the rare earth and / or alkaline earth element compound added is preferably 0.5 to 15% by weight. If it is less than 0.5% by weight, the effect of the additive is not sufficiently exerted, the densification of the sintered body becomes insufficient, and oxygen is solid-dissolved in the AlN crystal, so that a high heat conductive sintered body cannot be obtained. On the other hand, 15
If it exceeds 5% by weight, a large amount of the grain boundary phase remains in the sintered body, which causes a problem that the volume of the grain boundary phase removed in the heat treatment process increases. The amount of the rare earth and / or alkaline earth element compound added is preferably 4.0 to 12
It is preferable to set it as a weight%, and it is more preferable to set it as 5 to 10% by weight.

In the present invention, the firing atmosphere in the sintering process is preferably a non-oxidizing atmosphere containing nitrogen gas constantly.

As a result of measuring and analyzing the characteristics and structure of the AlN sintered body obtained by the above-described method for producing an aluminum nitride sintered body of the present invention, the heat conduction of 170 w / mK or more, which is extremely high as a polycrystalline body. The constituent phase is only AlN crystal grains or AlN crystal grains and rare earth and alkaline earth oxides. The thermal conductivity is uniform with almost no difference between the surface part and the central part. It has been found. The final impurity oxygen of the aluminum nitride sintered body obtained by the manufacturing method of the present invention is preferably 2.0 wt% or less. If the impurity oxygen is contained in excess, the adverse effects on the object of the present invention of uniform thermal conductivity and high thermal conductivity will occur.

[0016]

Next, the factors for achieving uniform characteristics of the aluminum nitride sintered body obtained by the method for producing aluminum nitride of the present invention will be described. In the early stage of the sintering process, for example, when Y is selected as a rare earth element, 3Y2O3, 5Al
Compounds such as 2O3, Y2O3 ・ Al2O3, 2Y2O3 ・ Al2O3 are CaO when Ca is selected as the alkaline earth element.
Compounds such as 6Al2O3, CaO.2Al2O3, CaO.Al2O3 are produced. Next, in the subsequent sintering process, carbon (C) in the body to be sintered or in the atmosphere reduces the grain boundary phase from the inside of the body to be sintered, and the grain boundary phase is gradually removed. As a result, the grain boundary phase moves out of the system of the sintered body, and
The thermal conductivity increases uniformly toward the 1N single phase and AlN is highly purified. In that case, in the sintering process, the partial pressure of N2 gas in the sintering atmosphere and the partial pressure of CO gas generated by the reduction counteract each other, reaching an apparent equilibrium state, and the sintering does not proceed. Therefore, in the present invention, the reaction can be further advanced by performing an operation of breaking the equilibrium state of the reaction on the surface portion of the sintered body. In other words, it does not occur in the present invention that the sintered body does not sufficiently react and a difference in characteristics between the inside and the surface portion of the sintered body is formed. When the reaction on the surface portion reaches an equilibrium state, the equilibrium state is broken to a non-equilibrium state, the reaction proceeds without stagnation, and sufficient sintering is performed.

[0017]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. Example 1 An aluminum nitride powder containing 1.2% by weight of oxygen as an impurity and having an average particle size of 0.5 μm was used as a sintering aid.
Yttrium oxide (Y2O3) was added at 5.7% by weight, and carbon was added at 0.5% for high thermal conductivity. After mixing and granulating this mixed powder with a ball mill, 100 × 100 × 15 mm
Was molded into a green compact. Further, the sintered body obtained by removing the binder from this molded body was placed in a BN container and sintered under normal pressure under the following conditions.

(1) Sintering temperature / heating rate / sintering time First stage sintering From 1200 ° C. to 1600 ° C., the temperature was raised at a heating rate of 5 ° C./min, and after holding at 1600 ° C. for 10 min, 120
The temperature was lowered to 0 ° C. at 5 ° C./min, and the temperature was kept at 1200 ° C. for 10 min. Second-stage sintering The temperature was raised from 1200 ° C. to 1700 ° C. at a heating rate of 5 ° C./min, and held at 1700 ° C. for 10 minutes, then 130
The temperature was lowered to 0 ° C at 5 ° C / min, and the temperature was kept at 1300 ° C for 10 min.

Third Stage Sintering: The temperature was raised from 1300 ° C. to 1800 ° C. at a heating rate of 5 ° C./min, and the temperature was maintained at 1800 ° C. for 10 min.
The temperature was lowered to 0 ° C at 5 ° C / min, and the temperature was kept at 1400 ° C for 10 min. Fourth Stage Sintering The temperature was raised from 1400 to 2000 ° C. at a heating rate of 5 ° C./min, held at 2000 ° C. for 10 minutes, and then lowered.

(2) Sintering atmosphere CO gas partial pressure -0.2 x 10 5 Pa Nitrogen gas partial pressure -1.8 x 10 5 Pa In the above sintering, the final carbon content is 0.05 wt% or less and oxygen content is 0%. To obtain a sintered body having a content of 2.0 wt% or less. The obtained sintered body was analyzed to measure the carbon content, oxygen content, and thermal conductivity.

Example 2 Dysprosium oxide (Dy2O3) 7.0 as a sintering aid
A sintered body was obtained in the same manner as in Example 1 except that the weight% (weight conversion of dysprosium element) was added, and the characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3 A sintered body was obtained in the same manner as in Example 1 except that the temperature rising rate in the first stage sintering was 3 ° C./min. evaluated. The results are shown in Table 1.

Example 4 Sc was added in the same manner as in Example 1 except that Sc was added as a sintering aid, and a sintered body was manufactured. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5 A sintered body was manufactured in the same manner as in Example 1 except that Sr was added as a sintering aid. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 6 A sintered body was produced in the same manner as in Example 1 except that Ca was added as a sintering aid. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 7 A sintered body was produced in the same manner as in Example 1 except that Ce was added as a sintering aid. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 8 A sintered body was manufactured in the same manner as in Example 1 except that Ba was added as a sintering aid. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 9 A sintered body was manufactured in the same manner as in Example 1 except that Er was added as a sintering aid. The characteristics of the sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 10 Aluminum nitride powder containing 1.2% by weight of oxygen as an impurity and having an average particle size of 0.5 μm was used as a sintering aid.
5.7% by weight of dysprosium oxide (Dy2O3) was added (in terms of weight of dysprosium element). This mixed powder was mixed by a ball mill, granulated, and then molded. In molding, 0.8% by weight of carbon-containing organic resin binder is added in terms of carbon content to granulate, and press molding (100
0kg / cm2) 100 × 100 × 15mm
Was molded into a rectangular shaped green compact. Furthermore, the sintered body obtained by removing the binder other than carbon from this molded body in N2 was placed in a carbon container and sintered under normal pressure under the following conditions.

(1) Sintering temperature / heating rate / sintering time First stage sintering The temperature was raised from 1200 ° C. to 1600 ° C. at a heating rate of 5 ° C./min and held at 1600 ° C. for 10 minutes, then 120
The temperature was lowered to 0 ° C. at 5 ° C./min, and the temperature was kept at 1200 ° C. for 10 min. Second-stage sintering The temperature was raised from 1200 ° C. to 1700 ° C. at a heating rate of 5 ° C./min, and held at 1700 ° C. for 10 minutes, then 130
The temperature was lowered to 0 ° C at 5 ° C / min, and the temperature was kept at 1300 ° C for 10 min.

Third Stage Sintering: The temperature was raised from 1300 ° C. to 1800 ° C. at a heating rate of 5 ° C./min, and the temperature was maintained at 1800 ° C. for 10 min.
The temperature was lowered to 0 ° C at 5 ° C / min, and the temperature was kept at 1400 ° C for 10 min. Fourth Stage Sintering The temperature was raised from 1400 to 1900 ° C. at a heating rate of 5 ° C./min, held at 1900 ° C. for 10 minutes, and then lowered.

(2) Sintering atmosphere Nitrogen gas -1 atm At last, a sintered body having a final carbon content of 0.05 wt% or less and an oxygen content of 2.0 wt% or less was obtained. The obtained sintered body was analyzed and the oxygen content, density, particle size and thermal conductivity were measured.

Example 11 An aluminum nitride powder containing 1.2% by weight of oxygen as an impurity and having an average particle size of 0.5 μm was used as a sintering aid.
Yttrium oxide (Y2O3) was added at 5.7% by weight, and carbon was added at 0.5% for high thermal conductivity. After mixing and granulating this mixed powder with a ball mill, 100 × 100 × 15 mm
Was molded into a green compact. Further, the sintered body obtained by removing the binder from this molded body was placed in a BN container and sintered under the following conditions.

(1) Sintering atmosphere Steady state Nitrogen gas partial pressure-Maintenance of 2.0 × 10 5 Pa Unsteady state (operation for breaking the equilibrium state of the surface reaction of the sintered body in the sintering process) 1600 ° C. and 1800 A vacuum state (0.04 torr) was maintained for 10 minutes each at 0 ° C.

(2) Sintering temperature / heating rate / sintering time First stage sintering The temperature was raised from 1200 ° C to 1600 ° C at a heating rate of 5 ° C / min and held at 1600 ° C for 10 minutes.

Second Stage Sintering The temperature was raised from 1600 ° C. to 1800 ° C. at a heating rate of 5 ° C./min, and the temperature was maintained at 1800 ° C. for 10 min. By the above-mentioned sintering, a sintered body having a final carbon content of 0.05 wt% or less and an oxygen content of 2.0 wt% or less was obtained. The obtained sintered body was analyzed to measure the carbon content, oxygen content, and thermal conductivity.

Example 12 In the same manner as in Example 11 except for the above, as an operation for breaking the equilibrium state of the surface reaction of the object to be sintered in the sintering process, 1600
An operation of maintaining a reduced pressure state (0.01 × 10 ⁵ Pa) at 30 ° C. and 1800 ° C. for 30 minutes was performed.

Comparative Example 1 An aluminum nitride sintered body was produced in the same manner as in Example 1 except that the sintering temperature range was set to 0 to 2000 ° C. and the temperature rising rate was 5 ° C./min to perform the sintering in one step. did. The results of examining the characteristics of the obtained sintered body in the same manner as in Example 1 are shown in Table 1.

[0039]

[Table 1]

As can be seen from Table 1 which shows the characteristics of the sintered bodies obtained in the respective examples and comparative examples, the sintered bodies of the examples all have a thermal conductivity of 170 or more, and S
It has a coefficient of thermal expansion comparable to i. On the other hand, it was confirmed that the sintered body of Comparative Example 1 had non-uniform thermal conductivity in each part of the sintered body, and in particular, when the cut surface was observed, it was confirmed that the color tone inside the sintered body was non-uniform. Was done.

[0041]

As described above, according to the method for producing an aluminum nitride sintered body of the present invention, the inside of the sintered body and the surface of the obtained sintered body have uniform properties and high thermal conductivity. It is possible to obtain an aluminum nitride sintered body having a thermal expansion coefficient comparable to that of Si and having less difference in color tone which is a problem during product inspection.

Claims (7)

[Claims] 1. In a method for producing an aluminum nitride sintered body, which comprises mixing and shaping aluminum nitride and a rare earth and / or alkaline earth compound, and sintering the mixture, an operation of breaking the equilibrium state of the surface reaction of the sintered body is burned. A method for manufacturing an aluminum nitride sintered body, which is characterized in that it is carried out in a binding process. 2. In a method for producing an aluminum nitride sintered body, which comprises mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, heating and cooling are repeated during the sintering process. A method for manufacturing an aluminum nitride sintered body, comprising: 3. An aluminum nitride sintered body obtained by mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, by repeatedly raising and lowering the temperature during the sintering process. An aluminum nitride sintered body characterized by being obtained. 4. In a method for producing an aluminum nitride sintered body, which comprises mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, reducing the sintering atmosphere in the sintering process. A method for producing an aluminum nitride sintered body, comprising: 5. An aluminum nitride sintered body obtained by mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, which is obtained by reducing the sintering atmosphere during the sintering process. An aluminum nitride sintered body characterized by being obtained. 6. In a method for producing an aluminum nitride sintered body, which comprises mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, a sintering atmosphere is a vacuum in the sintering process. A method for manufacturing an aluminum nitride sintered body, comprising: 7. An aluminum nitride sintered body obtained by mixing and molding aluminum nitride, a rare earth and / or alkaline earth compound and a reducing agent, and sintering the mixture, which can be obtained in a sintering atmosphere in a vacuum atmosphere. An aluminum nitride sintered body characterized by the above.