JP2001139379A - Method of producing highly thermal conductive aluminum nitride sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an aluminum nitride sintered compact, by which a dense sintered compact having high thermal conductivity can easily be produced. SOLUTION: This method of producing an aluminum nitride sintered compact comprises the process for adding 0 to 3 wt.% Y2O3 and 1 to 5 wt.% YAG, each being based on the weight of an aluminum nitride raw material, to the aluminum nitride raw material, then mixing the obtained mixture with an organic binder and forming the resulting mixture, the dewaxing process for heating the formed body to decompose the organic binder so that residual carbon of 0.1 to 0.5 wt.%, based on the aluminum nitride raw material, is generated and the process for sintering the dewaxed body thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing a highly thermally conductive aluminum nitride sintered body.

[0002]

2. Description of the Related Art Aluminum nitride is used in electronics-related applications such as multilayer wiring boards, microwave transmission windows, electrostatic chucks for Si wafers, and heaters by utilizing its properties such as high thermal conductivity, electrical insulation, and fluorine plasma resistance. It is used for member applications.

Conventionally, an aluminum nitride sintered body is prepared by adding a sintering aid to an aluminum nitride sintering raw material, mixing an organic binder to form a desired shape, and then performing a heat treatment to remove the binder (degreasing). ), And sintered under a non-oxidizing gas atmosphere.

In this manufacturing process, when the sintering material is heated in a degreasing process or the like, a phenomenon occurs in which aluminum nitride is oxidized and the oxygen concentration in the aluminum nitride crystal increases. When oxygen is present as an impurity in the aluminum nitride crystal, the thermal conductivity is greatly reduced due to phonon scattering. Therefore, in order to improve the thermal conductivity of the aluminum nitride sintered body, it is necessary to reduce oxygen from the aluminum nitride crystal.

Heretofore, as a method for reducing oxygen in aluminum nitride crystals, there are (1) a method in which carbon is left in a degreased body and oxygen in aluminum nitride is reduced and removed by the residual carbon (Japanese Patent Laid-Open No. -172272 No. see Japanese) or the like are known (2) a method of using such _Y 2 _{O 3} as a sintering aid (see Japanese Patent Laid-Open No. 5-238830).

In the first method, in the step of degreasing the sintered material, degreasing is performed in an oxidizing atmosphere or a non-oxidizing atmosphere, and the residual carbon is converted to 0.05 to 1.0% by weight in terms of C element. Degreasing is performed so as to remain. by the way,
If carbon remains in the degreased body, there is a problem that the sinterability of aluminum nitride is reduced and the densification is not sufficiently performed. This is because the residual carbon is Y at the beginning of the firing process.
It is considered that the cause is that ₂ O ₃ and Al—O are reduced and a liquid phase required for sintering is not sufficiently generated.

A second method is to add a rare earth oxide such as yttrium oxide (Y ₂ O ₃ ) or an alkaline earth metal oxide such as calcium oxide as a sintering aid to a sintering raw material, followed by firing. It is. As a result, Y ₂ O _{3 and the} like are converted into oxygen (Al-
O) to form Y ₃ Al ₅ O ₁₂ (YAG),
This becomes a liquid phase and contributes to the liquid phase sintering of aluminum nitride, which is a hardly sinterable material. Thus, the amount of oxygen in the aluminum nitride crystal is reduced, and a sintered body having a high thermal conductivity of 100 W / mK or more can be obtained.

In order to sufficiently react oxygen contained in the aluminum nitride raw material with YAG, it is desirable to add as much Y ₂ O ₃ as possible.
Has a low thermal conductivity of about 10 W / mK, so if a large amount of the second phase mainly composed of YAG is present in the sintered body, the thermal conductivity will decrease. Therefore, it is conceivable to improve the thermal conductivity by reducing the second phase in the sintered body by utilizing the phenomenon that YAG is reduced and nitrided in a high-temperature reducing atmosphere and then volatilized and reduced. However, in order to sufficiently remove YAG from the aluminum nitride sintered body, 1
It is necessary to maintain at a temperature condition of 900 ° C. or more for 24 hours or more, which is not preferable in terms of time and energy.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve these problems of the prior art, and has provided a method for easily producing a dense sintered body having high thermal conductivity. It is intended to provide.

[0010]

SUMMARY OF THE INVENTION The present invention uses Y ₂ O ₃ and YAG as sintering aids for aluminum nitride, and further forms residual carbon in the compact to form a compact aluminum nitride sintered body. And that the thermal conductivity is significantly improved, and in the degreasing step of the present invention, the organic component of the binder is not completely decomposed and removed and remains as a carbon component. carbon, reducing the Al-O in the firing step, but acts to reduce the oxygen concentration in the sintered body, at that time, Y ₂ O
_The amount of the liquid phase generated by the reaction between No. ₃ and Al-O is reduced by Al-O being reduced by the residual carbon and Al-O deficiency. It does not hinder the progress of aluminum sintering.

The method for manufacturing an aluminum nitride sintered body according to the present invention, which has been completed based on such knowledge, comprises the following steps. (1) 0 to 3% by weight of aluminum nitride sintering raw material with respect to aluminum nitride sintering raw material as a sintering aid
Added a Y ₂ O ₃ and 1-5 wt% of YAG, then the aluminum nitride sintered material by heating the molded body obtained step (2) of molding by mixing this organic binder Degreasing step of thermally decomposing the organic binder so as to produce 0.1 to 0.5% by weight of residual carbon (3) Step of firing the degreased body thus obtained

Further, the present invention provides a sintering aid in which 1-2 wt% of Y based on aluminum nitride sintering raw material is used.
It is characterized by using ₂ O ₃ and also 1 to ₂ wt% YAG.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the production method of the present invention will be described in detail according to steps. As the aluminum nitride sintering raw material used in the present invention, commercially available aluminum nitride particles for producing an aluminum nitride sintered body can be used. The purity is desirable if it is high purity,
It may be of normal grade. As for the particle size, those having an average particle size of 0.05 to 5 μm are desirable.

In the present invention, YAG and Y ₂ O ₃ are used in combination as a sintering aid. These sintering aids are
Similar to the sintering raw material, a particulate material is used, and YAG is added to the aluminum nitride sintering raw material in a range of 1 to 5 wt% and Y ₂ O ₃ is added in a range of 0 to ₃ wt%. The mixing ratio of these components is determined based on the denseness and thermal conductivity of the aluminum nitride sintered body. YAG
And the Y ₂ O ₃ are each less than the above range, a dense sintered body can not be obtained, also when the YAG and Y ₂ O _3, respectively exceeds the above range, the thermal conductivity of the sintered body decreases. The amount of the second phase around the low thermal conductivity YAG properly maintained, and to combined effect of the oxygen withdrawal by _Y 2 _{O 3,} the amount of Y 2 _{O 3} is preferably 1 to 2 wt%.

The mixing of the sintering aid with the sintering raw material can be carried out by a method known as a usual means for mixing ceramic raw materials, such as mixing with a ball mill. In the mixing, mixing can be performed uniformly in a short time by adding an organic solvent such as methanol.

Next, an organic binder is added to and mixed with the sintering raw material containing the sintering aid. Generally, since only sintering raw material particles do not have a shape-forming property, an organic binder is added to form a desired shape. As an organic binder,
Polyvinyl butyral and carboxymethylcellulose (CMC), etc. are thermally decomposed at relatively low temperature and carbon dioxide, water,
A resin that does not generate substances other than residual carbon is desirable. The compounding amount can be selected in the range of about 2 to 5 wt% based on the firing raw material. In mixing, it is convenient to use the same organic solvent used for mixing the sintering raw materials.

Next, the slurry-like composition obtained by mixing is dried by a spray dryer or the like, and granulated into powder granules. Considering ease of handling in the subsequent molding step, the particle size is desirably about 5 to 500 μm. The molding can be performed by mold molding or CIP molding usually performed in the production of a ceramic sintered body.

Next, degreasing is performed to decompose and remove the organic binder of the obtained molded body. In the present invention, the amount of carbon remaining in the molded body in this degreasing step is 0.1 to 0.5.
It controls so that it may become wt%. 0.1wt of residual carbon
%, The effect of reducing the oxygen concentration by carbon is insufficient. If it is more than 0.5 wt%, the carbon is reduced to YAG, and the amount of liquid phase is insufficient, so that the densification of the sintered body is hindered.

The residual carbon content can be controlled by changing the conditions of the degreasing step. That is, if the degreasing temperature is lowered, the residual carbon amount of the degreased body increases, and if the degreasing temperature is raised, the residual carbon amount decreases. In addition, since degreasing efficiency is reduced in non-oxidizing atmosphere degreasing, the amount of residual carbon increases as compared to air atmosphere degreasing. Degreasing depends on the type of organic binder used, but is usually performed by heating to 400 to 700 ° C. in an oxidizing gas or a non-oxidizing gas.

Subsequently, the obtained compact is fired to obtain the aluminum nitride sintered body of the present invention. The firing can be performed under a reduced pressure of about 15 Pa or less or a normal pressure non-oxidizing atmosphere under a heating condition of 1800 to 2000 ° C. for 1 to 10 hours.

[0021]

EXAMPLES (Examples 1-3 and Comparative Examples 1-2) Aluminum nitride powder (MAN-2 manufactured by Mitsui Chemicals) and Y ₂ O ₃ 1w
A sintering aid consisting of t% and 1 wt% of YAG was mixed in methanol for 18 hours by a ball mill. to this,
3 wt% of a methanol solution of polyvinyl butyral (PVB) as a binder based on aluminum nitride powder
And further mixed by a ball mill for 1 hour. The obtained slurry is dried and granulated, and 30 MPa
A uniaxially molded product was subjected to a cold isostatic pressure of 100 MPa to obtain a molded product. The molded body was degreased under various degreasing conditions, and the residual carbon content of the degreased body was changed. At the same time, a small piece of degreased body was prepared, from which the residual carbon content was measured by a combustion infrared absorption method. The obtained degreased body was placed in a nitrogen atmosphere 190
Atmospheric pressure sintering was performed at 0 ° C. for 2 hours. The thermal conductivity of the sintered body was measured by a laser flash method, and the oxygen concentration was measured by an infrared absorption method.

Table 1 shows the residual carbon content of the degreased body, which is changed by controlling the degreasing conditions, and the measurement results of the thermal conductivity and the oxygen concentration of the sintered body. As the residual carbon content of the degreased body increases, the thermal conductivity of the sintered body increases. Further, it can be seen that the oxygen concentration also decreased, and the thermal conductivity increased due to the removal of oxygen by carbon. In the comparative example in which the residual carbon content of the degreased body was excessive, densification was not sufficiently performed even after the firing step.

[0023]

[Table 1]

(Examples 4 to 8 and Comparative Examples 3 to 6) Table 2 shows the thermal conductivity and oxygen concentration of the sintered body when the sintering aid was changed under the condition of degreasing in air at 500 ° C. Comparative Examples 3 and 5 did not sufficiently densify. Al-O is reduced in Comparative Example 5, the residual carbon, it is due to the fact that sufficient YAG from Y ₂ O ₃ is not generated. In Comparative Examples 4 and 6, the thermal conductivity is significantly reduced due to the excessive existence of the second phase centered on YAG. By using YAG as a sintering aid in addition to Y ₂ O ₃ , a dense sintered body can be obtained even if a relatively large amount of carbon remains in the degreased body. It was found that the conductivity increased. Also, from the comparison of Examples 6 to 8, Y ₂ O ₃ 1-2
By setting the wt% and YAG to 1 to 2 wt%, it is possible to manufacture aluminum nitride having high thermal conductivity, which is more preferable.

[0025]

[Table 2]

[0026]

According to the present invention, by adopting the above-described steps, a dense sintered body can be obtained even if carbon remains in the degreased body. This has the effect of obtaining an aluminum nitride sintered body having thermal conductivity.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichiro Aonuma 30 Soya, Hadano-shi, Kanagawa Prefecture Toshiba Ceramics Co., Ltd. (72) Inventor Shigeko Muramatsu 30 Soya, Hadano-shi, Kanagawa Prefecture F-term ( Reference) 4G001 BA09 BA36 BA65 BB36 BB73 BC17 BC34 BC56 BD03 BD38 5F036 AA01 BB01 BD13

Claims (2)

[Claims] 1. An aluminum nitride sintering raw material, and 0 to aluminum sintering raw material as a sintering aid, respectively.
Adding ₃ % by weight of Y ₂ O ₃ and 1 to 5% by weight of YAG, and then adding an organic binder to the mixture to form the mixture; High thermal conductive aluminum nitride sintering, comprising: a degreasing step of thermally decomposing an organic binder so as to produce 0.1 to 0.5% by weight of residual carbon by heating; and a step of firing the obtained degreased body. Body manufacturing method 2. As a sintering aid, 1 to 2 wt% of Y ₂ O ₃ and 1
2. The method according to claim 1, wherein YAG is used in an amount of 2 wt%.
Method for producing high thermal conductive aluminum nitride sintered body