JP2661113B2 - Manufacturing method of aluminum nitride sintered body - Google Patents

Description

The present invention relates to a method for manufacturing an aluminum nitride sintered body.

(Prior Art) In recent years, the integration and function of semiconductor elements have been advanced and
With Al ₂ O ₃ , it is difficult to cope with the problem of thermal expansion mismatch due to an increase in the heat generation of the Si chip and an increase in chip size, and a new high thermal conductive insulating material is required.

Aluminum nitride (AlN) has attracted particular attention as a substrate material for semiconductor mounting because it has excellent thermal conductivity, a coefficient of thermal expansion close to that of a Si chip, and excellent material properties such as high electrical insulation.

Since AlN is a hard-to-sinter material, it is difficult to obtain a dense sintered body. In addition, impurity oxygen is usually contained in the raw material.
About 3wt%, even if it is densely sintered by hot press etc. without sintering aid, Al-O-N
It is known that an oxygen solid solution layer is formed and the thermal conductivity is significantly reduced.

Conventionally, in order to make AlN denser and higher thermal conductivity,
Various sintering aids have been studied.
Oxides such as ₂ O ₃ and CaO have been found to be particularly effective. (Proc.1st IEEE CHMT Syms., 15 (1984)) for example Y ₂ O ₃ Y ₂ O ₃ reacts with oxygen impurity is the mechanism of the high thermal conductivity of by addition, compounds such as YAG in the triple point of AlN grain boundaries Is believed to form and trap oxygen.
As described above, high thermal conductivity can be achieved by adding Y ₂ O ₃ , but it is hard to say that the thermal conductivity is about 100 W / mk, which is sufficiently higher than the theoretical value of 320 W / mk. A number of other sintering aids have been proposed, but some prior arts relating to the addition of carbon of the present invention have been reported.

The method of adding carbon to a molded product is described in JP-A-60-186479 and JP-A-61-155263. In the former, a compound that becomes carbon or decomposes into carbon into AlN powder, and in the latter, free carbon and yttrium oxide are added to AlN powder, and after molding and firing, the thermal conductivity of AlN is about 50 W / mk and 150 W / mk, respectively. We have a sintered body.

Further, in Japanese Patent Application Laid-Open No. 61-270263, an element or a compound such as Ti is added to AlN powder and calcined in a non-oxidizing atmosphere having a source of boron and / or carbon to obtain a powder of about 90%.
A sintered body with a thermal conductivity of W / mk has been obtained. As mentioned above, several systems related to carbon addition have been reported, but the thermal conductivity of each is insufficient at about 150 W / mk,
Further, an aluminum nitride sintered body having a higher thermal conductivity has been demanded.

[Problems to be Solved by the Invention] The present invention is intended to solve the above-mentioned disadvantages of the prior art relating to carbon addition, and has a high thermal conductivity of about 200 W / mk. An object of the present invention is to provide a manufacturing method for stably supplying an aluminum sintered body.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and after mixing and molding aluminum nitride powder and a sintering aid, this aluminum nitride compact An object of the present invention is to provide a method for producing an aluminum nitride sintered body, characterized in that a carbon supply source is placed in a sheath having at least an inner surface made of non-carbon material and fired in a non-oxidizing atmosphere.

(Detailed Description of Configuration) Hereinafter, the present invention will be described in detail.

First, the aluminum nitride powder is preferably of a high purity, for example, 98% or more, but a powder of about 95 to 98% can also be used. Particle size is 10 μm or less, preferably 2 μm
The following are good. If the particle size exceeds 10 μm, the sinterability decreases, which is not preferable.

The sintering aid added to the aluminum nitride powder is for obtaining a dense sintered body, and is preferably Y ₂ O ₃ , CaO, or the like.However, any material that promotes densification is not limited thereto. Not something. On the other hand, if the addition amount of the sintering aid is too large, the crystal phase other than aluminum nitride increases and the thermal conductivity decreases, which is not preferable. Therefore, the preferable addition amount of the sintering aid is 10% by weight or less, particularly preferably 5% by weight or less.

Further, the particle size of the sintering aid is preferably small,
μm or less is desirable. After mixing the aluminum nitride powder and the sintering aid in a predetermined ratio, the mixture is formed into a predetermined shape by a doctor blade method or a press method, and is mixed with nitrogen or the like to prevent a reduction in thermal conductivity due to a reaction between Al and oxygen. Baking in a non-oxidizing atmosphere. In this case, at least the inner surface of the molded body is housed in a non-carbon sheath, but as a material of the sheath, for example, aluminum nitride having a melting point or a sublimation decomposition temperature higher than the aluminum nitride firing temperature at normal pressure,
Boron nitride, silicon carbide and the like are desirable. In particular, a sheath made of aluminum nitride or boron nitride is more preferable because it does not hinder the improvement of the sinterability and thermal conductivity of the aluminum nitride sintered body.
When using carbon that is inexpensive, light, and excellent in workability as a sheath, at least the inner surface of the sheath is coated with the above-mentioned materials such as aluminum nitride and boron nitride, thereby suppressing the release of carbon during firing. It is desirable to have

Further, at least one of carbon powder, carbon ceramics, and a carbon compound which can be easily converted to carbon (for example, a carbon compound used as a binder) is supplied into the sheath at the same time as a carbon supply source. These carbon sources have an appropriate amount that affects the physical properties of the AlN sintered body.If the supply amount is insufficient, the thermal conductivity is 100 to 120 W /
When the supply is excessive, the thermal conductivity increases to about 200 W / mk, but the insulation resistance deteriorates to 10 ⁹ to 10 ¹⁰ Ωcm, which is not preferable.

When the amount of carbon source is appropriate, the thermal conductivity exceeds 200 W / mk and the insulation resistance is 10 ¹⁴ Ωcm or more, showing good characteristics. As described above, it is important to add an appropriate amount of a carbon source.For example, when carbon such as a carbon sheath used for firing and a heating element is used as the source, the sheath, the shape of the heating element, the surface state,
The amount of carbon supply varies remarkably depending on the position of use, etc., and it is difficult to stably secure an AlN sintered body having good characteristics. Therefore, in order to add an appropriate amount of carbon in the present invention, at least the inner surface of the sheath is made of non-carbon as described above to prevent the invasion of carbon from the sheath and the heating element. The method of putting was adopted.

An experiment was also conducted on a method in which carbon was added to the composition, but the thermal conductivity increased only to about 150 W / mk.

[Operation] In the present invention, it has been found that the thermal conductivity is significantly improved by adding an appropriate amount of a carbon source to the sheath.
Although the mechanism of this high thermal conductivity is not yet clear, the optimal amount of carbon tends to increase with the weight of the aluminum nitride molded body put into the sheath,
In general, impurity oxygen is closely related to the high thermal conductivity of AlN. Therefore, by adding an appropriate amount of carbon into the sheath by the impurity oxygen contained in the compact, the triple point of the grain boundary is consequently obtained during the sintering process. It is considered that high thermal conductivity has been achieved because the material is trapped in the material or removed outside the system.

Therefore, the optimal amount of carbon is not only the weight of the aluminum nitride molded body, but also the amount of impurity oxygen contained in the aluminum nitride raw material, the type and amount of the firing aid, the amount of impurities mixed during the process, and the amount of the forming aid such as a binder. It is conceivable that it depends on the kind, the amount, the firing temperature and the like.

Example 1 2.5 wt% of Y ₂ O ₃ powder was added to aluminum nitride powder having an average particle size of 2 μm, and wet-mixed in alcohol. Next, after drying, it was formed into a shape of 70 × 70 × 3 mm at a pressure of ² t / cm ² . One of the compacts was placed in an aluminum nitride sheath (100 x 100 x 20 mm in size), carbon black powder was spread around it, and the sheath was covered with a lid at 1850 ° C for 5 hours in a nitrogen atmosphere. By holding, an aluminum nitride sintered body was obtained. The relative density, thermal conductivity, and insulation resistance of this aluminum nitride sintered body were measured. Table 1 shows the amount of carbon black powder added and the measurement results. Sample NO1,2
Although the amount of carbon added was small and the thermal conductivity was as low as 150 W / mk or less, carbon was excessively added in samples NO5 and 6, and the insulation resistance was deteriorated. On the other hand, in samples 3 and 4, the thermal conductivity was around 200 W / mk, and the insulation resistance was 10 ¹⁴ Ω
m and good results were obtained.

EXAMPLE _2] Y 2 O ₃ powder except that the CaO was added 1.5 wt% instead of calcined in the same manner as in Example 1, to obtain an aluminum nitride sintered body. Table 2 shows the amount of carbon black powder added and the measurement results. The same tendency as that of the system to which Y ₂ O ₃ was added was exhibited, and NO9 and 10 in which an appropriate amount of carbon black powder was added had good characteristics in both thermal conductivity and insulation resistance.

Example 3 An experiment was performed in the same manner as in Example 1, except that a carbon sheath (inner dimensions 100 × 100 × 20 mm) having an inner surface coated with boron nitride was used instead of the aluminum nitride sheath. The addition amount and measurement results of the carbon black powder were as follows.

Carbon black addition amount: 0.4 g Relative density: 99.2% Thermal conductivity: 230 W / mk Insulation resistance: 7 × 10 ¹⁴ Ωcm In this way, good characteristics were obtained even with a carbon sheath coated with boron nitride on the inner surface. .

Comparative Example 1 The AlN, Y ₂ O ₃ , and carbon black powders used in Example 1 were mixed according to the composition shown in Table 3 and similarly molded into 70 × 70 × 3 mm. The calcination was performed in the same manner as in Example 1 except that the carbon black powder was not spread around the formed body. Table 3 shows the measurement results.

The thermal conductivity was only about 150 W / mk and the relative density was lower than that of Example 1.

Comparative Example 2 In Example 1, an experiment was performed in the same manner as in Example 1 except that a carbon sheath (internal dimensions 100 × 100 × 20) was used instead of the aluminum nitride sheath. Table 4 shows the amount of carbon black powder added and the measurement results.

In sample NO19, despite the fact that no carbon black powder was laid in the carbon sheath, the carbon was excessively supplied from the carbon sheath, the insulation resistance was deteriorated, and the thermal conductivity and the bulk density were low.

[Effect of the Invention] The aluminum nitride sintered body manufactured according to the present invention is excellent in thermal conductivity at around 200 W / mk at high density and exhibits good electric characteristics, so that it can be used not only as a substrate for semiconductor mounting and various heat sinks, It can be applied as a high-temperature material such as a crucible, a container for vapor deposition, and a heat-resistant jig high-temperature member, and has many industrial advantages.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-277573 (JP, A) JP-A-62-252374 (JP, A) JP-A-59-207882 (JP, A)

Claims (1)

(57) [Claims] An aluminum nitride powder and a sintering aid are mixed and molded, and then the aluminum nitride compact and a carbon supply source are placed in a sheath having at least an inner surface made of non-carbon material, and the mixture is placed in a non-oxidizing atmosphere. A method for producing an aluminum nitride sintered body, characterized by firing.