JPH02296709A - Aluminum nitride powder and its production - Google Patents

Abstract

PURPOSE:To obtain aluminum nitride powder of small particle size containing little oxygen and carbon by hydrolyzing a solution of org. aluminum compd. with carbon dispersed and then baking the product of hydrolysis in an atmosphere of such as nitrogen. CONSTITUTION:Carbon is dispersed in an org. solution of org. Al compd. and then the solution is hydrolyzed to obtain a mixture of aluminum hydroxide and carbon. Then the mixture is baked in a nitrogen atmosphere and then baked in an atmosphere containing both hydrogen and nitrogen. Thus, aluminum nitride with the primary particle size <=0.5mum, oxygen content <=0.6wt.% and carbon content <=0.1wt.% can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high purity aluminum nitride powder and a method for producing the same.

[Prior Art] Aluminum nitride sintered bodies are attracting attention as substrate materials for semiconductors because of their high heat conductivity, high insulation properties, and high mechanical strength. The following method is known as a method for synthesizing aluminum nitride powder, which is a raw material for this sintered body.

l) Direct nitriding method in which aluminum is heated in nitrogen.

2) A reductive nitriding method in which a mixture of alumina and carbon is nitrided in a nitrogen atmosphere.

3) A gas phase synthesis method in which an aluminum compound (gas) is reacted with nitrogen or ammonia in the gas phase.

In order for the aluminum nitride sintered body to exhibit the above-mentioned excellent properties such as high heat conductivity and high strength, the raw material aluminum nitride powder is required to have high purity and a fine particle size.

Method l) above is inexpensive, but since the reaction proceeds from the surface, the center tends to remain unreacted, and the aluminum nitride produced also becomes lumpy and needs to be pulverized, resulting in a fine powder with uniform particle size. is difficult to obtain. Although method 3) yields very fine powder, it has a large surface area, so it is susceptible to surface oxidation and a large amount of oxygen is adsorbed. Also, industrial productivity is poor. Although method 2) allows aluminum nitride powder to be obtained with a relatively fine particle size, it has not yet been able to obtain a powder of satisfactory purity.

One reason for this is that, due to the reaction mechanism in which oxygen in alumina is reduced by carbon and eliminated as carbon oxide, it is important to improve the mixing of alumina and carbon to complete the reaction, but this is difficult. can be mentioned. As a way to solve this problem,
No. 08 discloses a method of hydrolyzing an alcoholic solution of aluminum alkoxide in which carbon is dispersed.

In this case, the carbon/alumina ratio is kept low so as not to leave as much excess carbon as possible, but it is still 1
Approximately % carbon remains. Also, JP-A-61-8
104 also aims to improve the dispersibility of alumina and carbon using a similar method. In this case, the carbon/alumina ratio is made quite high, and excess carbon is removed by heating in air. Therefore, the amount of residual carbon is less than 0.1%, but the amount of oxygen is around 1%.

Another problem is that an excessive amount of carbon is required to complete this reaction, but this carbon may remain after the reaction, or if heated in air to remove the remaining carbon, Oxidation of aluminum nitride inevitably occurs. Also, 1600℃
If nitriding is performed at higher temperatures, the oxygen content can be reduced, but
A drawback is that grain growth of aluminum nitride occurs during nitriding, resulting in a large grain size of the resulting grains.

That is, at present, aluminum nitride powder with low carbon and oxygen contents and fine particle size has not yet been obtained.

[Problems to be Solved by the Invention] The present invention solves the problems of low purity and large particle size of raw material aluminum nitride powder, which are problems in obtaining aluminum nitride sintered bodies with excellent sinterability and heat transfer properties. This is an attempt to solve both problems.

[Means for Solving the Problems] As a result of intensive research to solve these problems, the present inventors found that compared to conventional aluminum nitride powder, both oxygen content and carbon content are extremely low. The inventors discovered an aluminum nitride powder that also has a small primary particle size, leading to the present invention.

That is, the present invention that achieves the above objects includes a primary particle size of 0.5μ or less, an oxygen content of 0.6ffI% or less,
This is an aluminum nitride powder characterized by having a carbon content of 0.1% by weight or less.

In addition, in the method for producing aluminum nitride powder of the present invention, carbon is dispersed in an organic solvent solution of an organoaluminum compound, and then a mixture of aluminum hydroxide and carbon obtained by hydrolysis is first calcined in a nitrogen atmosphere. and then firing in an atmosphere containing hydrogen and nitrogen at the same time.

Aluminum alkoxide is used as the organoaluminum compound, and the mixing ratio of carbon is 1:0.5 to 1.5 in weight ratio of alumina to carbon in terms of alumina. The firing is preferably carried out at 1300°C to 1600°C under a nitrogen atmosphere or an atmosphere containing hydrogen and nitrogen at the same time.

To explain the present invention in more detail, the aluminum nitride powder referred to in the present invention has a primary particle size of 0.5μ or less, an oxygen content of 0.6% by weight or less, and a carbon content of 0.1% by weight or less. Powder that satisfies all of these conditions has significantly improved sinterability and heat conductivity.

Oxygen, which is an impurity, is thought to have a particularly bad effect on heat transfer properties, and carbon is thought to have a bad effect on sinterability. It is desirable that these amounts be as low as possible. Further, the primary particle size is related to sinterability, and there is a certain appropriate range, and smaller is not necessarily better. This range is more preferably 0.1μ to 0.4μ in view of the oxidation resistance, handling properties, etc. of the particles.

Next, a method for producing aluminum nitride powder of the present invention will be explained. Examples of raw material organic aluminum compounds include trimethylaluminum, triethylaluminum,
Alkylaluminum such as diethyl heptanoheroaluminum, aluminum alkoxide such as aluminum ethoxide, aluminum isopropoxide, aluminum butoxide, aluminum monobutoxydiisopropoxide, and further aluminum chelate compounds such as diisopropoxyaluminum ethyl acetoacetate. can be mentioned. Among these, aluminum alkoxide is particularly preferred in terms of hydrolyzability, shape of particles obtained, etc.

The organic solvent for dissolving this organoaluminum compound is not particularly limited as long as it dissolves the organoaluminum compound, but alcohols such as methanol, ethanol, n-propanol, isopropanol, and butanol are used in the subsequent hydrolysis process. This is suitable considering the following.

When aluminum alkoxide is dissolved in alcohol, the appropriate concentration is 5 to 20% by weight. Further, it is preferable that the carbon to be dispersed in the organic solvent solution has a high purity and a particle size of 0.1 μm or less, such as carbon black or acetylene black. If the particle size exceeds 0.1μ, it will be difficult to obtain a uniform and fine mixture, and the reaction will not be completed.

The mixing ratio of the organic aluminum compound and carbon is 170.The ff1ffi ratio of alumina to carbon is 170.
It is desirable that it is 5 to 1.5. If this ratio is less than 0.5, the reaction will not be completed and the oxygen content will increase. On the other hand, if it exceeds 1.5, carbon will remain, which is not preferable. The range of the alumina to carbon weight ratio of the present invention is in a region where the ratio of carbon is higher than the conventional range of the prior art. In the conventional technology, the decarbonization process is performed in air, so the temperature cannot be raised too much and the amount of carbon added cannot be increased too much. In the present invention, as will be described later, firing is performed in two stages, and in particular, the second stage is performed in an atmosphere containing hydrogen and nitrogen at the same time, so that sufficient decarbonization is possible even if the amount of carbon added is increased compared to conventional methods. ing. Next, water in an amount of 2 to 20 times the amount of the organoaluminum compound in molar ratio is added to the organic solvent solution of the organoaluminum compound in which carbon is dispersed, and hydrolysis is carried out. This decomposition may be carried out at room temperature or under heating. It is even more preferred to add water while stirring. In this way, the particle size of aluminum hydroxide, which is a hydrolyzate of an organoaluminum compound, becomes 0.5 μm or less.

The mixture of aluminum hydroxide and carbon is filtered, if necessary, dried or dehydrated by heating, in a conventional manner, and then subjected to the -stage firing. - Stage baking is performed at a temperature of 1300° C. to 1600° C. for 1 to 10 hours under a nitrogen atmosphere. 1
The reaction does not proceed easily below 300℃, and
When the temperature exceeds .degree. C., grain growth of aluminum nitride occurs, and the grain size exceeds 0.5 micron. Subsequently, the second stage of firing was performed at 1,300℃ to 1,300℃ in an atmosphere containing hydrogen and nitrogen at the same time.
It is carried out at a temperature of 600° C. for 1 to 10 hours. The atmosphere containing hydrogen and nitrogen at the same time may be obtained by mixing hydrogen gas with nitrogen gas, or more preferably by using ammonia gas as it is. Ammonia decomposes into hydrogen and nitrogen at temperatures above 1000°C. In the second stage firing, nitriding and decarbonization proceed simultaneously.

Decarbonization progresses slowly below 1300°C;
If the temperature exceeds ℃, grain growth occurs as in the first stage, which is not desirable. - The firing in the second stage and the second stage may be performed continuously or separately by simply changing the type of gas in the atmosphere.

However, firing under a nitrogen atmosphere takes precedence. If fired in an ammonia atmosphere from the beginning, carbon will disappear and nitriding will not proceed sufficiently.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 48 g of aluminum isopropoxide was dissolved in 400 g of isopropanol, and 9 g of acetylene black having a particle size of 0.04 μm was dispersed therein. Next, 50 g of distilled water was added over 1 hour while stirring the solution at room temperature to effect hydrolysis. After that, the mixture was ground in a ball mill for 6 hours, and after the ball mill was finished, it was filtered. II) It was dried in the air at 0°C for 3 hours. This solid material was placed on a graphite flat plate, and nitrogen gas was heated for 15 minutes in a tubular electric furnace.
The mixture was heated and maintained at 1500° C. for 6 hours with a 1/2-minute flow.

After the electric furnace had cooled to room temperature, the graphite flat plate was taken out and the contents were transferred to an alumina boat, and heated and maintained at 1500°C for 3 hours while flowing ammonia gas in a tubular electric furnace again to obtain a white powder. Ta.

The oxygen content of this powder is 0.4% by weight, and the carbon content is 0.
．． 06%, and the primary particle diameter by electron microscopy was 0.3μ. Further, no peaks other than aluminum nitride were detected in the X-ray diffraction.

Example 2 A white powder was obtained in the same manner as in Example 1 except that the amount of acetylene black added was 12 g.

This powder had an oxygen content of 0.45% by weight, a carbon content of 0.09%, and a primary particle diameter of 0.3 μ by electron microscopy. Further, no peaks other than aluminum nitride were detected in the X-ray diffraction.

Example 3 A white powder was obtained in the same manner as in Example 1 except that the amount of acetylene black added was 7.5 g.

The oxygen content of this powder is 0.5% by weight, and the carbon content is 0.
．． 05%, and the primary particle diameter by electron microscopy was 0.3μ. Further, no peaks other than aluminum nitride were detected in the X-ray diffraction.

Comparative Example 1 Example 1 except that the addition of acelene black was 5 g.
A white powder was obtained in the same manner as above. This powder had an oxygen content of 1.0% by weight, a carbon content of 0.04%, and a primary particle diameter of 0.3 μ by electron microscopy. Further, no peaks other than aluminum nitride were detected in the X-ray diffraction.

Comparative Example 2 A white powder was obtained using the same procedure as in Example 1 except that the amount of acetylene black added was 20 g.

The oxygen content of this powder is 0.5% by weight, and the carbon content is 0.
．． 4%, and the primary particle diameter by electron microscopy was 0.3μ. Further, no peaks other than aluminum nitride were detected in the X-ray diffraction.

[Effects of the invention] The present invention makes it possible to obtain aluminum nitride powder that satisfies both high purity and small particle size at the same time.If this powder is used, good sinterability and high heat conductivity can be expected. can.

Patent applicant: Asahi Kasei Industries, Ltd. Agent Patent Attorney Hidetake Komatsu

Claims (2)

[Claims] (1) Primary particle size is 0.5μ or less, oxygen content is 0.6
An aluminum nitride powder characterized in that the carbon content is 0.1% by weight or less. (2) After dispersing carbon in an organic solvent solution of an organoaluminum compound, the mixture of aluminum hydroxide and carbon obtained by hydrolysis is first calcined in a nitrogen atmosphere, and then contains hydrogen and nitrogen at the same time. The method for producing aluminum nitride powder according to claim 1, characterized in that the firing is performed in an atmosphere.