JPH03218909A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To improve thermal conductivity by producing Al(OH)3 by the hydrolysis of an org. solvent solution of org. Al compd. into which polyacrylonitrile powder is dispersed and then calcining the mixture in a N2 atmosphere followed by a mixture gas atmosphere of N2 and H2. CONSTITUTION:Polyacrylonitrile powder is dispersed in an org. solvent solution such as isopropanol of org. Al compd. such as Al isopropoxide in a manner that the amt. of the powder in terms of Al2O3 is 1/(1 to 3) (weight ratio) of the org. Al compd. Then water 2-20 times as much as the org. Al compd. is added into this solution to effect the hydrolysis which produces Al(OH)3. The mixture of Al(OH)3 and polyacrylonitrile is then filtered. dried, formed into perrets, and then calcined in a N2 atmosphere at 1400-1700 deg.C for 0.5-10 hours as the first calcination stage and further in a mixture gas atmosphere comprising N2/H2=0.05 to 5 (molar ratio) or in a NH3 atmosphere at 1000-1700 deg.C for 0.5-10 hours as the second calcination stage. Thus, the AlN powder expressed by the formula (wherein X is the average particle size (mu) and Y is the content of O2 (%)) is obtained.

Description

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

[Conventional technology] CoAluminum 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.

■》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 excellent properties such as the above-mentioned high heat conductivity, the raw material aluminum nitride powder is required to have high purity and a fine particle size.

Although method 1) above is inexpensive, 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. Those with high purity have large particle sizes, and if you want to obtain fine particle sizes,
Oxidation during grinding reduces purity.

Although method 3) can yield very fine powder,
Because it has a large surface area, it is susceptible to surface oxidation and adsorbs a large amount of oxygen. Also, industrial productivity is poor.

Although method 2) yields aluminum nitride powder with a relatively fine particle size, it has not yet been able to obtain one with satisfactory purity.

One of the reasons for this is that due to the reaction mechanism in which oxygen in alumina is reduced by carbon and eliminated as carbon monoxide, it is important to improve the mixing of alumina and carbon, but this is difficult. . To solve this problem, Japanese Patent Laid-Open No. 81-6104 discloses a method of hydrolyzing an alcoholic solution of aluminum alkoxide in which carbon is dispersed. Although this has considerably improved the mixing condition of alumina and carbon, it is still not sufficient. That is, the oxygen content in this case is still around I%.

In addition, a method of using ammonium aluminum alum instead of aluminum alkoxide is disclosed in JP-A-63-2.
70302, a method of using basic aluminum chloride is disclosed in JP-A-63-210002, and a method of using urea resin, polyimide resin, polyamide resin, polyurethane resin, or melamine resin instead of Rikibon is disclosed in JP-A-61.
-178409, but high purity aluminum nitride powder has not been obtained by any of the methods. Of course, if you only want to increase the purity, nitriding at a high temperature of 1700°C will reduce the oxygen content, but grain growth of aluminum nitride will occur during nitriding, resulting in a larger grain size of the resulting particles. There are drawbacks.

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

[Problem to be solved by the invention] The problem with the characteristics of aluminum nitride sintered bodies is how to lower the sintering temperature and increase the thermal conductivity. It is necessary to improve the purity and refinement of the powder.

The present invention solves both the purity and particle size problems of aluminum nitride powder.

[Means for Solving the Problems] The present inventors have conducted intensive research to solve these problems, and have found that there is a relationship between particle size and oxygen content.
He discovered and invented aluminum nitride powder. That is, the present invention, which has achieved the above object, is an aluminum nitride powder that satisfies the following relational expression, where the average particle diameter as determined by scanning electron microscopy is X (μ), and the oxygen content is Y (%). It is a manufacturing method.

(Y + 0.4) After the mixture of aluminum and polyacrylonitrile is pelletized in some cases, it is fired under a nitrogen atmosphere,
Next, the mixing ratio of the organic aluminum compound and polyacrylonitrile is preferably 1 to 3 (weight ratio of alumina to polyacrylonitrile in terms of alumina). The atmosphere containing is preferably an atmosphere consisting of heating ammonia, and the firing temperature in a nitrogen atmosphere is 1400 to 1
The firing temperature is preferably 700°C, and the firing temperature in an atmosphere containing hydrogen and nitrogen at the same time is preferably 1000 to 1700°C.

To explain the present invention in more detail, the aluminum nitride powder produced by the present invention has an average particle diameter of X (μ) and an oxygen content of Y (%) as determined by scanning electron microscopy.
It is an aluminum nitride powder that satisfies the following relational expression: (Y+o.4)x≦0.4 A powder that satisfies this condition has good sinterability and thermal conductivity.

The lower the oxygen content, the better the thermal conductivity. The particle size is related to sinterability, and the smaller the particle size, the better the sinterability.
There is a certain appropriate range depending on the oxidation resistance, handling properties, etc. of the particles, and smaller is not necessarily better. This range is 0.1-1.0μ. Specific examples of oxygen content and particle diameter within this range are as follows.

X (particle size) Y (oxygen content) 0.25μ 068% 0.3μ 0.6% 0.4μ 0.4% 0.6μ 0.1% Note that the particle size in the present invention refers to scanning electron This is the average temporary particle size observed under a microscope, and is different from the secondary particle size, including aggregated particles, measured by centrifugal sedimentation.

Next, the method for producing the aluminum nitride powder of the present invention will be explained in more detail.

Examples of organic aluminum compounds as raw materials include aluminum alkyls such as trimethylaluminum, triethylaluminum, and diethylmonobutylene, aluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide, aluminum butoxide, and aluminum monobutoxydiisobutoxide; Examples include aluminum chelate compounds such as diisobropoxyaluminum ethyl acetoacetate.

Among these, aluminum alkoxide is particularly preferred in terms of hydrolyzability, shape of particles obtained, etc.

The organic solvent that dissolves this organoaluminum compound is
Although there are no particular limitations as long as the organic aluminum compound can be dissolved therein, alcohols such as methanol, ethanol, n-brobanol, isobrobanol, butanol are suitable in consideration of the subsequent hydrolysis step.

Considering the subsequent hydrolysis step, the concentration of the organoaluminum compound in the organic solvent is preferably 1 to 20% in terms of alumina.

The polyacrylonitrile dispersed in this organic solvent solution preferably has a particle size of 1 to 50 microns. More preferably 1 to 20
μ. In the subsequent hydrolysis step, fine precipitates of aluminum hydroxide are deposited on the surface of the polyacrylonitrile particles, so the polyacrylonitrile particles themselves do not need to be very fine.

The mixing ratio of the organoaluminum compound and polyacrylonitrile is preferably 1:1 to 3 in weight ratio of alumina to polyacrylonitrile in terms of alumina. If this ratio is less than 1, the reaction will not be completed and the oxygen content will increase. On the other hand, if it exceeds 3, carbon will remain, which is not preferable. The alumina to polyacrylonitrile weight ratio range of the present invention is in a region with a higher proportion of carbon source than the carbon 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 steps.
Because the process is carried out in stages, and especially the second stage is carried out in an atmosphere containing hydrogen and nitrogen at the same time, sufficient decarbonization is possible even if the amount of carbon source added is increased compared to conventional methods, and the carbon content in aluminum nitride is, for example, The amount is as small as 0.1% by weight or less. Furthermore, polyacrylonitrile has not only a carbon source but also a nitrogen source, which is considered to promote nitriding effectively. This polyacrylonitrile is not limited to a homopolymer, but may contain some copolymer as long as it is essentially polyacrylonitrile.

Next, water in an amount of 2 to 20 times the amount of the organoaluminum compound in molar ratio is added to an organic solvent solution of the organoaluminum compound in which polyacrylonitrile is dispersed, and hydrolysis is performed. 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, will be about 0.2 μm. The mixture of aluminum hydroxide and polyacrylonitrile is filtered if necessary and subjected to drying or heat dehydration in a conventional manner, and then undergoes the first stage of calcination.

This first stage firing is usually done in powder form,
For the purpose of improving handling properties during firing, the mixture may be formed into pellets. When the pelletized material is fired, the polyacrylonitrile used in the present invention is bulkier than carbon black or the like, so after decomposition, the pellet becomes porous and has the function of promoting the progress of nitriding. When pelletizing, the mixture may be pelletized in a wet state, or it may be pelletized with compactidin or the like after drying. The powder or pellets of the mixture are fired in the first stage at a temperature of 1400 to 17 ℃ under a nitrogen atmosphere.
Preferably, the temperature range is 00°C. The reaction does not proceed easily below 1400°C. Grain growth occurs as the firing temperature increases. In particular, when the temperature exceeds 1700℃, grain growth of aluminum nitride occurs rapidly, and the particle size decreases to 1.0μ.
will exceed. If the particle size exceeds 1.0μ, sinterability will deteriorate. The firing time depends on the temperature, but it is 0.5~IO
A time range is preferred.

Subsequently, it is preferable to carry out the second firing in an atmosphere containing hydrogen and nitrogen at a temperature in the range of 1000 to 1700°C. 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 is 1000
Decomposes into hydrogen and nitrogen at temperatures above ℃. When hydrogen gas and nitrogen gas are mixed, the molar ratio of hydrogen gas/nitrogen gas is preferably in the range of -0.05 to 5.0. In the second firing, nitriding and decarbonization proceed simultaneously.

Decarbonization progresses slowly below 1000°C.
If the temperature exceeds ℃, grain growth will occur as in the first stage, which is undesirable. The firing time varies depending on the temperature, but is preferably in the range of 0.5 to 10 hours. The first and second stages of firing 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 fly off and nitriding will not proceed sufficiently.

[Example] The present invention will be specifically explained below using Examples.

The bulk density of the aluminum nitride sintered body obtained by sintering the powder of the present invention was measured by the Archimedes method using kerosene.

Thermal conductivity was measured using a laser flash method thermal constant measuring device (F/TCM-FA8510B) manufactured by Rigaku Corporation.

Oxygen content was measured using an oxygen analyzer (EMGA) manufactured by Horiba, Ltd.
2200 model).

The average particle diameter was determined by taking a photograph at 10,000 times magnification using a scanning electron microscope.
The population size was set to 300 to 800, and the size was measured and determined by simple arithmetic mean.

In addition, all the amounts of each component described in the examples are based on weight.

Example 1 48 parts of aluminum isobroboxoxide was dissolved in 400 parts of isopropanol, and 30 parts of polyacrylonitrile powder having a particle size of 1 to 20 μm was dispersed therein. Next, 50 parts of distilled water was added over 1 hour while stirring the solution at room temperature to effect hydrolysis. The mixture was then mixed in a ball mill for 12 hours. After completing the ball milling, it was filtered and dried in the air at 100°C for 3 hours.

This powdery solid was placed on a flat graphite plate, and heated and held at 1500° C. for 4 hours in a tubular electric furnace while nitrogen gas was flowing at 15 I/min. After the electric furnace cooled down to room temperature, the graphite flat plate was taken out and the contents were transferred to an alumina boat, and heated to 1500°C while ammonia gas was flowing in 19/20 minutes in the tubular electric furnace.
The mixture was heated and held for 2 hours to obtain a white powder.

The oxygen content of this powder is 0.4% and the carbon content is 0.0
5%, and the average particle diameter by electron microscopy was 0.3μ.

(Y + 0.4)X is calculated to be 0.21, which is 0.4 or less.

Example 2 A white powder was obtained in the same manner as in Example 1 except that the amount of polyacrylonitrile powder added was 22 parts. This powder had an oxygen content of 0.4%, a carbon content of 0.04%, and an average particle diameter of 0.3 μm as determined by electron microscopy. (Y
+0.4) When calculating X, it is 0.24, 0.
4 or less.

Example 3 48 parts of aluminum isobroboxoxide was dissolved in 400 parts of isopropanol, and 30 parts of polyacrylonitrile powder having a particle size of 1 to 20 μm was dispersed therein. Next, 50 parts of distilled water was added over 1 hour while stirring the solution at room temperature to effect hydrolysis. The mixture was then mixed in a ball mill for 12 hours. After completion of the ball milling, the mixture was filtered and pelletized in a wet state, and the shape of the pellet was a cylinder of 4 φ * 4iI1. After drying the pellets in air at 100°C for 3 hours, they were placed on a graphite flat plate and heated with nitrogen gas at 15 I/min in a tubular electric furnace.
The mixture was heated and maintained at 1500° C. for 4 hours while the flow was divided. After the electric furnace had cooled down to room temperature, the graphite flat plate was taken out and the contents were transferred to an alumina boat, and heated and held at 1500°C for 2 hours while ammonia gas was being flowed in IQ/divided flow in the tubular electric furnace to obtain a white powder. Ta.

The oxygen content of this powder is 0.4% and the carbon content is 0.0
7%, and the average particle diameter by electron microscopy was 0.4μ.

When (Y + 0.4)X is calculated, it is 0.28, which is 0.4 or less.

Example 4 Using the pellets synthesized in Example 3, a white powder was obtained by scanning in the same manner as in Example 3, except that the first stage firing temperature in nitrogen gas was 1550° C. for 4 hours.

The oxygen content of this powder is 0.25% and the carbon content is 0.25%.
05%, and the average particle diameter by electron microscopy was 0.4μ. (Y + 0.4)X is calculated to be 0.26, which is less than 0.4.

Example 5 Using the pellets synthesized in Example 3, a white powder was obtained in the same manner as in Example 3, except that the first stage firing temperature in nitrogen gas was 1650° C. for 4 hours.

The oxygen content of this powder is 061% and the carbon content is Oo0
3%, and the average particle diameter by electron microscopy was 0.6μ.

(Y + 0.4)X is calculated to be 0.30, which is less than 0.4.

Comparative Example 1 48 parts of aluminum isobroboxide was dissolved in 400 parts of isopropanol, 9 parts of acetylene black having a particle size of 0.04 μm was added thereto, and the mixture was mixed in a ball mill for 12 hours. Next, 50 parts of pure water was added at room temperature to perform hydrolysis. After mixing in a ball mill for 6 hours, the mixture was filtered and dried in the air at 100° C. for 3 hours.

This powdery solid was placed on a graphite flat plate, and heated and held at 1650° C. for 4 hours in a tubular electric furnace while flowing nitrogen gas at 15 I/minute. After the electric furnace had cooled to room temperature, the graphite flat plate was taken out, the contents were transferred to an alumina boat, and decarbonization was performed again in the tubular electric furnace at 700° C. for 2 hours in air. A white powder was thus obtained.

The oxygen content of this powder is 0.9% and the carbon content is 0.0
7%, and the average particle diameter by electron microscopy was 0.6μ.

(Y+0.4)X is calculated to be 0.78, which is 0.
It exceeds the range of 4 or less. Sintering Example Y203 was added as a sintering aid to the aluminum nitride powder obtained in Examples 3 to 5 and Comparative Example 1 in an amount of 4% based on the aluminum nitride powder.

The sintering aid was mixed in a ball mill for 12 hours using ethanol as a solvent. After that, press pressure 2 to 20φ* 5m+w
Press molding was carried out at t12.

This molded body was placed in a carbon container and heated for 18 hours under an N2 atmosphere.
Sintering was performed at 00°C for 6 hours and at 1650°C for 6 hours.

Table 1 shows the bulk density and thermal conductivity of the obtained sintered body.

Table 1 [Effects of the invention] As stated above, the aluminum nitride powder of the present invention satisfies both high purity and small particle size, which were difficult to achieve with conventional products. It can be sintered at high temperatures and has high thermal conductivity. Furthermore, since a cheap raw material is used as the aluminum raw material, the manufacturing cost is low, which is advantageous. The fact that aluminum nitride powder with such characteristics can be obtained industrially at low cost greatly expands its use as integrated circuit boards and structural materials.

[Brief explanation of drawings]

Figure 1 shows the average particle diameter (
This is a graph showing the relationship between μ) and oxygen content Y (%), and the range surrounded by the following formula and the X and Y axes is the range of aluminum nitride obtained by the method of the present invention. (Y+0.4)X-0.4

Claims (1)

[Claims] (1) The average particle diameter obtained by scanning electron microscopy is
), a method for producing aluminum nitride powder that satisfies the following relational expression when the oxygen content is Y (%). When (Y+0.4) A method for producing aluminum nitride powder, which comprises firing in an atmosphere and then firing in an atmosphere containing hydrogen and nitrogen at the same time.