JPH02239109A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To produce high-purity aluminum nitride powder having uniform grain diameter by supplying an alkylaluminum to a reaction system with ammonia in a specified ratio to the whole gas in the system and allowing the alkylaluminum to react with ammonia in the gaseous phase. CONSTITUTION:An alkylaluminum such as triethylaluminum is heated to about 120-170 deg.C, and gasified by supplying a nonoxidizing gas such as nitrogen gnd hydrogen as a carrier gas. The gaseous alkylaluminum is introduced into a reaction system, and allowed to react with ammonia in the gaseous phase. The molar ratio of the alkylaluminum to ammonia to be supplied to the reaction system is controlled to 1:1-1:100. The volume ratio of the alkylaluminum to the whole gas in the system is adjusted to 0.01-0.2. Consequently, high-purity aluminum nitride powder having uniform particle diameter is obtained. The powder is sintered, and the sintered body has uniform crystal grain diameter distribution, high density and excellent heat conductivity, heat resistance and insulating property and is appropriately used for an aluminum nitride substrate, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing aluminum nitride powder, and more particularly to a method for producing aluminum nitride powder with good thermal conductivity, which is used for aluminum nitride substrates, etc. [Prior art] In recent years, the field of microelectronics has been aiming for higher integration and higher output, and the alumina substrates that have been used in the past are becoming insufficient as heat dissipation substrates for semiconductor mounting.As a result, , aluminum nitride substrates are attracting attention as a new heat dissipation substrate with high thermal conductivity, heat resistance, and high insulation properties.

As described above, the following methods are conventionally known as methods for producing aluminum nitride powder used for aluminum nitride substrates.

For example, (1) a method of heating metal aluminum in a nitrogen or ammonia atmosphere (Japanese Unexamined Patent Publication No. 50-16019
9), (2) Mixing alumina powder and carbon powder,
A method of heating in a nitrogen or ammonia atmosphere (JP-A-60-180906), (3) a method of heat-treating a reaction product of an organoaluminum compound and amines (JP-A-53-68700), (4) Chlorination A method of reacting aluminum or aluminum bromide gas, or a mixture of both, with ammonia gas in the gas phase (JP-A-61-91008), (5) Nitriding by reacting an organic aluminum compound with ammonia gas in the gas phase. Examples include a method for producing aluminum powder (Japanese Unexamined Patent Publication No. 63-60102). [Problems to be Solved by the Invention] However, the aluminum nitride precursor obtained by reacting the above-mentioned organoaluminum compound and ammonia gas in the gas phase is ultrafine particles, and fusion between particles occurs during crystallization. It is thought that this occurs, forming a collection of particles with a very high degree of aggregation. Therefore, the density of aluminum nitride powder obtained by sintering it is low, and its heat resistance, high insulation properties, and especially thermal conductivity are still insufficient when used as ceramic materials for electronic equipment. Its development was highly desired.

[Means to solve the problem]

In order to solve the above problem, the present inventors conducted intensive research on the correlation between the thermal conductivity of the sintered body and the gas phase reaction conditions. The present invention was accomplished by discovering a method for obtaining high-purity aluminum nitride powder that has a uniform particle size and a uniform distribution of crystal grains in the sintered body. That is, in the method for producing aluminum nitride powder of the present invention, when producing aluminum nitride powder by reacting aluminum alkyl and ammonia in the gas phase, the molar ratio of aluminum alkyl and ammonia supplied to the reaction system is 1:1 to 1. 1:1OO, and the volume ratio of the alkyl aluminum to the total gas in the system is 0.01 to 0.2.

As the alkyl aluminum in the present invention, trialkylaluminum and dialkyl aluminum halide can be used, and specifically, trimethylaluminum, trimethylaluminum,
Examples include triethylaluminum, triisobutylaluminum, dimethylaluminum halide, diethylaluminum halide, diisobutylaluminum halide, etc., but it is economically advantageous to use triethylaluminum and triisobutylaluminum, which are industrially mass-produced. Of these, triethylaluminum is preferably used.

It is important to supply these alkyl aluminums to the reactor in gaseous form. When supplied in liquid form, the stability of the reactor is intermittently impaired due to the latent heat of vaporization of the compound, which is undesirable as the particle size of the aluminum nitride precursor produced becomes irregular. As a method of supplying in gaseous form, aluminum alkyl may be heated and supplied as steam, but nitrogen, hydrogen,
A non-oxidizing gas such as helium, argon, or a mixed gas thereof may be supplied as a saturated vapor as a carrier gas. At this time, the temperature of the alkyl aluminum tank is controlled so as to be finely variable depending on the amount of carrier gas introduced and the amount of alkyl aluminum supplied. For example, the amount of carrier gas introduced may be kept constant and the amount of alkyl aluminum supplied may be controlled by changing the temperature inside the alkyl aluminum tank.
20-170'C is preferred.

The process of particle generation in a gas-phase reaction begins with nucleation due to chemical reactions between raw material components, and then initial particles are generated. In the growth process of these particles, it is thought that collisions between particles while these microparticles are suspended lead to aggregation, and in the actual process, these phenomena occur simultaneously and in a chaotic manner. It is a complex phenomenon. The state of agglomeration of the compound obtained in this way in a gas phase reaction is thought to be greatly influenced by the concentration of each raw material gas during synthesis and the ratio of each component in the two-component reaction system. The physical properties of the aluminum nitride sintered body show a correlation with the physical properties of the final aluminum nitride sintered body. In view of these phenomena, the supply amount of alkyl aluminum and ammonia in the reaction system is set at a molar ratio of 1:1 to 1:10.
0 is preferred. If the molar ratio of ammonia to aluminum alkyl is less than 1, the aluminum alkyl will self-decompose in the reaction zone, and an aluminum nitride precursor containing aluminum metal as an impurity will be produced, which is undesirable.

On the other hand, if the molar ratio of ammonia exceeds 100, the shape of the particles produced will vary greatly, resulting in a fluffy, bulky, agglomerated powder that is undesirable. Furthermore, such a high molar ratio not only reduces the production efficiency per unit volume of the reactor but also increases the ammonia consumption rate, making it uneconomical. In the present invention, the total gas in the system refers to the alkyl aluminum gas and ammonia gas in the reaction zone, and the carrier gas when supplying the alkyl aluminum as gas,
Alternatively, the nitrogen, hydrogen, and helium mentioned above are used as a barge gas to prevent the powder produced in the reactor from adhering to the vessel wall, and as a diluent gas to adjust the linear velocity of the gas in the reactor. , all gases present in the reactor, including non-oxidizing gases such as argon, and the concentration of alkyl aluminum is 0.0 in volume ratio to all gases in the system.
It is preferable to set it to 1-0,2. If the volume ratio of the aluminum alkyl to the gold gas in the system is less than 0.01, the particle size produced will be ultrafine, and abnormal grain growth will occur when the resulting amorphous reactant is crystallized at a higher temperature. aggregate. The density of a sintered body obtained using such aluminum nitride powder is low, and high thermal conductivity cannot be obtained. Fork,
If it exceeds 0.2, particles containing metallic aluminum as an impurity will be generated due to self-decomposition of the alkyl aluminum. In any case, if the temperature exceeds the above range, it will not be possible to obtain an aluminum nitride precursor for obtaining a sintered body exhibiting good thermal conductivity.

The alkyl alkylene containing non-oxidizing gas such as nitrogen and ammonia supplied to the reactor in this way have a
The reaction takes place at a temperature of 1400°C to form an aluminum nitride precursor as a fume-like product. If the reaction temperature deviates from the above range, it is not preferable because not only the desired product cannot be obtained, but also the production reaction efficiency decreases.

The product obtained in this way depends on the reaction temperature, but
When observed by X-ray diffraction, etc., it is not a perfect aluminum nitride crystal, but contains non-quality components, and is extremely unstable against active gases such as oxygen, so it cannot be used in a strictly controlled inert gas atmosphere. It is important to handle the

Furthermore, by crystallizing the obtained powder at a temperature of 1400°C or higher in a non-oxidizing gas atmosphere or in vacuum, a crystalline aluminum nitride powder with low impurity content and no agglomeration can be obtained. [Example] The present invention will be further explained below with reference to Examples. Example 1 A sky reactor having an external electric furnace with an internal diameter of 6 (hm) controlled at 800″C was used, and ammonia gas was supplied from the bottom of the reactor at 400 g/H, and then triethylaluminum was separately added. Nitrogen was introduced into the alkylaluminium tank as a carrier gas at 100 f/}I, and 300 g/H of triethylaluminum was supplied to the lower part of the reactor for reaction.The molar ratio of ammonia to triethylaluminum at this time was 8.95. The volume ratio of triethylaluminum gas to gold gas in the system is 0.
It was 086. The product obtained by the reaction is
When observed by diffraction, the powder was of poor quality and showed a slight pattern of aluminum nitride. Next, this amorphous aluminum nitride powder was heated for 30 minutes using a batch-type high-temperature electric furnace.
The temperature was raised to 0°C/H and the mixture was fired at 1600°C for 3 hours to effect crystallization. The obtained crystalline powder had a milky white color and was observed as crystalline aluminum nitride by X-ray diffraction.
As a result of elemental analysis, the AI content was 65.8% and the N content was 34%.
．． 1%, which is almost the same as the theoretical value for aluminum nitride. Yttria was added as a sintering aid to this crystalline aluminum nitride and sintered at 1800°C for 3 hours, and the thermal conductivity of the resulting sintered body was measured and was found to be 187 W/m・K, which was a good result. ．． The results are shown in Table 1.

Examples 2 to 5, Comparative Examples 1 to 3 Sintered bodies were produced in the same manner as in Example 1, except that the amount of triethylaluminum supplied was changed by changing the amount of carrier gas introduced into the alkyl aluminum tank or the temperature inside the tank. Obtained. The results are shown in Table 1.

Example 6 A sintered body was obtained in the same manner as in Example 1 except that 520 g of triisobutylaluminum was used instead of triethylaluminum. The results are shown in Table 1.

〔Effect of the invention〕

The aluminum nitride powder obtained by the method of the present invention is
When used as a ceramic material for electronic devices, it has excellent heat resistance, high insulation properties, and especially thermal conductivity, making it extremely valuable in industry. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] When producing aluminum nitride powder by reacting aluminum alkyl and ammonia in the gas phase, the molar ratio of aluminum alkyl and ammonia supplied to the reaction system is 1:1 to 1:100, and the aluminum alkyl is A method for producing aluminum nitride powder, characterized in that the volume ratio to the total gas is 0.01 to 0.2.