JPH01252510A - Production of aluminum nitride - Google Patents

Abstract

PURPOSE:To inexpensively obtain uniform and fine AlN having low oxygen content and small amount of carbon, etc., by reacting an organoaluminum compound with an aminotriazine in an organic solvent, partially collecting the precipitated reaction product and calcining at specific two stages. CONSTITUTION:An organoaluminum compound (e.g., triethylaluminum) is reacted with an aminotriazine (e.g., melamine) in an organic solvent (e.g., hexane). Then AlN precursor precipitate obtained as the reaction product is separated from the organic solvent and primarily calcined in a reducing gas atmosphere (e.g., hydrogen gas) at 600-1,300 deg.C. Then the calcined material is secondarily calcined in an inert gas atmosphere (e.g., nitrogen gas) at 1,400-1,650 deg.C to give AlN. By using the prepared AlN, a radiating substrate having high thermal conductivity and heat resistance for packaging semiconductor can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing aluminum nitride. More specifically, it relates to a method for producing fine-particle aluminum nitride powder with low oxygen content and carbon content, which is used for aluminum nitride substrates, etc. [Prior art] In recent years, the field of microelectronics has become increasingly highly integrated and With the trend towards increased output, the alumina substrates that have been used in the past are becoming insufficient as heat dissipation substrates for semiconductor devices. As a result, nitride nanolaminium substrates are attracting attention as a new heat dissipation substrate with high thermal conductivity and heat resistance.

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

(1) A method of heating metal aluminum in a nitrogen or ammonia atmosphere.

(2) A method in which alumina powder and carbon powder are mixed and heated in a nitrogen or ammonia atmosphere.

(3) A method of heat treating a reaction product of organoaluminium and amines.

However, in the method (1), since the melting point of aluminum and the nitriding temperature are close to each other, the product solidifies, so a pulverization step of the product is necessary. For this reason, it has the disadvantage that impurities such as oxygen easily enter during pulverization, and it is difficult to produce high-purity products because impurities in the raw aluminum cannot be removed. In addition, in method (2), the particle size and impurities of the alumina are maintained as they are until the product stage, so the raw alumina needs to be a high-purity, fine powder product.
Raw material costs will increase. Another drawback is that unreacted carbon remains in the product, and when this is removed by oxidation, part of the aluminum nitride product is also oxidized.

On the other hand, in method (3), the organic aluminum used as the raw material is usually liquid, and a highly purified product can be easily obtained by operations such as distillation. Therefore, this method makes it easy to obtain highly pure aluminum nitride. However, in practice, there are various problems and it has not been put to practical use. For example, in Japanese Patent Application Laid-open No. 53-68700, an aluminum nitride precursor is prepared by reacting an organoaluminum compound with ammonia or primary or secondary amines. There is a description of a method of preparing aluminum nitride and then heating it to a temperature of 400"C or higher in an inert gas, vacuum, or ammonia stream. However, with this method, a large amount of carbon remains in the aluminum nitride produced, and it is difficult to remove it. Furthermore, in JP-A-62-108720, an aluminum nitride precursor is prepared by reacting a high-purity organoaluminum compound with organic amines or hydrazines, and then a non-oxidizing gas There is a description of a method for producing high-purity aluminum nitride, which is characterized by first firing in an air stream and then second firing in a reducing gas stream.
This is a method in which carbon content is removed by secondary firing aluminum nitride with a high carbon content produced by the same method as No. 68700 in a reducing gas stream. However, although this method can reduce the residual carbon content,
It is not economical and cannot be said to be a safe method as hydrogen is used at higher temperatures and the firing operation is performed twice.Also, in all of the above methods, fine particles with low cohesion are produced. It is difficult to obtain with good reproducibility, and when used as a raw material for a sintered body, a prior crushing step is required.

[Problem to be solved by the invention]

To summarize the problems in the method (3) of heat-treating the reaction product of organoaluminum and amines, including those already mentioned, (a) a large amount of carbon remains. (b) Unavoidable increase in danger due to heating to 1000°C or higher in hydrogen to remove carbon content, (C)
Introducing a post-treatment step such as air oxidation treatment to remove carbon content increases the oxygen content. ((To) There are problems such as the inability to produce fine particles of 0.3μ or less with good controllability, and a simple and safe method for producing fine particles of aluminum nitride with low carbon content and oxygen content is desired. Ta.

[Means to solve the problem]

As a result of intensive research to solve the above problems, the present inventors synthesized an aluminum nitride precursor using a compound having a triazine ring as an amine compound, and fired the precursor in a reducing gas atmosphere. The present invention was completed by discovering that decarbonization can be carried out efficiently (with fine particles) by re-firing in an inert gas atmosphere. The method for producing aluminum is a method for producing aluminum nitride by reacting an organoaluminum compound and an aminotriazine in an organic solvent, in which an aluminum nitride precursor precipitate obtained as a reaction product is separated from the organic solvent. After that, primary firing is performed at a temperature of 600°C or higher and 1300°C or lower in a reducing gas atmosphere, and then 14 days in an inert gas atmosphere.
It is characterized by performing secondary firing at a temperature of 00°C or higher and 1650°C or lower.

The present invention will be explained in detail below.

Preferred examples of the organoaluminum compound used in the present invention include trialkylaluminum, dialkylaluminum monochloride, monoalkylaluminum dichloride, and alkylaluminum sesquichloride, and the alkyl group here refers to a methyl group, an ethyl group, It is an isobutyl group.

Furthermore, the aminotriazines used in the present invention have an amino group. -triazine or -triazine, specifically melamine, melam, melem, melon, ammeline, ammelide, guanamine, 3-amino, 3-
Preferred examples include triazine.

In the present invention, the organic solvent in which the reaction is carried out refers to a solvent inert to organoaluminiums and aminotriazines, such as hexane, heptane, toluene, and liquid paraffin.

In the present invention, the organoaluminium and aminotriazines described above are reacted in the organic solvent described above. In order to react the organoaluminum and aminotriazines, the aminotriazines are dispersed in a solvent. , Add organic aluminum diluted with an organic solvent to this and stir.

When reacting the two, if the amount of aminotriazines added to the organic aluminum is too small, the organic aluminum will remain, which is dangerous, and conversely, if the amount of aminotriazines added is too large, it will be involved in the formation of aluminum nitride. The proportion of aminotriazines that are not used increases, making it uneconomical.

Therefore, the ratio of reacting organoaluminum and aminotriazine is such that the ratio of the number of moles of organoaluminium to the number of moles of amino groups in the aminotriazine compound is 1 to 10.
For example, when triethylaluminum and melamine are reacted in equimolar amounts, this ratio is 3.

Heat as necessary during stirring. The heating temperature ranges from room temperature to 300°C, up to the temperature at which organic aluminum decomposes.

When the reaction is carried out as described above, the aluminum nitride precursor formed forms a precipitate, and the aluminum nitride precursor precipitate formed after the reaction can be removed using ordinary solid-liquid separation methods such as filtration and decantation. Separate from the solvent by In this case, even if aminotriazines are mixed in the precursor precipitate, they can be separated in the next firing step, so there is no problem in practice.

The aluminum nitride precursor precipitate thus separated is further dried as required, and is converted into aluminum nitride in the next firing step. Since this aluminum nitride precursor is easily oxidized and generates heat in the atmosphere, it is necessary to store it in an inert gas atmosphere such as dry nitrogen until the firing process begins.

In the present invention, a firing step is performed at the end, and in the firing step, the aluminum nitride precursor is heated and fired at a temperature of 600° C. or higher and 1300° C. or lower in a reducing gas atmosphere as a secondary firing. The second firing step has an important meaning as a step for decomposing the precursor and further removing carbon remaining in the aluminum nitride. If the firing temperature is lower than 600°C, a large amount of carbon remains in the precursor. Further, 1300° C. or lower is an economical temperature that reduces the residual carbon content and does not require any further particle growth, and the particle size of the product aluminum nitride can also be adjusted at this primary firing temperature.

Reducing gas in this case refers to reducing gases such as ammonia and hydrogen, or mixed gases of these reducing gases and inert gases such as nitrogen. For example, in the case of a mixed gas of hydrogen and nitrogen, The ratio of hydrogen is preferably 30% or more.

Next, in an inert gas atmosphere at 1400°C or higher, 1650°C
The inert gas in this case, which performs secondary firing at temperatures below ℃, is
Nitrogen, helium, argon, etc. By successively performing the secondary firing, the crystallinity of the aluminum nitride produced in the secondary firing can be improved and the grain size can be made uniform. Naturally, as the firing temperature increases, sintering progresses and the particle size increases, but the degree of this is smaller when using an inert gas such as nitrogen than when using a reducing gas such as ammonia, and the particle size increases. It is possible to improve only the crystallinity while keeping the change small.

In other words, this suggests that the reducing gas has the effect of promoting the sintering growth of particles.

The aluminum nitride powder obtained as described above has a low carbon content, usually 0.2% by weight or less, and therefore does not require a post-treatment step for decarbonization.

In addition, only compounds that do not contain oxygen are used as raw materials, and the process does not require the use of oxygen as mentioned above, so in principle, the oxygen contained in the aluminum nitride of the product can be reduced to zero. .

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Example-1 [5 Oad of heptane and 1.5 g of melamine were placed in a 30M Erlenmeyer flask equipped with a funnel and a three-way cock, and the inside was purged with nitrogen. This melamine slurry was stirred with a magnetic stirrer, and a solution of triethylaluminum in hebutane (10 wt'1) was added dropwise in an amount equimolar to the melamine. After 0 dropwise addition, the dropping funnel was replaced with a reflux condenser and refluxed for 3 hours. The generated precipitate was filtered in a nitrogen box, washed with heptane, and then dried to obtain a white aluminum nitride precursor powder.

This aluminum nitride precursor was placed on an alumina boat and fired in a silicon carbide furnace at a heating rate of 300°C/h to 800°C under ammonia flow, and then the gas atmosphere in the furnace was changed to nitrogen and the temperature was raised to 1500°C. Heat it up and at that temperature 3
Holds time. The obtained powder was grayish white, and the X-ray diffraction results matched the peak of aluminum nitride, and the carbon and oxygen contents were measured to be 0.01% by weight and 0.0% by weight, respectively.
．． It was 5% by weight.

In addition, as a result of measuring the specific surface area of this powder using the BET method, it was found that 1
5.2 bo/g, transmission electron micrograph (TEM)
When observed, a uniform particle size distribution was observed without agglomeration, and the particle size was in good agreement with the value calculated from the specific surface area by the BET method.

In Comparative Example, aluminum nitride was obtained in the same manner as in Example 1, except that the next firing atmosphere gas was not changed to nitrogen, and the firing was carried out under ammonia flow until the end. The obtained powder was grayish white, and
As a result of line diffraction, a peak of aluminum nitride was observed, and as a result of analysis, the content of carbon and oxygen was 0.01% by weight each.
It was 0.3% by weight. The specific surface area of this powder is 5
．． It was 6rrr/g. However, when observed using a transmission electron micrograph (TEM), coarse particles in the form of agglomerates of several microns were partially observed, and a uniform particle size distribution as observed in Example 1 was not shown. .

Example 2 Aluminum nitride was obtained in the same manner as in Example 1, except that in the firing step, firing was performed in an ammonia atmosphere up to 600°C, and then the atmosphere was switched to nitrogen. The obtained powder was grayish white, and X-ray diffraction results showed that the peak coincided with that of aluminum nitride.As a result of analysis, the carbon and oxygen contents were each 0.
01% by weight and 0.48% by weight. The specific surface area of this powder was 18.4%/g. As a result of 72M observation, it was found to be a good powder with no agglomeration and a uniform particle size distribution.

Example 3 Aluminum nitride was obtained in the same manner as in Example 1, except that in the firing process, firing was performed in an ammonia atmosphere up to 1000°C, and then the atmosphere was switched to nitrogen. The obtained powder is ash i
As a result of XvA diffraction, the color was 0, which coincided with the peak of aluminum nitride.As a result of analysis, the content of carbon and oxygen was 0, respectively.
．． 01% by weight and 0.8% by weight. The specific surface area of this powder was 13.9 nf/g. As a result of 72M observation,
It was a good powder with no agglomeration and a uniform particle size distribution.

Comparative Example-2 In the firing process, firing was performed at up to 1000°C under a nitrogen atmosphere.
The procedure was the same as in Example 3, except that the atmosphere was then switched to an ammonia atmosphere and the temperature was sintered to 1500°C. The obtained powder was black, and only an aluminum nitride peak was observed as a result of X-ray diffraction, but analysis revealed that the carbon and oxygen contents were 3.4% by weight and 0.9% by weight, respectively. However, it was not satisfactory as aluminum nitride.

〔Effect of the invention〕

According to the method of the present invention, decarbonization steps such as post-oxidation treatment can be omitted, and aluminum nitride can be produced that is rich in uniform fine particles with little oxygen content and residual carbon, and has high thermal conductivity and heat resistance. It can be used as a raw material for heat-dissipating substrates with a high temperature, and has extremely high industrial applicability.

Claims (1)

[Claims] (1) In a method for producing aluminum nitride by reacting an organoaluminum compound and an aminotriazine in an organic solvent, the aluminum nitride precursor precipitate obtained as the reaction product is separated from the organic solvent, and then reduced. Primary firing at a temperature of 600°C or higher and 1300°C or lower in an inert gas atmosphere, then 1400°C or higher in an inert gas atmosphere,
A method for producing aluminum nitride, which comprises performing secondary firing at a temperature of 1650° C. or lower.