JPH07187620A - Production of high purity aluminum nitride powder - Google Patents

Abstract

PURPOSE:To obtain high purity aluminum nitride powder having low uranium and thorium contents, low radiating property, a proper average particle diameter of 2-10mum, high heat conductivity and satisfactory suitability to compacting and sintering and suitable for use as the material of the substrate of a highly integrated semiconductor device. CONSTITUTION:Org. aluminum purified by distillation and ammonia are brought into a vapor phase reaction at 400-1,200 deg.C and a formed precursor is decarbonized and fired at 1,600-1,900 deg.C to produce the objective high purity aluminum nitride powder suitable for use as the peripheral material of a semiconductor device.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing aluminum nitride powder. More specifically, it relates to a method for producing a high-purity aluminum nitride powder as a raw material for a low-radiation aluminum nitride sintered body that is preferably used as a peripheral material for semiconductors.

[0002]

2. Description of the Related Art Aluminum nitride sintered bodies have been attracting attention as various sintered materials because they have characteristics such as high thermal conductivity, good corrosion resistance, and high temperature strength. Among them, in recent years, the use as a semiconductor substrate material has rapidly expanded due to its high thermal conductivity, high resistance and well-balanced electrical properties. Recent progress in high integration of semiconductors is remarkable, and there are severe demands for substrates. Conventional aluminum nitride powder has been obtained in a fairly high purity as shown in Ceramic Industry Association Journal 93 [9] 517 (1985) and the like.

Conventionally, the following two methods have been industrialized as methods for synthesizing aluminum nitride powder. One is the direct nitriding method of nitriding metallic aluminum powder with nitrogen or ammonia gas, and the other is the alumina reduction method of firing a powder mixture of alumina (aluminum oxide) and carbon in a reducing atmosphere. Recently, production of aluminum nitride by a gas phase reaction of organic aluminum and ammonia has also been proposed. In these methods, metallic aluminum or alumina used as a raw material is prepared by dissolving alumina hydrate, i.e., bauxite, which is a raw material, in an alkali and hydrolyzing it to Al (OH) ₃ and igniting it to 1000 ° C or higher. Alumina is used. Furthermore, it is metallic aluminum that is obtained by melting and electrolyzing this together with cryolite.

It is known that bauxite contains uranium and thorium. However, due to their chemical properties, uranium and thorium are difficult to remove from aluminum by the above process, and aluminum and alumina produced from them necessarily contain uranium and thorium.

Conventionally existing aluminum nitride powders necessarily contain uranium and thorium because they are used as raw materials. Similarly, organic aluminum also contains uranium and thorium. [Table 1] shows uranium and thorium content concentrations of typical commercially available metal aluminum particles and aluminum nitride powder.

[0006]

[Table 1]

[0007]

However, recently, as semiconductors have become more highly integrated, not only the thermal conductivity but also the radiation generated by the material thereof, in other words, the concentration of radioactive elements such as uranium and thorium contained therein are problems. It has become apparent as a point. This is because the probability of causing a malfunction called a soft error due to α rays emitted from a radioactive element increases as the degree of integration increases.

[0008] For example, DRAM, which is a kind of memory device having a high degree of integration among semiconductors, stores data in the form of whether or not there is a small number of carrier charges in a storage capacitor. , Alpha emitted when radioactive elements such as thorium decay
(Approximately 5 MeV per particle) is an electron in Si of the semiconductor device.
Since hole pairs are generated (about 1.4 × 10 ⁶ particles / 1 α particle), data inversion occurs when this charge exceeds the critical charge.

[0009] Currently, the allowable limit of this soft error, roughly 1000FIT are said to (1FIT = 10 ⁹ hours failure of 1 times the probability that occurs), in order to satisfy this condition in 64KBitDRAM grade the degree of integration is uranium, Thorium content of 50ppb
It is said that it is necessary to do the following (Hirai, Bunseki, 9, 639 (1988)).

Conventionally, what is called high-purity aluminum nitride powder has been commercially available. The meaning of high-purity is F
It means that the content of cationic impurities such as e, Si and Ca, or the content of oxygen is small, and the content of radioactive elements is high,
It could not be used for semiconductor substrate applications with a high degree of integration.

Further, the thermal conductivity of pure aluminum nitride is said to be about 320 W / m · K, but the actual thermal conductivity of aluminum nitride single crystals and ceramics has not been obtained. The main cause of this is oxygen. Oxygen replaces nitrogen in aluminum nitride to form a solid solution (the solid solution limit is about 0.5%). For this reason, vacancies are formed at the Al positions in the lattice and the atomic mass at the lattice point is 27 to 0. Changes to. In aluminum nitride, heat conduction due to phonon conduction is dominant, and it is said that this causes a large decrease in heat conductivity.

Further, it is known that when oxygen is present beyond the solid solution limit or when silicon oxide coexists, an oxynitride of aluminum is formed and the thermal conductivity further decreases. According to Slack et al., Between the thermal resistance K ^-1 of the aluminum nitride sintered body and the oxygen content,
It is shown that the relationship shown in (1) holds and the thermal conductivity of aluminum nitride becomes 319 W / m · K when the oxygen content is extrapolated to 0.

[0013]

[ _Formula 1] K ⁻¹ = K ⁻¹ _theor + C · Δn / n ₀ (where C = 0.43 is an experimental value, and Δn / n ₀ represents the atomic density (atom / cm ³ ) of oxygen).

The problem of containing oxygen impurities is not limited to the problem of the manufacturing method, but the problem of oxidation during handling when aluminum nitride is used as a product such as a sintered body cannot be ignored. Aluminum nitride has the property of easily reacting with water by the reaction represented by the following reaction formula [Chemical formula 1]:
If the particle size is too small, the water content in the air is likely to oxidize during handling, resulting in a decrease in purity. Further, since ammonia is also produced at the same time, aluminum nitride having high stability in terms of work environment and safety has been desired.

[0015]

[Chemical formula 1] AlN + 3H ₂ O → Al (OH) ₃ + NH ₃

[0016]

In order to solve the above problems, the inventors of the present invention have conducted earnest research on a method for inexpensively producing high-purity aluminum nitride powder. As a result, it has been possible to develop a method for producing aluminum nitride powder in which the concentration of uranium is kept low, which has been considered impossible in the past, and the present invention has been completed.

That is, the method for producing a high-purity aluminum nitride powder of the present invention is a method for producing aluminum nitride by reacting an organoaluminum compound and ammonia in a gas phase reaction. The reaction is carried out at a temperature of 400 to 1200 ° C, and the obtained intermediate is calcined at a temperature of 1600 to 1900 ° C.

According to the method of the present invention, the content of thorium is
It is possible to obtain a high-purity aluminum nitride powder having a content of 10 ppb or less and a total content of uranium and thorium of 50 ppb or less. Compared with the conventional aluminum nitride powder containing several hundred ppb and several tens ppb of uranium and thorium, respectively, these concentrations are less than one tenth. This is an epoch-making thing, in which the α-ray generation rate also decreases in proportion, and its industrial value is very high.

The average particle size of the aluminum nitride powder is preferably 2 to 10 μm as described later, but in the method of the present invention, the precursor obtained by the gas phase reaction of organoaluminum and ammonia is 1600 to 1900. A particle size in this range can be easily obtained by firing at a temperature of ℃. If the particle size is less than 2 μm, the stability is poor and the oxygen concentration increases during handling, and ammonia is easily generated. Again 10
If it is more than μm, the sinterability tends to be poor and atmospheric pressure sintering tends to be difficult.

The organoaluminum used as the raw material of the present invention is AlR ₁ R ₂ R ₃ (R ₁ , R ₂ and R ₃ are CH ₃ , C ₂ H ₅ , nC ₃ H ₇ and iC ₃
H ₇ and other C ₁ -C ₄ alkyl groups), which are similar to alumina in that they use metallic aluminum as a starting material, but organoaluminum is metallic aluminum, hydrogen, and ethylene-based carbon. Synthesized by reaction with hydrogen.

Typical organoaluminums include triethylaluminum and triisobutylaluminum, which are industrially easily available, but these are liquids at room temperature and are not so stable compounds against heating. However, it is possible to remove uranium, thorium, etc. contained in the raw material by purifying by purification under reduced pressure and highly purified.

However, since organoaluminum has a very high activity and cannot be handled in air, the contents of uranium and thorium contained in it cannot be measured in advance. By distilling and purifying at a reflux ratio of 1 or more in a rectification column having two or more theoretical plates, the thorium in the synthesized aluminum nitride can be 10 ppb or less, and the total amount of uranium and thorium can be 50 ppb or less.

The present invention is made by using the organoaluminum compound purified according to the above method, wherein the vaporized purified organoaluminum compound is converted into H ₂ , N ₂ ,
By introducing into the reactor with a carrier gas such as He and Ar, simultaneously introducing NH ₃ into the reactor, and reacting organoaluminum and NH ₃ in a gas phase at a temperature of 400 to 1200 ° C. It is possible to obtain high-purity aluminum nitride having a very low content of uranium and thorium.

The average particle size in the present invention is measured by a laser diffraction / scattering type particle size distribution measuring device. uranium,
The analysis value by ICP-MS was used for the concentration analysis of thorium. An oxygen / nitrogen analyzer in ceramics (EMGA-2800 manufactured by Horiba Ltd.) was used for analysis of oxygen concentration.

[0025]

EXAMPLES The present invention will now be specifically described by way of examples, but the present invention is not limited to these examples.

Example 1 After synthesizing triethylaluminum, it was used as a raw material after rectifying distillation at a temperature of 135 ° C., a pressure of 14 mmHg and a reflux ratio of 1.5 in a rectification column having 5 theoretical plates. 660 g (38.8 mol) / hour of NH ₃ was stored in a superficial reactor whose temperature was controlled at 800 ° C. by an external heating furnace having an inner diameter of 8 cm and a length of 2 m, and triethylaluminum purified by distillation was used as a carrier of nitrogen gas and 240 g / hour.
(2.11 mol) was fed and reacted, and the fumed reaction product was collected by a SUS316 sintered metal filter to obtain about 84 g of product.

Then, the aluminum nitride precursor was continuously supplied in a fixed amount to a rotary kiln through which a part of the reactor vent gas was passed, and decarburization treatment was carried out at 1200 ° C. The resulting product was put into a carbon crucible, heated to 1750 ° C. under a nitrogen gas atmosphere, held at the same temperature for 3 hours, and then cooled to room temperature. IC for the obtained white powder
P-MS analysis and laser diffraction / scattering particle size distribution measurement were performed. The results are shown in Table 2.

[0028]

[Table 2]

COMPARATIVE EXAMPLE 1 660 g (38.8 mol) / hour of NH ₃ was added to a superficial reactor whose temperature was controlled at 800 ° C. by an external heating furnace having an inner diameter of 8 cm and a length of 2 m.
Triethylaluminum purified by distillation was fed with nitrogen gas as a carrier at 240 g (2.11 mol) per hour, and the fumed reaction product was collected by a SUS316 sintered metal filter to obtain about 84 g of aluminum nitride precursor. Obtained.

Thereafter, the aluminum nitride precursor was continuously supplied in a fixed amount to a rotary kiln through which a part of the reactor vent gas was passed, and decarburization treatment was performed at 1200 ° C.
The resulting product was put into a carbon crucible, heated to 1500 ° C. under a nitrogen gas atmosphere, kept at the same temperature for 3 hours, and then cooled to room temperature. The obtained white powder was subjected to ICP-MS analysis and laser diffraction / scattering particle size distribution measurement. The results are shown in Table 3.

[0031]

[Table 3]

Comparative Example 2 NH ₃ was fed to an empty column reactor whose temperature was controlled at 800 ° C. by an external heating furnace having an inner diameter of 8 cm and a length of 2 m, and 660 g (38.8 mol) of NH ₃ per hour.
The unpurified triethylaluminum was fed with nitrogen gas as a carrier at 240 g / hour (2.11 mol) and reacted to collect a fumed reaction product with a SUS316 sintered metal filter to obtain about 84 g of a product. .

Thereafter, decarburization treatment was carried out at 1200 ° C. while continuously supplying a fixed amount of the aluminum nitride precursor to the rotary kiln through which a part of the reactor vent gas was passed. The obtained product was put in a carbon crucible, heated to 1750 ° C. under a nitrogen gas atmosphere, kept at the same temperature for 3 hours, and then cooled to room temperature. IC for the obtained white powder
P-MS analysis and laser diffraction / scattering particle size distribution measurement were performed. The results are shown in Table 4.

[0034]

[Table 4]

Example 2 3% by weight of yttrium oxide was added to the aluminum nitride powder obtained in Example 1 and uniformly mixed in ethanol. After the mixture was dried, about 2 g of the mixture was uniaxially molded at 300 kg / cm ² using a mold having an inner diameter of 1 cm, and further rubber-pressed at a pressure of 1 t / cm ² to obtain a molded body. This compact was held in a carbon crucible at 1800 ° C. for 3 hours to obtain a sintered body. When the density of this sintered body was measured by the Archimedes method,
It was 3.26 g / cc. Further, when the thermal conductivity was measured by the laser flash method after polishing the sintered body to a thickness of 3 mm, the thermal conductivity was 210 W / m · K.

Example 3 Using the powders obtained in Example 1 and Comparative Example 1, they were stored at room temperature in a desiccator containing a desiccant and in air, and the time-dependent change in oxygen concentration was examined. The results were obtained.

[0037]

[Table 5]

Example 4 The aluminum nitride powder after being left in the air in Example 3 was sintered according to the same formulation as in Example 2, and the density and thermal conductivity of the sintered body were measured. The result was obtained.

[0039]

[Table 6]

Comparative Example 3 In the same manner as in Comparative Example 1, NH ₃ was reacted with purified triethylaluminum to obtain an aluminum nitride precursor, and the aluminum nitride precursor was continuously supplied to a rotary kiln in which a part of the reactor vent gas was passed. Quantitatively supplied and decarburized at 1200 ° C. The obtained product was put in a carbon crucible and heated to 1950 ° C. under a nitrogen gas atmosphere, and the temperature was kept at 3 ° C.
After holding for a while, the temperature was lowered to room temperature.

The obtained white powder was partially lumpy, and it was ground in a mortar and the particle size distribution was measured. The average particle size was 34 μm. Further SEM observation revealed that the particles were strongly aggregated and partially sintered, but these partially coarsened particles could not be pulverized by pulverization with an air stream pulverizer. .

[0042]

INDUSTRIAL APPLICABILITY The aluminum nitride powder of the present invention has a low content of uranium and thorium, which makes it possible to make a semiconductor substrate produced with low emissivity, and also has an appropriate average particle size and a low oxygen concentration. A material having high conductivity, good sinter moldability and suitable for high integration of semiconductors can be obtained, which is extremely industrially advantageous.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuo Wakimura 1-6 Takasago, Takaishi-shi, Osaka Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. A method for producing aluminum nitride by subjecting an organoaluminum compound and ammonia to a gas phase reaction, which comprises first distilling and purifying organoaluminum, and then reacting this with ammonia at a temperature of 400 to 1200 ° C. A method for producing a high-purity aluminum nitride powder, which comprises firing the above precursor at a temperature of 1600 to 1900 ° C.