JPH07157307A - Production of high purity beta-type silicon carbide powder for producing silicon carbide single crystal - Google Patents

Abstract

PURPOSE:To obtain a high purity beta-type silicon carbide powder by hardening and drying a mixed solution of a liquid silicon compound, an organic compound and a polymerizing or cross-linking catalyst, which do not practically contain any impure element, and burning after carbonizing by heating. CONSTITUTION:A precursor material is obtained by polymerizing or cross-linking the mixed solution of the liquid silicon compound and the liquid organic compound having a functional group and forming carbon by heating and the polymerizing or cross-linking catalyst, which do not practically contain any impure element respectively. An intermediate material 2.3-2.5 in the mol ratio of carbon/ silicon is obtained by heating and carbonizing the precursor material at 700-1100 deg.C in a non-oxidizing atmosphere. Further, by burning the intermediate material at 1600-2000 deg.C in the non-oxidizing atmosphere under the selected condition of temp. and time, the beta-type silicon carbide powder <=1ppm in the content of the impurity element is obtained. A high purity silicon carbide single crystal small in crystal defect is grown at a high yield by using the high purity silicon carbide powder as the raw material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity β-type silicon carbide raw material powder for growing a silicon carbide single crystal having high purity, few crystal defects and good yield.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a silicon carbide single crystal, a high-purity graphite container shown in FIG. 1 was used, and silicon carbide powder was sublimated at a high temperature of 2000 ° C. or higher on a seed crystal of silicon carbide and carbonized. An improved Rayleigh method (improved sublimation recrystallization method) for obtaining a silicon single crystal is known (FC report 1
1 No1 P22 [1993]).

On the other hand, as a method for producing the above-mentioned silicon carbide powder, the Acheson method for obtaining silicon carbide powder from silica sand and petroleum coke as raw materials is known. However, according to this method, when the above-mentioned raw material contains a large amount of impurities, when a silicon carbide single crystal is grown, not only impurities are mixed into the single crystal but also crystal defects frequently occur (Reference 5).
Proceedings of the 1st JSAP Academic Lecture 29-W-1 [199
0]).

[0004]

DISCLOSURE OF THE INVENTION According to the present invention, in order to produce a high-quality silicon carbide single crystal having a low content of impurities and a small number of crystal defects, the content of each impurity element in the silicon carbide powder as a raw material is improved. It is an object of the present invention to provide a method for producing a silicon carbide powder having a small particle size and a particle size that does not significantly reduce the specific surface area during the sintering step.

[0005]

The method for producing a high-purity β-type silicon carbide powder for producing a silicon carbide single crystal according to the present invention comprises a liquid silicon compound containing substantially no impurity element and a functional group, and Curing and drying a mixed solution of a liquid organic compound that does not substantially contain an impurity element that generates carbon and a polymerization or crosslinking catalyst that does not substantially contain an impurity element, and obtain a solid product under a non-oxidizing atmosphere. After carbonization by heating, the obtained intermediate substance is further subjected to 1600 to 1600 under a non-oxidizing atmosphere.
By firing at 2000 ° C, the average particle size is 10 μm
~ 500 μm and the content of each impurity element is 1 p
It is characterized in that β-type silicon carbide powder having a particle size of pm or less is obtained.

That is, the inventors of the present invention have conducted intensive studies in the method of producing high-purity β-type silicon carbide powder, paying attention to impurities in all steps, composition of carbides (intermediate products), etc. By using a liquid substance that does not substantially contain as a raw material, an intermediate substance having a good dispersion of silicon and carbon can be obtained. As a result, a high-purity β-type silicon carbide polycrystalline powder with a relatively uniform particle size is obtained. The present invention has been completed by establishing a manufacturing method for obtaining In addition, as a result of reexamination of the carbon / silicon molar ratio of the carbide intermediate and the temperature and time of the firing step, the carbon / silicon molar ratio of the carbide intermediate was set to 2.3 to 2.5, and the temperature was changed to the conventional temperature. It was found that by firing at a relatively low temperature (1600 to 2000 ° C.), a high-purity β-type silicon carbide polycrystalline powder having a desired average particle size and substantially free of residual carbon can be obtained. .

[0007]

In the high-purity β-type silicon carbide powder, it is preferable that the content of the impurity element is reduced and the grain size is adjusted so that the specific surface area is not significantly reduced during the growth of the single crystal. The powder contains impurities as a raw material, for example, silica sand or petroleum coke, and has undergone a pulverizing step, and impurities are mixed in the powder. By producing a silicon carbide single crystal using the high-purity β-type silicon carbide powder obtained by the production method, a single crystal with high purity and few crystal defects can be obtained. It has an excellent effect that the particle size can be adjusted without causing a large decrease in

[0008]

The present invention will be described in detail below. In the present invention, examples of the liquid silicon compound include an alkyl silicate such as methyl silicate and ethyl silicate, an aqueous solution of silicic acid polymer, an ester solution of an organic compound having a hydroxyl group and silicic acid, and in particular, an ethyl silicate monomer and an oligomer. preferable.

In the present invention, the liquid organic compound having a functional group to generate carbon by heating has a particularly high residual carbon content, and is an organic compound which is polymerized or crosslinked by a catalyst or heating, such as phenol resin or nitrile. Resin, furan resin, polyimide resin, styrene resin, xylene resin,
Polyphenylene oxide, polyphenylene sulfide,
Examples thereof include resin (polymer) monomers and prepolymers such as polyaniline, and a resol-type or novolac-type phenol resin is preferable.

In the present invention, when a phenol resin is used as a raw material, the polymerization or cross-linking catalyst which is uniformly solubilized in the raw material is preferably an acid such as toluenesulfonic acid, hydrochloric acid, sulfuric acid or oxalic acid, and particularly has a surfactant effect. More preferred is toluene sulfonic acid. When using monomers or oligomers of nitrile resin, ammonium persulfate,
Radical polymerization initiators such as hydrogen peroxide, various hydroperoxides, alkyl peroxides, peroxide esters, and azo compounds are preferable. Also, when other organic compounds are used, generally used polymerization or crosslinking catalysts are preferable.

In the present invention, the precursor substance obtained by polymerizing or cross-linking the raw material is heated and carbonized in a non-oxidizing atmosphere, and the carbonization temperature is 700 to 1100 ° C., preferably 800. ~ 1000 ° C is adopted. The intermediate product obtained by carbonizing the precursor substance is fired at a higher temperature in a non-oxidizing atmosphere, and the firing temperature is 1600 to 2000 ° C, preferably 1600 to 1900 ° C. Is adopted.

The matters related to impurities, which are important elements in the present invention, will be described below. Although the high-purity β-type silicon carbide powder does not substantially contain impurity elements, the content of each impurity element needs to be 1 ppm or less even if it is included. The raw material used in the present invention contains substantially no impurity element, but even if it is contained, the content of each impurity element is 0.5 ppm or less, preferably 0.
1ppm, but firing temperature (1600-2000 ° C)
This does not apply to elements or compounds of elements that evaporate at.

The term "impurity element" used herein means an element of group Ia (excluding hydrogen) to group IIIa, an element of group Ib to group VIIb, an element of group VIII, an element of group IVa having an atomic number of 32 or more, and a group Va of the periodic table. An element with an atomic number of 33 or higher.

As the substances used in the previous step, such as the catalyst, additives, solvents (including water) used in the present invention, it is necessary to use high-purity substances that do not substantially contain impurities. In addition, raw materials and products are preferably handled in a clean booth of class 1000 or lower.

In the present invention, the carbon / silicon molar ratio in the intermediate product obtained by carbonizing the precursor material is 2.3.
~ 2.5 is preferred. At this molar ratio, the carbonization temperature is 700-
Pure silicon carbide is obtained under the conditions of 1100 ° C. and a firing temperature of 1600 to 2000 ° C. Originally, theoretically, the carbon amount in the obtained silicon carbide should be 0% by weight when the carbon / silicon molar ratio in the intermediate product is 3.0. It was found that a high-purity β-type silicon carbide in which the carbon number is 2.3 to 2.5 and carbon does not exist, and carbon remains when the molar ratio exceeds 2.5.

The average particle size of the obtained silicon carbide is 10 to 5
The thickness is 00 μm, preferably 100 to 300 μm. When the average particle diameter is 10 μm or less, sintering occurs at the sublimation temperature (2000 to 2500 ° C.) of silicon carbide for forming a single crystal, the sublimation surface area becomes small, and the growth of the single crystal becomes slow. On the other hand, when the particle size is 500 μm or more, the non-surface area of the particles themselves is small, so that the growth of the single crystal is also delayed.

In order to obtain a silicon carbide powder having an average particle size of 10 to 500 μm, it is necessary to properly select the temperature and time during firing. For example, when firing at 1900 ° C., a heating time of about 3 hours is required to obtain a particle size of 150 μm. However, if the temperature is 1600 ° C. or lower, the growth rate of crystal grains becomes very high, so that practically no silicon carbide can be obtained, and if the temperature is 2000 ° C. or higher, sublimation decomposition of silicon carbide occurs with the grain growth. Therefore, high-purity silicon carbide cannot be obtained.

In the present invention, since the raw materials of the liquid silicon compound as the silicon source and the liquid organic compound as the carbon source are polymerized or crosslinked, the obtained precursor substance is homogeneous in both silicon and carbon in molecular order. Therefore, the silicon carbide that has been fired through the intermediate substance after carbonization is a good quality crystal with few grain boundaries, and there is no mixing of impurities due to crushing or the like to control the particle size during firing,
The target powder can be obtained with good productivity.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded. In this example, in order to confirm the superiority to the conventional manufacturing method, an attempt was made to grow a single crystal by using an improved Rayleigh method (sublimation recrystallization method).

(Production Device for High Purity Silicon Carbide Single Crystal) The production device for silicon carbide powder uses the cylindrical high purity graphite container 1 and the lid 2 shown in FIG. The coil 6 was used for heating so that the temperature of the heated portion and the upper side surface portion near the seed crystal 4 could be measured. The reactor used was one capable of vacuum or substitution with an inert gas and capable of controlling the internal pressure.

Example A1 S as a liquid silicon compound
High-purity ethyl silicate 690 with iO ₂ content of 40%
g and 305 g of a high-purity liquid resol-type phenol resin having a water content of 20%, 137 g of a 25% aqueous solution of high-purity p-toluenesulfonic acid as a catalyst was added, and the mixture was cured and dried to give a homogeneous resinous solid. Obtained. This was carbonized at 900 ° C. for 1 hour in a nitrogen atmosphere. The carbon / silicon molar ratio of the obtained carbide was 2.4 based on elemental analysis. This carbide was heated to 1900 ° C. in an argon atmosphere, heated, and held for 4 hours to carry out silicon carbide reaction and crystal grain growth. The color of the obtained powder was yellow-green. Also, X
The crystal form of silicon carbide by line diffraction was β type (cubic crystal). The results of impurity analysis (ICP-mass spectrometry and flames atomic absorption method) of this powder are shown in Table 1. Moreover, when the present powder was measured with a particle size distribution analyzer (TSUB-TEC), the average particle size was 185 μm.

[Table 1]

(Comparative Example A1) Silicon carbide reaction temperature was 1
Silicon carbide powder was obtained in the same manner as in Example 1 except that the temperature was 700 ° C. and the heating temperature was 30 minutes. The color of the obtained powder was grey-white, the crystal form of silicon carbide by X-ray diffraction was β type (cubic crystal), and the average particle size of this powder was 1.2 μm.
The results of the impurity analysis of this powder are shown in Table 1.

(Comparative Example A2) The # 100 polishing silicon carbide powder was thoroughly washed with a high-purity hydrochloric acid solution containing no impurities, dried, and then subjected to high-purity treatment at 2000 ° C. for 10 minutes.
The color of the obtained powder was black, and the crystal form of silicon carbide by X-ray diffraction was α type. The results of the impurity analysis of this powder are shown in Table 1.

(Example B1) About 100 g of the powder obtained in Example A1 was placed in the graphite container of FIG. 1 and 6H {000 produced by the Acheson method as a seed crystal in the lid portion.
1mm surface cut wafer 10mm × 10mm is installed,
The powder portion was placed in a reaction furnace and kept at 2350 ° C. by high frequency induction heating under a reduced pressure of 10 Torr of argon. The temperature of the upper part of the container at this time was 2280 ° C. About 5 under these conditions
When a single crystal was grown for an hour, a single crystal with a diameter of 10 mm and a length of 5.5 mm could be obtained. A portion of the crystal as far as possible from the seed crystal was sliced and mirror-polished. When this was ashed with molten alkali and the defects were observed, the defect density was 1.0 × 10 ³ defects / cm ^2.
Met. In addition, Table 2 shows the results of impurity analysis (ICP-mass spectrometry and flames atomic absorption method) of this crystal.

[Table 2]

Comparative Example B1 Example A2 as raw material powder
A single crystal was grown in the same manner as in Example B1 except that the one obtained in 1. was used, and the grown length was about 2 mm.
Further, when the cooled raw material was observed, it was found to be sintered and solidified. The defect density of this crystal was 3.3 × 10 ³ defects / cm ² . Table 2 shows the results of impurity analysis of this crystal.

Comparative Example B2 Comparative Example A1 as raw material powder
A single crystal was grown in the same manner as in Example B1 except that the one obtained in 1. was used, and the grown length was about 4.5 mm. Further, when the cooled raw material was observed, it was found to be sintered and solidified. The defect density of this crystal is 8.7 × 10 ⁴ defects / cm
^{Was 2} . Table 2 shows the results of impurity analysis of this crystal.

[0027]

As described above, by using the high-purity silicon carbide obtained by the production method of the present invention,
It is possible to provide a silicon carbide single crystal wafer having high purity, few crystal defects, and good yield, which makes it possible to grow a silicon carbide single crystal and shows good characteristics in, for example, a power device, a high frequency device, a blue emitting diode, and the like. It will be possible.

[Brief description of drawings]

FIG. 1 is a sectional view of a high-purity β-type silicon carbide single crystal manufacturing apparatus of the present invention.

[Explanation of symbols]

 1 high purity graphite container 2 high purity graphite lid 3 raw material silicon carbide 4 seed crystal 5 grown single crystal 6 high frequency coil

Claims (1)

[Claims] 1. A liquid silicon compound which does not substantially contain an impurity element and a liquid organic compound which has a functional group and which produces carbon by heating and does not substantially contain an impurity element and does not substantially contain an impurity element. After curing and drying the mixed solution with the polymerization or crosslinking catalyst and heating and carbonizing the obtained solid matter in a non-oxidizing atmosphere, the obtained intermediate substance is further calcined at 1600 to 2000 ° C. in a non-oxidizing atmosphere. By doing
A method for producing a high-purity β-type silicon carbide powder for producing a silicon carbide single crystal, which comprises obtaining a β-type silicon carbide powder having an average particle size of 10 μm to 500 μm and a content of each impurity element of 1 ppm or less.