JPH06298515A - Alpha-silicon carbide and its production - Google Patents

Abstract

PURPOSE:To provide alpha-type silicon carbide used for producing semiconductors including light-emitting elements and useful as a heat treatment material for devices used for producing semiconductors, such as diffusion ovens. CONSTITUTION:The alpha-type silicon carbide comprises impurities containing an iron content of <1.00ppm, a copper content of <1.00ppm and an aluminum content of <1.00ppm. A method for producing the alpha-type silicon carbide comprises charging metallic silicon and a carbonaceous raw material in a recrystallized silicon carbide crucible and subsequently holding the mixture at 2000-2200 deg.C in an inert gas atmosphere.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to α-type silicon carbide and a method for producing the same. In particular, the present invention relates to α-type silicon carbide suitable for manufacturing semiconductor devices including light emitting devices and the like, heat treatment members for manufacturing semiconductors, and the manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, silicon carbide has been used as a raw material for grinding materials and heating elements, and its crystal structure is roughly classified into two types, α type and β type. Is known to exist.

By the way, as a conventional method for producing silicon carbide, a so-called Acheson is used in which a mixture of silica stone and coke is fixed at both ends of the furnace and the electrodes are connected at a high temperature by an electric resistance furnace in which a resistance core made of carbon such as graphite is connected. A method is known, and according to this manufacturing method, a crystal mass made of α-type silicon carbide is formed on the outer peripheral portion of the furnace core, and a β-type silicon carbide crystal is generated on the outer periphery of the crystal mass.

In order to obtain high-purity α-type silicon carbide from α-type silicon carbide by the Acheson method, first, the α-type silicon carbide lumps formed on the outer peripheral portion of the furnace core are appropriately pulverized and subjected to an oxidizing atmosphere. After baking to remove residual carbon, acid treatment with hydrofluoric acid or hydrofluoric nitric acid is repeated for high purification.

However, purification of α-type silicon carbide obtained by the Acheson method requires a great deal of labor, and it is extremely difficult to completely remove impurities such as aluminum solid-solved in silicon carbide. .

Further, as factors that hinder the purification of such silicon carbide, specifically, unreacted raw materials such as silica, free carbon, and silicon remain, and silicon carbide is caused by contamination due to mechanical pulverization. Metallic impurities such as iron, aluminum, and nickel contained in, as well as silicon, free carbon, and the like generated by thermal decomposition of silicon carbide reduce the purity of silicon carbide.

In Japanese Unexamined Patent Publication No. 52-117899, high-purity silica stone and high-purity carbon powder are mixed and filled in a graphite hermetically sealed container, which is continuously moved in a tubular furnace to control the temperature in the furnace. A method for producing a high-purity silicon carbide powder by keeping the temperature of 1800 to 2200 ° C. and reacting silica in the container with carbon is disclosed.

However, according to this method, the conversion rate of the silicon carbide synthesized from the raw material is poor, and although silicon carbide is synthesized in the graphite sealed container, a large amount of carbon monoxide gas is generated in the reaction process, and it is resistant. Not environmentally friendly.

Further, since the high-purity starting material is filled in the graphite hermetically sealed container, the synthetic silicon carbide is liable to be contaminated by sublimation or volatilization of impurities contained in the container during the synthesis of silicon carbide.

Further, β synthesized by vapor phase synthesis of silicon tetrachloride and methane or solid phase reaction of silica and carbon
For β-type silicon carbide, if a starting material having a relatively high purity is used, the obtained β-type silicon carbide can be easily purified to high purity by acid cleaning.

However, since β-type silicon carbide has too fine particles, it has a problem in moldability and has a sufficient corrosion resistance to hydrofluoric acid, hydrochloric acid, nitric acid, or a mixed acid thereof, compared to α-type silicon carbide. Is soluble in acid,
A heat treatment member for semiconductor manufacturing, which is repeatedly subjected to acid cleaning, has a drawback of poor corrosion resistance.

On the other hand, 6H-type silicon carbide, which is one of the polymorphs of α-type silicon carbide as a light emitting device material, has a wide band gap of about 2.9 eV and has both p-type and n-type conductivity. Both are stable materials, and thus are expected as light emitting element materials for blue light emitting diodes.

However, in order to obtain the light emitting device material for this blue light emitting diode, nitrogen or aluminum is added to the n layer of the epitaxial junction of the 6H type silicon carbide single crystal, but a more highly controlled n layer is used. The 6H-type silicon carbide single crystal serving as a substrate for forming the layer requires high-purity silicon carbide having no crystal defects that does not cause impurity diffusion into the n-layer to be formed. High-purity silicon carbide has been demanded as a raw material for growth.

[0014]

DISCLOSURE OF THE INVENTION The present invention is to provide a high-purity α-type silicon carbide suitable for manufacturing a semiconductor device including a light-emitting device, a heat treatment member for manufacturing a semiconductor such as a diffusion furnace, and a method for manufacturing the same. To do.

[0015]

The present invention is an α-type silicon carbide characterized in that the content of impurities is less than 1.00 ppm of iron, less than 1.00 ppm of copper, and less than 1.00 ppm of aluminum. In addition, a carbonaceous raw material and metallic silicon are filled in a silicon carbide crucible, which is heated under a vacuum with a vacuum degree of 0.2 mmHg or less, and then maintained at a temperature of 2000 to 2200 ° C. in an inert gas atmosphere. And a method for producing α-type silicon carbide.

[0016]

According to the above-mentioned manufacturing method, the impurity element in the starting material composed of the metallic silicon and the carbonaceous material with which the silicon carbide crucible is filled has a degree of vacuum of 0.2 due to the vapor pressure of each.
It is volatilized and partially adsorbed by the silicon carbide crucible during heating at a temperature of mmHg or less, preferably in the temperature rising process up to 1000 ° C.

Next, in the temperature rising process, a silicon carbide precursor (β-type silicon carbide) is once generated, and high-purity α-type silicon carbide is synthesized at 2000 to 2200 ° C. in an inert gas atmosphere.

On the other hand, in the manufacturing method of forming silicon carbide by filling a graphite crucible with a starting material of silicon or a compounding material of silica and carbon, which is found in most of the prior arts, and firing.
Since the graphite crucible is a carbon-based material of the same quality as the starting material, it is difficult to avoid leaving free carbon, silicon, silica, etc. attached to the generated silicon carbide even if the mixing ratio of the starting material is strictly controlled. Therefore, the reaction yield of silicon carbide was reduced and high purification was hindered.

However, according to the present invention, since the container for synthesizing silicon carbide is a crucible made of silicon carbide, unnecessary reaction between the starting material and the graphite crucible can be prevented, and as a result, residual of silicon, carbon, etc. can be prevented. It becomes possible to prevent it.

The present invention will be described in detail below. High-purity metallic silicon is used as the starting material metallic silicon, but powdery materials such as commercially available silicon powder obtained by crushing and purifying polycrystalline silicon for semiconductor production are preferable. Further, it is preferable to wash the product with an acid, for example, an inorganic acid such as hydrochloric acid, hydrofluoric acid, or hydrofluoric nitric acid in advance.

Examples of the carbonaceous raw material include graphite powder and carbon black such as furnace black, thermal black or acetylene black, and carbon black is preferable.

The molar ratio of the metallic silicon and the carbonaceous raw material is Si / C of usually 0.8 to 1.2, preferably 0.9.
˜1.1, especially 0.95 to 1.05. A mixture of metallic silicon and a carbonaceous raw material is filled in a silicon carbide crucible. The silicon carbide crucible is preferably recrystallized.

Next, this is placed in a heating furnace at a vacuum degree of 0.2 m.
Heat under vacuum below mHg. Next preferably 100
An inert gas is introduced into the heating furnace from 0 ° C., the atmosphere is maintained in an inert gas atmosphere, and the temperature is 2000 to 2200 ° C., but it cannot be unequivocally limited depending on the amount of the raw material to be mixed, but the time is appropriate (6 to 9
Hold for a time) to synthesize α-type silicon carbide. As the inert gas, a rare gas such as an argon gas, a helium gas, or a neon gas is preferable because silicon nitride is generated by firing in a nitrogen atmosphere.

The obtained α-type silicon carbide has an extremely high purity as compared with the conventional one, and the impurity content is less than 1 ppm of iron, preferably 0.05 to 0.30 ppm, and copper 1.00.
less than ppm, preferably 0.00 to 0.03 ppm, aluminum less than 1.00 ppm, preferably 0.03 to
The content is 0.40 ppm, which is an extremely useful material for manufacturing semiconductors and semiconductor elements.

[0025]

【Example】

Example 1 Metallic silicon powder having an average particle size of 300 μm, which was soaked in 15% hydrochloric acid for 24 hours and washed with an acid, and an average particle size of 0.0
4 μm of acetylene black with a molar ratio Si / C =
It was compounded at 1.00 and used as a starting material. This starting material was filled in a recrystallized silicon carbide crucible and heated in a heating furnace up to 1000 ° C. at a vacuum degree of 0.2 mmHg or less, and then argon gas was introduced into the heating furnace and maintained in an argon gas atmosphere.
It was heated to 200 ° C. and kept for 8 hours to synthesize silicon carbide.

The crystals of silicon carbide thus obtained were identified by powder X-ray diffractometry, and impurities were measured by inductively coupled high frequency plasma emission spectroscopy. The results are shown in Table 1.

[Table 1]

Example 2 Silicon carbide was synthesized in the same manner as in Example 1 except that the starting material was a mixture of metallic silicon and acetylene black in a molar ratio Si / C of 1.03. did.

(Comparative Example 1) In Example 1, a starting material was filled in a graphite crucible to synthesize silicon carbide.

(Comparative Example 2) In Example 2, a starting material was filled in a graphite crucible to synthesize silicon carbide.

(Comparative Example 3) Silicon carbide obtained by heating a mixed raw material of silica sand and coke by the Acheson method was crushed to obtain a silicon carbide powder having an average particle size of 110 μm, which was acidified with a mixed acid of hydrofluoric acid and nitric acid. It was washed and used as a comparative sample.

Table 1 shows the content of impurities in the silicon carbide obtained in Examples and Comparative Examples and the crystal form thereof. From this table, it is recognized that the silicon carbide of the present invention has extremely high purity.

[0032]

According to the present invention, the recrystallized silicon carbide crucible is filled with metallic silicon and a carbonaceous raw material, in contrast to the conventional operation involving a complicated acid treatment step for obtaining high-purity α-type silicon carbide. By heating in an inert gas atmosphere,
High-purity α-type silicon carbide can be synthesized and can be provided as a raw material for the production of semiconductor elements and heat treatment members for semiconductor production, and its field of application can be expected widely.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Ryuhei Makimura, 1st Iwase Akada-cho, Toyama City, Toyama Prefecture Hiroshi Ohira Randam Co., Ltd. Iwase Factory (72) Kenji Tsukamoto 1st place, Iwase-Akatacho, Toyama City, Toyama Prefecture Hiroshi Ohira Random Co., Ltd. Iwase factory

Claims (2)

[Claims] 1. Impurity contents of less than 1.00 ppm iron, less than 1.00 ppm copper, and 1.00 aluminum.
Alpha-type silicon carbide characterized by being less than ppm. 2. A carbonaceous raw material and metallic silicon are filled in a silicon carbide crucible, which is heated under a vacuum with a vacuum degree of 0.2 mmHg or less, and then 2000-2 in an inert gas atmosphere.
The method for producing α-type silicon carbide according to claim 1, wherein the temperature is maintained at 200 ° C.