JPH062568B2 - Method for producing high-purity silicon carbide powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-purity silicon carbide powder.

The silicon carbide powder according to the present invention is useful as a raw material for materials such as semiconductor manufacturing jigs that require a small amount of metal impurities.

[Conventional technology]

The main methods for producing silicon carbide include (1) direct reaction of metallic silicon and carbon at high temperature.
That is, a method of producing silicon carbide by the reaction of Si + C → SiC.

(2) A method of thermally decomposing a silane or a mixture of a silane and a hydrocarbon compound represented by RnSiX _4-n (wherein R is a hydrogen atom or an alkyl group, X is a halogen atom, n = 1 to 4) at a high temperature.

(3) Silica reduction method. That is, a method of producing silicon carbide by the reaction of SiO ₂ + 3CSiC + 2CO. Α-type silicon carbide and β-type silicon carbide are formed depending on the treatment temperature. In particular, a method for producing a high temperature α-type silicon carbide is generally called the Acheson method, and is widely produced by this method from abrasive materials to so-called fine ceramic raw materials.

As low-temperature β-type silicon carbide, various methods have been devised as raw materials for so-called fine ceramics in order to obtain finer and more uniform silicon carbide particles having a narrow particle size range. For example, Japanese Unexamined Patent Publication (Kokai) No. 58-204813 using fine particle silica obtained by hydrolysis of SiF ₄ as a raw material
No. 58-50929, which uses a mixed powder of silica / carbon and silicon carbide as a raw material. Further, the above-mentioned method is a batch method, but it is disclosed in JP-A-54-33899 and JP-A-5-35899.
No. 5,405,527, JP-A-58-20708, JP-A-58-194731, and JP-A-59-39709 disclose methods for continuously producing β-type silicon carbide.

Further, in Japanese Examined Patent Publication No. 60-44280, the β-type silicon carbide obtained is in the form of whiskers, but silica gel and carbon black are used as raw materials. Etc. are known.

As a method for purifying silicon carbide powder, HC1, HF, HF
Cleaning with an inorganic acid such as + HNO ₃ is generally performed.

In addition, cleaning of a silicon carbide sintered body such as a semiconductor manufacturing jig is performed by gas cleaning with chlorine or hydrogen chloride in addition to the above-described cleaning with an inorganic acid.

[Problems to be solved by the invention]

A silicon carbide sintered body used as a semiconductor manufacturing jig or the like is required to contain a small amount of metal impurities such as iron and copper that adversely affect the semiconductor.

The raw material for producing the silicon carbide sintered body for the above-mentioned use is
It is required that the content of metal impurities such as iron and copper is small, and that the required amount can be supplied industrially stably, quickly, and at low cost. Comparing each manufacturing method from the above viewpoint, in the manufacturing method (1) using metallic silicon as a raw material, it is difficult to control the reaction because high-purity metallic silicon is expensive and carbonization of metallic silicon is an exothermic reaction. Moreover, the particles of silicon carbide synthesized are relatively large. In order to obtain a fine powder, it is necessary to carry out pulverization and it is contaminated with metal impurities. In order to remove the metal impurities, the above-mentioned cleaning with the inorganic acid is required, which makes the cost more expensive.

The production method (2) using silane as a raw material gives high-purity silicon carbide fine particles. However, the raw material gas used is extremely expensive and the reaction yield is low. Although this production method is excellent in terms of purity, it is difficult to supply a necessary amount in a stable and inexpensive manner industrially.

The production method (3) that uses silica as a raw material
It is advantageous in that it can be made cheaper than the method.

The α-type silicon carbide produced by the Acheson method is in a lump form and needs to be pulverized as in the production method (1). The contamination amount of metal impurities is so large that it cannot be compared with the production method (1), and it is extremely difficult to completely remove the impurities even if a large amount of labor such as washing with the above-mentioned inorganic acid is carried out several times. .

Regarding the production of low temperature β-type silicon carbide, JP-A-58-
In No. 204813, although the impurity concentration of silica used as a raw material is extremely low, the purity of the raw material silica cannot be maintained due to contamination during synthesis.

In Japanese Examined Patent Publication No. 58-50929, the purity of the synthesized silicon carbide is not discussed, and it is clear that the object of the invention is different from the object of the present invention.

JP-A-54-33899, JP-A-55-40527
JP-A-58-20708, JP-A-58-1947
No. 31, JP-A-59-39709 relates to a continuous method for producing β-type silicon carbide, and there is no discussion about the purity of the synthesized silicon carbide. Also,
The silicon carbide thus synthesized contains unreacted silica content in%, and HF treatment is required to remove the silica.

In Japanese Patent Publication No. 60-44280, iron, nickel, cobalt and sodium chloride, which adversely affect the semiconductor, are added for the purpose of obtaining a β-type silicon carbide whisker, which is used as a jig for semiconductor production. It is unsuitable as a raw material for a silicon carbide sintered body.

The object of the present invention is to solve the above-mentioned problems, by improving the silica reduction method, the content of metal impurities such as iron and copper is small, and the required amount is industrially stable and quickly,
Moreover, it is to provide a method for producing a high-purity silicon carbide powder that can be inexpensively supplied.

[Means for solving problems]

That is, the present invention provides a method for producing silicon carbide using silica and carbon as starting materials, wherein the starting materials are synthesized at 1500 ° C or higher in a non-oxidizing atmosphere containing hydrogen chloride to obtain silicon carbide. Characterize. Further, as silica used in the present invention, silica gel is preferable, as carbon, carbon black and / or a carbonaceous substance which is changed into carbon by heating are preferable, and carbon black and / or carbon black is present on the surface and fine pores of the silica gel. It is preferable to impregnate with a carbonaceous substance that changes into carbon by heating.

By the way, in the present invention, the concentration of hydrogen chloride is 3 vol% to 10%.
It is preferably vol%.

[Action]

In a general silica reduction method, a raw material in which silica and carbon are mixed is heated in a non-oxidizing atmosphere to synthesize silicon carbide.

The present invention, by adding hydrogen chloride during the above silicon carbide synthesis, by volatilizing metal impurities such as iron and copper contained in silica and carbon as a raw material as chlorides, high purity silicon carbide. It was made based on the finding that

The silicon carbide synthesis temperature may be 1,500 ° C or higher.
Β-type silicon carbide is synthesized in the temperature range of 500 ° C to 2050 ° C, and α-type silicon carbide is synthesized in the temperature range of 2050 ° C or higher.

Further, at a temperature of 1500 ° C. or less, the yield of silicon carbide is extremely deteriorated, which is not preferable.

When silica gel surface and fine pores impregnated with carbon black and / or a carbonaceous substance that changes into carbon by heating are used as the starting material, the silica reduction reaction will be carried out extremely efficiently, so that after the silicon carbide synthesis reaction Is
Almost no unreacted silica remains.

In addition, the mixing ratio of silica and carbon is the reaction formula SiO ₂ + 3C → Si
1.1 to 2.0 times the theoretical carbon amount for completing the silica reduction reaction with C + 2CO is good. When the amount is 1.1 times or less of the theoretical carbon amount, unreacted silica remains, and even when it is added in an amount of 2.0 times or more the theoretical carbon amount, a large amount of carbon not involved in the reaction remains after the reaction, which is not preferable.

Although the reaction product contains some excess carbon, it can be removed by oxidizing the carbon at 500 ° C. to 700 ° C. in an oxidizing atmosphere.

The concentration of hydrogen chloride added to obtain high-purity silicon carbide is preferably 3 vol% to 10 vol%. 3 vol
If it is 10% by volume or less, the silicon carbide synthesized is decomposed by hydrogen chloride and the yield of silicon carbide is deteriorated.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 To 500 g of silica fine powder, 210 g of carbon black and 430 g of phenol resin (150 g in terms of carbon) were added and mixed well. The amount of carbon added corresponds to 1.2 times the theoretical amount of carbon. Note that the magnification in Table 1 is (added carbon amount /
The theoretical carbon amount) is shown.

Next, after drying the raw material at 200 ° C for 10 hours, Ar95vol
%, HC 15 vol%, the synthesis reaction was carried out at 1650 ° C. for 4 hours. After cooling, 228.5 g of reaction product was obtained. The reaction product was kept in the atmosphere at 650 ° C. for 5 hours to oxidize and remove excess carbon, to obtain 194 g of silicon carbide.

It was identified as β-type silicon carbide from the X-ray diffraction pattern of the obtained silicon carbide. Unreacted free silica by chemical analysis,
When iron and copper were quantified, free silica was 3.4 wt%, iron was 10 ppm, and copper was 1 ppm.

Comparative Example Silicon carbide was synthesized in the same manner as in Example 1 except that the atmosphere was Ar100 vol%. The obtained silicon carbide was identified as β-type silicon carbide from the X-ray diffraction pattern,
As a result of chemical analysis, free silica is 3.3 wt%, iron is 540 ppm,
Copper was 10 ppm.

Examples 2 and 3 To 550 g of fine silica gel powder, 1300 g of phenol resin (455 g in terms of carbon) was added and mixed well. The amount of added carbon is 1.38 times the theoretical amount of carbon.

Silicon carbide was synthesized from the raw material under the conditions shown in Table 1. The obtained silicon carbide was identified as β-type silicon carbide from the X-ray diffraction pattern. The results of the chemical analysis are shown in Table 1.

Comparative Examples 2 and 3 Using the same raw materials as in Examples 2 and 3, silicon carbide was synthesized under the conditions shown in Table 1. As a result of chemical analysis, the amount of unreacted free silica was large, and the yield of silicon carbide was extremely poor.

Example 4 Using the same raw material as in Examples 2 and 3, a synthesis reaction was carried out at 2200 ° C. for 2 hours in an Ar atmosphere containing 3 vol% of HC1.
The obtained silicon carbide was identified as α-type silicon carbide from the X-ray diffraction pattern. The results of the chemical analysis are shown in Table 1.

Comparative Example 4 Silicon carbide was synthesized in the same manner as in Example 4 except that the atmosphere was Ar100 vol%. The obtained silicon carbide was identified as α-type silicon carbide from the X-ray diffraction pattern. The results of the chemical analysis are shown in Table 1.

[Effects of the Invention] As described above, according to the present invention, in the synthesis of silicon carbide by the silica reduction method, by adding hydrogen chloride during the synthesis, a silicon carbide sintered body used as a jig for semiconductor production or the like. A high-purity silicon carbide powder having a low content of metal impurities such as iron and copper, which is suitable as a raw material for industrial use, could be industrially stably supplied in a required amount promptly and at low cost. It can be said that the industrial role of the present invention will be great as the use of silicon carbide spreads in the future.

Claims (3)

[Claims] 1. A method for producing silicon carbide using silica and carbon as starting materials, wherein the starting materials are synthesized at 1500 ° C. or higher in a non-oxidizing atmosphere containing hydrogen chloride to obtain silicon carbide. And a method for producing high-purity silicon carbide powder. 2. Silica gel is used as silica, carbon black is used as carbon, and / or a carbonaceous substance that is converted into carbon by heating is used, and carbon black and / or carbon is heated by heating on the surface and fine pores of the silica gel. The method for producing a high-purity silicon carbide powder according to claim 1, which comprises impregnating a carbonaceous substance that changes into a powder. 3. The method for producing a high-purity silicon carbide powder according to claim 1 or 2, wherein the concentration of hydrogen chloride is 3 vol% to 10 vol%.