JP3442803B2 - Method for producing high-purity β-type silicon carbide powder - Google Patents

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 powder for producing a high-purity sintered body from a raw material containing a small amount of impurity elements, mainly without using a sintering aid. .

[0002]

2. Description of the Related Art The Acheson method has hitherto been known as a method for producing low-quality silicon carbide, and the silica reduction method is used as a method for obtaining silicon carbide having a slightly high purity. This is a method in which silica powder and carbon are mixed and fired at 1700 ° C. to 2200 ° C. in an inert gas to obtain silicon carbide, and it is possible to obtain medium-quality silicon carbide at a relatively low cost.

Further, as a method for obtaining a high quality product,
In recent years, a method of obtaining silicon carbide by a vapor phase method has also been proposed. This is to use a silane-based gas as a raw material and a hydrocarbon gas as a carbon source, for example, methane, ethane, propane, ethylene, etc., to decompose silicon carbide by thermally decomposing or mixing these mixed gases in plasma. I will get it. Further, as a liquid phase method, a liquid silicon compound such as an alkyl silicate or a silicic acid aqueous solution is mixed with a liquid organic compound or a resin aqueous solution having a high residual carbon ratio, dried, and then carbonized and baked in an inert gas to form a β type A method for obtaining a silicon carbide powder is known (Japanese Patent Publication No. 1-242886).

Further, as a method for obtaining high-purity silicon carbide, Japanese Patent Laid-Open No. 2-204318 discloses that α-type and β-type silicon carbide containing several hundred ppm of impurities represented by iron (Fe) is previously pulverized to 1 μm or less. After that, a method of heat-treating at a high temperature to recrystallize to obtain an average particle size of 100 μm or less and washing with a hydrofluoric acid-nitric acid mixed solution is disclosed. JP-A-61-611
In No. 0, a silicon solid and a carbonaceous solid such as carbon black are added to a liquid silicon compound such as ethyl silicate and an organic compound having a functional group such as a liquid phenol resin to produce a precursor solid, which is carbonized, A method for obtaining β-type silicon carbide powder by firing is described.

[0005]

As described above, many techniques have been proposed to obtain high-purity silicon carbide.
In the silica reduction method, it is difficult to obtain high-purity carbon as a raw material, and there is a problem that impurities are mixed in in the mixing step. Although the gas-phase method can obtain a high-purity product, the productivity is poor and the cost is high. Therefore, it cannot be used industrially, and the liquid phase method also has a problem that an ultrahigh-purity product with impurities of ppb order is required as a raw material in order to obtain a desired high-purity product. Further, the method described in JP-A-2-204318 is 1500 to 500 for 1 hour in a non-oxidizing atmosphere.
Since the high temperature treatment at 2200 ° C. is required, the cost becomes high, and the impurities represented by iron cannot be removed to a desired order. In the method described in JP-A-61-1610, the carbonaceous solid as a raw material is used. Since the amount of metal impurities in it cannot be suppressed to a desired amount or less, there is a problem that it is difficult to obtain a desired high-purity product.

As described above, since it is difficult to obtain a high-purity silicon carbide raw material, in the field of the semiconductor industry, etc., which requires an ultra-high-purity silicon carbide sintered body, a sintered product having insufficient purity can be used as a C product.
A method of forming an ultra-high-purity silicon carbide coating film by the VD method and preventing scattering of impurities is used.

That is, the object of the present invention is to provide ultra-high-purity raw material powders for various silicon carbide products used in the field of semiconductor industry, etc. which require ultra-high-purity silicon carbide sintered bodies, that is, respective impurity concentrations. The present invention provides a method for industrially using ultrahigh-purity β-type silicon carbide powder, which is preferably 1 ppm or less.

[0008]

The method for producing a high-purity β-type silicon carbide powder according to claim 1 of the present invention comprises a liquid silicon compound and a liquid organic compound which has a functional group and produces carbon by heating. Using a compound as a raw material, a high-purity polymerization or cross-linking catalyst that uniformly solubilizes them, and polymerize or cross-link them to obtain a uniform precursor substance in a non-oxidizing atmosphere,
In a method for producing a β-type silicon carbide powder, which comprises firing an intermediate product obtained by heating and carbonizing at a higher temperature in a non-oxidizing atmosphere, each impurity concentration is 50 ppm or less.
It is characterized in that high-purity hydrofluoric acid , which is a halogen compound containing substantially no metal component , is added to the raw material and / or the catalyst .

[0009]

The method for producing high-purity β-type silicon carbide powder according to claim 2 of the present invention is the method according to claim 1, wherein a high-purity carbonaceous solid and a siliconaceous solid are added to the raw material. It is characterized by

That is, the inventors of the present invention have made intensive studies in the method for producing high-purity β-type silicon carbide by paying attention to the reaction mechanism of impurities, and as a result, they can be simply and simply added at the time of mixing the raw materials and the catalyst in a liquid state. The inventors have achieved the object and completed the present invention by finding out that impurities can be converted to chlorides by evaporation to remove impurities during high temperature firing by homogeneously containing a halogen compound containing no metal component.

The high purity of the high-purity β-type silicon carbide in the present invention preferably means that each impurity concentration is 1 ppm or less, more preferably 0.5 ppm or less.

The halogen compound is preferably hydrogen halide, a non-metallic compound which generates hydrogen halide by hydrolysis, or ammonium halide.
Specific examples include hydrogen chloride, ammonium chloride, silicon chloride (SiCl ₄ ), thionyl chloride, phosphorus chloride, hydrogen fluoride, ammonium fluoride, silicon fluoride, hydrogen bromide (HBr), ammonium bromide, iodine chloride, Examples thereof include iodine bromide, and hydrogen chloride, ammonium chloride and silicon chloride are preferable. It is preferable that these halogen compounds have high purity and do not contain a metal component.

As a method of adding the halogen compound, it may be added in advance to the catalyst aqueous solution or may be added in the mixing step, and it is not necessary to change the subsequent steps, that is, the carbonization and firing steps.

The amount of the halogen compound added is 0.001 as the halogen ion concentration with respect to 1 kg of the raw material mixture.
1 mol to 0.3 mol is preferable, 0.01 mol to 0.1
Molar is more preferred. The amount of the halogen compound added, that is, the halogen ion concentration, can be lowered as the amount of impurities in the raw material decreases.

The present invention will be described in detail below. The liquid silicon compound used in the present invention includes methyl silicate, alkyl silicates such as ethyl silicate, silicic acid or silicic acid polymer aqueous solution obtained by dealkalizing alkali silicate, and organic compounds having a hydroxyl group and silicic acid. Examples thereof include ester solutions. Among them, methyl silicate monomer, ethyl silicate monomer and oligomer are preferably used.

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

In the present invention, as the high-purity polymerization or crosslinking catalyst which is uniformly dissolved in the raw material, when a phenol resin or furan resin monomer or oligomer is used as the raw material,
Acids such as toluene sulfonic acid, nitric acid, sulfuric acid, and oxalic acid are preferable, and toluene sulfonic acid having a surface-active effect is particularly preferable. When a monomer or oligomer of a nitrile resin is used, a commonly used radical polymerization initiator such as ammonium persulfate, hydrogen peroxide, various hydroperoxides, alkyl peroxides, peroxide esters, and azo compounds is suitable. Further, when other organic compound is used, a polymerization or crosslinking catalyst which is usually used can be used.

In the present invention, the precursor substance obtained by polymerizing or cross-linking the raw materials is heated and carbonized in a non-oxidizing atmosphere, and the carbonization temperature in that case is 700 to 1100 ° C.
Is used, and preferably 800 to 1000 ° C. is adopted. The intermediate product obtained by carbonizing the precursor substance is fired at a higher temperature in a non-oxidizing atmosphere. In that case, the temperature is 1600 to 2200 ° C., and 1700 to 2
000 ° C. is preferably used.

Matters concerning the removal of impurities, which is an important element in the present invention, will be described below. The β-type silicon carbide does not substantially contain an impurity element, but even if it is contained, the content of each impurity element needs to be 1 ppm or less. The raw material used in the present invention has a content of each impurity element of 50 ppm or less, preferably 10 ppm or less.

In the process of mixing the raw materials, the halogen compound is added, mixed well, and polymerized or cured by a catalyst. At this time, the catalyst addition timing can be delayed so that the halogen ions sufficiently react with the impurities.

At this time, for example, when silicon chloride is used as the halogen compound, hydrogen chloride and an aqueous solution of silicic acid are hydrolyzed, and silicic acid becomes a part of the raw material of silicon carbide, which is preferable in terms of reaction efficiency. Further, when a resol type liquid phenol resin is used as an organic compound that generates carbon, hydrogen chloride (hydrochloric acid) also serves as a crosslinking catalyst, which has an advantage that the amount of the catalyst added can be reduced. As described above, by selecting the halogen compound to be added depending on the raw material used, not only the removal of impurities but also other effects can be obtained.

Here, the impurity elements are Ia to V in the periodic table.
A group IIa element, a group VIII element, a group Ib to group IIIb element, a group IVb element having an atomic number of 32 or more and a group Vb element having an atomic number of 33 or more.

In the present invention, the carbon / silicon molar ratio in the intermediate product obtained by carbonizing the precursor material is 2.
It is 0 to 4.0, and preferably 2.3 to 3.4.

Silicon carbide obtained by firing this carbide at 1600 to 2200 ° C. in a non-oxidizing atmosphere may or may not contain residual carbon. It can be arbitrarily selected according to the purpose of use. The particle size of the obtained silicon carbide powder is 0.1.
μm to 10 μm is suitable.

As described above, the method of obtaining high-purity β-type silicon carbide of the present invention is a simple method of adding a solution of a halogen compound in the process of mixing liquid raw materials, and from a raw material containing impurities to some extent, It is intended to provide means for efficiently obtaining high-purity silicon carbide powder.

Further, in the production method of the present invention, a high-purity carbonaceous solid and a siliconaceous solid can be added to the raw materials for the purpose of cost reduction. The carbonaceous solid is preferably carbon black or graphite having an impurity content of 10 ppm or less, and the siliconaceous solid is amorphous silica, quartz powder or silicon monoxide (SiO 2) powder having an impurity content of 10 ppm or less. However, the present invention is not limited to these.

[0028]

The reaction mechanism for removing impurities of the present invention is not clear. However, by adding a halogen compound to a catalyst or a mixture of a raw material and a catalyst, impurities containing a metal component contained in the raw material and the catalyst are contained in the halogen. It reacts with a compound to form a metal halide having a lower boiling point than that of an oxide or the like, which is 800 ° C. to 1200 ° C. in the next non-oxidizing atmosphere.
1600 in carbonization process and non-oxidizing atmosphere at ℃ condition
It is presumed that this is due to vaporization and disappearance in the firing process under the condition of ℃ to 2200 ℃.

[0029]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

Comparative Example 1 Silicon dioxide content as liquid silicon compound 40% by weight
Commercially available ethyl silicate (ethyl silicate 40:
Liquid resol-type phenol resin (PR50) not treated with high purity having 620 g of water content of 20% and made by Koruko.
(75: manufactured by Sumitomo Durres Co., Ltd.) To a mixed solution of 290 g, 50 g of a 50% aqueous solution of p-toluenesulfonic acid as a catalyst and 63 g of a 2% aqueous solution of high-purity hydrochloric acid as a halogen compound were added and cured to obtain a homogeneous resinous solid. . This was carbonized at 900 ° C. for 1 hour in a nitrogen atmosphere. From the elemental analysis of the obtained carbide, the molar ratio of carbon and silicon was 2.32. This carbide is heated in an argon atmosphere at a heating rate of 40 ° C /
The temperature was raised to 1900 ° C. in minutes, heated, and held for 45 minutes to carry out the silicon carbide reaction. The color of the obtained powder was green-white.

The crystal form of silicon carbide of this powder by X-ray diffraction was β type (cubic crystal). Impurity analysis of this powder (I
The results of CP-mass spectrometry and flames atomic absorption method are shown in Table 1.

Example 1 A β-type silicon carbide powder was obtained in the same manner as in Comparative Example 1 except that 50 g of a highly pure 2% aqueous solution of hydrofluoric acid was added instead of hydrochloric acid as a halogen compound. The results of the impurity analysis of this powder are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that 690 g of ethyl silicate and 326 g of phenol resin were used, and 3.4 g of silicon tetrachloride was added as a halogen compound instead of hydrochloric acid. As a result of elemental analysis of the obtained carbide, the molar ratio of carbon to silicon was 2.58. Comparative Example 1 with this carbide
The results of carbon analysis and X-ray diffraction of the obtained powder were 5.2% by weight and β-type silicon carbide, respectively. The results of the impurity analysis of this powder are shown in Table 1.

[Comparative Example 3] 68 wt% of ethyl silicate and liquid phenol resin 32
To a liquid substance in which the weight% is uniformly mixed, a powder obtained by mixing high-purity amorphous silica fine powder and high-purity synthetic graphite fine powder in a weight ratio of 2: 1 is added by 1/4 in a weight ratio, and further, , P
5% by weight of a 50% aqueous solution of toluenesulfonic acid and 10% by weight of a 2% aqueous solution of high-purity hydrochloric acid were added, stirred, solidified and dried to obtain a resinous solid. This was carbonized in the same manner as in Comparative Example 1 to form silicon carbide.

The β-type silicon carbide powder thus obtained was analyzed for impurities in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 4 The procedure of Comparative Example 1 was repeated, except that high-purity hydrochloric acid was not added. As a result of elemental analysis of the obtained carbide,
The molar ratio of carbon to silicon was 2.35. This carbide
When silicon carbide was formed in the same manner as in Comparative Example 1 , yellow green powder was obtained. The results of carbon analysis and X-ray diffraction of this powder were 0.05% by weight and β-type silicon carbide, respectively. The results of the impurity analysis of this powder are shown in Table 1.

[Comparative Example 5] β-type silicon carbide was obtained in the same manner as in Comparative Example 3 except that high-purity hydrochloric acid was not added. Table 1 shows the result of performing an impurity analysis on this in the same manner as in Comparative Example 1 .

[0038]

[Table 1]

As is clear from the results shown in Table 1, in comparison with the comparative example, the β-type silicon carbide powder obtained in the examples of the present invention contained the respective impurity elements in spite of using the same raw materials. Was an ultra-high purity product having a content of 1 ppm or less, which was obtained by a simple method.

[0040]

Since the method for producing high-purity β-type silicon carbide powder of the present invention has the above-mentioned constitution, it is possible to adjust the impurity concentration to 1 by using a relatively high-purity raw material which is usually commercially available.
High-purity β-type silicon carbide powder can be obtained relatively inexpensively because it is possible to easily obtain ultra-high-purity β-type silicon carbide that is suppressed to ppm or less, and to add silicon-based solids such as silica and carbon or carbon-based solids. It has an excellent effect that can be obtained.

─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-4-149017 (JP, A) JP-A-62-212213 (JP, A) JP-A-63-170207 (JP, A) JP-A-60- 226406 (JP, A) JP-A-54-67599 (JP, A) JP-A-2-204318 (JP, A) Ikuo Kurachi, Hidehiko Tanaka, silicate ester and phenol resin condensate as precursors, and their thermal decomposition Of β-SiC Powder Synthesized by J., Polymer Society of Japan Proceedings, Japan, 1989, Vol. 38, No. 12, p. 4303-4305 Hidehiko Tanaka, Ikuo Kurachi, Synthesis of β-SiC powder from ethyl silicate phenol resin, Proceedings of the 1987 Ceramic Society of Japan, Japan, 1987, Vol. 1987, No. 2, p. 271-272 (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01B 31/36 C04B 35/56 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A raw material is a liquid silicon compound and a liquid organic compound which has a functional group and produces carbon by heating.
An intermediate product obtained by adding a high-purity polymerization or crosslinking catalyst that solubilizes uniformly to these, polymerizing or crosslinking reaction, and heating and carbonizing the obtained uniform precursor substance in a non-oxidizing atmosphere, In the method for producing β-type silicon carbide powder, which comprises firing at a higher temperature in a non-oxidizing atmosphere, each impurity
High purity , which is a halogen compound containing substantially no metal component in the raw material and / or catalyst having a concentration of 50 ppm or less
1. A method for producing a high-purity β-type silicon carbide powder, characterized in that the hydrofluoric acid is added. 2. High purity carbonaceous solid and silicon as the raw material
High-purity according to claim 1, characterized in that a high quality solid is added.
Method for producing β-type silicon carbide powder.