JPS6369758A - Manufacture of silicon carbide sintered body - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing a silicon carbide sintered body, and more particularly, to a reactive sintering type silicon carbide-silicon sintered viscous body. By decomposing it into silicon carbide,
The present invention relates to a method for manufacturing a silicon carbide sintered body that is highly pure, dense, and can withstand use at high temperatures of 1,700°C, and is useful in the semiconductor industry.

(Prior technology) Silicon carbide sintered bodies are widely used as heat treatment jigs because of their excellent heat resistance and strength. Reaction sintering in which silicon particles are shaped using a rubber press or the like and fired, then brought into contact with gaseous or liquid silicon metal to impregnate silicon, and then sintered to obtain a silicon carbide-silicon sintered body. It is manufactured by an atmospheric pressure sintering method in which silicon carbide particles are added with boron or a boron compound, carbon, or beryllium oxide as a sintering aid, and then sintered in an inert gas atmosphere or vacuum.

However, although this reaction sintering method has the advantage that the resulting silicon carbide-silicon sintered body has almost no shrinkage during firing and can be fired at a low temperature, this method does not contain free silicon from 2 to 30%. 1, since it contains 20%
At temperatures above 200°C, the strength becomes extremely weak, and the maximum operating temperature is 1, 4. Pressureless sintering has the disadvantage that it cannot be used as a jig for the semiconductor industry, where peripheral equipment is becoming larger and operating temperatures are rising as the diameter of silicon wafers increases. Silicon carbide sintered bodies made by this method have large firing shrinkage, making large products difficult to manufacture as they break during firing.
This has the disadvantage of using silicon carbide sintered bodies with submicron particle size as a raw material and requiring high-temperature firing, so silicon carbide fired products are of high purity, dense, and have no shrinkage during firing. Small, 1,700-1,800℃
There is a demand for products that can be used even at high temperatures such as

(Structure of the Invention) The present invention relates to a method for manufacturing a silicon carbide sintered body that meets such demands, and this involves molding a mixture consisting of silicon carbide powder, graphite powder, and a binder, pyrolyzing the binder, and then pyrolyzing the binder. This is impregnated with metallic silicon and sintered to produce a silicon carbide-silicon sintered body, which is then passed through a halogen gas to remove silicon, and then impregnated with polycarbosilane. It is characterized by thermally decomposing silane into silicon carbide.

That is, the present inventors have studied various methods for manufacturing silicon carbide sintered bodies that have small firing shrinkage and can withstand high-temperature use. After the silicon is volatilized as a silicon halide by the flow of a halogen-based gas, the pores from which the silicon has disappeared are impregnated with polycarbosilane, and then heated to convert the polycarbosilane into silicon carbide. A high-strength silicon carbide sintered body is obtained in which the pores are filled with silicon carbide, and since it is made by a reaction sintering method, the firing shrinkage is small, and it does not contain silicon. They found that it can withstand use at high temperatures such as 1,700 to 1,800°C, and completed research on the reaction conditions in each of these steps to complete the present invention.

In the method of the present invention, as described above, a silicon carbide-silicon sintered body is produced by the reaction sintering method, and then, after desilicating, this is impregnated with polycarbosilane to turn it into silicon. This silicon carbide-silicon sintered body is produced in the following steps.

In the method of the present invention, a silicon carbide sintered body is first made by mixing silicon carbide powder, graphite powder, and a binder, molding it, and then thermally decomposing the binder to form β-type silicon carbide. Bye.

Examples of the binder include organopolysiloxane, phenol resin, cellulose, and tar pitch, and at least one of these or a mixture thereof may be used.

The silicon carbide powder has a particle size of less than 10 µl, preferably 5 µl.
The material may have a tn of 5 or less, and may be either the α-type or the β-type, but it is preferably one that has been previously treated with hydrofluoric acid, nitric acid, etc. to remove silica, alkali, etc. Further, it is preferable that this graphite powder has a particle size of 54 or less, is heat treated in a vacuum at around 1,800° C., and is purified with a chlorine-based or fluorine-based gas.

In addition, as mentioned above, the binders used in this product include organopolysiloxane, phenolic resin, cellulose,
This organopolysiloxane, which is considered to be at least one type of tar pitch, may have a methyl group or a phenyl group as an organic group, and this organopolysiloxane may have a complex structure such as that represented by the general formula %. Preferably, it is crosslinked.

If the amount of graphite powder used in a molded body made of fine silicon carbide powder, graphite powder, and binder is too small, it will be difficult to impregnate metal silicon (described later), and if it is too large, the molded body will crack when impregnated with metal silicon. If the amount of binder is too small, the calcined body will be weak and difficult to handle, and if it is too large, gas will be generated during calcining and the pores will become too large. Therefore, silicon carbide powder is 45 to 80% by weight, preferably 50 to 80% by weight.
70% by weight and 5-40% by weight of graphite powder, preferably 10% by weight.
-35% by weight, 5-30% by weight of binder, preferably 10-300-30% by weight, then thoroughly mixed, packed in a rubber container, and pressed using a rubber press for 7 o'clock.
The molding may be performed at a molding pressure of 0 to 2,000 kg/d.

This molded body is then fired to form a calcined body, but this firing can be done by heating at 400 to 00°C in an inert gas atmosphere or in vacuum, and during this heating Co, CH, gas Since a large amount of gases such as the like are generated and these become pores, this heating is preferably performed in an inert gas atmosphere such as argon or helium. Note that this heating may be heated to 1,000°C or higher, but usually 100°C or higher.
After preheating to 0~300℃ and degassing, rapidly heat to 800~1.
It is preferable to raise the temperature to 000°C and carry out the process in a steamed state.

The silicon carbide plate sintered body thus obtained is then impregnated with metallic silicon and sintered to produce a silicon carbide-silicon sintered body. It is preferable that the silicon be of semiconductor grade and high purity. If this impregnation with metallic silicon is carried out in air, the metallic silicon will react with oxygen and impregnation will not be possible, so it is necessary to heat the silicon carbide sintered body and metallic silicon in a vacuum. However, this temperature should be at least 1,414°C, which is the melting point of silicon metal, and if it exceeds 1,800°C, silicon metal will evaporate, so the temperature should be 1°420 to 1,800°C.
It is preferable to set it in the range of 0°C.

By the way, the metallic silicon that enters the silicon carbide sheet fired body through impregnation at this temperature reacts with the carbon present in the calcined body, and a part of it becomes silicon carbide. The silicon plate sintered body is a silicon carbide-silicon sintered body.

The method of the present invention involves removing silicon from the reactively sintered silicon carbide-silicon sintered body obtained in this way, impregnating it with polycarbosilane, and then thermally decomposing it to form silicon carbide. However, this removal of silicon is carried out by heating the silicon carbide-silicon sintered body to 1.400 to 1,800°C in a vacuum.
When a halogen-based gas such as chlorine-based gas or fluorine-based gas is passed through the gas, metallic silicon easily reacts with the halogen gas and becomes a halide and volatilizes, making it easy to remove silicon. can. Note that when halogen gas is passed through, the alkali metals and transition metals contained in the sintered body are also halogenated and volatilized, so this method not only removes silicon but also improves the purity of the silicon carbide sintered body. However, since the alkali metals and transition metals have a small diffusion coefficient, it is preferable to carry out this heating at a high temperature such as 1,600 to 1,800°C.

By removing silicon, the silicon carbide-silicon sintered body becomes a sintered body consisting only of silicon carbide, but this product has some pores due to the removal of silicon. Impregnated with polycarbosilane. This carbosilane has the general formula (where R1 is a methyl group, R2, R3, R
4 has a main skeleton of silicon and carbon represented by a hydrogen atom, alkyl group, or aryl group, but 4 has a particularly high silicon content, and therefore β-5iC by heating
It is preferable because it has a good yield and is easily soluble in a solvent and can be easily impregnated into a silicon carbide sintered body. Impregnation with polycarbosilane can be achieved by dissolving it in a solvent such as benzene or toluene and then bringing it into contact with the silicon carbide sintered body. This impregnation is carried out under pressure.
This may be carried out either under normal pressure or reduced pressure, but if the solvent is volatilized at room temperature after impregnation, a dense silicon carbide sintered body impregnated with polycarbosilane can be obtained.

In silicon carbide sintered bodies impregnated with polycarbosilane, polycarbosilane thermally decomposes at 800°C in an inert gas atmosphere, becomes β-type silicon carbide at temperatures above 1,200"C, and When heated at 1,800°C, a three-dimensional network is formed that fills the pores, so by firing at 1,500 to 1,800°C in an inert gas atmosphere, a sintered body consisting only of silicon carbide is formed. It is said that

Since the silicon carbide sintered body obtained in this way is of the reaction sintering type, the firing shrinkage is small, and therefore it can be made into large molded products, and this product does not contain silicon. Since the bending strength does not decrease even at high temperatures, it can be used at high temperatures such as 1,700 to 1,800°C. Therefore, for example, when the inner surface of this product is coated with a 5iC-CVD film, if the base material is a silicon carbide-silicon sintered body, cracks will occur due to a decrease in strength at high temperatures, but this is a silicon carbide sintered body. Therefore, the strength does not decrease and no cracking occurs even at high temperatures, so it can be used as a furnace core tube for electric furnaces, a blowing pipe for aluminum smelting, a heating element protection tube, a furnace core tube for high frequency furnaces, a process tube, and a liner tube. It is said to be useful, and because it has very high purity, it is also useful for jigs such as semiconductor wafers.

Next, examples of the present invention will be given.

Example 1 α-type silicon carbide powder (#
3000) 70% by weight, 15% by weight of graphite powder with an average particle size of 3, and 15% by weight of organopolysiloxane/silicone varnish KR-260 [manufactured by Shin-Etsu Chemical Co., Ltd.] After drying and pulverizing a mixture, aluminum Filled in a rubber mold with a plastic core and molded at a pressure of 1,000 kg/d, outer diameter 300 m1 x thickness 10 m x length 2,000 m
A 0wn pipe was made, held at 250° C. for 1 hour under an argon gas atmosphere, and then heated at 1,000° C. for 3 hours to produce a silicon carbide sheet fired body.

Next, metal silicon is inserted into this calcined pipe and heated to 1,600'C under a vacuum of 1 Torr to impregnate the metal silicon into the pipe and perform silicon carbide-silicon sintering. After making it into a body, it was heated under a vacuum of 10 torr for 1,80 m
Hydrogen chloride gas IoQ/min and argon gas 5CII/min were passed through the pipe for 3 hours during vulcanization at 0°C to remove silicon and purify the pipe. As a result, the pipe had a bulk specific gravity of 1. It became 9th one.

Next, this silicon carbide sintered body was immersed in a rubber container prepared by dissolving the formula polycarbosilane in 30% by volume of benzene, and was left under a pressure of ]-, OO○kg/d for 1 hour. After impregnating polycarbosilane, dry it at room temperature to volatilize the benzene, and then heat it at 1,600°C for 3 hours in an argon gas atmosphere to convert the polycarbosilane into a β-type silicon carbide sintered body and sinter the silicon carbide. I made a solid pipe.

When we chemically analyzed the silicon carbide sintered pipe obtained in this way, it showed the results shown in Table 1 below, but when we investigated its physical properties, we found that it was The results were shown in Table 2.

Table 1 Table 2 Example 2 α-type silicon carbide powder (#3000) with an average particle size of 5p
) 50% by weight, 25% by weight of graphite powder with an average particle size of 3p and organopolysiloxane silicone varnish KR-2
After drying and pulverizing a mixture consisting of 60C Shin-Etsu Chemical Co., Ltd. product name) 2 parts by weight, it is packed into a rubber mold containing an aluminum core, and molded at a pressure of 1,000 kg/a— 3001m x thickness 10mn x length 2,000w
n pipe, and calcined it in the same manner as in Example 1,
By pre-impregnation with metal silicon and desilicification treatment using hydrogen chloride gas, a silicon carbide burner pipe with a bulk specific gravity of 1.85 was obtained.

Next, this pipe was immersed in a rubber container containing the same polycarbosilane used in Example 1 dissolved in 30% by volume of tetrahydrofuran.
/a# for 1 hour to impregnate polycarbosilane, dry at room temperature to volatilize tetrahydrofuran, and then heat under argon gas atmosphere for 3 hours at -9800°C to form polycarbosilane. When a silicon carbide combustion body pipe was made by repeating the process of converting the β-type silicon carbide into β-type silicon carbide twice, this product exhibited physical properties as shown in Table 3 below.

Table 3 Comparative Example 1.2 Using a rubber press, a mixture of 80% by weight of graphite powder with an average particle size of 5 mm and 20% by weight of phenol resin,
Molded under pressure of 2,000 kg/ffl to form an outer diameter of 300
mm×thickness], Own x length 2,000 mm pipe was made, packed in graphite powder and fired at 2°000℃ for 20 hours, then packed in 5in2 powder and heated to 1,800℃. It was then silicified and made into a silicon carbide burner pipe. Next, this was heated to 1,800°C in a vacuum of 50 Torr, and purified by flowing hydrogen chloride gas at 10 ρ/min and argon gas at 50 Q/min. 1°500 in a crucible under a vacuum of 1 Torr
C. and impregnated with metallic silicon to obtain a silicon carbide-silicon burner pipe (Comparative Example 1).

Separately, 96 parts by weight of α-type silicon carbide with an average particle size of 0.57 m, 4 parts by weight of phenol resin, 0.5 parts by weight of granular carbonized boron, and 1.5 parts of polyvinyl alcohol were added to an acetone solution. After drying in a nitrogen gas atmosphere, the powder was packed into a rubber mold containing an aluminum core and molded under a pressure of 1,400 kg/ffl to an outer diameter of 300 nu x thickness. −〇1nllll×length 2,
After making a pipe of 1,000 m long, it was heated at 100° C. for 2 hours to obtain a calcined body. Next, this calcined pipe was heated at 2°000°C for 1 hour in argon gas to make a blue-white sintered silicon carbide pipe, which resulted in cracks at both ends of the pipe (comparative example). 2) measured the physical properties of these pipes together with the pipe of Comparative Example 1 described above, and they exhibited the physical properties as shown in Table 4 below.

Table 4

Claims (1)

[Claims] 1. After molding a mixture consisting of silicon carbide powder, graphite powder, and a binder and thermally decomposing the binder, it is impregnated with metallic silicon and sintered to form a silicon carbide-silicon sinter. Silicon carbide sintering, which is characterized by forming a compact, then flowing a halogen gas through it to remove silicon, impregnating it with polycarbosilane, and thermally decomposing the polycarbosilane to form silicon carbide. How the body is manufactured. 2. The binder is at least one of organopolysiloxane, phenolic resin, cellulose, and tar pitch.
A method for producing a silicon carbide sintered body according to claim 1.