JPH05851A - Silicon carbide-based material and its production - Google Patents

Abstract

PURPOSE:To improve corrosion resistance by depositing C formed by thermally decomposing C-contg. gas in a porous body of synthetic quartz glass while continuously varying the amt. of C in a certain direction, firing the C-contg. porous body and impregnating metallic Si into the resulting porous SiC material. CONSTITUTION:Gas contg. gaseous hydrocarbon or halogenated hydrocarbon is fed at a prescribed flow rate and thermally decomposed by heating at a prescribed temp. to deposit C in a porous body of synthetic quartz glass by an amt. expressed by the inequality (where (x) is the bulk density (g/cm<3>) of the porous body, 0<x<2.3 and (y) is the molar ratio of C to SiO2) while continuously varying the amt. of C from the surface of the porous body toward the interior. The resulting SiO2-C composite body is fired at a prescribed temp. in a nonoxidizing atmosphere or in vacuum to convert the SiO2 into SiC. Metallic Si melted by heating to the m.p. or above is impregnated into the formed SiC-C composite body in vacuum and converted into SiC by reaction with the C in the porous body. After this reaction, metallic Si is further filled into the pores in the sintered body to obtain a dense SiC-based sintered body having continuously varying ratio between Si and SiC in a certain direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide material and a method for producing the same, more particularly, a jig for semiconductor production, for example, a heat resistance of a process tube or a wafer board used for thermal diffusion treatment of a silicon wafer. The present invention relates to a high-purity silicon carbide material useful as a jig material and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
As a heat resistant jig for semiconductor manufacturing that requires high purity,
Those mainly made of quartz glass were used. The quartz glass jig has advantages that it is possible to easily manufacture a jig having extremely high purity, and that it is transparent because it is easy to observe the inside.

However, this quartz glass is 1000 ° C.
When the temperature exceeds 1150, deformation due to viscous flow begins to occur.
It has a drawback that it can hardly be used for heat treatment at a temperature of ℃ or more, and has a short life such as devitrification, damage or deterioration by acid.

In recent years, as a material capable of solving such drawbacks, a composite in which metallic silicon is filled in a porous silicon carbide compact formed by molding silicon carbide powder has been developed in place of quartz glass, and is used for semiconductor manufacturing. Used as a heat resistant jig. However, it is difficult to obtain a high-purity silicon carbide raw material powder, and the manufacturing process such as raw material blending, molding, high-purification treatment, firing, etc. is complicated, and a binder such as a phenol resin is required. It was difficult to obtain a high-purity silicon carbide composite material due to the impurities and the like. In addition, since the metal silicon impregnated portion is exposed on the surface of this heat-resistant jig for semiconductor production,
When treated with a gas or a cleaning agent such as an HF-NO ₃ solution, metallic silicon easily reacts with HCl or the like to decompose and separate, resulting in a decrease in strength.

On the other hand, as a method of suppressing the diffusion of impurities to reduce the contamination of a silicon wafer or the like and further suppressing the reaction of metallic silicon, a silicon carbide or silica film or the like is vapor-deposited on the surface of silicon carbide. A method for forming a dense silicon carbide film (Japanese Patent Application Laid-Open No. 62-122212, Japanese Patent Application Laid-Open No. 64-61376) has been proposed.

However, this silicon carbide-based material has the problems that pinholes are generated in the silicon carbide or silica film on the surface, the adhesion strength of the film is low, and cracks occur due to mechanical and thermal shocks. It was

The present invention has been invented in view of the above problems, is not deformed at a high temperature, is excellent in purity and corrosion resistance, and can contaminate a silicon wafer during diffusion processing. An object of the present invention is to provide a silicon carbide based material useful for a semiconductor jig and a method for manufacturing the same.

[0008]

In order to achieve the above object, in the silicon carbide based material according to the present invention, the composition ratio of silicon and silicon carbide is continuously changed in a certain direction. Further, in the above silicon carbide based material, the surface of the silicon carbide based material is substantially silicon carbide.

In the method for producing a silicon carbide material according to the present invention, carbon produced by thermal decomposition of a gas containing a hydrocarbon gas or a halogenated hydrocarbon gas is produced in a certain direction in a porous body of synthetic quartz glass. Is deposited with an amount that continuously changes with respect to the porous silicon carbide material obtained by firing, and then filled with metallic silicon.
Further, in the method for producing a silicon carbide based material described above,
When the bulk density of the synthetic quartz glass porous body is xg / cm ³ , the amount of carbon deposited on the surface thereof is characterized by satisfying the following formula.

Y ≧ 4.78 / x + 2 (Y: carbon / silicon dioxide molar ratio, 0 <x <2.3)

[0011]

[Function] VAD (Vapor-phase Axial)
Deposition) vapor-phase synthetic quartz glass is porous, so that it is possible to deposit carbon even inside by heat treating in a carbon-containing gas atmosphere.
At this time, by controlling the processing conditions such as temperature and gas flow rate, and by controlling the decomposition rate of the carbon-containing gas,
It is possible to continuously change the amount of carbon deposited on the surface and the inside of the porous synthetic quartz glass. Further, by firing this silicon dioxide-carbon composite, a porous silicon carbide-carbon composite is obtained.

Therefore, in the present invention, first, a porous synthetic quartz glass is used as a starting material, and heat treatment is performed in a carbon-containing gas atmosphere. At this time, the pyrolysis rate of the carbon-containing gas is controlled by adjusting the reaction temperature, the gas flow rate, etc., and the amount of pyrolytic carbon deposited from the surface of the porous synthetic quartz glass to the inside is continuously changed. This carbon deposition amount must be at least 3 or more in terms of molar ratio to the silicon dioxide in the porous synthetic quartz glass which is the base material, based on the number 2 described later.
This is because when the amount of deposited carbon is less than 3 in terms of molar ratio, excess silicon dioxide remains, and this silicon dioxide volatilizes as SiO gas during heat treatment and volatilizes, resulting in collapse of the shape of the porous body and reduction in strength. Alternatively, it may cause pulverization. When the amount of precipitation is the largest, the surface of the porous synthetic quartz glass may be formed substantially by simple carbon.

After carbon is deposited on the synthetic quartz glass porous body, the synthetic quartz glass-carbon composite is fired in a non-oxidizing atmosphere or in a vacuum, whereby ultrafine particles of pyrolytic carbon are converted into silicon dioxide fine particles. Is reduced extremely quickly and completely converted into silicon carbide.

Thereafter, when the porous silicon carbide-carbon composite is further impregnated with metallic silicon which is heated to a temperature equal to or higher than the melting point under vacuum and melted, it reacts with carbon inside the porous body,
Densification occurs while producing silicon carbide, and the pores of the sintered body after the reaction are further filled with metallic silicon to form a dense sintered body. At this time, when a large amount of excess carbon is present in the open pores, the silicon / silicon carbide composition ratio is small because a large amount of silicon carbide is also generated by reaction sintering. Conversely, when the excess carbon is small, , The composition ratio of silicon / silicon carbide becomes large. If carbon remains on the surface after impregnation with silicon, it can be easily removed by heat treatment in an oxidizing atmosphere.

When the amount y of carbon deposited on the surface of the synthetic quartz glass porous body reaches a value satisfying the following equation, the surface after impregnation with silicon is substantially formed by simple substance of silicon carbide.

Y ≧ 4.78 / x + 2 where x: bulk density (g / c) of the synthetic quartz glass porous body
m ³ ) y: carbon / silicon dioxide molar ratio This will be described with reference to FIG. 4, that is, as shown in FIG. 4A, there is a synthetic quartz glass porous body having a bulk density of xg / cm ³ and a volume of Zcm ^3. And the number of moles of SiO ₂ at this time is

[0017]

[Equation 1]

It is represented by After carbon is deposited on this synthetic quartz glass porous body (FIG. 4 (b)), heat treatment is performed to produce silicon carbide according to the following equation 2 (FIG. 4 (c)).

[0019]

[Equation 2] SiO ₂ + 3C → SiC + 2CO Therefore, the number of moles of the desorbed carbon gas is

[0020]

## EQU3 ## It is represented by y (CO) = 2 × y (SiO ₂ ). After that, by further impregnating metallic silicon, silicon carbide is generated by the following formula.

Si + C → SiC At this time, assuming that there is no volume change of the porous silicon carbide-carbon composite, the number of moles of silicon carbide is

[0022]

[Equation 4]

It is represented by The carbon / silicon dioxide molar ratio y (C / SiO ₂ ) is

[0024]

[Equation 5]

[Mathematical formula-see original document] By substituting the equations 1, 3, and 4 into this equation 5, and taking into account the minute pores inside, the following equation 6 is obtained.

[0026]

Y ≧ 4.78 / x + 2 where x: bulk density of the silica glass porous body (g / cm
³ ), 0 <x <2.3 y: molar ratio of carbon / silicon dioxide Here, since the true specific gravity of quartz glass is 2.3, the bulk density of the quartz glass porous body is 0 <x <2.3. However, the range of 0.2 to 1.2 is preferable.

By controlling the amount of carbon deposited on the porous synthetic quartz glass in this manner, the composition ratio of silicon to silicon carbide in the obtained silicon carbide material can be controlled.

According to the silicon carbide-based material of the present invention produced as described above, the composition ratio of silicon and silicon carbide is
Since it continuously changes in a certain direction, there is no interface in the composition of silicon / silicon carbide, and there is no problem such as film peeling due to a difference in thermal expansion coefficient.

Further, in the above-mentioned silicon carbide-based material, when the surface of the silicon carbide-based material is substantially silicon carbide, the surface is not attacked by HCl gas, HF-NO ₃ solution or the like.

Further, according to the method for producing a silicon carbide-based material according to the present invention, carbon produced by the thermal decomposition of a gas containing a hydrocarbon gas or a halogenated hydrocarbon gas is present in the porous body of synthetic quartz glass. Since the porous silicon carbide material obtained by precipitating in an amount that continuously changes in a certain direction and then firing is filled with metallic silicon, a dense silicon carbide material can be easily obtained.

In the production of the above-mentioned silicon carbide material, the bulk density of the synthetic quartz glass porous body is xg / cm.
^In the case of ³ , when the amount of carbon deposited on the surface satisfies the formula 6, a silicon carbide-based material whose surface is substantially formed by simple silicon carbide is produced after silicon impregnation, and The surface is not attacked by gas or HF-NO ₃ solution.

[0032]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples according to the present invention will be described below. Example Bulk density synthesized by VAD method is about 0.5 g / cm
³ , specific surface area of about 12m ² / g, average particle size of about 0.2
A synthetic quartz glass porous body having a diameter of 10 μm was processed into a cylindrical shape having a radius of 10 mm, and treated at a temperature of 1000 ° C. for 6 hours in an atmosphere of 100% methane gas, and the total molar ratio of silicon dioxide to carbon was about 9.8. A silicon dioxide-carbon composite having a molar ratio of 13.7 from the surface to about 0.5 mm was obtained.

The composite is then placed under vacuum at 2000.degree.
Firing for 3 hours at an average bulk density of about 0.80 g /
A porous silicon carbide-carbon composite having a cm ³ , an average porosity of about 35%, and a total molar ratio of silicon carbide to carbon of about 6.8 was obtained.

This porous body was inserted into a graphite crucible coated with silicon carbide, metallic silicon was placed around the crucible and heated at 1500 ° C. to allow the molten silicon to penetrate into the open pores of the porous body. Silicon Carbide Material 10 Shown in 1
Got The cross section and silicon / silicon carbide composition ratio of the obtained silicon carbide based material 10 are shown in FIG. 1, and the mechanical properties and corrosion resistance are shown in Table 1.

Comparative Example 1 80% by weight of silicon carbide powder having an average particle size of about 5 μm, 10% by weight of carbon powder having an average particle size of about 2 μm, and phenol resin 10
% By weight was mixed and molded into a cylindrical shape with a radius of 10 mm. After firing the molded body at 900 ° C., molten silicon was permeated at 1500 ° C. and reaction sintering was performed to obtain a silicon carbide-based material 11 shown in FIG. The cross section and silicon / silicon carbide composition ratio of this silicon carbide material 11 are shown in FIG. 2, and the mechanical properties and corrosion resistance are shown in Table 1.

Comparative Example 2 Silicon carbide material 11 obtained by the same method as Comparative Example 1
In addition, as shown in FIG.
Was coated by CVD to obtain a silicon carbide based material 12.
The cross section and silicon / silicon carbide composition ratio of this silicon carbide material 12 are shown in FIG. 3, and the mechanical properties and corrosion resistance are shown in Table 1.

[0037]

[Table 1]

The corrosion resistance test was carried out by HCl / H ₂ = 1 /
These are the results when the treatment was performed at 1200 ° C. for 4 hours in the gas No. 1 and the thermal shock resistance test was conducted under an inert atmosphere at 12
It is a result when the sample heated at 00 degreeC is put in water and rapidly cooled.

As is clear from Table 1, in the examples, the bending strength was high, and the corrosion resistance and thermal shock resistance were good. On the other hand, in Comparative Example 1, the bending strength was smaller than that in Examples, and further, good results were not obtained in terms of corrosion resistance. In addition, also in Comparative Example 2, the bending strength was smaller than that of the Examples, and good results were not obtained regarding thermal shock resistance.

As described above, in the silicon carbide based material and the method for manufacturing the same according to the above-mentioned embodiment, the jig for semiconductor manufacturing is
For example, it is possible to provide a high-purity silicon carbide material useful for heat-resistant jigs such as process tubes and wafer boats used for thermal diffusion treatment of silicon wafers, which is extremely useful industrially.

[0041]

As described above in detail, in the silicon carbide based material according to the present invention, the composition ratio of silicon and silicon carbide is
Since it continuously changes in a certain direction, there is no interface in the composition of silicon / silicon carbide, and there is no problem such as film peeling due to a difference in thermal expansion coefficient.

Further, in the above-mentioned silicon carbide-based material, when the surface of the silicon carbide-based material is substantially silicon carbide, the surface is not corroded by HCl gas, HF-NO ₃ solution or the like.

Further, in the method for producing a silicon carbide based material according to the present invention, carbon produced by thermal decomposition of a gas containing a hydrocarbon gas or a halogenated hydrocarbon gas is added to the porous body of synthetic quartz glass. Since the porous silicon carbide material obtained by precipitating with a continuously changing amount in a certain direction and then firing is filled with metallic silicon,
A dense silicon carbide material can be easily obtained.

In the production of the silicon carbide material described above, the bulk density of the synthetic quartz glass porous body is xg / cm.
^In the case of ^3, the amount of carbon deposited on the surface satisfies the following formula, so that a silicon carbide-based material whose surface after silicon impregnation is substantially formed of silicon carbide is obtained,
The surface is not attacked by HCl gas or HF-NO ₃ solution.

Y ≧ 4.78 / x + 2 (y: carbon / silicon dioxide molar ratio, 0 <x <2.3) Therefore, a process used for a semiconductor manufacturing jig, for example, thermal diffusion treatment of a silicon wafer. It is possible to provide a high-purity silicon carbide material useful for heat-resistant jigs such as tubes and wafer boards, which is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a silicon carbide based material according to the present invention and a diagram showing changes in a silicon / silicon carbide composition ratio in a radial direction.

FIG. 2 is a cross-sectional view of a silicon carbide based material in a comparative example and a diagram showing changes in the silicon / silicon carbide composition ratio in the radial direction.

FIG. 3 is a cross-sectional view of a silicon carbide based material in another comparative example and a diagram showing changes in the silicon / silicon carbide composition ratio in the radial direction.

FIG. 4 is a conceptual diagram for explaining a process for producing a silicon carbide based material.

Claims (4)

[Claims] 1. A silicon carbide-based material, characterized in that the composition ratio of silicon and silicon carbide continuously changes in a certain direction. 2. The silicon carbide based material according to claim 1, wherein the surface of the silicon carbide based material is substantially silicon carbide. 3. Precipitation of carbon produced by thermal decomposition of a gas containing a hydrocarbon gas or a halogenated hydrocarbon gas in a porous body of synthetic quartz glass in an amount that continuously changes in a certain direction. A method for producing a silicon carbide-based material, which comprises filling the porous silicon carbide material obtained by firing and then filling with metallic silicon. 4. The bulk density of the synthetic quartz glass porous body is xg.
/ Cm ^3, the amount of carbon deposited on the surface thereof satisfies the following formula: y ≧ 4.78 / x + 2 (y: molar ratio of carbon / silicon dioxide, 0 <x <2.3)