JPH0583517B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a graphite-silicon carbide composite and a method for producing the same, and in particular, the surface layer of a graphite base material is a composite of graphite and silicon carbide, and silicon carbide is further formed on the surface layer of the graphite base material. It relates to a coated composite and a method for producing the same, the purpose of which is to provide oxidation- and corrosion-resistant structures used in the manufacturing process of integrated circuits, particularly for processing semiconductor wafers, susceptors for epitaxial growth, and diffusion furnaces. parts, plasma CVD parts,
An object of the present invention is to provide a composite material suitable for boats and the like. [Prior Art] Structural materials in which the surface of a graphite base material is coated with a silicon carbide layer are known. In such a silicon carbide-coated graphite composite material, a graphite base material having a thermal expansion coefficient close to that of silicon carbide and having small pores on the graphite surface has been used. The reason for this is that if a material whose thermal expansion coefficient is not close to that of silicon carbide is used, peeling or cracking will occur between the graphite and silicon carbide, and if the pores are large, pinholes will occur. Several techniques have already been proposed to alleviate these problems. For example, in Japanese Patent Publication No. 48-26597, it is proposed to provide an intermediate layer consisting of silicon carbide (hereinafter sometimes referred to as SiC) and graphite, and the thickness of the intermediate layer is limited to 50 to 100 μm. There is. Furthermore, in JP-A No. 49-83706, by infiltrating molten silicon into a graphite base material having pores of 5 μm or less, the silicon and graphite react to form SiC, and all the pores are sealed with silicon carbide. It is disclosed that a composite material is obtained. The thickness of the composite layer at this time is 0.125 mm or more. Further, in Japanese Patent Application Laid-Open No. 130363/1983, it is proposed to form an intermediate layer of pyrolytic carbon with a thickness of 10 to 100 μm. [Problems to be Solved by the Invention] However, the graphite-silicon carbide composite substrates proposed above still do not have satisfactory performance and cannot be formed under harsh conditions such as rapid heating and cooling.
Cracks and peeling of the SiC film occur, and pinholes are still quite common. Moreover, with recent technological advances, increasingly harsh conditions are required, and there is an ever-increasing demand for solutions to the above-mentioned problems. For example, in Special Publication No. 48-26597,
The thickness of the intermediate layer in the SiC-graphite mixture is 50~
Since the thickness is limited to 100 μm, if a thin graphite base material is used, cracks and deformation will occur, and if a thick base material is used, pinholes, peeling, etc. will occur. In JP-A No. 49-83706, the thickness of the silicon carbide layer infiltrated into the graphite is set to 0.125 mm or more, which causes the same problem as above, and furthermore, sealing the graphite pores with silicon carbide is not suitable for the graphite base material. When it becomes silicified, it expands, causing cracks and deformation, making it impractical. Furthermore, in JP-A-50-130363, it is extremely difficult to make the thermal expansion coefficient of pyrolytic carbon close to that of silicon carbide, 4.4×10 ^-6 /K, and it is difficult to avoid peeling of the silicon carbide film. . [Means for Solving the Problems] The present inventors investigated various problems faced by the above-mentioned conventional technology and found that when the graphite surface is reacted with molten silicon, the molten silicon permeates through the graphite pores and binds the binder. It was found that some of the aggregate graphite was silicified. In particular, it has become clear that the impregnation rate of the total pore volume of graphite is correlated with the pore radius and the coefficient of thermal expansion. It has been found that by effectively utilizing these phenomena, a graphite-silicon carbide composite for silicon carbide coating without pinholes, peeling, and cracks in the silicon carbide coating can be obtained, and the conventional problems can be solved. The present invention was completed based on this new fact, and the present invention consists of a graphite-silicon carbide composite in which the surface layer of a graphite base material is impregnated with silicon carbide, and then silicon carbide is coated thereon. This relates to its manufacturing method. [Operation] When the graphite surface is reacted with molten silicon as in the present invention, the molten silicon penetrates into the pores of the graphite, and a portion of the graphite becomes silicon carbide (this reaction is called an impregnation treatment).
Through this reaction, graphite base materials having various coefficients of thermal expansion converge to the coefficient of thermal expansion of silicon carbide (4.4×10 ⁻⁶ /K). The pore radius and pore volume also become smaller. These things can be done using chemical vapor deposition method (hereinafter referred to as
When coating silicon carbide using the CVD method, the former has the effect of preventing peeling and cracking.
The latter has the effect of preventing pinholes from forming. However, impregnation of silicon carbide accounts for 5% of the total pore volume.
%, it is difficult to approximate the thermal expansion coefficient, and the pore radius is also difficult to be less than 1 μm, which causes pinholes. If it exceeds 60%, the coefficient of thermal expansion will be similar, but the graphite base material will tend to deform or crack due to volumetric expansion. Therefore, in order to exhibit the above-mentioned effects of the present invention particularly markedly, 5 to 60% of the total pore volume of the graphite base material used should be impregnated with silicon carbide. The present invention will be explained below according to its manufacturing method. The basic principle of the present invention is to infiltrate molten silicon into a graphite base material and carry out a reaction.
The graphite base material used at this time is preferably one with relatively low porosity, and usually has a bulk density of 1.70 to 1.70.
1.90 g/cm ³ , a total pore volume of 10-20 cm ³ /g and an average pore radius of 1.0-2.0 μm graphite substrate is used. However, each of the above characteristics indicates the following. Bulk density: mass per total volume of graphite base material (g/
cm ³ ) Porosity: Percentage of total pores in the volume of graphite substrate True specific gravity - Bulk density / True specific gravity x 100% Total pore volume: Total volume of open pores determined by Hg porosimeter (Hg intrusion method) (cm ³ / g) Average pore radius: Average pore radius of pore volume determined from Hg porosimeter (μm) Furthermore, in the present invention, by using a highly purified graphite base material, a composite material with even higher purity can be obtained. can be obtained. The purity of the high-purity graphite base material is preferably one containing impurities (ash) of 10 ppm or less, particularly preferably 2 ppm or less. The method for high purification is not particularly limited, and various methods can be arbitrarily applied. The preferred method is
An example of this method is the method described in No. 61-224131. As for the silicon, not only the graphite base material is immersed in molten metal silicon, but also silicon may be formed on the graphite base material by a CVD method or silicon vapor, and then the silicon may be melted and reacted. However, since it is difficult to control the impregnation rate with the molten silicon immersion method, the CVD method is preferable. In the present invention, when reacting silicon and a graphite base material, in particular, 5 to 50% of the total pore volume of the graphite base material
Adjust so that 60% is impregnated with silicon carbide. 5
As mentioned above, the thermal expansion coefficients of silicon carbide and graphite are not close to each other, and the pore radius is not small, causing pinholes, peeling, cracks, etc. Then, the graphite base material deforms and cracks occur due to volumetric expansion. For the reaction between silicon and graphite base material, there is a method of immersing the graphite base material in molten silicon to react;
The surface of the graphite base material may be coated with silicon by CVD or silicon vapor, and then heat treated at a temperature equal to or higher than the melting point of silicon. The CVD method uses halogenated silanes such as SiCl ₄ or SiHCl ₃ or SiH ₄ and performs chemical vapor deposition on a graphite substrate at 1300 to 1600 K with hydrogen as a carrier gas, producing a uniform Si film. . Subsequently, heat treatment is performed at a temperature higher than the melting point of silicon, preferably 1750 to 1900K, and the coated silicon is heated.
More than 90% of it penetrates into the pores of graphite and becomes silicon carbide. As shown in the reference photograph, the graphite-silicon carbide composite material thus obtained has a substantially uniform surface layer consisting of graphite and silicon carbide. However, the reference photograph is a scanning electron micrograph (100x magnification) of a cross section of the composite material produced in Example 1, and the white part is silicon carbide, and the black part is graphite. In the present invention, after forming a molten silicon carbide layer on a graphite base material, a layer of molten silicon carbide is further applied on the graphite base material by a conventional method.
It is to perform SiC coating. That is, in the present invention, since the surface of the composite material before SiC coating is made of a composite layer of graphite and silicon carbide, when SiC coating is applied on top of this, an extremely strong SiC coating is formed. . The result is a three-layer composite material that is extremely resistant to thermal shock and completely free of pinholes. Such three-layer composites further coated with SiC have the above-mentioned properties and are therefore useful for example in oxidation- and corrosion-resistant structures used for processing semiconductor wafers during integrated circuit (IC) manufacturing processes, epitaxy, etc. It is an extremely suitable material for susceptors for barrel growth, parts for diffusion furnaces, parts for plasma CVD, boats, etc. The means for forming the SiC layer, which is the third layer, is not limited in any way, and any of the various conventionally known means can be effectively used, and one example is a coating method using the CVD method. More specifically, halogenated silanes such as SiCl ₄ and SiHCl ₃ , SiH ₄ and hydrocarbons such as CH ₄ and C ₃ H ₈ , or CCl ₄
etc. into the furnace using hydrogen as a carrier,
Or organic silane gas such as CH ₃ SiCl ₃ or quartz.
The vapor deposition may be performed using carbon-based SiO gas or the like. [Example] Next, an example will be described. Examples 1 to 3 High purity graphite (bulk density 1.78 g/cm ³ , average pore radius 1.4 μm, total pore volume 0.085 cm ³ /g, thermal expansion coefficient
4.0×10 ^-6 /K) was processed into a diameter of 100 mm and a thickness of 5 mm. This graphite base material is heated to a temperature of 1400K, and SiCl ₄
0.9×10 ⁻² mol/min and H ₂ 0.9 mol/min were flowed to perform silicon coating. Furthermore, the temperature was raised to 1800K while flowing H ₂ at 0.05 mol/min, and the mixture was heated for 1 hour.
The silicon coating time was determined based on the impregnation rate of silicon carbide with respect to the total pore volume. As a result, three types of samples with silicon carbide impregnation rates of 5, 30, and 60% were obtained. The thermal expansion coefficient and pore radius of these samples were measured. The results are shown in Table 1. Next, the obtained graphite-silicon carbide composite was
Heated to 1500K, SiCl ₄ 0.9×10 ^-2 mol/min, H ₂
1.8 mol/min, C ₃ H ₈ 1.3×10 ^-3 mol/min for 90 minutes,
Furthermore, coating was carried out for 90 minutes by changing the fulcrum between the base material and the support in the furnace. The film thickness was calculated from the weight increase to be 100 μm. Comparative Examples 1 to 3 In the above examples, the silicon carbide impregnation rate was 0,
0.2 and 80%, and everything else was treated in the same manner as in the example. The results are shown in Table 1. The samples obtained in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to a running test (heated in air at 90°C for 35 hours) and a thermal shock test (held in an electric furnace heated to 450°C for 30 minutes). Then, the test was immersed in water, and the checking operation (cracking, etc.) was repeated 10 times. The results are shown in Table 2.

【table】

〔Effect of the invention〕

The silicon carbide-coated graphite, which is obtained by coating the graphite-silicon carbide composite material of the present invention with silicon carbide, has no pinholes and has very little peeling or cracking, making it extremely suitable as a material for manufacturing semiconductors and various other products, and is suitable for industrial use. The utility value of the above is high.

Claims (1)

[Scope of Claims] 1. An impregnated silicon carbide layer in which 5 to 60% of the total pore volume of the graphite base material is impregnated with silicon carbide on the surface layer of the graphite base material, and a further carbonized layer on this impregnated silicon carbide layer. A graphite-silicon carbide composite having a silicon coating layer. 2. Infiltrate and react with molten silicon so that 5 to 60% of the total pore volume of the graphite base material is impregnated with silicon carbide, and then further carbonize the graphite and silicon carbide composite layer formed here. A method for producing a graphite-silicon carbide composite according to claim 1, which comprises coating silicon.