JPH08188408A - Silicon carbide molded product by chemical vapor deposition and its production - Google Patents

Abstract

PURPOSE: To obtain a CVD-SiC molded product prevented from the generation of cracks and warpage, and further to provide a method for producing the same. CONSTITUTION: A SiC molded product by the CVD method, wherein SiC films are formed on both the sides of an SiC substrate formed by the CVD method. The method for producing the SiC molded product comprises forming a SiC film on the surface of the substrate by the CVD method, removing the substrate, and further forming the SiC films on both the sides of the obtained SiC substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide molded body by a chemical vapor deposition (CVD) method and a method for manufacturing the same, and particularly various characteristics such as high purity, compactness, heat resistance and chemical resistance are required. The present invention relates to a silicon carbide molded body that can be suitably used as a member and a method for producing the same. More specifically, a member for carrying a wafer such as silicon, a dummy wafer for epitaxial growth or plasma CVD, a monitor wafer,
Various members used during semiconductor manufacturing such as susceptors and sputtering targets, various furnace members used in CVD furnaces, PVD furnaces, ceramic sintering furnaces, heat treatment furnaces, high-purity furnaces, jigs for chemical resistance, analysis TECHNICAL FIELD The present invention relates to a silicon carbide molded body suitable for containers and the like and a method for producing the same.

[0002]

2. Description of the Related Art Silicon carbide is excellent in heat resistance and chemical stability, and is frequently used as various members mainly used for manufacturing semiconductors. Such a material mainly composed of silicon carbide includes a method of reacting a carbon material with silicon monoxide gas to form silicon carbide, a method of impregnating a carbon material with metallic silicon and heating it to form silicon carbide, or It can be produced by a method of mixing silicon powder and a sintering aid and sintering. However, the silicon carbide-based material produced by these methods is poor in denseness, and thus fine particles are easily generated from the surface. for that reason,
It easily causes contamination of products such as semiconductors. On the other hand, CV
Since the silicon carbide film formed by the D method is dense and has a high purity, a carbon material, ceramics, or the like is used as a substrate, a silicon carbide film is formed on the surface by the CVD method, and then the substrate is removed to remove carbonization. There is a method for producing a silicon molded body (JP-A-5-124863, JP-A-5-124864,
JP-A-5-90184).

In order to obtain a silicon carbide compact (hereinafter also referred to as a CVD-SiC compact) by this CVD method,
Although the substrate must be removed without fail, this CVD-S
Since the iC molded body is mainly used when manufacturing a semiconductor, it is necessary to remove the substrate so as to reduce the warpage and the amount of impurities. Usually, a carbon material is used as a base material and is burned to remove it, or a material having a coefficient of thermal expansion greatly different from that of SiC is used as the base material and is removed by utilizing the difference in thermal expansion coefficient,
The substrate is removed by a method such as grinding or cutting which is performed by machining.

[0004]

[Problems to be Solved by the Invention] However, CVD
When a SiC compact is manufactured by vapor-depositing SiC on the surface of a substrate by a method to form a film and then removing the substrate,
Since internal stress such as tensile stress or compressive stress is generated in the film as the crystal grains forming the C film grow, when the film becomes thick,
Even if the substrate was removed by various methods, cracks were generated in the SiC molded body and only the SiC molded body having a convex warped surface was obtained. To show this, S
FIG. 2 shows a schematic conceptual view when the iC film is formed on the surface of the substrate and the substrate is removed. S is formed on the surface of the substrate A by the CVD method.
When the iC film 21 is formed, first the SiC is formed on the surface of the base A.
Nuclei (not shown) are generated, and substantially columnar SiC crystal grains 21a grow in the direction perpendicular to the surface of the substrate A [(i) in the figure]. Then, when the film formation is continued as it is, the columnar SiC crystal grains 21a gradually grow so that the columns become thicker and have a cone shape 21b [(i)
i)]. At this time, the other cone-shaped SiC crystal grains 21b adjacent to each other push the SiC film 21, so that the SiC film 21 accumulates an internal stress to spread the film surface. As a result, even if the substrate A was removed by various methods, only the SiC molded body B having a crack or a convex warped surface could be obtained in the obtained SiC molded body [FIG.
ii)]. Further, the thickness required for this type of SiC molded body is usually 500 to 3000 μm, and even with this thickness, cracks may occur or the amount of warpage may increase.

Therefore, the present invention is a CV in which cracks and warpage are suppressed.
An object is to provide a D-SiC compact and a method for manufacturing the same.

[0006]

In order to achieve the above object, the CVD-SiC compact according to the present invention has a SiC film formed on both sides of a SiC substrate formed by a CVD method. In addition, the manufacturing method is such that CV
A SiC film is formed by the D method, and the SiC film is further formed on both surfaces of the SiC substrate obtained by removing the base body. In these cases, the thickness of the SiC substrate is optimally 300 μm or less.

The CVD-SiC compact according to the present invention will be described according to its manufacturing method. A schematic conceptual diagram of the manufacturing method of the present invention is shown in FIG. C on the surface of a substrate A made of carbon material or the like
The SiC film 11 for a substrate is formed by the VD method [(i) in the figure]. The optimum film thickness is 300 μm or less. Then, the base A is removed to obtain the SiC substrate 10 [(ii) in the figure]. Then, CVD is performed on both the upper surface and the lower surface.
Method to form the SiC films 12 and 13 with substantially the same thickness,
The SiC molded body B having a small warpage is formed [see the same figure (ii
i)]. In addition, 12 is a SiC film formed on the lower surface of the SiC substrate 10 (the surface that was in contact with the base), and 13 is a SiC film.
The SiC film formed on the upper surface of the substrate 10 (the surface on which the film was grown) is shown. Here, although not shown in this figure, the processing of the product shape is performed by the SiC molded body B having a desired thickness.
I'm going after I got. Of course, the SiC substrate 10
Is processed into a product shape in advance, and then the SiC film 12,
13 may be formed and processed into a desired thickness or a desired shape.

The present invention will be described in more detail below.

[0009]

The substrate for forming the SiC film for the substrate may be ceramics or the like, but the adhesion to the SiC film,
A carbon material is suitable in terms of purity and easy removal of the substrate.
Hereinafter, the carbon material will be described as a substrate. There is no limitation on the carbon material used as the substrate, and any carbon material such as so-called isotropic graphite or anisotropic graphite may be used. The thickness of the carbon substrate may be such that the carbon substrate does not warp due to the formation of the SiC film for the substrate. Usually, it is sufficient to use a material having a thickness of 5 mm or more, but if it is too thick, it takes time to remove the base material, so that a carbon material having a thickness of 5 to 20 mm is preferably used as the base material.

When forming a SiC film for a substrate,
In order to prevent impurities from volatilizing and diffusing from the carbon substrate and contaminating the film, the purity of the carbon substrate is ash value (JIS R7
It is particularly preferable that the ash value measured according to 223) is 20 mass ppm or less, and most preferably 5 mass ppm.
The following carbon materials are preferably used as the base. The bulk density of the carbon substrate is not limited, and it is usually preferable to use one having a bulk density of 1.6 to 1.9 g / cm ³ . Further, the cumulative pore volume (cumulative pore volume measured by mercury porosimetry at a pore radius of 0.01 to 10 μm) and average pore radius (pore radius corresponding to 1/2 of the cumulative pore volume) are not restricted. However, in order to be a substrate having adhesiveness with respect to the SiC film,
0 × 10 ^{−2 to} 10.0 × 10 ⁻² cm ³ / g and 1.
It is preferable to use a carbon material of 0 to 5.0 μm as a base.

Further, since the SiC film formed by the CVD method has a thermal expansion coefficient of 3.5 × 10 ⁻⁶ / K (room temperature to 673K), a carbon material having a thermal expansion coefficient close to this value is used for the substrate. Is preferred. Especially the coefficient of thermal expansion is 3.0 × 1
The carbon material of 0 ^{−6 to} 4.0 × 10 ⁻⁶ / K (room temperature to 673 K, parallel to the surface to be deposited) is most suitable. The reason is that when a SiC film is formed on a carbon material in which the thermal expansion coefficient of the carbon substrate exceeds 4.0 × 10 ⁻⁶ / K (room temperature to 673K), the difference in thermal expansion coefficient between the two becomes large, so that when cooled. A compressive stress is applied to the SiC film, a crack is generated when the substrate is removed, or the obtained SiC body for a substrate is greatly warped, which may make it unsuitable as a SiC substrate. Similarly, the coefficient of thermal expansion of the substrate is 3.0 × 10 ^−6.
/ K (room temperature to 673K) when using a carbon material, S
Tensile stress is applied to the iC film, causing cracks and warpage, and
It may not be suitable as an iC substrate. For this reason, the coefficient of thermal expansion is 3.0 × 10 ^{−6 to} 4.0 × 1.
It is better to use a carbon material of 0 ⁻⁶ / K (room temperature to 673K) as the base.

As the carbon substrate, a carbon substrate which has been processed so that a SiC substrate having a desired shape can be easily obtained is used. For example, when a CVD-SiC compact for a dummy wafer having an orientation flat is manufactured, it is preferable to use a substrate whose outer shape is processed according to the dummy wafer shape. In the case of producing a CVD-SiC molded body having a concave or convex portion, the appearance shape of the substrate is adjusted to the shape and the surface to be vapor-deposited is provided with unevenness opposite to the unevenness of the member. The work such as machining after removing the substrate is omitted, and the SiC molded body is made to have a desired product shape as easily as possible.

On the surface of such a carbon substrate, S is formed by the CVD method.
iC is vapor-deposited to form a SiC film for the substrate. This film formation may be carried out by a conventional method, and usually 1000 to 180 under reduced pressure.
Under a temperature condition of 0 ° C., a SiC film can be formed by using a gas (raw material gas) serving as a Si source and a C source, and if necessary, H ₂ and Ar (carrier gas). As the source gas, CH ₃ SiCl ₃ , (CH ₃ ) ₃ SiC
l or other organic silane compound, or SiC as a Si source
l ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiH _4, etc., and CCl ₄ , CH ₄ , C ₃ H ₈ , C ₆ H ₁₄ as a C source.
It can be used by appropriately combining from the above. In vapor deposition, if the film formation is performed under a diffusion-controlled temperature condition such that the temperature exceeds 1300 ° C., the SiC nuclei attached to the protrusions, which are advantageous for diffusion, grow faster.
It becomes difficult for SiC crystal grains of uniform size to grow, and it is difficult to obtain a uniform film. Moreover, the warp becomes large, which is not suitable for the present invention. Therefore, it is optimal to perform the film formation at a temperature of 1300 ° C. or lower during vapor deposition. If the temperature is lower than this temperature, the temperature condition becomes almost rate-determining the surface reaction. At this time, when a carbon substrate having an ash content of 20 mass ppm or less is used, the SiC film for a substrate becomes a high-purity film having a purity of 99.99% or more, which is suitable for a jig for semiconductor manufacturing. The formed SiC film is composed of β-SiC which is dense and tends to be highly pure.

The SiC film for a substrate is optimally formed so that an SiC substrate having a thickness of 300 μm or less can be obtained.
This is because when the film thickness exceeds 300 μm, the internal stress accumulated in the film becomes significantly large and the size of the crystal grains becomes non-uniform, so that the obtained SiC substrate has a large warp or a uniform SiC substrate is obtained. This is because it may not be obtained and may not be suitable as a SiC substrate. On the other hand, the lower limit of the thickness of the SiC film for a substrate is not particularly limited, but if the SiC substrate has a thickness of less than 200 μm, the strength becomes insufficient, so that a crack may occur during the removal of the carbon substrate, or an S
When the SiC film is formed on both surfaces of the iC substrate, the SiC film may be largely warped. Therefore, the SiC film for a substrate is usually formed so that a SiC substrate having a thickness of 300 μm or less, most preferably 200 to 300 μm can be obtained.

Then, the carbon substrate is removed to obtain a SiC substrate.

Here, SiC formed by the CVD method
Since the surface of the film has irregularities to some extent, when the film is formed using the SiC substrate in this surface state, the above-mentioned irregularities clearly appear, and internal stress is generated or the heterogeneous film is formed. Leads to the formation of. Therefore, it is preferable to flatten the surface of the SiC substrate by polishing or the like. In this case, the surface roughness Rmax and Ra (JIS
Centerline average roughness measured according to
It is optimal to flatten the surface so that it is below μm and below 2 μm. Usually, if SiC having a thickness of 5 to 15 μm is removed from the surface, it is possible to obtain such a surface roughness.

The removal of the carbon substrate may be carried out by a conventionally used method. The carbon substrate is removed by a grinding process such as a surface grinding, an outer surface grinding, an inner surface grinding, a coreless grinding or a cutting process. Or, a carbon substrate is, for example, 500 to 900.
The method of burning at ℃ and removing (ashing method) can be illustrated. In order to prevent the resulting SiC substrate from being contaminated during mechanical processing such as grinding or cutting,
Using a tool made of high-purity diamond or high-purity silicon carbide, etc., a wet grinding machine that uses a grinding fluid to prevent alteration and cracking of the film surface due to localized high temperatures in the grinding and cutting parts. It is preferable to carry out.

The SiC substrate removed from the substrate is formed into a desired product shape by machining, if necessary. The carbon base may be removed at the same time as this product shape processing.

In addition, since the SiC substrate may be contaminated by a machining process such as the removal of the substrate or the formation of a desired product shape, some impurities may remain on the surface of the SiC substrate.
It is preferable to purify the iC substrate. This purification treatment is performed by dipping in hydrofluoric acid, nitric acid, hydrofluoric nitric acid, etc., and then washing and then drying (wet method), or chlorine gas (Cl ₂ ) under conditions of 1000 to 1500 ° C. and pressure of 0.1 to 100 Torr.
It may be performed by a method (dry method) for performing a purification treatment by. Of these, the dry method is a method that does not require drying of the member and can be purified particularly well.

SiC films are further formed on the upper and lower surfaces of the thus obtained SiC substrate by the CVD method. As the method for forming the SiC film, it is sufficient to form the SiC film by the conventional method as described above. At this time, the thickness of the film to be formed should be equal to or larger than the thickness of the desired product. If the film is formed to a thickness exceeding the desired thickness, the thickness of the film is reduced by polishing, etc. You can put it on your body.

In the case where the SiC molded body is used for an application requiring higher purity, the above-mentioned purification treatment may be applied to this SiC molded body.

[0022]

As described above, the main operation of the present invention is as follows.

When SiC is vapor-deposited by the CVD method, Si atoms and C atoms adsorbed on the surface are diffused toward a stable lattice point, and by combining with other atoms, crystal nuclei are generated to grow into crystal grains. However, in the initial stage of vapor deposition, the SiC crystal grains grow in a substantially columnar shape, and become a cone-shaped crystal grain in which the columns gradually become thicker as the growth progresses. Therefore, S to be formed
As the iC film becomes thicker, more internal stress for spreading the film surface is accumulated. Further, the crystal grains that have grown in this way have various sizes depending on the growth rate of each crystal grain, and the film surface becomes uneven. Therefore, with the conventional manufacturing method, it is not possible to suppress the occurrence of cracks or warpage, and it has not been possible to manufacture a uniform SiC body. Therefore, in the present invention, the SiC film is not formed to a desired thickness all at once, but is stopped midway.
Try to minimize the internal stress accumulated in the film.
Further, by stopping the film formation on the way, the sizes of the crystal grains can be made uniform, and the degree of unevenness on the film surface can be reduced. After forming such a SiC film, the carbon substrate is removed to obtain a SiC substrate. And this S
By forming the SiC film on both the upper surface and the lower surface of the iC substrate, it is possible to cancel the warpage caused by the film formation. Further, by adjusting the film thicknesses formed on the upper surface and the lower surface, respectively, the warp originally generated in the SiC substrate can be corrected, and the SiC with a very small warp can be corrected.
It is also possible to obtain a molded body. For example, if the upper surface of the SiC substrate has a slightly convex warp, the warp can be corrected by forming more SiC film on the lower surface than on the upper surface. As a result, the film formed on the upper surface and the film formed on the lower surface have almost the same thickness or have a slightly thicker film on the lower surface. In addition, this film formation also has a function of masking impurities attached to the SiC substrate.

[0024]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 As a substrate, isotropic graphite (dimensions: diameter φ120 × thickness 10)
mm, bulk density 1.85 g / cm ³ , surface roughness Rmax
20 μm, thermal expansion coefficient 3.5 × 10 ⁻⁶ / K (room temperature to 6
73 K), cumulative pore volume 6.6 × 10 ⁻² cm ³ / g,
An average pore radius of 1.8 μm and an ash content of 10 mass ppm) and a thickness of 20 at 1000 to 1300 ° C. by a CVD method.
A SiC film for a substrate having a thickness of 0 μm was formed. 80 in the air
The isotropic graphite substrate was removed by holding at 0 ° C. for 24 hours (ashing method) to obtain a 200 μm thick SiC substrate. After that, the upper surface and the lower surface of this SiC substrate are subjected to 650 by a CVD method.
A SiC film with a thickness of 1500 μm is formed by forming a SiC film for each μm.
A D-SiC compact was obtained. By wet grinding this,
Grinding the same amount from both sides, diameter φ100 × thickness 800 μm
Shape, and φ-inch dummy wafer CVD-SiC
A molded body was manufactured.

Example 2 Example 1 was repeated except that the thickness of the SiC film for the substrate and the SiC substrate was 260 μm, and the film thicknesses formed on the upper and lower surfaces were 620 μm each to produce a 1500 μm thick CVD-SiC compact. A φ4 inch dummy wafer CVD-SiC compact was manufactured in the same manner as described.

Example 3 For a φ4-inch dummy wafer in the same manner as in Example 1, except that the thickness of the SiC film for the substrate and the SiC substrate was 300 μm, and the film thicknesses formed on the upper surface and the lower surface were each 600 μm. A CVD-SiC compact was manufactured.

Example 4 For a φ4-inch dummy wafer in the same manner as in Example 1 except that the thickness of the SiC film for the substrate and the thickness of the SiC substrate were 500 μm, and the film thicknesses formed on the upper surface and the lower surface were each 500 μm. A CVD-SiC compact was manufactured.

Comparative Example 1 The same isotropic graphite as described in Example 1 was used as a substrate, and C was used.
Thickness 800 μm at 1000-1300 ° C. by VD method
Was formed. Then, the isotropic graphite substrate was removed by holding at 800 ° C. for 24 hours (ashing method) to manufacture a CVD-SiC compact for φ4 inch dummy wafer.

CVs obtained in Examples 1 to 4 and Comparative Example 1
The amount of warpage of the D-SiC molded body was measured by observing its appearance and using a three-dimensional shape measuring instrument. Table 1 shows the results. As can be seen from this table, the CVD-
No cracks were generated in the SiC compact. In particular, in the case of Examples 1 to 3 in which the thickness of the SiC substrate was 200 to 300 μm, the amount of warpage was extremely small, 0.10 mm or less, and an optimum CVD-SiC compact could be obtained. On the other hand, the CVD-S obtained in Comparative Example 1
The iC molded body had cracks because the warp amount was too large.

[0031]

[Table 1]

Further, the thickness of the SiC film for the substrate and the SiC substrate is set to 250 μm, and 1500 μm is formed on the upper surface and the lower surface.
A SiC film having a thickness of 3250 μm is formed by CVD-S.
Even when the iC molded body was manufactured, a CVD-SiC molded body having a very small warp of a warpage amount of 0.05 mm could be manufactured without cracking unlike the conventional method.

[0033]

When the CVD-SiC compact is constructed as in the present invention, the amount of warpage becomes extremely small. For this reason, for example, the adhesiveness with the contacting counterpart member is increased, and heat or the like is evenly transferred. Further, according to the manufacturing method of the present invention, CVD-S in which cracks do not occur and the amount of warpage is small
An iC molded body can be obtained. According to the invention, a thickness of 5
A CVD-SiC compact having a thickness of 00 μm or more could be made extremely small in warpage without causing cracks.

[Brief description of drawings]

FIG. 1 is a schematic conceptual view of a CVD-SiC compact and a method for manufacturing the same according to the present invention.

FIG. 2 is a schematic conceptual view of a conventional CVD-SiC compact and a method for manufacturing the same.

[Explanation of symbols]

 10 SiC substrate 11 SiC film for substrate 11a Crystal grain of SiC film for substrate 12 Lower surface SiC film 12a Lower crystal grain of SiC film 13 Upper surface SiC film 13a Upper crystal grain of SiC film 21 SiC film 21a Crystal grain of SiC film 21b SiC film Cone-shaped crystal grains A Base B CVD-SiC compact

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C23C 16/42 16/56 H01L 21/203 S 21/205

Claims (3)

[Claims] 1. A silicon carbide formed body by a chemical vapor deposition method, which has a silicon carbide film on both surfaces of a silicon carbide substrate formed by the chemical vapor deposition method. 2. A silicon carbide film is formed on a surface of a substrate by a chemical vapor deposition method, and a silicon carbide film is further formed on both surfaces of a silicon carbide substrate obtained by removing the substrate. A method for producing a silicon carbide molded body by a vapor deposition method. 3. The silicon carbide substrate has a thickness of 300 μm
The following is a silicon carbide molded body by the chemical vapor deposition method according to claim 1 or 2, or a method for producing the same.