JPH10245266A - Purification of silicon carbide-based molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove impurities in a molded product without causing the deterioration in strength of the molded product itself according to a simple method by forming an Si membrane on the surface of a silicon carbide-based molded product according to a chemical vapor deposition(CVD) method, then heat-treating the formed membrane, diffusing and adsorbing the impurities into the Si membrane and removing the whole membrane by an etching method. SOLUTION: The surface of a silicon carbide-based molded product having the surface comprising silicon carbide is coated with an Si membrane according the a CVD method and the formed membrane is then heat-treated at >=1,000 deg.C for several to some ten hr to diffuse and adsorb impurities in the interior of the molded product into the Si membrane. The whole Si membrane into which the impurities are diffused and adsorbed is subsequently removed by a dry or a wet etching method. A mixed gas containing a halogen is preferably used as a washing medium in the dry etching method and a solution containing the halogen is preferably used as a washing medium in the wet etching method. The silicon carbide-based molded product obtained by the method is suitably used as a constituent member for producing semiconductors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing impurities inside a silicon carbide molded article suitable as a component for manufacturing semiconductors by a simple method and efficiently without lowering the strength of the molded article itself. The present invention relates to a method for increasing the purity of a molded article.

[0002]

2. Description of the Related Art In general, lightweight, high-strength, heat-resistant materials such as core tubes for semiconductor manufacturing, liners, boats, and other components are commonly used.
A silicon carbide molded body (hereinafter referred to as “Si
It is referred to as "C molded body". ) Is used. However, the SiC molded body generally has a high porosity, and the amount of impurities retained therein is much larger than that of a quartz glass-made semiconductor manufacturing component. If it is applied, there is a disadvantage that impurities retained inside the semiconductor during manufacturing thereof diffuse to the outside and contaminate the semiconductor.

Therefore, various proposals have been made in order to improve such disadvantages. The direction of the proposal can be broadly divided into two. One is a means for preventing impurities from diffusing as much as possible from the silicon carbide molded body as a constituent member during semiconductor production, and the other is a means for removing impurities from the silicon carbide molded body as a constituent member before semiconductor production. And
It is a means to keep high purity.

[0004]

As the former means, for example, as disclosed in Japanese Patent No. 2548949, a silica film and a CVD-film are formed on the surface of a SiC molded body (substrate).
There has been proposed a constituent member for semiconductor manufacturing in which a SiC coat film is formed by lamination. However, the substrate, the silica film and the CVD-S
Due to the fact that the thermal expansion coefficients of the iC coat films are slightly different, and the thermal expansion coefficient difference itself varies, the silica is removed from the SiC molded body (substrate) during the heat cycle during semiconductor manufacturing. Membrane and CV
There is a problem that the D-SiC coat film is easily peeled irregularly. Of course, once delamination occurs, the semiconductor is contaminated and the life of the component ends there. The occurrence of such a situation ultimately leads to a decrease in the productivity of the semiconductor product and an increase in the production cost.

[0005] The latter means can be broadly divided into a wet cleaning method and a dry cleaning method. In the wet cleaning method, although alkalis and the like among impurities can be largely removed by HF-HNO ₃ treatment, it is extremely difficult to remove heavy metals such as Fe. In addition, there are drawbacks in that the number of cleaning steps is very large and complicated work is required.

On the other hand, the dry cleaning method requires a small number of steps and improves the efficiency of removing impurities such as Fe. However, this can only be said as to the efficiency of removing impurities in the vicinity of the surface of the substrate, and the internal cleaning method is employed. Since the efficiency of removing the impurities is very poor, the impurities are also diffused during the manufacture of the semiconductor, and the semiconductor is contaminated. In addition, in order to remove impurities inside the SiC molded body (substrate), a high-temperature halogen gas must be kept flowing for a very long time. However, the substrate itself is attacked and its strength is reduced. There is a problem that the life as a member is shortened. It is also very uneconomical.

The present invention has been made in view of the above circumstances, and an object of the present invention is to remove impurities inside a SiC-based molded body suitable as a component for manufacturing a semiconductor by a simple method and with a compact. Productivity and economics of semiconductor manufacturing by using a component made of a SiC-based molded body that is efficiently removed beforehand without lowering its strength and that is highly purified to a level commensurate with the semiconductor level. The point is to provide technology that can enhance

[0008]

According to the present invention, which has attained the above objects, the present invention provides a purification method in which a Si film is formed on a surface of a SiC material formed of SiC by a CVD method. After coating, heat treatment is performed to diffuse and adsorb impurities inside the compact or graphite body into the Si film, and the whole of the diffused and adsorbed Si film is removed by a dry or wet etching method. As a result, impurities can be removed very efficiently in a simple process and without lowering the strength of the SiC-based molded body itself, so that an ultra-high-purity product SiC-based molded body suitable as a component for semiconductor manufacturing. Can be obtained. In addition, by appropriately changing the heat treatment conditions, it is possible to change the speed and amount of the impurities inside the SiC-based molded body that are diffused and adsorbed to the Si film on the surface. It is also possible to get Examples of the SiC-based molded body in the present invention include a SiC molded body composed of only silicon carbide, a carbon material (including graphite material) whose surface is coated with silicon carbide, and ceramics such as silicon nitride and boron nitride.

According to a second aspect of the present invention, in the configuration of the first aspect, the cleaning medium in the dry etching method is a mixed gas containing halogen. This makes it possible to make the purifying method more versatile while effectively exhibiting the effect of the invention described in claim 1. Examples of the gas containing halogen include, for example, HCl (hydrogen chloride), Cl ₂ (chlorine), and HF (hydrogen fluoride). In addition, H containing no halogen
Not only can ₂ SO ₄ (sulfuric acid), HNO ₃ (nitric acid), H ₂ O ₂ (hydrogen peroxide), NH ₃ (ammonia) and the like be used, but also a mixture with the halogen-containing gas.

[0010] Further, the invention according to claim 3 is based on claim 1.
In the structure of the invention described above, the cleaning medium in the wet etching method is a solution containing halogen.
This makes it possible to make the purifying method more economical and more versatile while effectively exhibiting the effects of the first aspect of the present invention.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic system diagram showing a method for purifying a SiC-based compact according to the present invention.

In FIG. 1, a plate material (base material) 1 of a predetermined size made of a high-purity graphite material is cut out from a bulk body of a high-purity graphite material not shown in the figure, and this is cut out by a CVR processing unit 2.
Lead to. In the CVR treatment section 2, the substrate 1 is heated in the presence of silicic acid or at least one of carbon, silicon and silicon carbide to generate a SiO gas, and the SiO gas and the substrate 1 are combined. By reacting, 1
A porous CVR-SiC molded body converted to 00% SiC is obtained.

Next, after leading the obtained CVR-SiC molded body to the thickness adjusting unit 3, cutting in the thickness direction is performed.
After the thickness of the target product is adjusted, the SiC molded body after the thickness adjustment is guided to the CVD processing unit 4. In the CVD processing unit 4, the surface of the SiC molded body is coated with a high-purity Si film by a predetermined thickness according to a normal CVD method.

Next, the Si film coated with the Si film is finished.
After guiding the C-shaped body to the heat treatment part 5, heat treatment is usually performed at a temperature of 1000 ° C. or more for several hours to several tens of hours to sufficiently diffuse impurities contained in the SiC body and form a Si film on the surface. Adsorb inside. The heat-treated SiC molded body is guided to the cleaning unit 6 and subjected to a dry etching method or a wet etching method to remove a Si film (an Si film to which impurities are adsorbed) on the surface of the SiC molded body and to be highly purified. The obtained SiC molded body 7 is obtained.

When dry etching is performed, a gas containing a halogen element such as chlorine or fluorine (Cl ₂ , HCl, H
F, NF ₃ , ClF _{3 and the} like are preferably used. For example, means for spraying a heated mixed gas of hydrogen chloride and hydrogen against the surface of the SiC molded body for a predetermined time is effective. Also in the case of performing wet etching, it is basically preferable to use a solution containing halogen. For example, it is effective to wash the surface of the SiC molded body with a mixed aqueous solution of hydrofluoric acid and nitric acid and further wash with pure water. It is.

In the above-described purification step, unlike the conventional dry cleaning method, the step of using a heated halogen gas involves the step of using SiC.
All of the impurities existing inside the molded body are adsorbed on the high-purity Si film on the surface side. Therefore, since the Si film can be removed only by using the heated halogen gas for a relatively short time, it is possible to obtain an extremely high-purity product SiC molded product without reducing the strength of the SiC molded product itself.

In addition, by appropriately changing the heat treatment conditions in the heat treatment section 5 in the above-mentioned purification step, the speed and amount of diffusion and adsorption of impurities inside the SiC compact can be changed. It is also possible to obtain a SiC compact. Therefore, it is possible to provide a SiC molded product purified to a level corresponding to a semiconductor level required as a component for semiconductor manufacturing to be applied, and to contribute to improvement in productivity and economy of semiconductor manufacturing. it can.

[0018]

The invention according to claim 1 of the present invention is constituted as described above, but the point is that all the impurities inside the SiC-based molded body are previously collected on the surface portion, and the impurities are concentrated. The surface portion is removed in a relatively short time. Therefore, impurities can be removed very efficiently in a simple process and without lowering the strength of the SiC molded product itself, so that an ultra-high-purity product SiC-based molded product suitable as a semiconductor manufacturing component is obtained. be able to.

Further, according to the purification method of the present invention, by appropriately changing the heat treatment conditions, it is possible to change the speed and the amount of the impurities inside the SiC-based molded body that are diffused and adsorbed to the Si film on the surface. , Various high purity products Si
It is also possible to obtain a C-shaped molded body. Therefore, it is possible to provide a SiC-based molded body that is highly purified to a level corresponding to a semiconductor level required as a constituent member for semiconductor manufacturing to be applied, thereby contributing to improvement in productivity and economy of semiconductor manufacturing. can do.

Further, in the invention according to claim 2, dry etching is performed using a gas containing halogen, thereby making the purification method according to claim 1 more versatile. it can. Further, in the invention according to claim 3, the cleaning medium in the wet etching method is wet-etched using a solution containing halogen, whereby the purification method of the invention according to claim 1 is more economical and versatile. It can be sexual.

[0021]

【Example】

(Example 1) A disk having a diameter of 200 mm x t3 mm was cut out from a bulk body made of a high-purity graphite material (manufactured by Toyo Tanso Co., Ltd.).
A porous SiC disc converted to 0% SiC was obtained. Next, this SiC disk was cut only in the thickness direction to adjust the thickness t to 0.485 mm. Next, the SiC disk after the thickness adjustment was subjected to a CVD process to coat the surface thereof with a high-purity Si film having a thickness of 40 μm. Thereafter, heat treatment is performed at 1300 ° C. for 10 hours,
The impurities contained in the SiC disk are sufficiently diffused to form S
Adsorbed in i-membrane. Finally, the surface of the SiC disk (the surface of the Si film) is cleaned (etched) by spraying a heated mixed gas of hydrogen chloride and hydrogen at 1300 ° C. for one hour to remove the Si film, thereby removing the dummy wafer. Was obtained. Table 1 shows the analysis values (measurement numbers) of impurities on the surface of the dummy wafer base material. Further, the dummy wafer base material is further subjected to a CVD process so that
After coating the film with a thickness of 120 μm, the dummy wafer was subjected to a heat treatment under a mixed gas of 1200 ° C. and heated to produce an oxide film of 100 to 200 ° on the surface, and the lifetime was measured. The life time was 2000 (μs).

(Example 2) CVD obtained in Example 1
After heat-treating the treated Si film-coated disk in the same manner,
The surface of the disk was washed (etched) with a mixed aqueous solution of hydrofluoric acid and nitric acid for 1 hour to remove the Si film, and then a dummy wafer base material was obtained. The analysis values (measurement numbers) of impurities on the surface of the dummy wafer base material are also shown in Table 1. In addition, CV is further applied to the dummy wafer base material.
After performing the D process to cover the surface with the SiC film by 120 μm, the same heat treatment was performed on the dummy wafer, and the lifetime of the dummy wafer was measured. The result was 2000 (μs).

Comparative Example 1 A SiC disk having a thickness of 0.485 mm obtained by performing the same CVR treatment as in Example 1 was subjected to the same dry etching treatment as in Example 1. First, the analytical values (measurement Nos.) Of impurities on the surface of the SiC disk at this time are also shown in Table 1. After that, the surface is continuously coated with Si by a thickness of 120 μm by the CVD process.
A dummy wafer coated with C was obtained, and the dummy wafer was subjected to the same heat treatment as in Example 1 to produce an oxide film, and the lifetime was measured. The life time was 1000 (μs). In addition, peeled portions were observed in the SiC film on the surface of the dummy wafer.

Example 3 and Comparative Example 2 A high-purity graphite disc (φ200 mm × t0.
485 mm) to produce a SiC coating on the surface with a thickness of 120 μm. First, the analysis values (measurement Nos.) Of impurities on the surface of the SiC disk at this time are shown in Table 1.
(Comparative Example 2). Continued, obtained SiC
The coated disk is further subjected to a CVD process to provide high-purity Si on its surface, that is, on the SiC coating layer.
The membrane was coated at a thickness of 40 μm. Thereafter, the same heat treatment as in Example 1 was performed to sufficiently diffuse the impurities contained in the SiC coating layer and to adsorb them in the Si film. Next, the surface of the Si film was subjected to the same dry etching treatment as in Example 1 to remove the Si film and obtain a dummy wafer. Table 1 also shows the analysis values (measurement numbers) of impurities on the surface of the dummy wafer. The lifetime of the dummy wafer was measured by performing the same heat treatment as in Example 1 to form an oxide film.
The life time was 2000 (μs) (Example 3).

[0025]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic system diagram showing a method for purifying a SiC-based compact according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High purity graphite board material (base material) 2 CVR processing part 3 Thickness adjustment part 4 CVD processing part 5 Heat treatment part 6 Cleaning part 7 Product SiC material molding

Claims (3)

[Claims] An Si film is coated on a surface of a silicon carbide molded body made of silicon carbide by a CVD method, and then heat-treated to diffuse and adsorb impurities inside the molded body into the Si film. A method for purifying a silicon carbide-based molded body, wherein the whole of a diffusion-adsorbed Si film is removed by a dry or wet etching method. 2. The method according to claim 1, wherein the cleaning medium in the dry etching method is a gas containing halogen. 3. The method according to claim 1, wherein the cleaning medium in the wet etching method is a solution containing halogen.