JP2003119566A - Reflecting mirror - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflecting mirror superior in long-term reliability, which has a low residual stress in a silicon carbide film applied on the surface of a substrate, does not generate cracking or the like during manufacturing or operation, and stably acquires a super flat surface with satisfactory reproducibility. SOLUTION: This reflecting mirror is characterized in that crystals with particle diameters of 3 μm or more occupy 20% or more in the polished surface area of the silicon carbide film applied on the surface of the substrate, and the silicon carbide film has the residual stress of 40 kg/mm<2> or less.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflecting mirror suitable for an X-ray, a laser or the like which requires a smooth surface. [0002] In recent years, ceramics have high strength and excellent properties such as heat resistance and abrasion resistance. Therefore, the application fields of ceramic products have been expanded and various products have been developed. Among them, it has been proposed to coat a ceramic on the surface of a substrate by means of a vapor phase synthesis method, for example, a chemical vapor deposition method or a physical vapor deposition method, so that a reflecting mirror having a ceramic surface on the substrate surface is proposed. [0003] For example, it is known that a silicon carbide film formed by a chemical vapor deposition method is dense and free from voids, and an ultra-smooth surface having high smoothness can be obtained by performing surface polishing. Although the surface roughness depends on the surface shape, a smooth surface can be obtained in the order of aspherical surface, spherical surface, and flat surface, and an aspherical surface can have a surface roughness of 100 ° or less, and a flat surface can have a surface roughness of 10 ° or less. It is used as a high-precision, high-reflectance reflecting mirror. However, since the silicon carbide film formed by the chemical vapor deposition method is extremely high in hardness among ceramics, it requires a large amount of labor and time for polishing.
In addition, defects such as chipping are likely to occur at the boundary between the crystals, which makes it difficult to obtain a highly accurate reflecting mirror having a high reflectance. Therefore, in order to facilitate polishing and reduce the incidence of defects such as chipping, it has been sought to make the crystal grains of the silicon carbide film to be coated into fine grains that can easily obtain an ultra-smooth surface. For example, it is disclosed in Japanese Patent Application Laid-Open No. 4-35806 that the crystal of the obtained silicon carbide film has a maximum width of 3 μm or less by devising the processing conditions of the chemical vapor deposition method.
No. 8 has been proposed. However, in the chemical vapor deposition method, the finer the crystal grains of the obtained silicon carbide film, the more the crystal grains are oriented to the (111) plane identified by X-ray diffraction. In a film containing a crystal which has undergone crystal growth, or a film which contains a crystal which is generally oriented to the (220) plane where the residual stress tends to be high at the time of film formation, the residual stress is further increased. As a result of the addition to the silicon carbide film, cracks may occur in the silicon carbide film. Further, even when a reflecting mirror in which the crystal grains of the silicon carbide film are made fine is used under conditions in which thermal history at high temperatures is repeated, cracks are liable to occur because thermal stress is applied. There was a problem that reliability was poor for use over a period. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object the purpose of forming a film made of a crystal oriented in the (111) plane, or having a high residual stress during film formation (220). ) The residual stress is low even in a film composed of crystals oriented in the plane and a film composed of a mixture thereof, and cracks do not occur during production and operation, and an ultra-smooth surface can be easily obtained.
An object of the present invention is to provide a reflecting mirror coated with a silicon carbide film having excellent long-term reliability. The present inventors specify the size of crystal grains and the area occupied by the correlation between the size of the crystal grains of the silicon carbide film coated on the base and the residual stress. Can reduce the residual stress of the silicon carbide film. As a result, cracks and chipping during polishing can be prevented by appropriately selecting the polishing method, and the square root of the root mean square value according to the ASTM standard can be reduced. Calculated surface roughness RM
The present inventors have also found that an S value can realize an ultra-smooth surface of 5 ° or less by plane polishing and 50 ° or less by curved surface polishing, and have reached the present invention. That is, in the reflector of the present invention, the polished surface of the silicon carbide film coated on the substrate surface is a crystal having a particle diameter of 3 μm or more when converted to a circle, occupying 20% or more of the film surface area, and The residual stress of the silicon film is not more than 40 kg / mm ² as measured by, for example, an X-ray stress measuring method. According to the reflector of the present invention, the crystal having a grain size of 3 μm or more on the polished surface of the silicon carbide film accounts for 20% of the film surface area.
And the residual stress of the silicon carbide film is 40 kg /
Since it is not more than mm ² , chipping does not occur during polishing processing, or even if pressure stress during polishing processing or thermal stress during operation is applied, cracks do not occur in the silicon carbide film. . Hereinafter, a reflector according to the present invention will be described in detail. In the reflector of the present invention, the polished surface of the silicon carbide film coated on the substrate surface is a crystal having a particle diameter of 3 μm or more and occupies 20% or more of the film surface area.
No residual stress exceeding 0 kg / mm ² was observed. In the present invention, when the occupation ratio of the crystal having a particle diameter of 3 μm or more on the polished surface of the silicon carbide film to the film surface area is less than 20%, the residual stress increases, so the film surface is polished. And when using a reflector, it is easy to cause defects such as cracks and chipping,
Not suitable. In the polished surface of the silicon carbide film coated on the substrate surface, for example, (111) plane, (220) plane, (311) plane, etc. are observed in X-ray diffraction measurement, and the detected crystal plane is It may be single or plural. By polishing the silicon carbide film as described above, excellent surface smoothness with a surface roughness of 100 ° or less can be obtained, and the surface determined from the square root of the root mean square value according to the ASTM standard can be obtained. The roughness RMS value is 5 for planar polishing.
Ultra-smooth surface of 50 ° or less can be realized even by polishing a curved surface. On the other hand, it is preferable that the substrate is similar to the silicon carbide film to be coated in terms of thermal expansion, such as a sintered body of the same kind as the silicon carbide film, or another ceramic material having similar thermal expansion characteristics to that of the silicon carbide film. Carbon, metal, etc. can be adopted. As a method of manufacturing the reflecting mirror of the present invention, a plasma CVD, a photo CVD, a thermal CVD, an MO (Metal-O
rganic) CVD or the like. However, according to the present invention, it is desirable that the growth direction of the crystal of the silicon carbide film to be coated is substantially perpendicular to the substrate, and in a general manufacturing method, the film may be formed at a level that does not become amorphous. It can be appropriately adjusted depending on the concentration of the raw material gas and the like. In evaluating the reflector of the present invention, first,
Using a silicon carbide sintered body as a base, a silicon carbide film was coated by a thermal CVD method. As the coating conditions by the thermal CVD method, specifically, methyltrichlorosilane and hydrogen are used as reaction gases, the flow rate ratio thereof is 1: 3 to 1:10, and the substrate temperature is 1300 to 1300. 10 to 2 at 1500 ° C
A silicon carbide film of about 0.2 to 0.3 mm was obtained under a reduced pressure of 00 Torr. The obtained silicon carbide film was subjected to X-ray diffraction measurement to investigate the crystal orientation, and the residual stress was measured by an X-ray stress measurement method. Next, the surface of the silicon carbide film is polished using diamond abrasive grains, and the surface roughness RM of the obtained polished surface is obtained.
S was measured, and the presence or absence of defects such as cracks was examined with a Nomarski differential interference microscope and a scanning electron microscope. Thereafter, the polished surface of the silicon carbide film is subjected to a chemical treatment, and a photograph is taken using a scanning electron microscope.
From the obtained photograph, the crystal particle diameter was measured using a particle diameter distribution measuring device, and the area ratio of crystals having a particle diameter of 3 μm or more in a fixed visual field was calculated as the occupancy. Table 1 shows the above results. [Table 1] As is clear from the results shown in Table 1, the sample Nos.
In any of 2, 15, 16, 29, and 30, the residual stress of the silicon carbide film was 43 kg / mm ² or more, and cracks were observed in the silicon carbide film. The residual stress was 40 kg / mm ² or less, and no defects such as cracks were found in the silicon carbide film. As described above, in the reflecting mirror of the present invention, the polished surface of the silicon carbide film coated on the substrate surface is a crystal of 3 μm or more, occupies 20% or more of the film surface area, and Since the residual stress of the film is 40 kg / mm ² or less, (11
1) Not only a silicon carbide film composed of crystals oriented in the plane,
Residual stress can be suppressed low even in a silicon carbide film or the like made of a crystal oriented in the (220) plane, and no crack or the like occurs during manufacturing or operation, and an ultra-smooth surface can be stably reproduced with good reproducibility. Thus, a silicon carbide reflecting mirror having excellent long-term reliability can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 14/58 C23C 14/58 Z 16/56 16/56 G02B 5/08 G02B 5/08 A F term ( Reference) 2H042 DA12 4K029 AA04 BA56 BD09 CA03 EA01 GA00 4K030 AA06 AA17 BA37 CA05 DA08 FA10 HA03 JA01 JA09 JA10 LA11

Claims (1)

Claims: 1. A reflecting mirror formed by polishing the surface of a silicon carbide film coated on the surface of a substrate, wherein the polishing surface of the silicon carbide film has a thickness of 3 μm.
A reflector having a crystal having the above-mentioned particle diameter occupying 20% or more of the film surface area, and having a residual stress of the silicon carbide film of 40 kg / mm ² or less.