Abstract: A dielectric multi layer thin film type band-pass filter provided with the function of transmitting a predetermined wavelength band, the function of reflecting a predetermined wavelength band or both functions, where a film structure of the dielectric multi layer thin film optical filter is configured of, with respect to the center wavelength ? as a reference of the optical film thickness, (1) mirror layers each comprised of alternately layered layers (H) of high refractive index material and layers (L) of low refractive index material each with an optical film thickness of ?/4, and (2) spacer layers each of which is configured in a combination of a layer (nH: n is an integer) of high refractive index material and a layer (nL: n is an integer) of low refractive index material each with an optical film thickness of ?/4 and has a total optical film thickness of an integral multiple of ?/2.

Abstract: A process for the preparation of a silicon carbide sintered body of high purity which has a content of 1 ppm or less of each atom harmful to the manufacture of semiconductor equipment including the step of shaping a silicon carbide powder, calcining the shaped body in a non-oxidizing atmosphere to form a porous body, and subjecting the porous body to reaction sintering while being impregnated with molten metallic silicon. The starting silicon carbide powder also has a content of 1 ppm or less of each harmful atom and it has a free carbon content of not greater than 20% by weight and an average particle diameter of 0.5-20 .mu.m.

Abstract: A process for producing silicon carbide-base complex is disclosed. In the process of this invention, a silicon carbide-base complex is produced by means of depositing carbon produced by means of pyrolysis of a gas comprising a hydrocarbon or a hydrocarbon halide on a porous synthesized silica glass body. As a result, the process of manufacture according to the present invention is capable of producing a high purity and a high strength silicon carbide-base material, which is useful as a jig for producing semiconductors, for example, a heat resistance jig material such as a process tube for wafer boats used for heat doping operation.

Abstract: A process for the preparation of a beta-silicon carbide powder of high purity which is suitable for use in the manufacture of semiconductor equipment and which has a content of 1 ppm or less of each atom harmful to the manufacture of semiconductor devices. The process comprises preparing a carbon- and silicon-containing starting mixture comprising (a) at least one siliceous material selected from liquid silicon compounds and solid siliceous substances derived from a hydrolyzable silicon compound, and (b) at least one carbonaceous material selected from polymerizable or cross-linkable organic compounds prepared in the presence of a catalyst which is substantially free from atoms harmful to the manufacture of semiconductor devices. The starting mixture comprises at least one liquid substance used as component (a) or (b). The starting mixture is then solidified by heating and/or by use of a catalyst or a curing agent.