GB946828A - Process for the manufacture of very pure silicon carbide - Google Patents

Abstract

Pure crystalline SiC is prepared by thermal splitting of a vaporized or gaseous organo-silicon compound in which the atomic ratio of C to Si is greater or smaller than 1 : 1. At least one such compound may be mixed with at least one other organo-silicon compound, say where the atomic ratio is 1 : 1, and decomposition may be effected in the presence of a gaseous diluent, e.g. H2, A, He, N2, or CO, employing 60% vol. or more diluent. The diluent may be recycled after purification, e.g. by cooling below - 60 DEG C., or washing. The splitting may be at 0.01-50 atmos. and 700-2500 DEG C., in the presence of heated rods, tubes, plates, spirals, or filaments of carbon, graphite, Si, Ta, Ti, W, Mo, SiC, or B4C1 on which the SiC is deposited. The gas velocity should be below 5 m./sec. The compounds may be silanes or halogeno-silanes containing one or more organic radicals, e.g. methyl, ethyl, propyl, butyl, vinyl, allyl, propenyl, butenyl, cyclohexyl, cyclohexenyl, phenyl, xenyl, tolyl, naphthyl, or benzyl, which may be bonded to Si through O, N, P, S, Se or B. The radicals may include substituents, e.g. halogen, nitro, amino, hydroxyl, mercaptyl, or cyano. Cyclic organo-silicon compounds may also be used. Doped SiC, containing 10-10-12% doping agent suitable for semi-conductor use, may be obtained if the organo-silicon compound contains an element of Groups 2-7, e.g. N, B, Al, or P, or if the vapour of such an element or a compound thereof is included in the splitting, e.g. NH3, AlCl3, or B hydride, or halide. The organo-silicon compounds exemplified are: dimethyl dichlorosilane, disilyl methane [CH2-(SiH3)2], benzyl silane, vinyl trichlorosilane, g -chloropropyl trichlorosilane, tris-(trimethyl - silyl - methyl) - arsine, or phosphine, (CH3)3SiCH2OH, [(CH3)3SiCH2]3B, or [(CH3)3 SiCH2]4Sn. Specification 899,947 is referred to.