GB871831A - Improvements in or relating to the production of elemental silicon - Google Patents

Abstract

<PICT:0871831/III/1> In the production of silicon of at least 99.99% purity by passing a silicon halide vapour, preferably silicon tetrachloride, and zinc or cadmium vapour into an enclosed reaction zone at a temperature above the boiling point of the metal and below the melting point of silicon, to form silicon which is deposited in the zone, and zinc or cadmium halide, which may be condensed outside the zone, the silicon halide and metal vapour reactants are purified by passing them into the reaction zone via an enclosed purification zone, in communication with the reaction zone, in which a pool of the boiling metal is maintained. The temperature of the silicon halide vapour here introduced is below the boiling point of the metal. It is thought that the small quantity of silicon which is formed in the purification zone, and is deposited in and about the pool, carries with it the impurities present in the reactants. In the Figure, a reservoir 1, which may be purged with an inert gas, feeds molten zinc or cadmium to vaporizer 4, from which the vapours are passed to purification zone 9 containing a pool of boiling metal 11. Silicon halide is vaporized in vaporizer 12, and is preferably introduced into the purification zone at 100 DEG C.-300 DEG C. The mixed vapours then pass into the reaction zone 15, which is preferably maintained at 907 DEG C.-1100 DEG C. Pure silicon is deposited, and metal halide is collected in by-product collecting zone 20. When the reactor is almost full of silicon the supply of metal vapour is cut off and the reactor is allowed to cool, preferably to 50 DEG C.-200 DEG C., the flow of silicon halide vapour being maintained. If desired, all or part of the silicon halide vapour employed may be bubbled through the metal pool. The apparatus is preferably constructed of silica. The silicon has improved electrical properties.