GB820192A - Process of producing pure silicon - Google Patents

Abstract

Pure silicon is produced by the thermal decomposition of silane or partially chlorinated silane in a silica reactor the inside walls of which are lined with a layer of vitreous carbon upon which the silicon is deposited. Methane which may be diluted with an inert gas, e.g. 1-100% methane: 0-99% inert gas preferably 10% methane: 90% inert gas is passed through a silica reactor heated in a furnace to 1000-1200 DEG C. preferably 1000-1100 DEG C. to deposit a vitreous layer of carbon on the inside walls of the reactor. The inert gas may be any noble gas, e.g. helium, neon or argon, or hydrogen, and the reactor may be cylindrical, polygonal or conical in shape. The flow of methane is interrupted and silane vapour or vapour of a partially chlorinated silane, which may be diluted with hydrogen or argon, is passed through the reactor at 600-1200 DEG C. Trichlorosilane is preferably employed at 900-1000 DEG C. When sufficient silicon has collected in the reactor it is allowed to cool to ambient temperature and the product removed. Vitreous carbon contaminating the silicon is removed by mechanical abrasion and/or by immersion in an etching solution of nitric acid (1 part) hydrofluoric acid (2 parts) in water (50%) whereby carbon separates and floats off leaving pure silicon which is washed with aqueous HCl and dried. The reactor after washing and drying is ready for re-use. Pure silane for use in the above process is prepared by reacting purified SiCl4 with LiAlH4 in a continuous manner in excess anhydrous ether over a period of some hours in an atmosphere of H2. Silane so produced is purified by passage together with 2-3 volumes of purified hydrogen through a reflux condenser cooled by dry-ice/acetone, a dry-ice cooled trap, an activated carbon bed, a dry-ice cooled trap and thence to the reactor.ALSO:Pure silicon is produced by the thermal decomposition of silane or partially chlorinated silane in a silica reactor the inside walls of which are lined with a layer of vitreous carbon upon which the silicon is deposited. Methane which may be diluted with an inert gas e.g. 1-100% methane : 0-99% inert gas preferably 10% methane : 90% inert gas is passed through a silica reactor heated in a furnace to 1000-1200 DEG C. to deposit a vitreous layer of carbon on the inside walls of the reactor. The inert gases may be any noble gas e.g. helium, neon or argon, or hydrogen and the reactor may be cylindrical, polygonal or conical in shape. The flow of methane is interrupted and silane vapour or vapour of a partially chlorinated silane, which may be diluted with hydrogen or argon, is passed through the reactor at 600-1200 DEG C. Trichloro silane is preferably employed at 900-1000 DEG C. When sufficient silicon has collected in the reactor it is allowed to cool to ambient temperature and the product removed. Vitreous carbon contaminating the silicon is removed by mechanical abrasion and/or immersion in an etching solution whereby carbon separates and floats off leaving pure silicon which is washed with aqueous HCl and dried. The reactor after washing and drying is ready for p re-use.