Silicon purification process

Abstract

A process for producing semiconductor grade silicon. Metallurgical grade silicon, silicon dioxide, and silicon tetrafluoride are chemically combined at an elevated temperature to form silicon difluoride gas. The silicon difluoride gas is then polymerized, preferably in a two-step process. An initial small quantity of silicon difluoride polymers is formed at a first temperature. This initial polymerization removes most of the impurities that were present in the original metallurgical grade silicon and which were transported by the silicon difluoride gas. The bulk of the remaining silicon difluoride gas is then polymerized at a second, lower temperature. These polymers are substantially free from all impurities. The pure silicon difluoride polymers are then thermally decomposed at temperatures below 400.degree. C. to form binary silicon fluoride homologues. The homologues can be distilled for even higher purity, or can be used or stored as formed. The binary silicon fluoride homologues produce pure silicon and silicon tetrafluoride when heated to a temperature between 400.degree. C. and 950.degree. C. The disproportionation of the homologues can be accomplished by chemical vapor deposition techniques onto heated substrates of silicon, metal, or quartz. This disproportionation will result in amorphous, polycrystalline, or monocrystalline silicon depending on the temperatures employed and on the substrate used for deposition.