Process for manufacturing dense, extra pure silicon

摘要

Ultra-pure silicon, which may be used for transistor manufacture, is produced by dissociation of trichlorsilane vapour in part in a first zone at 800-900 DEG C. to remove impurities and in part in a second zone at least 950 DEG C. Crude silicon, which may be produced in an electric furnace, is reacted with dry hydrochloric acid gas, and the trichlorosilane formed is purified. Dry HCl gas enters, at 6 (Fig. 1), steel tube 1 containing silicon, mixed with at least 5% copper to act as catalyst, supported on grid 2. The HCl enters very slowly, or may be diluted with H2 or N2. Resistors, an oil bath, or warm air are used to heat the reactor to 200-250 DEG C., preferably the temperature is maintained at 240 DEG C. with a temperature around the reactor of 220 DEG C. SiHCl3, which may contain 10-20% SiCl4, passes through 7 to a condenser cooled to -20 DEG C. or under pressure. The condensate is purified by distillation from first stage vessel 10 (Fig. 2), in a heating bath, through column 11, cooling control unit 12, to increase separation efficiency, and condenser 13. The impure part of the resulting condensate collects in receiver 14, but most passes to second stage vessel 15 where it is redistilled into receiver 18. The two stage distillation apparatus is made of "Pyrex" (Registered Trade Mark) glass. A non-reactive gas, e.g. A, N2, or, preferably, H2, is passed at 28 into vessel 19, to which the SiHCl3 is transferred from 18, and the mixture of H2 and SiHCl3, containing less than 20% SiHCl3, flows through 26 to quartz tube 20, part 23 of which is heated to 850 DEG C. by resistors 22, while part 24 is heated to 950 DEG C. Part of the SiHCl3 is decomposed in 23 and retains last impurities, and dense silicon is deposited in 24, while SiCl4 is withdrawn and condensed. When a layer of silicon has been formed, the SiHCl3 content of the gas may be increased to 20%. On cooling, the tube 20 breaks due to the adherent silicon layer, so surrounding tube 21 is provided through which A or H2 is passed. The recovered silicon is finally washed successively with hot hydrofluoric acid, distilled water, caustic soda solution, distilled water, hydrofluoric acid, and distilled water, and then dried. The hydrogen for diluting SiHCl3 is purified by passage through tubes packed with palladium-coated asbestos to remove oxygen, and caustic soda to remove CO2 and moisture. The gas is finally dried with magnesium perchlorate and then passes through an absorbent cotton filter.