GB1532649A - Production of polycrystalline silicon - Google Patents

Abstract

1532649 Deposition from gaseous state MONSANTO CO 23 Dec 1975 [26 Dec 1974] 52562/75 Heading B1F [Also in Division C1] High purity crystalline silicon suitable for semiconductor use is made by using an elongate tubular reaction vessel 13 comprising a carbon tube and having at one end an inlet 23 for the supply of a gaseous stream of silicon-containing reactants and at one end a reactant exhaust outlet 21 and having as deposition surface an interior carbon tube 15 lined with graphite 25. The interior of the vessel is purged with an inert gas, the deposition surface is heated to a temperature sufficient for formation of silicon (suitable 1100 to 1200‹C) by means of carbon resistance heater 27, a stream of silicon-forming reactants (suitably a mixture of hydrogen and or more compounds selected from silanes and silicon tetrachloride) is introduced into the vessel to form a layer of high purity polycrystalline silicon on the graphite deposition surface, the surface cooled, and the polycrystalline silicon layer removed for further processing As shown a quartz heat shield 39 may surround the heater, and a double walled enclosure vessed 41, the vessel also being provided with cooling water inlet 43 and outlet 45, and inlets and outlets for purge gases and reactants. In a preferred embodiment, after purging with inert gas, the graphite deposition surface is heated to a temperature sufficient for deposition of silica, e.g. 700 to 800‹C, and a stream of a silicaforming composition, suitable tetraethyl silicate vapour, is introduced into the vessel to form a layer of silica on the graphite deposition surface. The deposition surface is then heated to a temperature sufficient for formation of silicon, a stream of siliconforming reactants is introduced into the vessel to form a layer of high purity crystalline silicon over the silica, and the deposition surface is then cooled and the silicon layer removed for further processing, suitably by removing the liner from the vessel and separating it from the silicon by burning it off in air. Silica is then removed from the silicon by etching in an aqueous solution of hydrofluoric acid.