Patent ID: 7736439
Filing Date: 2010-06-15
Classification: C01B,Y10S

Abstract:
1. A method for removing metal impurities from a polycrystalline silicon fraction containing small fragments of polycrystalline silicon derived from crushing rods of polysilicon, without dissolving the polycrystalline silicon, consisting of the steps of: removing metal impurities by contacting a polycrystalline silicon fraction at least once with an aqueous cleaning solution consisting essentially of water and metal removing reagents consisting essentially of from about 5 to about 10 weight percent HF, and from about 1 to about 2 weight percent H removing the aqueous cleaning solution, and washing the polycrystalline silicon fraction thereby obtained with highly pure water having an electrical resistivity of from 1 MΩ to 18 MΩ, to form a washed polycrystalline silicon fraction, and drying the washed polycrystalline silicon fraction thereby obtained to obtain a dry polycrystalline silicon fraction having metal impurities of less than 100 ppbw, wherein the polycrystalline silicon fraction has polycrystalline silicon fragments with a maximum particle size in the range of 10 μm to about 25 mm and wherein an additional washing of the polycrystalline silicon fraction with said highly pure water may take place prior to drying the washed polycrystalline silicon fraction.