Patent ID: 7708970

Claim:
A process for preparing polycrystalline silicon, comprising introducing a reaction gas comprising hydrogen and a silicon-containing gas into a reaction chamber of a silicon deposition reactor and thermally decomposing the silicon-containing gas onto heated silicon, forming an offgas; and separating the offgas into a first offgas fraction comprising trichlorosilane and chlorosilanes having a lower boiling point than trichlorosilane, and a second offgas fraction comprising components having a higher boiling point than trichlorosilane; supplying the first offgas fraction to the reaction gas of a polycrystalline silicon deposition; separating the second offgas fraction into a tetrachlorosilane fraction, and a high boiler fraction containing high boilers, optionally still containing tetrachlorosilane; and supplying the high boiler fraction to trichlorosilane-containing reaction gas of a silicon deposition and heating the reaction gas to a temperature at which the high boiler fraction is present in gaseous form on entry into the reaction chamber of the deposition reactor.