Silicon Production

This chapter describes the process of producing high-purity polycrystalline silicon, up to 99.999999999% (11N) purity, from metallurgical grade silicon (MG Si) at 98% purity. The preparation and uses of MG Si are briefly discussed, along with efforts to metallurgically refine MG silicon to higher purity for use in solar cells. The chemical processes for producing high-purity polysilicon are detailed, including the two large-volume production processes for synthesis of trichlorosilane (TCS), purification of TCS, decomposition of TCS to form polysilicon, and recovery and recycle of by-product gases. The major applications for high-purity polysilicon in the semiconductor and photovoltaic industries are described, with requirements for single crystal growth for each application. The largest volume by-product of the process is silicon tetrachloride (STC), and conversion of STC to TCS is detailed. The discussion also includes the use of other silicon source gases and other silicon deposition processes.