Production of Solar Grade Silicon in an Arc Furnace Using High Purity Starting Materials

The carbothermic reduction of silica has been adopted to produce solar-grade silicon using high-purity raw materials. Inexpensive and abundant quartz sand is purified by fusing it with glass-forming oxides to form a melt from which glass fibers are drawn. Subsequent treatment of the fibers with hot HC1 leaches out all impurities, resulting in high-purity Si02 analysed to have B, P and transition metal concentrations of less than 1 ppmw. High-purity carbon (B, P and transition metal concentration < 1 ppm) is prepared by treating carbon black with hot HC1. When reacting these purified materials in a small arc furnace, the impurity concentration of the silicon obtained corresponded to the impurities present in the starting materials. A three-phase, 550 kVA-arc furnace was constructed to prepare silicon on a larger scale. Quartz and charcoal were used as raw materials to gain experience in operating the furnace and to study the process parameters. The silicon produced from these impure materials was further purified employing the Czochralski method.