process for the production of raw materials of high purity for the production of silicon for solar cells with the reduction process carbotermica

摘要

Highly purified starting materials for the production of silicon suitable for fabrication of solar cells are produced via the carbo-thermal reduction process. A carbon-containing material with impurities therein, either by itself or admixed with glass bodies, which are attained from a melt of quartz sand and glass-forming additives formed into a fiber form and pulverized, is converted into a granulate form with the aid of a bonding agent. The resultant granulates are contacted with a hot inorganic acid, such as 3N HCl at about 90 DEG C., to extract substantially all impurities from the granulates, which can be in pellet or tablet form. The resultant purified pellets are then directly charged into an electrical arc furnace to yield solar-quality silicon. With this process, highly purified SiO2 and highly purified carbon are produced in a simple and cheap manner. The impurity level for boron, phosphorus and transition metal in these starting materials is less than about 10 ppm.