Solar Grade Silicon By a Direct Route Based on Carbothermic Reduction of Silica: Requiremetns and Production Technology

摘要

In the European projects SOLSILC and SPURT, a process is developed for the production of solar grade silicon (SOG-Si) by carbothermic reduction of silica, based on very pure raw materials. The purity of the raw materials greatly reduces the requirements on purification of the silicon, from dopants and other impurities. This paper reports the technology used for the Si production, which is suitable for the available high purity silica and carbon materials. It also reports results from the carbon removal process, which brings the carbon content of the silicon from several hundred ppmw to below 5 ppmw. Finally, it discusses experiments on the allowable impurity concentrations in SOGSi feedstock for directional solidification. Segregation observed during directional solidification is better than previously published, and allowable concentrations of Fe and Ti are similar to what was previously published for monocrystalline material by Westinghouse Corp.