New Method for Production of Solar-Grade Silicon by Subhalide Reduction

In this study, a new method for producing Si, called “halidothermic reduction,” was investigated with the purpose of producing solar-grade silicon (SOG-Si); by this method, SiCl4 was reduced by gaseous subhalide used as the reductant. Silicon was produced by reacting SiCl4 with Al subhalides, which were produced by reacting AlCl3 with metallic Al. Fibrous Si with diameters ranging from submicrons to several tens of micrometers was deposited as a result of halidothermic reduction of SiCl4 by an Al subchloride (AlClx) reductant at 1273 K. The size of Si deposits and the reaction rate were increased by simultaneously supplying AlCl3 and SiCl4 vapors to a reaction tube holding Al metal. The impurity level of the obtained Si was found to be lower than the detection limit of X-ray fluorescence. Halidothermic reduction is suitable for producing high-purity Si since all reactants and byproducts exist in the vapor phase. Further, this process has high productivity since the overall reaction is a highly scalable metallothermic reduction reaction.