Quantitative evaluation of methods for effective removal of impurities to produce solar-grade silicon

The quantitative evaluation of impurities in Si was performed and their thermodynamic behaviors were investigated using acid leaching treatment and oxidation/vaporization of metallurgical-grade Si (MG-Si). HCl and aqua regia solution are found to be more effective than HF solution for the removal of Ca, Fe, and Al in the Si. The mechanism by which the impurities dissolve was investigated using the FactSage™ software program. As the oxidation layer at the Si interface becomes thicker, the removal rate associated with vaporization of the impurities decreases. This seems to occur because the evaporation potential is decreased by the formation of an oxidation layer that interrupts the evaporation process. The efficiency of the removal of impurities from MG-Si can be evaluated quantitatively using acid leaching and oxidation/vaporization treatments of Si.