Silicon purification in vacuum induction furnace

Abstract

In this paper the removal of impurities from metallurgical grade silicon by melting in a vacuum induction furnace was studied, in order to produce solar grade silicon, which is the raw material of the photovoltaic cells to convert solar energy into electricity. The work was focused on the removal of phosphorus, which is one of the most difficult impurities to remove from silicon. Refining was obtained 119 ppm to 8 ppm of phosphorus in 3 hours at 1650°C under pressure of 0.2 Pa, obtained by a set of mechanical, “roots” type, and diffusing pumps. It was concluded that this method is technically feasible for purification of metallurgical grade silicon. The rates constants were obtained for phosphorus (kP=5•10-6 m/s), aluminum (kAl=2•10-6 m/s) and calcium (kCa=1•10-5 m/s). Silicon losses by vaporization during the test averaged around 13%.