Optimization of boron, phosphorus, carbon extraction from metallurgical-grade silicon

Abstract

To ensure the solar silicon purity level of 99.9999% (6N), it is necessary to reduce the content of Fe, Al, Ca, Ti, Cr, B, P, O and C impurities in the metallurgical-grade silicon within two-five orders of magnitude. Boron (B) and phosphorus (P) are elements technologically difficult to remove from silicon. The content of boron (B), phosphorus (P) and carbon (C) in solar-grade silicon should not exceed 0.38 ppmw, 0.79 ppmw and 43 ppmw, respectively. In this paper, the problem of determining the thermodynamic parameters (temperature and pressure), ensuring the formation of volatile (gaseous) components removing B, P and C impurities, is solved.