Simultaneous removal of phosphorus and boron from silicon via Na2O assisted by intensified temperature field in electron beam melting

Abstract

Optimizing the purification process of metallurgical-grade Si via metallurgical routes supports the advancement of solar-grade silicon manufacturing. Herein, P and B impurities are simultaneously removed during the electron beam melting (EBM) with a few Na₂O and graphite lining, abridging the two purification processes into a single melt. The simulation results indicate that graphite lining can intensify the temperature field of Si melt, which is favorable for P removal by evaporation. Significantly, the width and depth of the temperature line for effective oxidation of B is greatly enhanced by the graphite lining, which increases the removal of B. As a result, without introducing additional impurities, the contents of P and B are reduced from 2.02 ppmw and 12.76 ppmw to 0.14 ppmw and 0.94 ppmw, achieving removal efficiencies of 93.07 % and 92.63 %, respectively. This work provides a smart technique for the simultaneous removal of P and B from Si by EBM and streamlining the metallurgical routes to manufacture solar-grade silicon.