Oxide unlocking electron beam melting to separate boron for impurities co-removal of metallurgical grade silicon

Abstract

Removing stubborn B from Si efficiently and simplifying the purification process are critical challenges that must be addressed in the manufacture of solar grade silicon (SoG-Si) via metallurgical routes. Herein, B is flexibly coupled with other impurities separation procedure, so that metallurgical grade silicon (MG-Si) is purified through simplified electron beam melting (EBM) unlocked by a few oxides (0.1 wt%). EBM fulfills three functions including promotion of oxidation, evaporation of impurities, and induction of directional solidification, giving high-temperature field, high vacuum field, and intense melt convection, which not only ensures the smooth process of B oxidation but also favors the co-removal of other impurities, obtaining high purity Si. As a result, purified Si ingot exhibits a low content of B (from 12.76 ppmw to 2.92 ppmw), and the total content of major impurities is reduced from 1217.24 ppmw to 5.66 ppmw. Significantly, pure SiO2 could more readily access the high-temperature region of Si melt during EBM, offering distinct advantages for the oxidation gas phase separation of B. This work provides an efficient and robust method for expanding ideas of B removal and simplifying metallurgical routes.