A simulation model for controlling mass transfer of vapor silicon and volatile impurities with gas flow guidance during refining of silicon

Abstract

The mass transfer behavior of vapor silicon (Si) and volatile impurities during refining of Si by electron beam melting is still unclear. In present work, with gas flow guidance, the mass transfer mechanism of vapor Si and volatile impurities, and corresponding heat transfer rule in the furnace chamber are investigated by simulation and experiment. Numerical simulation shows that vapor Si is preferentially transferred to the outlet, and temperature in the outlet is lower than the solidification temperature of vapor Si when gas flow is fixed at 0° and 1.16 m s−1 (optimal conditions). Experimental results show that volatile impurities are effectively removed (P and Al both are less than 0.01 ppmw in the refined Si ingot with >99% of removal efficiency). Moreover, volatile impurities flux positively increases with increase of vapor Si flux. Gas flow significantly gathers the vapor Si in the outlet, reinforcing evaporation kinetics of molten Si and volatile impurities, which demonstrates the numerical simulation model is feasible to control the mass transfer and evaporation kinetics. Gas flow guidance may be a promising way to improve volatile impurities removal from Si.