Silicon carbide particle formation/engulfment during directional solidification of silicon

The formation of SiC particles and their engulfment in directional solidification of silicon for PV application are investigated. A mathematical model is proposed to describe reaction mechanism, particle formation, forces acted on the particles in silicon melt, and engulfment/pushing of particles by the solidification interface. Simulation results show that carbon and SiC particle concentrations in silicon ingot are mainly affected by the impurities of feedstock and furnace material, the interface shape and the growth rate. It is proposed that the precipitation of SiC particles occurs when carbon concentration reaches to its solubility. Carbon is accumulated in the central region of silicon melt due to the concaved interface and thermally driven flow. The density of SiC particle is higher than the melt and the particles are entrapped to the interface quickly. Whether the particle is pushed away or engulfed by the moving solidification interface is determined by the particle size and solidification interface moving rate.