High-Frequency Electromagnetic Purification of Silicon

The effect of a high-frequency electromagnetic (EM) field on the removal of nonmetallic inclusions from molten silicon was experimentally investigated. Inclusion separation efficiencies of up to 99 pct were reached. The separation efficiency was independent of the particle concentration in the melt and increased significantly with increases in the frequency, separation time, and coil current. Particles were separated from the silicon matrix and relocated to the top, bottom, and side walls of the crucible due to the effect of three mechanisms: induced secondary fluid flow which carried particles from the bulk of the melt; EM body force which worked in the skin-depth area to trap particles on the side wall; and fluid shear force due to the local acceleration of molten silicon, which promoted the settling of particles to the bottom of the crucible and also carried particles toward the top. Higher coil current enhanced the strength of the magnetic field which enhanced fluid flow, while higher frequency also enhanced the fluid acceleration, and the effect of current was more pronounced leading to better particle separation.