Removal of metallic impurities in metallurgical grade silicon by directional solidification

Abstract

Multicrystalline silicon ingot of w 130 × 120 mm, with characteristics of large and well directional columnar crystals, is obtained by Bridgman directional solidification (DS). Metallic impurities mainly form impurity particles instead of depositing in the grain boundaries. Solid/liquid interface is changed from concave to convex during DS process. Removal efficiencies of Al, Fe, Ca, Ti and Cu reach 96.4, 90.5, 96.6, 95.7 and 96.3% respectively, at the edge of ingot with the height of 32.5 mm. Contents of metallic impurities in solar grade silicon can be satisfied by DS twice through theoretical calculation.