Boron removal by dissolution and recrystallization of silicon in a sodium-silicon solution

Low-purity Si powder was dissolved in Na solvent, and Si recrystallized by the evaporation of Na from the Na-Si solution at 1173 K in a magnesium oxide crucible. Several impurity elements precipitated as compounds at the bottom of the crucible. Glow-discharge mass spectrometry showed a decrease in the concentration of most impurity elements, except Na and Mg, in the crystallized Si. The boron (B) concentration was reduced from 9.1 to 0.3 mass ppm by recrystallization. In addition, solidification segregation was confirmed by the depth profile of the B concentration from the crystal surface.