PURIFICATION OF METALLURGICAL SILICON FOR SOLAR-GRADE SILICON BY ELECTRON-BEAM BUTTON MELTING

Behavior of various impurities such as carbon, phosphorus, boron, calcium, aluminum, iron and titanium in metallurgical-grade silicon has been investigated during electron beam button melting with various modifications. Carbon, phosphorus, calcium and aluminum were removed by Electron Beam Remelting (EBR) treatment under 10(-2) Pa for 30 min. Ninety percent of carbon, 75% of aluminum, 89% of calcium and 93% of phosphorus was removed. The lowest content of these impurities were 15 ppmw C, 470 ppmw Al, 150 ppmw Ca and 3 ppmw P, respectively. First order rate equation was used for the removal of carbon, calcium and aluminum, and second order equation fit for the dephosphorization. Rate constants for calcium, aluminum and carbon ranged from 0.01 to 0.1 min-1. That of phosphorus was from 0.003 to 0.01 ppmw-1 . min-1.