Purification of metallurgical‐grade silicon up to solar grade

An estimate has been made of the feasibility of a metallurgical purification process, the NEDO (New Energy and Industrial Technology Development Organization) melt-purification process, for manufacturing solar-grade silicon from metallurgical-grade silicon. Equipment has been developed to pilot manufacturing plant scale. The system comprises an electron-beam furnace for phosphorus removal and a plasma furnace for boron removal. Each furnace has a mold for directional solidification to remove metallic impurities. The concentration of each impurity in the silicon ingot purified through the whole process satisfied the solar-grade level. The Solar-grade silicon produced showed p-type polarity and resistivity within the range 0·5–1·5 Ω cm. Copyright © 2001 John Wiley & Sons, Ltd.