A commercial debut for a process to make silicon for solar cells
By Chemical Engineering |
This month, JFE Steel Corp. (Tokyo, Japan; edlinks.chemengonline.com/6517-532) started up a new production plant that produces 100 m.t./yr of solar-grade (SOG) silicon (Si) from crude Si metal. The company also started to design a 500-1,000-m.t./yr plant for making SOG Si, and plans to start operations by March 2008.
Up to now, JFE Steel used directional-solidification (DS), which aligns the Si crystals in one orientation by controlled thermal flow, to manufacture Si ingots from molten polysilicone and scrap Si from the semiconductor industry. But the quantity of such scrap available is insufficient to meet the growing market for solar-cells, so the company decided to develop its own Si-refining process. The process was first developed by a consortium of industry and research partners, with support from the New Energy & Industrial Technology Development Organization (Kawasaki, Japan; CE, August 1999, p. 19), and subsequently improved by JFE Steel.
In the process, crude Si (95 wt.%) is melted under vacuum at 1,500°C and phosphorous impurities vaporized by an electron beam. DS is then used to separate most of the metal impurities, followed by a plasma melting and oxidation process for removing carbon and boron impurities. A second…