日本金属学会誌

J. Japan Inst. Metals, Vol. 54, No. 2 (1990),
pp. 161-167

Gaseous Removal of Phosphorus and Boron from Molten Silicon

Kichiya Suzuki1, Kouichi Sakaguchi2, Toshio Nakagiri3 and Nobuo Sano1

1Department of Metallurgy, Faculty of Engineering, The University of Tokyo, Tokyo
2Department of Metallurgy, Faculty of Engineering, The University of Tokyo, Tokyo. Present address: Central Laboratory, Nippon Sheet Glass Co. Ltd., Itami
3Department of Metallurgy, Faculty of Engineering, The University of Tokyo, Tokyo. Present address: Matsuda Co. Ltd., Hiroshima

Abstract:

The purification of metallurgical grade silicon (MG-Si), especially the removal of phosphorus and boron, was investigated by applying the vacuum evaporation for phosphorus and plasma treatment for boron, respectively, to develop a new production technique of solar grade silicon (SOG-Si) at low cost.
The concentration of phosphorus in the MG-Si decreased from 32 mass ppm to 6 to 7 mass ppm after 3.6 ks by vacuum treatment at 0.027 Pa. The concentration of calcium and aluminum also decreased. It has been demonstrated that the overall evaporation of phosphorus and calcium is controlled by the diffusion of these elements through silicon melt to the gas-metal interface.
In the experiment of plasma treatment, the MG-Si was melted under various oxidizing plasma conditions by using Ar+O2 or Ar+CO2 as an operating gas for 30 to 1800 seconds. It has been found that the concentration of boron in MG-Si decreased from 28 mass ppm to 2 to 4 mass ppm and boron in MG-Si can be removed as a gaseous boron oxide. A mechanism of boron elimination under the oxidizing plasma conditions is discussed.


(Received 1989/8/24)

Keywords:

refining, metallurgical silicon, vacuum evaporation, plasma treatment, phosphorus, boron


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