Boron Removal from Silicon by Humidified Gases
Journal article, Peer reviewed
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OriginalversjonMetallurgical and Materials Transactions E. 2014, 1 (1), 41-47. 10.1007/s40553-014-0007-8
Boron (B) is one of the most problematic impurities to remove from metallurgical grade silicon in the production of more pure solar grade silicon (SoG-Si). In the present work, recent progresses in the application of reactive gases for B removal from molten silicon is reviewed. Moreover, in order to clarify the mechanisms and kinetics of gas-based B-refining, an experimental procedure using humidified Ar, N2, and H2 gases applied to boron-doped silicon melt is described. It is shown that the kinetics and extent of B removal is depending on the type of humidified gas. The thermodynamics and kinetics of B removal from molten silicon are studied to explain experimental observations. The mass transfer coefficients of B are calculated and possible mechanisms for B removal by the reactive gases are proposed: 1/2H 2 (g) B − +H − +H 2 O(g) =H, − \hfill =HBO(g)+H 2 .\hfill It is shown that the lower equilibrium partial pressure of HBO gas at higher temperatures causes slower B removal rate.