Method for purification of silicon

Abstract

Disclosed is an efficient and inexpensive method for the purification of low-grade silicon such as metallurgical-grade metallic silicon to give solar cell-grade silicon. The method comprises: (a) melting the starting low-grade silicon in a melting crucible; (b) bringing an end of an elongated linear fiber compact body of a refractory material, e.g., bundles of carbon fibers, into contact with the molten silicon in the crucible so that the molten silicon infiltrates and migrates through the fiber compact body by the capillary phenomenon to reach the other end of the fiber compact body held at a lower level than the first end; and (c) receiving the effluent of molten silicon discharged out of the second end of the fiber compact body in a receptacle crucible. The atmospheric gas is preferably a gaseous mixture of an inert gas, e.g., argon, and a small amount of a reactive gas, e.g., oxygen and hydrogen chloride, which reacts with the impurity elements such as boron and phosphorus in the starting low-grade silicon material to form a more volatilizable compound of the impurity element.