Calcium and titanium as impurity getter metals in purification of silicon

In this paper, the results of solvent refining experiments are described with primary focus on the removal of boron and phosphorus from silicon. Either calcium or titanium was melted with metallurgical grade silicon to form an alloy phase into which impurity elements are rejected. The melt was then slow cooled to allow solid Si to separate from the mixture. The solidified sample was crushed to liberate the alloy phase before leaching in acid to allow the purified silicon product to be collected. Titanium additions were followed by leaching with a mixture of hydrochloric, nitric and sulphuric acids, but were not effective for removing B or P, serving only to contaminate the Si with the getter metal. Adding calcium was very effective for removing phosphorus when leached in two stages, with near complete removal achieved with 4wt.% addition of Ca.