Removal of iron and titanium in poly-crystalline silicon by acid leaching

Abstract

Removal of Fe and Ti from Si by acid leaching method was examined, the optimum condition for acid leaching was obtained and the mechanism of removal of impurities in Si was estimated. Si-Ca-(Fe, Ti) alloys with various compositions were subjected to acid leaching procedure using aqua regia. For most of the samples, 85∼96% of Fe and 80∼93% of Ti were removed from Si and the effects of cooling rate and alloy composition were studied. Slow cooling (4.4 K/min) was found to be better for effective removal of impurities than quenching. In order to give a higher removal rate of iron, acid soluble CaSi2 phase should be precipitated as a secondary phase, namely XCa/XFe > 6.5. On the other hand, the optimum composition for the removal of Ti is considered to be XCa/XTi = 3.