Purified Silicon Film Formation from Metallurgical-Grade Silicon by Hydrogen-Plasma-Induced Chemical Transport

Abstract

A purified Si film is prepared directly from metallurgical-grade (MG) Si by chemical transport using sub-atmospheric pressure H2 plasma. The purification mechanism is based on the selective etching of Si using atomic H. It is demonstrated that the concentrations of most metal impurities (e.g., Fe, Cr, Ni, Ti, and Mn) in the prepared Si film are in the acceptable range for solar-grade Si material, or below the determination limit of the several impurity measuring methods employed in this study. From the infrared absorption measurements of the etching product produced by the reaction between H2 plasma and MG-Si, it is found that the main etching product is SiH4. Therefore, a remote-type chemical transport process is developed to produce SiH4 gas directly from MG-Si. Using other purifying principles (such as a pyrolysis filter in combination with this process), it is demonstrated that purified Si films about B, P and metal atoms can be produced from metallurgical-grade Si (<98% purity).