Gettering of metal impurities by using phosphorus diffusion in UMG silicon wafers

Abstract

Upgraded metallurgical grade (UMG) silicon is a cost-effective and energy-efficient silicon material for the production of solar cells. UMG silicon wafers with 5N purity include various kinds of metal impurities like Fe, Ni, Cu, and Co, which may limit the electrical performance of UMG silicon wafers and solar cells. Phosphorus diffusion gettering, which can effectively reduce the transition-metal impurities in the bulk of UMG silicon wafers and enhance the minority carrier lifetime (MCLT), is a well-known process to improve the performance of solar cells in the photovoltaic (PV) industry. In this study, phosphorus diffusion gettering was used at a constant temperature of 700 for 5 hours, and the effects of the gettering process were confirmed by measuring the MCLTs and the efficiencies of the solar cells. Depth profiles of the Fe concentration before and after the gettering process were compared using secondary ion mass spectroscopy (SIMS) measurements.