Purification of SoG silicon by millisecond range internal gettering of metal impurities

Cost reduction is the overall goal in the further development of the photovoltaic technologies. The solar-grade (SoG) mc-Si produced by upgrading metallurgical-grade silicon is an attractive material for low-cost solar cells. The remaining impurities after the purification process, mainly transition metals, are the main obstacle towards highly efficient solar cells, effectively limiting the minority carrier lifetime. Here we propose a novel method for the purification of SoG silicon by a millisecond range low thermal budget internal gettering process. The solar cells were produced by Plasma Immersion Ion Implantation of phosphorous using PH3 gas source and millisecond range Flash Lamp Annealing (ms-FLA). To study the metal distribution during ms-FLA, Cz-Silicon wafer were intentionally doped with iron. An influence of different thermal treatments on the diffusion of iron and the optoelectronic properties of metal contaminated silicon wafers were investigated by RBS, cross-section TEM, Raman spectroscopy, photoluminescence and surface photovoltage spectroscopy. We have shown that diffusion of metal impurities into the space charge region can be avoided by an one step ms-FLA step, only. It will be presented that the implanted phosphorous is electrically activated and all defects introduced into silicon during the ion implantation process are removed while metal impurities are kept far away from the p-n junction region. The effect of hydrogen co-implanted with phosphorous on the redistribution of iron will be explored. ms-FLA is demonstrated here as a very promising technique for the emitter formation in SoG silicon using an low thermal budget, only.