Dry phosphorus silicate glass etching for crystalline Si solar cells

Dry plasma etching techniques could be of permanent importance in future complete in-line fabrication of crystalline silicon solar cells. Phosphorus silicate glass (PSG) etching represents the most challenging process step, since it has to be etched fast and residual free, without damaging the underlying emitter layer. In this paper we present a process sequence which meets all this requirements. With different CF-containing etch gas mixtures high SiO2 to Si selectivities together with high etch rates could be reached enabling short process times. A plasma post cleaning step ensures a clean and well conditioned surface for the subsequent SiNx deposition. Dry PSG etched solar cells reached efficiencies of 14.6 % on mc-Si and 15 % on Cz-Si, having similar or even better performance in all solar cell parameters compared to wet chemically PSG etched reference cells. Upscaling of the selective etching processes to an industrially suitable in-line etching system with high wafer throughput has been successfully demonstrated.