Impact of solar cell manufacturing processes on thermal oxide-passivated silicon surfaces

In this paper, we investigate the impact of a solar cell fabrication process on the properties of thermal oxide-passivated Si surfaces. Therefore, symmetric thermally oxidized silicon wafers are exposed to the cell process and analyzed by means of quasi steady-state photoconductance and capacitance-voltage-measurements. The oxide thickness reduces during processing. Alkaline texturing, diffusion and firing processes are shown to decrease the effective carrier lifetime. Moreover, the total charge density decreases and the interface trap density at midgap increases along the manufacturing process. The latter complies with the observed reduction of the effective carrier lifetime. Nevertheless this process induced degradation of the oxide passivation is fully reversible with aluminum deposition and subsequent annealing in forming gas. After a post-metallization anneal, on saw damage etched surfaces of 1 ?cm p-type floatzone material, surface recombination velocities of less than 50 cm/s are measured.