Dry texturing of mc‐Si wafers

Texturing of mc-Si is a prevailing research topic to improve solar cell efficiency in production. Surface texturing for enhanced absorption in Si has been historically obtained by creating randomly distributed pyramids using anisotropic etchants; but this preferential etching works only on single crystalline silicon because of its crystallographic orientations. A low-cost, large area, random, mask-less texturing scheme is expected to significantly impact terrestrial PV technology and reduce the amount of wet-chemical waste. We propose an approach based on randomly etched mc-Si by RIE system using NF3 instead of SF6 or CF4 to reduce the detrimental formation of carbonaceous or sulfurous contamination at the silicon surface, which results in a surface recombination. To obtain a fast process we have investigated the effect of the chemical etching due to the NF3 radicals and the ion bombardment induced by Ar. We have found that Arions promote a helpful surface pre-conditioning, while fluorine radicals, produced by NF3 dissociation, are needed to increase the Si etching rate. Different combinations of flux ratios, gas pressures and RF power have been explored. Efforts have been devoted in obtaining a homogeneous texture on large area wafers, which is inescapable for industrialization. After 10 minutes process effective reflectance values have been measured within the range of 12-14%, and with a-Si/SiNx the value reduced to 7%. Post-processing minority carrier lifetime values in the range of 10 microseconds have been measured without applying any further chemical cleaning. Additionally, microscopic analysis has been performed to evaluate the surface microstructure morphology (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)