Focused ion beam strategy for nanostructure milling in doped silicon oxide layer for light trapping applications

Focused ion beam milling is used to nanopattern doped silicon oxide layer in view of light trapping application in thin film photovoltaics. Different working conditions, such as ion beam currents, milling times, dwell times, etc., are optimized in order to improve the nanochannel shape by reducing the effect of redeposition of sputtered target material on the sidewalls. This phenomenon, due to ion beam striking on the target layer, induces a V-shape instead of the desired box-shape for the nanochannels. A suitable milling strategy is here explored to reduce this effect. The results show that the parallel scan routine with "bottom to top" direction gives a more appropriate shape. Also parallel multi-pass milling and 3 × 1017 ions/cm2 ion dose result in reduced redeposition. Sputtering yield is calculated both experimentally and theoretically, and correlated with the redeposition. Due to the focused ion beam peculiarity, nanopatterning can be achieved, without utilizing an etching mask or resist layer, which is advantageous for fabrication of prototype devices.