Isotropic etching of polycrystalline silicon wafer by acidic solution

Abstract

In photovoltaic technology, texturing of base wafer has great importance since it reduces the reflectance of incident light that leads to improvement in the conversion efficiency. Due to different orientations present in polycrystalline silicon wafer an isotropic etching and the texturing without grain boundary delineation is great challenge. In this study, an attempt has been made to get isotropic etching by acidic solution. The volume ratios of HF/HNO3/ CH3COOH have been chosen in such a way that it fell in lower part of iso-etch curve where the solution is HNO3 rich. The presence of high concentration of HNO3 leads to the rapid oxidation of silicon surface and hence makes the etching rate limited through the diffusion of HF into the SiO2. This study shows the isotropic etching of poly-Si wafer which is confirmed by scanning electron microscopy. Moreover, the reflectance measurements show that the average reflectance reduces from 20.5 to 8.5 % over 350 to 800 nm range.