Study of the Anisotropic Wet Etching of Nanoscale Structures in Alkaline Solutions

A qualitative and semi quantitative analysis of anisotropic etching of silicon nanostructures in alkaline solutions was done. Dedicated nanostructures were fabricated on 300mm wafers and their geometric change during wet etching was analyzed, stepwise, by top down SEM or TEM. We challenge the previously described wagon wheel technique towards nanodimensions and describe the pros and cons of the technique using relevant experimental conditions. The formation of specific geometric patterns are explained by the face-specificity of the etch rates. Clear differences in anisotropy were revealed between pillars etched in KOH or in TMAH, and for wagon wheels etched in TMAH or in NH4OH. Finally etch rates were extracted for the different types of crystal planes and compared.