Temporal evolution of silicon surface roughness during anisotropic etching processes

An analysis of the surface roughness of (100) silicon planes during anisotropic etching processes is presented. Phase-measurement microscopy was used to reveal surface roughnesses with nanometer-scale depth and submicron lateral resolution. The potential and the limits of this metrology method for application in silicon micromachining technology are demonstrated. The dependence of surface roughness on concentration and temperature of KOH is investigated systematically in the range of 25-45% and 60-80°C, respectively, and the results are compared with results for TMAH-based etchants. The impact of various wafer treatments prior to the anisotropic etching process on the final smoothness of the silicon surface is discussed. Optimum etching conditions are derived for both the wet chemical etching process and the preparation cycle of the wafers prior to the etching. It is shown that minimum microroughness and macroscopic planarity of the etched grooves are obtained for different etch parameters