Comparison of anisotropic etching properties between KOH and TMAH solutions

We compared the anisotropic etching properties of KOH and TMAH solutions. We used hemispherical specimens of single-crystal silicon on where surface whole crystallographic orientations appeared, in order to evaluate the etching properties as a function of the orientations. We carried out a series of the experiments using different concentrations of two etchants and different etching temperatures. The dependence of the etching rates on the orientation of the surface crystals significantly differed between the two etchants, in particular at orientations of (111) and (221) planes. We concluded that the two etchants have different etching mechanisms at least around these two plane orientations. The etching rates depended on the concentration of the etchants and the etching temperature. The concentration levels that maximize the etching rate were 25 wt.% for KOH and 20 wt.% for TMAH. The activation energy of the two etchants was about 0.6 eV. The effects of etchant circulation on the etching rates were significant in TMAH but not in KOH solution.