Differences in anisotropic etching properties of KOH and TMAH solutions

We compared the anisotropic etching properties of KOH and TMAH solutions. We used hemispherical specimens of single-crystal silicon whose surface exhibited every crystallographic orientation, in order to evaluate the etching properties as a function of the orientation. We carried out a series of experiments using different etchant concentrations and etching temperatures. The orientation dependence in the etching rates of the surface crystals significantly differed between the two etchants, especially for the (111) and (221) planes. We conclude that the two etchants have different etching mechanisms at least in an area including these two planes. The etching rates varied with etchant concentration and etching temperature. The concentrations that maximized the etching rate were 25 wt.% for KOH and 20 wt.% for TMAH. The activation energies in KOH and TMAH were almost the same for the (100), (110), and (320) planes but not for the (221) and (111) planes. Etchant circulation had a significant effect on the etching rates in diluted TMAH solution but not in KOH solution. The roughness of the (100) plane in KOH was one order smaller than that in TMAH. (C) 2000 Elsevier Science S.A. All rights reserved.