Nanometer physics in microsystem research: reversed anisotropy observed in wet chemical etching of silicon

Microsystem research is reinforced by nanometer physics introducing atomistic models. We found that anisotropy in wet chemical etching of silicon was dominated not only by the surface orientation of single crystal wafer but also by the activeness of atomic steps on Si [111] surface as well. The activeness of the atomic step on [111] surface was highly oriented, and was reversely oriented between two etchants of KOH and of TMAH. The differences in macroscopic etching behavior between the two etchants were explained by the difference in activeness of the atomic steps. It should be noted that conventional static model counting the number of dangling bond on a surface atom is no more applicable to discuss anisotropy in etching which is quite a dynamic phenomena.