Handbook of Silicon Based MEMS Materials and Technologies

24.2.4. Orientation Dependence of the Etch Rate (M.A. Gosálvez and I. Zubel)

The dependence of the silicon etch rate on the crystallographic orientation of the etched substrate and solution composition can be connected to the differences in the local neighborhood of the exposed surface atoms, such as the numbers of neighbors, dangling bonds, and surface bonds. The arrangement of the atoms on the different planes has been described and classified in different ways, resulting in different models of etching [16, 17, 59, 61, 68–75]. The most accepted classification identifies four key surface sites, as shown in Figure 24.3a, b: (1) the terrace monohydrides (TM), appearing on {111} terraces; (2) the step monohydrides (SM), located at the steps of ...