Handbook of Silicon Based MEMS Materials and Technologies

24.10. Concentration Dependence of the Etch Rate

24.10.1. Experimental Considerations (I. Zubel)

Aqueous solutions of KOH and NaOH are often used as anisotropic etchants of silicon. Due to the small dimension of the Na⁺ ions and their harmful penetration into the bulk of the substrate, they are, preferably, avoided during fabrication. The variation of the etch rate of Si{100} and Si{110} as a function of the concentration of KOH and NaOH is shown in Figure 24.14a, b. The curves show peak values at roughly the same medium concentration for both orientations, and the relation R¹¹⁰ > R¹⁰⁰ holds. Other hydroxides from the first group of the periodic table, such as RbOH and CsOH, are rarely used in practice. The characteristics of the corresponding ...