Highly selective KOH-based etchant for boron-doped silicon structures

Mixtures of Ethylenediamine, Pyrocatechol and Water (EPW) are highly selective but extremely toxic silicon etchants that are widely used in fabricating boron-doped P++ silicon structures. A safer etchant based on KOH-H2O-Isopropyl alcohol (IPA) solution has been investigated and shown to display a selectivity comparable to EPW. The following dual etchant system has been used successfully for the selective etching of P++ silicon membranes: (1) 20% aqueous KOH at 80°C for unlimited bulk etching of (100)-Si wafers, and (2) 20% aqueous KOH saturated with IPA at 80°C for maximum P/P++ selectivity and limited etching of (100)-Si. © 1989.