Effect of Surfactant and Alcohol Additives on Etching Characteristics in Aqueous Potassium Hydroxide Solutions

Anisotropic wet etching is a simple and low cost technique for silicon bulk micromachining to fabricate microelectromechanical systems (MEMS) components. In this work, we have systematically studied the etching characteristics of Si{100}, Si{110}, and Si{111}) in various concentration of KOH (5-40 wt% in step of 5 wt%) without and with addition of surfactant Triton-X-100 and isopropyl alcohol (IPA). KOH solution with addition of IPA and Triton is termed as ternary solution. The addition of Triton and IPA affects the etching characteristics dramatically, especially the undercutting at convex corners on Si{100} surface and the etch rate of Si{110}. The undercutting at convex corners and the etch rate of Si{110} in ternary solution suppress to a significantly low level. Low undercutting is very useful for the formation of microstructure with protected corners such as mesa, while significantly low etch rate of Si{110} can be exploited to fabricate microstructure with 45o sidewall (or 45o micromirror). In addition, ternary solution with low concentration KOH provides smooth etched surface morphology.