ABSTRACT
This chapter focuses on the etching characteristics of pure and surfactant-added tetramethylammonium hydroxide (TMAH) solutions. In the case of pure TMAH, undercutting increases with its concentration, while in surfactant-added TMAH, it is almost the same for all ranges of TMAH concentration. In the design of microelectromechanical systems structures many kinds of shapes such as mesa structures and proof masses for accelerometers include convex corners. A wet-etched profile is strongly affected by mechanical agitation, especially in surfactant-added TMAH where surfactant adsorption on the silicon surface alters the etching characteristics. The etching characteristics of TMAH strongly depend on the etchant concentration and the type and concentration of the additive. Etching temperature mainly influences the etch rates of silicon and the masking layer. Anisotropic etching consists of two alternating reactions, namely oxidation and etching, with the peculiarity that oxidation is very slow as compared to etching.
