FABRICATION OF NON-UNDERETCHED CONVEX CORNERS IN ANISOTROPIC ETCHING OF (100)-SILICON IN AQUEOUS KOH WITH RESPECT TO NOVEL MICROMECHANIC ELEMENTS

The planes occurring at convex corners during anisotropic etching of (100)-silicon in aqueous KOH were identified as {411}-planes, with the help of a specially developed measuring technique. The etching rate of these planes in relation to the rate of the {100}-planes declines with increasing potassium hydroxide concentration. In contrast, the temperature dependence of this etch rate ratio is negligible in the relevant range between 60°C and 100°C. Based on these results, special structures suited for the compensation of the undercutting in the case of very narrow contours were developed. With the help of these structures it is feasible to realize, for instance, bent V-grooves or structures with a very low ratio between lateral expansion and etching depth, e.g., a discrete pyramid-trunk with minimum dimensions on the wafer surface. This offers access to completely new applications, among others spiral channels with double-sided anisotropic etching for micromechanical heat exchangers; corrugated diaphragms stiffened in two dimensions with low thermal resistance and arbitrary wall thickness; and bellow structures for decoupling mechanical stresses between micromechanical devices and their packaging. Furthermore, this technology paves the way for designing novel types of accelerometers and inclination sensors with external seismic mass. © 1990, The Electrochemical Society, Inc. All rights reserved.