A study of two-step silicon anisotropic etching for a polygon-shaped microstructure using KOH solution

This paper proposes a novel fabrication method for micromechanical structures which are defined by two planes, the (111) plane and a high-index crystal plane. The structure is obtained by a two-step etching process on a (100) silicon wafer using a 40%, 85 degrees C KOH silicon anisotropic etch solution. The (111) plane is created during the first normal anisotropic etching process and the high-index plane is obtained from a second etching step without a silicon dioxide mask. The new plane is considered as a (310) plane, having a 18.43 degrees angle to the (100) plane. A polygon-shaped microstructure can easily be obtained by this method and the structure has excellent reproducibility due to the anisotropic characteristics of the silicon orientation. The method has been sucessfully applied to fabricate a silicon micromould for a plug-type microvalve. The results indicate exact reproduction both in size and shape of the micromould. (C) 1997 Published by Elsevier Science S.A.