Pattern induced convex corner undercutting of oriented silicon microridges in potassium hydroxide

Abstract

Modelling and fabrication of corner compensation structures is an active area of research involving KOH based wet etching. A useful data set has been generated to enable fabrication of efficient compensation structures used to prevent undercutting of convex corners during KOH etching. In this work, the effect of the mask pattern on the extent of undercutting the convex corners of microridges that occur during KOH etching was investigated. Microridges on silicon <100> substrates oriented at varying angles with respect to the <110> crystal orientation were etched in KOH solution. The ensuing undercut in the convex corners during the etching process was ascribed to the crystallographic orientation of the substrate, i.e. some crystal planes etch faster than others, contributing to a deformation of a desired structure. It was observed that the damage of the convex corners and the front face of the microridges increased with increasing angle of microridge orientation with respect to the <110> direction. {311} planes arising from the corners making acute angles with the <110> wafer orientation take longer to acquire a saddle point in the etching diagram. This is postulated to cause the observed complete wash out of the microridge faces for extremely acute angles.