Investigation of KOH Anisotropic Etching for the Fabrication of Sharp Tips in Silicon-on-Insulator (SOI) Material

Abstract

KOH etching may be used to create V-shaped features in silicon that are aligned with the (111) planes at an angle of 54.74 from the (100) surface. To investigate the eect of hydrogen bubbles on the formation of features such as sharp isolated tips, we carried out etching of (100) silicon on insulator (SOI) wafers over a wide range of reaction temperatures and KOH concentrations. We determined that the critical factors determining the silicon etch rate are, in decreasing order of importance, the reaction temperature, the KOH concentration, and the interaction between temperature and KOH concentration. Initially, both the sharpness of the silicon tip and the etch rate increase with temperature and KOH concentration and then decrease above critical values of both. Hydrogen bubbles formed during etching are very important in determining both the etch rate and the sharpness of the tips. The diameter of the bubbles decreases with increasing temperature. The size of the bubbles decreases signicantly and the density of bubbles increases drastically as the KOH concentration increases. The shapes of the tips were determined using transmission electron microscopy, and the sharpest emitter diameter was estimated to be 3 nm at a 30 % KOH concentration and a 70 C reaction temperature.