Analysis of KOH etching of (100) silicon on insulator for the fabrication of nanoscale tips

Anisotropic etching of Si with KOH is a well-known method of forming grooves in the Si surface. We report here on the use of KOH solutions for etching extremely sharp silicon tips on silicon on insulator (SOI) material. Etching of (100) silicon on SOI wafers was carried out over a wide range of reaction temperatures and KOH concentrations. Using statistical methods, we show that the factors important in the silicon etch rate are, in decreasing order of importance, reaction temperature, KOH concentration, and interaction between temperature and KOH concentration. The activation energy of etching at different KOH concentration was calculated from Arrhenius plots to be between 0.43 and 0.59 eV. In addition, in this article we report a qualitative study of the sharpness of Si tips formed by KOH etching. The sharpness increases with temperature to a critical point and then decreases at very high temperature and KOH concentration. Hydrogen bubbles formed during etching are very important in determining both etch rate and sharpness of the tips. The sharpest tip dimension was found to occur at 30% KOH and 70°C reaction temperature.