Fabrication of vertical optical plane using DRIE and KOH crystalline etching of (1 1 0) silicon wafer

The present study aims at obtaining a novel fabrication method to realize smooth vertical sidewalls for optical micro/nanoelectromechanical system applications. To reduce the surface defects of the vertically etched sidewall, KOH crystalline etching is employed after silicon deep reactive ion etching process of a (1 1 0) silicon-on-insulator wafer. The effects of additional KOH etching on the sidewall morphology are investigated with respect to the etching temperature and concentration of KOH. The optimized process conditions of KOH etching are found to be 45 wt.% KOH concentration and 70 °C temperature. To evaluate the morphological characteristics of the vertical sidewall, optical resonators consisting of a single silicon plate are fabricated using an optimized process with additional KOH crystalline etching. The experimental effective finesse of the fabricated optical resonator is compared with theoretically simulated finesse and is found to be improved by 21.8% compared with a reference sample fabricated only by the deep reactive ion etching process.