Double-Step Plasma Etching for SiO<sub>2</sub> Microcantilever Release

Abstract

In this paper, an isotropic dry plasma etching was used to release the suspended SiO2 microcantilever from the substrate of SOI wafer. Employing the plasma dry etching technique, the frontside etching for the SiO2 microcantilever release is done using the Oxford Plasmalab System 100. To obtain the optimum condition for the microcantilever release using the plasma etcher, the etching parameters involved are 100 sccm of SF6 flow, 2000 W of capacitively coupled plasma (CCP) power, 3 W of inductively coupled plasma (ICP) power, 20°C of etching temperature and 30 mTorr chamber pressure. The optimum parameters yield lateral etch rate of about 5 μm/min and vertical etch rate of about 8 μm/min. Two etching methods have been considered in this study. The first method employs only the isotropic etching to realize the microcantilever release while the second method utilizes both the anisotropic etching and the isotropic etching. For the second method, the process starts with the anisotropic etching from the deep reactive ion etching (DRIE) system which is then followed by the isotropic etching to complete the microcantilever releasing process. The purpose of the anisotropic etching is to create an etching window for the subsequent isotropic etching process. By using double-step etching method which combines both isotropic and anisotropic plasma etching for the microcantilever release process, the releasing process of suspended microcantilever is significantly improved.