Iranian Journal of Materials Science and Engineering

Abstract: In this paper, a DRIE process for fabricating MEMS silicon trenches with a depth of more than 250 m is described. The DRIE was produced in oxygen-added sulfur hexafluoride (SF6) plasma, with sample cooling to cryogenic temperature using a Plasmalab System 100 ICP 180 at different RF powers. A series of experiments were performed to determine the etch rate and selectivity of the some masking materials such as resists, and metal (Al). Experiments show that different materials have different etch rates, but for the Al mask, an etch rate of 5.44x10-3 nm/min was achieved, that exhibits very stronger resistance against RIE than resists. By controlling the major parameters for plasma etch, an etch rate of 2.85 microns per minute for silicon and a high selectivity of 5.24x105 to the Al etch mask have been obtained. A 90 min etching experiments using etching gas SF6 of 60 standard cubic centimeters per minutes (sccm) with oxygen (13 sccm) were performed by supplying RF power of 5 W to an ICP of 600 watts, and silicon etching process with a depth of 257 m was demonstrated. Our experiments show that Al is the best mask material for very deep trenches in silicon.