VERY DEEP TRENCHES IN SILICON WAFER USING DRIE METHOD WITH ALUMINUM MASK

Abstract: In this paper, a DRIE process for fabricating MEMS silicon trenches with a depth of more than ۲۵۰ m is described. The DRIE was produced in oxygen-added sulfur hexafluoride (SF۶) plasma, with sample cooling to cryogenic temperature using a Plasmalab System ۱۰۰ ICP ۱۸۰ 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 ۵.۴۴x۱۰-۳ 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 ۲.۸۵ microns per minute for silicon and a high selectivity of ۵.۲۴x۱۰۵ to the Al etch mask have been obtained. A ۹۰ min etching experiments using etching gas SF۶ of ۶۰ standard cubic centimeters per minutes (sccm) with oxygen (۱۳ sccm) were performed by supplying RF power of ۵ W to an ICP of ۶۰۰ watts, and silicon etching process with a depth of ۲۵۷ m was demonstrated. Our experiments show that Al is the best mask material for very deep trenches in silicon.

Keywords:

DRIE , deep trench , silicon structure , Al mask , etch rate , selectivity