Development of Si DRIE process allowing simultaneous etching from narrow and wide mask openings

Abstract

We have developed a new Si DRIE process, which allows simultaneous etching of both narrow and wide mask opening patterns. MEMS devices often contain a wide range of mask opening sizes ranging from micrometer to millimeter scale on the same chip. Conventional DRIE process suffered from a trade-off between minimizing mask-undercut for narrow grooves and eliminating black Si on an etched bottom surface for large mask apertures. This was caused by nonuniformity in the deposition of the protective polymeric layer during etching in mask aperture areas having different sizes. Our new DRIE process technique, alternating conventional DRIE with O2 plasma irradiation, adds a SiO2 layer onto the polymeric layer. We have ascertained that the new DRIE process can form a SiO2 protective layer of uniform thickness regardless of the mask aperture size. This uniformity is considered a result of equilibrium between surface oxidation and sputtering of oxygen by plasma irradiation. We have demonstrated that our newly developed process allows simultaneous etching of narrow, deep grooves 1 μm wide and 73 μm deep, and wide aperture areas 500 μm square without black Si on the same chip. © 2011 Wiley Periodicals, Inc.