Advances in Deep Anisotropic Silicon Etch Processing for Mems

This paper presents the latest developments in high rate deep silicon etching for MEMS applications. Since its introduction by STS over 5 years ago, the Advanced Silicon Etch (ASE (R)) process has provided the MEMS community with a method of fabricating high aspect ratio structures in silicon, with accurate critical dimension control, and a high degree of anisotropy. High selectivity to photoresist (up to 170:1) has also enabled replacement of hard masks, and in turn, this has simplified process flows for MEMS manufacturers. The ASE (R) technology uses non-toxic, fluorine-based chemistry, operates at room temperature, and has been shown to be production worthy for the volume manufacture of MEMS devices such as inertial sensors. As the MEMS industry matures, it places ever more demands on the processes and there is a growing requirement to achieve the same degree of anisotropy and critical dimension control, but at much higher etch-rates. An exhaustive series of trials to increase etch rates have successfully shown a nominal rate increase by a factor of > 2. These results are presented in this paper.