The DRIE (Deep Reactive Ion Etching) process is one of the most important processes for MEMS field. Especially, a high aspect ratio etching is essential for state-of-the-art devices. This paper describes a new DRIE process that drastically improves the highest aspect ratio of conventional DRIE process. The conventional process deposits a protection layer not only on a trench sidewall, but also on a trench bottom. This isotropic deposition causes a limitation of aspect ratio. To avoid this situation, we have developed a new process that alternately repeats the conventional DRIE process and a O2 plasma irradiation which forms a thin SiO2 layer inside the trench within a same chamber. The SiO2 layer remains on the sidewall during the DRIE proceeds while it on the bottom is removed at the beginning of each DRIE. Therefore, the etching anisotropy is improved. A switching between the conventional DRIE and the O2 plasma irradiation needs only to change introducing gasses. This simple process can widen a possibility of the conventional DRIE.
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