New DRIE Process with Sidewall Protection Layer Formed by O₂ Plasma Irradiation

Abstract

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.