Vertical profiles and CD loss control in deep RIE technology [MEMS fabrication applications]

Deep reactive ion etching (DRIE) technology is widely used to fabricate high aspect ratio structures in MEMS devices. The vertical profiles of the trenches etched by normal advanced silicon etching are not always satisfactory enough for some applications such as a vibratory lateral gyroscope. Bad vertical profiles will decrease the capacitance signal of a lateral comb, change the designed stress of a cantilever beam, reduce the weight of the mass and finally affect the sensitivity and stability of MEMS devices, especially small dimension MEMS structures. We introduce a new technology to improve the vertical profiles, which is realized by decreasing the etching time each cycle. This anisotropy parameter improves from 25 to 175. Moreover, we introduce a method to reduce CD loss. It is realized by adding descending passivation gasses C₄F₈ in the first several minutes and decreasing the etching time in the switch periods. The CD loss is decreased from 145 nm to 55 nm.