Mitigating the Insufficient Etching Selectivity in the Wet Release Process of CMOS-MEMS Metal Resonators Via Diffusion Control
Journal
Journal of Microelectromechanical Systems
Journal Volume
29
Journal Issue
6
Pages
1415-1417
Date Issued
2020
Author(s)
Abstract
This letter presents an effective approach to mitigating the prolonged issue of the insufficient etching selectivity between the sacrificial oxide and structural metal Al during the final release step of the CMOS-MEMS metal resonators. Particularly, the approach purposely slows down the etching rate not only for the sacrificial oxide but also more effectively for the structural metal by covering the resonator devices with upper metal layers in the CMOS process that contain release holes to pinch the diffusion of the etchant. Doing so realizes a 10× extension in the allowable time window for over-etch, from a rather critical 5 min to over 50 min. This work further investigates the influence of the HF-based etchant temperature from 20°C to 40°C on the etch rate. The results show that the technique introduces the diffusion limiting effect at lower temperatures, leading to a less temperature sensitive etch rate compared to that of the reference counterpart. This method provides a promising and effective remedy for improving the yield during the time- and solution condition-sensitive oxide wet release step of CMOS-MEMS-based resonant devices. [2020-0299] ? 1992-2012 IEEE.
Subjects
Diffusion; Etching; Metals; Resonators; Diffusion control; Effective approaches; Etching selectivity; Lower temperatures; Resonator devices; Sacrificial oxide; Solution conditions; Temperature sensitive; CMOS integrated circuits
SDGs
Type
journal article