Release etch modeling analysis and the use of Laser Scanning Microscopy for etch time prediction of micromachined structures

An alternative non-destructive analysis method using Laser Scanning Microscopy (LSM) was used to study etch release distances in MEMS pressure sensors. The LSM method eliminates sample preparation and is easy to implement in a MEMS manufacturing environment. In this study, various diaphragm structures were etched using a highly concentrated HF based solution. Experimental etch data were obtained for both SiO ₂ and PSG films under these various structures. Both the height and the width of the sacrificial layer port/channel had a significant effect on etch rate for both films. As expected, a non-linear etch rate was obtained for both SiO ₂ and PSG films. Since the HF concentration changes over time in a manufacturing bath process, careful selection of processing time is required in order to fully release MEMS structures. Future theoretical modeling with the assistance of experimental data obtained in this study is being pursued to strengthen past work done by Eaton et al., Monk et al., and Liu et al.