Electrochemcial Etch Stop
Electrochemical etch-stop (ECES) is a popular method for bulk micromachining of a p-n junction silicon wafer in MEMS applications.
Bias-voltage dependent etching of silicon in alkaline solutions (KOH, TMAH) is a regular anisotropic etch. Etching stops at passivation potential (PP) due to excess generation of SiO2 on the wafer surface, when reached the n epi layer – this is a local effect contributing to uniformity. ECES allows
- Fabricating membranes with precise thickness control.
- Achieving un-paralleled membrane thickness uniformity usually better +/- 0.8%
- Precise thickness control independent from precise etchant concentration and temperature control
