Electrochemical etch-stop control for silicon structures containing electronic components

Abstract

A predictive analysis of the feasibility of electrochemical etch-stop control in the fabrication of some silicon sensors was validated experimentally. The application is for sensors with thin silicon structures containing electronic components, such as cantilever accelerometers and diaphragm pressure gauges with strain gauges in the surface to detect deflection. Such structures are formed by deep anisotropic etching of silicon. Since the depth of the etch determines the thickness of the cantilever or diaphragm, the ability to stop the etching precisely is critical. Accurate etch-stop control can be accomplished by electrochemical passivation of an n-type epitaxial layer on a p-type silicon wafer, where the epi layer thickness becomes that of the diaphragm or cantilever. The analysis shows that passivation of the epi layer can be maintained even underneath the electronic components for conditions which allow etching of the p-type silicon substrate. Therefore, electrochemical etch-stop control appears feasible in most practical sensor designs.