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A method is described to control the thickness of singlecrystal silicon membranes, fabricated by wet anisotropic etching. The technique of an electrochemical etch-stop on an epitaxial layer is used to yield better thickness control over the silicon membranes (k0.2 pm s.d.) and hence improve the reproducibility of piezoresistive pressure sensors. Although the electrochemical etch-stop is not new, this paper reports the characterization and evaluation of the technique as a fabrication process. The output characteristics of piezoresistive pressure sensors fabricated using the electrochemical etch-stop technique are compared with previously fabricated pressusre sensors not utilizing accurate control over membrane thickness. The benefits of the etch-stop approach become apparent when reductions in the pressure-sensitivity variations are considered. Without etch-stop, the sensitivity on one wafer varied by a factor of two from one sensor to the other. With etch-stop, the pressure sensitivity of devices fabricated on the same wafer can be controlled to within +4 percent s.d.

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As part of a comprehensive electrochemical investigation of silicon etching and anodic passivation in KOH , chronoamperometric experiments were performed on precisely oriented {111} silicon to elucidate the mechanistic course of silicon {111} passivation. The resulting current vs. time relationships display multiple current maxima that obey two‐dimensional nucleation and first‐order reaction rate laws. Each current peak has been associated with either the formation of an anodic oxide or the dissolution of an open‐circuit oxide film. Data analysis confirms previous results which show that anodic oxide formation on {111} silicon consumes a fixed quantity of charge of approximately 2.4×10−3C/cm2 for both n‐ and p‐type silicon.

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