Galvanic Cell Formation During MEMS Release Processes: Implications for Sub-Micron Device Fabrication

Abstract

The addition of a noble metallization layer to doped polysilicon results in the formation of a galvanic cell when the composite is submerged in aqueous hydrofluoric acid. A corrosion current created by the galvanic cell promotes the electrochemical etching of silicon in contact with the acidic solution. Here, we demonstrate the galvanic corrosion of phosphorus-doped polysilicon when a gold metallization layer is used. As a consequence of galvanic corrosion, a number of significant changes to the polysilicon structural layers are observed including a finite polysilicon etch rate, an increase in electrical resistance (both ohmic and non-ohmic), a change in curvature (i.e. mechanical shape), and a decrease in mechanical resonant frequency. The observed change in electrical and mechanical performance on micromechanical structures necessitates more careful consideration of the post-processing procedures, as well as the choice of device metallization layer. The physical impact of corrosion becomes even more significant as device scale is decreased.

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Identifiers

DOI

10.1115/imece2004-62088

Journal

Microelectromechanical Systems

Year

2004