Studies on Galvanic Corrosion on Floating and Grounded Bondpads in Wafer Fabrication

Abstract

Galvanic corrosion is well known to impact the quality of microchip Al bondpads. In this paper, we will further study the characteristics of galvanic corrosion and understand why galvanic corrosion is more serious on the floating or non-grounded bondpads as compared to the grounded Al bondpads. A phenomenological model of the Al pad corrosion, based on the oxidation-reduction reactions, will be invoked so as to explain why the floating pads with thinner Al oxide are more likely to suffer galvanic corrosion. Experimental data from cross-sectional TEM investigations provide the evidence of Al oxide thinning in the floating pads as compared to the non-floating or grounded Al bondpads. We recommend that during the initial process or recipe optimization DOE(s) (design of experiments) in the far-backend of line (FBEOL) one may use short-loop wafers with floating pads as they represent the 'worst-case-scenario', insofar as galvanic corrosion is concerned.