Galvanic Corrosion of Aluminum in Metal Stacks

D. Eaves, J. Chen, I. Smorchkova, W. Sutton, J. Uyeda, and M. Barsky
Northrop Grumman Space Technology
One Space Park, Redondo Beach, CA 90278
David M. Eaves, Email: david.eaves@ngc.com Tel: (310) 813-5569

Keywords: Galvanic, corrosion, Aluminum, etching, metal, solvent.

Abstract
We report an analytical method and results for a chemical’s potential for corrosion of metal contacts. Corrosion rates were measured via a galvanic cell, where
we measure the current and potential between two wafers coated with dissimilar metals, submerged in process solvents, strippers, and etch solutions (see Figure 1). Galvanic corrosion was more closely correlated to the current of the galvanic as opposed to the potential in static sovent tests. In addition to the static-solvent tests, large current spikes were observed when transitioning from one solvent to another as shown in Figure 3 and Figure 4. Based on these results, the fundamental design of the metallization scheme as well as multi-solvent process flows can be optimized to minimize galvanic corrosion and subsequent electrical and visual defects. Visual defects were observed on metal stacks consisting of metals with high galvanic potentials, specifically Aluminum  Anodic) , Nickel, Platinum and Gold (Cathodic). The corrosion effect was verified to be due to galvanic corrosion versus purely chemically etching the metal layers by solvents. Electrically isolated Al pads were unaffected by process chemistry, while Al pads overlapping with Au/Ni pads showed severe corrosion patterns.
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