Galvanic corrosion mechanism and suppressed solution on Al/Cu pads

Galvanic corrosion generally occurred on Al/Cu bond pads post wafer saw resulted in pitting but no pitting was observed at wafer incoming. There is significant interest in the corrosion behavior of Cu-containing Al alloy, such as PL455, which remain of importance for automotive application due to bondability and reliability safety concern. All of pitting existed Cu precipitation on central of pit holes. A simple experiment simplifies galvanic corrosion condition and reveals its mechanism for definition root cause of pitting. Incoming wafer immerse into di-water in various temperature and air/nitrogen dissolved for 40 and 60 minutes. The experiment results conducted that low temperature and nitrogen dissolved into di-water can suppressed galvanic corrosion however it can't be fully suppressed due to halogen residual on bond pad post CF
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plasma descum (accelerated corrosion rate) and copper precipitation on Al grain boundary during anneal. Copper precipitated in the Al grain boundary that created Al/Cu galvanic potential and interface, which was galvanic corrosion staring point and then galvanic reaction occurred while Al/Cu couple immersed into electrolyte environment which trigger galvanic corrosion. It interprets galvanic corrosion is observed post wafer saw.