Microcorrosion of Al–Cu and Al–Cu–Si alloys: Interaction of the metallization with subsequent aqueous photolithographic processing

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Abstract
The objective of this work was to systematically study the localized corrosion which can occur when Al–Cu and Al–Cu–Si metallizations are exposed to conventional photolithographic processing. The study includes electrical evaluations of a standard 1.6‐m interdigitated serpentine and comb test pattern which was reactive ion etched to quantify the effect of surfacecorrosion on serpentine yield. Al–Cu and Al–Cu–Si (0.5%–1.5% Cu and Si by weight) films were sputter deposited at temperatures ranging from 305–465 °C and patterned using batch photolithographic processing. Localized surfacecorrosion was found on all metallizations, to varying degrees, after a standard 90‐s batch development on both patterened and unpatterened metal substrates. Al–0.5%Cu–0.5%Si was found to have the least surfacecorrosion while Al–1.5%Cu had the most. Electrical shorting was observed in those cases where the corrosion site diameter was greater than the space between adjacent metal lines after RIE. The corrosion is correlated with theta phase precipitates which are known to induce corrosion on Al–Cu alloys by galvanic action in the appropriate electrolyte. The corrosion occurred when the wafer was exposed to the rinse water after the develop step. Postdeposition baking in the range 200–450 °C dramatically affects the concentrations of theta phase precipitates and as a result, the corrosion and yield. The addition of silicon to the Al–Cu alloy was found to improve its corrosion resistance.

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