Stress-induced nucleation of voids in narrow aluminum-based metallizations on silicon substrates

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Abstract
This work investigates thermal stress-induced voiding, and void nucleation in particular, in narrow, passivated aluminum-based metallizations on silicon substrates. After excursions to a higher temperature, the thermal stress is tensile, and increases during cooldown to room temperature, after which it relaxes with time. Experiments conducted on two aluminum alloy metallizations suggest that stress-induced void nucleation is a one shot phenomenon during cooldown from the heat treatment temperature. Further, the high thermal stresses present, and the strong constraints against deformation provided by the substrate and passivation layer, make void nucleation unique in narrow passivated metallizations. Finally, voids always appear to be connected to grain boundaries. The above experimental evidence and theoretical considerations together suggest that grain boundary sliding is the main mechanism facilitating void nucleation in passivated aluminum alloy metallizations.

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