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Published online by Cambridge University Press: 10 February 2011
Stress and electromigration voids are believed to nucleate at the metal/passivation interface. In this study, modified interfaces were synthesized to experimentally elucidate the role of the interface on stress voiding for comparison with theoretical predictions. Interfaces were modified by depositing photoresist in a controlled manner on Ti/Algfi lines prior to passivation deposition. Stress voiding susceptibility was assessed in as-received lines as well as those subjected to storage anneals for 1, 5, and 25 days at 190°C to accelerate void formation. The global textures of all the lines were <111> fiber and were not significantly affected by the interface modification. Differences in stress voiding were attributed to the different interfaces. Higher ratios of voids in modified regions to voids in unmodified regions were observed both in as-received lines and those given a 1 day storage anneal due to the heterogeneous nucleation sites provided by the photoresist contamination in the modified regions. However, the void ratio appears to decrease exponentially with longer time anneals. Lowered driving force for void formation in the modified regions leads to less voiding with time, while higher driving force and a limited number of nucleation sites in the unmodified regions leads to more voiding with time. Local textures at a limited number of voided sites in modified and unmodified regions were identical to the global texture of the line. In our limited sampling, voids did not form in local regions of weaker <111> texture.