Effects of precipitate distribution on electromigration in Al–Cu thin-film interconnects

This letter reports that electromigration lifetimes of Al–2Cu (wt. %) thin-film conducting lines increase by more than three times when the lines are optimally aged to facilitate finely dispersed ${\mathrm{Al}}_{\mathrm{2}}\mathrm{Cu}$ precipitates in the interior of the grains. In contrast to other studies which did not report a beneficial aging effect for Al–Cu films, the present work substantiates the fact that proper control of ${\mathrm{Al}}_{\mathrm{2}}\mathrm{Cu}$ precipitates improves resistance to electromigration failure. However, the benefit of aging the Al-2Cu lines investigated here was less pronounced and confined to a more narrow heat-treatment “window” than that previously found for the Al–2Cu–1Si lines.