Stacked film structured dependence of electromigration in Al-Cu interconnect terminated with W plug

We have investigated the stacked film structure dependence of the electromigration (EM) lifetime in AlCu interconnects terminated with W-plugs, the structures of which are Ti-TiN-AlCu-TiN, Ti-AlCu-TiN, and Ti-AlCu-Ti-TiN. It has been clarified that the dependence is caused by the difference in the time to deplete Cu atoms over a critical length. We found that the difference is caused by a reduction in the cross-section of the AlCu portion and the reduced Cu concentration in the AlCu portion which is induced by Al/sub 3/Ti formation. In addition, the difference is also caused by the increase in the interface between Al/sub 3/Ti and AlCu, which is the dominant Cu diffusion path.