Analysis of electromigration induced early failures in Cu interconnects for 45 nm node

Bi-directional current stressing was used for monitoring electromigration (EM) lifetime evolution in 45 nm node interconnects. Experimental results show that an initial bimodal distribution of lifetimes can be modified into a more robust mono-modal distribution. Since the bi-directional tests provide successive void nucleation and void healing phases, the Cu microstructure is thought to evolve once the formed void is filled thanks to EM induced matter displacement. FEM modeling is used to compare the predicted location of void nucleation for given microstructures at the cathode end: a multigrain structure is compared to a perfect bamboo microstructure. Experimental and modeling results let us assume that small grains (