Stress-induced and electromigration voiding in aluminum interconnects passivated with silicon nitride

Void nucleation in aluminum interconnects passivated with silicon nitride was studied using a high voltage scanning electron microscope. Extensive stress-induced voiding was observed in these interconnects independent of the passivation thickness. Some of the stress-induced and electromigration-induced voids formed away from the interconnect sidewall in contrast to results from other studies of void nucleation in passivated aluminum lines. Nuclear reaction analysis measured large amounts of hydrogen in the aluminum films passivated with silicon nitride. Transmission electron microscopy showed a high density of nanometer-sized bubbles in the aluminum. These bubbles, which are thought to have formed from hydrogen that evolved from the silicon nitride layer during processing, served as nucleation sites for stress- and electromigration-induced voids.