Electromigration in thin films was studied by using a cross-strip configuration. Lines of Cu, with isolated areas of Cu-Al or Cu-Sn, were tested at between 250 and 390C. Hillock and void marker motion indicated that Sn moved in the direction of the electron flow. The marker polarity indicated that it decreased the grain boundary electromigration of Cu; in agreement with previous studies. Evidence was found for active surface migration in Cu. During tests under forming gas, hillocks and voids formed next to native Al2O3 layers at all temperatures; thus suggesting that Cu migrated faster through the Cu free surface than through the interface between surface layers of Al2O3, and Cu-Al. Active surface migration in Cu thin films was also revealed by the growth of hillocks having highly developed facets; most of which were attached to the underlying film by narrow necks.

Electromigration in Cu Thin Films with Sn and Al Cross Strips. N.L.Michael, C.U.Kim: Journal of Applied Physics, 2001, 90[9], 4370-6