Fatigue of damascene copper lines under cyclic electrical loading

Fatigue in damascene copper lines has been investigated by using alternating currents to generate cyclic temperatures and stresses/strains. Interconnects using beyond 65 nm node design rules and materials have been studied. We demonstrate here that cyclic thermal strains lead to Cu or Cu/Co-based cap surface modification and open circuits in Cu lines during the application of an alternating electrical current. We underline that the narrower the copper lines are, the more reliable they are and the major role of the cap layer to improve the Cu lines reliability.