Unusual thermal fatigue behaviors in 60 nm thick Cu interconnects

Thermal fatigue of Cu interconnects 60 nm thick and 5–15 μm wide was investigated by using alternating current to generate cycling temperature and strain/stress. The fatigue curves exhibit two regions, i.e. high- and low-cycle regions, which correspond to low and high thermal strains, respectively. The high-cycle region is found to be controlled by an unusual thermal fatigue mechanism of damage bands, which is related to a unique structure comprising only a single layer of grains distributed along the thickness.