Bias polarity and frequency effects of Cu-induced dielectric breakdown in damascene Cu interconnects

Cu-ion-migration-induced dielectric breakdown in damascene Cu interconnect was studied in alternating polarity-bias conditions using a metal–insulator–semiconductor (MIS) structured sample and a damascene Cu interconnect sample. Compared to a direct-current (DC) stress condition, the time to failure (TTF) obtained in the alternating-polarity test was twice as high in the damascene structure and more than five times greater in the MIS structure. This increased lifetime under alternating polarity over that in DC stress resulted from recovery due to the backward migration of Cu ions during the reverse-bias stress. However, the TTF increase was saturated due to the hindrance of backward Cu migration by diffusional flux during reverse-bias stress. The longest TTFs were obtained with the largest-polarity alternating frequency and this effect was analyzed through a one-dimensional finite-difference method simulation.