Effects of Al Doping on Electromigration Performance of Narrow Single Damascene Cu Interconnects

Cu interconnects are required for high-performance system-on-a-chip because of their high performance and reliability (Yokogawa et al., 2001) and (Yokogawa, 2004). However, electromigration lifetime decreases with the cross-sectional area of the line (Yokogawa and Tsuchiya, 2005). To improve reliability, Cu-alloys such as CuSn (Tonegawa et al., 2003) and (Lee et al., 1995) and CuAl (Matsubara et al., 2003) were investigated; therefore, the lifetime was increased by a factor of 10. However, the electromigration characteristics and effects of Al doping have not been determined in detail. In this paper, we report the effects of Al doping from seed layer to Cu on electromigration in narrow single damascene lines. The test structure proposed by Kawasaki and Hu (Kawasaki and Hu, 1996) was used to measure the drift velocities accurately. In addition, to investigate the dependencies of Al concentration, the seed layer thickness was changed from 40 to 90nm. The effects of Al doping on incubation time, drift velocity, and critical threshold current density are discussed