Impurity doping effects on electromigration performance of scaled-down Cu interconnects

To study of the impurity effect of electromigration kinetics, we have investigated the effects of Al doping in Cu interconnects. The effects of Al doping on the incubation time, drift velocity, and critical product of electromigration were investigated. The drift velocity of Cu mass transport in CuAl alloys decreases with an increase in the concentration of Al atoms. The observed critical product of electromigration is 1500 A/cm, and it is independent of the Al concentration. The activation energy of the normalized drift velocity increases with an increase in Al concentration. The Al concentrations at Cu/SiCN interface, grain boundary, Ta/Cu interface, and bulk were investigated along the length of a line by the electron microprobe technique. The time dependent Al concentration at the Cu/SiCN interface near the cathode end of the line is observed. These characteristics indicate that the doped Al affects the electromigration-induced Cu diffusion and does not affect the driving force.