Electromigration-resistance enhancement with CoWP or CuMn for advanced Cu interconnects

Suppressing Cu diffusion along the Cu/Cap interface has proven to be one of the most effective ways to enhance the electromigration (EM) resistance of advanced Cu interconnects. Two methods, depositing a thin layer of CoWP on the Cu surface and doping the Cu seed layer with Mn, are presented in this paper. While each effectively enhanced the EM performance, they behaved somewhat differently in improving the line-depletion and via-depletion EM performance. CoWP functioned primarily as a Cu surface modifier and did not alter the Cu diffusion behavior below the surface, making Cu interconnects capped with CoWP very sensitive to defects in the via. As a result, the hardware processed with CoWP had greatly increased EM failure times, but also had large variability in failure times and activation energy. On the other hand, the hardware with the CuMn seed layer relied on Mn segregation to the Cu surface to slow down the Cu diffusion, plus Mn also may have diffused to grain boundaries and defective areas of the liner. Although the EM failure times of Cu interconnects with CuMn seed in some cases were not as long as those with CoWP, the variability and sensitivity to process defects was reduced.