Improving Reliability of Copper Dual-Damascene Interconnects by Impurity Doping and Interface Strengthening

Electromigration (EM)-derived void nucleation and growth in 65-nm-node dual-damascene interconnects were investigated, and the effects of impurity doping as well as copper adhesion strength to a capping-dielectric layer (CAP) are clarified. It is found that surface-reductive treatment of the copper line improves its adhesion to the SiCN-CAP, elongating the incubation time of voiding at the via bottom. An aluminum doping is effective in suppressing both the void nucleation and growth. Consequently, an aluminum-doped copper alloy with the strong copper/CAP interface improves the EM lifetime by 50 times compared to that of a conventional pure copper. These results clearly indicate that blocking migration paths of vacancies through both grain boundaries and the copper/CAP interface is essential in improving the EM reliability.