Barrier/liner stacks for scaling the Cu interconnect metallization

Self-forming barriers and advanced liner materials are studied extensively for their Cu gapfill performance and interconnect scaling. In this paper, 22nm 1/2 pitch Cu low-k interconnects with barrier (Mn-based, TaN) /liner (Co, Ru) combinations are compared and benchmarked for their resistivity, resistance scaling, and electromigration (EM) performance. Extendibility to 16nm copper width was explored experimentally and a projection towards 12nm width is performed. It is found that the Ru-liner based systems show a higher overall Cu-resistivity. We show that this increase can be compensated by combining Ru with a thinner Mn-based barrier, which increases the effective Cu-area at a particular trench width. The EM performance reveals that the Ru-liner systems have a better EM lifetime compared to the Co-liner based systems. More interestingly, in a comparison of the maximum current density Jmax a significant improvement is found for the scaled Mn-based/Ru system, making it therefore a serious candidate to extend the Cu metallization.