Role of Grain Size on the Effective Resistivity of Cu-Graphene Hybrid Interconnects

At sub-22nm technology nodes, size effects play a prominent role in the performance degradation of Cu interconnects. Several scattering mechanisms contribute to size effects, including surface roughness and grain boundary scattering as grain sizes in Cu decreases with reduced line widths. Due to these scattering phenomena, the resistivity of Cu interconnects increases drastically, which leads to electrical and thermal performance degradation and reliability issues. To address these limitations, researchers have proposed Cu-Graphene hybrid interconnects, where the line resistance due to Cu and Graphene is connected in parallel leading to smaller effective resistances. In this paper, we present analytical models of the reduction in effective resistivity obtained due to enlargement of grain size. The reduction in effective resistivity is due to the hybrid interconnect geometry and grain size enlargement. We present a qualitative analysis for the resistivity, mean free path, delay and energy delay product of the three interconnect technology nodes from 22nm to 7nm Cu widths. Our analysis shows that Cu on-chip interconnects with Graphene as a barrier layers shows 47%, 30% and 19% improvement in resistivity, delay and energy delay product respectively due to grain size enlargement at 13nm technology node.