Impact of Cross-Sectional Current Crowding on Electromigration in Interconnects

As the critical dimensions of interconnect scaling, the enhancement of surface scattering increases the resistivity, contributing to the reduction in electromigration lifetime. Besides, the enhanced surface scattering can lower surface conductivity, resulting in cross-sectional current crowding and potentially decreasing the interconnect's electromigration resistance. Through finite element simulation, this work demonstrates the appearance of this extra decrement when the positive feedback between the Joule heat and resistivity is enhanced. As the metal's electric and thermal conductivity degrade with scaling, the crosssectional crowding effect becomes significant, resulting in the electromigration stress increment by 10 %, 33 %, and 7 % for Cu, Co, and Ru compared to the uniform current case at 9 nm thickness. This work reveals a potential influence on EM lifetime at advanced technology nodes and highlights Ru as an alternative interconnect metal that can effectively resist this adverse effect.