Lower limits of line resistance in nanocrystalline back end of line Cu interconnects

Abstract

The strong non-linear increase in the Cu interconnect line resistance with decreasing linewidth presents a significant obstacle to their continued downscaling. In this letter we use the first principles density functional theory based electronic structure of Cu interconnects to find the lower limits of their line resistance for metal linewidths corresponding to future technology nodes. We find that even in the absence of scattering due to grain boundaries, edge roughness or interfaces, quantum confinement causes a severe increase in the line resistance of Cu. We also find that when the simplest scattering mechanism in the grain boundary scattering dominated limit is added to otherwise coherent electronic transmission in monocrystalline nanowires, the lower limit of line resistance is significantly higher than projected roadmap requirements in the International Technology Roadmap for Semiconductors.