Lower limits of line resistance in nanocrystalline Back End of Line Cu interconnects

TL;DR

This paper uses first principles calculations to determine the fundamental limits of copper interconnect line resistance at nanoscale dimensions, revealing quantum confinement effects that challenge future technology scaling.

Contribution

It provides the first theoretical analysis of the lower bounds of Cu interconnect resistance considering quantum effects and scattering, highlighting limitations for continued miniaturization.

Findings

Quantum confinement significantly increases resistance at small scales.

Even ideal, defect-free Cu nanowires face resistance limits exceeding roadmap targets.

Transport anisotropy influences resistance behavior in Cu nanostructures.

Abstract

The strong non-linear increase in Cu interconnect line resistance with a decrease in linewidth presents a significant obstacle to their continued downscaling. In this letter we use 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 reduction in current carrying capacity of Cu. We discuss the causes of transport orientation dependent anisotropy of quantum confinement in 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 limits of line resistance are significantly higher than projected roadmap requirements in the International Technology Roadmap for Semiconductors.