Understanding limits to conductivity of metal nanowires

Reduced conductivity in sub-100 nm metal wires used as interconnects is a performance limiting factor in integrated circuits. In order to understand the sources of conductivity degradation with the aim of optimizing metal nanowire conductivity, we have analyzed potential sources of electron momentum loss, including surface roughness scattering, grain boundary reflection and interactions with Ta liner layers. Based on the roughness spectrum of metal films, we conclude that primarily specular scattering should be achievable at metal/dielectric interfaces for Cu technology. Using non-equilibrium Green´s function methods, we find substantial reflection at Cu and Ag grain boundaries and find that both the change in grain orientation and disorder in the boundary contribute significantly to reflectivity. Using the same approach for Cu/Ta interfaces, we predict substantial conductivity degradation due to electron interactions with thin liner layers. Based on our analyses, we conclude by suggesting promising directions for maximizing conductivity as interconnect dimensions shrink further below 100 nm.