Modeling Current Flow Through Copper with Surface Substituted Intermetallic Barrier Layers

With the continuous shrinking of integrated circuits comes the likewise size reduction of their interconnects. This comes at the cost of increased resistivity of the interconnects, being exacerbated by surface roughness which is required for adhesion to circuit components. The size of these interconnects, being on the order of a few nanometers, warrants consideration of electronic scattering effects to determine their transport behavior. We employ a first-principles approach using density functional theory (DFT) in conjunction with the Keldysh non-equilibrium Green's functions (NEGF) formalism to determine the electronic structure of nanoscale Cu interconnects with roughened intermetallic barriers under a bias voltage. Tangible properties such as conductance are recovered with NEGF-DFT. We hypothesize that introducing a barrier layer may mitigate electronic scattering at the roughened surface and recover some of the conductance that is lost when said roughness is introduced in a pure Cu interconnect. In particular, we probe barrier layers composed of Mn, Ni, Zn, Ag, Sn, and Cu3Sn with five distinct roughness configurations, where half of the top barrier layer atoms have been randomly removed. We also investigate the effects of a non-ideal interface by intermixing barrier layer atoms below the roughened surface, creating an "interphase" between the barrier and the Cu film.