Theoretical screening of Co- and Mo-based binary alloys as interconnect metals

Abstract

With continued device scaling, the use of copper (Cu) as an interconnect material has reached its limit for two main reasons. First, electron–phonon scattering, which dominates in the bulk form, becomes overshadowed by surface roughness and grain boundary scattering as the dimensions shrink. Second, electromigration becomes increasingly severe under high electric fields, compromising reliability. Each of these degradation factors can be quantitatively evaluated using the figure of merit (FoM) and cohesive energy. In the search for next-generation interconnect materials, Co- and Mo-based binary alloys were investigated using density functional theory (DFT) calculations combined with Boltzmann transport theory. The directionally averaged FoM and cohesive energy were computed as indicators of size-dependent resistivity and electromigration resistance, respectively. By applying screening criteria—cohesive energy greater than 5.5 eV per atom and FoM less than 6.70 × 10⁻¹⁶ Ω m² (the FoM of Cu)—four promising Co-based alloys and seven Mo-based alloys were identified. These results highlight the strong potential of Co- and Mo-based binary alloys for future interconnect applications. Furthermore, similarities in Fermi surfaces, coupled with the FoM analysis, validate these alloys as suitable candidates for advanced interconnect technologies.