Metal nitride diffusion barriers may be included between cobalt-based structures and ruthenium-based structures to reduce, minimize, and/or prevent intermixing of cobalt into ruthenium. A metal nitride diffusion barrier layer may include a cobalt nitride (CoNx), a ruthenium nitride (RuNx), or another metal nitride that has a bond dissociation energy greater than the bond dissociation energy of cobalt to cobalt (Co-Co), and may therefore function as a strong barrier to cobalt migration and diffusion into ruthenium. Moreover, cobalt nitride and ruthenium nitride have lower resistivity relative to other materials such as titanium nitride (TiN), tungsten nitride (WN), and tantalum nitride (TaN). In this way, the metal nitride diffusion barriers are capable of minimizing cobalt diffusion and intermixing into ruthenium-based interconnect structures while maintaining a low contact resistance for the interconnect structures. This may increase semiconductor device performance, may increase semiconductor device yield, and may enable further reductions in interconnect structure size.