Review of the thermal and mechanical stability of TiN-based thin films

This paper is a review of the thermal and microstructural stability of stare-of-the-art TiN-based thin films during exposure to elevated temperature and mechanical deformation. We consider both pure TiN films and TiN-based nanolaminates, metastable alloy nitrides, carbonitrides, and Rims in a state of compressive intrinsic stress. New results are presented from studies of single-crystal TiN and TiN/NbN superlattice films, (Ti,Al)N and Ti(C,N) alloy films as well as Cr-N films, synthesised by the physical vapour deposition techniques reactive magnetron sputtering and cathodic are evaporation. TiN/NbN superlattices exhibit plastic deformation and dislocation glide limited to within individual layers in scratching experiments. This provides support for theories of superlattice hardening that presumes dislocation confinement with barriers to dislocation glide across layer interfaces. The apparent activation energy for metal interdiffusion in the TiN-NbN system is temperature-dependent with values in the range of 2.6 to 4.5 eV for annealing at T-a less than or equal to 930 degrees C. Compressive-stress relaxation in Ti(C,N) films has activation energies in the range of 2.1 to 4.5 eV depending on deposition process parameters. Al-rich (Ti,Al)N films were found to be stable in the as-deposited cubic phase during annealing at temperatures as high as 900 degrees C. Substoichiometric cubic delta-phase CrN exhibits phase separation into delta-CrN and Cr2N during annealing at 550 degrees C. Activation energies for relaxation of residual stress in the Cr-N system was in the range of 2.1 to 3.1 eV.