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

This paper is a review of the thermal and microstructural stability of star e-of-the-art TiN-based thin films during exposure to elevated temperature a nd mechanical deformation. We consider both pure TiN films and TiN-based na nolaminates, 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) all oy films as well as Cr-N films, synthesised by the physical vapour depositi on techniques reactive magnetron sputtering and cathodic are evaporation. T iN/NbN superlattices exhibit plastic deformation and dislocation glide limi ted to within individual layers in scratching experiments. This provides su pport for theories of superlattice hardening that presumes dislocation conf inement with barriers to dislocation glide across layer interfaces. The app arent activation energy for metal interdiffusion in the TiN-NbN system is t emperature-dependent with values in the range of 2.6 to 4.5 eV for annealin g 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 dep ending on deposition process parameters. Al-rich (Ti,Al)N films were found to be stable in the as-deposited cubic phase during annealing at temperatur es as high as 900 degrees C. Substoichiometric cubic delta-phase CrN exhibi ts phase separation into delta-CrN and Cr2N during annealing at 550 degrees C. Activation energies for relaxation of residual stress in the Cr-N syste m was in the range of 2.1 to 3.1 eV.