Mechanical and thermal stability of TiN/NbN superlattice thin films

High-temperature stability and mechanical deformation mechanisms of TiN/NbN superlattice structures have been investigated. Single-crystal TiN/NbN superlattices were deposited by reactive dual-cathode unbalanced magnetron sputtering in an Ar/N2 discharge onto MgO(001) substrates held at a temperature of 700°C. The thermal stability was studied by X-ray measurements of superlattice satellite peak intensity variation during and after annealing at up to 950°C. The apparent activation energy for metal interdiffusion in the TiN–NbN diffusion couple is temperature-dependent, with values ranging from 2.6 to 4.5 eV. Film hardness as measured by nanoindentation was observed to decrease during annealing, as the result of effective alloying of the nitride layers. TiN/NbN superlattices are ductile at room temperature and exhibit dislocation glide limited to within individual layers in scratching experiments.