The influence of thermal annealing on residual stresses and mechanical properties of arc-evaporated TiCxN1−x

We report the stress relaxation behavior of arc-evaporated TiCxN1−x thin films during isothermal annealing between 350 and 900°C. Films with x=0, 0.15, and 0.45, each having an initial compressive intrinsic stress σint=−5.4 GPa, were deposited by varying the substrate bias Vs and the gas composition. Annealing above the deposition temperature leads to a steep decrease in the magnitude of σint to a saturation stress value, which is a function of the annealing temperature. The corresponding apparent activation energies for stress relaxation are Ea=2.4, 2.9, and 3.1 eV, for x=0, 0.15, and 0.45, respectively. TiC0.45N0.55 films with a lower initial stress σint=−3 GPa, obtained using a high substrate bias, show a higher activation energy Ea=4.2 eV. In all the films, stress relaxation is accompanied by a decrease in defect density indicated by the decreased width of X-ray diffraction peaks and decreased strain contrast in transmission electron micrographs. Correlation of these results with film hardness and microstructure measurements indicates that the stress relaxation is a result of point-defect annihilation taking place both during short-lived metal-ion surface collision cascades during deposition, and during post-deposition annealing by thermally activated processes. The difference in Ea for the films of the same composition deposited at different Vs suggests the existence of different types of point-defect configurations and recombination mechanisms.