Stress gradients in titanium nitride thin films

Abstract

Titanium nitride films, as used for hard coatings, were deposited on silicon wafers by reactive unbalanced magnetron sputtering. For thinner films we find a higher compressive average residual stress than for thicker films. In the paper it is shown that this reduction in average stress is not due to relaxation, but to a stress gradient in the film. Experiments in which the film thickness was reduced in steps by wet chemical etching show a stress gradient present in the films. Releasing the films from the wafer, by etching away the silicon, results in bent film flakes. The flakes' bending is close to the bending calculated from the measured stress gradient, proving once more the existence of a stress gradient.