Internal Stress and Microstructure of Titanium Nitride Coatings

Abstract

Titanium nitride coatings were deposited on various substrates by sputter ion plating and the state of stress was determined by the sin² Ψ method. The lattice distortions which occur in the nitride coatings have been resolved in terms of a macros train and microstrain, as determined from the breadth of the xray reflections, and the origins of each are discussed. The internal stress present in a coating is shown to consist of two components, one thermal in origin and the other structural, its sign and magnitude varying with substrate material and bias potential. During cooling from the deposition temperature partial relaxation of this internal stress (macrostrain) occurs via two mechanisms: plastic deformation of the substrate and yield of the film. The internal stress was completely relaxed on dissolution of the substrate, accompanied by a decrease in the lattice parameter of the film. By comparing the results from substrates biased and unbiased during deposition, and measurements made on adherent and free standing coatings, the microstrain measurements have been separated into two parts, one due to distortions at the grain boundaries and one due to the presence of defects in the crystallites. A model is proposed that accounts for all the experimental observations; this also provides an explanation for the distortions from cubic symmetry reported in titanium and hafnium nitride films.