Simultaneous determination of experimental elastic and thermal strains in thin films

A methodology is presented that allows the separation and quantification of temperature-dependent phenomena influencing the mechanical behaviour of thin films. The approach is based on high-temperature X-ray diffraction and supposes a structural characterization of the thin film and the substrate during temperature cycling. The diffraction data are used to determine simultaneously elastic strains and in-plane thermal expansion coefficients (TECs) in the thin film as well as in-plane TECs of the substrate. The dependency of the experimental elastic strains on the virtual thermal strains provides an opportunity to identify the elastic behaviour as well as to resolve temperature-dependent phenomena influencing the residual stress state in the film. The approach is demonstrated on three model structures: Al/Si(001), AlN/Al₂O₃(0001) and Mg-implanted GaN/Al₂O₃(0001).