Determination of Young's modulus and Poisson's ratio of thin films by combining sin 2ψ X-ray diffraction and laser curvature methods

Abstract

In this study, we have proposed a nondestructive method to simultaneously determine the Young's modulus ( E) and Poisson's ratio ( ν) of polycrystalline thin film materials. The method involved independent stress measurement by laser curvature technique and strain components determination by sin 2 ψ X-ray diffraction (XRD) method, and afterward, elasticity theory was employed to calculate E and ν. The proposed method was applied on two model specimens, TiN and ZrN thin films, using synchrotron X-ray and laboratory X-ray sources, respectively. The cos 2 αsin 2 ψ XRD method which measured the strain for diffraction planes at different location was performed on the same film, and the previously determined E and ν were used to calculate the stress. The residual stresses derived from cos 2 αsin 2 ψ method were close to the stresses from laser curvature measurements, which validated the measured values of E and ν. The depth profile of residual stress of the TiN thin film was assessed using cos 2 αsin 2 ψ method by appropriately adjusting the X-ray incident angle. In addition, the E value determined from nanoindentation (NIP) may depend on the indentation depth. Therefore, one should be cautious when employing the NIP-determined E in sin 2 ψ or cos 2 αsin 2 ψ methods to calculate the residual stress because the modulus may not always give correct stress value.