Determination of Young's modulus and Poisson's ratio of thin films by combining sin2ψ X-ray diffraction and laser curvature methods

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 sin2ψ 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 cos2αsin2ψ 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 cos2αsin2ψ 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 cos2αsin2ψ 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 sin2ψ or cos2αsin2ψ methods to calculate the residual stress because the modulus may not always give correct stress value.