Stress-field in Sputtered Mo Thin Films and Mo/Ni Superlattices: Origin and Evolution after Ion-Irradiation

Abstract

ABSTRACTIn the present study the ion irradiation technique is used to investigate the origin of the stress-field in Mo layers grown by ion beam sputtering. Strain measurements were performed by X- ray Diffraction (XRD) using the sin2ψ method. The evolution of the sin2ψ plots with ion irradiation shows that the usual assumption of a biaxial stress state is not adequate to determine the true stress-free lattice parameter a0 of the film. A new stress model based on a triaxial state of stress, which includes a hydrostatic component linked to point defects induced volume distortions, is derived to interpret the XRD results. For pure Mo films, the obtained a0 parameter is close to the bulk value, while for Mo sublayers in Mo/Ni superlattices, the a0 value is lower due to intermixing between Ni and Mo. These results demonstrate that ion irradiation is a powerful tool for stress relaxation, which allows to obtain additional information on the respective contribution of chemical effects and growth defects to the a0 value.