Relation between residual stresses and microstructure in Mo(Cr) thin films elaborated by ionized magnetron sputtering

Abstract

Mo(Cr) thin films were deposited by an Ionized Physical Vapor Deposition process i.e. Ionized Magnetron Sputtering (IMS). This deposition technique enables to ionize the neutral metallic sputtered species by a secondary plasma generated through a radio-frequency (RF: 13.56 MHz) powered coil. Thus, by acting on the substrate bias voltage, on the argon pressure and on the RF power applied to the coil, the ion energy and flux onto the substrate can be controlled. Various types of microstructure are then obtained, leading to a wide range of residual stresses in films from compressive to tensile. The control of both the microstructure and the related stress using the IMS process offers new opportunities in elaborating stress-engineered micro-objects for micro-electromechanical systems (MEMS). Residual stresses in the whole volume of the film were measured ex situ by Stoney curvature method and X-ray diffraction was applied to get the in-grain contribution (i.e. the crystallites) to the total residual stresses using the sin 2 ψ method. Besides, the grain morphology and local structure of the film were characterized by transmission electron microscopy. Relationship between synthesis conditions, microstructure, film morphology and residual stresses in Mo(Cr) films deposited by IMS is presented in this study and leads to a multi-scale description of the mechanisms of stress formation. The stress values determined from both techniques may be explained thanks to the analyzed morphological and microstructural features in the films.