Electromigration-driven complex dynamics of void surfaces in stressed metallic thin films under a general biaxial mechanical loading

摘要

We report results of a systematic computational study of the electromigration-driven complex surface dynamics of voids in mechanically stressed thin films of face-centered cubic metals with <100>-oriented film planes. The films are subjected to an external electric field simultaneously with biaxial mechanical loading, which can be either purely compressive, ranging from purely isotropic to strongly anisotropic including uniaxial, or a mixed type of loading with both tensile and compressive stress components in the applied stress tensor. Our analysis is based on self-consistent dynamical simulations of driven void surface morphological evolution following a well validated, two-dimensional, and fully nonlinear model. We find that depending on the electromechanical conditions, void size, and surface diffusional anisotropy, two types of asymptotic states can be stabilized in the void surface dynamical response, namely, morphologically steady or time-periodic traveling voids, and film failure can be caused by void tip extension. The loading mode as well as the loading anisotropy are found to be the significant factors in determining the void morphological stability domains and can be tailored to stabilize steady or time-periodic states and to increase the film's resistance to failure. Under a mixed (tensile + compressive) loading mode, we find that it is impossible to stabilize steady states in the void morphological response and that the stress levels that the film can sustain prior to failure are much lower than those under purely tensile or purely compressive biaxial loading.%39