Role of conductivity on the electromigration-induced morphological evolution of inclusions in {110}-oriented single crystal metallic thin films

Abstract

The electromigration-induced microstructural evolution of inclusions such as voids, precipitates, and homoepitaxial islands is of technological importance to the reliability, the performance of the thin film interconnects, and surface nanoengineering. In the present article, we report the results on the migration of cylindrical inclusion in the {110}-oriented single crystal of face-centered-cubic metals under the action of electromigration. To this end, we employ a phase-field model based on the Cahn-Hilliard equation with anisotropy in adatom mobility. Emphasis is laid on the role of conductivity contrast between the inclusion and the matrix, and the misorientation of the fast diffusion directions with respect to the applied electric field. Numerical simulations indicate that lower misorientations favor a steady state, while higher values render the inclusion unstable, initiating a complex cycle of splitting and coalescence. At intermediate misorientations, the inclusion undergoes a time-periodic oscillation, the amplitude and the frequency of which is strongly dependent on the values of conductivity. Furthermore, higher conductivity of the matrix relative to the inclusion promotes a transverse elongation, while the similar conductivities lead to slitlike features along the direction of the electric field. Finally, a morphological map is constructed by delineating the dependence of various migration modes on conductivity contrast and misorientation. Results presented here have important implications on void dynamics in interconnects and the fabrication of nanostructures of desired features and dimensions.