Device interconnections in modern integrated circuits consist of metallic lines with cross-sections characterized by sub-micron length scales. Electromechanically-induced failure of such metallic lines is a major materials reliability problem in microelectronics. Failure is commonly mediated by the dynamics of microvoids that exist in these metallic lines. Void migration, growth, and morphological change are driven by electromigration, curvature-driven surface diffusion, and stress-induced surface diffusion, coupled with plastic flow in the strained metallic film. Fundamental understanding of such microstructural-scale dynamical phenomena and development of computational tools for their quantitative analysis are necessary for enabling engineering strategies to improve interconnect reliability. Toward this end, the proposed research addresses systematically the complex, nonlinear void dynamics in ductile metallic thin films over the range of electromechanical conditions that interconnect lines are subjected to. A number of interrelated problems will be pursued that involve single- and multiple-void dynamics, including: (i) combined effects of electromigration and mechanical stress on the migration and morphological stability of single voids, (ii) current-induced wave propagation on single void surfaces, (iii) void-void interactions that may lead to void breakup and coalescence phenomena, (iv) plastic deformation mechanisms around evolving voids, and (v) the role of plastic flow in interconnect failure. The proposed research plan emphasizes a self-consistent mesoscopic formulation of void surface evolution due to surface mass transport and plastic flow under the action of electric and stress fields, as well as systematic parametric studies to determine the onset of instabilities that may trigger failure modes. Computational implementation of the self-consistent model will be based on novel boundary-integral methods, standard finite-element methods, and recently developed methods for tracking moving interfaces. The predictive capabilities of this mesoscopic modeling will be enhanced by atomistic calculations of surface and interface properties according to many-body interatomic potentials. In addition, multi-million-atom molecular-dynamics (MD) simulations will be carried out to probe the nano-scale mechanisms that govern plastic deformation in the vicinity of voids in strained ductile metallic systems. Analysis of the MD results will provide the constitutive relations for plastic deformation required for the closure of the meso-scale problem. ***
