Analysis of damage formation and propagation in metallic thin films under the action of thermal stresses and electric fields

Abstract

A quantitative analysis is presented of void formation, morphological stability, and evolution in metallic thin films, which are problems that underlie serious reliability issues in interconnections used in integrated circuits. The analysis is based on the coupling of bulk and interfacial mass transport phenomena with elastic deformations and current stressing. The formation and growth of intergranular voids in bamboo-structure conductor lines due to stresses that develop during processing is investigated. The investigation is aided by self-consistent simulation of bulk and grain-boundary diffusional processes using bicrystal models with elastic grains. A systematic analysis is presented of the morphological evolution of transgranular voids in passivated and unpassivated aluminum lines under current densities that are typical of electromigration testing. The effects of the electric field and surface properties on the morphological stability of voids are examined and morphologies that bifurcate from rounded or wedge-like void shapes are predicted. The theoretical results are discussed in the context of experimental data of void propagation under electromigration conditions.