Physics-Based Model for Understanding Electromigration-Induced Cavity Evolution in Advanced Narrow Line Copper Interconnects

In the interconnects of microelectronic package with high current density and high-frequency fluctuation, electromigration (EM) events cause the cavities nucleation at the metal lines cathode and hillock pile-up at anode, which further lead to short circuit/open circuit and influence the overall device reliability substantially. In this work, mechanical modeling of EM-induced cavity failure was investigated and a modeling theory of efficient EM cavity morphology evolution based on physics was comprehensively introduced. According to mass diffusion theory, a dynamic model of elliptical cavity shape evolution with velocity and shape parameters was established. Meanwhile, kinetic equations of shape evolution expansion connected to cavity velocity and shape were proposed to explain the cavity expansion and cavity collapse processes, respectively. Based on the surface morphology analysis, it is obvious that cavity evolution form is determined by the competition between surface tension and electron wind. It is revealed that both them encourage cavity stretching in the direction of electric field intensity while compressing in the opposite. In addition, the mismatch of matter concentration between the left and right ends of the cavity will drive the cavity to migrate against the electric field intensity.