Study on thermomigration-induced void formation in advanced copper interconnects

With the miniaturization of microelectronic components and the increase in chip power densities, thermomigration driven by complex thermal gradients has become a critical reliability concern for microelectronic interconnects. In this work, we developed a phase field model to investigate the formation and evolution of voids in copper interconnects due to thermomigration. Simulations effectively captured the experimental findings, revealing that voids tend to emerge near the hot end, prominently influenced by grain morphology. In the surface diffusion-limited scenario (SDLS), grain boundaries notably facilitated void formation, increasing void size. In the grain boundary diffusion-limited scenario (GBDLS), void nucleation in bamboo structure (BS), polycrystalline structure (PS) copper interconnects tended to initiate relatively early and occurred near the interface between the copper and the capping layer. Moreover, the thermal distribution showed uneven patterns, with high gradients at grain boundaries and void surfaces. The thermomigration mass flux predominantly flowed from the hotter left side towards the colder right side. Increasing the number of copper grains resulted in larger voids, with a more pronounced effect in the SDLS. Furthermore, the thermomigraiton-induced void led to a decrease in thermal conductivity over time. This study clarified the complex relationship between grain morphology, void formation due to thermomigration, and the degradation of thermal properties in copper interconnects, enhancing the understanding of performance degradation and failure mechanisms.