Exploring Cu-Cu Hybrid Bonding Failure Mechanisms under Current Stress via 3D Focused Ion Beam Tomography

This work investigates the reliability limits of Cu–Cu hybrid bonding interconnects under extreme current stressing at sub-micron dimensions. High-temperature (300°C) and high-current-density (up to 20 MA/cm²) conditions were applied to accelerate electromigration (EM) degradation, revealing three dominant failure modes: (i) interconnect burnout; (ii) dielectric breakdown; (iii) Cu migration and voiding. Notably, Cu migration and void formation were observed not only in directly stressed interconnects but also in adjacent bonded structures, indicating the influence of localized thermo-electrical effects. A high-resolution focused ion beam (FIB) 3D tomography technique was developed to reconstruct Cu migration extrusion pathways, void networks, and microstructural evolution at sub-micron resolution. These findings highlight the critical role of interfacial Cu migration in failure initiation and establish key reliability constraints for further pitch scaling into sub-micron pitch hybrid bonding.