Stress Analysis of Cu-Cu Hybrid Bonding Interface Under Thermal Loading

Three-dimensional (3D) packaging has become critical in advancing semiconductor technology, primarily relying on interconnect technologies such as TSV, micro-bumps, and hybrid bonding to achieve high-density vertical integration. Cu-Cu hybrid bonding has emerged as a solution for next-generation 3D integration platforms, owing to its high interconnect density and superior electrical performance. Nonetheless, the reliability of this technology remains a critical challenge. Previous studies have indicated that residual stresses at the bonding interface, arising from material mismatch and thermal processing, can lead to thermomechanical failures, such as delamination and cracking. However, research regarding the evolution of interfacial stress driven by microstructural changes during the annealing process remains limited. This work investigates the influence of annealing periods on the distribution of residual stresses and the morphology of the Cu-Cu hybrid bonding interface. Corresponding microstructural evolutions were characterized via Scanning Electron Microscopy (SEM), while the stress evolution at the interface under varying annealing times was analyzed using nanoindentation. The results reveal that initial bonding induces residual tensile stress at the interface due to constrained thermal contraction, reaching a peak value of 215 MPa after 6 hours of annealing at 400 ℃. Upon achieving complete Cu-Cu bonding at 12 hours, stress reduced to 63 MPa. The interfacial stress transitions into compressive stress by 16 hours (26 MPa), eventually, the interfacial stress increased to 54 MPa after annealing for 24 hours. Furthermore, a finite element model incorporating a creep constitutive law was developed to simulate the evolution of both the interface structure and stress states. Finally, the underlying mechanisms governing the evolution of interfacial micro-morphology and stress states during the annealing of hybrid bonding structures are elucidated. These findings provide theoretical guidance for optimizing annealing processes and enhancing the reliability of hybrid bonding interfaces.