Optimized ultra-thin Manganin alloy passivated fine-pitch damascene compatible Cu-Cu bonding at sub 200°C for 3D IC integration

Enhanced Cu diffusion, Cu surface passivation, and surface smoothness at the bonding interface are the key requirements for high quality Copper-Copper (Cu-Cu) thermocompression bonding. In our previous work, we have demonstrated the usage of optimized Manganin metal alloy of 3 nm not only helps in passivating the Cu surface even at high temperature (<300°C) but also reduces the surface roughness to about 0.8 nm which substantially led to high quality Cu-Cu bonding. In this paper, we demonstrate an ultra-fine pitch Cu-Cu thermocompression bonding using an optimized ultra-thin damascene compatible Manganin metal alloy passivation. This engineering surface passivation approach has led to high quality bonding at sub 200° C temperature and a nominal contact force of 4kN. Furthermore, electrical characterization using modified kelvin structure, and reliability assessment of this bonded structure was investigated under multiple current stressing, temperature cycling test and the results indicate excellent stability without electrical performance degradation. This practical finding has immense potential to leads into practical realization of 3D IC integration.