Copper nanoparticles (Cu NPs) fabricated by physical vapor deposition (PVD) were introduced in Cu-Cu bonding as surface modification. The bonding structure with Ti adhesive/barrier layer and Cu substrate layer was fabricated on both surfaces first. Loose structure with Cu NPs was then deposited by magnetron sputtering in a high pressure environment. Solid state Cu-Cu bonding process was accomplished at 200°C for 3min under the pressure of 20MPa. Die shear test was carried out and an average bonding strength of 36.75MPa was achieved. The analysis of fracture surface revealed a high-reliability bonding structure. According to cross-sectional observations, a void-free intermediate Cu layer with thickness around 10nm was obtained. These results demonstrated that a reliable low temperature time-saving Cu-Cu bonding was realized by Cu NPs between the bonding pairs. This novel bonding method might be one of the most attractive techniques in the application of ultra-fine pitch 3D integration.
Wu, Z., Cai, J., Wang, Q., & Wang, J. (2017). Low temperature Cu-Cu bonding using copper nanoparticles fabricated by high pressure PVD. AIP Advances, 7(3). https://doi.org/10.1063/1.4978490