A Cu-Cu Bonding Method Using Preoxidized Cu Microparticles under Formic Acid Atmosphere

Many power semiconductor devices now require high tolerance of current density and reliability at high temperature, therefore Cu-Cu bonding using an insert material has raised the level of concerns for its great thermal stability and conductivity. In this study, a low-pressure bonding process was developed to achieve a Cu-Cu bonding using preoxidized Cu microparticles under formic acid atmosphere. The Cu microparticles were preoxidized to generate oxide films and Cu oxide nanostructures, which were then reduced and bonded at 300 °C under formic acid atmosphere to achieve a Cu-Cu bonding. Shear strength of the Cu-Cu bondings were tested to optimize the parameters of bonding process. Fracture surfaces of the Cu-Cu bonding, as well as cross-sectional microstructures, were observed by scanning electrical microscope (SEM) and components were identified by X-ray diffraction (XRD) to investigate the bonding mechanism. The findings reveal that the oxide films and the nanostructures play key roles in this reduction bonding process, which is a promising method to obtain a Cu-Cu bonding satisfying the requirements of power device packaging.