A Novel Low-temperature Co-Co Direct Bonding for Future 3D Interconnection

3D interconnection enables a significant performance leap in computing capability and memory/processor fabrication. However, the shrinkage of interconnects pitch using common copper joints suffers from electromigration and grain boundary obstacles. Cobalt (Co), as the next-generation interconnection metal, offers great potential to overcome these scaling limitations for high-density and fine-pitch integration. Nonetheless, the inherent electro-stability of Co introduces a higher diffusion potential barrier. Additionally, the intrinsic high Young’s modulus (~209GPa) of Co requires a large force for deformation to bond pads with each other. These properties necessitate high temperatures (~400°C) or significant high compression (~8 MPa) to achieve a reliable Co interconnection. In this paper, we proposed a Co-Co direct bonding strategy implemented at 200°C and with 2 MPa compression. By ultilizing the Ar plasma activation, the density of oxygen vacancy and hydroxyl on Co surface is increased, leading to improved planarization and electrical properties. Consequently, we successfully achieved the Co-Co bonding with a void-free bonding interface.