Direct Cu films bonding via surface-activated bonding method at room temperature

The microstructures and electrical properties of Cu–Cu film direct-bonding interfaces prepared via room-temperature surface-activated bonding were evaluated before and after annealing. Transmission electron microscopy (TEM) images taken before annealing revealed a zigzag morphology without a clearly distinguishable bonding interface. In contrast, after annealing at 350 °C for 1 h in N₂ atmosphere, the bonding interface was no longer visible and the grain boundaries disappeared. The bonding strength of the specimens exceeded 8 MPa both before and after annealing, with no fractures observed at the bonding interface during tensile testing. The electrical resistance of the Cu–Cu bonded films was approximately 17 mΩ before annealing and 7 mΩ after annealing. These findings demonstrate the feasibility of employing low- or room-temperature bonding methods for three-dimensional integration technologies.