Micro-cones Cu fabricated by pulse electrodeposition for solderless Cu-Cu direct bonding

In the post-Moore's era, Cu-Cu direct bonding has garnered significant attention as a promising alternative to solder joints for chip interconnection in advanced electronic packaging technology. Its advantages lie in reduced process restrictions and steps, as well as lower bonding temperature, which align with the demands for low cost and high compatibility. In this study, (1 1 0)-oriented micro-cones Cu was fabricated via template-free pulse electrodeposition, enabling solderless Cu-Cu direct bonding at 250 degrees C under three distinct bonding pressures without chemical mechanical polishing (CMP). The contact bonding area and shear strength gradually increased corresponding to the applied bonding pressure. Seamless bonding interface was achieved under high bonding pressure, leading to high shear strength of 116.4 MPa for Cu-Cu bonding joints. The obtuse polygon pyramid micro-cones, characterized by an enlarging cross-sectional area from apex to base, coupled with inherent mechanical properties, induce high applied stress at micro-cone's tip and a low yield stress, facilitating the initiation and propagation of plastic deformation during the bonding process. This study has demonstrated the feasibility of utilizing the micro-cones Cu for low-temperature bonding without CMP treatment, offering valuable insights into the advanced interconnection technologies.