Low-temperature Solid-state Bonding of Micro-bumps Arrays with Flat-to-Convex Structure via Plasma-induced Silver Oxide Nanoparticles

For advanced 3D-IC packaging, we have previously invented a new bonding technology utilizing plasma-induced Ag₂O nanoparticles (Ag₂O NPs) and disclosed the growth mechanism of plasma-induced Ag₂O NPs. In this study, we firstly established suitable parameters for the growth of plasma-induced Ag₂O NPs on Ag films deposited by magnetron sputtering. Moreover, a novel structure, namely flat-to-convex structure, was designed to facilitate the bonding of a micro-bump array and a surface of plasma-induced Ag₂O nanoparticles atop the as-deposited Ag film. This structure enhances the localized pressure at the interface between the micro bumps and the film, thereby promoting the lateral plastic deformation of the micro-bumps. Additionally, the Ag-Ag direct bonding of flat-to-convex structure was achieved by applying an oxygen and argon plasma to the surface of Ag films, followed by in-situ reduction of plasma-induced Ag₂O NPs under a low-temperature (220 °C). The in-situ reduction of silver oxide wetted the original interface, enhancing surface diffusion and promoting material connection at the atomic scale, as well as the merging of grains at the original bonding interface. This provides a highly reliable design for applications in flip-chip interconnects and 3D-IC heterogeneous integration.