Low-Temperature Solid-State Bonding of Microbumps Arrays With Flat-to-Convex Structure via Plasma-Induced Silver Oxide Nanoparticles

Abstract

For advanced 3-D-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 first established suitable parameters for the growth of plasma-induced Ag2O NPs on Ag films deposited by magnetron sputtering. Moreover, a novel structure, namely a flat-to-convex structure, was designed to facilitate the bonding of a microbump array and a surface of plasma-induced Ag2O NPs atop the as-deposited Ag film. This structure enhances the localized pressure at the interface between the microbumps and the film, thereby promoting the lateral plastic deformation of the microbumps. 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 ( $220~^{\circ }$ 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 3-D-IC heterogeneous integration.