Direct Ag-Ag bonding by in-situ reduction of surface oxides for advanced chip-package interconnection

Direct Ag-Ag bonding was achieved at 210 °C with 1.38 MPa static pressure through in-situ reduction of surface Ag₂O, which was produced by applying oxidizing plasma on the surface of Ag films. During bonding, Ag₂O decomposed into the in-situ formed Ag atoms, which significantly enhanced surface diffusion. It facilitated the joining of materials at atomic scale and merging of grains at the original bonding interface. Cross-sectional studies showed that two Ag films join together to form a “bulk-like” polycrystalline material without any trace of the original interface. This new bonding technique is promising in flip chip interconnect and 3D integration.