Cu/SiO2 hybrid bonding obtained by surface-activated bonding method at room temperature using Si ultrathin films

The hybrid bonding technique, used for the bonding of metal-electrode and insulator hybrid interfaces with a high alignment accuracy, is very important for the three-dimensional integration technology. Bonding of Cu and SiO2 hybrid interfaces was performed by surface activated bonding (SAB) method at room temperature using a Si ultrathin film, which we previously proposed. Transmission-electron-microscopy (TEM) observations reveal that no microvoids and gaps are present at the interfaces of bonded Cu/Cu electrodes and SiO2/SiO2. The intermediate layer with the thickness of approximately 5 nm was confirmed at both bonding interfaces. The contact resistance of a pair of bonded electrodes was approximately 4.1 Ω. The bonded specimen fractured at the bonded interface by tensile test, and the bonding strength was then approximately 2 MPa. An electron-energy-loss spectroscopy analysis combined with TEM confirmed that SiO2 was present in the intermediate layer with a two-layer structure including an amorphous Si and SiO2 layers. It seems that the two-layer structure resulted in high contact resistance and low bonding strength. Although the contact resistance was not sufficiently low, the electrical connection of the bonded Cu/Cu electrodes was achieved. These results suggested that hybrid bonding was achieved at room temperature using our novel bonding technique.