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 Omega. The bonded specimen fractured at the bonded interface by tensile test, and the bonding strength was then approximately 2 MPa. An electronenergy-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. (c) 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).