Room temperature bonding of SiO₂ and SiO₂ by surface activated bonding method using Si ultrathin films

The bonding of metal electrodes and insulator hybrid interfaces is one of the key techniques in three-dimensional integration technology. Metal materials such as Cu or Al are easily directly bonded by surface activated bonding at room temperature, but insulator materials such as SiO 2 or SiN are not. Using only Si ultrathin films, we propose a new bonding technique for SiO 2 /SiO 2 bonding at room temperature. Two SiO 2 surfaces, on which Si thin films were deposited, were contacted in vacuum. We confirmed that the thickness of the layer was about 7 nm by transmission electron microscopy observation and that the layer was non crystalline by electron energy loss spectroscopy analysis. No metal material was found in the bonding interface by energy-dispersive X-ray spectroscopy analysis. The surface energy was about 1 J/m 2 , and the bonding strength was more than 25 MPa. This bonding technique was successfully realized to enable SiO 2 /SiO 2 bonding without a metal adhesion layer.