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

Abstract

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 SiO2 or SiN are not. Using only Si ultrathin films, we propose a new bonding technique for SiO2/SiO2 bonding at room temperature. Two SiO2 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/m2, and the bonding strength was more than 25 MPa. This bonding technique was successfully realized to enable SiO2/SiO2 bonding without a metal adhesion layer.

Combined Surface Activated Bonding Technique for Low-Temperature Cu/Dielectric Hybrid Bonding

“…The SiO 2 -SiO 2 bonding strength is around 0.5 J/m 2 , which is higher than that obtained by using the conventional SAB method (less than 0.1 J/m 2 ) but lower than that using the deposited Si intermediate layer (>1.0 J/m 2 ). 23,33 The SiO 2 -SiN x bonding strength of 1 J/m 2 is higher than the SiO 2 -SiO 2 bonding strength. Postbonding annealing at 200 • C for 2 hours results in no significant change of the bonding strength of all the bonded pairs.…”

“…However, the SiO 2 -SiO 2 bonding strength of 0.5 J/m 2 is lower than the value of >1.0 J/m 2 obtained by bonding with the deposited Si intermediate layer. 33 This can be because the absence of coverage of Si atomic layers on the as-activated SiO 2 surfaces. Monte Carlo simulations by using the stopping and range of ions in matter (SRIM) program showed that Si ions with energy as low as 20-100 eV can be even subplanted into the 0.45-1.50 nm depth range on amorphous SiO 2 surface.…”

Fabrication of High Power Deep Ultraviolet Light-Emitting Diodes with Glass Lenses Using Atomic Diffusion Bonding

“…It has also been proposed that amorphous Si could be used for bonding based on the SAB process. 39 In the SAB technique, a Si target is placed between the Ar ion gun and the wafer to be bonded and is then etched by Ar ions. The scattered Si subsequently deposits on the surface of the wafer and bonding is accomplished via the resulting layer of amorphous Si.…”

Room-Temperature Bonding of Indium Phosphide Wafers and Their Atomic Structure at the Bond Interface

“…A Si atomic layer can be a good alternative in this regard, as it is highly transparent over a wide range of infrared wavelengths. Meanwhile, a bonding method using an activated Si atomic layer was demonstrated to be effective for improving the bond strength in the bonding of oxide materials. ,− It might be interesting to apply both SAB and bonding using an activated Si atomic layer for the bonding of InP wafers. Moreover, it would be meaningful to analyze the effect of bonding and observe the state of the bond interface for investigating the mechanism of the room-temperature bonding of InP.…”