Room temperature bonding of silicon and lithium niobate

The feasibility of wafer-level bonding was examined for silicon (Si)/lithium niobate (LiNbO3) wafers by using a modified surface activated bonding process at room temperature. A low energy argon ion source of 80eV energy with 3A current was used, which was capable of sputter cleaning and depositing Fe nanolayers on the surfaces. Visual inspection showed that almost all of the 4in. Si∕LiNbO3 wafers were bonded. The measured bond strengths were as high as 37MPa but were inhomogeneous. This is due to the lack of uniform application of force over the surfaces (which are not parallel to the jigs) and the pulling angles during the pulling test. A 5nm thick amorphous layer was observed across the Si∕LiNbO3 interface. Electron energy loss spectroscopy analysis confirmed the presence of Fe in the interfacial amorphous layer. This Fe-containing interfacial layer appears to be responsible for the high bonding strength observed between Si∕LiNbO3 at room temperature.