Novel hydrophilic SiO2wafer bonding using combined surface-activated bonding technique

Low-temperature hydrophilic SiO 2 –SiO 2 wafer bonding has been performed in vacuum by a new combined surface-activated bonding (SAB) technique. In this technique, wafers are irradiated by ion beam bombardment and simultaneously deposited with silicon by in situ silicon sputter deposition, and then terminated with Si–OH groups by water vapor exposure prior to bonding in vacuum. A surface energy of more than 1 J/m 2 was achieved by 200 °C postbonding annealing. A void-free oxide intermediate layer with a thickness of about 15 nm was observed at the bonding interface by transmission electron microscopy (TEM). The increased bonding energy can be attributed to the greater number of Si–OH formed through hydroxylation of the silicon deposited on the SiO 2 surfaces.