Low-temperature direct bonding of silicon and silicon dioxide by the surface activation method

We have investigated low-temperature bonding of Si and SiO₂ by the surface activation method in vacuum. In the method, Ar beam etching is used to create a clean surface which has strong bonding ability. The specimens are bonded in the vacuum without exposing them to the atmosphere. The strength of Si/Si bonding prepared at room temperature by die method is equivalent to the bulk strength. SiO₂/SiO₂ bonding by the method is twice as strong as conventional bonding before annealing. In addition, the bonding prepared by Ar beam is stronger than that prepared by reactive molecule beam etching such as H₂O and NH₃. The influence of surface oxidation was examined by exposing an etched Si surface to residual gas in the vacuum chamber. Adsorption of reactive molecules such as H₂O on the etched surface causes reduction of bonding strength, whereas Ar gas does not affect the bonding. These results mean that a clean surface etched by Ar beam has strong bonding ability even at room temperature.