Room temperature silicon wafer direct bonding in vacuum by Ar beam irradiation

We have developed a new method for the direct bonding of silicon wafers at room temperature. In the method Ar fast atom beam etching is used to modify the surface of the specimens, and they are bonded in the vacuum. With the appropriate Ar beam etching, the bonding prepared at room temperature is as strong as that prepared by conventional wet surface modification treatment and high temperature annealing. In the process, pressing load is not necessary when two specimens are mated. Intimate contact at the bonding interface is supposed to be achieved by the attractive force between the surface. Therefore surface roughness of the specimen is quite important in the method. On the other hand, this method does not need ultrahigh vacuum condition. Especially, the influence of inert gas in the vacuum chamber is quite small. Even in the 1000 Pa of Ar, strong bonding can be attained. The applicability of this method to the small area bonding was proved by the bonding of 200 μm diameter bumps and 100 μm wide lines. These results demonstrate the advantages of this method. This method is promising as a assembling and packaging method for MEMS.