Effects of a hydrophilic surface in anodic bonding

This paper presents a study of the anodic bonding technique using a hydroph ilic surface. Our method differs from conventional processes in the pre-tre atment of the wafer. Hydrophilic surfaces were achieved from dipping in H2O /H2O2/NH4OH solution. The hydrophilic surface has a large number of -OH gro ups, which can form hydrogen bonds when two wafers are in contact. This ind uces a higher electrostatic force, because of the decreasing gap between th e glass and silicon wafer. We achieved improved properties, such as a wider bonded area and a higher bond strength than those of conventional methods. Also, the fabricated pressure sensors on the 5-inch silicon wafer were bon ded to Pyrex #7740 glass of 3 mm thickness. In order to investigate the mig ration of the sodium ions, the depth profile at the glass surface by second ary-ion mass spectroscopy and the bonding current were compared with that o f conventional methods.