Room Temperature Si/Si Wafer Direct Bonding in Air

Wafer direct bonding technique offers flexible and inexpensive ways to fabricate novel semiconductor devices. But its application is much limited by high temperature process and void problem. In this study, room temperature Si/Si wafer direct bonding has been performed using sequential plasma pretreatment prior to bonding. A shorter O₂ reactive ion etching (RIE) pretreatment (~10 s) and followed by N₂ radicals for 60 s is used for surface activation. Strong bonding strength (about 2-2.5 J/m²) is achieved at room temperature without requiring any annealing process. It is close to the bulk-fracture of silicon. Furthermore, no voids are observed at Si/Si interfaces even if the bonded wafer pairs are heated from 200degC to 800degC in subsequent annealing process. The bonding mechanism is proposed in this paper. The authors believe that this void-free, room temperature bonding technique by sequential plasma activation is suitable for the microelectromechanical systems manufacture process and wafer-scale packaging.