Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers
The bonding energy of bonded native-oxide-covered silicon wafers treated in the HNO3/H2O/HF or the HNO3/HF solution prior to room-temperature contact is significantly higher than bonded standard RCA1 cleaned wafer pairs after low-temperature annealing. The bonding energy reaches over 2000 mJ/m(2) after annealing at 100 degreesC. The very slight etching and fluorine in the chemically grown oxide are believed to be the main contributors to the enhanced bonding energy. Transmission-electron-microscopic images have shown that the chemically formed native oxide at bonding interface is embedded with many flake-like cavities. The cavities can absorb the by-products of the interfacial reactions that result in covalent bond formation at low temperatures allowing the strong bond to be retained. (C) 2004 American Institute of Physics
Tong, Q-Y., Gan, Q., Fountain, G., Enquist, P., Scholz, R., & Gosele, U. (2004). Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers. Applied Physics Letters, 85(17), 3731-3733.