Abstract： Ultraviolet (UV) exposure, as an additional technique following the traditional wet chemical activation processes, is applied to enhance hydrophilic silicon direct bonding. The effects of UV exposure on silicon wafers’ nano-topography and bonding strength are studied. It is found that the surface roughness of silicon wafers initially decreases and then increases with UV exposure time, and the bonding strength increases and then decreases accordingly. The correlations of annealing temperature and annealing time vs. bonding strength are experimentally explored. Results indicate that the bonding strength increases sharply then gently with increasing annealing temperature and annealing time using UV exposure. Besides, the reliability of silicon direct bonding with UV exposure enhancement after the high/low temperature cycle test, constant temperature and humidity test, vibration test and shock test is investigated. It follows from the results that the bonding strength of silicon wafer pairs with UV exposure decreases after the environmental tests, whereas the residual strength is still higher than that without UV exposure, and the variation trends of bonding strength vs. UV exposure time, annealing temperature and annealing time remain unchanged. Therefore, following the traditional wet chemical activation processes, appropriate UV exposure (about three minutes in this study) is effective and promising to enhance silicon direct bonding.
Lasky J B. Wafer bonding for silicon-on-insulator technologies. Applied Physics Letters, 1986, 48(1): 78–80 doi: 10.1063/1.96768
Huang L J, Chu J O, Goma S A, D’Emic C P, Koester S J, Canaperi D F, Mooney P M, Cordes S A, Speidell J L, Anderson R M, Philip Wong H S. Electron and hole mobilityenhancement in strained SOI by wafer bonding. IEEE Transactions on Electron Devices, 2002, 49(9): 1566–1571 doi: 10.1109/TED.2002.802675
Kang P, Tanaka S, Esashi M. Cavity-through deep reactive ion etching of directly-bondedsilicon wafers. In: Proceedings of the4th International Conference on Solid-State Sensors, Actuators andMicrosystems, Transducers and Eurosensors '07. 2007, 549–553
Dragoi V, Farrens S, Lindner P. Plasma activated wafer bonding for MEMS. In: Cané C, Chiao J C, Verdú F V, eds. Proceedings of SPIE: Smart Sensors, Actuators, and MEMS II. 2005, 179–187
Tang Z R, Shi T L, Liao G L, Liu S Y. Modelingthe formation of spontaneous wafer direct bonding under low temperature. Microelectronic Engineering, 2008, 85(8): 1754–1757 doi: 10.1016/j.mee.2008.04.038
Verdiel M, Protz J. Advanced microfabricationtechniques for millimetre band cavities. In: Proceedings of the 8th IEEE International Vacuum Electronics Conference,IVEC 2007. 2007, 131–132
Huang Y L, Ergun A S, Haeggstrom E, Badi M H, Khuri-Yakub B T. Fabricating capacitive micromachinedultrasonic transducers with wafer-bonding technology. Microelectromechanical Systems, 2003, 12(2): 128–137 doi: 10.1109/JMEMS.2003.809968
Sanz-Velasco A, Amirfeiz P, Bengtsson S, Colinge C. Room temperature wafer bonding using oxygen plasma treatment in reactiveion etchers with and without inductively coupled plasma. Electrochemical Society, 2003, 150(2): G155–G162 doi: 10.1149/1.1536182
Zhang X X, Raskin J P. Low-temperature wafer bonding:a study of void formation and influence on bonding strength. Microelectromechanical Systems, 2005, 14(2): 368–382 doi: 10.1109/JMEMS.2004.839027
Tong Q Y, Gan Q, Fountain G, Enquist P. Fluorine-enhanced low-temperature wafer bonding of native-oxide coveredSi wafers. Applied Physics Letters, 2004, 85(17): 3731–3733 doi: 10.1063/1.1809279
Pasquariello D, Hjort K. Plasma-assisted InP-to-Silow temperature wafer bonding. IEEE Journalon Selected Topics in Quantum Electronics, 2002, 8(1): 118–131 doi: 10.1109/2944.991407
Holl S L, Colinge C A, Hobart K D, Kub F J. UV activationtreatment for hydrophobic wafer bonding. Electrochemical Society, 2006, 153(7): G613–G616 doi: 10.1149/1.2196673
Dang H, Holl S L, Colinge C A, Hobart K D, Kub F J. UV activation treatment for hydrophobicwafer bonding. In: Hobart K D, Hont C E, Baumgait H,. eds. Semiconductor Wafer BondingVIII: Science, Technology; and Applications-Proceedings of the InternationalSymposium, 2005, 376–384
Hobart K D, Kub F J, Coling C A, Ayele G. UV/ozone activationtreatment for wafer bonding. In: Proceedingof the 7th International Symposium on Semiconductor Wafer BondingScience, Technology, and Applications, 2003
Kasi S R, Liehr M. Vapor phase hydrocarbon removalfor Si processing. Applied Physics Letters, 1990, 57(20): 2095–2097 doi: 10.1063/1.103952
Vig J, LeBus J. UV/ozone cleaning of surfaces. IEEE Transactions on Parts, Hybrids and Packaging, 1976, 12(4): 365–370 doi: 10.1109/TPHP.1976.1135156
