Combined Surface Activated Bonding Technique for Hydrophilic SiO₂-SiO₂ and Cu-Cu Bonding

As an evolution of the Cu-Cu bonding and SiO2-SiO2 bonding, Cu/SiO2 hybrid bonding is a promising approach to the emerging three-dimensional (3D) integration of microelectronic/photonic systems, since it obtains both direct metal interconnection and enhanced thermal/mechanical stability with a seamless bonding structure during the single bonding process.1,2 However, because of the different features of Cu-Cu and SiO2-SiO2 bonding, Cu/SiO2 hybrid bonding at low temperatures of no more than 200 °C remains challenging. For instance, the Cu-Cu thermo-compression bonding is typically conducted in vacuum or dry protecting/reducing atmospheres after removal of surface oxides,3–7 while the SiO2-SiO2 bonding needs a humid environment to facilitate termination of Si-OH bonding sites.8–12 It is highly desired to develop a new bonding process that is effective for both Cu-Cu and SiO2-SiO2 bonding in H2O-free ambient, such as vacuum, for improvement of the Cu/SiO2 hybrid bonding. Recently, we proposed a combined surface-activated bonding (SAB) method, which involves a combination of surface bombardment using a Si-containing Ar beam and prebonding attach-detach procedure prior to bonding in vacuum. High SiO2-SiO2 bonding strength of close to the Si bulk fracture strength has been realized at 200 °C. In this paper, we report our recent results of Cu-Cu and SiO2-SiO2 bonding by using the combined SAB method. The mechanism is discussed to understand the present low-temperature bonding technique. References 1. L. D. Cioccio et al., J. Electrochem. Soc., 158, P81–P86 (2011). 2. H. Moriceau et al., Microelectron. Reliab., 52, 331–341 (2012). 3. W. Yang, M. Akaike, M. Fujino, and T. Suga, ECS J. Solid State Sci. Technol., 2, P271–P274 (2013). 4. W. Yang, M. Akaike, and T. Suga, IEEE Trans. Compon. Packag. Manuf. Technol., 4, 951–956 (2014). 5. B. Rebhan and K. Hingerl, J. Appl. Phys., 118, 135301 (2015). 6. T. H. Kim, M. M. R. Howlader, T. Itoh, and T. Suga, J. Vac. Sci. Technol. A, 21, 449–453 (2003). 7. A. Shigetou, T. Itoh, K. Sawada, and T. Suga, IEEE Trans. Adv. Packag., 31, 473–478 (2008). 8. Q.-Y. Tong and U. M. Gösele, Adv. Mater., 11, 1409–1425 (1999). 9. T. Suni, K. Henttinen, I. Suni, and J. Mäkinen, J. Electrochem. Soc., 149, G348–G351 (2002). 10. F. Fournel et al., ECS J. Solid State Sci. Technol., 4, P124–P130 (2015). 11. H. Takagi, J. Utsumi, M. Takahashi, and R. Maeda, ECS Trans., 16, 531–537 (2008). 12. R. He, M. Fujino, A. Yamauchi, and T. Suga, Jpn. J. Appl. Phys., 54, 030218 (2015).