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

Abstract

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.