Low-temperature hybrid bonding using sequential ArH2 and ArH2N2 low-inductance antenna plasma-assisted activation

Hybrid bonding involves simultaneously bonding of two different materials, viz., interlayer dielectric film (ILD)–ILD and Cu–Cu. This process requires the simultaneous involvement of two distinct bonding mechanisms with different participating functional groups and requires high bonding energy as well as an oxide-free Cu–Cu bonding interface. In hybrid bonding, hydrophilic groups are formed at the bonding interface to achieve ILD bonding. This inevitably forms Cu oxide on the Cu surface at the bonding interface. To address this issue, a plasma chamber equipped with a low-inductance antenna (LIA) was utilized in our previous study, enabling to achieve Cu–Cu direct bonding at low temperatures. In this study, sequential ArH2 and ArH2N2 plasma-assisted activation using an LIA enables the termination of a higher density of hydrophilic groups, which serve as bonding groups in ILD bonding, thereby achieving high bonding energy at temperatures <200 °C. This new surface-activation method for hybrid bonding enables simultaneous bonding of the ILD–ILD film and Cu–Cu at a postannealing temperature significantly lower than that required for conventional hydrophilic bonding. Furthermore, high bonding energy and good bonding quality can be achieved without forming an oxide film on the Cu–Cu bonding interface, thus overcoming a major limitation associated with low-temperature hydrophilic bonding. These features enable significant lowering of the postannealing temperature in hybrid bonding, thereby enabling the fabrication of highly integrated devices for future three-dimensional device technology.