Exploring Bonding Mechanism of SiCN for Hybrid Bonding

The demand for technologies enabling higher performance, greater capacity at lower cost has been growing. Wafer-to-Wafer hybrid bonding for three-dimensional architectures allows for high interconnect density with a minimal footprint. SiCN has been considered as a superior dielectric layer. However, the mechanism of SiCN-SiCN bonding has not been clearly described in comparison to SiO2-SiO2 bonding. In this study, we investigated the surface and subsurface of dielectric films (SiCN, SiO2) at several post-process steps to understand their characteristics. Positron Annihilation Spectroscopy was employed to detect open spaces. This measurement revealed that SiCN film possesses a higher density of atomic-level voids, fewer outgasses, and more dangling bonds (DBs) than SiO2 film. These results were consistent with the tendency of water desorption observed through thermal desorption spectroscopy. Based on these findings, it is assumed that a large number of water stored in the dielectric film affects the generation of interfacial voids when wafers are bonded and annealed at decent temperatures. However, many DBs in the SiCN film enable the suppression of voids, leading to void-free. Additionally, the impact of pre-surface cleaning/conditioning prior to physical vapor deposition (PVD) barrier deposition was investigated. It was found that strong Ar plasma has a negative impact on the in-situ plasma cleaning for bonding when the process is not well optimized.