Surface Chemistry Effects on Bond Wave Dynamics and Distortion-Induced Scaling Errors during Plasma-Activated Direct Bonding of SiCN

Hybrid bonding is an important aspect of advanced three-dimensional integration. However, as the Cu pad pitch is scaled down, wafer-scale alignment accuracy becomes increasingly limited due to postbonding in-plane displacement (IPD), which appears as overlay loss and scaling mismatch across the wafer. The present work investigated the factors governing bond-front (that is, bond wave) propagation, wafer-scale distortion, and bond strength during wafer-level direct bonding in association with SiCN films produced using plasma-enhanced chemical vapor deposition. In trials employing N2 or O2 plasma activation, the bonding characteristics were correlated with surface chemical states. The bond-front speed remained nearly unchanged with variations in the plasma conditions, whereas the extent of postbonding IPD increased markedly when using the N2 plasma, indicating a larger risk of field-dependent overlay errors and systematic scaling distortion in conjunction with fine-pitch hybrid bonding. In contrast, the bond strength was maximized by N2 plasma treatment at 100 W. Surface and interface analyses suggested that the N2 plasma generated both −NH and C-based surface groups that promoted interfacial reactions, enabling high bond strength but simultaneously amplifying local reaction-driven distortions. Conversely, the O2 plasma generated a more uniform, SiO2-like surface, leading to bonding with reduced IPD and improved wafer-scale alignment stability, albeit with lower strength than was obtained using the optimal N2 plasma conditions. These results demonstrate a trade-off relationship between strength and alignment rooted in surface chemistry and provide guidelines for the optimization of fine-pitch hybrid bonding for the fabrication of next-generation devices.