Electric-Field-Driven Surface Ionic Transport on Hydroxylated SiO2 Governs Transient Leakage and Hybrid Bonding Reliability

Cu/SiO2 hybrid bonding is critical for 3D integrated circuit packaging, where dielectric surface activation impacts bonding quality and long-term reliability. NaOH-based wet chemical activation is a promising approach for a scalable and cost-effective processing under ambient conditions. However, this route introduces residual ions at the SiO2 surface, raising concerns regarding electrical leakage and dielectric stability. In this study, electric-field-driven surface ionic transport on NaOH-activated SiO2 and its role in transient leakage and hybrid bonding reliability were investigated. Reversible and polarity-dependent transient current peaks observed in cyclic electrical measurements provide evidence for electric-field-driven migration of the mobile ionic species at the SiO2 interface. In addition, higher NaOH concentrations promoted greater residual Na+ accumulation and intensified transient leakage peaks, supporting the selection of 0.5 M NaOH as an effective activation condition. Systematic decoupling experiments demonstrate that residual mobile Na+ ions are the dominant contributors to the transient leakage current rather than fixed hydroxyl groups. Quantitative analysis reveals Na+ surface mobility of approximately 3 × 10-10 m2V-1s-1, an order-of-magnitude upper-bound estimate that is consistent between constant-bias and ramped-bias measurements and about six orders of magnitude higher than that in bulk SiO2, suggesting a surface-dominated transport. An optimized 3 min deionized water (DI) rinse reduces the mobile Na+ population below the electrical detection limit and decreases the Na 1s XPS intensity by roughly an order of magnitude, suppressing the transient leakage to near-baseline levels while maintaining hydrophilicity and achieving the SiO2-SiO2 bonding strength of 19.7 ± 1.8 MPa, comparable to Ar plasma activation. The leakage measurements were performed on Cu/SiO2 damascene comb structures, whereas the bonding validation addresses the dielectric part of the hybrid-bonding interface; Cu-Cu contact and long-term stress testing remain to be verified. This work provides a framework for understanding electric-field-driven surface ionic transport and practical guidelines for contamination control of the dielectric surface in wet-activated Cu/SiO2 hybrid bonding.