Boosting non-oxide interfacial Co/SiO₂ hybrid bonding by selective surface activation

Due to its superior nanoscale properties, cobalt (Co) is highly desirable for ultrahigh-density 3D integration into materials through metal/dielectric hybrid bonding. However, this process is very challenging through Co/SiO₂ hybrid bonding, as very hydrophilic SiO₂ surfaces are needed for bonding during dehydration reactions and oxidation of the Co surfaces must be avoided. Additionally, the substantial coefficient of thermal expansion mismatch between the robust capping layers (Co and SiO₂ layers) necessitates hybrid bonding with minimal thermal input and compression. In this study, we introduce a ternary plasma activation strategy employing an Ar/NH₃/H₂O gas mixture to facilitate Co/SiO₂ hybrid bonding at temperatures as low as ~200 ℃, which is markedly lower than the melting point of Co (~1500 ℃). Intriguingly, non-oxide metallization at the Co–Co interface can be realized without the hindrance of a bonding barrier, thereby reducing the electrical resistance by over 40% and compression force requirements. Moreover, the enhancement in the SiO₂ surface energy through active group terminations fosters extensive interfacial hydration and strengthens the mechanical properties. This research paves the way for fine-tuning bonding surfaces using a material-selective strategy, which should advance metal/dielectric hybrid bonding for future integration applications.