Low-Temperature Ru–Ru Hybrid Bonding: Ar/H ₂ Plasma and NH ₄ OH Synergistic Activation for Ultrahigh Density Interconnection

Ruthenium (Ru) has emerged as a promising next-generation metal for ultrahigh-density interconnects, offering superior electrical performance and electromigration resistance at submicrometre dimensions, and thus is a strong candidate to replace Cu in future very-large-scale integration (VLSI) technologies. However, enabling Ru/dielectric hybrid bonding at low temperatures remains exceedingly challenging. The intrinsically high melting point of Ru(∼2334 °C) and its extremely low diffusion coefficient (∼1 × 10⁻⁷⁰ m²·s⁻¹) typically necessitate high-temperature, high-pressure thermal compression bonding. In parallel, hydrophilic bonding with dielectric materials such as SiO₂ must be achieved while suppressing Ru surface oxidation. In this study, we introduce a synergistic surface-activation strategy─Ar/H₂ plasma treatment followed by immersion in NH₄OH─that enables robust Ru-Ru bonding at 250 °C without oxidation. Moreover, the activated surfaces yield a 20% reduction in Ru surface resistance. This approach generates abundant -OH and -NH₂ functional groups on the Ru surface, promoting interfacial reactions and the formation of a void-free interface. Intriguingly, the bond strengths exceeded 12 MPa after 1000 thermal cycles between -45 °C and +125 °C. This synergistic activation route provides a viable pathway for low-temperature Ru/dielectric hybrid bonding with high reliability. The demonstrated bonding performance underscores Ru potential as a Cu replacement in BEOL interconnects and establishes a foundation for metal/dielectric hybrid bonding in forthcoming high-density integration technologies.