Reduction behavior and mechanism of copper oxide in Ar/H2 pulsed plasma

Copper (Cu) is widely utilized as a core material in various next-generation electronic device processes, including semiconductor interconnects, Through-Silicon Vias (TSVs), micro-bumps, and hybrid bonding. However, oxide layers formed by air exposure or during processing act as major factors causing increased electrical contact resistance, reduced interfacial bonding strength, hindered elemental diffusion, and degraded device reliability. In this study, the reduction behavior of copper oxide films was analyzed using an Ar/H 2 pulsed plasma process and the effects of plasma power and gas composition on the reduction characteristics were systematically evaluated. Reduction treatment was carried out on copper samples prepared under different oxidation conditions, and the behavior of plasma active species during the process was analyzed in real time by optical emission spectroscopy (OES). Furthermore, changes in the surface characteristics of the treated samples were investigated in detail using spectrophotometer-based color difference analysis and X-ray photoelectron spectroscopy (XPS). As a result, the behavior of active species in the plasma changed distinctly according to the On/Off cycle of hydrogen supply and this behavior showed a close correlation with the actual reduction characteristics of the samples. In addition, the reduction efficiency and surface state exhibited different tendencies depending on the applied power and gas composition, thereby clarifying a process mechanism governed by the combined effects of physical surface activation and chemical reduction reactions. This study suggests that Ar/H₂ pulsed plasma can be effectively applied to the low-thermal-budget (LTB) reduction process of copper oxide films and also provides useful process guidelines for optimizing the surface cleaning and reduction processes of various metal oxide films.