Two-Step Ar/N₂ Plasma Treatment on SiO₂ Surface for Cu/SiO₂ Hybrid Bonding

A surface pretreatment is a critical process in low-temperature Cu/SiO2 hybrid bonding, significantly improving the quality of bond for both the Cu–Cu and SiO2–SiO2 interfaces. Previously, we demonstrated that a two-step Ar/N2 plasma treatment could effectively enhance both the quality of Cu–Cu bonding and the antioxidative properties of copper surfaces through copper nitridation. In this study, we investigated the effects of a two-step Ar/N2 plasma treatment on a SiO2 surface for application to Cu/SiO2 hybrid bonding. The chemical states of a SiO2 surface were measured using X-ray photoelectron spectroscopy (XPS) after the two-step Ar/N2 plasma treatment, indicating that the SiO2 surface reacted with the N2 plasma and led to the substitution of oxygen in the Si–O bonds with nitrogen and the formation of three distinct entities, -N(-Si) 2, N+(-Si)2, and N(-Si)3. After SiO2–SiO2 bonding, Si nanocrystals were exclusively observed at the bonding interface in the two-step Ar/N2 plasma-treated specimen, in contrast to nonplasma-treated specimen, as indicated by a transmission electron microscope (TEM) analysis. Shear tests were conducted to assess the bonding strength of SiO2–SiO2, revealing that the specimens treated with the two-step Ar/N2 plasma process exhibited on average double the shear strength compared to nonplasma-treated specimens.