Two-Step Ar/N Plasma Treatment on SiO Surface for Cu/SiO 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.