Effects of two-step plasma treatment on Cu and SiO2 surfaces for 3D bonding applications

Cu-to-Cu bonding is necessary for high density, fine-pitch interconnect and high bandwidth in 3D stacking technology. Although various Cu-to-Cu bonding studies have been reported so far, few challenges still are remaining such as atmospheric oxidation of Cu, high bonding temperature and pressure not suitable for mass production. In this study, we evaluated low temperature Cu-to-Cu bonding with two step plasma treatment using Ar and N2. The effects of Ar and N2 plasma treatment on Cu and SiO2 surfaces were investigated especially for Cu/SiO2 hybrid bonding applications. The two-step plasma treatment was produced copper nitride passivation layer to prevent further oxidation of copper in the air. The two-step plasma treated SiO2 surface showed some nitrogen bonding with Si, but no effects on electrical property.