Low temperature Au-Au surface-activated bonding using nitrogen atmospheric-pressure plasma treatment for optical microsystems

This study investigated the effect of nitrogen (N₂) atmospheric-pressure (AP) plasma treatment on the Au-Au bonding property. Surface analysis using x-ray photoelectron spectroscopy (XPS) before and after AP plasma treatment with different gases: N₂ and Ar+O₂ was performed. In the case of Ar+O₂ AP plasma treatment, the oxidation of the Au surface (Au₂O₃) was detected by the chemical shift of the 4f levels in XPS spectra. In contrast, no oxidation of Au surfaces was observed after N₂ AP plasma treatment. N₂ AP plasma treatment was effective in improving the bondability between Au/Au compared with Ar+O₂ AP plasma treatment (bonding temperature: 150°C).