Prolongation of the Surface Activation Effect using Self-Assembled Monolayer for Low Temperature Bonding of Au

Surface activation is a key technology to lower the process temperature of the direct bonding of Au for device packaging. However, the effect of surface activation does not last long due to re-adsorption on the activated surface by exposure to ambient air. In this study, the protection of the activated Au surface is demonstrated using a self-assembled monolayer of 1-hexadecanthiol (1-HDT). The bare Au layers result in low bond strength when bonded 5 days after surface activation. On the other hand, the activated and SAM-coated Au layers are successfully bonded at a low temperature of 100 °C even 5 days after the surface activation, showing the equivalent bond strength to that of bonding right after surface activation. The proposed process combining surface activation and SAM protection maintains the clean and activated Au surface for low temperature bonding.