Substrate bonding at low temperature by using plasma activated porous gold

Porous gold with porosity in nanoscale which indicates a highly reactive surface has shown its potential for low temperature bonding. Recently, thermo-compression bonding between nanoporous gold (NPG) and gold film at 200°C has been reported. In this study, with plasma activation, silicon chips with Au film and nanoporous gold structure respectively bonded at room temperature is demonstrated. First, nanoporous gold is fabricated by electrodeposition of gold-tin alloy, followed by chemical dealloying where the Sn component is removed. Then, with Ar plasma treatment, two silicon chips, one side with sputtered Au film and the other with nanoporous gold, are bonded face to face in ambient air. Bonding temperature starting from 150°C down to room temperature are achieved. Results show that by combining plasma activation and nanoporous gold structure, the bonding temperature can be reduced dramatically and is able to be applied to MEMS/sensor packaging technologies.