Enabling Low Temperature Copper Bonding with an Organic Monolayer

Typically, copper material is used as a bonding material in MEMs devices for its excellent mechanical, electrical and hermetic properties. Direct copper bonding, however, requires high temperature (>300°C) to forge a bond due to the oxidative nature of copper. In this study, using an alternative approach based on an organic monolayer coating, we demonstrate metallurgical bonding between two copper surfaces under ambient condition at low bonding temperature below 140°C, while maintaining reliable mechanical joint integrity of 50MPa. This monolayer is believed to behave as a passivation layer, protecting the copper surface against oxidation under ambient conditions. In contrast to a bulk oxide layer, this layer can be easily displaced during mechanical deformation at the bonding interface.