Characterization of Nitride Passivated Cu Surface for Low-Temperature Cu-Cu Bonding

Copper nitride passivated surface has been characterized and optimized by the design of experiment (DOE) technique with the aim of low-temperature (300°C) Cu-Cu bonding. In order to generate an oxidation-free surface prior to Cu-Cu bonding process, N2 plasma treatment was performed on Cu surface followed by Cu surface activation and cleaning by Ar plasma in the same conventional DC sputter chamber. In this study, N2 plasma treatment conditions were optimized using the response surface methodology (RSM) based on central composite design (CCD) in DOE. The chemical states of nitride passivated Cu surface were analyzed by XPS profiles and then, several meaningful peak areas of each element were calculated by a deconvolution technique. These peak areas and surface roughness by AFM were used as the input values for the response optimization process. Cu-Cu bonded interface quality using optimized plasma conditions at low-temperature (300°C) has been significantly improved and it shows this research has great potential for Cu-Cu bonding in mass production.