Cu–Cu Bonding in Ambient Environment by Ar/N₂ Plasma Surface Activation and Its Characterization

Ar/N2plasma surface activation in ambient environment for Cu–Cu bonding has been performed and characterized. Cu–Cu bonding occurs at room temperature and under normal atmospheric conditions. Postbonding annealing is performed at 300 °C and below to control the overall thermal budget. Shear strength and hermeticity property of samples with varying annealing temperature are investigated. Samples annealed at 250 °C demonstrate the highest average shear strength of 20.3 MPa and the lowest average helium leak rate of8.7 × 10⁻⁹\,\,atm· cc/s. Daisy chain structures are used to examine the electrical property of sample bonded at 300 °C, and the temperature cycling tests from −40 °C to 125 °C for 1000 cycles have been performed for the reliability assessment. It is observed that the dies are well-bonded and intact after 1000 cycles even though the exposed Cu surface is heavily oxidized.