Direct copper-copper wafer bonding with Ar/N2 plasma activation

Metal bonding is an attractive solution for vertical interconnection formation in three dimension (3D) integration of microelectronic device. Cu-Cu direct "fusion" bonding is able to form vertical interconnection and provides great advantages compared to thermo-compression metal to metal bonding. It requires no heating and short period of time during the bonding process. Hydrophilic Cu metal films surface is achieved with Ar / N₂ plasma activation. Room temperature fusion bonding is performed on blanket wafers with the activated Cu films at atmospheric pressure and ambient air, followed by annealing at 300°C. C-mode scanning acoustic microscopy (C-SAM) is performed on the bonded wafer. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) are performed on the bonded sample. Zigzag bonding interface is observed and N₂ is not present at the bonding interface.