Characterization of Wafer Level Metal Thermo-Compression Bonding

摘要

Metal thermo-compression bonding is a wafer level bonding technique with many applications inrnthe manufacturing of microelectromechanical systems and integrated circuits. In this work werncharacterized the aluminum thermo-compression and the copper thermo-compression wafer bondingrntechnique. The effects and significance of various bond process parameters and surface treatmentrnmethods are reported on the final bond interface’s integrity and strength. Experimental variables includernthe bonding temperature, bonding time, bonding atmosphere (forming gas and inert gas), pre- and postbondingrnanneal, and wet etch treatments of metal surface prior to wafer level bonding. Bonded waferrnsamples were investigated with scanning acoustic-, scanning electron-, atomic force-, and focused ionrnbeam microscopy, and four point bending test. Interfacial adhesion energy and bond quality were found tornbe positively correlated with bonding temperature. Interfacial adhesion energies of greater then 10 J/m2rncan be achieved for both metal systems while the required minimum bonding temperature for the copperrnsystem is significantly lower. Copper thermo-compression bonding results are found to be very sensitivernto surface state of the metal requiring a metal surface oxide removal prior to bonding. Aluminum creatingrna chemically resistant and mechanically strong passivation layer is insensitive to surface treatmentrnmethods.