Effect of Post-Annealing Conditions on Cu-Cu Wafer Bonding Characteristics

We have evaluated the interfacial adhesion energy of Cu-to-Cu bonding by using a 4-point bending test. Cu films are sputter deposited on Si(100) wafers. The bonding of Cu to Cu is successfully achieved by using a thermo-compression method at 25000 mbar and 415℃ for 40 min. The interface between the Cu films before the bonding was not observed after thermo-compression bonding. Only a few voids were observed at the middle of the Cu bonding layer. The quantitative interfacial adhesion energy of the Cu bonding without post annealing was 10.4 J/m2. The interfacial adhesion energy was changed high post-annealing of the bonding until a temperature of 300℃. However, very weak interfacial adhesion energy is observed after post annealing under an oxygen environment at temperatures over 400℃. Growth of brittle interfacial oxides is suggested as possible explanation for the effect of the environment on the weak interfacial adhesion energy. KCI Citation Count: 4