Demonstration of sub 150 °C Cu-Cu thermocompression bonding for 3D IC applications, utilizing an ultra-thin layer of Manganin alloy as an effective surface passivation layer

Abstract

Damascene process compatible Copper (Cu) surface passivation, ultra-smooth surface and enhanced Cu diffusion at the bonding interface are the key requirements for high quality, low temperature and low pressure Cu-Cu bonding for 3D integration applications. Manganin alloy deployed in this work as a passivation layer, performs dual role of protecting Cu surface from oxidation even at higher temperature (<300°C) and provides surface smoothness of about 0.8nm. Furthermore there is an inherent Cu 〈111〉 oriented plane formation with Manganin alloy passivated Cu surface. All the aforementioned factors are key enablers in enhancing diffusion of Cu across the bonding interface. This led to high quality Cu-Cu thermocompression bonding at sub 150°C temperature and at a nominal contact force of 5kN. Very low specific contact resistance of 1.45×10−7Ω-cm2 and excellent bond strength of 186MPa is clear evidence of the efficacy of optimized ultra-thin Manganin alloy as a passivation layer.