High Quality Fine-Pitch Cu-Cu Wafer-on-Wafer Bonding with Optimized Ti Passivation at 160°C

In this paper, we investigate low temperature, low pressure and fine-pitch Copper-Copper thermo-compression bonding using an optimized Titanium (Ti) passivation layer. Ultra-thin Ti layer not only accomplishes the dual role of protecting surface of Cu from oxidation and reducing the effective surface roughness, but also allows the Cu to diffuse. The novelty of this surface passivation approach is the accomplishment of bonding at low temperature of 160° C and pressure to 3.5 KN. The lower bonding temperature and pressure exhibits a very good bond at the interface may give realistic chance to use 3D IC platform. Surface analysis of post patterned Cu/Ti pads were analyzed using X-Ray Photoelectron Spectroscopy (XPS) measurement of the surface corroborates proper passivation of Cu pads. The quality of bonded wafer was tested in Instron microtester measurement system. Also the morphology of bonded wafer was examined using Cross-sectional FE-SEM and Idonus Wafer Bonder IR Inspection (WBI) tool.