Low-Temperature Diffusion Behavior of Ti in Cu/Ti-Ti/Cu Bonding

The integration of vertically stacked interconnects as promising technology with improved performance, reduced size, and low cost has been studied. Because of its performance and fine pitch pattern advantages, Cu is gaining importance over traditional solder materials. However, both the high bonding temperature requirement and the oxidation of Cu must be addressed. In this study, Cu bonding using a 12-nm Ti nanolayer as a metal passivation layer was studied as regards the effect of anti-oxidation of the Cu surface and solid diffusion between Ti and Cu. Ti rapidly oxidized upon exposure to air, and the diffusion of Ti and TiO_2-x from the bonding interface to the Cu layer was observed, although some remained at the bonding interface. It was found that the diffusion of Cu into the Ti nanolayer was slower than the diffusion of Ti/TiO_2-x into the Cu layer due to a higher activation energy. The bonding of Cu/Ti-Ti/Cu was performed at 200°C, and the average shear strength was 13.2 MPa. Graphical Abstract: [Figure not available: see fulltext.]