The study of Cu-Cu low temperature bonding using formic acid treatment with/without Pt catalyst

Cu low temperature bonding is one of important technologies for high performance 3-D interconnection. In order to remove Cu surface oxide and contaminations for low temperature bonding, formic acid vapor treatment process was proposed to treat Cu film surface for clean Cu surface. In this study, Cu sample surfaces were treated by formic acid vapor with Pt or without Pt catalyst. Through XPS surface analysis, it is found that Cu sample surface oxide was reduced by formic acid vapor treatment with/without Pt catalyst. However, the effect of reduction is different for with/without Pt. The effect of formic acid vapor treatment with Pt catalyst is better than that without Pt catalyst. In order to measure the contact resistance and bonding strength, a new type Cu electrodes sample was designed and fabricated for low temperature bonding. Cu electrodes bondings were performed at 200°C using formic acid treatment with Pt catalyst and without Pt catalyst, respectively. For he treatment with Pt catalyst, the bonding is stronger than that without Pt catalyst, and the strength is about 40Mpa.