Formic acid with Pt catalyst combined treatment process for Cu low temperature bonding

In this study, formic acid combined Pt catalyst in situ pretreatment process was developed for low temperature Cu/Cu direct bonding. Cu film surface was treated by formic acid without/with Pt as catalyst at 200°C for 10min to reduce Cu surface oxide. Through XPS analysis, it is found that, with Pt as catalyst, formic acid reduction effect on Cu film surface is better than that of formic acid treatment without Pt as catalyst. Cu film and Cu micro-electrodes was bonded together at 200°C in N₂ atmosphere after formic acid treatment without/with Pt catalyst. The bonding strength is evaluated using die shear tester. When sample was treated by formic acid with Pt catalyst, the bonding is stronger compared with the bonding treated by formic acid without Pt catalyst. Bonding strength also increases with keeping the contact load for long time during the bonding. When sample was treatedat200°C for 10min with Pt catalyst, and the contact load as 1000N was kept for 60min during bonding, the bonding strength is about 28.5MPa. Finally, the cross-section image of bonding interface is obtained through SEM observation.