Formic acid treatment with Pt catalyst for Cu direct and hybrid bonding at low temperature

A new process of Cu-Cu direct bonding at lower than 200°C in atmospheric atmosphere was developed. The method is composed of formic acid treatment with Pt catalyst. To demonstrate the feasibility of the method, Cu electrodes samples were designed for characterizing the bonding strength and the contact resistance for the Cu-Cu direct bonding. The bonding strength is about 40MPa, and the contact resistance at the bonding interface is about 0.17mΩ. Both of them are better than those without Pt catalyst. The effects of the Pt catalyst on bonding were investigated and it is concluded that the surface oxide of Cu is reduced effectively by the hydrogen radical generated by formic acid decomposition with Pt catalyst and the Cu formats resulted by the formic acid treatment is decomposed to precipitate very fine Cu grains at the bonded interface.