A Combined Process of Formic Acid Pretreatment for Low-Temperature Bonding of Copper Electrodes

Abstract

A new combined process of formic acid pretreatment for low temperature Cu direct bonding was proposed. Cu film and Cu micro-electrodes samples were treated by formic acid and successfully bonded together at 200°C. Cu surface oxide was reduced at 200°C using formic acid treatment without/with Pt catalyst. Particularly, the treatment with heated Pt catalyst is more effective for Cu surface reduction than that without Pt catalyst or with room temperature Pt catalyst. After formic acid treatment under various conditions, Cu film and Cu micro-electrodes samples were bonded together at 200°C in N2. Among them, the bonded samples treated by formic acid using heated Pt catalyst showed the strongest bonding strength. Very few oxide and carbon was remained at the bonding interface. It also proves that the treatment can reduce surface oxide resulting in strong bonding at low temperature.