Effects of forming gas plasma treatment on low-temperature Cu-Cu direct bonding

Low-temperature Cu-Cu direct bonding becomes of great importance as Cu is widely used as an interconnection material in the packaging industry. Preparing a clean surface is a key to successful Cu-Cu direct bonding. We investigated the effects of forming gas plasma treatment on the reduction of Cu oxide and Cu-Cu bonding temperature. As plasma input power and treatment time increased, Cu oxide could be effectively reduced, and this could be attributed to the enhanced chemical reaction between forming gas plasma and Cu oxide. When the bonding temperature was reduced from 415 to 300 °C, the bonding strength of the plasma-treated interface was increased from 1.8 to 5.55 J/m² while that of the wet-treated interface was decreased.