Electropolishing and electroless plating of copper and tin to replace CMP and lithographic processes in Cu/Sn bump fabrication

A serial electrochemical process consist of copper via filling, electropolishing, electroless copper plating and electroless tin plating is presented for the TSV 3D SiP application. Defect-free copper via filling was achieved by controlling current modes and additives. After via filling, electropolishing was performed to planarize over-plated copper. Electropolishing within the potential of mass-transfer region and with the assistance of additives, fine polished surface without thickness disparity was achieved. For bump formation process, electroless copper and tin plating which is a self-aligned process was applied. Consequently, Cu/Sn bump on via patterned wafer was obtain without using the conventional CMP and lithographic processes.