Enhanced Reactivity of Electroless Cu Interconnection by Surface Oxidation Pretreatment

The microfluidic electroless interconnection (MELI) process has gained attention as a low temperature, pressureless method for achieving Cu-to-Cu direct bonding. However, challenges have been observed with non-uniform plating at finer pitch interconnection, which is thought to be caused by incompatible bath loading leading to lower activity of the electroless plating in certain areas. In this study, a surface oxidation pretreatment process was introduced to the MELI process in order to increase the catalytic activity of the Cu pillar surface. The results demonstrated that the surface oxidation pretreatment was effective in eliminating skip plating at the corners of the Cu pillar array and achieving uniform plating across the entire array. This is believed to be due to the improved wettability of the Cu pillar surface following the pretreatment, which enhances the mass transfer of the plating solution and reduce the impact of bath loading incompatibilities.