Electroless plating of copper at a low pH level

A new process for electroless copper plating at a pH level of ≤9 is described. The process uses amine borane reducing agents and ligands based on neutral tetradentate nitrogen donors. The use of a variety of buffer systems is demonstrated. Electroless bath performance over a wide range of conditions is presented. The quality of the plated copper is comparable to that obtained by currently used electroless plating processes, and has a resistivity of about 1.8–2 µΩ-cm, depending on bath composition and process parameters. Use of the process is illustrated for forming conductors and filling via holes having submicron minimum dimensions.