Roles of Chloride Ion in Microvia Filling by Copper Electrodeposition

The interactions among additives employed in acidic copper plating solution for microvia filling are characterized by galvanostatic measurement (GM) and electron paramagnetic resonance (EPR), respectively. These additives include polyethylene glycol (PEG), chloride ion, 3-mercapto-1-propanesulfonate (MPS), and bis-(3-sulfopropyl) disulfide (SPS). EPR patterns show that MPS can reduce to before electrochemical reduction. However, the GMs show that MPS is an inhibiting reagent for copper electrodeposition. An inhibition mechanism of the MPS is proposed according to the EPR patterns. GMs also revealed that the combination of MPS and could result in a strongly catalytic effect on the reduction rate. This synergistic effect between MPS and on enhancing copper electrodeposition is attributed to an inner sphere electron transfer net constructed by a competitive coordination of MPS and on complexes. SPS also exhibits similar electrochemical behavior to MPS. However, the response speed of SPS in enhancing the reduction rate is slower than that of MPS. GM results obtained by adopting two different rotating speeds of the working electrode demonstrate that PEG competes with MPS to grab through and that the competitive adsorption between PEG- and on the cathodic surface is strongly convection-dependent.