PEG, PPG, and their triblock copolymers as suppressors in copper electroplating

As studies of suppression during copper electrodeposition have typically involved polyethylene glycol (PEG), a deposition study was undertaken varying the chemistry of the suppressor molecule. Other polyether additives were compared to PEG in plating solutions of varying acidity, such as polypropylene glycol (PPG) and triblock copolymers of PEG and PPG, those with ethylene oxide terminal blocks termed EPE, and propylene oxide terminals termed PEP. The extent of suppression observed on a rotating disk electrode varied over similar to 50 mV, with PEG suppressing the least and PPG the most. When both homopolymers were present, results were very near those of PEG alone. Also, a variation in Tafel slope was observed, with PPG exhibiting a more activated reaction. These results were interpreted by a significant difference in surface coverage between PEG and PPG (1.4 vs 0.25% surface availability). Using a microfluidic electrochemical cell, differences were observed in suppressor adsorption and desorption on copper under galvanostatic plating conditions. Copolymers desorbed with characteristics of both PEG and PPG. Planar copper films plated in the presence of each of the suppressors showed significant differences in surface luster and roughness, with the copolymer EPE resulting in extremely bright and smooth deposits. (C) 2008 The Electrochemical Society.