Acceleration Kinetics of PEG, PPG, and a Triblock Copolymer by SPS during Copper Electroplating

Three copper-plating suppressors are examined in three-additive baths: a polyethylene glycol (PEG), a polypropylene glycol (PPG), and a triblock copolymer of the two. Bis(3-sulfopropyl)-disulfide (SPS) is found to transition each to a state of nonsuppression, i.e., accelerate each, at a rate dependent on the suppressor molecule, the SPS concentration, and, to a lesser extent, the suppressor concentration. Using a planar microscale working electrode (d=100 mu m), the kinetic currents of the plating reactions are observed without the influence of ohmic resistance, revealing far higher current densities than previously reported. Potentiostatic and galvanostatic experiments of additive adsorption at short times, t < 20 s, are compared quantitatively using a surface-blocking model to transform the data to effective surface coverage, theta(EFF), vs time. A major difference is found in SPS acceleration between galvanostatic and potentiostatic experiments, with the rate of change in suppression being proportional to the current density. This results in a constant rate of change in theta(EFF) under constant current but a self-reinforcing rate of change in theta(EFF) at constant potential. A simple additive model is introduced to characterize the results.