Analysis of current-potential hysteresis during electrodeposition of copper with additives

Two models are described for cyclic voltammetry during electrodeposition of copper from an acid sulfate bath containing the additives polyethylene glycol (PEG), chloride ions, and mercapto-1-propanesulfonate (MPSA). The same bath may be used for superfilling of cavities during fabrication of copper on-chip metallization. Experimental current-potential scans show a characteristic hysteresis in solutions with all three additives, which demonstrates the presence of both activated and inhibited kinetics. Both models assume that deposition is inhibited by a PEG-chloride adsorbed surface complex, as established previously. One model further hypothesizes that PEG is incorporated into grain boundaries in the copper at the same fractional coverage found on the external surface. The second model neglects PEG incorporation, but assumes that adsorbing MPSA directly displaces PEG from the surface. Both models predict hysteresis quantitatively similar to experiments, without the use of fitting parameters. The competitive adsorption model is favored because, unlike the PEG incorporation model, it yields realistic predictions of carbon and sulfur concentrations in the deposit. (C) 2001 The Electrochemical Society.