This paper documents an experimental study to compare the behavior of bis-͑3-sodiumsulfopropyl͒ disulfide ͑SPS͒-Clpolyethylene glycol ͑PEG͒ and 3-mercaptopropanesulfonic acid sodium salt ͑MPSA͒-Cl-PEG additive systems during copper electrodeposition. These systems are analogous to those used industrially to plate copper lines onto integrated circuits. Galvanostatic experiments show that in the absence of chloride ion, either SPS or MPSA added to the plating solution inhibited copper deposition. Upon the addition of Cl − , a rapid transition from inhibition to acceleration was observed for both additives, illustrating the critical role played by the chloride ion in these systems. Potentiostatic experiments performed for the Cl-PEG-SPS and Cl-PEG-MPSA additive systems show that the potential dependency of the Cl-PEG-SPS system was much stronger than that of the MPSA-Cl-PEG system. Differences between the SPS and MPSA additive systems suggest that acceleration may occur through an MPSA pathway. Finally, results with chemical compounds similar to MPSA indicate that the thiol group is associated with inhibition and that a synergistic accelerating relationship exists between the sulfonate group and chloride, presumably due to complex formation.

We present a simple classical method for treating charge mobility in metals adjacent to liquid solutions. The method, known as electrode charge dynamics, effectively bridges the computational gap between ab initio calculations on small metal clusters and large-scale simulations of metal surfaces with arbitrary geometry. We have obtained model parameters for a copper (111) metal surface using high-level quantum-mechanical calculations on a 10-atom copper cluster. We validated the model against the classical image-charge result and ab initio results on an 18-atom copper cluster. The model is used in molecular dynamics simulations to predict the structure of the fluid interface for neat water and for aqueous NaCl solution. We find that water is organized into a two-dimensional ice-like layer on the surface and that both Na + and Cl − are strongly bound to the copper. When charging the metal electrode, most of the electrolyte response occurs in the diffuse part of the double layer.

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Molecular dynamics simulations have been carried out for aqueous electrolyte solutions between model electrode surfaces. The effect of solvent model flexibility on bulk and double layer properties was observed for electrode surface charge densities of 0, Ϯ0.1, and Ϯ0.2 C/m 2 and ion concentrations of 0, 0.5, and 1 M. Two flexible models were used to isolate the effects of flexibility from the effects of a change in the condensed-phase dipole moment. Model flexibility increases the pure water self-diffusion coefficient while a larger liquid dipole moment substantially decreases it. There is an increase in ion contact adsorption and counter ion affinity with the flexible models, suggesting that the ions are less tightly solvated. This conclusion is consistent with observed enhancements of solvated ion densities near uncharged electrodes for the flexible water case. Mobile ions in high concentration quickly damp out the electric field even at high electrode charge densities, but for dilute ion concentrations the field may extend to the center of the cell or beyond. In these cases it is more appropriate to integrate Poisson's equation from the electrode surface outward instead of the common method of assuming zero field at the center of the simulation cell. Using this methodology, we determine the voltage drop across the half-cell for both the rigid and flexible models. The half-cell voltage drop shows some dependence on ion concentration, but solvent flexibility has little effect on that behavior.

In superconformal filling of copper-chip interconnects, organic additives are used to fill high-aspect-ratio trenches or vias from the bottom up. In this study we report on the development of intermolecular potentials and use molecular dynamics simulations to provide insight into the molecular function of an organic additive (3-mercaptopropanesulfonic acid or MPSA) important in superconformal electrodeposition. We also investigate how the presence of sodium chloride affects the surface adsorption and surface action of MPSA as well as the charge distribution in the system. We find that NaCl addition decreases the adsorption strength of MPSA at a simulated copper surface and attenuates the copper-ion association with MPSA. The model also was used to simulate induced-charge effects and adsorption on a nonplanar electrode surface.