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A model of superconformal electrodeposition is presented based on a local growth velocity that is proportional to coverage of a catalytic species at the metal/electrolyte interface. The catalyst accumulates at the interface through reaction with the electrolyte. More importantly, if the concentration of the catalyst precursor in the electrolyte is dilute, then surface coverage within small features can change far more rapidly due to changing interface area. In such a case, the catalyst effectively floats on the interface during deposition, with changes in coverage coupled to alterations in arc-length of the moving surface. The local coverage therefore increases during conformal growth on a concave surface, resulting in a corresponding increase in the local deposition rate. The opposite is true for a convex surface. The model is supported by experiments and simulations of superconformal copper deposition in 350-100 nm wide features. The model also has significant implications for understanding the influence of adsorbates on the evolution of surface roughness during electrodeposition.

The kinetics of copper electrodeposition from an acidified cupric sulfate electrolyte containing SPS-PEG-Cl were examined. Voltammetric and chronoamperometric experiments reveal a competition between poly͑ethylene glycol͒ ͑PEG͒ and Na 2 ͓SO 3 (CH 2 ) 3 S͔ 2 ͑SPS͒ for surface sites. PEG interacts synergistically with Cl Ϫ and Cu ϩ to form a passivating film that inhibits the metal deposition rate by two orders of magnitude. Subsequent adsorption of short chain disulfide or thiol molecules with a sulfonate-end group͑s͒ leads to the disruption and/or displacement of the passivating surface complex and acceleration of the metal deposition rate. The effect of submonolayer quantities of catalytic SPS is sustained even after extensive metal deposition, indicating that the catalyst largely remains segregated on the growth surface. Multicycle voltammetry reveals a significant potential dependence for SPS adsorption as well as its subsequent deactivation. Catalyst deactivation, or consumption, was examined by monitoring the quenching of the metal deposition rate occurring on SPS-derivatized electrodes in a SPS-free electrolyte. Catalyst consumption is a higher order process in terms of its coverage dependence and a maximum deactivation rate is observed near an overpotential of Ϫ0.1 V. Derivatization experiments are shown to be particularly effective in revealing the influence of molecular functionality in additive electroplating. Specifically, the charged sulfonate end group is shown to be central to effective catalysis.

No abstract

Superconformal electrodeposition is explained based on a local growth velocity that increases with coverage of a catalytic species adsorbed on the copper-electrolyte interface. For dilute concentration of the catalyst precursor in the electrolyte, local coverage in fine features changes more due to interface area change than by accumulation from the electrolyte, yielding superconformal growth. The model is supported by experiments and simulations of copper deposition in 350-100 nm wide features, helping to explain the influence of adsorbates on roughness evolution.