Electrodeposition of Copper in the SPS-PEG-Cl Additive System I. Kinetic Measurements: Influence of SPS

1to 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 group~s! 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 20.1 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. In the last three years, a curvature-enhanced accelerator coverage ~CEAC! mechanism has been shown to quantitatively describe superconformal film growth which is responsible for ‘‘bottom-up superfilling’’ of submicrometer features in damascene processing. 1-3 The mechanism has also been shown to apply to silver electrodeposition 4 as well as copper chemical vapor deposition. 5 A key characteristic of superfilling electrolytes, disclosed to date, is the competition between inhibitors and accelerators for electrode surface sites. According to the CEAC model, a thiol or disulfide accelerator, or catalyst, displaces an inhibiting halide-cuprouspolyether species from the interface and remains segregated at the surface during metal deposition. 1-3,6,7 A key consequence of these two stipulations is the possibility that local area change associated with metal deposition on a nonplanar surface may give rise to changes in the local catalyst coverage, ~e.g., increases on concave sections and decreases on convex segments! and thereby superconformal film growth. This process is particularly important for surface profiles with dimensions in the submicrometer regime and naturally provides an explanation for the beneficial effects induced by certain additives known as ‘‘brighteners.’’ 1,6 In this first of a series of papers, a more complete assessment of the electrochemical response of planar electrodes in copper superfilling electrolytes is presented. A typical electrolyte contains a dilute, i.e., micromolar, concentration of accelerator in the presence of an inhibitor concentration that is usually an order of magnitude greater. This configuration gives rise to hysteretic voltammetric curves, rising chronoamperometric transients, and decreasing chronopotentiometric traces, all of which reflect the competitive adsorption dynamics occurring between the two species. An underdeveloped aspect of this system is a quantitative description of the mass balance of the additives during plating. Of specific interest is the partitioning of the catalyst between segregation to the free surface vs. deactivation by either incorporation into the growing deposit or desorption into the electrolyte. Examination of the metal deposition kinetics on catalyst-derivatized electrodes in a catalyst-free electrolyte is shown to be particularly helpful in quantifying the deactivation process. These experiments also provide an avenue for exploring the impact of various additive functional groups on the metal deposition kinetics. Experimental