Stability of iodine on ruthenium during

Cyclic voltammetry, current–time–transient measurements, and X-ray photoelectron spectroscopy (XPS) have been used to study the nucleation behavior of electrochemically deposited Cu films on Ru substrates as a function of Ru pre-treatment. Pre-treatment consisted of cathodic polarization in either 1 M H2SO4 or in 1 M H2SO4 + 1 mM CuSO4, followed by sample emersion and placement in a 1 M H2SO4 + 500 mM CuSO4 plating bath. XPS measurements confirmed the presence of adsorbed I on the Ru surface following pretreatment in the K1/H2SO4 solution. Cyclic voltamogram (CV) data for electrodes either as-received or pre-reduced in H2SO4 and then immersed in the plating solution exhibited a broad peak in the overpotential region consistent with oxide reduction followed by Cu deposition. No underpotential deposition (UPD) feature was observed for these electrodes. In contrast, the sample pre-reduced in I-containing electrodeposition exhibited a narrow CV peak in the overpotential region and a UPD feature centered at 80 mV vs. Ag/AgCl. Current-time-transient (CTT) measurements of Cu deposition on as-received electrodes or electrodes pre-reduced in I-free solution exhibited potential-independent kinetics that are consistent with long timescales diffusion control. XPS results also indicate that the iodine adlayer on Ru reduced during the electrodeposition electrolyte is stable upon polarization at least −200 mV vs. Ag/AgCl. These data indicate that a protective adlayer may be deposited on an air-exposed Ru substrate as the oxide is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electropolishing process. Therefore, electrochemical pre-treatment in I-containing electrolyte may be of practical utility under industrial conditions for Cu electroplating.