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The use of water-in-salt electrolytes is evaluated for the electrodeposition of metallic ruthenium. The mechanisms of proton reduction inhibition by concentrated LiCl and dilute tetrabutylammonium is evaluated. Concentrated LiCl is found to disrupt the hydrogen bonding network within the solution bulk, whereas TBA is found to adsorb onto the electrode surface, blocking proton access. Ruthenium exists as a different complexed species in water-in-salt electrolytes vs dilute aqueous electrolytes, leading to a −300 mV shift in the deposition onset potential. Greater current efficiencies of Ru deposition can be obtained when depositing at proton overpotentials by the use of water-in-salt electrolytes, and TBA can offer further improvements. The grain structure and resistivities of Ru thin films are studied.

The nucleation and growth of cobalt (Co) on blanket Si with extremely thin Co seed was studied in the presence of furil dioxime (FD). Cyclic voltammetry (CV), chronoamperometry, and galvanostatic nucleation studies were conducted to understand the effects of FD on Co nucleation process. A potential dependent suppression effect was observed at low potential with a breakdown of the suppression at high potential, resulting in a hysteresis in CV. The potentiostatic current transient experiments showed that side reactions and adsorption process both greatly affected Co nucleation. A well-established model, which deconvolutes the individual contributions to the total current transient, was applied to fit the experimental curves. Progressive and instantaneous Co nucleation were observed across different FD concentrations and applied potentials. Galvanostatic studies further proved the suppression effect of FD and the effects on film morphology were studied at different conditions.