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Tantalum has been used as the barrier material for copper interconnects for decades. This paper mainly investigated the effect of potassium ions on tantalum chemical mechanical polishing in H2O2-based alkaline slurries. The results reveal that, with the increase in the H2O2 concentration, the tantalum material removal rate (MRR) gradually increases via forming a structurally weak oxide film mainly composed of Ta2O5 and small amount of soluble tantalum species. On the basis of H2O2, with the increase in the concentration of potassium ions, the tantalum MRR first linearly increases and then becomes saturated, while Ra keeps almost unchanged. Additionally, the change of the tantalum MRR is independent of the anions of the potassium salts. The enhancement of the tantalum MRR is due to the slight increase in Icorr and the anodic current density possibly, and more significantly, the remarkable increase in the interactions between silica particles and the tantalum surface caused by the decrease in the absolute value of the zeta potentials and the thickness of the electrical double layers of both silica particles and the tantalum surface. Moreover, a tunable MRR selectivity of Ta vs. Cu can be obtained by adjusting H2O2, potassium ions and the copper chelating agent/inhibitor.