Effect of potassium ions on tantalum chemical mechanical polishing in H₂O₂-based alkaline slurries

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 R_a 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 I_corr 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.