Electrochemical mechanical planarization (ECMP) is being actively explored for removal and planarization of copper films. Development of a full sequence ECMP process would require the removal of the barrier layer as well. Chemical systems that exhibit a 1:1 selectivity between the barrier layer and copper would be ideal for the barrier removal step of ECMP. A fundamental study was undertaken to evaluate the usefulness of a sulfonic acid based chemical system for the removal of tantalum under ECMP conditions. Copper and tantalum samples were polished at low pressures (∼0.5 psi) under galvanostatic conditions in sulfonic acid based solutions maintained at different pH values. At a current density of 0.25 mA/cm 2 and pH of 10, tantalum removal rate of ∼100 Å/min with a 1:1 selectivity to copper has been obtained in 0.3M sulfonic acid solutions. The presence of a small amount (∼ 0.1%) of colloidal silica particles is required to obtain good removal rates.