A method of removing a material from a surface includes providing a substrate comprising a material having a surface, contacting the surface with a polishing medium, applying a voltage to the substrate to remove material from the surface, and changing the voltage during the removing material from the surface. An electro-chemical mechanical polishing method includes providing a substrate having a surface, applying a platen to the surface, applying a first voltage to the substrate, rotating the platen and surface relative to each other at a first rotational speed, increasing to a second voltage, and decreasing to a second rotational speed.