Electrolytic etching of metal layers

A method for selectively removing a layer of electrolytically dissoluble metal such as copper overplate from a substrate such as a low-k dielectric comprising

• providing a substrate bearing on a major surface thereof a layer of electrolytically dissoluble metal, the metal layer serving as a dissoluble electrode and having a central region and an adjacent peripheral region;
• providing at least a first counterelectrode and a second counterelectrode;
• positioning the counterelectrodes opposite the metal layer and spaced from the metal layer and spaced from each other;
• in a first electrolytic step, passing an electric current between the first counterelectrode and the central region of the metal layer, wherein the first counterelectrode is cathodic with respect to the metal layer, and the first electrolytic step includes a first phase, a second phase, and a third phase and during the first phase the electric current is a low amperage current, during the second phase the electric current includes a train of anodic pulses having a short on time and a higher amperage than during the first phase, and during the third phase the current includes a train of higher amperage DC current or anodic pulses having a longer on time than the second phase, wherein during said first phase of the first electrolytic step removal of metal is confined to an area approximately the size of the counterelectrode and a depth that is less than the thickness of the metal layer, and during the second phase of the first electrolytic step the removal of the metal continues in a conformal manner to a predetermined depth, and during the third phase of the first electrolytic step the area of removal of metal is extended beyond the periphery of the area removed during said first phase and second phase of the first electrolytic step;
• and
• in a second electrolytic step, passing an electric current between the second counterelectrode and the peripheral region of the metal layer, wherein the second counterelectrode is maintained cathodic to the metal layer, and the second electrolytic step includes a first phase, a second phase, and a third phase and during the first phase the current is a low amperage current, during the second phase the current includes a train of anodic pulses having a short on time and a higher amperage than during the first phase, and during the third phase the electric current includes a train of the higher amperage DC current or anodic pulses having a longer on time than the second phase.