Control of current density in an electroplating apparatus

A method of electroplating metal onto a semiconductor substrate, the method comprising:

• immersing the substrate in electrolyte in an electroplating chamber;
• monitoring a potential difference between the substrate and a reference electrode, wherein the reference electrode is between about 10×-225× as conductive as the electrolyte;
• and
• electroplating metal onto the substrate.

An apparatus for electroplating metal onto a substrate, the apparatus comprising:

• a chamber for holding electrolyte;
• a substrate holder for holding the substrate in the chamber;
• a reference electrode;
• and
• a controller having instructions for:
• immersing the substrate in the electrolyte at an angle such that a leading edge of the substrate contacts the electrolyte before a trailing edge of the substrate, the leading edge of the substrate first contacting the electrolyte at a substrate entry position,
• controlling a potential difference between the substrate and the reference electrode during immersion, and
• electroplating metal onto the substrate;
• wherein the reference electrode is positioned radially outside of the periphery of the substrate at a location that is angularly offset from the substrate entry position, the angular offset being between about 5-60°.