Patent ID: 8147660

Claim:
An apparatus for performing electroplating on a wafer substrate surface having a layer of conductive material, the apparatus comprising: a substrate holder said substrate holder being operable to hold the wafer substrate; an electrical substrate connector said electrical substrate connector being operable to make an electrical contact with the layer of conductive material at the periphery of the wafer substrate and to electrically connect the periphery of the wafer substrate to a terminal lead of a power supply, wherein the apparatus is configured for negatively electrically biasing the wafer substrate surface during use; an electric current buss, said electric current buss being part of a counter electrode assembly, and said electric current buss having a working surface and being operable to connect electrically to a terminal lead of a power supply; a partially resistive counter electrode, said partially resistive counter electrode being part of said counter electrode assembly, and said partially resistive counter electrode disposed on and covering said working surface of said electric current buss, wherein the resistance of the partially resistive counter electrode is such that during the apparatus use, the voltage drop across the partially resistive counter electrode is greater than the voltage drop from the electrical contact at the wafer substrate periphery to the center of the wafer substrate, and wherein the partially resistive counter electrode is non-porous to liquids and electrolytes; and wherein said counter electrode assembly and said substrate holder are operable to form a thin fluid gap between said partially resistive counter electrode and a wafer substrate surface during use, wherein the width of the gap is in a range of about from 1 mm to 30 mm.