Abstract: A tri-polar electrostatic chuck has both positive and negative electrodes housed on a non-polarized base housing. A non-polarized guard ring surrounds the outer periphery of the chuck and enclosing the electrodes. A wafer is placed atop the chuck with its back-side cooled by a cooling gas that is piped up through the chuck. The edge of the wafer is made to reside over the guard ring, instead of over one of the polarized electrodes. The proximity of the non-polarized guard ring to the wafer edge helps to reduce the amount of plasma leakage around the edge of the wafer, resulting in less breakdown of the dielectric coating of the chuck. The positioning of the electrodes also provides for a uniform impedance across the processing surface of the wafer.