This disclosure relates to a plasma processing system for controlling plasma density near the edge or perimeter of a substrate that is being processed. The plasma processing system may include a plasma chamber that can receive and process the substrate using plasma for etching the substrate, doping the substrate, or depositing a film on the substrate. This disclosure relates to a plasma processing system that may include a power electrode that may be opposite a bias electrode and a focus ring electrode that surrounds the substrate. In one embodiment, the power electrode may be coupled to a direct current (DC) source. Power applied to the bias electrode may be used to draw ions to the substrate. The plasma density may be made more uniform by applying a focus ring voltage to the focus ring that is disposed around the substrate and/or the bias electrode.