A plasma processing chamber, which includes an upper electrode assembly, a lower electrode assembly, and a plasma confinement assembly. The upper electrode assembly includes an upper electrode, a backing member, the backing member attachable to an upper surface of the upper electrode, and a guard ring surrounding an outer surface of the backing member and located above the upper surface of the upper electrode, wherein the guard ring is configured to provide an inner gap between the outer surface of the backing member and an inner periphery of the guard ring. The lower electrode assembly is adapted to receive a semiconductor substrate. The plasma confinement assembly is separated from an outer periphery of the upper electrode and the backing member by the guard ring.