An apparatus for processing a substrate with a plasma. The apparatus includes first and second electrodes positioned with a spaced apart relationship. A separating ring has a vacuum-tight engagement with confronting surfaces of the first electrode and the second electrode to define an evacuatable processing region therebetween. Communicating with the processing region is a process gas port for introducing a process gas to the processing region. The processing region may be evacuated through a vacuum port defined in one of the first and second electrodes to a pressure suitable for exciting a plasma from the process gas in the processing region when the first and second electrodes are powered.