vacuum seal between the housing 78 and the substrate to be processed not shown the embodiment of fig8 has a primary advantage in being simple to manufacture referring now to fig9 a schematic illustration of a third embodiment is shown designated generally as 93 in which a housing 94 is of unitary construction including vacuum flange the preferred material for the housing is metal a non conductive insulation material 96 such as fiberglass is bonded to the housing 94 material 96 is coated with a metal film 98 which serves as an electrode a silicon based coating is provided on the surface of coating 98 to provide protection of the electrode from the plasma a 34 hot 34 electrical connector 100 is in electrical contact with the electrode 98 a ground electrical connector 102 is connected to the housing 94 the embodiment illustrated in fig9 like the fig8 embodiment is a relatively inexpensive system however it is perhaps more rugged than the fig8 embodiment because of the added strength of the metal housing 94 fig1 is a schematic illustration of an embodiment which involves field use of film electrodes for arbitrary shaped surfaces this embodiment being designated generally as 104 a non conductive frame or housing 106 provides rigid mechanical support for metalized film electrode 108 a vacuum flange 110 is provided and sealed with a zinc oxide seal 112 zinc oxide seals 114 seal the apparatus 104.