UNIFORM RF DISCHARGE PLASMAS PRODUCED BY A SQUARE HOLLOW-CATHODE WITHTAPERED SHAPE

A square hollow cathode with a tapered shape (square HCT) is developed in order to produce highly uniform and dense plasmas (density similar to 6 x 10(10) cm(-3)) with a wide range of operating pressures. It is shown experimentally that the plasma density produced by the HCT is h igher than that produced by a plane cathode from 0.02 Torr to 0.2 Torr . It is demonstrated experimentally that uniform plasmas can be produc ed by modifying the structure of the HCT for different operating press ures. It is shown that an additional outer hollow cathode is useful to compensate the nonuniformity of plasmas due to edge effects. With the use of the outer hollow cathode for the modified HCT, highly uniform plasmas are produced within almost the entire surface of the grounded square electrode.