Uniform RF Discharge Plasmas Produced by a Square Hollow Cathode with Tapered Shape

A square hollow cathode with a tapered shape (square HCT) is developed in order to produce highly uniform and dense plasmas (density ∼ 6×1010 cm-3) with a wide range of operating pressures. It is shown experimentally that the plasma density produced by the HCT is higher than that produced by a plane cathode from 0.02 Torr to 0.2 Torr. It is demonstrated experimentally that uniform plasmas can be produced by modifying the structure of the HCT for different operating pressures. 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.