Capacitive radio frequency discharge plasma containing negative ions

The parallel-plate RF discharge in oxygen has been investigated in the pressure between 10(-3) and 1 Torr. The discharge mechanism is considered by comparing the electron energy distribution f(E) in O-2 and N-2 discharges, In O-2, the low energy part of f(E) becomes deficient; a broad peak of thermal electrons appears to be shifted into the medium energy range; and the population of a higher energy group of electrons coming from the cathode sheath is less than that of N-2 discharge. These are related to the negative ion formation in O-2. Negative ions in the discharge in O-2 are measured not only by the probe but also by using the laser photodetachment technique. The result of measurements have revealed that optimum RF power and pressure to make the negative ion density maximum exist while positive ions increases with the RF power.