EFFICIENT PRODUCTION OF O- IONS IN A HELICON WAVE OXYGEN DISCHARGE( AND O)

High density oxygen plasmas (n(e)=10(10)-10(13) cm(-3)) are produced b y a helicon wave discharge source with rf powers of 0.1-3 kW. Positive and negative ion species in the plasmas are measured by a time-of-fli ght mass spectrometer. The intensity ratio of O+ to O-2(+) increases w ith the electron density ne and is almost proportional to it in the re gion of n(e)=10(10)-10(12) cm(-3). When the electron density increases up to 8X10(12) cm(-3), the ratio becomes about 4. In a high density p lasma of 1.3X10(13) cm(-3) obtained by mixing Ar gas, about 83% of the positive oxygen ions becomes O+, By using pulse modulation of the rf power, O- ions are mainly observed with remarkable increase in the aft erglow. The maximum density of O- is about 3X10(11) cm(-3) at 30 mu s after turning off the rf power of 0.85 kW and the decay time of O- is about 60 mu s. (C) 1996 American Institute of Physics.