SPATIALLY AVERAGED (GLOBAL) MODEL OF TIME MODULATED HIGH-DENSITY CHLORINE PLASMAS

Properties of chlorine plasmas generated in a high-density, low pressu re (similar to 5 m Torr) plasma source using a pulsed-power modulation method are calculated by a spatially averaged (global) model. Both ti me resolved and time average plasma properties are discussed. The reco mbination coefficient for chlorine atoms at the wall plays an importan t role in determining the electronegativity of the plasma, since the d issociation fraction of the gas greatly affects the generation of nega tive ions. Even for such discharges, which have substantial electroneg ativity in the bulk plasma, it is only possible to extract negative io ns at the walls by using modulations having longer ''off'' times than a few tens of microseconds. This is the time scale required for the sh eath voltage, which confines negative ions within the bulk plasma, to collapse, due to thermalization and loss of electrons.