Spatially Averaged (Global) Model of Time Modulated High Density Chlorine Plasmas

Properties of chlorine plasmas generated in a high-density, low pressure ( ∼5 mTorr) plasma source using a pulsed-power modulation method are calculated by a spatially averaged (global) model. Both time resolved and time average plasma properties are discussed. The recombination coefficient for chlorine atoms at the wall plays an important role in determining the electronegativity of the plasma, since the dissociation fraction of the gas greatly affects the generation of negative ions. Even for such discharges, which have substantial electronegativity in the bulk plasma, it is only possible to extract negative ions at the walls by using modulations having longer “off” times than a few tens of microseconds. This is the time scale required for the sheath voltage, which confines negative ions within the bulk plasma, to collapse, due to thermalization and loss of electrons.