AVS 47th International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP23
Ion-Iion Plasma Formation in Chlorine in an Inductively Coupled Plasma Etch Reactor

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: L.J. Overzet, University of Texas at Dallas
Authors: M.H. Khater, University of Texas at Dallas
S.K. Kanakasabapathy, University of Texas at Dallas
L.J. Overzet, University of Texas at Dallas
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We will show time-resolved characteristics of pulsed chlorine plasmas in an industrial, inductively coupled plasma etch reactor. Using pulsed-plasmas may enhance processing and reduce charge-up damage of sub-micron features. Electron free or "ion-ion" plasma forms during the afterglow of highly electronegative discharges (e.g. Cl@sub 2@) due to electron attachment. The electron loss can be characterized by a "transition time" after which ion-ion plasma exists within the reactor. Such electron free plasma can provide both positive and negative ion fluxes to a substrate potentially reducing charge-up damage as well as enabling negative ion assisted processing. The transition time to ion-ion plasma (8-25 µsec) is mostly dependent on pressure and power while varying only slightly with pulse frequency and duty ratio. Larger Cl@sub 2@ concentrations at high pressure and/or lower power discharges result in smaller transition times due to dissociative attachment. Measurements of the plasma parameters time evolution were obtained at 1 cm above the substrate for 500 W peak power, 1 kHz pulse frequency and 50% duty ratio. The ion densities generally decreased as expected during the afterglow, except they increased slightly near the end of the afterglow at higher pressures. This suggests a transport of ions from the source towards the substrate. Spatio-temporal measurements showed electron and ion density profiles that peaked at the center during the active glow with similar uniformities to those obtained in CW operation. The ion density uniformity improved gradually during the beginning of the afterglow (~ factor of 2) but degraded back to active glow values near the end of the afterglow. This is likely related to the ion loss mechanisms. Ion-ion recombination should tend to flatten the ion density profile in the early afterglow whereas ion loss due to diffusion should tend to cause a peak in the center and dominate at the end of the afterglow.