AVS 47th International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS1-MoA

Paper PS1-MoA4
Ion-Ion Plasma Formation and Negative Ion Extraction

Monday, October 2, 2000, 3:00 pm, Room 310

Session: Emerging Plasma Applications
Presenter: S.K. Kanakasabapathy, University of Texas, Dallas
Authors: S.K. Kanakasabapathy, University of Texas, Dallas
M.H. Khater, University of Texas, Dallas
L.J. Overzet, University of Texas, Dallas
Correspondent: Click to Email
Ion-ion plasmas are relatively electron-free, positive and negative ion only plasmas formed in the afterglow of Pulsed-power high electron affinity gas@footnote 1@ (Eg: Cl@sub 2@) discharges. They hold the potential to provide ambipolar fluxes of positive and negative ions that could reduce differential charging of high anisotropy structures which cause@footnote 2@ etch non-idealities. Time-resolved Langmuir probe and Microwave Interferometry measurements in a pulsed ICP discharge show that electrons are quickly lost (~ 10's of µmsecs) to dissociative attachment after turning power off. Time-resolved mass spectrometry has correlated the vanishing of electrons and consequently the confining plasma potential to the incipience of a negative ion (Cl@super -@) surface flux. Parametric characterization of Pulsed Cl@sub 2@ discharges has indicated that low pressures (1 mTorr), high powers (300 W peak), mid duty ratios (50%) and low pulse frequency (500 Hz) maximize this negative ion flux. Langmuir probe ion density decay rate measurements have shown ion-ion recombination to be the dominant loss process. We observe reproducible alternating irradiations of positive (Cl@sub 2@@super +@) and negative (Cl@super -@) ions corresponding to the negative and positive half-cycles respectively when a low frequency (20 kHz) bias applied to the mass spectrometer pinhole. This bias is applied as a phase-locked burst that is synchronized with the formation of ion-ion plasmas. Parametric characterization of this novel extraction technique reveals a bi-modal frequency response of the Cl@super -@ surface flux. This presentation is based upon work supported by the NSF under Grant No. CTS-9713262. @FootnoteText@ @footnote 1@D. Smith, A.G. Dean and N.G. Adams, J. Appl. Phys. 7, 1944-1962(1974) @footnote 2@G.S. Hwang and K.P. Giapis, J. Appl. Phys. 81(8) 3433-3439(1997).