AVS 45th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS1-MoA

Paper PS1-MoA1
Scaling of PFC Abatement Using Plasma Burn-Boxes@footnote 1@

Monday, November 2, 1998, 2:00 pm, Room 314/315

Session: Environmental Issues and Emerging Technologies
Presenter: X. Xu, University of Illinois, Urbana-Champaign
Authors: X. Xu, University of Illinois, Urbana-Champaign
M.J. Kushner, University of Illinois, Urbana-Champaign
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Perfluorinated compounds (PFCs), gases which have large global warming potentials, are widely used in plasma processing for etching and chamber cleaning. Due to underutilization of the feedstock gases or by-product generation, the effluent from plasma tools typically have large mole fractions of PFCs. The use of plasma "burn-boxes" located downstream of the plasma chamber is being considered as a remediation method for abating PFCs emissions. In the burn-box, typically located between the turbo- and roughing pumps, O@sub 2@ is injected into a high density plasma with the goal of converting PFCs into products such as CO, CO@sub 2@, and COF@sub 2@. Results from the 2-dimensional Hybrid Plasma Equipment Model (HPEM) have been used to investigate the scaling of plasma abatement of PFCs using burn-boxes with ICP reactors. The HPEM is used to model the etching chamber of the ICP reactor to determine the utilization of the feedstock gases and generation of by-products. The effluent from the etching chamber is then passed through the burn-box using O@sub 2@ injection and excited by a second inductively coupled source. Results will be discussed for Ar/CF@sub 4@/C@sub 2@F@sub 6@/O@sub 2@ mixtures. We found that reassociation of PFCs after dissociation in the burnbox, particularly problemmatic for CF@sub 4@, is an important by-product generation mechanism which can be controlled to some extent by controlling the gas temperature. The abatement of C@sub 2@F@sub 6@ is approximately 4 times more efficient that CF@sub 4@ due to both the cited reassociation and and larger dissociation cross sections for C@sub 2@F@sub 6@. Full oxidation of the PFCs is possible, though large mole fractions of O@sub 2@, typically on order of 50%, are required. The radius of the burn-box, skin depth of the inductively coupled field and residence time of gases in the burnbox must be optimally selected in order to minimize "pass-through" of the effluent which reduces the abatement efficiency. @FootnoteText@ @footnote 1@Work supported by NSF and SRC.