AVS 46th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuA

Paper PS-TuA10
UV Absorption Spectroscopy of Pulsed Fluorocarbon Plasmas

Tuesday, October 26, 1999, 5:00 pm, Room 609

Session: Plasma Diagnostics II
Presenter: B.A. Cruden, Massachusetts Institute of Technology
Authors: B.A. Cruden, Massachusetts Institute of Technology
K.K. Gleason, Massachusetts Institute of Technology
H.H. Sawin, Massachusetts Institute of Technology
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Thin polytetrafluoroethylene(PTFE)-like films have been deposited in a pulsed capacitively coupled plasma from a variety of fluorocarbon precursors. It has been shown that pulsing of the plasma allows for composition control, giving reduced amounts of cross-linking and branching, and a higher CF@sub 2@ content. While some precursors, such as hexafluoropropylene oxide (HFPO), appear to deposit primarily in the off-time and is believed to be dominated by long-lived difluorocarbene species, other precursors, such as tetrafluoroethylene (TFE) show a linear dependence of deposition on duty cycle, suggesting deposition occurs primarily in the on-time period. To help elucidate the nature of the deposition processes and the differences between these precursors, UV absorption has been used to measure CF@sub 2@ concentrations quantitatively. In the plasmas examined here partial pressures of CF@sub 2@ are observed in the range of 5-15 mtorr for a 1 torr total pressure. Transients in concentration have been modelled by a elementary mole balance and effective reaction constants have been obtained. Optical emission spectroscopy and actinometry are also used to study the role of other species including O, F, CF and CF@sub 3@. XPS is used to study how the composition of the films varies with precursor and pulsing conditions, and can be related to the gas phase concentrations as measured by UV Absorption. Additionally, a quartz-crystal microbalance (QCM) has been used to measure deposition rates during the plasma on and off times.