AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeM

Paper PS2-WeM1
Langmuir Probe Measurements of Change in Plasma Parameters with Change in Chamber Geometry in Electronegative Plasmas

Wednesday, November 17, 2004, 8:20 am, Room 213B

Session: Plasma Sources
Presenter: S.P. Sant, University of Texas at Dallas
Authors: S.P. Sant, University of Texas at Dallas
E.A. Joseph, University of Texas at Dallas
B.S. Zhou, University of Texas at Dallas
L.J. Overzet, University of Texas at Dallas
M.J. Goeckner, University of Texas at Dallas
Correspondent: Click to Email
The affect of chamber geometry on the characteristic behavior of two electronegative gases commonly used in the processing industry, namely CF@sub 4@ and O@sub 2@ were studied. The chamber used is the modified Gaseous Electronics Conference (mGEC) reference cell. The mGEC was designed to allow rapid changes to its geometrical structure and wall materials, allowing us to closely inspect various plasma-wall interactions. A Langmuir probe was used to obtain axial and radial measurements of ion density, electron density, plasma potential, electron temperature and floating potentials. These parameters were measured for a combination of two different source â?" chuck gaps (4 cm and 9.8 cm) and chamber diameters (20 cm and 64 cm). It is observed for both gases, that the electron temperature ranges from ~ 5 eV to ~ 1 eV as we move from the center towards the walls in the 64 cm diameter case with the narrow gap. For wider gap the peak temperatures are ~ 30% lower for O@sub 2@ case only, while they remain approximately the same for CF@sub 4@. In comparison, the plasma density drops by a factor of 2 in the center (1.5 E 11 to 0.8 E 11) with decrease in gap, but the center density remains fairly constant independent of chamber diameter. In general, it is observed that the experimental values vary with change in gap (coil to chuck distance), but remain fairly constant with change in chamber diameter. This work is supported by a grant from NSF/DOE, CTS â?" 0078669.