IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Tuesday Sessions
       Session PS1-TuM

Paper PS1-TuM8
Use and Limitations of In-situ FTIR Spectroscopy for Fluorocarbon Plasma Analysis

Tuesday, October 30, 2001, 10:40 am, Room 103

Session: Diagnostics II
Presenter: B.A. Cruden, Eloret Corp., NASA Ames Research Center
Authors: B.A. Cruden, Eloret Corp., NASA Ames Research Center
M.V.V.S. Rao, Eloret Corp., NASA Ames Research Center
S.P. Sharma, NASA Ames Research Center
M. Meyyappan, NASA Ames Research Center
Correspondent: Click to Email
Fourier Transform Infrared (FTIR) Absorption Spectroscopy has been used in an inductively coupled GEC Reference Cell for analysis of CF@sub 4@ plasmas. It was possible to detect undissociated CF@sub 4@ fraction and quartz window etch products (SiF@sub 4@, CO, COF@sub 2@) with this technique. From knowledge of the rotational/vibrational structure of the various bands, it is also possible to extract a gas rotational and vibrational temperature from this data. In interpretation of this data, many of the oft-ignored non-idealities of quanitative FTIR analysis are addressed. Of particular concern is the fact that Doppler-broadened absorption lines are significantly smaller than the instrument resolution. The resulting data represents a non-linear averaging of closely spaced absorbing lines. This produces cross-sections that do not obey Beer's law, i.e. are not constant. By examining the theory behind FTIR, these variations in cross-section are predicted for CF4. These theoretical errors are also manifested in inaccuracies in analyzing overlapping spectra. In FTIR, (as well as other absorption techniques) there is an additional averaging of absorption spectra over spatial coordinates. As a significant portion of the absorption signal will typically lie outside of the plasma, this averaging results in measurements that are not representative of the plasma species in terms of both number density and temperatures. When combined with the resolution limitations, it is predicted that a maximum measurable temperature exists that can differ significantly from the true plasma temperature. The results of a more carefully controlled absorption pathlength will also be presented.