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The Importance of Optical Pathlength Control for Plasma Absorption Measurements
- Publication Year :
- 2001
- Publisher :
- United States: NASA Center for Aerospace Information (CASI), 2001.
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Abstract
- An inductively coupled GEC Cell with modified viewing ports has been used to measure in-situ absorption in CF4 plasmas via Fourier Transform Infrared Spectroscopy, and the results compared to those obtained in a standard viewport configuration. The viewing ports were modified so that the window boundary is inside, rather than outside, of the GEC cell. Because the absorption obtained is a spatially integrated absorption, measurements made represent an averaging of absorbing species inside and outside of the plasma. This modification is made to reduce this spatial averaging and thus allow a more accurate estimation of neutral species concentrations and temperatures within the plasmas. By reducing this pathlength, we find that the apparent CF4 consumption increases from 65% to 95% and the apparent vibrational temperature of CF4 rises by 50-75 K. The apparent fraction of etch product SiF4 decreases from 4% to 2%. The data suggests that these density changes may be due to significant temperature gradients between the plasma and chamber viewports.
- Subjects :
- Optics
Subjects
Details
- Language :
- English
- Database :
- NASA Technical Reports
- Publication Type :
- Report
- Accession number :
- edsnas.20020039148
- Document Type :
- Report