| AVS 59th Annual International Symposium and Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeA |
| Session: | Plasma Diagnostics, Sensors and Control 2 |
| Presenter: | G. Franz, Hochschule München, Germany |
| Authors: | G. Franz, Hochschule München, Germany I. Krstev, Hochschule München, Germany F. Schamberger, Hochschule München, Germany |
| Correspondent: | Click to Email |
Optical emission spectroscopy has evolved a mighty tool for evaluating the high-energy tail of the electron energy distribution function EEDF [1]. Since it is a non-evading technique, a spatially-resolved measurement cannot be performed, which limits its general applicability, especially for inhomogeneous plasmas, in particular capacitively-coupled discharges with their thick plasma sheaths and large rf electric fields, and microwave-driven plasmas which exhibit a very high plasma density in front of the microwave window which prevents the penetration of the microwave into deeper regions of the reactor. A spatially averaging technique therefore overdraws the region close to the window leading to erroneous results and conclusions.
To overcome these limitations, a cyclindrical parallel-plate reactor was equipped with a magnifying double lens system with different focal lengths halfway between the two “electrodes” to resolve radially dependent spectroscopic data obtained with the two actinometric gases Kr and Xe [2]. From these data, the electron temperature of the high-energy tail of the EEDF of capacitively coupled discharges through argon and the weakly electronegative gas mixture CF4/O2 can be calculated [3].
These data are modeled with ray tracing programs to evaluate the degree of magnification. Compared with an experimental setup with a plane window instead of a converging lens and only one focusing lens for the glass fiber, we can enhance the S/N ratio by a factor of at least 100 yielding a radial resolution of about 1 – 2 mm which is in the same range of Langmuir probes.
Compared with measurements obtained with Langmuir probes in the plasma bulk, electron temperatures show in fact the expected behaviour of definitely hotter temperatures.
[1] V.M. Donnelly, J. Phys. D: Appl. Phys. 37, R217 (2004)
[2] G. Franz, I. Krstev, F. Schamberger, Plasma Sci. Techn. 14(8), to be published 2012
[3] M.V. Malyshev and V.M. Donnelly, J. Vac. Sci. Technol. A15, 550 (1997)