AVS 45th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS2-MoA

Paper PS2-MoA7
VUV-Visible Emission Spectroscopy Investigation of Frequency Effects in Low Pressure Plasmas

Monday, November 2, 1998, 4:00 pm, Room 318/319/320

Session: Diagnostics I
Presenter: A.C. Fozza, École Polytechnique, Canada
Authors: A.C. Fozza, École Polytechnique, Canada
M. Moisan, Université de Montréal, Canada
M.R. Wertheimer, École Polytechnique, Canada
Correspondent: Click to Email
Low pressure (p@<=@10 Torr), high frequency (HF) plasmas have been used for many years in various processing steps in very-large scale integration (VLSI) manufacturing of integrated circuits, and are now increasingly used as an efficient method for surface modification of polymers. In order to optimize a particular plasma process, the operator can vary such "external" (operator-set) parameters as the HF power, pressure, feed gas composition, reactor geometry, excitation frequency, etc. In the present study, we focus on the effect of the excitation frequency, f, a parameter which has received relatively little attention in the literature over the years. The difficulties encountered in designing meaningful frequency - dependent experiments are the following: - varying f over a wide range requires that one change the reactor and/or the power-delivery system, which usually calls for a change of the plasma volume; - working at constant electron density, n@sub e@, or absorbed HF power density, P@sub a@, has frequently not been taken into consideration. These difficulties can be avoided by the use of surface wave discharges (SWD), which constitute the most thoroughly modeled type of HF plasmas. SWD plasma sources possess great flexibility: a very broad (continuous) range of excitation frequencies, wide ranges of operating pressures and plasma densities, and high coupling efficiency. In earlier experiments in these laboratories, we have examined f-dependence of plasma deposition and etching experiments.@footnote 1@ The present experiments have been designed to investigate f-dependence more "directly", by studying optical emission from pure gases or their mixtures, as recently reported for the case of 2.45 GHz excitation.@footnote 2@ The vacuum ultraviolet (VUV) to visible emission from SWD plasmas in pure hydrogen or 0.07 H@sub 2@/0.93 Ar mixture have been investigated over a broad range of excitation frequency (50@<=@ f @<=@ 200 MHz) using a spectrophotometer with a known (calibrated) transfer function. As in earlier experiments,@footnote 1@ we have been able to interpret the f-dependence of emission intensity (atomic lines and molecular bands) in terms of changes of the electron energy distribution function. @FootnoteText@ @Footnote 1@ M. Moisan, C. Barbeau, R. Claude, C.M. Ferreira, J. Margot, J. Paraszczak, A.B. Sá, G. Sauvé, and M.R. Wertheimer, J. Vac. Sci. Technol. B9, 8 (1991). @Footnote 2@ A.C. Fozza, A. Kruse, A. Holländer, A. Ricard, and M.R. Wertheimer, J. Vac. Sci. Technol. A16, 72 (1998).