The plasma potential of 13.56-MHz low-pressure argon glow discharges has been measured for various modes of applying the rf power in a geometrically asymmetric planar system. The plasma potential is determined from the energy distribution of positive ions incident on the grounded electrode. The voltages on the excitation electrode (target electrode) are carefully measured and the capacitive sheath approximation is used to relate these measured voltages to the measured plasma potential. This approximation is successful in most of the situations encountered in this low-pressure (20 mTorr) relatively low-power density regime. The effects of superimposing dc voltages on the excitation electrode are discussed.
The energy distribution of positive ions incident on a grounded surface in a low-pressure argon planar rf glow discharge system has been measured as a function of excitation frequency from 70 kHz to 13.56 MHz for both capacitive and direct coupling of the rf power to the excitation electrode. The results are interpreted by taking into consideration both the transit time for the ion to traverse the sheath relative to the period of the rf excitation voltage, and the resistive or capacitive characteristics of the sheaths. The importance of system geometry and of the dc potential of the excitation electrode (as determined by external circuitry) on the maximum energy of ions incident on grounded surfaces is shown.
28) The mass spectrometer was obtained through the National Science Foundation Instrument Grant GP-32797 to the University of Minnesota. We are grateful to Dr. Roger Upham for his very resourceful operation of the instrument. (29) A. J. Gordon and R. A. Ford, "The Chemist's Companion", Wiley,
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