Langmuir probe measurements of a radio frequency induction plasma

Abstract

In this work a planar, radio frequency induction plasma source is characterized in terms of ion density, electron temperature, and plasma potential using a single Langmuir probe in oxygen and noble gases. Probe measurements of density were also verified using microwave interferometry. Measured argon ion densities increase nearly linearly with power from 1X 10cm “at 300 W rf power to 6x 10cm “at 1.2 kW at 1X 10“Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2X 10 cm ~at 1X 10 Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26 X 10“Torr to 7 eV at 0.3 X 10“Torr. Plasma potentials are typically 15–30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5 X 10“Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. Ion generation energy cost in argon is 100–250 W/A. © 1993, American Vacuum Society. All rights reserved.