LANGMUIR PROBE MEASUREMENTS OF A RADIO-FREQUENCY INDUCTION PLASMA

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 1 x 10(11) cm-3 at 300 W rf power to 6 x 10(11) cm-3 at 1.2 kW at 1 x 10(-3) Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2 x 10(12) cm-3 at 1 x 10(-3) Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26 x 10(-3) Torr to 7 eV at 0.3 x 10(-3) Torr. Plasma potentials are typically 15-30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5 x 10(-3) Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. lon generation energy cost in argon is 100-250 W/A.