The Effects of Radio Frequency Waves on the Sputtering of Ion Cyclotron Resonance Heating Antenna Faraday Shields

July 1, 1987

J. Vac. Sci. Technol., A 5, 2301-2304 (1987).

Caughman, J. B. O., Ruzic, D. N., Hoffman, D. H.

The sputtering of the graphite covered Faraday shield of an ion cyclotron resonance heating loop antenna has been studied. The antenna operated at 50 MHz and was exposed to a weakly magnetized plasma produced by the High Particle Flux Facility at Oak Ridge National Laboratory. The flux at the antenna was on the order of 3×1017 cm–2 s–1. A dc bias voltage applied to the antenna allowed the effective energy of the impinging hydrogen ions to be varied up to 65 eV. Coupled rf power varied from 0 to 3 kW. Sputteringdepths were directly measured by surface topography. Sputtering enhancement due to rf was between a factor of 2 to 4, depending on the position along the antenna. Antenna voltage profiles were calculated and used to correlate measured erosion coefficients with ion energies. Various sputtering theories and possible chemical sputtering effectsare discussed.