Measurements and modeling of ion energy distributions in high-density, radio-frequency biased CF4 discharges

Abstract

Models of ion dynamics in radio-frequency (rf) biased, high-density plasma sheaths are needed to predict ion bombardment energies in plasma simulations. To test these models, we have measured ion energy distributions (IEDs) in pure CF4 discharges at 1.33 Pa (10 mTorr) in a high-density, inductively coupled plasma reactor, using a mass spectrometer equipped with an ion energy analyzer. IEDs of CF3+, CF2+, CF+, and F+ ions were measured as a function of bias frequency, bias amplitude, and inductive source power. Simultaneous measurements by a capacitive probe and a Faraday cup provide enough information to determine the input parameters of sheath models and allow direct comparison of calculated and measured IEDs. A rigorous and comprehensive test of one numerical sheath model was performed. The model, which includes a complete treatment of time-dependent ion dynamics in the sheath, was found to predict the behavior of measured IEDs to good accuracy over the entire range of bias frequency, including complicated effects that are observed when the ion transit time is comparable to the rf bias period.