Measurements and models of ion energy distributions in high-density, radio-frequency-biased CF/sub 4/ discharges

Abstract

Listen

Translate article

Summary form only given. Ion dynamics in the narrow sheaths of high-density plasmas, especially in sheaths biased by radio-frequency (RF) voltages, are complicated and nonlinear. Models of such high-density, RF sheaths are needed to predict ion bombardment energies in simulations of high-density plasma etching. To provide data to test these models, we have measured ion energy distributions (IEDs) in CF, discharges in a high-density, inductively coupled plasma reactor, at a pressure of 1.33 Pa (10 mTorr), using a mass spectrometer equipped with an ion energy analyzer. Energy distributions of CF/sub 3//sup +/, CF/sub 2//sup +/, CF/sup +/ and F/sup +/ ions were measured as a function of RF bias frequency, RF bias amplitude, and inductive source power. Simultaneous measurements by a capacitive probe and a Faraday cup provide enough information to completely determine the input parameters of sheath models and allow direct comparison of calculated and measured IEDs. For conditions where the RF bias period is much smaller than, or much larger than, the time it takes ions to cross the sheath, very simple models are able to predict the features of the measured IEDs. When the RF bias period approaches the ion transit time, however, more complicated models are required. One recently developed model, which include a complete treatment of time-dependent ion dynamics in the sheath, was found to accurately predict the behavior of measured IEDs over the entire range of RF bias frequency.