Global model of inductively coupled Ar plasmas using two-temperature approximation

Abstract

The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively coupled rf (13.56 MHz) Ar discharge in the pressure range from 5 to 70 mTorr, by changing the power injected into the plasma up to 100 W. The EEDFs measured at a pressure of 5 mTorr formed a bi-Maxwellian structure, which is not prominent due to high electron density, in the energy region lower than the lowest excitation threshold energy. The EEDF structure in the energy region higher than the threshold has a significant depletion of high energy electrons. The EEDF measured at a pressure higher than 10 mTorr can be approximated using a two-temperature distribution, which consists of the higher temperature in a low-energy region below the lowest excitation threshold and the lower temperature in a high-energy region. A global model using the two-temperature distribution is proposed and compared with the experimental results. The model consists of the rate equations for neutrals and charged particles and an energy-balance equation for electrons together with the balance equation for high-energy electrons. Pressure dependences of the electron density and temperatures predicted in this global model agree well with the experimental results except in the pressure range lower than 10 mTorr.