Measurement of the electron energy distribution functions in low density RF plasmas through a tunable external RF filter

Abstract

The electron energy distribution function (EEDF) measurement in radio frequency (RF) plasmas is of fundamental interests, especially in low-density RF capacitively coupled plasma. For this purpose, a new external filter with very high impedances is developed. The impedance of the filter at the fundamental and its harmonic frequencies (13.56, 27.12 and 40.68 MHz) through careful circuit design is maximized. Experimental verifications are performed by measuring the EEDFs in RF discharges. The result shows that the RF distortion in the EEDF measurement is significantly reduced by tuning the filter under various discharge conditions in an inductively coupled plasma. Accurate plasma densities can be obtained and the electron heating mode transition is observed through high-quality EEDF measurement in an capacitively coupled plasma, where RF plasma potential fluctuates severely.