Electrical probes for electron energy distribution function (EEDF)measurements in low pressure hydrogen plasmas

摘要

The EEDF is of special interest in low pressure plasmas and often measured using the conventionalLangmuir probe technique, which relies on the numerical analysis (second derivative) of the V/Icharacteristics. In order to measure the second derivate directly, the Boyd-Twiddy [1] method wasused, where a voltage ramp is superimposed by an AC modulated signal. The current at the modula-tion frequency directly yields the EEDF. Measurements were carried out at ECR and ICP discharges,operating in a similar pressure and plasma parameter range. The results show a good agreementbetween the Langmuir probe and the Boyd-Twiddy technique, whereas the Boyd-Twiddy method ismuch less noisy. In addition, in ICP discharges the RF disturbance is automatically filtered, using themodulation technique.