Langmuir probe diagnostics of electronegative discharges

Summary form only given, as follows. The Langmuir probe technique has some drawback in applying to electronegative plasma since it is difficult to determine both the positive ion current and negative charge saturation current. The planar probe ion current is modified due to the presence of negative ions. In this study, an inductively coupled oxygen RF plasma is employed as an example of electronegative discharge. Plasma parameters are obtained from Langmuir probe method based on modified Bohm flux theory and from the method based on electron energy distribution function (EEDF) integrals. The EEDF was measured by a double differentiation of the I-V characteristic according to the Druyvesteyn formula. The charged particle densities estimated based on both methods are compared. The effect of the ratio of electron temperature to negative ion temperature on the determination of the charged particle densities is also discussed. It is observed that at low pressure the EEDF is close to a Maxwellian Generally, as the pressure increases, the distributions switch to bi-Maxwellian and to Druyvesteyn, and suggest some depletion of electrons with larger energies.