PROBE DIAGNOSTICS OF NON-MAXWELLIAN PLASMAS

Various probe diagnostic methods have been applied to rf plasmas with non-Maxwellian electron energy distribution functions (EEDF) and the results of these diagnostic methods have been compared. Plasma density and electron temperature were obtained using standard procedures from the electron retardation region (classic Langmuir method), the ion saturation region, and the electron saturation region of the measured probe I/V characteristic. Measurements were made in a 13.56-MHz capacitive argon rf discharge at two gas pressures: p=0.03 Torr, where stochastic electron heating is dominant, and p=0.3 Torr, where collisional electron heating dominates. Thus, the measured EEDF at each gas pressure manifests a distinct departure from thermodynamic equilibrium being bi-Maxwellian at 0.03 Torr and Druyvesteyn-like at 0.3 Torr. Considerable differences in electron density and temperature were obtained from the different parts of the probe characteristic and these values differ dramatically in many cases from those found from integration of the measured EEDF's, thus demonstrating that using standard procedures in non-Maxwellian plasma can give misleading results.