Development of a Radiofrequency Plasma Diagnostic System with a Langmuir Probe and Study of a Capacitively Coupled Argon Plasma

Abstract

A single rf-compensated cylindrical Langmuir probe has been developed in order to characterise a plasma RF discharge. A circuit using radiofrequency filtering and the passive compensation method was employed to minimize the probe curve distortions. The effect of the rfcompensation on the probe measurements was discussed. The latter were performed at power and pressure of 50 W and 510-2–1.2 mbar, respectively. Compensated measurements of the electron energy distribution function (EEDF) and plasma parameters were conducted at powers ranging from 5 to 120 W and pressure of 0.3 mbar. They exhibit a transition between the stochastic electron heating mode operating at low powers and the secondary-electron emission heating mode (γ) operating at high powers. The electronic density increases from 1.5×109 to 3.2×1010 cm-3 while the effective electron temperature decreases from 3.7 to 2.3 eV. The EEDFs were found to be Druyvesteyn-like in the range of 5–80W and then evolve to the Maxwellian beyond 90W.