Improved RF-driven probe method for RF discharge plasma diagnostics

Abstract

The authors describe an electrostatic probe technique for radio-frequency (RF) plasmas. The presence of RF potential fluctuations between probe and plasma distorts the Langmuir probe characteristic; it therefore introduces large errors into plasma parameters. The method presented an improved version of that proposed by Braithwaite et al. to remove the effect of an RF fluctuation on probe characteristics. It consists in superimposing the fluctuation of the space potential measured by an emissive probe to the DC voltage applied to the probe. This technique is applied to the measurement of electron temperature and density in 13.56 MHz RF discharges in helium and argon. The results are compared with direct-current (DC) discharge plasmas with identical input power. The electron temperature in the RF plasmas is higher than that in the equivalent DC plasmas and the electron density in the RF plasmas is lower than that in the equivalent DC plasmas.