Measurement of electron energy distribution in low-pressure RF discharges

Electron energy distribution functions (EEDFs) have been measured in low-pressure capacitive RF discharges over a wide range of well defined (geometrically and electrically) discharge conditions. Measurements have been made in argon and helium ranging in gas pressure between 3 mTorr and 3 Torr and in discharge current density between 0.1 mA cm-2 and 10 mA cm-2. The measurements show changes in the EEDF due to the occurrence of physical phenomena such as stochastic electron heating and the effect of discharge transition into the gamma mode. Substantial differences in the EEDF in Ramsauer and nonRamsauer gases are also demonstrated and discussed. To achieve these results a higher level of performance was required from the measurement system than had been attained in previous EEDF measurements in RF discharges. EEDF measurements were made using a probe system specifically designed to remove or reduce the severity of many problems inherent to such measurements in RF discharges. The rationale and considerations in the probe system design, as well as many construction details of the probe system itself, are discussed.