Effect of multistep ionizations on the electron temperature in an argon inductively coupled plasma

Electron energy distribution functions (EEDFs) are measured in an argon inductively coupled plasma. It is observed that the measured EEDFs are nearly Maxwellian distributions, and the electron temperature derived from the EEDFs decreases with increasing input radio-frequency (rf) power. It appears that additional ionization processes exist. To investigate this decrease in the electron temperature, multistep ionizations are taken into account. An analytical particle balance equation, including the multistep ionizations, are derived. According to the new balance equation, to balance between the total volume ionization and the total surface particle loss, the electron temperature should be decreased with increasing rf power. The comparison between the model and the experiment are presented, and the model agrees well with the experiment.