Modulation of electron energy distribution functions and plasma parameters in a dual-frequency cylindrical ICP source

In this paper, a new dual-frequency cylindrical inductively coupled plasma source which operates with dual-frequencies (high-frequency (HF) 13.56 MHz and low-frequency (LF) 2 MHz) and dual-antennas (a 2-turn HF antenna and a 6-turn LF antenna) is designed, and the effects on electron energy distribution function and plasma parameters (i.e., plasma density ne, electron temperature Te, plasma floating potential Vf and plasma potential Vp) in the following cases are investigated: (1) fixed HF power of 500 W and LF power varying from 300 W to 900 W, (2) fixed LF power of 500 W and HF power varying from 300 W to 900 W. It is found that increasing HF power enhances the population of high-energy electrons, while increasing LF power increases the population of low-energy electrons. This result can be explained by the different electron heating mechanisms, i.e., ohmic heating for the LF discharge and collisional-less heating for the HF discharge at an argon gas pressure of 15 mTorr. Moreover, the different influences of HF power on ne, Te, Vf, Vp at fixed LF 500 W and that of LF power on ne, Te, Vf, Vp at fixed HF power 500 W are compared. It is found that although ne increases with both HF and LF power, it increases more significantly with the change of HF power. This indicates that ne is mainly determined by the HF power and slightly influenced by the LF power. Furthermore, the Te, Vf and Vp decrease with increasing LF power at a fixed HF power of 500 W, which is contrary to the trend of Te, Vf and Vp with increasing HF power at the same LF power of 500 W.