Variation of the electron energy distribution with He dilution in an inductively coupled argon discharge

Abstract

We present experimental evidence of different behaviors of plasma parameters depending on changes in the electron energy distribution (EED), caused by an electron heating mechanism and electronneutral collision processes in an Ar/He mixture inductively coupled plasma. At a low gas pressure of 3 mTorr, where the electron neutral collision frequency m is much smaller than the driving frequency x RF , the EEDs evolved from a bi-Maxwellian distribution to a Maxwellian distribution, due to the efficient heating of low energy electrons when the He flow rate increased at a fixed total gas pressure. The plasma density slowly decreased with the He flow rate portion ([He]/[Ar] þ [He]) in a range of 0%-70%, while the plasma density largely decreased in the He flow rate portion of 70%-100%. On the other hand, at a high gas pressure of 350 mTorr where m ) x RF , the EEDs evolved from a Druyvesteyn-like distribution to a Maxwellian distribution, due to a cooling of low energy electrons and an increase in the population of high energy electrons, when the mixing ratio of the He gas is increased. In this case, plasma density abruptly decreased for a He flow rate ratio of 0%-30%. This result directly shows that the EEDs significantly affect the different variations of plasma parameters, even in the case of the same mixing ratio of the gases. V C 2012 American Institute of Physics. [http://dx.

E-H heating mode transition in inductive discharges with different antenna sizes

“…Because x RF coincides with m at about 20 mTorr of Ar gas, 1 the plasma production in this condition can be enhanced at a given electric field. 44 For this reason, the minimum transition power is usually observed at a gas pressure of 20 mTorr, and this result coincides with the theoretical approaches by Yoon et al 45 and Lee and Chung. 34 However, the minimum transition power is observed at a relatively high gas pressure (40 mTorr-60 mTorr) in the case of the large antenna (ICP coil D¼36 ), as shown in Fig.…”

Measurements of the spatially resolved electron temperature and plasma potential in ferrite-core side type Ar/He inductively-coupled plasmas

“…This is quite different to other studies where the EEPFs had a Maxwellian or bi-Maxwellian distribution [19][20][21][22][23], because a lower driving frequency (400 kHz) than the conventional radio frequency (13.56 MHz) was used in this work. Therefore, since the discharge condition in this work was in the collisional dominated region where the driving frequency (ω RF ) was much lower than the electron-neutral collision frequency (ν m ).…”

“…(Ramsauer gas) discharge, the heated electrons in the low energy region were cooled because the Ohmic heating process was inversely proportional to the ν m in this discharge condition, where ω RF << ν m [22]. As the helium gas had a higher threshold energy for the inelastic collision process, the EEPF changed to the Maxwellian distribution as shown in Fig.…”

“…Therefore, since the discharge condition in this work was in the collisional dominated region where the driving frequency (ω RF ) was much lower than the electron-neutral collision frequency (ν m ). The low energy electrons could be efficiently heated and the EEPF showed the Druyvesteyn-like distribution due to the Ramsaure minimum [20,22] of the low energy electrons (~ 0.7 eV) in an argon plasma. Thus, the energy gain of the low energy electrons was much larger than that of the high-energy electrons in the collisional dominated regime [20,23].…”

Investigation of E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma

“…Similarly, these electrons cannot contribute in the collisional heating where electrons gain energy from thermalization of electron-neutral collisions. Thus, these electrons absorb a slight quantity of energy from either collisional or collision-less heating and just fluctuate in the barrier of the ambipolar potential [40]. The EEPF transition from bi-Maxwellian to Druyvesteyn distribution in E-mode at a pressure of 5 and 10 Pa takes place as shown in figures 11(b) and (c).…”