Tuning effect of inert gas mixing on electron energy distribution function in inductively coupled discharges

Abstract

Measurements on electron energy distribution function (EEDF) by a Langmuir probe show that inert gas mixing can change EEDF from a Maxwellian to a 'two-temperature' structure in an inductively coupled low pressure nitrogen discharge. This result suggests the existence of two groups of electrons: low and high energy. Each group of electrons has distinct behaviour as gas mixing ratio changes. As a result, this causes discrepancies between the measured electron temperature by a Langmuir probe and that by optical line-ratio technique, since these two techniques are sensitive to the energy distribution of low and high energy electrons, respectively. A detailed experimental investigation of the evolution of EEDF with different inert gas mixtures (Ar/N 2 , He/N 2 , Ne/N 2 and Xe/N 2 ) at an operating pressure of 10 mTorr is performed, from which the distribution temperature of both low and high energy electrons is calculated and compared with the temperature obtained from the Global Model. It is found that with the measured energy range and under the experimental condition studied, inelastic collisions (both excitation and ionization) play a key role on the shape of EEDF when inert gas is mixed in the discharge.

Symmetric and Asymmetric Double Langmuir Probes Characterization of Radio Frequency Inductivley Coupled Nitrogen Plasma

“…It is clear from the figure that the high energy tail of EEPF increases with the decrease in filling gas pressure, showing its non-Maxwellian behavior. This increment in the tail confirms the presence of large number of highly energetic electrons in the discharge plasma [18] along with the least energetic electrons. But at higher pressures the high energy tail of the EEPF depletes to the lower energies, indicating the Maxwellian approach of EEPF.…”

“…It shows that rather an increase in electron energy, more and more energy transfer from electrons to the discharge plasma species takes place. Under these conditions the kT e decreases and neutral gas temperature increases due to the existence of a balance between the total ionization events and the total particle losses to the plasma chamber walls [7,18]. The particle-wall recombination probability is different for different wall surfaces.…”

Double and Triple Langmuir Probes Measurements in Inductively Coupled Nitrogen Plasma

“…When the filling pressure inside the chamber increases, the electron collision frequency with the plasma species also increases and the mean free path between the successive collisions decreases which shows that rather than gain of energy by the electrons, more and more energy transfer from electrons to the plasma species takes place and under this situation the balance between the total ionization events and the total particle losses to the chamber walls [23,24] results in decrease of the electron temperature and an increase in the neutral gas temperature as we increase the filling pressure inside the chamber. A similar decreasing trend with the increase of filling pressure at constant input RF power of 250 W is found in electron number density measured by the double and triple Langmuir probe methods.…”

“…Similarly at higher pressure, the high energy tail of the electron energy distribution function depletes to the low energies and the availability of the highly energetic electrons for the electron impact ionization processes decreases and consequently the electron number density. This depletion in the tail of the electron energy distribution function may be due to the rapid diffusion and recombination of the highly energetic electrons at the chamber walls [23].…”

Ion Heating in Dusty Plasma of Noble Gas Mixtures

“…Besides energetic ions, high energy electrons can also exist in low-pressure discharges in noble gas mixtures [6]. Measurements of electron energy distribution function (EEDF) shows that mixing of noble gas mixtures can change EEDF from Maxwellian to "two-temperature" structure what suggests the existence of two groups of electrons: with low and high energies.…”