Investigation of a radio-frequency inductive- coupled-plasma discharge afterglow in noble gases

Abstract

It has been shown (Demidov et al 2005 Phys. Rev. Lett. 95 215002) that even a small number of nonlocal fast electrons, which do not significantly affect the overall mean electron energy, can dramatically change both the plasma and near-wall sheath properties. In this work, Langmuir probe measurements of the electron energy distribution function (EEDF) show the presence of fast electrons created due to collisions of pairs of metastable atoms and collisions of the second kind between metastable atoms and bulk electrons. These measurements were made in the afterglow of a 100% modulated radio-frequency inductive-coupled-plasma discharge in argon, neon and helium. It is shown that this fast component of the EEDF can be controlled independently of the slow electrons, which is a direct consequence of the EEDF nonlocality. Both EEDF and plasma emission spectroscopy measurements are presented for the helium afterglow. These data allow us to determine the absolute density of metastable atoms and their temporal decay during the afterglow. It is shown that under the experimental conditions, stepwise excitation of helium metastable atoms is the primary process for populating excited states and, therefore, decay of the excited atoms is governed by the decay of metastable states. The presence of a trace amount of nitrogen in the system, which does not significantly change the properties of the helium discharge, allowed us to independently measure the decay of helium metastables by monitoring the N+2(B–X) emission resulting from Penning ionization of N2(X) and confirmed the above conclusions regarding the presence and importance of metastable atoms.

Effect of electron energy probability function on plasma CVD/modification in a 13.56 MHz hollow cathode discharge

“…In the pure argon plasma, the EEPF shows two maxima at 11.6 eV and 18.3 eV and the EEPF in the Ar-He plasma shows two maxima at 14.4 and 22.5 eV. The appearance of these maxima could indicate the presence of fast electrons created due to collisions of pairs of metastable atoms of the same gas and collisions of the second kind between metastable atoms and bulk electrons [38]. The measured EEPFs also show a depletion of the tail of high energy electrons (>∼5 eV) with increasing argon pressure because of inelastic collisions between high-energy electrons and neutrals.…”

Comparison of helium two-step plasma emission with that predicted from measured cross sections

“…A schematic of the experiment is shown in figure 1, taken from [6]. The experiment has been described in some detail in previous papers [6,7] and will be only briefly described here.…”

“…Therefore, experiments which compare plasma emission with that calculated from measured cross section data can yield insight into the sensitivity of various cross sections to overall plasma conditions [3]. In previous work [6], it was shown that the plasma emission in the afterglow of a 100% modulated radio frequency (rf) helium discharge originates from collisions of fast electrons with metastable species and that the electron energy distribution function (EEDF) for these fast electrons is made up of narrow peaks at discrete energies. Since the emission involves collisions of electrons with previously excited states, this process is frequently referred to as two-step emission.…”

The Properties of Inductive Coupled Radio-Frequency Neon Flowing Discharge at Low-Pressure

“…Diğer bir çalışmada ise soygazlar ile deşarj odasında plazma oluşturulduktan sonra vakum odasında geçiş yapan deşarjın elektron enerji dağılım fonksiyonları incelenmiştir. Ancak, yapılan çalışmalarda indüktif olarak bağlı RF Ne deşarjların 2. bölgedeki özellikleri OES tekniği ile incelenmemiştir [18][19][20][21].…”