On the E-H transition in inductively coupled radio frequency oxygen plasmas: I. Density and temperature of electrons, ground state and singlet metastable molecular oxygen

Abstract

In this series of two papers, the E-H transition in a planar inductively coupled radio frequency discharge (13.56 MHz) in pure oxygen is studied using comprehensive plasma diagnostic methods. The electron density serves as the main plasma parameter to distinguish between the operation modes. The (effective) electron temperature, which is calculated from the electron energy distribution function and the difference between the floating and plasma potential, halves during the E-H transition. Furthermore, the pressure dependency of the RF sheath extension in the E-mode implies a collisional RF sheath for the considered total gas pressures. The gas temperature increases with the electron density during the E-H transition and doubles in the H-mode compared to the E-mode, whereas the molecular ground state density halves at the given total gas pressure. Moreover, the singlet molecular metastable density reaches 2% in the E-mode and 4% in the H-mode of the molecular ground state density. These measured plasma parameters can be used as input parameters for global rate equation calculations to analyze several elementary processes. Here, the ionization rate for the molecular oxygen ions is exemplarily determined and reveals, together with the optical excitation rate patterns, a change in electronegativity during the mode transition.

Investigation of the radially resolved oxygen dissociation degree and local mean electron energy in oxygen plasmas in contact with different surface materials

“…In the above form, accurate results can only be obtained when the dominant sources of production of the considered excited states are via electron impact with ground state atomic and molecular oxygen. However, recent publications have detected the presence of significant quantities of vibrationally 39 and electronically excited states 40 of molecular oxygen in oxygen plasmas. If the electron impact cross sections for dissociative excitation from these states into the O(3p 3 P) state were to be significant, this may affect the atomic oxygen densities derived via actinometry.…”

Dependence of E-H transition in argon ICP discharges for treatment of organic molecules

“…It is remarkable because, in oxygen containing plasmas, the degradation processes at higher temperatures are accompanied of oxygen functionalization of the organic sample, leading to production of resistant products [25]. H-mode is known to have a higher ion temperature than E-mode [12,13,15] and this is a considerable source of heating in plasmas. Additionally, the higher electron density and electron energy distribution function (EEDF) at lower values, found in H-mode, can also lead to dissociative electron attachment (DEA) on sample surface, which could also increase heating by bond dissociation [26].…”

“…, while H-mode ranges from 10 10 to 10 11 cm -3 at the same applied power [8,10,11]; the plasma potential is reduced at the H-mode even with the increase of applied power [12,13]; the EEDF changes to a more Maxwellian electron distribution at the Hmode [9,10,14]; electron temperature is reduced at H-mode, while gas temperature is increased [13][14][15]; electron-electron collision frequency is greatly increased [12]; after the H-mode is initiated, it can be sustained even at lower powers [12,16]; finally, both E and H modes can coexist inside the reactor [9].…”

E‐ and H‐mode transition in a low pressure inductively coupled ammonia plasma

“…The transition between capacitive and inductive mode is usually abrupt and occurs when the discharge power reaches a certain value, which depends on peculiarities of a particular discharge configuration. Such transitions have been studied for many gases by different authors …”

“…Such transitions have been studied for many gases by different authors. [1][2][3][4][5][6] Plasma created by electrodeless discharges represents a rich source of reactive gaseous species. As in many other types of discharges, the gaseous molecules are excited, dissociated or/and ionized upon interacting with electrons from the high-energy part of their distribution function.…”