Oxygen discharges diluted with argon: dissociation processes

Abstract

We use a global (volume averaged) model to study the dissociation processes and the presence of negative ions and metastable species in a low pressure high density O 2 /Ar discharge in the pressure range 1-100 mTorr. The electron density and the fractional dissociation of the oxygen molecule increases with increased argon content in the discharge. We relate this increase in fractional dissociation to an increase in the reaction rate for electron impact dissociation of the oxygen molecule which is due to the increased electron temperature with increased argon content in the discharge. The electron temperature increases due to higher ionization potential of argon than for molecular and atomic oxygen. We find the contribution of dissociation by quenching of the argon metastable Ar m by molecular oxygen (Penning dissociation) to the creation of atomic oxygen to be negligible. The negative oxygen ion O − is found to be the dominant negative ion in the discharge. Dissociative attachment of the oxygen molecule in the ground state O 2 (X 3 − g ) and in particular the metastable oxygen molecule O 2 (a 1 g ) are the dominating channels for creation of the negative oxygen ion O − .

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

“…As a result HeþO 2 plasmas are typically operated with reduced amount of oxygen and maximum process efficacy is often encountered at oxygen concentrations below 1%. 44,45 In the last decades, global models have been used to study low-pressure electronegative plasmas [46][47][48][49] and in recent years these models have been extended to the study electronegative atmospheric-pressure discharges. [15][16][17][18] In these models it is customary to assume that the input power is mainly coupled to the electrons 50 with various approximations regarding the power coupled to ions in the sheath.…”

Selective Plasma Etching of Polyphenolic Composite in O2/Ar Plasma for Improvement of Material Tracking Properties

“…The addition of Ar increases plasma density and consequently the dissociation of oxygen molecules, since it has higher electron impact dissociation cross-section. [22] Based on results as from Figure 8B, one presumes that the etching process efficiently starts only after 2 min of exposure. Until then the functionalization with polymer bond breaking is the leading process.…”

“…[26] The report by Gudmundsson and Thorsteinsson, revealed that the metastable oxygen atom densities at lower pressures (below 15 Pa) increased for 15% with Ar addition (up to $43%). [27] Oxygen metastables at higher pressures (above 100 Pa) were measured by Rakhimova et al and showed that the number density of metastable oxygen molecules and atoms decreased with the increase in the concentration of argon. [28] In the case of 98% Ar gas mixture, the poor etching rate seems obvious, due to the lack of chemical assistance in the absence of dissociated O atoms.…”

Measurement of Argon emission spectral of ICP plasma using a diagnostic system based on photomultiplier tubes array

“…In our ICP rf Argon discharge process, the pressure is 20mTorr and the flow is 200sccm, hence the corona model is valid for analyzing the process. The reason is that other collisional processes are trivial and the density of metastables is too low to make a significant contribution to the excitation of the excited species under these conditions [9][10][11]. In a corona model for these levels, we have the electron-impact excitation from the ground-state atom, Ar(gs) + e Ar(2p1 ) + e (1) and the spontaneous radiation, Ar(2p 1 )Ar(1s 2 ) + hv…”

“…The symbol A is the Einstein coefficient, n is the density and Q exc denotes the excitation rate coefficient [11].…”