Global model simulations of low-pressure oxygen discharges

Abstract

We use a global model (volume averaged) to study plasma discharges in molecular oxygen gas in the 1-100 mTorr pressure range. This model determines densities of positive ions O + 2 and O + , negative ion O − , electrons, ground state O 2 and O atoms, and metastables O 2 (a 1 ∆g) and O( 1 D), and electron temperature as function of gas pressure and input power, for a cylindrical discharge. We apply the model to O 2 discharges and the results are compared to a particle-in-cell simulation (PIC), experimental data and a volume-averaged global model developed at the University of California at Berkeley. We find that the total positive ion density increases with pressure at low pressures (up to approximately 30 mTorr), and decreases at higher pressures. The electronegativity decreases with increased power and increased pressure as predicted by the global models presented in the literature. The predictions for electron temperature are also in agreement with these models. However, there is a discrepancy betweeen these global models and PIC simulations and experimental data, for 20 and 40 mTorr cases, concerning electronegativity calculations. PIC simulations yield much higher electronegativities. There are strong indications that this is due to the assumption of Maxwellian electron energy distribution functions in the global model, while in the PIC simulations this is clearly not the case.

Controlled Oxidation of Alkyl Monolayers Grafted onto Flat Si(111) in an Oxygen Plasma of Low Power Density

“…In addition, at 10 mW cm −3 the molar fraction of O 2 ( 1 Δ g ) is much larger than that of O( 3 P), while the two molar fractions are in comparable amounts at 500 mW cm −3 (crossover at about 700 mW cm −3 ). In our geometry and operating conditions (see Experimental Methods), these two active species are most probably the ones to be considered at the sample surface, because they need about half a second to reach the sample region, a delay smaller than their lifetime (in the range of seconds, the loss processes being very slow at glass walls − ).…”

Experimental and numerical investigations of electron density in low-pressure dual-frequency capacitively coupled oxygen discharges

“…5, one can see that the EEPFs exhibit biMaxwellian distributions and the number of high-energy electrons increases with increasing HF power. It is known that the electrons with energy higher than the ionization threshold 41,42 can produce the ionization. Therefore, the increase in the electron density with the HF power results from the increasing ionization of oxygen molecular.…”

Particle-in-Cell Simulation at Low Pressure Oxygen Discharges: Comparison with Experimental Data

“…Currently, the study of plasma through diagnostic techniques such as Langmuir probe (2,3), optical emission spectroscopy (3,4), mass spectrometry (3), etc., and simulations as particle-in-cell method (5,6) and global model (7)(8)(9) is of great interest to understand the dependences of the plasma compositions and the electron kinetics on the external parameters (10).…”