Experimental and simulation study of a capacitively coupled oxygen discharge driven by tailored voltage waveforms

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A thorough understanding of the energy transfer mechanism from the electric field to electrons is of utmost importance for optimization and control of different plasma sources and processes. This mechanism, called electron power absorption, involves complex electron dynamics in electronegative capacitively coupled plasmas (CCPs) at low pressures, that are still not fully understood. Therefore, we present a spatio-temporally resolved analysis of electron power absorption in low pressure oxygen CCPs based on the momentum balance equation derived from the Boltzmann equation. Data are obtained from 1d3v Particle-In-Cell / Monte Carlo Collision simulations. In contrast to conventional theoretical models, which predict 'stochastic/collisionless heating' to be important at low pressure, we observe the dominance of Ohmic power absorption. In addition, there is an attenuation of ambipolar power absorption at low pressures due to the strong electronegativity, and the presence of electropositive edge regions in the discharge, which cause a high degree of temporal symmetry of the electron temperature within the RF period.

Section: Methodsmentioning

confidence: 99%

Electron power absorption in low pressure capacitively coupled electronegative oxygen radio frequency plasmas

Vass¹,

Wilczek²,

Lafleur³

et al. 2020

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“…The surface recombination of the singlet delta oxygen metastable molecules has been addressed in [62][63][64]. A comparison between experiments and simulations for peaks-and valleys-type waveforms, focusing on the DC self-bias, the ion flux, the discharge power, and the ion flux-energy distributions has been presented in [65]. These investigations have been extended by Phase Resolved Optical Emission Spectroscopy (PROES) studies.…”

Section: Introductionmentioning

confidence: 99%

Ion energy and angular distributions in low-pressure capacitive oxygen RF discharges driven by tailored voltage waveforms

Derzsi

Vass

Schulze

et al. 2018

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We investigate the energy and angular distributions of the ions reaching the electrodes in low-pressure, capacitively coupled oxygen radio-frequency discharges. These distributions, as well as the possibilities of the independent control of the ion flux and the ion energy are analysed for different types of excitation: single-and classical dual-frequency, as well as valleys-and sawtooth-type waveforms. The studies are based on kinetic, particle-based simulations that reveal the physics of these discharges in great details. The conditions cover weakly collisional to highly collisional domains of ion transport via the electrode sheaths. Analytical models are also applied to understand the features of the energy and angular distribution functions.

“…It is also known that surface interaction probabilities for reactive neutral species can strongly influence the properties and charged particle dynamics of low pressure plasma sources [38,[57][58][59][60][61][62]. A prominent example is the role played by the surface quenching probability of the molecular oxygen metastable molecule O 2 (a g 1 D ) in determining the electronegativity (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…A prominent example is the role played by the surface quenching probability of the molecular oxygen metastable molecule O 2 (a g 1 D ) in determining the electronegativity (i.e. the ratio of the negative ion density to the electron density) of oxygen plasmas [38,48,57,59,63]. This dependence occurs as a result of the high rate coefficient for electron detachment from O -ions in collisions with O 2 (a g 1 D ) molecules in comparison with the equivalent reaction with ground state molecular oxygen [64].…”

Section: Introductionmentioning

confidence: 99%

“…To do this, plasmas driven by the waveform described in equation (1) are characterised under the variation of (i) high and low frequency components (V hf and V lf ) and phase shift (θ) and (ii) the contribution of O 2 (a g 1 D ) to the background gas. Two values of the O 2 (a g 1 D ) density are chosen which represent the two extremes predicted in the literature through the variation of the O 2 (a g 1 D ) surface quenching probability [38,57]. The plasma electronegativity resulting for each of these O 2 (a g 1 D ) densities thus represent approximate extremes in the electronegativity of oxygen plasmas.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation

Gibson

Gans

2017

The charged particle dynamics in low-pressure oxygen plasmas excited by odd harmonic dual frequency waveforms (low frequency of 13.56 MHz and high frequency of 40.68 MHz) are investigated using a one-dimensional numerical simulation in regimes of both low and high electronegativity. In the low electronegativity regime, the time and space averaged electron and negative ion densities are approximately equal and plasma sustainment is dominated by ionisation at the sheath expansion for all combinations of low and high frequency and the phase shift between them. In the high electronegativity regime, the negative ion density is a factor of 15-20 greater than the low electronegativity cases. In these cases, plasma sustainment is dominated by ionisation inside the bulk plasma and at the collapsing sheath edge when the contribution of the high frequency to the overall voltage waveform is low. As the high frequency component contribution to the waveform increases, sheath expansion ionisation begins to dominate. It is found that the control of the average voltage drop across the plasma sheath and the average ion flux to the powered electrode are similar in both regimes of electronegativity, despite the differing electron dynamics using the considered dual frequency approach. This offers potential for similar control of ion dynamics under a range of process conditions, independent of the electronegativity. This is in contrast to ion control offered by electrically asymmetric waveforms where the relationship between the ion flux and ion bombardment energy is dependent upon the electronegativity.