Collisionless heating in radio-frequency discharges: a review

Turner, M. M.

doi:10.1088/0022-3727/42/19/194008

Cited by 120 publications

(121 citation statements)

References 99 publications

(190 reference statements)

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“…the electrons adjacent to the sheath edge are accelerated by a single interaction with the expanding sheath into the plasma bulk. This is similar to Fermi heating [15] and has been described by the Hard Wall Model [16] or other more elaborated models [17][18][19][20][21][22][23][24][25][26][27][28][29]. Here, we demonstrate that this understanding is not complete, via a modeling study of symmetric argon and helium plasmas driven at 13.56 MHz.…”

Section: Introductionsupporting

confidence: 75%

The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas

Schulze

Donkó

Derzsi

et al. 2014

Plasma Sources Sci. Technol.

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Abstract. We investigate the electron heating dynamics in electropositive argon and helium capacitively coupled RF discharges driven at 13.56 MHz by Particle in Cell simulations and by an analytical model. The model allows to calculate the electric field outside the electrode sheaths, space and time resolved within the RF period. Electrons are found to be heated by strong ambipolar electric fields outside the sheath during the phase of sheath expansion in addition to classical sheath expansion heating. By tracing individual electrons we also show that ionization is primarily caused by electrons that collide with the expanding sheath edge multiple times during one phase of sheath expansion due to backscattering towards the sheath by collisions. A synergistic combination of these different heating events during one phase of sheath expansion is required to accelerate an electron to energies above the threshold for ionization. The ambipolar electric field outside the sheath is found to be time modulated due to a time modulation of the electron mean energy caused by the presence of sheath expansion heating only during one half of the RF period at a given electrode. This time modulation results in more electron heating than cooling inside the region of high electric field outside the sheath on time average. If an electric field reversal is present during sheath collapse, this time modulation and, thus, the asymmetry between the phases of sheath expansion and collapse will be enhanced. We propose that the ambipolar electron heating should be included in models describing electron heating in capacitive RF plasmas.

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Section: Introductionsupporting

confidence: 75%

The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas

Schulze

Donkó

Derzsi

et al. 2014

Plasma Sources Sci. Technol.

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“…Changing these two global control parameters affects the electron heating dynamics and the plasma density. Under such low-pressure conditions the electron heating is typically dominated by stochastic [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and ambipolar heating [20] during the phases of sheath expansion at both electrodes in electropositive discharges. This heating mode is typically called the α-mode [21].…”

Section: Introductionmentioning

confidence: 99%

The effect of the driving frequency on the confinement of beam electrons and plasma density in low-pressure capacitive discharges

Wilczek

Trieschmann

Schulze

et al. 2015

Plasma Sources Sci. Technol.

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The effect of changing the driving frequency on the plasma density and the electron dynamics in a capacitive radio-frequency argon plasma operated at low pressures of a few Pa is investigated by particle-in-cell/Monte-Carlo collision simulations and analytical modeling. In contrast to previous assumptions, the plasma density does not follow a quadratic dependence on the driving frequency in this non-local collisionless regime. Instead, a step-like increase at a distinct driving frequency is observed. Based on an analytical power balance model, in combination with a detailed analysis of the electron kinetics, the density jump is found to be caused by an electron heating mode transition from the classical α-mode into a low-density resonant heating mode characterized by the generation of two energetic electron beams at each electrode per sheath expansion phase. These electron beams propagate through the bulk without collisions and interact with the opposing sheath. In the low-density mode, the second beam is found to hit the opposing sheath during its collapse. Consequently, a large number of energetic electrons is lost at the electrodes resulting in a poor confinement of beam electrons in contrast to the classical α-mode observed at higher driving frequencies. Based on the analytical model this modulated confinement quality and the related modulation of the energy lost per electron lost at the electrodes is demonstrated to cause the step-like change of the plasma density. The effects of a variation of the electrode gap, the neutral gas pressure, the electron sticking and secondary electron emission coefficients of the electrodes on this step-like increase of the plasma density are analyzed based on the simulation results.

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“…The detailed description of the sheath formation in CCP discharges can be seen in literature [6][7][13][14][15][16]. In order to analyze the effect of ion mass and charge, a selfconsistent semi-infinite particle-in-cell (PIC) scheme has been used to investigate the spatio-temporal evolution of electric field in CCP discharges; in this algorithm both the electrons/ ions respond self-consistently as in conventional PIC method.…”

Section: Simulation Approach and Parametersmentioning

confidence: 99%

“…In general the capacitive discharge is agitated by applying a potential across the electrodes in contact with plasma [6]; naturally it leads to a plasma sheath formation near electrodes with a span of electric field characterised by Debye length (λ d ). This leads to substantial potential drop across the sheath and hence a large time varying disturbance of the plasma density which causes a complex electric field in the plasma layers adjacent to the electrode [7]. The electrons interacting with oscillating sheath on an average gain energy in traversing across this field and redistribute this excess energy with low energy electrons in the phase mixing (transition) regime [5] between sheath and bulk plasma.…”

Section: Introductionmentioning

confidence: 99%

Effect of Mass and Charge of Ionic Species on Spatio‐Temporal Evolution of Transient Electric Field in CCP Discharges

Sharma

Mishra

Kaw

et al. 2015

Contrib. Plasma Phys.

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The formation of capacitive sheath and existence of the transition electric field between sheath edge and bulk plasma in RF-CCP discharge is predicted (PRL 89, 265006 2002); such structures are sensitive to the plasma composition. On the basis of semi-infinite particle-in-cell (PIC) simulation the effect of charge and mass of ionic species on the spatio-temporal evolution of the transient electric field and phase mixing phenomena in linear and weakly nonlinear regime has been explored. As an important feature, the simulation results predict that the maximum amplitude of the transient electric field decreases with increasing ionic mass and charge; further the sheath width increases with increasing ionic mass while follow opposite trend with increasing ionic charge. The excitation of wave like structures in the transition region and efficient energy transport to the bulk region of CCP discharges in a nonlinear regime has also been predicted.

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Collisionless heating in radio-frequency discharges: a review

Cited by 120 publications

References 99 publications

The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas

The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas

The effect of the driving frequency on the confinement of beam electrons and plasma density in low-pressure capacitive discharges

Effect of Mass and Charge of Ionic Species on Spatio‐Temporal Evolution of Transient Electric Field in CCP Discharges

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