Charged-species profiles in electronegative radio-frequency plasmas

Vender, D.; Stoffels, WW Winfred; Stoffels, E.; Kroesen, G.M.W.; Hoog, F. J. de

doi:10.1103/physreve.51.2436

Cited by 70 publications

(56 citation statements)

References 19 publications

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“…The negative ions are confined within this region; due to their low kinetic energy, they cannot penetrate into the sheath regions, where the time averaged potential is much lower than the plasma potential in the bulk. Similar density profiles are found in capacitively coupled single frequency oxygen discharges by different authors [41,42,44,49].…”

Section: Control Of the Density Profilessupporting

confidence: 70%

“…This has been our motivation of conducting a combined experimental, numerical and analytical investigation of CCRF discharges in pure oxygen. Oxygen discharges, being one of the simplest electronegative plasma system, provide an interesting scenario for theoretical modeling (see for example [41][42][43][44][45][46][47][48][49][50]52] and references therein) and experimental diagnostics [49,50,[52][53][54][55][56][57] of electronegative plasmas. In contrast to the previous work of the EAE in oxygen discharges with only numerical simulation [36], our complementary approach here certainly promises a more comprehensive description of the discharge properties.…”

Section: Introductionmentioning

confidence: 99%

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Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

Schüngel¹,

Zhang²,

Iwashita³

et al. 2011

J. Phys. D: Appl. Phys.

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To cite this version:E Schüngel, Q-Z Zhang, S Iwashita, J Schulze, L-J Hou, et al.. Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect. Journal of Physics D: Applied Physics, IOP Publishing, 2011, 44 (28) Abstract. By using a combined experimental, numerical and analytical approach, we investigate the control of plasma properties via the Electrical Asymmetry Effect (EAE) in a capacitively coupled oxygen discharge. In particular, we present the first experimental investigation of the EAE in electronegative discharges. A dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode and the discharge symmetry is controlled by adjusting the phase angle θ between the two harmonics. It is found that the bulk position and density profiles of positive ions, negative ions, and electrons have a clear dependence on θ, while the peak densities and the electronegativity stay rather constant, largely due to the fact that the time averaged power absorption by electrons is almost independent of θ. This indicates that the ion flux towards the powered electrode remains almost constant. Meanwhile, the dc self-bias and, consequently, the sheath widths and potential profile can be effectively tuned by varying θ. This enables a flexible control of the ion bombarding energy at the electrode. Therefore, our work proves the effectiveness of the EAE to realize separate control of ion flux and ion energy in electronegative discharges. At low pressure, the strength of resonance oscillations, which are found in the current of asymmetric discharges, can be controlled with θ.

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Section: Control Of the Density Profilessupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

Schüngel¹,

Zhang²,

Iwashita³

et al. 2011

J. Phys. D: Appl. Phys.

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“…These negative ion density fronts have been observed experimentally in steady state oxygen rf glow discharges sustained in capacitively-coupled parallel plate reactors [30,31]. The measured negative ion density profile tends to form a front at the electrode.…”

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confidence: 75%

“…(11) Fig.2 The experimental negative ion density profiles in the RF discharge in oxygen, pressure 100mtorr, frequency 13.56MHz, input power 10W [30]. Fig.…”

Section: Negative Ion Fronts In Afterglowmentioning

confidence: 99%

Negative ion density fronts

Kaganovich

2001

Physics of Plasmas

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Negative ions tend to stratify in electronegative plasmas with hot electrons (electron temperature T e much larger than ion temperature T i , T e >>T i ). The boundary separating a plasma containing negative ions, and a plasma, without negative ions, is usually thin, so that the negative ion density falls rapidly to zero -forming a negative ion density front. We review theoretical, experimental and numerical results giving the spatio-temporal evolution of negative ion density fronts during plasma ignition, the steady state, and extinction (afterglow). During plasma ignition, negative ion fronts are the result of the break of smooth plasma density profiles during nonlinear convection. In a steadystate plasma, the fronts are boundary layers with steepening of ion density profiles due to nonlinear convection also. But during plasma extinction, the ion fronts are of a completely different nature.Negative ions diffuse freely in the plasma core (no convection), whereas the negative ion front propagates towards the chamber walls with a nearly constant velocity. The concept of fronts turns out to be very effective in analysis of plasma density profile evolution in strongly non-isothermal plasmas.

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“…Nonlinear potential structures occur in plasma stratification between an electropositive outer shell (no negative ions in the plasma) and an electronegative core (negative ion containing plasma). This feature was theoretically studied [24][25][26][27][28] and experimentally observed [29,30]. Furthermore, it has been shown that inductive discharges are subject to relaxation oscillations near the capacitive to inductive mode transition (at intermediate powers) in the presence of negative ions [31][32][33][34].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of double layers in expanding plasmas

2007

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Double layers (DLs) have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures (between 0.1 and 1 mTorr) with the plasma expansion forced by a strongly diverging magnetic field. The DL remains static, robust to changes in boundary conditions, and its position is related to the magnetic field lines. The voltage drop across the DL increases with decreasing pressure, i.e. with increasing electron temperature (around 20 V at 0.17 mTorr). DLs were also observed in electronegative gases without a magnetic field over a greater range of pressure (0.5 to 10 mTorr). The actual profile of the electronegative DL is very sensitive to external parameters and intrusive elements, and they propagate at high negative ion fraction. Electrostatic probes measurements and laser induced photodetachment show discontinuities in all plasma parameters (electron density, electron temperature, negative ion fraction) at the DL position. The voltage drop across the electronegative DL is about 8 V, is independent of the gas pressure and therefore of the electron temperature.

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Charged-species profiles in electronegative radio-frequency plasmas

Cited by 70 publications

References 19 publications

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

Negative ion density fronts

Experimental investigation of double layers in expanding plasmas

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