Structured discharges in high frequency plasmas

Penfold, A. S.; Thornton, J. A.; Warder, R.C.

doi:10.1007/bf01594013

Cited by 15 publications

(15 citation statements)

References 9 publications

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“…However, the number of striations per unit length remained constant at different interelectrode distances. For driving frequencies of 70, 29,6, 4.2, and 3.7 MHz, they observed 8,9,10,11,and 12 striations at L=30 cm. Light emission oscillated at the second harmonic of the applied voltage.…”

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confidence: 95%

“…Plasma stratification in molecular gases remains poorly understood.Standing striations have been also observed in radiofrequency (RF) discharges [5]. In Capacitively Coupled Plasma (CCP) created between two wires wrapped around a long dielectric tube, standing striations were observed in Argon over a certain range of frequencies and gas pressures [6,7]. Their wavelength is proportional to the tube radius and decreases with increasing gas pressure.…”

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confidence: 99%

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Plasma stratification in radio-frequency discharges in argon gas

Kolobov¹,

Arslanbekov²,

Levko³

et al. 2020

J. Phys. D: Appl. Phys.

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We conducted experimental studies and computer simulations of standing striations in capacitive coupled plasma in Argon gas. Standing striations were observed at frequencies 3.6, 8.4 and 19.0 MHz, in a pressure range 0.05-10 Torr, tube radius R=1.1 cm, for a certain range of discharge currents (plasma densities). Numerical simulations revealed similar nature of standing striations in CCP and moving striations in DC discharges under similar discharge conditions. Comparison of computer simulations with experimental observations helped clarify the nature of these striations. The non-linear dependence of the ionization rate on electron density is shown to be the main underlying mechanism of the stratification phenomena. DOI:XXXPlasma stratification often occurs in laboratory devices and has been observed in space plasmas [1]. The most studied are striations in direct current (DC) glow discharges [2]. Moving striations are usually observed in noble gases, while standing striations are typical for molecular gases. The nature of moving striations (also called ionization waves) in noble gases is relatively well understood [3,4]. Plasma stratification in molecular gases remains poorly understood.Standing striations have been also observed in radiofrequency (RF) discharges [5]. In Capacitively Coupled Plasma (CCP) created between two wires wrapped around a long dielectric tube, standing striations were observed in Argon over a certain range of frequencies and gas pressures [6,7]. Their wavelength is proportional to the tube radius and decreases with increasing gas pressure. The wavelength varies discontinuously with changing the interelectrode distance in such a way that an integer number of standing waves always forms between the electrodes. The wavelength weakly depends on driving frequency in the range from 3 MHz to 60 MHz. Although discussions of surface-wave and kinetic effects can be found in the literature, no satisfactory explanations of these striations have been proposed so far. Standing striations have been also observed in Inductively Coupled Plasma (ICP) for certain geometries and discharge conditions [8,9].Striations appeared also in Particle-in-Cell (PIC) simulations of plasmas in different gases and gas mixtures [10,11,12]. Plasma stratification, as an example of selforganization at the kinetic level, remains a great challenge for the plasma science and physics of gas discharges [13].Previously, standing striations in argon CCP have been observed in a range of frequencies 3-80 MHz and gas pressure 2 Torr, in a tube with radius R=1.25 cm [7]. By changing the driving frequency and the distance L between the electrodes, the researchers were able to change the number of striations. However, the number of striations per unit length remained constant at different interelectrode distances. For driving frequencies of 70, 29,6, 4.2, and 3.7 MHz, they observed 8,9,10,11,and 12 striations at L=30 cm. Light emission oscillated at the second harmonic of the applied voltage. The nature of the striations remained unclear...

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Plasma stratification in radio-frequency discharges in argon gas

Kolobov¹,

Arslanbekov²,

Levko³

et al. 2020

J. Phys. D: Appl. Phys.

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“…In these systems, the mechanisms of striation formation are still not fully understood, although efforts have been made to explain them via theories based on the electron kinetics. Several types of striations in electropositive RF discharges were analyzed by Penfold and coworkers, and they concluded that the underlying mechanisms in RF and DC glow discharges are similar [23].Until recently, striated structures have never been observed in electronegative Capacitively Coupled RF (CCRF) plasmas, which have important applications in the semiconductor industry for etching and 3 / 31 Striations in electronegative capacitively coupled radio-frequency plasmas: analysis of the pattern formation and the effect of the driving frequency 3 / 31 deposition processes [24]. In electropositive CCRF plasmas the RF voltage between the two electrodes drops primarily across the sheath regions, while the electric field strength in the bulk plasma is quite weak.The electrons gain energy primarily at the edges of the oscillating sheaths (α-mode) [25][26][27][28].…”

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confidence: 99%

Striations in electronegative capacitively coupled radio-frequency plasmas: analysis of the pattern formation and the effect of the driving frequency

Liu

Korolov

Schüngel

et al. 2017

Plasma Sources Sci. Technol.

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Self-organized striated structures of the plasma emission have recently been observed in capacitive radiofrequency CF 4 plasmas by Phase Resolved Optical Emission Spectroscopy (PROES) and their formation was analyzed and understood by Particle in Cell / Monte Carlo Collision (PIC/MCC) simulations [Y.-X.Liu, et al. Phys. Rev. Lett. 116, 255002 (2016)]. The striations were found to result from the periodic generation of double layers due to the modulation of the densities of positive and negative ions responding to the externally applied RF potential. In this work, an in-depth analysis of the formation of striations is given, as well as the effect of the driving frequency on the plasma parameters, such as the spatially modulated charged species densities, the electric field, and the electron power absorption is studied by PROES measurements, PIC/MCC simulations, and an ion-ion plasma model. The measured spatiotemporal electronic excitation patterns at different driving frequencies show a high degree of consistency with the simulation results. The striation gap (i.e., the distance between two ion density maxima) is found to be inversely proportional to the driving frequency. In the presence of striations the minimum (CF 3 + , F − ) ion densities in the bulk region exhibit an approximately quadratic increase with the driving frequency. For these densities, the eigenfrequency of the ion-ion plasma is near the driving frequency, indicating that a resonance occurs between the positive and negative ions and the oscillating electric field inside the plasma bulk. The maximum ion densities in the plasma bulk are found not to exhibit a simple dependence on the driving frequency, since these ion densities are abnormally enhanced within a certain frequency range due to the ions being focused into the "striations" by the spatially modulated electric field inside the bulk region.2 / 31 Striations in electronegative capacitively coupled radio-frequency plasmas: analysis of the pattern formation and the effect of the driving frequency 2 / 31 deposition (PECVD) -often performed at relatively high pressures, low driving frequencies, and in electronegative gasessince the striations can drastically affect various process relevant plasma parameters, e.g., the flux-energy distribution functions of different charged species.One of the most well-known scenarios is the self-organized striated structure occurring in the positive column region of dc glow discharges, wherein ion-acoustic or ionization waves are generally considered to be responsible for their appearance [1,[11][12][13]. Over the past few years, several types of striated structures have been observed in different versions of atmospheric pressure plasma jets (APPJ). Depending on the discharge conditions, the plasma streamer ejected from the nozzle was found in [14,15] to be stratified into stationary bright and dark slender regions between the nozzle and the target plate. Very recently, a stratified filament occurring in the discharge tube of a RF argon APPJ was observed in num...

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“…25,26) Striations have been found in electropositive pure Ar discharges. 2,3) In this sense, striations are apparently different from instabilities (transitions between low-density capacitively driven discharge and high-density inductively driven discharge) found only in inductively coupled electronegative plasmas. 27) Figure 2 shows the time variation in the instantaneous electron density profile after each cycle, showing the evolution of a striation from an initially uniform discharge at 100 mTorr driven by a coil current of 35.0 A.…”

Section: Resultsmentioning

confidence: 97%

“…These mechanisms considered together may be the so-called ''ionization wave''. 2,3) At the end of this section, a comment will be made about another limitation of the 1D ICP model developed and used in this work. One may be curious about how many striations appear when the length of the computation domain is doubled (2L) or tripled (3L).…”

Section: Resultsmentioning

confidence: 99%

Particle-in-Cell/Monte Carlo Collision Simulations of Striations in Inductively Coupled Plasmas

Denpoh¹

2012

Jpn. J. Appl. Phys.

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Striations in inductively coupled plasmas (ICPs) appear as a series of cocoons beneath a coil through which a source current is driven. In this study, we have simulated striations in ICPs using the particle-in-cell/Monte Carlo collision method. The simulated effects of pressure on striation characteristics are in good agreement with experimental observations. It is found that the discharge structure and electron heating mechanism of striated ICPs are markedly different from those of normal ICPs. In particular, electron heating occurs once in one rf cycle in striated ICPs but twice in normal ICPs. Electron heating in striated ICPs may be ascribed to a strong self-excited electric field induced by the oscillating motion of the electron density at approximately the ion density, resulting in a high electron temperature. Furthermore, the relationship between the spatial period of the striation and the discharge space is put forward as a generation criterion for striations in rf discharges. Striations tend to occur when the region of plasma generation due to ionization is adjacent to walls where plasma is lost. #

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Structured discharges in high frequency plasmas

Cited by 15 publications

References 9 publications

Plasma stratification in radio-frequency discharges in argon gas

Plasma stratification in radio-frequency discharges in argon gas

Striations in electronegative capacitively coupled radio-frequency plasmas: analysis of the pattern formation and the effect of the driving frequency

Particle-in-Cell/Monte Carlo Collision Simulations of Striations in Inductively Coupled Plasmas

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