How sheath properties change with gas pressure: modeling and simulation

Beving, Lucas; Hopkins, Matthew M.

doi:10.1088/1361-6595/ac85d7

Cited by 4 publications

(1 citation statement)

References 47 publications

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“…Many authors have used molecular dynamics and fluid simulations to study the characteristics of complex plasmas [14][15][16][17][18][19]. In former studies, electrons are considered to follow the Maxwellian distribution, but recently many studies have shown that electrons in the sheath region could vary from the Maxwellian distribution [20][21][22][23][24][25]. In 2000, Lima et al [26] first applied non-extensive statistics to investigate the propagation of electrostatic plane waves in collisionless and unmagnetized hot plasmas, and their simulation results were in good agreement with experimental data.…”

Section: Introductionmentioning

confidence: 99%

Properties of collisional plasma sheath with ionization source term and two-temperature electrons in an oblique magnetic field

Chen,

An,

Tan

et al. 2024

J. Phys. D: Appl. Phys.

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A collisional magnetized plasma sheath with two groups of electrons has been studied using a fluid model including the effects of the ionization source term and the collisional force between ions and neutral atoms. Two kinds of non-Maxwellian descriptions of electron velocity distribution, non-extensive distribution and truncated distribution, are applied in the model, and the ionization effects of both kinds are considered. By applying Sagdeev potential, the modified Bohm sheath criterion is derived. The effects of ionization, magnetic field, and high-temperature electron concentration ratio on plasma sheath density, potential, sheath thickness, and ion kinetic energy are studied. In cases with high background gas density, ion density accumulates at the sheath edge position, forming a peak and manifesting as a rapid drop in the potential profile. The distribution characteristics of electrons have a significant impact on the transport properties of ions. Oscillations and non-monotonic characteristics of net charge near the sheath edge occur as the magnetic field angle increases, leading to an increase in the sheath layer width. It can be seen that in the case of a collisional sheath structure with high-temperature electrons, it is essential to consider the sheath changes induced by the ionization and the collisional force. Compared to a symmetric electron velocity distribution, the actual thickness of the sheath layer in a truncated electron distribution assumption could be significantly reduced.

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Section: Introductionmentioning

confidence: 99%

Properties of collisional plasma sheath with ionization source term and two-temperature electrons in an oblique magnetic field

Chen,

An,

Tan

et al. 2024

J. Phys. D: Appl. Phys.

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Experimental quantification of ion flux reduction at the sheath edge due to ion–neutral collisions in low temperature plasmas

Lim,

Ghim

2024

Applied Physics Letters

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Reduction of the ion flux at the sheath edge due to ion–neutral collisions in low temperature DC plasmas is experimentally quantified for low to intermediate neutral gas pressures (<102 mTorr). The reduction factor is defined as a ratio of the ion flux at the sheath edge in a collisional plasma to that in a collisionless limit in this work. Its quantification as a function of the collisionality with a Langmuir probe has been hindered since the measured data contain two intermingled effects, namely, the flux reduction and the sheath expansion, which are difficult to isolate one from the other. The sheath expansion effect with and without the flux reduction effect are analyzed, and by comparing the two, the reduction factor as a function of the collisionality has been estimated with Langmuir probe data from approximately 1000 systematic scans of the plasma conditions. Neutral gas pressures ranging from 0.2–30.0 mTorr for Ar and 1.0–65.0 mTorr for He discharges are generated in a multidipole chamber with hot filaments. The estimated reduction factors are found to agree with the results from the particle-in-cell simulations for He discharges [Beving et al., Plasma Sources Sci. Technol. 31, 084009 (2022)]. The estimated reduction factors for Ar discharges are larger than those for He discharges, and the dependence of the reduction factor on species is discussed. Reduction of the ion flux at the sheath edge at intermediate gas pressures highlights the importance of taking into account ion–neutral collisions in many plasma applications.

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Voltage waveform tailoring for high aspect ratio plasma etching of SiO2 using Ar/CF4/O2 mixtures: Consequences of low fundamental frequency biases

Krüger,

Lee,

Nam

et al. 2024

Physics of Plasmas

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The use of non-sinusoidal waveforms in low pressure capacitively coupled plasmas intended for microelectronics fabrication has the goal of customizing ion and electron energy and angular distributions to the wafer. One such non-sinusoidal waveform uses the sum of consecutive harmonics of a fundamental sinusoidal frequency, f0, having a variable phase offset between the fundamental and even harmonics. In this paper, we discuss results from a computational investigation of the relation between ion energy and DC self-bias when varying the fundamental frequency f0 for capacitively coupled plasmas sustained in Ar/CF4/O2 and how those trends translate to a high aspect ratio etching of trenches in SiO2. The fundamental frequency, f0, was varied from 1 to 10 MHz and the relative phase from 0° to 180°. Two distinct regimes were identified. Average ion energy onto the wafer is strongly correlated with the DC self-bias at high f0, with there being a maximum at φ = 0° and minimum at φ = 180°. In the low frequency regime, this correlation is weak. Average ion energy onto the wafer is instead dominated by dynamic transients in the applied voltage waveforms, with a maximum at φ = 180° and minimum at φ = 0°. The trends in ion energy translate to etch properties. In both, the high and low frequency regimes, higher ion energies translate to higher etch rates and generally preferable final features, though behaving differently with phase angle.

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How sheath properties change with gas pressure: modeling and simulation

Cited by 4 publications

References 47 publications

Properties of collisional plasma sheath with ionization source term and two-temperature electrons in an oblique magnetic field

Properties of collisional plasma sheath with ionization source term and two-temperature electrons in an oblique magnetic field

Experimental quantification of ion flux reduction at the sheath edge due to ion–neutral collisions in low temperature plasmas

Voltage waveform tailoring for high aspect ratio plasma etching of SiO2 using Ar/CF4/O2 mixtures: Consequences of low fundamental frequency biases

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