Trapping of radiation in plasmas

Riley, Merle E.; Alford, W. J.

doi:10.2172/88576

Cited by 3 publications

(5 citation statements)

References 3 publications

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“…This radiation trapping [45][46][47][48] can lengthen the effective radiative lifetime of the excited state that produces the photon dramatically. This, in turn, gives nonradiative quenching processes much more time to quench the excited state before it emits a VUV photon.…”

Section: Resultsmentioning

confidence: 99%

Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges

Woodworth

Riley

Amatucci

et al. 2001

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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@In this paper, we report the absolute intensities of ultraviolet light between 4.9 eV and 24 eV ( 250 m-n to 50 mn ) striking a silicon wafer in a number of oxide-etch processing discharges. Our emphasis is on photons with energies greater than 8.8 eV, which have enough energy to damage Si02. These discharges were in an inductively-driven Gaseous Electronics Conference reference cell which had been modified to more closely resemble commercial etching tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the VUV light in these discharges is strongly trapped. For the pure halocarbon gases examined in these experiments ( CzF& CHF3, C4F8 ), the fluxes of VUV photons to the wafer varied fi'om 1 x 1015 to 3 x 1015photons/cm2sec or equivalently from 1.5 to 5 mW/cm2. These measurements imply that O.10/0to 0.3 0/0 of the rf source power to these discharges ends up hitting the wafer as VUV photons for our typical 20 mT, 200 W rf discharges. For typical "ashing" discharges containing pure oxygen, the VUV intensities are slightly higher -about 8 mW/cm2 . As argon or hydrogen diluents are added to the fluorocarbon gases, the VUV intensities increase dramatically, with a 10/1 0/1 Omixture of Ad C2F~H2yielding VUV fluxes on the wafer 26 mW/cm2 and pure argon discharges yielding 52 mWlcm2 . Adding an rf bias to the wafer had only a small effect on the VUV observed through a side-port of the GEC cell.

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Section: Resultsmentioning

confidence: 99%

Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges

Woodworth

Riley

Amatucci

et al. 2001

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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“…From about 20% xenon concentration and higher, the dimer emission is stronger than emission from the resonant line. The emission from the resonant line is reduced because of enhanced radiation trapping by the collisional broadening of the resonance line [20,21]. At these pressures, collisional broadening is the dominant broadening mechanism of the resonance lines in the helium-xenon mixture [21].…”

Section: Resultsmentioning

confidence: 99%

“…The emission from the resonant line is reduced because of enhanced radiation trapping by the collisional broadening of the resonance line [20,21]. At these pressures, collisional broadening is the dominant broadening mechanism of the resonance lines in the helium-xenon mixture [21]. Although emission from the transitions from higher excited states to the [6s] and [6s ] states which emit in the range from about 450 nm in the blue extending into the infrared does exist, the details of those lines are beyond the scope of the present model.…”

Section: Resultsmentioning

confidence: 99%

“…The cross sections for xenon excitation and ionization reactions were all obtained from ab initio calculations [17,18] except for ionization from the xenon ground state for which we used experimental cross section data [19]. A simple model for the resonant decay rate based on the Holstein model [20,21], which includes the effect of radiation trapping of the resonant 147 nm and 129 nm lines, is used to estimate the resonant VUV emission in the discharge. At these pressures of several hundred torr, most of the resonant trapping in xenon is due to collisional pressure broadening [21] rather than Doppler broadening.…”

Section: Heavy-body Reactions and Resonant Photon Trappingmentioning

confidence: 99%

“…A simple model for the resonant decay rate based on the Holstein model [20,21], which includes the effect of radiation trapping of the resonant 147 nm and 129 nm lines, is used to estimate the resonant VUV emission in the discharge. At these pressures of several hundred torr, most of the resonant trapping in xenon is due to collisional pressure broadening [21] rather than Doppler broadening. The emission from the xenon dimer peaks at 173 nm with a full width at half maximum of about 10 nm on either side and is not trapped.…”

Section: Heavy-body Reactions and Resonant Photon Trappingmentioning

confidence: 99%

See 2 more Smart Citations

One-dimensional fluid simulations of a helium - xenon filled ac colour plasma flat panel display pixel

Veerasingam

Campbell

McGrath

1997

Plasma Sources Sci. Technol.

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fluid simulations are used to model a helium-xenon filled ac plasma display pixel. The model includes four levels for helium atomic states, seven levels for xenon atomic states and a xenon dimer state. The model also includes VUV emission including photon trapping due to collisional broadening from the resonant atomic xenon at wavelengths of 129 nm and 147 nm and from non-resonant emission by the xenon dimer molecule peaked at 173 nm. Simulations are performed for a gap width (d ) of 100 microns at a pressure (P ) of 400 Torr using varying xenon concentrations. At low xenon concentrations, emission is primarily in the 147 nm wavelength but shifts toward the xenon dimer above about 20% xenon in the mixture. At 2% xenon, the calculated VUV emission is about 85% from the resonant atomic xenon state at 147 nm, about 13% from the dimer and about 2% from the resonant 129 nm line. Emission from the 129 nm line is insignificant due to collisional quenching of the xenon 6s states. The discharge efficiency, defined as the VUV photons/watt dissipated, increases with xenon content with an optimum at about 30% xenon. For opposed electrode geometry, as the xenon concentration is increased from 2% to X % xenon, the simulations show that the applied voltages scale approximately as (X /2) 1/4 . At a fixed Pd , a higher pressure yields more VUV emission than using a larger gap width.

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Photoionization of air species as impurities in atmospheric pressure helium plasma

Janalizadeh,

Pasko

2023

Plasma Sources Sci. Technol.

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We revisit the problem of photoionization of small admixtures of nitrogen and oxygen molecules in atmospheric pressure helium plasma originally formulated in pioneering work of [Naidis, J. Phys. D: Appl. Phys., 43(40):402001, 2010]. Radiation trapping of resonance emission lines of atomic helium is quantified, and it is demonstrated that photoionization occurs due to radiative decay of the electronic A state of helium molecule. Collisions and atomic precursors that populate the excited A state of the helium molecule are clearly identified. Einstein probabilities for transition from bound and quasi-bound rovibrational levels of the A state to the continuum of the ground X state are provided. A kinetic scheme for production of the fast component of ultraviolet emissions in atmospheric helium plasma is proposed. Photoionization of molecular oxygen and molecular nitrogen as impurities in a 99.9% and 99.99% purity helium is studied.

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Trapping of radiation in plasmas

Cited by 3 publications

References 3 publications

Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges

Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges

One-dimensional fluid simulations of a helium - xenon filled ac colour plasma flat panel display pixel

Photoionization of air species as impurities in atmospheric pressure helium plasma

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