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Title: Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer

Abstract

Low-energy neutral beam sources are very promising candidates for realization of next generation ultralarge-scale integrated devices. The use of pulsed inductively coupled plasma and surface (wall) neutralizer appears to be an efficient way of producing high-flux low-energy neutral beams. Measurement of the time evolution of ion fluxes entering the neutralizer plays an essential role in understanding and control of these neutral beam systems. Here the authors present a simple method for measuring the temporal dynamics of ion fluxes in neutral beam source described elsewhere [S. Samukawa et al., J. Vac. Sci. Technol. A 20, 1566 (2002)]. The method is based on the use of a low aspect ratio orifice in the center of neutralizer, magnetic filter, and Faraday cup. At some conditions, it allows (1) to measure the magnitudes of positive and negative wall ion fluxes in pulsed plasmas with an extremely high temporal resolution (better than 1 {mu}s) and (2) to examine the difference in surface neutralization between positive and negative ions. The measurements show that neutralization of hyperthermal ions is mainly controlled by geometry of plasma sheath adjacent to the surface neutralizer; however, negative ions are neutralized more easily than positive ones. The experimental results for SF{sub 6}more » (ion-ion) and Ar plasmas in combination with dc/rf bias are reported.« less

Authors:
; ;  [1]
  1. Institute of Fluid Science, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan)
Publication Date:
OSTI Identifier:
20853941
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films; Journal Volume: 25; Journal Issue: 1; Other Information: DOI: 10.1116/1.2402154; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANIONS; BEAM NEUTRALIZATION; FARADAY CUPS; ION BEAMS; MAGNETIC FILTERS; NEUTRAL BEAM SOURCES; ORIFICES; PLASMA; PLASMA SHEATH; SURFACES

Citation Formats

Abolmasov, Sergey N., Ozaki, Takuya, and Samukawa, Seiji. Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer. United States: N. p., 2007. Web. doi:10.1116/1.2402154.
Abolmasov, Sergey N., Ozaki, Takuya, & Samukawa, Seiji. Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer. United States. doi:10.1116/1.2402154.
Abolmasov, Sergey N., Ozaki, Takuya, and Samukawa, Seiji. Mon . "Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer". United States. doi:10.1116/1.2402154.
@article{osti_20853941,
title = {Characterization of neutral beam source based on pulsed inductively coupled discharge: Time evolution of ion fluxes entering neutralizer},
author = {Abolmasov, Sergey N. and Ozaki, Takuya and Samukawa, Seiji},
abstractNote = {Low-energy neutral beam sources are very promising candidates for realization of next generation ultralarge-scale integrated devices. The use of pulsed inductively coupled plasma and surface (wall) neutralizer appears to be an efficient way of producing high-flux low-energy neutral beams. Measurement of the time evolution of ion fluxes entering the neutralizer plays an essential role in understanding and control of these neutral beam systems. Here the authors present a simple method for measuring the temporal dynamics of ion fluxes in neutral beam source described elsewhere [S. Samukawa et al., J. Vac. Sci. Technol. A 20, 1566 (2002)]. The method is based on the use of a low aspect ratio orifice in the center of neutralizer, magnetic filter, and Faraday cup. At some conditions, it allows (1) to measure the magnitudes of positive and negative wall ion fluxes in pulsed plasmas with an extremely high temporal resolution (better than 1 {mu}s) and (2) to examine the difference in surface neutralization between positive and negative ions. The measurements show that neutralization of hyperthermal ions is mainly controlled by geometry of plasma sheath adjacent to the surface neutralizer; however, negative ions are neutralized more easily than positive ones. The experimental results for SF{sub 6} (ion-ion) and Ar plasmas in combination with dc/rf bias are reported.},
doi = {10.1116/1.2402154},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 1,
volume = 25,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • This study examined the optimal conditions of neutral beam generation to maintain a high degree of neutralization and focusing during beam energy variation for a neutral beam source based on inductively coupled plasma with a three-grid ion beam acceleration system. The neutral beam energy distribution was estimated by measuring the energy profiles of ions that 'survived' the neutralization after reflection. The energy measurements of the primary and reflected ions showed narrow distribution functions, each with only one peak. At higher beam energies, both the ratio of the ion energy loss to the primary energy and the degree of energy divergencemore » decreased, confirming the precise alignment of the neutral beam. The neutralization efficiency of the neutral beam source with a three-grid acceleration system was found to be affected mainly by the beam angle divergence rather than by the particle translation energy.« less
  • The authors developed a neutral beam source consisting of a 200-mm-diameter inductively coupled plasma etcher and a graphite neutralization aperture plate based on the design of a neutral beam source that Samukawa et al. [Jpn. J. Appl. Phys., Part 2 40, L779 (2001)] developed. They measured flux and energy of neutral particles, ions, and photons using a silicon wafer with a thermocouple and a Faraday cup and calculated the neutralization efficiency. An Ar neutral beam flux of more than 1 mA/cm{sup 2} in equivalent current density and a neutralization efficiency of more than 99% were obtained. The spatial uniformity ofmore » the neutral beam flux was within {+-}6% within a 100 mm diameter. Silicon etching using a F{sub 2}-based neutral beam was done at an etch rate of about 47 nm/min, while Cl{sub 2}-based neutral beam realized completely no undercut. The uniformity of etch rate was less than {+-}5% within the area. The etch rate increased by applying bias power to the neutralization aperture plate, which shows that accelerated neutral beam was successfully obtained. These results indicate that the neutral beam source is scalable, making it possible to obtain a large-diameter and uniform neutral beam, which is inevitable for application to mass production.« less
  • Key elements regarding the use of non-radioactive ionization sources will be presented as related to explosives detection by mass spectrometry and ion mobility spectrometry. Various non-radioactive ionization sources will be discussed along with associated ionization mechanisms pertaining to specific sample types.
  • Using a Langmuir probe, time resolved measurements of plasma parameters were carried out in a discharge produced by a pulsed dual frequency inductively coupled plasma source. The discharge was sustained in an argon gas environment at a pressure of 10 mTorr. The low frequency (P{sub 2} {sub MHz}) was pulsed at 1 kHz and a duty ratio of 50%, while high frequency (P{sub 13.56} {sub MHz}) was maintained in the CW mode. All measurements were carried out at the center of the discharge and 20 mm above the substrate. The results show that, at a particular condition (P{sub 2} {sub MHz} = 200more » W and P{sub 13.56} {sub MHz }= 600 W), plasma density increases with time and stabilizes at up to ∼200 μs after the initiation of P{sub 2} {sub MHz} pulse at a plasma density of (2 × 10{sup 17} m{sup −3}) for the remaining duration of pulse “on.” This stabilization time for plasma density increases with increasing P{sub 2} {sub MHz} and becomes ∼300 μs when P{sub 2} {sub MHz} is 600 W; however, the growth rate of plasma density is almost independent of P{sub 2} {sub MHz}. Interestingly, the plasma density sharply increases as the pulse is switched off and reaches a peak value in ∼10 μs, then decreases for the remaining pulse “off-time.” This phenomenon is thought to be due to the sheath modulation during the transition from “pulse on” to “pulse off” and partly due to RF noise during the transition period. The magnitude of peak plasma density in off time increases with increasing P{sub 2} {sub MHz}. The plasma potential and electron temperature decrease as the pulse develops and shows similar behavior to that of the plasma density when the pulse is switched off.« less
  • In situ Fourier transform infrared spectroscopy is used to characterize the plasma chemistry of pulsed 1,3-butadiene (H{sub 2}C=CHCH=CH{sub 2}) discharges subject to varying percentages of the duty cycle in a gaseous electronics conference cell. Variations in densities associated with the major observed spectral bands are closely examined as a function of duty cycle. The possible dissociation mechanisms responsible for all observed vibrations are investigated. For example, the data show that about 44% of CH{sub 2} stretching vibrations during continuous wave biasing are due to free CH{sub 2} daughter species, while only bound CH{sub 2} are observed during pulsing of themore » discharge. This indicates that only the {pi} bond of the C=C bond is cleaved during pulsed mode operation, with the {sigma} being cleaved during cw biasing.« less