Now showing 1 - 10 of 17
  • Publication
    Shorter-wavelength extreme-UV sources below 10nm
    A next-generation laser-produced plasma system based on rare-earth targets generates strong resonant line emissions at 6.5–6.7nm.
  • Publication
    Configuration Interaction in Charge Exchange Spectra of Tin and Xenon
    Charge state specific extreme ultraviolet spectra from both tin ions and xenon ions have been recorded at Tokyo Metropolitan University. The Electron Cyclotron Resonance Source spectra were produced from charge exchange collisions between the ions and rare gas target atoms. In order to identify unknown spectral lines of tin and xenon, atomic structure calculations were performed for Sn14+ - Sn17+ and for Xe 16+ - Xe20+ using the Hartree-Fock with Configuration Interaction code of Cowan. The energies of the capture states involved in the single electron process that occurs in these slow collisions are estimated using the classical over barrier model.
      683Scopus© Citations 2
  • Publication
    The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm
    We have demonstrated the effect of viewing angle on the extreme ultraviolet (EUV) emission spectra of gadolinium (Gd) near 6.7 nm. The spectra are shown to have a strong dependence on viewing angle when produced with a laser pulse duration of 10 ns, which may be attributed to absorption by low ion stages of Gd and an angular variation in the ion distribution. Absorption effects are less pronounced at a 150-ps pulse duration due to reduced opacity resulting from plasma expansion. Thus for evaluating source intensity it is necessary to allow for variation with both viewing angle and target orientation.
      487Scopus© Citations 17
  • Publication
    Dielectronic recombination of Pd-like gadolinium
    (American Physical Society, 2012-01) ; ; ;
    As research and development of extreme ultraviolet lithography (EUVL) sources at 6.7 nm (which will be based on emission from ionized gadolinium) has already begun, reliable atomic data are required in order to determine the optimum plasma conditions. However, the complexity of the atomic structure means that ab initio level-resolved dielectronic recombination (DR) calculations are currently unavailable for the ions of interest. Here we report the first detailed calculation of the DR rate coefficients for the ground state and first excited states of Pd-like gadolinium. Energy levels, radiative transition probabilities, and autoionization rates of Ag-like gadolinium for [Kr]4d94fnl, [Kr]4p54d104fnl, [Kr]4d95l'nl, and [Kr]4d96l'nl (n ≤ 18) complexes were calculated using the flexible atomic code (FAC). It was found that inclusion of 4p54d104fnl configurations has significant influence on the total DR rate coefficient. The DR rate coefficients obtained here are compared with radiative recombination and three-body recombination coeffcients. The results show that the DR rate coefficient is almost an order of magnitude higher than the coefficients for the other two recombination processes combined at plasma electron temperatures around 110 eV, which suggests that the DR process should be included in theoretical modeling for Pd-like gadolinium in EUVL source plasmas.
      393Scopus© Citations 5
  • Publication
    Feasibility study of broad band efficient "water window" source
    We demonstrate a table-top broadband emission water window source based on laser-produced high-Z plasmas. Resonance emission from multiply charged ions merges to produce intense unresolved transition arrays in the 2 to 4 nm region, extending below the carbon K edge (4.37 nm). Arrays resulting from n = 4−4 transitions are overlaid with n = 4−5 emission and shift to shorter wavelength with increasing atomic number. From spectral analysis, a guideline for microscope construction design for single-shot live cell imaging is proposed based on the use of a bismuth plasma source, coupled with multilayer mirror optics.
      617Scopus© Citations 66
  • Publication
    Scaling of laser produced plasma UTA emission down to 3 nm for next generation lithography and short wavelength imaging
    An engineering prototype high average power 13.5-nm source has been shipped to semiconductor facilities to permit the commencement of high volume production at a 100 W power level in 2011. In this source, UTA (unresolved transition array) emission of highly ionized Sn is optimized for high conversion efficiency and full recovery of the injected fuel is realized through ion deflection in a magnetic field. By use of a low-density target, satellite emission is suppressed and full ionization attained with short pulse CO2 laser irradiation. The UTA is scalable to shorter wavelengths, and Gd is shown to have similar conversion efficiency to Sn (13.5 nm) at a higher plasma temperature, with a narrow spectrum centered at 6.7 nm, where a 70% reflectivity mirror is anticipated. Optimization of short pulse CO2 laser irradiation is studied, and further extension of the same method is discussed, to realize 100 W average power down to a wavelength of 3 nm
      602Scopus© Citations 9
  • Publication
    Interpretation of spectral emission around 20 nm region from tungsten ions observed in fusion device plasmas
    We have measured extreme ultraviolet (EUV) spectra from tungsten ions around 20 nm region in plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The spectra after injecting a tungsten pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer. Quasicontinuum spectral feature arising from unresolved transition array (UTA) was observed around 20 nm region in plasmas with temperatures below 1.0 keV. This structure is reasonably considered to be the same one as those observed in another tokamak device or laser produced plasmas under low temperature conditions. Atomic structure calculations have been performed for tungsten ions with open 5p, 5s and 4f subshells (W7+–W27+) to interpret this commonly observed feature around 20 nm. Wavelengths and gA values for these transitions were calculated, and their mean wavelengths and extent were compared with the observations, which suggests that the emission largely arises from n = 5–5 transitions in stages lower than W27+.
      207Scopus© Citations 26
  • Publication
    Simplified 1-D calculation of 13.5-nm emission in a tin plasma including radiation transport
    (American Institute of Physics, 2009-12-04) ; ; ;
    Many next generation lithography schemes for the semiconductor industry are based on a 13.5-nm tin plasma light source, where hundreds of thousands of 4d-4f, 4p-4d, and 4d-5p transitions from Sn5+–Sn13+ ions overlap to form an unresolved transition array. To aid computation, transition arrays are treated statistically, and Hartree-Fock results are used to calculate radiation transport in the optically thick regime with a 1-D Lagrangian plasma hydrodynamics code. Time-dependent spectra and conversion efficiencies of 2% in-band 13.5-nm emission to laser energy are predicted for a Nd:YAG laser incident on a pure tin slab target as a function of laser power density and pulse duration at normal incidence. Calculated results showed a maximum conversion efficiency of 2.3% for a 10-ns pulse duration at 8.0 x 1010 W/cm2 and are compared to experimental data where available. Evidence for the need to include lateral expansion is presented.
      220Scopus© Citations 9
  • Publication
    Tungsten spectra recorded at the LHD and comparison with calculations
    We have measured extreme ultraviolet (EUV) spectra from highly charged tungsten ions in low-density and high-temperature plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The EUV spectra emitted after injection of a tungsten pellet into a hydrogen plasma were recorded at plasma temperatures of 1.5 and 3 keV and were dominated by an intense transition array in the 4.5–6.5 nm region, the profile and extent of which was different in both spectra. Some discrete lines present were identified by comparison with existing spectral data while atomic structure calculations showed that the dominant emission in both arose from Δn = 0, n = 4–n = 4 transitions and the main differences could be attributed to the appearance of the 4p–4d and 4s–4p transitions from W XXXIX to W XLVI in the higher temperature spectrum. Comparison with calculations showed that the dominant emission in both temperature regimes arose from stages where the 4f subshell was either almost or completely stripped. We also investigated if the effect of low density favours transitions to the lowest level as observed in recently reported results.
      650Scopus© Citations 82
  • Publication
    Ground-State Configurations and Unresolved Transition Arrays in Extreme Ultraviolet Spectra of Lanthanide Ions
    (American Physical Society, 2010) ;
    Theoretical ground-state configurations of lanthanide ions calculated with the Cowan suite of codes are presented. Theoretical 4d - 4f and 4p - 4d spectra of Pd-like to Rb-like lanthanide ions calculated using the FAC relativistic code are also shown. The effects of configuration interaction are investigated and results compare favorably with experiments where, for increasing nuclear charge, strong emission peaks are observed to move towards shorter wavelength. The application of these strong emitters as extreme ultraviolet radiation sources, a topic of emerging interest, is discussed.
      723Scopus© Citations 28