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Yugami, Noboru
Preferred name
Yugami, Noboru
Official Name
Yugami, Noboru
Research Output
Now showing 1 - 8 of 8
- PublicationShorter-wavelength extreme-UV sources below 10nm(SPIE, 2011-10-07)
; ; ; ; ; ; ; A next-generation laser-produced plasma system based on rare-earth targets generates strong resonant line emissions at 6.5–6.7nm.347 - PublicationThe effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm(American Institute of Physics, 2012)
; ; ; ; ; ; ; ; ; ; 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.497Scopus© Citations 18 - PublicationGd plasma source modeling at 6.7 nm for future lithography(American Institute of Physics, 2011-12-05)
; ; ; ; ; ; ; Plasmas containing gadolinium have been proposed as sources for next generation lithography at 6.x nm. To determine the optimum plasma conditions, atomic structure calculations have been performed for Gd11+ to Gd27+ ions which showed that n=4 - n=4 resonance transitions overlap in the 6.5 – 7.0 nm region. Plasma modeling calculations, assuming collisional-radiative equilibrium, predict that the optimum temperature for an optically thin plasma is close to 110 eV and that maximum intensity occurs at 6.76 nm under these conditions. The close agreement observed between simulated and experimental spectra from laser and discharge produced plasmas indicates the validity of our approach.487Scopus© Citations 32 - PublicationOptimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma(American Institute of Physics, 2012)
; ; ; ; ; ; ; ; ; ; We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.626Scopus© Citations 42 - PublicationSystematic investigation of self-absorption property and conversion efficiency of 6.7-nm extreme ultraviolet sources(American Institute of Physics, 2010-12)
; ; ; ; ; ; ; ; ; We have demonstrated rare-earth plasma extreme ultraviolet sources at 6.7 nm to investigate the spectral behavior and the conversion efficiencies to different laser wavelength and the initial target densities. The conversion efficiency was maximized to be 0.9% at laser intensity of 7 × 1012 W/cm2 at its wavelength of 1064 nm, which is attributed to the minimum self-absorption effect by use of the low initial density target, together with the narrow spectrum. It is important to use a low initial density target and to produce low electron density plasmas for efficient EUV sources using the high-Z targets.411Scopus© Citations 51 - PublicationFeasibility study of broad band efficient "water window" source(American Institute of Physics, 2012)
; ; ; ; ; ; 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.618Scopus© Citations 67 - PublicationScaling of laser produced plasma UTA emission down to 3 nm for next generation lithography and short wavelength imaging(Society of Photo-optical Instrumentation Engineers, 2011-08-22)
; ; ; ; ; ; ; ; ; ; ; 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 nm604Scopus© Citations 9 - PublicationSpectral and temporal behavior of an alkali metal plasma extreme ultraviolet source for surface morphology applications(American Institute of Physics, 2011-02-28)
; ; ; ; ; ; ; ; We have characterized the emission spectrum and temporal history of a pure potassium plasma in a capillary discharge. Strong broadband emission was observed around 40 nm due to 3s−3p, 3p−3d, and 3d−4f transitions in ions ranging from K2+ to K4+ at a time-integrated electron temperature of about 12 eV. The temporal behavior of this emission strongly follows the recombination phase in the plasma and it was successfully reproduced by a hydrodynamic simulation of the potassium plasma which accounted for atomic processes.388Scopus© Citations 3