A Study of tungsten spectra using Large Helical Device and Compact Electron Beam Ion Trap in NIFS

Morita, Shigeru*; Dong, C. F.*; Goto, Motoshi*; Kato, Daiji*; Murakami, Izumi*; Sakaue, Hiroyuki*; Hasuo, Masahiro*; Koike, Fumihiro*; Nakamura, Nobuyuki*; Oishi, Tetsutaro*; et al.

AIP Conference Proceedings 1545, p.143 - 152, 2013/07

https://doi.org/10.1063/1.4815848

Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. The ablation cloud of the impurity pellet is directly measured with visible spectroscopy.

Theoretical investigation of the spectrum and conversion efficiency of short wavelength extreme-ultraviolet light sources based on terbium plasmas

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*

Applied Physics Letters, 97(23), p.231501_1 - 231501_3, 2010/12

https://doi.org/10.1063/1.3524494

Emission spectrum and conversion efficiency of laser produced terbium plasmas are investigated theoretically on the basis of computational atomic data. It is shown that calculation reproduces the main peak of the experimental spectrum at nm, which originates from 4-4 transitions of near palladium like ions (Tb). Simple model of the isothermal expansion of plasma suggests that efficient emission can be obtained by pumping a plasma with a laser pulse with an intensity approximately one order of magnitude grater than in the case of tin sources at nm.

Atomic modeling of the plasma EUV sources

Sasaki, Akira; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

High Energy Density Physics, 5(3), p.147 - 151, 2009/09

https://doi.org/10.1016/j.hedp.2009.04.002

We study the radiative properties of the EUV source to address conditions to achieve an output power and efficiency required for its application to the next generation microlithography. An atomic model is developed based on the atomic data calculated by Hullac code, which is validated through detailed comparisons with experimental emission and a absorption spectra. The atomic model is improved with respect to the wavelength of the strong emission lines, and the number of satellite channels taken into account. As a result, the radiation hydrodynamics model is shown to successfully reproduce the experiments. We show Sn plasma is more efficient than Xe plasma because of the atomic number dependence of the emission wavelength, and the use of CO lasers as a pumping source has an advantage to reduce satellite contribution and to have narrower emission spectrum to obtain higher conversion efficiency.

Atomic processes in the LPP and LA-DPP EUV sources

Sasaki, Akira; Nishihara, Katsunobu*; Sunahara, Atsushi*; Furukawa, Hiroyuki*; Nishikawa, Takeshi*; Koike, Fumihiro*

Alternative Lithographic Technologies (Proceedings of SPIE Vol.7271), p.727130_1 - 727130_8, 2009/03

We investigate characteristic feature of the atomic radiation from tin plasmas, which allow one to obtain high power EUV emission efficiently. We develop a collisional radiative model of tin ions to calculate steady-state and time dependent ion abundance, level population, and coefficients of radiative transfer of the plasma. The model, which is based atomic data calculated using the Hullac code is refined both theoretically and experimentally. Calculation of the spectral emissivity and opacity are carried out over a wide range of plasma density and temperature, and pumping conditions to obtain high conversion efficiency are discussed.

Atomic model and optimization of EUV light source

Nishihara, Katsunobu*; Sunahara, Atsushi*; Sasaki, Akira; Tanuma, Hajime*; Koike, Fumihiro*; Fujioka, Shinsuke*; Nishimura, Hiroaki*; Shimada, Yoshinori*

Reza Kenkyu, 36(11), p.690 - 699, 2008/11

https://ci.nii.ac.jp/naid/10024447909

The critical issue for realization of a laser produced plasma (LPP) extreme ultraviolet (EUV) light source is the conversion efficiency (CE) from incident laser power to EUV radiation of 13.5 nm wavelength. From an atomic physics, we show that tin is the most suitable radiation material compared with xenon and lithium. We also show the optimization of laser and target conditions to obtain high CE using a power balance model. We propose a double-pulse irradiation scheme for high CE using a carbon dioxides laser and a droplet target.

Plasma physics and radiation hydrodynamics in developing an extreme ultraviolet light source for lithography

Nishihara, Katsunobu*; Sunahara, Atsushi*; Sasaki, Akira; Nunami, Masanori*; Tanuma, Hajime*; Fujioka, Shinsuke*; Shimada, Yoshinori*; Fujima, Kazumi*; Furukawa, Hiroyuki*; Kato, Takako*; et al.

Physics of Plasmas, 15(5), p.056708_1 - 056708_11, 2008/00

https://doi.org/10.1063/1.2907154

Atomic modeling of the plasma EUV sources

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Fujima, Kazumi*; Kagawa, Takashi*; Koike, Fumihiro*; Tanuma, Hajime*

High Energy Density Physics, 3(1-2), p.250 - 255, 2007/05

https://doi.org/10.1016/j.hedp.2007.02.031

no abstracts in English

Theoretical RCI simulation for spectra emitted from Sn and Xe ions as an EUV light source

Kagawa, Takashi*; Nishihara, Katsunobu*; Sasaki, Akira; Koike, Fumihiro*

Journal of Plasma and Fusion Research SERIES, Vol.7, p.245 - 248, 2006/00

no abstracts in English

Theoretical simulation of extreme UV radiation source for lithography

Fujima, Kazumi*; Nishihara, Katsunobu*; Kawamura, Toru*; Furukawa, Hiroyuki*; Kagawa, Takashi*; Koike, Fumihiro*; More, R.*; Murakami, Masakatsu*; Nishikawa, Takeshi*; Sasaki, Akira; et al.

Emerging Lithographic Technologies VIII, Proceedings of SPIE Vol.5374, p.405 - 412, 2004/00

no abstracts in English

Detailed modeling of the atomic process in the EUV source

Sasaki, Akira; Sunahara, Atsushi*; Nishihara, Katsunobu*; Nishikawa, Takeshi*; Koike, Fumihiro*; Tanuma, Hajime*

no journal, , 

We present a detailed atomic model of Sn plasmas. It is found that the conversion efficiency of the EUV source depends critically on the wavelength as well as the structure of emission lines. We calculate the wavelength and transition probabilities of Sn ions using the HULLAC code. The satellite line emission channels, which have significant contribution to the spectral width of the emission, are determined after iterative calculations, by changing the number of groups of multiply excited configurations included in the CR-model. Using the improved radiative constants, the radiation hydrodynamics simulation is shown to reproduce experimental spectrum. Calculation indicates increased spectral efficiency using low density plasmas, due to narrow spectrum in the absence of satellite lines, which suggests an advantage of using of a carbon dioxide laser as a pumping source.