49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007;
Orlando, Florida
Session TI2: Plasma Technology, Nozzles, and the First Wall
9:30 AM–12:30 PM,
Thursday, November 15, 2007
Rosen Centre Hotel
Room: Salon 3/4
Chair: David Ruzic, University of Illinois
Abstract ID: BAPS.2007.DPP.TI2.4
Abstract: TI2.00004 : Plasma Physics and Radiation Hydrodynamics in Development of EUV Light Sources for Lithography*
11:00 AM–11:30 AM
Preview Abstract
Abstract
Author:
Katsunobu Nishihara
(Osaka University)
Understanding of radiation generation in laser-produced high-Z
plasma (LPP) is important for inertial fusion, astrophysics and
x-ray source development. Extreme ultraviolet (EUV) light of 13.5
nm wavelength is strongly desired for manufacture of
next-generation microprocessors with node size less than 45 nm. A
commercial EUV lithography system would require output EUV power
of about 400 W into a solid angle of 2$\pi$ str within a 2{\%}
bandwidth (BW). Laser-produced tin (Sn) plasma at electron
temperature of 30-70 eV and ion density of 10$^{17-20}$ cm$^{-3}$
is an attractive light source due to its compactness and high
conversion efficiency (CE) from laser to EUV light [1]. The
critical issues for practical use are high CE and damage caused
by target debris.
Many 4d-4f transitions of Sn$^{8+}$ to Sn$^{13+}$ ions mainly
contribute to strong emission around 13.5 nm. We first discuss
the importance of satellite lines, opacity and photo excitation
in radiation transport, especially in high density plasmas
produced by 1 $\mu$m laser. Experiment and simulation
indicate that the maximum CE of 3{\%} is limited by these effects
for 1$\mu$m laser. We show that the use of a long wavelength
laser, such as CO$_{2}$ laser, results in higher CE of 3-6{\%},
since the spectral efficiency, the ratio of 13.5 nm emission
within 2{\%} BW to total radiation, increases with the reduction
of the plasma density. We present theoretical and experimental
results of the CE dependence on laser intensity, pulse duration
and laser wavelength. Radiation hydrodynamic simulations agree
fairly well with EUV spectra observed in the experiments.
High energy ions up to 10 keV generated in LPP cause damage to a
collecting mirror. We show that the maximum energy is essentially
determined from the ratio of plasma radius to Debye length. We
also show that the use of the long wavelength laser also reduces
the ion energy. We discuss mitigation of high energy ions by a
magnetic field and the stability of plasma expansion taking
finite ion Larmor radius effects into account.
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[1] K. Nishihara et al., Conversion Efficiency of LPP Sources,
EUV Sources
for Lithography (SPIE Press, Edited by V. Bakshi, (2006)).
*Work performed under the auspices of a Leading Project promoted by MEXT in Japan.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.TI2.4