2012 International Workshop on EUV and Soft X-Ray Sources
October 11th, 2012, UCD, Dublin, Ireland
Takeshi Higashiguchi
1
1
Utsunomiya University
2
HiLASE Project, Institute of Physics AS, Czech Republic
3
University College Dublin (UCD)
Akira Endo
2
and Gerry O'Sullivan
3
Session 11, S12
Highlights from a Recent BEUV
Source Workshop & Activities
JSAP, JPS, LSJ Ad-hoc workshop
Sep. 11
th
: JSAP @ Matsuyama
Sep. 18
th
: JPS@Yokohama
Ad-hoc EUV & BEUV workshop
On Sep. 26, half-day
Ad-hoc EUV & BEUV workshop
Fundamental property of BEUV sources
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Wavelength (nm)
APL
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100, 061118 (2012).
low density target
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Wavelength (nm)
1064 nm
532 nm
355 nm
Laser
10.1117/2.1201109.003765Shorter-wavelength extreme-UV
sourcesbelow 10nm
Takeshi Higashiguchi, Takamitsu Otsuka, Noboru Yugami, Weihua Jiang, Akira Endo, Padraig Dunne, Bowen Li, and Gerry O’Sullivan
A next-generation laser-pr oduced plasma system based on rare-earth targets generates strong resonant line emissions at 6.5–6.7nm.
In recent years, laser-produced dense plasmas have been attract-ing attention as high-ef ficiency, high-power sources of extreme UV (EUV) radiation. Sour ces with a wavelength less than 10nm are of particular interest for use in next-generation semicon duc-tor lithography and for other applications, such as materials sci-ence and biological imaging. Manufactur er Cymer, for example, has already shippe d a high-average-power 13.5nm engineer-ing prototype to a semiconductor device company that would enable high-volume production at a power level of 80W.1 This source optimizes unresolved transition array (UTA) emission of highly ionized tin for high conversion efficiency (CE) of the in-put laser energy to the in-band (i.e., a bandwidth of about 2% around 13.5nm) EUV energy. Full recovery of the injected fuel is realized through ion deflection in a magnetic field. Low-d ensity targets like tin further enable suppression of satellite (i.e., peri-pheral) emission. Full ionization, which helps to contr ol debris and thus avoid damage to the sour ce mirror, is attained with short-pulse CO2 laser irradiation.
Recently, the possibility of switching to an even shorter EUV wavelength of 6.Xnm was suggested. 2 In fact, 6.Xnm beyond-EUV (BEUV) emission can be coupled with a molyb-denum/ bor on carbide (Mo/ B 4C) or lanthanum/ bor on carbide (La/ B 4C) multilayer mirror whose reflectivity is currently 40% at 6.5–6.7nm (theor etical maxim um >70%). The UTA emission exploited in tin is scala ble to shorter wavelengths. The rare-earth element gadolinium (Gd) has a CE similar to that of tin, though at a higher plasma temperatur e, within a narrow spectral range center ed near 6.7nm. However, no fundamental research has been reported on spectral behavior at 6.7nm and its depen-dence on various parameters, such as laser wavelength, initial target density, and dual-laser -pulse delay. EUV emission at this level could be tuned for use with a Mo/ B 4C multi layer mirror to power practical sources.
Figur e 1. Electron temperatur e dependence of the gadolinium (Gd) ion
population according to the steady-state collisional-radiative model (a). The weighted oscillation strength (gf) spectra of the resonant lines for each contributing ion stage are shown in (b) and (c).
In a proof-of-principle experiment, we produced a source with peak emission around 6.5–6.7nm. 3, 4 gadolinium and terbium (another rare-earth element) produce strong narrow-band emis-sion, again attributable to thousands of resona nce lines that
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