A wide band transmission mode spectrometer for diagnosis of EUV sources

(1)

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Transmission Grating

 Flat efficiency curve from 10 nm to 100 nm  Diffraction efficiency in the first order ≈ 10%

 Available gratings on a single chip: 500, 780, 1500, 1850, 2500 lines/mm and from 1000 to 10.000 lines/mm (by steps of 1000 lines/mm)

 Large grating set provides wide working range of the spectrometer spanning from EUV to UV

 Fabrication process:

 Pattern definition by UV-NIL in resist on Si₃N₄ coated Si wafer  Planarization and pattern transfer down to Si₃N₄ layer by RIE  Deposition of Cr (etch mask) and Au (absorber) layers

 Lift-off to form etch mask and absorber layer  Back etch of Si by wet etching

 Grating etching in Si₃N₄

1_{Laser Physics and Nonlinear Optics, MESA+ Institute for Nanotechnology, University of Twente, The Netherlands} 2_{XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, The Netherlands}

3_{Scientec Engineering, The Netherlands,}4_{NT&D – Nanotechnology and Devices, Germany}

*m.bayraktar@utwente.nl

J.L.P. Barreaux

1

, M. Bayraktar

2*

, H.M.J. Bastiaens

1

, C. Bruineman

3

, B. Vratzov

4

, and F. Bijkerk

2

A wide band transmission mode spectrometer

for diagnosis of EUV sources

Motivation

 Comprehensive spectral characterization for critical optimization of EUV sources

 Measurement of both in-band and out-of-band spectrum from EUV to UV  A compact spectrometer to enable cross comparison between sources

 Reproducible fabrication of high density transmission gratings, up to 10.000 periods/nm, to enable high resolution in wavelengths

Compact High-Resolution Spectrometer for VIS, UV, EUV

 Compact size: (L) 300 × (W) 240 × (H) 200 mm  Easy alignment:

 Computer-controlled positioning of components with motorized stages  GUI to control the optics and record/process spectrum

 Vacuum rating: down to 10-6_mbar

 Integrated shutter to block light beam

 Filter wheel to select specific wavelength ranges

This work has been enabled by the FOM Valorisation Prize 2011, awarded to Fred Bijkerk.

Summary & Outlook

 Measurement of EUV spectrum enables optimization of EUVL sources for in-band radiation

 Measurement of UV-EUV spectrum allows quantification of OoB radiation  Compact device due to the design with unique transmission grating chip

that is containing a set of high-density gratings

 High-resolution spectrometer covering a wide spectral range from UV to EUV wavelengths by stitching the spectrum recorded by set of filters

Demonstration

High-harmonic generation source with Neon gas

[1]

 Al filter: Bandpass 17-86 nm

 High spectral resolution is demonstrated: better than 0.13 nm

Discharge produced plasma source with Xenon gas

 Measurement in the EUV wavelength range (in-band)  Fine features in the spectrum are resolvable

 Measurement in the DUV wavelength range (out-of-band)

 Switched from EUV meas. to DUV meas. without breaking vacuum  SiO₂ filter: Lower cutoff wavelength ~160 nm

Au Cr Si Si3N4 Front Back bar slit

Cross section grating

0 50 100 150 200 0 0,5 1,0 1,5 lambda = 100 nm, TG= 330 nm period lambda = 13.5 nm, TG= 330 nm period lambda = 13.5 nm, TG= 100 nm period Re s o lutio n  [nm ] Pinhole diameter [m]

 High spectral resolution

 λ/Δλ > 100 at 13.5 nm ≈ 0.1 nm

 Operation with high/low dispersion gratings allows fast switching between high resolution or wide spectrum

 Wide spectral range, EUV to UV, without breaking vacuum

 Flat-field spectrum, no aberrations  Higher order suppression by filters

Calculated spectral resolution

EUV

VUV-UV

wit

hout br

eaking

vacu

um

Filter cutoff

EUV

[1] S.J. Goh, H.J.M. Bastiaens, B. Vratzov, Q. Huang, F. Bijkerk, and K.J. Boller, “Fabrication and characterization of free-standing, high-line-density transmission gratings for the vacuum UV to soft X-ray range”, Opt. Express., vol. 23, no. 4, pp. 4421-4434 (2015).