Direct comparison of EUV and visible-light interferometries

Goldberg, Kenneth A.; Naulleau, Patrick; Chang, Chang-Hasnain C.; Bresloff, Cynthia J.; Gaughan, Richard J.; Chapman, Henry N.; Goldsmith, J. E. M.; Bokor, Jeffrey

doi:10.1117/12.351138

Cited by 17 publications

(8 citation statements)

References 14 publications

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“…16 waves rms over a NA of 0.08, whereas current state-of-the-art optics2° have been measured to have wavefront aberrations below 0.05 waves rms over a slightly larger NA. 21 Although not yet verified with subsequent null tests, the accuracy obtained when testing these newer optics is expected to be better than the results presented in Table 1.…”

Section: Characterizing Accuracymentioning

confidence: 79%

<title>Recent advances in EUV phase-shifting point diffraction interferometry</title>

Naulleau

Goldberg²,

Chang

et al. 1999

SPIE Proceedings

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The extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PSIPDI) was developed and implemented at Lawrence Berkeley National Laboratory to meet the significant measurement challenge of characterizing EUV projection lithography optics. The PS/PDI has been in continuous use and under ongoing development since 1996. Here we describe recent improvements made to the interferometer, and we summarize metrology results from state-of-the-art lOx-reduction EUV projection optics.

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Section: Characterizing Accuracymentioning

confidence: 79%

<title>Recent advances in EUV phase-shifting point diffraction interferometry</title>

Naulleau

Goldberg²,

Chang

et al. 1999

SPIE Proceedings

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“…Furthermore, the presence of carbon contamination on a mirror's surface can create a significant difference between the measured visible-light and EUV reflected phase (and amplitude). 5 While the former concerns have been significantly allayed by recent improvements in the accuracy and repeatability of multilayer-deposition techniques, 6 carbon contamination has the potential to compromise visible-light measurements made on systems that have been exposed to EUV light and have suffered carbon deposition on the mirror surfaces.…”

Section: Introductionmentioning

confidence: 99%

Honing the accuracy of extreme-ultraviolet optical system testing: at-wavelength and visible-light measurements of the ETS Set-2 projection optic

Goldberg¹,

Naulleau

Bokor

et al. 2002

Emerging Lithographic Technologies VI

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As the quality of optical systems for extreme ultraviolet lithography improves, high-accuracy wavefront metrology for alignment and qualification becomes ever more important. To enable the development of diffraction-limited EUV projection optics, visible-light and EUV interferometries must work in close collaboration. We present a detailed comparison of EUV and visible-light wavefront measurements performed across the field of view of a lithographic-quality EUV projection optical system designed for use in the Engineering Test Stand developed by the Virtual National Laboratory and the EUV Limited Liability Company. The comparisons reveal that the present level of RMS agreement lies in the 0.3-0.4-nm range. Astigmatism is the most significant aberration component for the alignment of this optical system; it is also the dominant term in the discrepancy, and the aberration with the highest measurement uncertainty. With EUV optical systems requiring total wavefront quality in the λ EUV /50 (0.25 nm) range, and even higher surface-figure quality for the individual mirror elements, improved accuracy through future comparisons, and additional studies, are required.

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“…State-of-the-art visible-light testing is used in the fabrication of the individual mirror elements, 1,2 and has been used in the alignment of numerous assembled EUV optical systems. 3,4,5 Interferometer absolute accuracies in the 50 pm range are a requirement for the measurement of production-quality EUV elements and assembled systems. 6 Visible-light interferometry continues to benefit by close, ongoing comparisons with EUV interferometric measurements performed on the same optical systems.…”

Section: Introductionmentioning

confidence: 99%

EUV interferometry of the 0.3-NA MET optic

et al. 2003

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A new generation of 0.3 numerical aperture prototype EUV optical systems is now being produced to provide an opportunity for early learning at 20-nm feature size. Achieving diffraction limited performance from these two-mirror, annular projection optics poses a challenge for every aspect of the fabrication process, including final alignment and interferometric qualification. A new phase-shifting point diffraction interferometer will be used at Lawrence Berkeley National Laboratory for the measurement and alignment of the MET optic at EUV wavelengths. Using the previous generation of prototype EUV optical systems developed for lithography research, with numerical apertures up to 0.1, EUV interferometers have demonstrated RMS accuracy levels in the 40-70 pm range. Relative to the previous generation of prototype EUV optics, the threefold increase to 0.3 NA in the image-side numerical aperture presents several challenges for the extension of ultra-high-accuracy.

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Direct comparison of EUV and visible-light interferometries

Cited by 17 publications

References 14 publications

<title>Recent advances in EUV phase-shifting point diffraction interferometry</title>

<title>Recent advances in EUV phase-shifting point diffraction interferometry</title>

Honing the accuracy of extreme-ultraviolet optical system testing: at-wavelength and visible-light measurements of the ETS Set-2 projection optic

EUV interferometry of the 0.3-NA MET optic

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