EUV/XUV Coatings

Coatings and coating systems for the extreme ultraviolet spectral range

New applications of optics for short wavelengths

In recent years, optics development has increasingly focused on optical components for ever shorter wavelengths. This trend is based on the one hand on the demand to increase the resolving power of optical systems and on the other hand on the availability of powerful beam sources in the extreme ultraviolet (EUV) and soft X-ray range.

In addition to EUV lithography (λ = 13.5 nm), outstanding applications of EUV and X-ray optics include: applications in astronomy, beamline optics for synchrotrons, optics for X-ray lasers and, in the future, XFELs. There is also great potential for microscopy in the so-called water window (λ = 2.4 nm ... 4.4 nm). In this spectral range, many biological samples are transparent and thus particularly easily accessible for investigations. The extremely short wavelengths enable unprecedented resolutions and thus completely new examination methods in biology and medicine. Reflection values of 5.2 % at 2.48 nm and 20 % at 3.1 nm were achieved by multilayer systems based on chromium, vanadium and scandium.

EUV collector mirror in the hands of a scientist.
© Fraunhofer IOF
Coated EUV collector mirror for high power laser plasma sources used in lithography.

High demands for coatings for the EUV spectral range

Special coatings are essential for optical components at extremely short wavelengths. The short wavelengths place stringent demands on film materials, thickness precision, composition, purity, roughness, morphology, as well as their interaction with surrounding materials. As a result, EUV / XUV coatings have to be fabricated with highest precision to achieve high quality. Moreover, the desired properties have to be stable even under harsh environmental conditions such as high temperatures. 

 

In-house EUV developments since 1997

In 1997, Fraunhofer IOF started with the design, manufacturing and characterization of multilayer systems for the EUV spectral range with a special focus on EUV lithography (EUVL) at a wavelength of 13.5 nm. In the past two decades, Fraunhofer IOF established itself as a reliable partner for various industrial suppliers of EUVL equipment.

Two researchers together carry a collector mirror in their hands.
© Fraunhofer IOF
660 mm collector mirror manufactured at Fraunhofer IOF for extreme ultraviolet lithography (EUVL)

Tailored solutions

In addition to the improvement of reflective properties at a wavelength of 13.5 nm, numerous R&D projects were successfully performed at Fraunhofer IOF for different industrial partners:

  • Thermally stable EUV coatings (T > 500 °C) with R > 60 % @ 13.5 nm,
  • Broadband and narrowband mirrors for the 10…100 nm spectral range,
  • Highly reflective layer systems for the 2.5 nm to 100 nm spectral range,
  • Development of the coating technologies for reducing layer stresses,
  • Construction of deposition tools for laterally graded multilayer coatings,
  • Capping layers for EUVL (with enhanced optics lifetime),
  • Cleaning strategies of contaminated EUV optics,
  • Roughness and defect mapping of EUV components before and after coating,
  • Roughness evolution modelling and virtual coating of EUV coatings,
  • Instrument for EUV scattering and reflectance measurements based on laboratory GDP source
Researcher sit at the characterization facility in the laboratory and measures the coatings of an EUV mirror.
© Fraunhofer IOF
Characterization of an EUV collector mirror with the versatile system ALBATROSS at Fraunhofer IOF.

Infrastructure and equipment

For our work we use a broad pool of design, coating, and characterization techniques (complete overview). The Nessy 3 coating system for coating production by means of magnetron sputtering is at the center of our work.

 

Future technologies on behalf of industry and science

While EUV coatings have now found their way into commercial production and represent a key element of the latest generation of lithography systems, we are working on further improvements and pushing the boundaries to ever shorter wavelengths, better performance and thus opening up new fields of application.

As an application-oriented research facility, we work together with project partners from science and industry to make new technologies and applications in the extreme ultraviolet spectral range of light possible. We develop optics adapted to the needs of our customers, whose coating systems provide excellent results under the extraordinary requirements of wavelengths in the EUV and soft X-ray range.  

Coating system Nessy in the laboratory of the Fraunhofer IOF.
© Fraunhofer IOF
Coating system Nessy at Fraunhofer IOF for EUV coatings produced by magnetron sputtering.
  • In the following you will find a list of our research results with a focus on EUV optics:

     

    • S. Yulin, T. Kuhlmann, T. Feigi, N. Kaiser, Damage resistant and low stress EUV multilayer mirrors, Proc. SPIE 4343, 607-614, (2001)
    • T. Feigl, S.  Yulin, T. Kuhlmann, N. Kaiser, "Damage resistant and low stress EUV multilayer mirrors," Jap. Journal of Applied Physics 41, 6B, (2002)
    • T. Kuhlmann, S. Yulin, T. Feigl, N. Kaiser, H. Bernitzki, H. Lauth, "Design and fabrication of broadband EUV multilayer mirrors, " Proc. SPIE 4688, 509-515, (2002)
    • S. Yulin, T. Kuhlmann, T. Feigi, N. Kaiser, "Spectral reflectance tuning of EUV mirrors for metrology applications, " Proc. SPIE 5037, 286-293, (2003)
    • S. Yulin: Multilayer coatings for EUV/Soft x-ray mirrors, N. Kaiser: Optical interference coatings, Berlin: Springer (Springer series in optical sciences 88), 281-308 (2003)
    • S. Yulin, F. Schäfers, T. Feigl, N. Kaiser, "Enhanced reflectivity and stability of Sc/Si multilayers," Proc. SPIE 5193, 155-163, (2004)
    • S. Yulin, N. Benoit, T. Feigl, N. Kaiser, "High-temperature multilayers," Proc. SPIE 6751, 1155-1161, (2005)
    • T. Feigl, S. Yulin, N. Benoit, N. Kaiser, N. Böwering, A. Ershov, O. Khodykin, J. Viatella, K. Bruzzone, I. Fomenkov, D. Myers, D. Brandt, "High-temperature LPP collector mirror, Proc. SPIE 6151, 1084 -1092, (2006)
    • H. Stollberg, S Yulin, P.A.C. Takman, H.M. Hertz, "High-reflectivity Cr/Sc multilayer condenser for compact soft x-ray microscopy," Review of scientific instruments 77, 12, 123101 (2006)
    • S. Yulin, N. Benoit, T. Feigl, N. Kaiser “Interface-engineered EUV multilayer mirrors,” Microelectronic Engineering 83, 692-694, (2006)
    • T. Feigl, S. Yulin, N. Benoit, N. Kaiser, "EUV multilayer optics," Microelectronic engineering 83, 4 - 9, 703-706, (2006) 
    • S. Schröder, T. Feigl, A. Duparré, and A. Tünnermann, "EUV reflectance and scattering of Mo/Si multilayers on differently polished substrates," Opt. Express 15, 13997-14012 (2007).
    • E. Taracheva, S. Yulin, T. Feigl, N. Kaiser, "High performance multilayer coatings for 106 nm," Proc. SPIE 6705, 67050Y (2007)
    • N. Benoit, S. Schroeder, S. Yulin, T. Feigl, A. Duparre, N. Kaiser, A. Tünnermann, "Extreme-ultraviolet-induced oxidation of Mo/Si multilayers," App. Optics 47/19, 3455-3462 (2008)
    • S. Yulin, N. Benoit, T. Feigl, N. Kaiser, M. Fang, M. Chandhok, "Mo/Si multilayers with enhanced TiO2- and RuO2-capping layers," Proc. SPIE 6921, 692118, (2008)
    • S. Yulin, T. Feigl, N. Benoit, M. Perske, E. Taracheva, S. Schröder, V. Nesterenko, N. Kaiser, "Hochreflektierende EUV/Röntgen-Mehrschichtspiegel," Photonik, 2, 48-50 (2008)
    • N. Benoit, S. Schröder, S. Yulin, T. Feigl, A. Duparré, N. Kaiser, and A. Tünnermann, "Extreme-ultraviolet-induced oxidation of Mo/Si multilayers," Appl. Opt. 47, 3455-3462 (2008).
    • S.B. Hill, N.S. Faradzhev, C. Tarrio, T.B. Lucatorto, T.E. Madey, B.V. Yakshins-kiy, E. Loginova, S. Yulin, "Accelerated lifetime metrology of EUV multilayer mirrors in hydrocarbon environments," Proc. SPIE 6921, 692117, (2008)
    • S. Yulin: Multilayer interference coatings for EUVL, B. Wu: Extreme ultraviolet lithography, New York, N.Y.: McGraw-Hill, 225-270 (2009)
    • S. Schröder, T. Herffurth, M. Trost, and A. Duparré, "Angle-resolved scattering and reflectance of extreme-ultraviolet multilayer coatings: measurement and analysis," Appl. Opt. 49, 1503-1512 (2010).
    • M. Schürmann, S. Yulin, V. Nesterenko, T. Feigl, N. Kaiser, B. Tkachenko, M.C. Schürmann, "Multi-technique study of carbon contamination and cleaning of Mo/Si multilayer optics exposed to pulsed EUV radiation," Proc. SPIE 7636, 76361P, (2010)
    • M. Schürmann, S. Yulin, V. Nesterenko, T. Feigl, N. Kaiser, B. Tkachenko, M.C. Schürmann, "Multi-technique study of carbon contamination and cleaning of Mo/Si multilayer optics exposed to pulsed EUV radiation," Proc. SPIE 7636, 76361P, (2010)
    • M. Trost, S. Schröder, T. Feigl, A. Duparré, and A. Tünnermann, "Influence of the substrate finish and thin film roughness on the optical performance of Mo/Si multilayers," Appl. Opt. 50, C148-C153 (2011).
    • S.B. Hill, N.S. Faradzhev, L.J. Richter, S. Grantham, C. Tarrio, T.B. Lucatorto, S. Yulin, M. Schürmann, V. Nesterenko, T. Feigl, "Optics contamination studies in support of high-throughput EUVL tools: Proc. SPIE 7969, 79690, (2011)
    • N.S. Faradzhev, B.V. Yakshinskiy, E. Starodub, T.E. Madey, S.B. Hill, S. Grantham, T.B. Lucatorto, S.  Yulin, E. Vescovo, J.W. Keister, "Resonance effects in photoemission from TiO2-capped Mo/Si multilayer mirrors for extreme ultraviolet applications," Journal of applied physics 109, 8, 083112, (2011)
    • H. Legall, G. Blobel, H. Stiel, W. Sandner, C. Seim, P. Takman, D.H. Martz, M. Selin, U. Vogt, H.M. Hertz, D. Esser, H. Sipma, J. Luttmann, M. Höfer, H.D. Hoffmann, S. Yulin, T. Feigl, S. Rehbein, P. Guttmann, G. Schneider, U. Wiesemann, M. Wirtz, W.  Diete, "Compact x-ray microscope for the water window based on a high brightness laser plasma source," Optics Express 20, 16, 18362-18369, (2012)
    • H. Legall, H. Stiel, G. Blobel, C. Seim, J. Baumann, S. Yulin, D. Esser, M. Hoefer, U. Wiesemann, M. Wirtz, G. Schneider, S. Rehbein, H.M. Hertz, "A compact laboratory transmission X-ray microscope for the water window," Journal of physics 463, 1, 012013, (2013)
    • M. Trost, S. Schröder, A. Duparré, S. Risse, T. Feigl, U. D. Zeitner, and A. Tünnermann,, “Structured Mo/Si multilayers for IR-suppression in laser-produced EUV light sources.,” Opt. Express, 21(23), 27852–64, (2013).
    • D. Bleiner, S. Yulin, J. Martynczuk, M. Ruiz-Lopez, Y. Arbelo, J.E. Balmer, D. Günther, "Actinic damage of Y/Mo multilayer optics in a table-top plasma-driven x-ray laser," Appl. Optics 53, 22, 4894-4902, (2014)