Simultaneous Reflection and Transmission Measurements Physics

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					       Simultaneous Reflection and
       Transmission Measurements
     of Scandium Oxide Thin Films in
          the Extreme Ultraviolet

         G. A. Acosta, D. D. Allred, D. Muhlestein,
            N. Farnsworth- Brimhall, and R. S.
            Turley,Brigham Young University,
                        Provo, UT

7 April 2006
                                                    EUV Astronomy
• Our goal is a better understanding of the
  optical properties of materials in the EUV.
                • The materials we have been     The Earth’s magnetosphere in the EUV

                  studying most recently are ThO2 &
                  Sc2O3 (scandia)

• GAA’s project was to see if we could get n as well as k
  from samples set up to measure transmission in the
• The films were deposited DIRECTLY on Absolute EUV
  silicon photodiodes. $$

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                         Important info
• The EUV offers special challenges
      – Where in the EM spectrum is EUV?
               • 1895 Roentgen discovers ~10 keV
               • 20 years later understood ~
      – What is between UV (3-7 eV) & x-rays?
               • VUV,
               • EUV & soft x-rays about 10 to 100 energy of UV
      – High absorption k = β = αλ/(4π)
                                                        EUV Astronomy
      – Refractive index ~ <1; n = 1-

                                                     The Earth’s magnetosphere in the EUV
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               EUV Applications
• Extreme Ultraviolet Optics has          EUV Lithography
  many applications.
• These Include:
      – EUV Lithography- α & β- 2008      EUV Astronomy

      – EUV Astronomy
      – Soft X-ray Microscopes
• A Better Understanding of            The Earth’s magnetosphere in the EUV

                                       Soft X-ray Microscopes
  materials for EUV
  applications is needed.

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       Optics like n-IR, visible, & n-
       UV? First you need a light.

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Optics like n-IR, visible, & n-UV?
• How to manipulate light?
• Lens? Prisms? Mirrors? Diff Gratings? ML
  interference coatings?
• We need to have optical constants;
• How to get in EUV?
      – Kramers-Kronig equations n ()  k ()
      – Variable angle of reflection measurements,
      – Real samples aren’t good enough.

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• T = (Corrections) exp (-αd);
• Corrections are due to R and can be small
• At normal incidence R goes as [2 + β2]/4
• If film is close to detector scattering due to
  roughness etc. is less important.
• But how to get an even, thin film?
      – A very thin membrane?

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    Transmission thru a film on PI

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        But reflectance is a problem

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     The problem is waviness of
  substrate. Sample on Si does fine.

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     The Solution: Deposit the film
           on the detector
• Uspenskii, Sealy and Korde showed that
  you could deposit a film sample directly
  onto an AXUV100 silicon photodiode.
  (IRD) and determine the films transmission
  ( by ) from the ratio of the signal of the
  coated diode to an uncoated diode.

• SPIE proc. (2002)

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          Our group’s improvements
1. Measure the reflectance of the coated
   diode at the same time I am measuring
   the transmission. And
2. Measure both as a function of angle. And
3. Get the film thickness from the (R)
   interference fringes (@ high angles).

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1. Either T or R have n and k data, but
2. Transmission has very little n data when d is
   small (the EUV).
3. Reflection  n, k and when interference
   fringes are seen, and
4. It has thickness (z) data.

What follows shows how we confirmed
  thickness for air-oxidized Sc sputter-
  coated AXUV diodes.

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  Fitting T() to get dead layer thickness
 (6nm) on bare AXUV diode @=13.5nm

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      Interference in R (50<φ<70 )
       zfit=19.8 nm @ =4.7 nm

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           The complete set of R data
       (6<θ<200) zfit =28.1 nm @ =4.7 nm

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  We might gone with z= 24 nm, but

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We looked at another = 7.7nm;
       needs z=29 nm

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       And the =4.7nm data is OK

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 Reflectance and transmittance of a ThO2-coated
diode at 15 nm fitted simultaneously to obtain n&k

• Green (blue) shows
  (transmission) as a
  function of grazing
  angle ()*
• Noted the interference
  fringes at higher angles
  in R.
* is always from grazing

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R &T of a ThO2-coated diode at 12.6 nm fitted
 simultaneously to obtain optical constants.
                       • The fits were not very
                         good at wavelengths
                         where the
                         transmission was
                         lower than 4%.
                       • All of these fits were
                         trying to make the fit
                         of transmission
                         narrower than the
                         data was.
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 • Thin films of scandium oxide, 15-30 nm thick, were
   deposited on silicon
 • photodiodes by
    – Sputtering Sc from a target & letting it air oxidize OR
    – reactively sputtering scandium in an oxygen
 • R and T Measured using synchrotron radiation at the als
   (Beamline 6.3.2), at LBNL
    – over wavelengths from 2.5-40 nm at variable
    – angles, were taken simultaneously.

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• The BYU EUV Thin Film Optics Group, past and present.
• ALS for beam time under funded proposals.
• BYU Department of Physics and Astronomy, including
  support staff: Wes Lifferth, W. Scott Daniel and John E.
• BYU Office of Research and Creative Activities, and
  Rocky Mountain NASA Space Grant Consortium for
  support and funding.
• SVC for scholarship support for Guillermo Acosta when
  this work was begun.
• Alice & V. Dean Allred (with matching contributions from
  Marathan Oil Company),
• ALS for beam time under funded proposals

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               Not shown in talk
• Data collected revealed the positions of
  electron transitions, which are displaced
  from the positions predicted by standard
  methods of calculation.
• Analysis of the data has provided optical
  constants for scandium oxide thin films,
  which have potential for use as a barrier or
  capping layer to prevent oxidation of
  sensitive optical coatings.

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