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Simultaneous Reflection and Transmission Measurements Physics

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Simultaneous Reflection and Transmission Measurements Physics Powered By Docstoc
					       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
                        Overview
                                                    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
  EUV.
• The films were deposited DIRECTLY on Absolute EUV
  silicon photodiodes. $$

 7 April 2006                                                                2
                         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
7 April 2006                                                                                3
               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.



7 April 2006                                                                  4
       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.
        Roughness

7 April 2006                                         6
               Transmissionk?
• 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?


7 April 2006                                       7
    Transmission thru a film on PI




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        But reflectance is a problem




7 April 2006                           9
     The problem is waviness of
  substrate. Sample on Si does fine.




7 April 2006                       10
     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)

7 April 2006                                 11
          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).



7 April 2006                              12
                Comments
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.

7 April 2006                                       13
  Fitting T() to get dead layer thickness
 (6nm) on bare AXUV diode @=13.5nm




7 April 2006                             14
                                0
      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




7 April 2006                     17
We looked at another = 7.7nm;
       needs z=29 nm




7 April 2006                 18
       And the =4.7nm data is OK




7 April 2006                        19
 Reflectance and transmittance of a ThO2-coated
diode at 15 nm fitted simultaneously to obtain n&k

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

 7 April 2006                                  20
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.
7 April 2006                                  21
                 “Conclusions”
 • 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
      environment.
 • 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.




7 April 2006                                               22
               Acknowledgements
• 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.
  Ellsworth.
• 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

7 April 2006                                            23
               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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