Novel Technologies for Future Large X-ray Telescopes  
 Shaping of Advanced Si wafer X-ray Optics  
  R. Hudec, , L. Pína, A. Inneman, V. Semencová, M. Skulinová, L. Švéda, V. Brožek, J. Šik, M. Míka, R. Kačerovský, T. Kubina, 
X-ray Multi Foil Optics (MFO)

  • X-ray optics based on multiple thin X-ray reflecting foils
  • The foils may be of various materials (e.g. glass, Si, metals)
  • Various arrangements and geometries possible, e.g. LOBSTER, K-B, Wolter, double conical approximation to Wolter, etc.


  • Various examples of X-ray MFO: foil thicknesses from 30 microns to 1 mm, foils 3 x 3 mm to 300 x 300 mm, planar & ellipsoidal
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    Our approach to X-ray MFO based on Si wafers

  • the Si wafers parameters are optimised already at the production stage
  • the Si wafers are shaped to precise optical surfaces/shapes
  • the internal stress is minimised
  • the shaped/bent Si wafers are stacked to form the MFO


  • MEASURING THE QUALITY OF SI WAFERS

  • the production of Si wafers is a complex process
  • at moment, the production of Si wafers is NOT optimised for X-ray optics applications
  • precise measurements and optimization already at production stage are important for X-ray optics based on Si wafers
  • Example of specification of standard Si wafers,
    individual parameters may be improved according to customer requirements.

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    Optical profilometer STIL
    Thickness homogenity of Si wafer produced by ON Semiconductor Czech Republic
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    Flatness and thickness uniformity of a Si wafer (diameter 150 mm)
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    Flat Si wafer, diameter 150 mm ON Semiconductor Czech Republic, profilometer measurement, 2 perpendicular axes
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    100 mm diameter, 0.8 mm thick Si wafer before (left) and after (right) bending (test cylinder R = 1.3 m)
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    Si WAFERS SHAPING . test cylindrical samples.gold-coated, d=100 mm, thickness 0.8 mm, R=1.3 m
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    DEVIATION / bent Si wafers
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    before processing (deviation from plane)
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    after processing (deviation from cylinder)
    Parabolized Si wafer, D=100 mm
    Interferometer ZYGO
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    profile plot
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    3D plot


    Parabolized Si wafer, sample 2, D=150 mm,
    ON Semiconductor profile measurement in 2 perpedicular axes
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    before processing (deviation from plane)
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    after processing (deviation from cylinder)
    Summary - Si wafers

  • Interdisciplinary co-operation (team with 10 members) created within the Czech Republic with experienced teams including researchers at the large company producing Si wafers
  • Si wafers succesfully bent to desired geometry by 2 different techniques, the 3rd technique will be tested within 1 month
  • The bending before stacking is advantageous eg. to avoid increase of internal stress and to allow very long-term stability of the mirror array
  • The production of Si wafers very complex, need to modify and optimize the parameters at the production stage
  • Need to minimize the internal stress (25 years lifetime...)
  • The production of Si wafers and related techniques carefully analysed
  • MLs succesfully deposited and tested


  • Next steps:

  • 3rd bending technology
  • bending of larger and high quality Si wafers
  • measurements of internal stress
  • tests of stacking
  • better measurements, metrology
  • tests at production stage to modify the parameters, decrease stress, allow more easy bending etc

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