Thermal oxide patterning method for compensating coating stress in silicon x-ray telescope mirrors

Youwei Yao, Brandon D. Chalifoux, Ralf K. Heilmann, Kai Wing Chan, Hideyuki Mori, William W. Zhang, Mark L. Schattenburg

Research output: Chapter in Book/Report/Conference proceedingConference contribution

7 Scopus citations


Segmented X-ray telescope mirrors fabricated from thin silicon substrates are being developed by a group at the NASA Goddard Space Flight Center for future generation telescopes such as the Lynx mission concept. The Goddard team has demonstrated high precision silicon mirrors with high angular resolution (∼1'') manufactured by a simple, low cost process. However, the required high-Z optical coatings on mirror front surfaces are difficult to deposit without significant compressive thin film stress, which threatens to distort mirrors and negate the benefits of the high quality substrates. Coating stress reduction methods have been investigated by several groups, but none to date have reported success on real mirrors to the required tolerances. In this paper, we report a new method for correcting mirrors with stress-induced distortion which utilizes a micro-patterned silicon oxide layer on the mirror's back side. Due to the excellent lithographic precision of the patterning process, we demonstrate stress compensation control to a precision of ∼0.3%. The proposed process is simple and inexpensive due to the relatively large pattern features on the photomask. The correction process has been tested on flat silicon wafers with 30 nm-thick chrome coatings under compressive stress and achieved surface slope improvements of a factor of ∼80. We have also successfully compensated two iridium-coated silicon mirrors provided by the Goddard group. The RMS slope errors on coated mirrors after compensation were only degraded by ∼0.06 arc-seconds RMS axial slope compared to the initial uncoated state.

Original languageEnglish (US)
Title of host publicationSpace Telescopes and Instrumentation 2018
Subtitle of host publicationUltraviolet to Gamma Ray
EditorsShouleh Nikzad, Jan-Willem A. Den Herder, Kazuhiro Nakazawa
ISBN (Print)9781510619517
StatePublished - 2018
Externally publishedYes
EventSpace Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray - Austin, United States
Duration: Jun 10 2018Jun 15 2018

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherSpace Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray
Country/TerritoryUnited States


  • X-ray
  • coating stress
  • figure correction
  • low cost
  • silicon mirror
  • stability
  • thermal oxide pattern

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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