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9 September 2019 Development of a thermal-oxide patterning method for mitigating coating stress-induced distortion in silicon mirrors for the Lynx X-Ray Telescope mission concept (Conference Presentation)
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Abstract
The thermal oxide patterning method has been proven effective for compensating coating stress on flat silicon wafers. In this paper we report progress of applying this method on thin X-ray telescope silicon mirrors, produced by GSFC, which are 100 mm long, 0.5 mm thick, 30 degree in azimuthal span and 312 mm in radius of curvature (Wolter-I geometry). The mirrors’ front sides are sputter coated by 20 nm iridium layers which have ~-70 N/m compressive stress. Due to the difference in geometries, we developed a new FEA model to calculate the duty cycle in thermal oxide hexagon patterns to compensate the coating stress. In addition, a new fabrication process with customized photo lithographic tools has been developed to achieve optimum patterning-precision on curved surfaces. Measurement results show that the developed method can mitigate coating-induced distortion by a factor of ~4, corresponding to ~0.5 arc-second in RMS slope error. The residual surface error is dominated by mid-frequency ripples produced by the annealing process, which will be resolved in the future. The developed thermal oxide patterning method could be inexpensive and precise, which could be a candidate to resolve coating stress issues for the Lynx telescope in the future.
Conference Presentation
© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Youwei Yao, Brandon Chalifoux, Ralf Heilmann, Kai-Wing Chan, Hideyuki Mori, Takashi Okajima, William Zhang, and Mark Schattenburg "Development of a thermal-oxide patterning method for mitigating coating stress-induced distortion in silicon mirrors for the Lynx X-Ray Telescope mission concept (Conference Presentation)", Proc. SPIE 11119, Optics for EUV, X-Ray, and Gamma-Ray Astronomy IX, 1111909 (9 September 2019); https://doi.org/10.1117/12.2531153
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