From Event: SPIE Optical Engineering + Applications, 2017
We present a thin wafer lamination method for producing X-ray telescope mirrors aiming at 1-10’’ optics quality and low fabrication cost. Traditional grinding/polishing and hot slumping methods find difficulty to meet the required figure accuracy when the mirror thickness is below 1 mm. In this paper, we introduce a new fabrication procedure to satisfy those requirements: first, we laminate flat and ultra-thin silicon wafers on a well polished mandrel via direct bonding until the wafer stack achieves the designed thickness. Second, we release the stack from the mandrel since the direct bonding is temporary. Third, we anneal the stack to create permanent bonding and stabilize the deformation. In such a manner, the intrinsic waviness of each wafer can be alleviated. Our FEA simulation shows the RMS slope error of the stack surface released from a flat mandrel is improved by a factor of 6 when the layer number is doubled, regardless of the total thickness. In the case of a cylindrical mandrel, the local waviness could be improved by a factor of 4000, while a cone angle problem appears and needs to be resolved in future work. We also developed the fabrication method and successfully optimized our wafer cleaning process.
Youwei Yao and Mark L. Schattenburg, "Lamination of ultra-thin silicon wafers for producing high-quality and low-cost x-ray telescope mirrors," Proc. SPIE 10399, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VIII, 1039912 (Presented at SPIE Optical Engineering + Applications: August 09, 2017; Published: 29 August 2017); https://doi.org/10.1117/12.2275330.
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