16 March 2015 Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection
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In this paper, we present an experimental verification of Zernike phase contrast enhanced EUV multilayer (ML) blank defect detection using the SHARP EUV microscope. A programmed defect as small as 0.35 nm in height is detected at focus with signal to noise ratio (SNR) up to 8. Also, a direct comparison of the through-focus image behavior between bright field and Zernike phase contrast for ML defects ranging from 40 nm to 75 nm in width on the substrate is presented. Results show the advantages of using the Zernike phase contrast method even for defects with both phase and absorption components including a native defect. The impact of pupil apodization combined with Zernike phase contrast is also demonstrated, showing improved SNR is due to the stronger reduction of roughness dependent noise than defect signal, confirming our previous simulation results. Finally we directly compare Zernike phase contrast, dark field and bright field microscopes.
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Yow-Gwo Wang, Ryan Miyakawa, Weilun Chao, Markus Benk, Antoine Wojdyla, Alex Donoghue, David Johnson, Kenneth Goldberg, Andy Neureuther, Ted Liang, Patrick Naulleau, "Enhancing defect detection with Zernike phase contrast in EUV multilayer blank inspection", Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94221C (16 March 2015); doi: 10.1117/12.2087532; https://doi.org/10.1117/12.2087532

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