28 May 2018 Fourier ptychography for lithography high NA systems
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Abstract
The aim of this research is to explore the limits of the basic Ptychography algorithm (FPA) at deep ultra violet (DUV) wavelength of 193 nanometers and for binary and phase shift masks. Furthermore, imaging at high numerical apertures involves polarization effects, which are not covered in the scalar phase retrieval algorithms of FPA. The impact of these effects on FPA is investigated for a test chart with feature sizes close to the resolution limit. The quality of the images before and after applying FPA was measured using different error criteria. The Normalized Image Log Slope (NILS) is the criterion which is most sensitive to the lithographically important change in the edge sharpness of features. The Michelson contrast provides a global assesment of the image contrast. The Mean squared Error (MSE) provides an overall assessment of the image quality with respect to a known object. When FPA is used to recover high resolution images of a phase shift mask, it is found out that the edge sharpness is increased but the overall contrast is declined. Additionally, the printability of side lobes contributed to increase of MSE. After using a rigorous method to compute the mask diffraction spectrum instead of the conventional Fourier transform imaging, it is confirmed that thin object assumption is not at all accurate for high numerical aperture DUV imaging applications. For the first time, the polarization effects at large NAs are introduced to FPA and the output is evaluated. Here, we verified that polarization can be used to increase the edge sharpness at a specific direction.
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Atoosa Dejkameh, Atoosa Dejkameh, Andreas Erdmann, Andreas Erdmann, Peter Evanschitzky, Peter Evanschitzky, Yasin Ekinci, Yasin Ekinci, } "Fourier ptychography for lithography high NA systems", Proc. SPIE 10694, Computational Optics II, 106940B (28 May 2018); doi: 10.1117/12.2311332; https://doi.org/10.1117/12.2311332
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