7 July 1997 Optical diffraction tomography for latent image metrology
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Abstract
Optical diffraction tomography (ODT) attempts to reconstruct the complex refractive index profile of an object by inverting its backscattered and/or transmitted fields. Owing to its integral formulation of the diffracted plane, the inverse scattering problem in ODT, i.e., reconstructing the object from its diffracted field, can be linearized via the Born approximation. The validity range of the Born approximation is limited to weakly scattering objects, or objects whose refractive index distributions are slowly varying and comparable in magnitude to their background. Such constraints are easily met in microlithography when considering the area of latent image metrology. Indeed, latent images are generally characterized by their relatively small and slowly varying refractive indices. An algorithm is presented for reconstructing the refractive index distribution of latent images from their first (+1) and second (+2) reflected diffraction orders at the Bragg angle.
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Ziad R. Hatab, Ziad R. Hatab, Nasir U. Ahmed, Nasir U. Ahmed, S. Sohail H. Naqvi, S. Sohail H. Naqvi, John Robert McNeil, John Robert McNeil, } "Optical diffraction tomography for latent image metrology", Proc. SPIE 3050, Metrology, Inspection, and Process Control for Microlithography XI, (7 July 1997); doi: 10.1117/12.275942; https://doi.org/10.1117/12.275942
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