Fast and robust diffraction based overlay metrology using dark-field digital holographic microscopy

Publication date
DOI http://dx.doi.org/10.1117/12.2591989
Reference T.T.M. van Schaijk, C. Messinis, N. Pandey, V.T. Tenner, A. Koolen, S. Witte, J.F. de Boer and A.J. den Boef: Fast and robust diffraction based overlay metrology using dark-field digital holographic microscopy In: Optical Measurement Systems for Industrial Inspection XII, in Proceedings of SPIE, vol 11782, SPIE., 2021.
Groups Computational Imaging, EUV Generation & Imaging

Digital holographic microscopy allows access to the complex electric field, enabling computational propagation of light. This enables computational corrections for lens aberrations, which remove the requirement for antireflective coatings on the lens and enable imaging over a wide spectral range. This makes digital holographic microscopy an interesting candidate for overlay metrology on semiconductor wafers. We show that a single holographic image contains all data that is required for computing the overlay, by using a source with a limited coherence length and incoherently adding multiple measurements on a camera. As an additional benefit we show that such parallel acquisition improves the reproducibility of the experiment by eliminating noise sources that are common to the two measurements that typically constitute a single overlay measurement.