Background: The continuous shrink of device dimensions in the semiconductor industry drives the need to improve optical microscopy techniques that are often used in overlay metrology. Achieving sub-nanometer overlay metrology precision requires near-perfect imaging conditions and an almost complete suppression of imaging artifact. Aim: Digital holographic microscopy (DHM) has been presented as a promising new overlay tool measuring the full complex-valued field, giving one computational access to the pupil plane. The unique characteristics of a holographic imaging system in combination with prior knowledge of the object under study show the capability to advance semiconductor metrology. This technique enables a further reduction in metrology target size while also offering opportunities to improve precision. Approach: We present experimental results on a model-based signal separation technique using digital pupil filtering for two different metrology challenges and demonstrate strong suppression of nuisance signals without resolution loss. Results: We will present two experimental examples of different types of pupil filtering in DHM allowing for larger region-of-interest selection to improve the diffraction-based overlay metrology precision and accuracy. Conclusion: We experimentally demonstrate that model-based signal separation in the pupil plane can significantly enhance the overlay metrology capabilities in cases where prior knowledge of the sample is present.

SPIE-Intl Soc Optical Eng
ASML, ARCNL, VU, UvA, RUG, NWO
doi.org/10.1117/1.jmm.23.4.044006
J. Micro/Nanopattern. Mater. Metrol.
EUV Generation & Imaging

van Gardingen-Cromwijk, T., Mathijssen, S., Noordam, M., Witte, S., de Boer, J., & den Boef, A. (2024). Enhancing diffraction-based overlay metrology capabilities in digital holographic microscopy using model-based signal separation. J. Micro/Nanopattern. Mater. Metrol., 23(4), 044006: 1–14. doi:10.1117/1.jmm.23.4.044006