In this paper we have evaluated alignment and overlay for a Ruthenium Direct Metal Etch process. Depending on the integration strategy, line resistance and lithography requirements, a process with no remaining topography may be preferred from a lithography point of view, but due to the Ruthenium light absorption alignment and overlay through a thick Ruthenium layer will be challenging. In this paper we have studied the maximum thickness of Ruthenium for which the alignment sensor can still detect the alignment marks below and quantify the quality of diffraction-based overlay on an ASML YieldStar overlay metrology tool.

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V. M. Blanco Carballo, E. Canga, C. Jehoul, A. Moussa, A. H. Tamaddon, C. Tabery, G. Gunjala, B. Menchtchikov, V. G. Zacca, S. Lalbahadoersing, A. den Boef, and R. Synowicki, "Alignment and overlay through opaque metal layers," Proc. SPIE 12496, Metrology, Inspection, and Process Control XXXVII, 124960I (Presented at SPIE Advanced Lithography + Patterning: February 28, 2023; Published: 27 April 2023); https://doi.org/10.1117/12.2658084.