US 12,487,533 B2
Amplitude asymmetry measurements in overlay metrology
Vladimir Levinski, Migdal HaEmek (IL); and Andrew V. Hill, Sunriver, OR (US)
Assigned to KLA Corporation, Milpitas, CA (US)
Filed by KLA Corporation, Milpitas, CA (US)
Filed on Jan. 25, 2024, as Appl. No. 18/422,668.
Prior Publication US 2025/0244682 A1, Jul. 31, 2025
Int. Cl. G03F 7/00 (2006.01)
CPC G03F 7/70633 (2013.01) [G03F 7/706837 (2023.05); G03F 7/706849 (2023.05); G03F 7/706851 (2023.05)] 34 Claims
OG exemplary drawing
 
1. A metrology system comprising:
a controller communicatively coupled to an optical sub-system configured to illuminate an overlay target on a sample with illumination from an illumination source when implementing a metrology recipe, wherein the overlay target in accordance with the metrology recipe includes first and second periodic features distributed along one or more measurement directions, wherein the first and second periodic features are associated with different patterning steps of a fabrication process for fabricating the overlay target, wherein the controller includes one or more processors configured to execute program instructions causing the one or more processors to implement the metrology recipe by:
receiving two or more images of the overlay target from one or more detectors of the optical sub-system, wherein the two or more images are generated with different measurement conditions, each measurement condition associated with at least one of a sample focal distance or a configuration of diffraction orders of the illumination by the overlay target that contributes to the associated one of the two or more images;
calculating an amplitude asymmetry associated of opposing diffraction orders of the illumination by the overlay target based on the two or more images; and
generating one or more quality metrics associated with the overlay target based on the amplitude asymmetry.