Parallax method for a single-cell diffraction based measurement of misregistration

An overlay metrology system, comprising:

• an optical sub-system comprising:
• one or more optical elements to illuminate a sample with a pair of two illumination beams per measurement direction when implementing a metrology recipe, wherein the illumination beams in each pair of illumination beams have a common altitude incidence angle and opposing azimuth incidence angles along the respective measurement direction, wherein the sample in accordance with the metrology recipe includes a plurality of overlay targets, each having one or more cells including overlapping first and second structures on two layers of the sample, wherein the first and second structures in each of the cells is characterized by an offset value f0;
• a detector;
• one or more additional optical elements configured to direct at least a portion of light from the sample to the detector;
• a controller communicatively coupled to the optical sub-system, the controller including one or more processors configured to execute program instructions causing the one or more processors to implement the metrology recipe by:
• receiving a first set of metrology data from the optical sub-system associated with two cells per measurement direction having nonzero offset values of ±f0 from a first set of the overlay targets;
• determining overlay measurements per direction for the first set of the overlay targets based on the first set of metrology data;
• generating effective stack heights representative of an effective distance between the first and second structures at locations of the first set of the overlay targets based on the first set of metrology data;
• receiving a second set of metrology data from the optical sub-system associated with a single cell per measurement direction from a second set of the overlay targets;
• determining the effective stack heights at locations of the second set of the overlay targets based on the effective stack heights at the locations of the first set of the overlay targets;
• and
• determining overlay measurements per direction for the second set of the overlay targets based on the effective stack heights.

An overlay metrology method, comprising:

• generating a first set of metrology data with an optical sub-system, wherein the optical sub-system is configured to illuminate a sample with a pair of illumination beams per measurement direction when implementing a metrology recipe, wherein the illumination beams in each pair have a common altitude incidence angle and opposing azimuth incidence angles along the respective measurement direction, wherein the sample in accordance with the metrology recipe includes a plurality of overlay targets, each having one or more cells including overlapping first and second structures on two layers of the sample, wherein the first and second structures in each of the cells is characterized by an offset value f0, wherein the first set of metrology data is associated with two cells per measurement direction having nonzero offset values of ±f0 from a first set of the overlay targets;
• determining overlay measurements per direction for the first set of the overlay targets based on the first set of metrology data;
• generating effective stack heights representative of an effective distance between the first and second structures at locations of the first set of the overlay targets based on the first set of metrology data;
• generating a second set of metrology data with the optical sub-system associated with a single cell per measurement direction from a second set of the overlay targets;
• determining the effective stack heights at locations of the second set of the overlay targets based on the effective stack heights at the locations of the first set of the overlay targets;
• and
• determining overlay measurements per direction for the second set of overlay targets based on the effective stack heights at the locations of the second set of the overlay targets and the second set of metrology data.