System and method for determining overlay measurement of a scanning target

An overlay metrology system comprising:

• an illumination sub-system comprising:
• an illumination source configured to generate one or more illumination beams;
• and
• one or more illumination optics configured to direct the one or more illumination beams to an overlay target on a sample as the sample is scanned relative to the one or more illumination beams along a scan direction when implementing a metrology recipe,
• wherein the overlay target in accordance with the metrology recipe includes a side-by-side grating, wherein the side-by-side grating includes one or more diffraction gratings in one or more cells, wherein at least one diffraction grating is a non-overlapping side-by-side grating, wherein the side-by-side grating includes at least a first exposure structure and a second exposure structure, wherein the first exposure structure is arranged adjacent to the second exposure structure, wherein the side-by-side grating is periodic along the scan direction;
• a collection sub-system comprising:
• two or more photodetectors located in a pupil plane to capture diffraction orders from the side-by-side grating in the one or more cells when implementing the metrology recipe;
• a controller communicatively coupled to the two or more photodetectors, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
• receive time-varying interference signals from the two or more photodetectors associated with the side-by-side gratings in the one or more cells as the overlay target is scanned in accordance with the metrology recipe;
• extract phase information from the time-varying interference signals associated with the non-overlapping first exposure structure and second exposure structure;
• synchronize the phase information from the non-overlapping first exposure structure and second exposure structure by at least one of (i) simultaneously interacting the one or more illumination beams with all gratings of the side-by-side grating during scanning, (ii) determining regions of interest (ROIs) for each exposure structure and aligning the phase information to a common starting point, or (iii) adjusting the phase information based on sample reference signals to compensate for scanning velocity instability;
• determine an overlay error between one of the first exposure structure and the second exposure structure of the sample based on the synchronized phase information from the non-overlapping first exposure structure and second exposure structure.