Scanning scatterometry overlay measurement

An overlay metrology system comprising:

• an illumination sub-system configured to provide a first pair of opposing illumination lobes along a first measurement direction and a second pair of illumination lobes along a second measurement direction orthogonal to the first measurement direction, wherein the illumination sub-system is further configured to sequentially illuminate an overlay target on a sample with first and second illumination configurations, the first illumination configuration including one illumination lobe from each of the first and second pairs of opposing illumination lobes, the second illumination configuration including a remaining illumination lobe from each of the first and second pairs of illumination lobes, wherein the overlay target comprises:
• a first set of one or more cells including one or more grating-over-grating features formed from periodic structures on a first sample layer and a second sample layer, wherein the one or more grating-over-grating structures are periodic along the first measurement direction;
• and
• a second set of one or more cells including one or more grating-over-grating features formed from periodic structures on the first sample layer and the second sample layer, wherein the one or more grating-over-grating structures are periodic along the second measurement direction;
• an imaging sub-system comprising:
• an objective lens;
• and
• a detector configured to generate a first image and a second image of the overlay target, wherein the first image is formed with a single non-zero diffraction order from each illumination lobe in the first illumination configuration, wherein the second image is formed with a single non-zero diffraction order from each illumination lobe in the second illumination configuration;
• and
• a controller communicatively coupled to the detector, the controller including one or more processors configured to execute program instructions causing the one or more processors to determine an overlay error between the first sample layer and the second sample layer of the sample along the first and second measurement directions based on the first and second images.

An overlay metrology method comprising:

• sequentially illuminating an overlay target on a sample with a first illumination lobe and a second illumination lobe, wherein the overlay target includes one or more grating-over-grating features formed from periodic structures on a first sample layer and a second sample layer, wherein the one or more grating-over-grating structures are periodic along a measurement direction;
• generating a first image and a second image of the overlay target with a detector, wherein the first image includes an unresolved image of the one or more grating-over-grating structures formed from a single non-zero diffraction order of the first illumination lobe from the one or more grating-over-grating structures along the measurement direction, wherein the second image includes an unresolved image of the one or more grating-over-grating structures formed from a single non-zero diffraction order of the second illumination lobe generated by the one or more grating-over-grating structures along the measurement direction;
• and
• determining an overlay error between the first sample layer and the second sample layer of the sample along the measurement direction based on the first image and the second image.