Single-cell scatterometry overlay with sensitivity calibration

A metrology system comprising:

• a metrology sub-system configured to generate metrology data associated with a sample, wherein the metrology sub-system is configured to illuminate a sample with at least one illumination beam from an illumination source and direct measurement light from the sample onto one or more detectors using one or more lenses;
• wherein the metrology sub-system is configured to implement a metrology recipe by:
• generating metrology data associated with a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample, wherein the metrology data associated with the first set of overlay targets is associated with separate pupil-plane measurements of intensities of two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
• and
• generating metrology data associated with a second set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets;
• and
• a controller communicatively coupled to the metrology sub-system, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
• receive, from the metrology sub-system in accordance with the metrology recipe, metrology data associated with the first set of overlay targets;
• receive metrology data associated with the second set of overlay targets;
• generate sensitivity metrics at locations of the first set of overlay targets based on the metrology data associated with the first set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with the pupil plane of the metrology sub-system based on one or more difference signals associated with differences between the pupil-plane measurements of the intensities of the two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
• determine sensitivity metrics at locations of the second set of overlay targets, wherein the sensitivity metric for a particular location of a particular one of the second set of overlay targets is generated based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is determined based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
• generate overlay measurements for the first set of overlay targets based on the sensitivity metrics and the metrology data associated with the first set of overlay targets;
• and
• generate overlay measurements for the second set of overlay targets based on the metrology data associated with the second set of overlay targets and the sensitivity metrics at the locations of the second set of overlay targets.

A method comprising:

• generating, with a metrology sub-system in accordance with a metrology recipe, metrology data associated with a first set of overlay targets and a second set of overlay targets on a sample, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample, wherein the metrology data associated with the first set of overlay targets is associated with separate pupil-plane measurements of intensities of two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets, wherein the metrology data associated with the second set of overlay targets is based on fewer cells than the metrology data associated with the first set of overlay targets;
• generating sensitivity metrics at locations of the first set of overlay targets based on the metrology data associated with the first set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with the pupil plane of the metrology sub-system based on one or more difference signals associated with differences between the pupil-plane measurements of the intensities of the two or more diffraction orders of the illumination beam by each of the at least two cells of the first set of overlay targets;
• determining sensitivity metrics at locations of the second set of overlay targets, wherein the sensitivity metric for a particular location of a particular one of the second set of overlay targets is generated based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is determined based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
• generating overlay measurements for the first set of overlay targets based on the sensitivity metrics and the metrology data associated with the first set of overlay targets;
• and
• generating overlay measurements for the second set of overlay targets based on the metrology data associated with the second set of overlay targets and the sensitivity metrics at the locations of the second set of overlay targets.

A sample comprising:

• a plurality of overlay targets distributed across a plurality of fields, wherein the plurality of overlay targets comprises:
• a first set of overlay targets, wherein each of the first set of overlay targets includes at least two cells with different intended offsets between overlapping features on two layers of the sample;
• and
• a second set of overlay targets, wherein each of the second set of overlay targets includes fewer cells than the first set of overlay targets
• wherein the first set of overlay targets and the second set of overlay targets are distributed across the sample such that a sensitivity metric for a particular location of a particular one of the second set of overlay targets is determinable based on N nearest overlay targets in the first set of overlay targets, wherein a value of N is based on at least one of a rate of change of the sensitivity metric across the sample or a density of the first set of overlay targets;
• wherein a distribution of the first set of overlay targets and the second set of overlay targets is configured to provide that overlay measurements for the second set of overlay targets are determinable based on metrology data associated with the second set of overlay targets and sensitivity metrics generated per pixel associated with a pupil plane of a metrology sub-system based on metrology data associated with separate pupil-plane measurements of intensities by the metrology sub-system of two or more diffraction orders of an illumination beam by the first set of overlay targets provides overlay measurements at locations of the first set of overlay targets;
• and
• wherein metrology data associated with diffraction by the second set of overlay targets and sensitivity metrics from the metrology data associated with the first set of overlay targets provides overlay measurements at locations of the second set of overlay targets, wherein the sensitivity metrics are generated per pixel associated with a pupil plane of a metrology sub-system based on metrology data associated with separate pupil-plane measurements of intensities by the metrology sub-system of two or more diffraction orders of an illumination beam by the first set of overlay targets provides overlay measurements at locations of the first set of overlay targets.