Parallel scatterometry overlay metrology

An overlay metrology tool comprising:

• an illumination source configured to generate a first illumination beam distribution with a first linear polarization and a second illumination beam distribution with a second linear polarization orthogonal to the first linear polarization;
• an illumination sub-system to sequentially illuminate two or more cell pairs of an overlay target on a sample, wherein a particular one of the two or more cell pairs includes a first-direction cell with a grating-over-grating structure having periodicity along a first direction and a second-direction cell with a grating-over-grating structure having periodicity along a second direction orthogonal to the first direction, the illumination sub-system comprising:
• a first illumination channel to direct the first illumination beam distribution to the first-direction cell of one of the two or more cell pairs, wherein the first illumination beam distribution includes one or more first illumination beams with the first linear polarization;
• and
• a second illumination channel to direct the second illumination beam distribution to the second-direction cell of one of the two or more cell pairs simultaneously with the first illumination beam distribution, wherein the second illumination beam distribution includes one or more second illumination beams with the second linear polarization;
• a collection sub-system comprising:
• a first collection channel including one or more first-channel detectors at a first-channel detection plane;
• a second collection channel including one or more second-channel detectors at a second-channel detection plane;
• an objective lens to collect light from the sample as collected light;
• and
• a polarizing beamsplitter to direct portions of the collected light associated with first-direction cells having the first linear polarization to the first collection channel and direct portions of the collected light associated with second-direction cells of the two or more cell pairs having the second linear polarization to the second collection channel;
• and
• a controller communicatively coupled to the first and second collection channels, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
• generate a first overlay measurement along the first direction based on data associated with the first-direction cells of the two or more cell pairs from the one or more first-channel detectors;
• and
• generate a second overlay measurement along the second direction based on data associated with the second-direction cells of the two or more cell pairs from the one or more second-channel detectors.

An overlay metrology method comprising:

• generating a first illumination beam distribution with a first linear polarization and a second illumination beam distribution with a second linear polarization orthogonal to the first linear polarization;
• sequentially illuminating two or more cell pairs of an overlay target on a sample with an illumination system, wherein each of the two or more cell pairs includes a first-direction cell with a grating-over-grating structure having periodicity along a first direction and a second-direction cell with a grating-over-grating structure having periodicity along a second direction orthogonal to the first direction, wherein the illumination system simultaneously illuminates the first-direction cell with the first illumination beam distribution and the second-direction cell with the second illumination beam distribution;
• collecting light from the sample as collected light;
• directing portions of the collected light associated with first-direction cells of the two or more cell pairs to a first collection channel;
• directing portions of the collected light associated with second-direction cells of the two or more cell pairs to a second collection channel;
• generating a first overlay measurement along the first direction based on data associated with the first-direction cells of the two or more cell pairs;
• and
• generating a second overlay measurement along the second direction based on data associated with the second-direction cells of the two or more cell pairs.