Multi-directional overlay metrology using multiple illumination parameters and isolated imaging

An optical metrology system comprising:

• one or more illumination optics configurable to illuminate an overlay target on a sample with one or more first illumination beams and one or more second illumination beams when implementing a metrology recipe, wherein at least one of the first illumination beams and at least one of the second illumination beams are incident on the overlay target simultaneously, wherein the overlay target in accordance with the metrology recipe includes first-direction periodic features in a first set of layers of the sample, the first-direction periodic features distributed along a first measurement direction, wherein the overlay target in accordance with the metrology recipe further includes second-direction periodic features in a second set of layers of the sample, the second-direction periodic features distributed along a second measurement direction different than the first measurement direction;
• one or more collection optics configurable to generate one or more images of the overlay target on one or more detectors based on diffraction of the one or more first illumination beams and the one or more second illumination beams by the overlay target when implementing the metrology recipe, wherein diffraction orders of the one or more first illumination beams contribute to resolved image formation of only the first-direction periodic features, wherein diffraction orders of the one or more second illumination beams contribute to resolved image formation of only the second-direction periodic features;
• and
• a controller communicatively coupled to the one or more detectors, 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 measurement direction based on the one or more images;
• and
• generate a second overlay measurement along the second measurement direction based on the one or more images.

An optical metrology method comprising:

• illuminating an overlay target on a sample with one or more first illumination beams and one or more second illumination beams, wherein at least one of the first illumination beams and at least one of the second illumination beams are incident on the overlay target simultaneously, wherein the overlay target in accordance with a metrology recipe includes first-direction periodic features in a first set of layers of the sample, the first-direction periodic features distributed along a first measurement direction, wherein the overlay target in accordance with the metrology recipe further includes second-direction periodic features in a second set of layers of the sample, the second-direction periodic features distributed along a second measurement direction different than the first measurement direction;
• generating one or more images of the overlay target on one or more detectors based on diffraction of the one or more first illumination beams and the one or more second illumination beams by the overlay target, wherein diffraction orders of the one or more first illumination beams contribute to resolved image formation of only the first-direction periodic features, wherein diffraction orders of the one or more second illumination beams contribute to resolved image formation of only the second-direction periodic features;
• generating a first overlay measurement along the first measurement direction based on the one or more images;
• and
• generating a second overlay measurement along the second measurement direction based on the one or more images.