| CPC G01J 1/0407 (2013.01) [G03F 7/70316 (2013.01)] | 40 Claims |
|
1. An overlay metrology system, comprising:
an objective lens;
one or more illumination optics configured to direct illumination from an illumination source to an overlay target on a sample through the objective lens when implementing a metrology recipe, wherein the overlay target in accordance with the metrology recipe includes a first grating with a first pitch on a first sample layer and a second grating with a second pitch on a second sample layer, wherein the second pitch is smaller than the first pitch, wherein the first and second sample layers are separated by a layer separation distance greater than a depth of field of the objective lens;
a detector; and
one or more collection optics configured to direct at least a portion of light collected by the objective lens to the detector, wherein the metrology recipe provides that diffraction orders of the illumination by the first grating collected by the objective lens are positioned below a threshold radius in a pupil plane and diffraction orders of the illumination by the second grating collected by the objective lens are positioned above the threshold radius in the pupil plane, wherein the one or more collection optics provide a radially-varying defocus distribution to compensate for the layer separation distance, wherein the first and second gratings are simultaneously in focus on the detector; and
a controller including one or more processors configured to execute program instructions causing the one or more processors to execute the metrology recipe by:
receiving one or more images of the overlay target from the detector in which the first and second gratings are simultaneously in focus on the detector; and
determining an overlay measurement between the first and second layers of the sample based on the one or more images.
|