Pupil-plane beam scanning for metrology

A metrology system comprising:

• an illumination source;
• a pupil-plane detector;
• a translatable stage configured to position a sample;
• a beamsplitter, wherein the beamsplitter is configured to receive illumination from the illumination source and direct the illumination along a measurement pathway;
• an objective lens configured to direct the illumination from the measurement pathway to the sample, wherein the objective lens is further configured to collect light from the sample and direct the collected light along the measurement pathway, wherein the beamsplitter is configured to receive the collected light from the measurement pathway and direct the collected light along a collection pathway to the pupil-plane detector;
• an optical relay between the objective lens and the beamsplitter along the measurement pathway, wherein the optical relay provides one or more relayed pupil planes between the objective lens and the beamsplitter, wherein the optical relay further provides a relayed field plane between the objective lens and the beamsplitter;
• one or more deflectors located at the one or more relayed pupil planes, wherein adjusting the one or more deflectors adjusts a position of the illumination from the illumination source on the sample while maintaining a stable optical path of the collected light along the collection pathway;
• a feedback detector located at the relayed field plane to image the position of the illumination from the illumination source on the sample;
• and
• a controller communicatively coupled to the translatable stage and the feedback detector, wherein the controller includes one or more processors configured to execute program instructions to:
• receive one or more images from the feedback detector including the location of the illumination from the illumination source on the sample;
• send control signals to the one or more deflectors to position the illumination from the illumination source, based on the one or more images from the feedback detector, on a selected measurement spot for a measurement;
• receive one or more measurement images from the pupil-plane detector;
• and
• generate one or more metrology measurements based on the one or more measurement images.

A metrology method comprising:

• illuminating a sample by directing illumination from an illumination source through a beamsplitter, along a measurement pathway, and through an objective lens;
• collecting light from the sample with the objective lens and directing the collected light along the measurement pathway and through the beamsplitter to a detector located at a pupil plane;
• and
• adjusting a position of the illumination from the illumination source on the sample with one or more deflectors located at one or more relayed pupil planes between the objective lens and the beamsplitter, wherein adjusting the one or more deflectors adjusts a position of illumination from the illumination source on the sample while maintaining a stable position of the collected light on the detector.