Patent ID: 11874102
Assignee: KLA CORPORATION
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 20:
21. A method comprising:
forming a first target structure on a sample in accordance with a metrology recipe, wherein the first target structure is formed within at least one of a first area and a third area of a first layer of a sample, the first target structure comprising two or more first cells containing two or more first cell pattern elements arranged periodically;
forming a second target structure on the sample from a photoresist material in accordance with the metrology recipe, wherein the second target structure is formed within at least one of a second area and a fourth area of a second layer of the sample, the second target structure comprising two or more second cells containing two one or more second cell pattern elements arranged periodically, wherein the second target structure is formed from a photoresist material with sufficient thickness to induce asymmetry in at least some of the second cell pattern elements when fabricated; and
receiving one or more images of the first and second target structures from an optical metrology tool;
determining a center of gravity for each of the two or more first cells based on averaging individual center of gravity positions of each of the associated first cell pattern elements from the one or more images;
determining a center of gravity of the first layer based on averaging the centers of gravity for the two or more first cells;
determining a center of gravity for each of the two or more second cells based on averaging individual center of gravity positions of each of the associated second cell pattern elements from the one or more images;
determining a center of gravity of the second layer based on averaging the centers of gravity for the two or more second cells; and
determining an overlay value of the sample from the first target structure and the second target structure by computing a difference between the center of gravity of the first layer and the center of gravity of the second layer.