Patent ID: 11921052
Assignee: KLA CORPORATION
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 17:
18. An inspection method comprising:
generating first-step images of a plurality of sample regions after a first process step;
generating second-step images of the plurality of sample regions after a second process step, wherein the second process step modifies the sample in at least one of the plurality of sample regions;
identifying one of the plurality of sample regions as a test region and at least some of the remaining sample regions as comparison regions, wherein the second-step image of the test region is a test image and the second-step images of the comparison regions are comparison images;
generating a multi-step difference image by a weighted subtraction of a combination of at least one of the second-step comparison images and at least two of the first-step images from the test image; and
identifying defects in the test region associated with the second process step based on the multi-step difference image.