Phase contrast monitoring for extreme ultraviolet (EUV) mask defect inspection

摘要

A method and apparatus for inspecting an extreme ultraviolet (EUV) reticle using an optical inspection instrument is disclosed. An inspection instrument with a pupil filter located in the imaging pupil is used to obtain a test image or signal from an output beam that is reflected and scattered from the test portion of the EUV test reticle. The pupil filter is configured to provide phase contrast within the output beam. A reference image or signal is obtained for a reference reticle portion that is designed to be the same as the portion of the test reticle. The test and reference images or signals are compared and based on the comparison it is determined whether the test reticle portion has any candidate defects. For each of the plurality of test reticle portions of the reticle, the operation for using the inspection instrument, the operation for acquiring the reference image or signal, the operation for comparing, and the operation for determining are repeated. Based on any candidate defects determined to be present, a defect report is generated.