摘要 |
Apparatus for optical inspection of a sample includes a detector assembly, which is configured to receive radiation from a focal area on the sample, and a translation mechanism, which is operative to impart motion to at least one of the detector assembly and the sample so that the focal area of the detector assembly translates over the sample along a translation path. A height sensor is positioned in a known location relative to the detector assembly so as to measure a height of the height sensor relative to a point on the sample that is ahead of the focal area by a predetermined distance along the translation path. A controller is adapted to determine an estimated height of the detector assembly, responsively to the height measured by the height sensor along the translation path.
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