Camera-aided focusing in optical metrology

摘要

A side camera is combined with a conventional optical metrology system to image the object during the focusing scan performed in normal focusing procedures. The camera is positioned in fixed spatial relation to the objective and with its focal plane in substantial alignment with the optical axis of the objective so as to image the object during the scan. The camera is used to monitor the illumination spot formed on the object by the beam projected through the system's objective. The in-focus position is found by moving the object such that the illumination spot coincides with the objective's focus seen through the camera.

主权项

1. Focusing apparatus in a measurement system for optical metrology wherein optical measurement signals are detected by a measurement detector through a measurement optical assembly, comprising:
a measurement optical assembly with a focal point along an optical axis thereof; a stage adapted to receive a sample; a scanning mechanism for effecting a focusing scan by varying a distance between the sample and the measurement optical assembly; and a side camera; said camera being in addition to the measurement detector of the system and having an optical axis positioned at an angle in relation to the optical axis of the measurement optical assembly so as to image an illumination spot produced on the sample during said focusing scan.