Inspection of a sample by optical metrology

摘要

A sample 1 to be inspected is illuminated using a line 2 of coherent radiation from a laser 3 which is scanned across the sample with zero shear in the direction of scan A. Two relatively phase stepped, laterally displaced images of the sample are generated via a shearing element 8 by stepping or ramping the phase of one of the two images before being observed by a video camera 9 as a single interferogram. Successive video line scans of one image are incremented in phase to encode temporally information about the sample in one frame. The line of coherent radiation is scanned across the sample in synchronism with the frame scan of the camera. The encoded information is decoded by running a vertical convolution mask (figure 3) over the frame thereby enabling real time phase map display from a single camera.