Large field of view, high spatial resolution, surface measurements

Abstract

It is difficult in interferometric metrology to maintain high spatial resolution over a large field of view. Interferometric microscope measurements yield high resolution, but only over a small area. Other conventional interferometric systems can measure large areas, but they fail to provide the necessary spatial resolution. High spatial resolution over a large field-of-view (FOV) can be obtained by stitching together multiple high spatial resolution measurements of adjacent areas of a measured surface. The measurements can be fit together in a global sense, or by matching the piston and tilt over the overlap region. Care must be taken in the stitching process to make sure the measurements are precisely overlapped to minimize errors. The larger the overlap the easier it is to match data sets, but of course more data sets are required to get a given field of view. This paper shows that a 20 percent overlap gives a good trade off between having good repeatability and obtaining a large field of view with a minimum number of data sets. Typical measurement results are shown for stitching as many as 285 sub-regions.