Patent ID: 7286238

Claim:
A method of measuring test objects having multiple surface regions comprising steps of: illuminating an imageable portion of a test object having a plurality of surface regions separated from each other by distinct surface discontinuities; gathering interference data for the imageable portion of the test object from a plurality of interference patterns taken over substantially the same imageable portion at different measuring beam frequencies; considering the interference data in sets of corresponding pixels within the interference patterns associated with points on the test object; evaluating the interference data sets to determine a topographical measures of associated points on the test object to a first accuracy; comparing the topographical measures against a benchmark to distinguish between points on the test object that are within a first of the surface regions from points on a boundary separating the first surface region from one or more other surface regions of the imageable portion of the test object; and further evaluating the interference data sets of points within the first surface region to determine topographical measures of the points within the first surface region to a second higher accuracy than the points within the other surface regions.