We have previously described a new noncontacting profilometer with Angstrom-level precision and accuracy,2,3. We have used this instrument to measure a variety of profiles, from diametral scans of steep aspheres to axial and circumferential scans of cylindrical elements. Here we review the theory of operation, show some relevant measurement results, and discuss the upgrades underway that will make the instrument particularly well suited to the exotic mirrors needed for soft X-ray lithography. Our technique is based on the measurement of test piece curvature along a line, and the double integration of the curvature to obtain a height profile. We measure curvature by differentially measuring the slope at two closely neighboring points. Because of its differential nature, the technique is self-referencing. But, it is self-referencing in a far more important respect than differential height measuring techniques. This is because slope, even when it is obtained differentially, is a relative quantity. Curvature, though, is unique because its value is intrinsic to the test piece.
This article is from 'OSA Proceedings of the Topical Meeting on Soft-X-Ray Projection Lithography Held in Monterey, California on 10-12 April 1991. Volume 12', AD-A252 998, p134-136.