Four-beam laser interferometry for three-dimensional microscopic coordinate measurement.
We propose a new method for calibrating the three-dimensional (3-D) behavior of a scanning stage. Four laser interferometers are used to determine the position of the corner point of a corner mirror attached to the stage. We calculated the 3-D coordinate of the corner point by using only the length information given by the four laser interferometers; thus a method is realized that is traceable from the practical definition of length and that facilitates the optical alignment that is necessary for the interferometers. We calibrated a commercial 3-D stage by the proposed method with a coordinate accuracy of 20-30 nm.
Development of a Coordinate Measuring System with Tracking Laser Interferometers
Summary A highly accurate co-ordinate measuring system for a large measurement area (larger than 1m×1m) is developed. The system consists of two target-tracking stations, each with a laser-interferometer and a twin cube-corner mirror attached to a target. Since the co-ordinate of the target is computed from the radial distances between the target and the rotation axes of the tracking stations, the system can give position-measuring accuracy better than 1μm, regardless of the absolute distances involved. Experimental comparisons between the system developed and a commercial co-ordinate measuring machine show that the position-measuring accuracy of the developed system is better than 1.0 μm in a plane that is 600-800 mm away from the tracking stations.
A New Differential Laser Interferometer with a Multiplied Optical Path Difference
Summary The new laser interferometer having, high sensitivity and good stability is described in this paper, which has been developed for the purpose of measuring the line widths and pitches of micropatterns like LSI. In order to get an optically high sensitivity of 10 times, the optical path difference of the interferometer is multiplied by two pairs of prisms and the differential displacement of a fine movement table. The optical paths multipassed between a pair of cube corner and right-angled prisms are arranged biaxially by using the peculiar characteristic of a cube corner prism. By the arrangement of optical elements used in the interferometer it is possible to reduce the influences of both thermal expansion and refractive index change of air. And it is confirmed by theoretical analysis and experimental results that the new interferometer is sensitive and stable enough to measure micropatterns.