Three-dimensional step-height measurement using Mirau-type spectral interference microscope with acousto-optic tunable filter as frequency scanning device

摘要

We propose a non-mechanical scanning Mirau-type spectral interference microscopic imaging system for the measurement of three-dimensional step-height of discontinuous objects. In this system a superluminescent diode is used as a broad-band light source, and an acousto-optic tunable filter (AOTF) as a high-resolution frequency scanning device. The interferometric system was made unbalanced by putting the reference mirror position exactly half-way between the top and bottom of the total step-height of the discontinuous object. While scanning the frequency of the broad-band light source using AOTF, the interference fringes move in opposite directions on the top and bottom of the object, respectively. A two-dimensional Fourier transform method was used for the unique determination of the sign of fringe movement over a large area of the object without any photo-detectors and fringe counters. From the detected sign of the fringe movement and phase information, the three-dimensional step-height is measured. Experimental results of the measurement of 100μm step-height are presented. The main advantages of the proposed system are non-mechanical scanning and large measurement range without ambiguity in the sign of phase.