Nanostructure identification using interference microscope with database

Interference microscopy with complex-amplitude pattern matching between an observed image and images stored in a database can observe nanostructures beyond the diffraction limit of light. The fundamental performance was investigated from size measurement of a single rectangular convex element with a height and width less than 100 nm under illumination light with a wavelength of 400 nm, using an objective lens with a numerical aperture of 0.85. A 50 nm rectangular convex element was reconstructed with an identification error rate of less than 1% and a root-mean square error lower than 1 nm in the presence of random noise. The element height could be detected with a lower error than its width when the element size was larger than ~ 50 nm. However, this tendency reversed when the size was smaller than ~ 50 nm, that is, the detection of the width had a slightly lower error than that of the height. In addition to these findings, position detection showed a small dependency on the element size when the position was in the laser beam.