We report on a method for microstructure inspection using the `edge-birefringence', i.e. the polarization anisotropy caused by the structure edges. A liquid-crystal phase- shifter is inserted into the imaging optics of a reflection- made microscope, and the principle of phase-shifting interferometry is applied to measure phase and contrast of the TE-polarized image with the TM-polarized image as reference. This common-path interferometrical method provides a selective edge detection because the polarization difference is localized at the structure edges. It is useful for a simple but accurate measurement of microstructure linewidths. The (unwrapped) phase image can show supersteep edges that we attribute to phase singularities. Because with decreasing structure width the polarization difference increases, the method is particular apt for subwavelength line-structures. The images, however, become then strongly dependent on the experimental parameters like focus- position, structure material, -width and -depth.
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