Absolute calibration of step height by a novel interferometric microscope

Abstract

As a numerical aperture of objective in interferometric microscope increases, the interference fringe spacing, in order word, the basic scale of the measurement becomes greater than half a wavelength of light source due to the obliquity effect of converging illumination. The effect is the most serious uncertainty source when the step height of the standard specimen is calibrated by the interferometric microscope. Therefore, we have developed a novel phase-shifting interferometric microscope whose interference fringe spacing is absolutely calibrated. The scheme and the instrument that realize the absolute fringe spacing calibration and 3D profile measurement by the phase-shifting interferometry (PSI) at the same time, are described. The PSI measurement is carried out under the condition in which two interference fringes are made in the field ofview. The phase calculation error by the PSI is also estimated under the condition. If the sample with 100 nm step height is measured, the typical expanded uncertainty is 0.6 nm.