Self-calibration of lateral non-linearities of an interference microscope

The accuracy of conventional interferometric methods for three-dimensional microscopy is limited by errors of intrinsic metrics inside interference microscopes. A simple self-calibration technique is proposed for evaluating linearity errors of an interference microscope in the X- and Y-directions, which result from distortions of the CCD pixel arrays and objective lens. In this self-calibration technique, an inclined flat surface is used as the specimen. Two sets of profile measurement data before and after a small shift of the specimen in the X- or Y-directions are used to obtain the linearity error in each direction. Computer simulations are carried out to analyze the influence of error sources. Experimental results of calibrating a commercially available scanning white light interference microscope are also presented.