Abstract: A new approach to measuring submicron linewidths using optical phase-shifting interferometry is proposed. The technique has two main features. First, the surface topography is measured directly by determining phase information from the wavefront reflected from the surface of the object. Theoretical analysis indicates that the phase image of a line feature gives better lateral resolution than that of the intensity image of the same optical system. By comparing the intensity images and phase images from the computer simulations, it will be shown that the phase image (1) is affected less by the diffraction limitation; (2) has sharper edge definition; and (3) is insensitive to the variations of material composition and step height of the object. Second, the surface reflectivity can also be measured using phase-shifting interferometry. Unlike the intensity image measured by conventional methods, the measured reflectivity is not affected by any variations associated with the light source across the entire illumination field. The relative reflectivity between the line feature and the substrate is then determined. These advantages will result in better resolution and accuracy in measuring submicron linewidths. Theory and simulations predict that accurate measurements of 0.2 $mu@m linewidths should be possible.!20
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