Differential interference contrast imaging on a real time confocal scanning optical microscope

The first uses of Nomarski differential interference contrast imaging with the real time confocal scanning optical microscope are described. The advantage of differential interference contrast imaging in a confocal scanning microscope is that both the height and width of an edge can be measured without ambiguity, even if the edge is taller than half of a wavelength. Imaging modes are described in which (1) average reflectivity changes of the sample have been eliminated but the resulting edge enhanced images are nonlinear in phase, or (2) linear phase images are superimposed on an average reflectivity image of the sample. A third method has been developed which both eliminates the reflectivity image of the sample and generates edge enhanced images which are linear in phase for small phase changes. Applications to box-in-box overlay targets, imaging the passivation layer of an integrated circuit, and the measurement of sidewall slope are described.