Simplified differential phase optical microscope

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.

Photoresist thickness measurement using laser-induced fluorescence

A technique is proposed to measure the thickness of a small area of photoresist film on a substrate. This technique uses the fluorescence (peak wavelength, ~600 nm) induced in the film by a focused laser beam (wavelength, 497 nm). An initial calibration line is obtained by comparing several thicknesses and their related fluorescence. The film's thickness is then determined from its fluorescence signal. The laser spot size and the accuracy of this measurement have also been estimated.

Full-field modeling of the longitudinal electro-optic probe

Optical polarization changes and mode coupling due to spatially varying anisotropic perturbations in caused by electro-optic, acousto-optic, and other effects have been widely studied for both plane-wave and fiber mode propagation. A new optical S-parameter analysis of these effects, applicable to arbitrary optical field distributions, is presented. It is applied to evaluating the performance of the longitudinal electro-optic probe used for noninva-sively examining GaAs integrated circuits. Error in probe measurements of circuit voltage distributions can be characterized by considering the probe as a scanned electro-optic spatial filter.

Angstrom resolution optical profilometry for microscopic objects

An instrument capable of recording the amplitude and phase of reflected light with a phase resolution of better than lambda/3000 and the lateral resolution of a confocal scanning microscope was built. The instrument is based on a commercial microscope body and uses the regular interference contrast optics. The modifications consisted of adding a coherent (heterodyne) detector and a confocal laser scanning system. Two-dimensional surface images of amplitude, slope, and profile were taken with a step height resolution of typically 0.5-2 A. The instrument is described, and its characteristics for surface profilometry are discussed.