Phase-stepping microscopy (PSM): a qualification tool for electronic and optoelectronic devices

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Abstract
Phase-stepping microscopy (PSM) is a useful optical metrology technique for the qualification of electronic and optoelectronic devices. Based on interference microscopy, the method uses a CCD camera and a digital image-processing system for automatic fringe analysis, leading to the calculation of the three-dimensional relief of a surface. A vertical resolution of 1 nm is achieved, with a horizontal resolution of 0.6 mu m. The authors describe the PSM system, the performance of the instrument and some of its limitations. To illustrate the uses of PSM, some applications are given in the analysis of defects in semiconductor materials. Results are given of a microprecipitate-related hillock defect on a quaternary layer of InGaAsP on InP made by MOCVD used in the fabrication of lasers. Surface analysis results of an optical guide etched on a quaternary layer are also described. Finally, some initial work is presented in the study of the cross-sectional geometry of the gate recess in FET devices.