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The results of recent research on synthetic electro-optic imaging using a Linnik interference microscope are presented. A new technique is used in which images are produced by calculating the degree of coherence between corresponding pixels in the object and reference image planes of the Linnik microscope. Each pixel in the synthetic image is a function of this degree of coherence. This amounts to what one might call "Coherence Probe Imaging." The images have the properties that all parts of the object which are out of focus appear dark, those in focus appear bright, and the depth of focus is very narrow. Three dimensional images can be produced by moving the object in the vertical direction and recording a number of optical sections of the image. Theoretical analyses and experimental results are presented. A model for the per-formance of the coherence probe microscope is first developed and then its performance is compared with that of a standard microscope and of a confocal laser scanning microscope within the context of this model. One figure shows the measured edge profile of a coherence probe microscope compared with a standard microscope for a clean edge of cleaved single crystal silicon. Another figure shows the measured z profile of the coherence probe microscope. Linewidth measurement algorithms are implemented on 3 dimensional images produced by the coherence probe microscope, and these measure the top width, the bottom width, and the height of the semiconductor lines independently. The amount of electronic hardware required for reasonable throughput is not prohibitive. Some results of comparison with Scanning Electron Microscopes are presented. Generally, the agreement is very good. Overall, the coherence probe microscope appears to have some promise for linewidth measurement applications. Several photographs show small defects on semiconductor devices as imaged by a coherence probe microscope and by a standard microscope, both illuminated with white light. Substantial resolution improvement is clearly discernable in these pictures suggesting that the coherence probe microscope may also be a promising imaging tool for defect detection.
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