Abstract

We report on the use of Fresnel lenses in the failure analysis (FA) of actual failures. The design parameters affecting the performance of Fresnel lenses in terms of resolution, magnification, and field of view have been analyzed. It is demonstrated that the magnification depends linearly on the change in focus distance caused by the lens, normalized by the silicon thickness. The focus distance shift that can be obtained with the Fresnel lens is observed to saturate, whose root-cause remains to be investigated. The field of view is shown to increase with the silicon thickness and, to a lesser extent, with the number of lens rings. It has also been shown that these lenses are robust against patterning distortions. The OBIRCh responses of actual device failures before and after lens placement have been compared, demonstrating clearly the increase in magnification, resolution, and the ability to focus light which all translate into a better electrical fault isolation. All in all, this study proves the usefulness of Fresnel lenses for FA purposes and offers clear guidelines that will facilitate proper lens design.

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