We apply the numerical aperture increasing lens technique to widefield subsurface imaging of silicon integrated circuits. We demonstrate lateral and longitudinal resolutions well beyond the limits of conventional backside imaging. With a simple infrared widefield microscope (lambda(0) = 1.2 microm), we demonstrate a lateral spatial resolution of 0.26 microm (0.22 lambda(0)) and a longitudinal resolution of 1.24 microm (1.03 lambda(0)) for backside imaging through the silicon substrate of an integrated circuit. We present a spatial resolution comparison between widefield and confocal microscopy, which are essential in integrated circuit analysis for emission and excitation microscopy, respectively.
We investigate the effect of an annular pupil-plane aperture in confocal imaging while using an NA increasing lens. We show that focal spot shape is highly sensitive to both polarization and angular spectrum of the incoming light. We demonstrate a lateral spatial resolution of 145 nm (lambda(0)/9) in the direction perpendicular to the polarization direction.
We apply the NA-increasing lens technique to confocal and wide-field backside microscopy of integrated circuits. We demonstrate 325 nm (lambda(0)/4) lateral spatial resolution while imaging metal structures located inside the interconnect layer of an integrated circuit. Vectorial field calculations are presented justifying our findings.
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