High numerical aperture subsurface imaging

Continuous miniaturization of integrated circuits (IC) requires more effective defect detection and failure analysis techniques. As a non-invasive technique, optical imaging is a ubiquitous tool for lateral registration of failure analysis measurements to the circuit layout. Backside imaging through the silicon substrate has become an industry standard since the presence of a multitude of opaque interconnect layers hinders optical imaging from the front side. Employing a numerical aperture increasing lens (NAIL) in backside imaging overcomes the limitations due to the planar silicon-air interface. A NAIL is a plano-convex lens when placed on a planar surface; it can improve the focusing and collection of light in subsurface microscopy of ICs.;Implementation of NAIL in IC imaging allows for numerical aperture (NA) values of up to 3.4 in silicon. While paraxial approximation holds for small NA, at very high NA focused light exhibits unique properties that cannot be predicted by scalar beam optics. In this dissertation, we demonstrate spatial resolution manipulation in selected directions controlling the polarization direction of the linearly polarized light. Experimental demonstration of 145nm (lambda/9) lateral resolution is presented by controlling the input beam shape besides the polarization direction in a fiber based confocal microscope. When combined with the high longitudinal magnification provided by the NAIL geometry, high NA imaging allows us to examine focused light near a dielectric interface in great detail. The experiments show that the optimum focus of a microscope depends on the polarization of light when imaging in the vicinity of a dielectric interface in a high NA microscope. In addition, the first characterization of the limits in imaging the interconnect layers of an IC is presented. Full vectorial modeling of optical fields is included supporting the experimental findings.;Generally considered as an unsophisticated imaging tool, the widefield microscope reveals impressive results when used in conjunction with a NAIL. A lateral resolution of 260nm (lambda/5) is achieved with minimal background effects. Moreover, individual layers of an IC are imaged separately due to the high NA provided by the NAIL method despite the lack of out-of-focus light rejection.