Nanoscale optical microscopy in the vectorial focusing regime

Abstract

It has been known since 1959 that the focal-plane intensity distribution produced by focusing polarized light with a high-numerical-aperture lens should be highly asymmetric¹. Remarkably, the consequences of this fundamental effect in direct image acquisition have remained unexploited, although vectorial effects have been observed in the contexts of free-space focusing², molecular fluorescence³ and photolithography⁴. By using extreme-numerical-aperture (values of 3.5), solid-immersion microscopy^5,6,7 we have obtained images of a silicon integrated circuit showing, for the first time, the dramatic influence of polarization on their spatial resolution, with values from 100 nm to 250 nm. Our data show that polarization-sensitive imaging can substantially surpass the scalar diffraction limit embodied by classical formulae such as Sparrow's criterion. Such performance will have an impact on activities such as integrated-circuit failure analysis, where optical inspection faces serious challenges from the sub-100-nm feature sizes routinely used in production devices.