High spatial resolution subsurface thermal emission microscopy

In this paper, we demonstrate the improvement the numerical aperture increasing lens (NAIL) yields in thermal emission microscopy of Si ICs. Current Si IC technology has reached submicron process size scales, well beyond the spatial resolution capability of conventional thermal emission microscopy. Thermal emission microscopy measures the spatial distribution of temperature in a sample. The spatial distribution of temperature within a sample can be calculated, because the optical power emitted by the sample is a function of its local temperature. To evaluate the longitudinal spatial resolution we take successive images at different defocus distances in the longitudinal direction. The FWHM of the signal from the positive defocus represents a significant improvement of the longitudinal spatial resolution over conventional thermal emission microscopy, where the ultimate limit is 18 /spl mu/m.