New concept of information resolution in scanning electron microscope images

As a new means to evaluate SEM images from the viewpoint of image information, we have proposed information resolution, Rinf, defined as a spatial length per bit in information-passing capacity (IPC). The IPC densities (per basic area) were carried out by both taking into account the signal-to-noise ratio of the statistical mean power densities and applying a previously reported fitting functions to an optical system with an arbitrary size of aberration, diffraction (including λ=0), and source. Here, the ν-independent specimen contrast of τs(ν)=1 [used in Eq. (9)] is assumed. General characteristics on Rinf are typically plotted as a curve of log (Rinf/Rinf,ideal) vs. log T, where T is (B2m+C4m)1/2, Bm and Cm are the modified spherical and chromatic aberrations, respectively. The subscript “ideal” represents an aberration-free optical system. The values of Rinf [calculated by Eq. (11)] are compared to those of the conventional beam size d [calculated by Eq. (1)] and the previously reported modified resolution Res [calculated by Eq. (7)]. It was found that Rinf, min value is 0.3–0.9 times as small as the dmin value and its corresponding beam semi-angle αinf,min is 1.2–1.8 times as large as the αconv,min value (depending on S/N).