New concept of information resolution in scanning electron microscope images

As a new means to evaluate SEM images from the viewpoint of image informati on, we have proposed information resolution, R-inf, defined as a spatial le ngth per bit in information-passing capacity (IPC). The IPC densities (per basic area) were carried out by both taking into account the signal-to-nois e ratio of the statistical mean power densities and applying a previously r eported fitting functions to an optical system with an arbitrary size of ab erration, diffraction (including lambda=0), and source. Here, the nu-indepe ndent specimen contrast of tau(s)(nu)=1 [used in Eq. (9)] is assumed. Gener al characteristics on R-inf are typically plotted as a curve of log (R-inf/ R-inf,R-ideal) vs log T, where T is (B-m(2) + C-m(4))(1/2), B-m and C-m are the modified spherical and chromatic aberrations, respectively. The subscr ipt "ideal" represents an aberration-free optical system. The values of R-i nf [calculated by Eq. (11)] are compared to those of the conventional beam size n [calculated by Eq. (1)] and the previously reported modified resolut ion R-es [calculated by Eq. (7)]. It was found that R-inf,R-min value is 0. 3-0.9 times as small as the d(min) value and its corresponding beam semi-an gle alpha(inf,min) is 1.2-1.8 times as large as the alpha(conv,min) value ( depending on S/N). (C) 2000 Elsevier Science B.V, All rights reserved.