Some effects on SEM imaging contrast will take place when the sample is tilting in SEM system. For instance, a change in tilt angle of sample in SEM system changes the secondary electron (SE) to backscattered electron (BSE) ratio, resulting contrast changes. Another example is that the contrast changes because sample tilting causes changes of generation (yield) and transmission (depending on the mean free path) of SEs as shown in Figure 4855a. Especially, the contrast of the edges of the structural features has more significant changes than that in the regions of the uniform materials. Due to these edge effects, the contrast distributions in the two A2 regions are different even though the materials in the two regions are identical. The contrast in B region is not symmetric even though the structure and compositions of the materials are identical.
Figure 4855a. Schematic shows contrast dependence on sample tilting: (a) cross-section showing that electron beam scans
at different locations. The ellipsoids are interaction volumes; (b) Schematic of SEM image contrast due to sample tilting.
Figure 4855b shows the emission of secondary electrons (SEs) as a function of the sample tilt angle (or incidence angle of the probe). As indicated, the emission of secondary electrons (SEs) increases as the tilt angle increases.
Figure 4855b. Emission of secondary electrons as a function of the sample tilt angle (or incidence angle of the probe).