Figure 10 shows the difference image in the case of extrusion defects on the -buffered Ru-capped ML. In the case of 1,000 eV, the 16-nm-sized defect was detected with . This peak signal intensity is 1.6 times higher than that of an Ru sample with 1,000 eV. Some false defects observed at 1,000 eV can be removed by elevating the threshold to as shown in Fig. 10(f). We already had reported that the SEEC of the Ru-capped ML was affected by the underlying Si and Mo with lower SEECs than that of Ru.10 In the case of -buffered Ru-capped ML, the thickness of Ru is two times thinner than that of the Ru-capped ML sample. Furthermore, density and SEECs of are much lower than those of Ru. Therefore, the SEECs of -buffered Ru-capped ML are much affected by the underlying layers.10,19 As shown in Fig. 11(a), the SEECs of -buffered Ru-capped ML were lower than those of Ru-capped ML when the incident beam energy was , whereas those SEECs are almost the same in the range of 200 to 500 eV. These phenomena affect the sensitivity of defect inspection as shown in Fig. 11(b). The defect signal intensity is almost the same in the case of 250 and 500 eV on both samples, while, on the other hand, in the case of 1,000 eV, the intensity for -buffered Ru-capped ML is 1.6 times higher than that for the Ru sample (intensities are 19.7 and 12.2, respectively) as indicated by the dashed circle in Fig. 11(b). However, in the case of 3,000 eV, the defect signal is lower than in the case of 1,000 eV in spite of the large SEEC difference. This phenomenon can be explained by electron scattering near the edge of a Ta-based absorber layer as shown in Fig. 12.20 In the case of 3,000 eV, electron scattering is severe and affects the opposite side wall and bottom of the pattern as compared with 500 and 1,000 eV. Such severely scattered electrons become a source of noise and degrade the signal-to-noise ratio of the defect. Figures 13(a) and 13(b) show the simulated images with extrusion defects on the -buffered Ru-capped ML at the incident beam energy of 1,000 and 3,000 eV, respectively. The L/S patterns are observed at the center of the images, and dark areas at the top and bottom sides of the image correspond to the capping layer. It is clearly shown that a blurred image was obtained at 3,000 eV as compared with the case at 1,000 eV. Figure 13(c) shows their signal intensity profiles along the arrows indicated in Figs. 13(a) and 13(b). The intensity difference between the two conditions with 1,000 and 3,000 eV for the capping layer indicated as (a) corresponds to its SEEC difference between these conditions. In a similar manner, the intensity difference between 1,000 and 3,000 eV for the absorber layer indicated as (b) corresponds to its SEEC difference between these conditions. However, peak-to-peak intensity swing of the L/S pattern signal at 3,000 eV (c) is smaller than that at 1,000 eV (d) in spite of the large SEEC difference. This is because the severely scattered electrons become the source of noise, and then the effect of the large SEEC difference is blocked by that noise. This result indicates that the sensitivity of defect detection is affected by the SEEC difference and also by electron scattering. Thus, the small incident beam energy is preferable when the SEEC difference is sufficiently high.