To simulate a defect inspection with a PEM technique, simulated images were obtained using CHARIOT Monte Carlo software (Abeam Technologies, Inc.).13 Software with 72 cores was installed in an all-in-one server computer, Proliant DL 980 G2 (Hewlett Packard), with 80 cores. Figure 1 shows schematic representations of a sample EUV mask used for the simulation. On this mask, defects with various sizes were fabricated on hp 64-nm line-and-space (L/S) patterns. Ta-based absorber layers with a 66-nm thickness were fabricated on EUV reflective multilayers (MLs) capped with 2.5-nm thick Ru. The MLs comprised 40 pairs of 3-nm thick Mo and 4-nm thick Si. The thicknesses of the defects were 66 nm, which were same as that of the absorber layers. The sizes of the defects were , , , and . According to the ITRS-2012 update, the defect size on the EUV mask is defined as the square root of the defect area on a 2-D mask surface. Because all the defects in this study were square, hereafter, we refer to them as 64-, 32-, 22-, and 16-nm defects. A square shaped collimated beam, in size, was used to demonstrate the PEM technique. To obtain the simulated image, a -sized image detector with a pixel size of was placed 40 nm away from the surface of the sample. In the real application, PEM image quality strongly depends upon the property of imaging optics. We have already reported that the PEM image of a hp 64-nm L/S pattern with a contrast of 0.5 can be experimentally obtained using our developing tool by improving its electron beam optics.4,5 In this simulation, the image contrast can be controlled by adjusting the distance between the image detector and the sample surface, because the simulated secondary electron image blurs as the distance becomes large. And, the image contrast of an hp 64-nm L/S pattern was confirmed to be 0.5 when the distance was 40 nm in this simulation. Therefore, the image detector was placed 40 nm away from the surface of the sample in order to demonstrate the same contrast as the experimentally obtained image. To investigate the dependency of the number of electrons per pixel on the defect inspection, the current densities of , , and , all with same dwell time of 1 ms, were used. Because the pixel size of the detector was , the average number of electrons per pixel in each current density corresponded to 50, 500, and 3000 electrons per pixel, respectively. Primary electrons with energies of 50, 250, 500, 1000, and 3000 eV were used to investigate the influence of the landing energies on the defect inspection. In the PEM system, only the secondary electrons with energies less than 50 eV can be selectively focused onto the detector by using electron energy filters in a real application. Therefore, the energy range of the detector was set from 0 to 50 eV to detect only those secondary electrons and to remove any influence of elastically backscattered electrons on the image, which may have similar energies to that of the primary electrons if the primary electrons of more than 250 eV were used. To improve the reliability of the simulation result, secondary electron yield curves of the utilized materials were applied for the calibration of experimental data. The difference between the simulated PEM image with defects and that without defects is defined as a difference image. To define the sensitivity of defect detection, we identified the intensity peak in the difference image with more than 10 times the intensity of the standard deviation of the background intensity levels as a defect. To enhance the detect signal intensities, image processing operations were applied to the simulated image.