Moreover, Kim et al. also confirmed this observation by numerical analysis.7,8 However, the mask structure should be taken into account when dealing with the mask fabrication processes, such as patterned mask inspection,9–13 critical dimension measurement (CD metrology),14,15 mask repair,16,17 and cleaning.18 Takai et al. reported that the reduction of the ML stack down to 20 pairs effectively avoided the collapse of the lines by the cleaning process.19 However, patterned mask inspection, CD metrology, and repair of this mask structure continue to pose challenges that need to be addressed. In these processes, electron beam (EB) techniques are often used; therefore, charging effects tend to cause some degradation of process accuracy. Takai et al. also reported that a conductive layer between the substrate [or some low thermal expansion material (LTEM)] and ML was effective to avoid an electrical floating of the EUV mask inside a black border of etched ML. With this approach, the EB image quality of the mask was effectively improved.20 As a result, the repeatability of metrology and the sensitivity of inspection for this type of EUV mask were also improved.20 However, the optimization of the material and structure of the conductive layer is critical, because this issue should be studied with taking into account the conductivity, durability for cleaning, oxidization, roughness, and etching selectivity of the material and the impact on the image contrast. We have learned that the image contrast is determined by the secondary electron emission coefficients (SEECs) of materials that the EUV mask is composed of and by the geometries involved. They also influence the defect detection sensitivity of a projection electron microscope (PEM) inspection system.21–25 The PEM has the advantage of a much higher throughput than what is achievable in the case of a conventional scanning electron microscope (SEM) type inspection system.9,11–13,21–26 That is because PEM probes a sample target with large field illumination, whereas SEM probes a sample with a spot beam. In this paper, we investigated the defect detectability of etched ML-EUV masks, and we propose a better and more feasible structure, which would improve the processing accuracy in working with EB systems.