In the extreme ultra-violet (EUV) lithography, a defect-free mask blank is one of the critical issues for high volume manufacturing. The defects of EUV mask are typically classified into phase defects and amplitude defects. The phase defects, which may be originally included in substrate or generated during multilayer deposition, are not easily detected after the deposition of absorber and buffer films, since an inspection tool using the visible light shows strong absorption in this wavelength range. In addition, it is important to confirm the level of blank mask defects before e-beam writing in order to prevent yield drop of mask manufacturing. Confocal inspection method has been developed and widely used to inspect substrate and blank mask in current optical and EUV lithography. However, this method can only detect defects which are located on flat surface and buried near the surface. In this paper, both the confocal inspection and patterned mask inspection are simulated by rigorous analysis method and also experimentally determined. As a result, simulation shows good agreement with experiments, and thus the simulation tool can be applied to estimate detectability and printability of multilayer defects. For patterned mask inspection, mask near field images are calculated by the rigorous method. Then, aerial images of EUV mask in patterned mask inspection system are simulated and several properties are also investigated.