In this paper, rigorous electromagnetic simulation is used to investigate the behavior of line defects in EUV masks. Using the Modal Method by Fourier Expansion, the geometry of the structure as well as the polarization state can be handled. A simple analytical model has been developed in order to generate the input geometry for the simulations. The deposition conditions can be mimicked by changing an empirical parameter representing the planarisation properties of the process. The influence of the defect size and of its position in the multilayer mirror is analyzed. The position of the defect with respect to an absorber feature is very important and is also considered.It is shown that the size of the nucleation particle by itself is not a relevant parameter to describe a defect. The process conditions modify largely the propagation of the defect into the multilayer mirror and induce very large variation of its printability. Some defects that do not affect the surface of the mirror can induce a non negligible intensity drop

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