In this study, the nodule growth in ion beam sputtering Mo/Si coatings used for extreme-ultraviolet (EUV) lithography masks has been studied in relation with the number of Mo/Si pairs (period 7 nm). To trigger this growth, initial particles of different sizes (d=40-155 nm) were used. With a deposition angle of 30degrees and after the deposition of 40-60 Mo/Si pairs, the lateral size of nodules was found to grow up to similar to2d while its height ranged from d/6 to d/2 depending on the initial particle diameter. This lateral growth was demonstrated to mainly result from shadowing effect. Besides. a vertical smoothing effect was evidenced even in the case of relatively large initial seed particles (70-155 nm). It is attributed to adatom Surface diffusion which is also thought to promote a slowdown in the nodule lateral growth when increasing the coating thickness. Finally, a real case of mask blank realization is presented showing that a good knowledge of nodule growth is essential to properly analyze the defect characteristics of EUV mask blanks. (C) 2004 American Vacuum Society.