We have investigated the thickness effect of Ge interlayers on the formation of nickel silicides as a function of the rapid-thermal-annealing temperature by means of glancing angle X-ray diffraction and scanning transmission electron microscopy combined with energy-dispersive X-ray spectrometry. It is shown that the insertion of 2 and 5 nm thick Ge interlayers between Ni films and Si substrates leads to an increase of the nucleation temperature for NiSi2 by higher than 150 degrees C. The increased nucleation temperature could be related to the formation of NiSi1-xGex in the interface regions between the NiSi films and Si substrates. It is further shown that the morphological degradation of the samples with interlayers is more severe than that of the samples without interlayers. The interlayer dependence of the structural changes of Ni silicide films is described and discussed in terms of surface energy and Ge diffusion behavior. (c) 2007 The Electrochemical Society.