The initial stage of iron silicide formation is investigated by high-resolution Rutherford backscattering spectroscopy. During the Fe deposition on Si(001) at 470 degrees C, the formation of FeSi2 is Confirmed by the surface peak analysis. Initially, FeSi2 grows epitaxially so that one of the major crystallographic axes is parallel to the < 111 > axis of the Si substrate. With increasing Fe deposition, the deviation between the major crystallographic axis of the silicide region and Si < 111 > increases although the electron diffraction pattern is independent of the amount of Fe deposition. Therefore, the subsurface crystallographic structure of iron silicide is transformed from a cubic-like to a low-symmetry structure. (c) 2007 Elsevier B.V. All rights reserved.