X-ray reflectivity was employed as a powerful tool for studying the surface and interface roughness and thickness, as well as density, of TiN/Ti/Si layers. X-ray reflectivity of the as-deposited samples. with nominal thickness of 17.5 nm of Ti and 3.0 nm of TiN, shows uniform oscillations. When the samples are annealed at 710 degrees C, residual strongly attenuated oscillations are still observed, while the 850 degrees C-annealed sample does not show oscillations, indicating high surface and interface roughness of the formed nitride and silicide layers. It is demonstrated that increased interface roughness, even for a layer with a larger average electron density difference, reduces the oscillations in the reflectivity curve very rapidly. For comparison, cross sectional transmission electron microscopy was employed to find the thickness of the surface and interface layers in silicide structures, which are in good agreement with the X-ray reflectivity results. The work was also supported by tapping mode atomic force microscopy observations, where we have observed nearly flat structures for the as-deposited sample surface and needle like protrusions for the annealed samples. The surface roughness of the top TiN layer was used to obtain simulated X-ray reflectivity spectra in good agreement with the experimental results. Preliminarily, the crystallography of the layers in the samples was determined by the grazing angle X-ray diffraction technique, to acquire knowledge on the Ti and Si compounds formed in the samples after the annealing.