In this work, an investigation of the properties of nanoscale-thick Ti/TiN, TiN, W, WN layers as diffusion barriers between Si and Al is carried out in view of Si-based electronic applications. Heat treatments were performed on the samples to activate interdiffusion between Si and Al. Changing annealing time and temperature, each sample was morphologically characterized by scanning electron microscopy and atomic force microscopy and compositionally characterized by Rutherford backscattering analysis. The aim is to evaluate the efficiency of the layers as diffusion barriers between Si and Al and, at the same time, to evaluate the surface morphological changes upon annealing processes.