Nanoscaled composite TiN/Cu multilayer thin films deposited by dual ion beam sputtering: growth and structural characterisation

We present a detailed structural characterisation of TiN/Cu multilayers, with bilayer period ranging from 5 to 20 nm, deposited by dual ion beam sputtering on Si(001) substrates. Low-angle X-ray diffraction scans exhibit Bragg reflections up to the 15th order, indicative of a well-defined periodicity and non-cumulative roughness. High-angle X-ray diffraction shows that the multilayers adopt a (001) TiN/(001) Cu texture and are polycrystalline in the plane, the mosaic spread for the TiN and Cu grains being of ∼6° and more than 9°, respectively. High Resolution Transmission Electron Microscopy (HRTEM) observations confirm the cube on cube epitaxial growth, but show the presence of several interfacial and growth defects, introduced to relieve the huge misfit (15.9%) between the two lattices. The HRTEM images also reveal facetted islands growth morphology of Cu, leading to lateral roughness at the TiN/Cu interface as well as fluctuations in the interplanar spacings, which could explain the lack of superlattice reflections in the high-angle X-ray diffraction.