Investigation of interface properties of sputter deposited TiN/CrN superlattices by low angle x-ray reflectivity

Approximately 1.8 μm thick nanolayered multilayer coatings of TiN/CrN (also known as superlattices) were deposited on silicon (1 0 0) substrates at different modulation wavelengths (4.6-12.8 nm), substrate temperatures (50-400 deg. C) and substrate bias voltages (-50 to -200 V) using a reactive direct current magnetron sputtering system. The x-ray reflectivity (XRR) technique was employed to determine various properties of the multilayers such as interface roughness, surface roughness, electron density, critical angle and individual layer thicknesses. The modulation wavelengths of the TiN/CrN superlattice coatings were calculated using a modified Bragg's law. Furthermore, the experimental XRR patterns were simulated using theoretically generated patterns and a good fit was obtained for a three layer model, i.e. (1) top surface roughness layer, (2) TiN/CrN multilayer coating (approximately 1.8 μm) and (3) Ti interlayer (∼0.5 μm) at the film-substrate interface. For the superlattice coatings prepared at a modulation wavelength of 9.7 nm, a substrate bias of -200 V and a substrate temperature of 400 deg. C the XRR patterns showed Bragg reflections up to 5th order, indicating well-defined periodicity of the constituent layers and relatively sharp interfaces. The simulation showed that the superlattice coatings prepared under the above conditions exhibited low surface and interface roughnesses. We also present the effect of substrate temperature and substrate bias, which are critical parameters for controlling the superlattice properties, onto the various interface properties of TiN/CrN superlattices.