Relation between interfacial structure and mechanical properties in AlN/TiN bilayers investigated by EXAFS

The relation between the mechanical properties and the structure of AlN/TiN bilayers prepared by reactive magnetron sputtering in the 600 nm range is investigated. Al and Ti K-edge extended X-ray absorption fine structure is used in order to determine the local order around Al and Ti by comparison with 300 nm thick AlN and TiN single layers. The use of this powerful local probe allows the evidence of intermixing between AlN and TiN deposited layers, which is suggested by glow discharge optical emission spectroscopy experiments. The effect of ionic bombardment applied at various steps of the deposition process is studied. The ionic bombardment applied during the deposit induces substantial changes in the absorption spectra that are assigned to a decrease of intermixing and an improvement of local order. Simulations of (Al, Ti)N ternary alloys Al and Ti K-edge absorption spectra for increasing mean occupation factors CTi (CAl) of Ti(Al) substituting Al(Ti) in hexagonal AlN (cubic TiN) lattice are performed in order to determine the initial parameters for the fit of the experimental data. The refinements performed by using FEFFIT software demonstrate that an ionic bombardment applied during the deposition phase results in a significant reduction of the number of Al-Ti pairs within the bilayer and an improvement of the local order around Ti and Al, which is quantified by a decrease of the Debye-Waller parameters. This structural evolution is tentatively correlated with the improvement of mechanical properties of the bilayers.