Formation of coherent structures and mechanical properties of AlN/TiN multilayers

摘要

AlN/TiN multilayered thin films with layer thickness ranging from 1 nm to 50 nm were synthesized using rf magnetron sputtering at 400°C. Two series of samples were prepared at the substrate bias of Vb = -25 V and -100 V to modify growth texture of individual layers and verify its influence on the formation of coherent structures. XRD and TEM observations showed that in large period films (t_c ≥ 30 nm) each constituent grows under its own growth kinetic, leading to the formation of nano-crystalline film randomly oriented with no pronounced texture. Decreasing progressively the layer thickness favours the alignment of (0002) basal plane of w-AlN on (111) plane of TiN, and results in development of strong (111) texture, prerequisite for stabilisation of c-AlN and the formation of epitaxial coherent structures. The degree of crystallographic coherence was found to be higher in TiN(111) oriented films than for TiN(002) textured films. The increase of hardness coincides with the structure transition from a randomly oriented nanocrystalline films to a highly (111) textured multilayers, and the maximum hardness was obtained for epitaxially coherent nanolayers.