Nucleation and growth of Ti2 AlN thin films deposited by reactive magnetron sputtering onto MgO(111)

• The nucleation and growth of Ti2 AlN thin films on MgO(111) substrates during dual direct current reactive magnetron cosputtering from Ti and Al targets in an Ar N2 atmosphere at a substrate temperature of 690 °C have been investigated. Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy reveal the formation of competing phases for slight N superstoichiometry with respect to Ti2 AlN. The stoichiometry deviations initiate the layer-by-layer growth of a ∼380 Å thick epitaxial N-substoichiometric cubic (Ti1-x Alx) Ny layer. N-vacancy driven diffusion of Ti and Al leads to decomposition of this metastable solid solution into nanosized cubic TiN y′ and AlN y″ domains as well as to a solid-state reaction with the MgO(111) by formation of a Mg2 (Al:Ti) O4 spinel, reducing the transformed (Ti1-x Alx) Ny layer thickness down to ∼60 Å. Local AlN y″ domains serve as templates for Ti2 AlN nucleation at higher thicknesses. At the same time TiN y′ and AlN y″ serve as a sink for excess gas phase N during the subsequent polycrystalline Ti2 AlN growth with random (Ti1-x Alx) Ny renucleation as a tissue phase along Ti2 AlN grain boundaries. The individual Ti2 AlN grains with vertical sizes up to the total thickness retain local epitaxy to the substrate, with basal planes nonparallel to the substrate interface. Concurrently the (Ti1-x Alx) Ny layer is further reduced by inward Ti2 AlN grain growth along the basal planes. © 2007 American Institute of Physics.

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