Structural, compositional, and optical characterization of thin TiOxNycoatings fabricated by dual ion beam sputtering

Abstract

A.Rizzo, L. Mirenghi. L. TapferPastis-CNRSM Scpa. Brindisi. ItalyM. Alvisi, L. VasanelliINFM Sez. Lecce. do Dipartimento di Scienza dei Materiali, Lecce. ItalyF. Sarto. S. ScaglioneDivisione Dispositivi Ottici. ENEA CRE Casaccia. Roma, ItalyABSTRACTTitanium oxynitride (TiON) thin films are of great interest for the fabrication of protective optical coatings. By varying theoxygen and nitrogen content in the films, the electrical. optical and mechanical properties of these coatings can be tailoredproperly. In this work. we fabricated TiN and TiOXNY films (thickness range of 28÷1 10 nm) by dual ion beam sputteringtechnique (Ti target). TiOXNY films were ion-assisted by a low energy (300 eV) oxygen and nitrogen mixed ion beam ofvariable 0/N flux ratio (0÷1). We observe that the incorporation of oxygen greatly improves the adhesion of the film on theglass substrate. Further. the optical extinction coefficient drastically decreases for increasing oxygen content. suggesting newapplications of TiOXN films as protective coatings on transparent substrates. The film composition by XPS analyses is inagreement with the results obtained by a simple model to describe the ion assistance phenomena. The crystallographicstructure of the deposited films was characterised by using e-2ex-raydiffraction and grazing incidence x-ray diffractionmeasurements. In the range up to 14 % of the oxygen to nitrogen flux ratio, a TiN fc.c. phase structure with preferred (111)growth-orientation of the grains is observed. For higher oxygen concentrations the absence of diffraction peaks suggests amore amorphous-like structure of the deposited film. Specular x-ray reflectivity measurements provide important andaccurate information about the film-air and film-substrate interface roughness. The Kiessig fringes are caused by multipleinternal interference of the x-ray beam and can be observed up to 3 degrees (20 angle). which is a clear indication of the highhomogeneity of the film thickness and of sharp interfaces.1. INTRODUCTIONThe high hardness together with the low friction coefficient are the main properties for which the titanium nitride can beconsidered an useful material for tribological applications as protective coatings on cutting tools.Unfortunately. golden-coloured TiN films (i.e. exact stoichiometry) have low resistivity and high compressive stress [1].However. as reported by Ping Jin and Shigeo Maruno [2], the incorporation of a large amount of oxygen into the titaniumnitride film decreases the compressive stress and increases the diffusion barrier performance [3j. At this purpose. the use of