A. Nebojsa

Ellipsometry and transport studies of thin-film metal nitrides

Abstract The results of a systematic spectroellipsometric and conductivity study of metallic titanium nitride thin films grown on silicon by the ion-beam-assisted deposition technique are presented. The directly measured electrical resistivity is correlated with the contactless, non-invasive ellipsometric method of extracting the free- and bound- carrier response in the infrared, visible, and ultraviolet spectral ranges. The d.c. resistivity of TiN films ranges from ∼100 to ∼500 μΩ cm. The high polarizibility of free carriers at optical frequencies presents non-trivial problems of the measurement optimization. The merit of the ellipsometric data taken at proper angles of incidence in different spectral ranges is discussed for homogeneous and graded layers. For TiN films of a good structural quality, the extrapolation of ellipsometric results is found to be in a fair agreement with d.c. data, providing an optical, contactless way of measuring the electrical conductivity. This can be achieved even with a very simple near-infrared ellipsometer.

Dual ion-beam deposition of metallic thin films

Abstract The influence of argon ion-beam bombardment of growing Al, Mo and Ti thin films deposited by ion-beam sputtering on their composition and optical properties was studied. The Ar ion energy and ion-to-atom arrival ratio were 100–600 eV and 0.15–1.75 respectively. The concentration of Mo (A1) in the thin films decreased (increased) with ion energy as the Ar content increased (decreased). The Ti content was below 35% for all ion energies. The ratio O/Ti was close to the stoichiometric value of two for all ion energies up to 400 eV. Higher ion-beam energies and doses led to higher values of the index of refraction for Al and Ti thin films. Furthermore, an increase in the energy of the ions caused a decrease in the deposition rates of all films due to resputtering of the thin film atoms and, in the case of Al thin films, intensified the amorphization process in the Al/Si structure.

Deposition of metal nitrides by IBAD

Abstract Nitrides of metallic elements like Ti, Mo and Al were synthesized by ion beam-assisted deposition (IBAD). This technique was provided via dual ion beam deposition method in an apparatus based on two Kaufman ion beam sources. In our study an influence of the energy of assisting nitrogen ions (50–400 eV) and of the substrate temperature (up to 400°C) on the characteristics and properties of deposited thin films (roughness, thickness, chemical composition, structure, electrical and optical properties, etc.) was investigated. Different ex situ analytical techniques and measurements such as XPS, RBA, XRD, STM, profilometry, ellipsometry and other methods were applied. The composition of thin films prepared by the sputtering of Ti, Mo and Al targets was close to oxinitrides for all ion energies (fluxes). The nitrogen content in all films was increased by assisting ion bombardment; however, it sustained under their stoichiometric values. Structure of all thin films was generally dependent on ion beam energy and substrate temperature. The roughness and thickness (50–400 nm) of the films increased, respectively, decreased with ion energy (flux). Higher substrate temperature (400°C) substantially improved the adhesion of MoN films to silicon substrates. A significant influence of the assisting ion beam on electrical resistivity and index of refraction of Ti–N and Al–N films was observed.

Deposition of magnetic thin films by IBAD

Abstract Cobalt and nickel magnetic films were prepared by ion-beam assisted deposition method (IBAD). The main goal of the work was to study the influence of the assisting low-energy-argon-ion beam and substrate temperature on the characteristics and properties of the films, in particular on thickness, roughness, chemical composition, structure and magnetic properties of thin films. The experiments revealed that the assisting argon ions influence most remarkably an in-plane magnetic anisotropy of the films. On the other hand, enhanced substrate temperatures suppress the anisotropy of the films. Influence of these two deposition parameters on roughness, composition and structure of thin films was not dramatic.