M. Bonelli

Chemical and compositional changes induced by N+ implantation in amorphous SiC films

The effects of 30 keV N+ implantation in amorphous silicon carbide films deposited on silicon substrates by rf sputtering over a fluence range of 1×1016–2×1017 ions cm−2, are studied by means of x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and infrared (IR) absorption techniques. The ion‐induced modifications of these films have been investigated on the basis of the chemical state evolution of Si, C, and N (using XPS and AES) and on the basis of the vibrational features of the films components (using IR absorption). The results show that implanted N bonds Si selectively, substituting the C atoms in the silicon carbide, and the C substitution by N results in a composite layer of carbonitrides and free C. An ion‐induced C transport has also been observed and correlations are established between the formation of silicon carbonitrides and the dynamical behavior of the C in the implanted layer. The latter appears as a superposition of (a) a chemically induced atomic redistribution...

Pulsed laser deposition apparatus for applied research

In this paper, we describe the apparatus for pulsed laser deposition of thin solid films that we have developed in our laboratories of Trento University. Our apparatus is original for many of its adopted technical solutions: (i) the substrate-manipulator mechanism possesses four degrees of freedom, x, y and z translation and a rotation, which permits one to treat samples with non-planar geometry; (ii) an independent target-handling mechanism moves a circular target with calculated speed profiles which permits a uniform ablation of the target surface to be obtained (normally, laser ablation deposition apparatus uses a beam-bending mechanism and a simple target translation at constant velocity); and (iii) the maximum substrate dimensions can be relatively large, about 85 mm × 85 mm, and, in the case of samples with approximately cylindrical symmetry, by exploiting the rotation, 85 mm × 85 mm × 85 mm.

Pulsed laser deposition of diamondlike carbon films on polycarbonate

Diamondlike carbon films have been deposited on polycarbonate by pulsed laser deposition technique by irradiating highly oriented pyrolytic graphite with high-energy excimer laser pulses (248 nm wavelength, 20 ns duration, and up to 37 J/cm2 energy density). Irradiations were performed in different atmospheres: (1) moderate vacuum (10−2 Pa), (2) nitrogen atmosphere (1 Pa), and (3) argon atmosphere (1 Pa). The structure of the deposited films was analyzed with Raman spectroscopy. In vacuum-deposited films, a transition from mainly disordered graphitic carbon to up to 80% ta−C occurs above a laser energy density threshold of 7 J/cm2. No such transition was observed in films deposited in nitrogen up to energy densities as high as 33 J/cm2. In argon atmosphere the transition is only observed at high-laser energy density, ≈23 J/cm2. The results are discussed in terms of combined ballistic and chemical effects affecting both plume dynamics and bonding configuration of the growing film. The Fourier transform inf...

Analysis of the hydrogen permeation properties of TiN-TiC bilayers deposited on martensitic stainless steel

Abstract The efficiency of TiN-TiC bilayer coatings, deposited by ion-beam-assisted deposition on martensitic steel, as a hydrogen permeation barrier was investigated by a gas phase method; the hydrogen permeability in the TiN-TiC bilayers is very low, at least 104 times lower than in the steel substrate in the temperature interval 470–570 K. Possible physical mechanisms, responsible for the reduced permeability of the ceramic bilayers, are discussed. In particular, from our experimental results, it can be concluded that chemisorption and/or hydrogen jumping from surface sites to the first subsurface atomic layer represents the hydrogen permeation limiting process.

Structure and optical properties of TiN films prepared by dc sputtering and by ion beam assisted deposition

Abstract Titanium nitride films have been deposited at 573 K on silicon substrates by dc magnetron sputtering, selecting different bias voltage values, in the 100–800 V range. Additional TiN layers on silicon have been obtained also by ion beam assisted deposition (IBAD) in a machine designed for ion implantation and physical vapour deposition (e-gun). TIN was formed by bombarding at room temperature with a nitrogen ion beam, of energy 30 keV, a growing Ti film, evaporated on silicon in the presence of a nitrogen atmosphere. The films obtained by the two techniques have been characterized with respect to composition, structure, microstructure and optical properties. The effect of ions of different energies impinging on the film during its growth has been found to influence the surface characteristics, among them the optical reflectivity. The importance of process cleanliness is emphasized.

Time-dependent evolution of thin TiN films prepared by ion beam assisted deposition

Thin titanium nitride (TiN) films have been prepared by simultaneous Ti evaporation and 30 keV N2+ implantation onto Si(100) wafers, in the presence of a N2 partial atmosphere. A systematic chemical and compositional evaluation of the films has been performed by Auger electron spectroscopy and x-ray photoemission spectroscopy checking the homogeneity level, the degree of gaseous contamination, the different compounds formed by titanium and nitrogen, and their depth distribution. The Rayleigh velocity at various angles of incidence has been determined via Brillouin scattering measurements. The evidence of a Sezawa mode confined in the overlayer was also found. The films, which consist of a homogeneous outer layer above a relatively wide interface region with the substrate, show aging effects. On a mesoscopic scale, the film structure appears porous.

Titanium nitride coatings obtained using new apparatus for ion beam assisted deposition

Abstract The advantage of the ion beam assisted deposition technique lies in the good control of process parameters such as film atomic composition, purity, density and adhesion, in addition to improved surface cleanliness of the substrate. A machine for combined ion implantation and physical vapour deposition (Joule effect and electron-gun) has recently been built at the Trento laboratories. It was designed with emphasis on easy and clean operation. To test the performance of the machine, with specific reference to the composition and structure of the coatings produced, we worked on a relatively well known system, titanium nitride, which was deposited with an electron gun in the presence of a nitrogen ion beam (characterized by an energy of 30 keV) and a nitrogen atmosphere. Samples of different stoichiometry were produced and characterized by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The results show, as expected, the important role played by the ion beam impinging on the sample.

COMPOSITION CHANGES IN N2+ BOMBARDED TI/SI BILAYERS AND MULTILAYERS : INTERPLAY BETWEEN RANDOM AND CHEMICALLY GUIDED EFFECTS

Abstract We have studied with Auger Electron Spectroscopy and Rutherford Backscattering Spectrometry the composition changes in Ti/Si bilayers and multilayers (Ti at the surface) induced by bombardment with 30 keV N2+ ions. In addition, the chemical bonding was investigated by Auger line-shape analysis. In N2+-bombarded systems the changes in the Si profiles and line shapes point to a sequence of chemical environments with SiN bonds near the Ti/Si interface, quasi-elemental Si plus overstoichiometric TiN at intermediate depths, and SiTi bonds near the surface. There is thus extensive transport of Si towards the surface. We conclude that chemistry plays at least four different roles in the system Ti/Si: chemically enhanced transport (Si in TiN), chemically inhibited transport (Si in Ti), bond formation in a binary situation (SiTi), and bond formation in a ternary situation (TiN). The latter case could also be described as preferentiality in bond formation (TiN but not Si3N4).

Synthesis and structural characterization of boron nitride thin films

Abstract The purpose of this paper is to present first results of an investigation on the properties of boron-nitrogen thin films obtained by different deposition techniques. Films of different stoichiometries were produced on silicon substrates using r.f. magnetron sputtering and ion-beam-assisted deposition. In order to study the influence of the deposition process parameters on the film properties, the films were characterized by scanning electron microscopy. Auger electron spectroscopy, secondary neutral mass spectrometry, IR spectroscopy and nanoindentation. With the chosen experimental conditions, only hexagonal BN is formed. A considerable dependence of hardness of film microstructure has been evidenced.

Elastic behaviour of TiN thin films

Abstract Thin films are increasingly being used in many technological areas. One of the problems in practical applications is the level of internal film stress, which, in severe cases, can lead to coating failure. In our laboratories we are currently studying the effect of deposition parameters and of post-deposition treatments on the stress behaviour of some coatings obtained by magnetron sputtering techniques and by ion beam assisted deposition (IBAD). In this work we concentrate on TiN since this compound is particularly valuable as a study system, in view of the good understanding of its physical properties and its wide range of applications, ranging from barrier layers in microelectronics to gas diffusion inhibition, and from optical coatings to sliding wear reduction. We have deposited thin films (ranging in thickness from 100 nm up to a few microns) of TiN in different experimental conditions, by d.c. magnetron reactive sputtering and by IBAD, and we have characterized the coatings with respect to composition, structure and microstructure by scanning electron microscopy. Auger electron spectroscopy and X-ray diffraction. The elastic response of the films has been studied in detail by surface Brillouin light scattering. Our results are in general agreement with other works in the literature; however, the Rayleigh wave velocities for IBAD samples are much lower than expected. Some preliminary explanations of this fact are presented.