L. Guzman

Spectroscopic characterization of thermally treated carbon-rich Si1−xCx films

Amorphous carbon-rich silicon carbide films Si0.45C0.55, deposited on silicon, were obtained by r.f. magnetron sputtering of sintered SiC targets in argon plasma and characterized by means of X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectroscopy and elastic recoil detection analysis. The structural evolution of these films upon thermal annealing at various temperatures in different atmospheres were investigated by means of Raman analysis and IR absorption. The formation of regions of crystallized SiC and diamond-like carbon as well as the hydrogen chemical state evolution are discussed in terms of chemical bondings. The processes of carbon segregation and crystallization of silicon carbide in the films are influenced by (i) high temperature treatments, (ii) annealing atmospheres and (iii) hydrogen dynamical behaviour.

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...

Ion beam induced enhanced adhesion of Au films deposited on polytetrafluoroethylene

Abstract Considerable efforts have been made to improve the physical and chemical properties of a large number of polymers by ion implantation, and the enhancement of various properties was attributed to different mechanisms like chain scission, cross-linking and carbonization. It was observed that ion implantation can also improve the surface properties of polytetrafluoroethylene (PTFE) but the mechanisms for such enhancement are not completely clear yet. In this work we have studied the adhesion of Au thin films on PTFE. The PTFE substrates were implanted with 160 keV N ions to a dose range between 1×10 14 and 1×10 17 ions/cm 2 . The treated samples were examined by visible (514.5 nm) and FT infrared (1064 nm) Raman spectroscopy as well as by scanning electron microscopy. Ion implantation on PTFE in the low dose range leads to the splitting of weaker CC bonds; in the intermediate dose range sputter loss effects are dominant, and at higher doses, the microstructure strongly evolves and double CC bonds are created. Before and/or after the ion pretreatment, the specimens were coated (with a sputtering technique) with 150 nm thick Au films. Adhesion properties of the films were assessed by conventional scratch- and scotch-tape tests in conjunction with optical microscopy. In the case of pre-deposited coatings, enhanced adhesion occurs only if the implanted dose is lower than 2×10 14 ions/cm 2 , in connection with the formation of dangling bonds in the polymer (‘chemical’ adhesion), as confirmed by contact angle measurements. In the case of post-deposited coatings, enhanced adhesion occurs in the whole dose range. In the medium-high dose range, the enhanced adhesion can be related to the development of surface topography of the polymer substrate (‘mechanical’ adhesion).

Mechanical behaviour of nitrogen-implanted aluminium alloys

Abstract The effect of nitrogen implantation into pure aluminium has been extensively explored, taking into account the variation of several physical and technological properties of the implanted layer. In particular, the formation of aluminium nitride, which occurs under specific choices of the implantation parameters, is associated with an increase in hardness. In this work, we consider two Al alloys (Al-7075 and Al-2011), frequently employed in the mechanical industry, with properties strongly dependent on the thermomechanical treatment. Molecular nitrogen bombardment at 150 keV (75keV N + ) was employed, up to a total dose of 3 × 10 17 N cm −2 , varying the substrate temperature from 373 to 473 K. The samples were then characterized with respect to composition, structure, morphology, microhardness, scratch resistance (also performing multi-pass testing) and friction coefficient. The results were interpreted within the framework of micromechanical models describing the hardness of thin coatings deposited onto soft substrates; the microhardness of the implanted layer increased by a factor of five. It appears that nitrogen-implanted aluminium alloy layers, in spite of their shallow thickness, behave better than hard TiN-coated surfaces. Care must be taken to implant both alloys at the lowest possible temperature to avoid degradation of the substrate properties.

Thick and homogeneous surface layers obtained by reactive ion-beam-enhanced deposition☆

Abstract A recently developed method, reactive ion-beam-enhanced deposition (RIBED), which consists of simultaneous or sequential deposition and implantation steps, has proved to be very effective in the production of surface compounds with interesting surface properties. This hybrid technique allows the depth of the treated region to be nearly independent of the projected range of the implanted ions and thereby thicker layers to be obtained than by conventional ion implantation. Moreover, with respect to unimplanted deposited layers, the ion beam increases the uniformity of the films and their adhesion to the substrate. In this work, we consider surface nitrides of chromium and boron, which are known to be hard and corrosion resistant. The surface compounds were characterized using various different techniques: Auger electron spectroscopy, secondary ion mass spectrometry, X-ray diffractometry and scanning electron microscopy. Electrochemical measurements were carried out on the chromium and boron nitride layers, obtained by RIBED, on iron.

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.

Hard coating adhesion on ion implanted polymer surfaces

Abstract Modern plastics are of great importance in many practical applications and their performance can be enhanced by surface modification to improve their hardness, wear and chemical resistance. Metallic coatings, in particular hard Cr, have been successfully deposited by various techniques; unfortunately, the low polymer surface tension opposed to the high intrinsic stresses of the coatings often gave adhesion problems. The conventional pre-treatment of polymers in view of metallization is based on hazardous and pollutive agents. We used a combination of ion implantation and vapor deposition (performed in the same chamber) allowing for the production of well adherent coatings. N + ions were implanted at medium–low doses on polycarbonate substrates. Following ion irradiation, chromium films were deposited by evaporation. The implanted substrates were characterized with respect to their structure by Raman spectroscopy, wettability and nanohardness. The mechanical properties of the coatings were examined as a function of the ion beam treatment. The coatings were characterized with respect to morphology, scratching resistance as well as nanohardness. It was observed that, without the ion pre-treatment, the coatings were poorly adherent. Due to the high level of stresses developed in the Cr layers, the coatings on unimplanted samples appeared broken, as expected. On the contrary, the adhesion of the coatings was appreciably better for the pre-implanted specimens. This was certainly due to the superior mechanical properties exhibited by the implanted polymers as well as to enhanced wettability induced by energetic ion bombardment. Scratch tests showed an optimized tribological behavior for the ion implanted/coated polymer surfaces.

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.

Stoichiometry in Ti-N barrier layers studied by X-ray emission spectroscopy☆

Titanium nitride is an interesting material for use in microelectronic devices, particularly for use as a barrier layer. Considerable work has been done on these films and the relationdhip between the resistivity and film composition is now fairly well known, with the minimum resistivity occuring at the stoichiometric concentration. However, it is rather difficult to evaluate quantitatively the deviation of the film composition from the stoichiometry. We have produced Ti-N films with d.c. reactive sputtering at different nitrogen concentrations. These films were characterized with Auger electron spectroscopy and wavelength dispersive spectroscopy (WDS) and with X-ray diffraction. The experimental results of resistivity vs. WDS Kα line shifts indicate a possible relationship between these two quantities. It could then be feasible to use the WDS Kα line shifts for determining the resistivity of films near the stoichiometric composition.