He+ backscattering and Auger electron spectroscopy study of the ion-induced modification of copper films deposited on single-crystal silicon

The sputtering yields of copper due to argon ion milling were measured by mega-electronvolt He⁺ Rutherford backscattering and Auger electron spectroscopy for thin copper films deposited on 〈111〉-oriented silicon substrates. We found that recrystallization occurs in the copper films during the argon ion bombardment. The copper profile broadens at the Si-Cu interface and the spread increases with the beam energy during ion milling.     

Angular distribution and sputtering yield of Al and Al2O3 during 40 key argon ion bombardment

The angular distribution and sputtering yield of Al and Al₂O₃ during 40 keV argon ion bombardment have been measured by collecting the sputtered particles on a semi-cylindrical collector and analysing them by Rutherford backscattering spectrometry (RBS). It was found that due to the relatively high residual pressures (1–4 · 1O^?4Pa) in the sputtering chamber not only aluminium but also oxygen atoms are deposited on the collector through the mechanism of reactive sputtering both when sputtering the oxide and the metal target. The angular distribution of the collected aluminium and oxygen atoms in the case of pure aluminium sputtering follows a cosine law while in the case of Al₂O₃ sputtering a considerable deviation from the cosine law is observed. This deviation is explained by a preferred orientation (texture) of the crystallites in the polycrystalline oxide targets. It was found that the very thin films deposited on the collector when sputtering both types of targets have a composition close to AlO₂. The sputtering yield of Al and Al₂O₃ by 40 keV argon ions has been determined. On the basis of the obtained values an estimation of the productivity of the reactive sputter deposition of Al₂O₃ films from oxidized and non-oxidized targets is made.     

Thermo-optic properties of TiO2, Ta2O5 and Al2O3 thin films for integrated optics on silicon

The direct measurement of the thermo-optic coefficients of aluminium oxide, tantalum pentoxide and titanium dioxide thin films is presented. Using ellipsometry on monolithically integrated permutations of the layers of silicon, silicon dioxide and the material under test, allows the direct measurement of the overall thermo-optic coefficient accounting for thermally induced changes in the dielectric permittivity and density of the materials as well as the elasto-optic effect due to the non-matching thermal expansion coefficients of the different materials.     

Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10⁻⁸ Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 10¹³ ions/cm² and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.     

Analytical electron microscopy of aluminium alloys

X-ray microanalysis and electron energy loss spectroscopy of thin foils constitute the important techniques of high resolution chemical analysis using the electron microscope. The technique of x-ray microanalysis is discussed in this paper with particular emphasis on the study of aluminium alloys using a dedicated scanning transmission electron microscope (stem). The principle of determining chemical composition from observed x-ray peak intensities including the absorption of x-rays and beam broadening in thin foils are considered. The accuracy of peak intensity measurement and detection limits in x-ray microanalysis are illustrated with reference to Al-Mn alloys. The Cliff-Lorimer (k) factors for manganese, iron and copper with respect to aluminium were obtained from standard samples. Identification of phases in 1100 and 1200 aluminium and 3008 (Al-Mn-Zr) alloy were carried out from measured intensities of x-ray peaks. The experimental results emphasize the value of developing techniques for extracting the particles from the aluminium matrix. The transition phases formed in Al-6%Zn-3%Mg and Al-4% Cu were investigated by micro-diffraction and x-ray microanalysis.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Anodic film formation on high strength aluminium alloy FVS0812

Barrier-type film growth on the high strength aluminium alloy FVS0812 has been studied by a combination of transmission electron microscopy and Rutherford backscattering spectroscopy. The film is composed mainly of amorphous anodic alumina, but is contaminated with iron species incorporated into the film from the alloy. The film may also be contaminated with silicon and vanadium species at levels below the detection limit of the present experiments. The contaminant species are primarily incorporated locally into the film during oxidation of Al₁₃(Fe, V)₃Si dispersoids and the resulting film material is of reduced resistivity compared with anodic alumina of high purity. As a consequence of the presence of regions of film material of differing resistivities, the film is of irregular thickness. The average thickness corresponds to a nm/V ratio of about 1.3. Iron species incorporated into the film migrate outwards at roughly 2.1 times the rate of Al³⁺ ions. The iron species are not ejected in significant amounts to the electrolyte on reaching the film/electrolyte interface and hence, a thin layer of film material highly enriched in iron species develops at the film surface. The layer may also be enriched in vanadium species, if these are incorporated into the film and migrate more rapidly than Al³⁺ ions. Enrichment of iron, and possibly other alloying element atoms, is found in a thin layer of alloy immediately beneath the anodic film, paralleling enrichments of alloying element atoms found following anodic oxidation of other aluminium alloys. The enrichments at both the alloy/film and film/electrolyte interfaces do not appear to be continuous across the macroscopic surface of the specimens, probably due to the non-uniformity of film growth on the two-phase substrate. The maximum voltage for the selected conditions of anodizing was limited to 68 V as a result of oxygen generation at flaws which are present extensively in the anodic film. This revised version was published online in November 2006 with corrections to the Cover Date.     

Comparative analysis of oblique impact on ceramic composite systems

An experimental programme is presented which investigated the performance of oblique, ceramic/metal, bilayer composite armours. The ceramics, alumina and silicon carbide, were backed by either Rolled Homogeneous Armour steel (RHA) or 7000 series aluminium. Using a model scale tungsten penetrator at two velocities (representing current and future ordnance threats) the effect of configuration on ballistic limit or depth of penetration (DOP) areal densities was determined. Areal densities of the DOP targets decreased with increasing ceramic thickness, achieving a minimum at zero residual penetration in the backing. The bilayer targets, loaded at the ballistic limit needed a larger areal density to defeat the penetrator. This areal density also decreased with ceramic thickness but showed a minimum with respect to ceramic thickness, as a result of reduced support by the thinner metallic backing. At 1450ms⁻¹ the most efficient system was found to be a SiC/Al, which demonstrated a 25% weight saving over the monolithic aluminium reference target. The Al-alloy backing performs better than RHA, and SiC better than Al₂O₃.     

Fabrication of W target on carbon backing

¹⁸⁴W enriched isotopic target of 210 μg/cm² thickness on carbon backing of 100 μg/cm² thickness has been made in ultra-high vacuum environment by evaporation method using 6 kW electron beam at Inter University Accelerator Centre (IUAC). Hundred and thirty milligrams of enriched ¹⁸⁴W powder was used in this target preparation process. This target has been successfully used in two nuclear reaction experiments performed at IUAC. Methods adopted to convert the tungsten powder to a special pellet form in order to minimize the consumption of the expensive material, preparation of stress relieved carbon-backing foil, steps taken to make the carbon withstand the heat generated during the tungsten evaporation, the method of tungsten fabrication and details of ultra-high vacuum evaporator facility of IUAC are discussed.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

Irradiation effects on solid surfaces by water cluster ion beams

The interaction between a water cluster ion beam and the surface of a silicon substrate was investigated. The sputtering yield of silicon by a water cluster ion beam was approximately ten times larger than that by an argon monomer ion beam. X-ray photoelectron spectroscopy was used to analyze the silicon surface irradiated with a water cluster ion beam. The analysis revealed that the surface was oxidized, and the oxidation was saturated approximately at the dose of 1 × 10¹⁴ ions/cm². The number of disordered atoms measured by the Rutherford backscattering also supported the result.     

Aluminum contact to nickel silicide using a thin tungsten barrier

An aluminum film in contact with NiSi is not stable in the temperature range around 450 °C usually applied for aluminum contact sintering. We used thin (about 2 kÅ) self-supported silicon substrates to investigate the interaction of aluminum films with NiSi by mega-electronvolt ⁴He⁺ backscattering spectrometry. The thin substrate enables us to distinguish between the aluminum and the silicon signals, to isolate them, and to analyze the reaction. It is found that the aluminum reacts with the silicide and forms an NiAl₃ layer in direct contact with the silicon substrate. Simultaneously, a rise in the Schottky barrier height of the contact is observed. A thin layer (250 Å) of tungsten placed as a barrier between the aluminum and the silicide is shown to inhibit the aluminum-silicide reaction. A process is described to prepare a reliable aluminum contact to NiSi on a silicon substrate in a single annealing step.     

Growth of dielectric films on semiconductors and metals using a multipole plasma

A multipole plasma source (a hot electron emitter associated with magnetic confinement by permanent magnets) is very suitable for plasma deposition and anodization because it can create a high density (10¹⁰-10¹¹ cm^-3) homogeneous plasma which is free from energetic particles. The anodization kinetics of metals and semiconductors as well as technological applications of the oxide layers were investigated. Space charge effects in the oxide are shown to control the transport of negative oxygen ions and positive substrate ions during growth. Anodization through a thin CaO-stabilized ZrO₂ (CSZ) film results in strong enhancement in the anodization rates of aluminium, tantalum and silicon, probably because of an alteration in the surface chemistry between the plasma and the oxide. The applications of this process are very attractive: the room temperature plasma anodization of silicon resulting in good quality SiO₂, and the protective filter effect of the CSZ layer.A combination of a multipole source and an ultrahigh vacuum system is described and will be used to study the first steps in the interactions of a surface (mostly GaAs) with a plasma.     

Copper and iron based thin film nanocomposites prepared by radio frequency sputtering. Part I: elaboration and characterization of metal/oxide thin film nanocomposites using controlled in situ reduction process

Copper and iron based thin films were prepared on glass substrate by radio-frequency sputtering technique from a delafossite CuFeO₂ target. After deposition, the structure and microstructure of the films were examined using grazing incidence X-ray diffraction, Raman spectroscopy, electron probe micro-analysis and transmission electron microscopy coupled with EDS mapping. Target to substrate distance and sputtering gas pressure were varied to obtain films having different amount and distribution of copper nanoparticles and different composition of oxide matrix. The overall reaction process, which starts from CuFeO₂ target and ends with the formation of films having different proportion of copper, copper oxide and iron oxide, was described by a combination of balanced chemical reactions. A direct relationship between the composition of the metal/oxide nanocomposite thin film and the sputtering parameters was established. This empirical relationship can further be used to control the composition of the metal/oxide nanocomposite thin films, i.e. the in situ reduction of copper ions in the target.     

Inspection of intermediate stress-induced electronic traps in Si/Al2O3 system

The physical characteristics of device-grade thin silicon film at (1 0 0) grown on α-Al₂O₃ substrate using the chemical vapour deposition (CVD) technique has been studied in this paper. Its thickness, crystalline structure, elemental inter-diffusion in the interface region and the quality were characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), core level X-ray photoelectron spectroscopy (XPS) and nuclear resonance reaction ²⁷Al(p,γ)²⁸Si, respectively. The results of stoichiometric defect profile and individual silicon suboxide (such as SiO, and Si₂O₃ components with respect to the metallic Si element) formation in the intermediate region were observed. The deep traps located around E_c=0.26eV, in ∼500 nm thick n-type Si films, were attributed to the defects caused by the strain of the silicon lattice. Raman spectroscopy was used to evaluate the compressive stress in the Si film.     

Rutherford backscattering investigation of thermally oxidized tantalum on silicon

The Rutherford backscattering technique utilizing 2 MeV He⁺ ions was used for studying Ta and thermally grown Ta oxide films on Si substrates. Significant impurity effects were observed for the as-deposited Ta films and are attributed to gettering during deposition. Partially oxidized Ta films exhibit a surface Ta₂O₅ layer with substantial oxygen incorporation in the underlying Ta film. In contrast with anodic Ta₂O₅ films on tantalum, there is no sharp boundary between Ta and Ta₂O₅. Tantalum oxide films on silicon are, to a first approximation, stoichiometric. Their apparent density, as determined from the areal density of Ta atoms, increases with thickness (from 4.7 to 7.3 g cm^-3) as do their refractive indices. This supports the contention that incorporation of silicon is responsible for these effects and that they are not merely due to a change in stoichiometry.     

Characterization of ion implantation through thin Ti metal layers on Si

Ion beam mixing of thin Ti films deposited on Si is investigated and its effect during subsequent thermal sintering determined. Both inert (Xe⁺) and dopant (As⁺) ions are used to intermix the metal films and Si substrate. The morphology of the suicide layer formed by this process and the structure of the silicide/Si interface is shown to be independent of the specific ions used for mixing. The structural differences observed are correlated to the electrical resistivity of the films. Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) including ion channeling are used to characterize the films.     

MnGeP2 Thin Films Grown by Molecular Beam Epitaxy

Growth conditions for MnGeP₂ thin films have been investigated by using molecular beam epitaxy (MBE) method. Mn and Ge were evaporated by K-cells, and P₂ was supplied by decomposing tertialybutylphosphine (TBP). GaAs (001) and InP (001) single crystals were used as substrates. An X-ray diffraction peak, which can be assigned to (008) peak of MnGeP₂, was observed at nearly the same position as the (004) peak of GaAs. The lattice constant of the MnGeP₂ thin film was determined to be 1.13 nm assuming its crystal structure is a c-axis oriented chalcopyrite type structure. Secondary phases such as GeP, MnGe_x and MnP were observed for beam fluxes of Mn and Ge as high as 1×10^–8 Torr.     

Gamma rays interactions with WO3-doped lead borate glasses

Optical and FT infrared spectral properties of tungsten ions in a host lead borate glass with composition PbO 55%, B₂O₃ 45% (wt%) were studied. The same spectral properties were re-measured after subjecting the samples to successive gamma irradiation. The work was undertaken to justify the state of tungsten ions in such glass system by combined spectral investigations. Optical and FTIR spectral studies were confirmed by investigating electron spin resonance (ESR) of the undoped and WO₃-doped samples before and after gamma irradiation. The optical spectrum of the undoped glass exhibits strong and wide UV absorption bands, which are related to the combined UV spectra of trace iron impurities (Fe³⁺ ions) and that from divalent lead (Pb²⁺) ions. Optical studies of WO₃-doped sample indicate the presence of tungsten ions mostly in the hexavalent W⁶⁺ state. The presence of tungsten ions as structural groups was obtained by comparing the FTIR spectra of the undoped and WO₃-doped samples. ESR spectra confirm the optical and FTIR spectral studies. The studied host lead borate glass has been found to show obvious shielding behavior towards successive gamma irradiation as revealed by the constancy of optical absorption spectral curves.