Pure Al Target Research Articles

Influence of sputtering conditions on crystalline quality of AlN layers deposited by RF reactive sputtering

AbstractAluminum nitride (AlN) is increasingly demanded for use in semiconductor‐related industries. This study was undertaken for fabrication of high‐quality AlN thick layers using radio‐frequency (RF) reactive sputtering with a pure Al target. The AlN layers were sputtered homoepitaxially on high‐quality thin AlN layers on sapphire substrates for 1.5 h with 300 to 650 W at 573 and 773 K. The AlN thin layers were grown using sapphire nitridation before sputtering. A N2‐Ar gas mixture was used as the sputtering atmosphere and N2 gas flow ratio was changed from 20 to 60 vol%N2. In all sputtering conditions c‐axis oriented AlN layers were fabricated. AlN layer sputtered with 400 W under 40 to 60 vol%N2 at 773 K was grown by about 1 μm thickness. The AlN layer sputtered with 400 W under 40 and 50 vol%N2 at 573 and 773 K showed superior quality, with almost identical crystal structural quality to that of each nitrided sapphire substrate. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.

Magnetron Sputtered nc-Al/<I>α</I>-Al<SUB>2</SUB>O<SUB>3</SUB> Nanocomposite Thin Films for Nonvolatile Memory Application

In this paper, we developed nc-Al/a-Al2O3 nanocomposite thin films using magnetron sputtering. The nc-Al/a-Al2O3 films were sputtered on p-type Si substrates from pure Al target in gas mixture of Ar and O2. X-ray photoelectron spectroscopy and high resolution transmission electron microscope studies confirm that the nanocrystalline Al are embedded in amorphous Al2O3 matrix thus nc-Al/ a-Al2O3 nanocomposite forms. This nanocomposite thin film exhibits memory effect as a result of charge trapping.

Laser-Plasma X-ray Sources Using Ceramic Target

Ceramic plates (AlN and alumina) were used as targets for laser-plasma X-ray sources for the first time. The radiation intensity of soft X-ray spectra from Li-like ions (Al XI) for the AlN target was almost the same as that in the case of pure aluminum target. It was found that the ceramic target can be irradiated at the same place up to 70 times or more, delivering soft X-rays with nearly the same intensity as in the case when a virgin surface was irradiated. The profiles of the crater marks formed on the target surface after irradiations were measured three-dimensionally and their hollow volumes below the initial surface were evaluated. The ablated mass for the AlN or alumina target was less than 1/6 of that for a pure Al target.

Properties of Al-doped copper nitride films prepared by reactive magnetron sputtering

Cu3N and Al x Cu3N films were prepared with reactive magnetron sputtering method. The two films were deposited on glass substrates at 0.8 Pa N2 partial pressure and 100 °C substrate temperature by using a pure Cu and Al target, respectively. X-ray diffraction (XRD) measurements show that the un-doped film was composed of Cu3N crystallites with anti-ReO3 structure and adopted [111] preferred orientation. XRD shows that the growth of Al-doped copper nitride films (Al x Cu3N) was affected strongly by doping Al, the intensity of [111] peak decreases with increasing the concentration of Al and the high concentration of Al could prevent the Cu3N from crystallization. AFM shows that the surface of Al x Cu3N film is smoother than that of Cu3N film. Compared with the Cu3N films, the resistivities of the Al-doped copper nitride films (Al x Cu3N) have been reduced, and the microhardness has been enhanced.

Oxygen partial pressure dependence of memory effect of sputtered nc-Al/α-Al 2O 3 thin films

Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al 2O 3) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al 2O 3 films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O 2. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al 2O 3 matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure.

Proton elastic scattering from aluminum for 120°, 150° and 165° in the energy interval from 2.4 to 5 MeV

The differential cross sections for elastic scattering of H ions from aluminum were measured at scattering angles of 120°, 150° and 165° in the energy range from 2.4 to 5MeV where no data relevant to backscattering analysis were previously reported. It was found that in the studied energy interval excitation functions show complex resonance structure with significant deviation from the Rutherford value. The benchmark experiment at 4.2 and 5.0MeV was performed in order to test how measured cross sections can interpret thick target yield from pure Al target.

Photoelectron spectroscopy of AlnD2− (n=3–15): Observation of chemisorption and physisorption of dideuterium on aluminum cluster anions

Photoelectron spectroscopy is used to investigate aluminum dideuteride cluster anions, AlnD2- (n=3,6-15), produced by laser vaporization of a pure Al target with a D2-seeded helium carrier gas. Comparison between the well-resolved photoelectron spectra of AlnD2- and Aln- reveals the nature of interactions between D2 and Aln-. Depending on the size of the Aln- clusters and their electronic structure, three types of AlnD2- species are observed, dideuteride (dissociative chemisorption), molecular chemisorption, and physisorption. Striking spectral similarities are observed between photoelectron spectra of AlnD2- and Aln- for n=9, 11, 13, and 15, suggesting that D2 is physisorbed on these closed-shell Aln- clusters. For AlnD2- with n=3, 6, 7, and 10, completely different spectra are observed in comparison with the corresponding Aln- clusters, suggesting that the AlnD2- species may be characterized as dideuterides. For AlnD2- with n=8, 12, and 14, in which the Aln- clusters are open shell, the D2 is characterized as chemisorption on the basis of spectral shifts and similarities relative to those of the corresponding Aln- clusters.

Structure and mechanical properties of Ti–Al films deposited by magnetron sputtering

Thin films of Ti–Al were deposited by d.c. magnetron sputtering on M2 (AISI) steel substrates. A composition scan of the Ti–Al system was carried out using pure Ti and Al targets placed at 90°. X-ray diffraction showed that for the high Al content films (71.5–86.1 at.% of Al) only the face centred cubic (f.c.c.) Al phase was deposited with a (111) preferential orientation. Within this range of compositions, both the width of the (111) planes diffraction peaks and the hardness of the films increased (from 8.9–13 GPa) with increasing Ti content. The Ti–Al films deposited with aluminium contents in the range from 32.5 to 57.1 Al at.% showed low hardness (8.8–10.3 GPa) and only a broad diffraction peak centred at 2θ≈45.4° was detected. For the high titanium content films (3.7–19.9 at.% of Al) the hexagonal close packed (h.c.p.) Ti phase peaks were detected by X-ray diffraction, superimposed on a broad diffraction peak centred at 2θ≈44.8°. These films showed the highest hardness values (up to 23 GPa). The composition range from 19.9 to 32.5 at.% of Al was selected for further work since it includes the films that presented the best combination between hardness and friction coefficient.

Dielectric properties of AlN x thin films prepared by RF magnetron sputtering of Al using a N 2/Ar sputtering gas mixture

Aluminium nitride is a low conductivity material which has applications as a dielectric and passivation layer in microelectronics. Normally, this material is prepared using chemical vapour deposition or molecular beam epitaxy, but following earlier work in which it has been demonstrated that silicon nitride may be successfully prepared by RF magnetron sputtering, we have investigated the electrical properties of aluminium nitride prepared by this technique. Al–AlN x –Al sandwich structure films were prepared by using a pure Al target with a sputtering gas mixture of N 2/Ar in the ratio 3:7 (partial pressures 0.40 Pa nitrogen and 0.93 Pa argon) using an RF discharge power of 180 W. Initial measurements indicated that the relative permittivity was approximately 9.1 and that the capacitance was independent of applied DC voltage, demonstrating that the contacts did not form Schottky barriers. The AC conductivity σ was observed to follow an expression σ= Aω s , where A is a constant, ω is the angular frequency and s is an index. Values of s were found to be in the range 0.62–1.31, increasing with increasing frequency in the range 100 Hz–20 kHz and decreasing with increasing temperature in the range 161–373 K. This type of behaviour was consistent with a carrier-hopping process having a density of localised states value N∼6×10 27 m −3. Low-temperature activation energies were in the range 0.001–0.008 eV, further indicating the presence of a carrier hopping process. The capacitance showed a decrease with increasing frequency and an increase with increasing temperature, tending towards a constant value at higher frequencies and lower temperatures. Measurements of loss tangent as functions of frequency and temperature showed a minimum in its frequency dependence, which appeared to shift to higher frequencies with increasing temperature. These measurements are in accordance with the model of Goswami and Goswami for samples with ohmic contacts, and are representative of results obtained on other insulating films, including nitrides.

High textured AlN thin films grown by RF magnetron sputtering; composition, structure, morphology and hardness

High quality thin aluminum nitride (AlN) films have been deposited onto a silicon (1 0 0) substrate by radio frequency magnetron sputtering of a pure Al target using different gas (Ar, N 2) mixtures. The depositions were carried out at substrate temperatures varying from room temperature (plasma heating) up to 400°C. The crystalline structures were investigated by X-ray diffractometry (XRD) revealing a pronounced texture of the deposited films. Some of the compounds investigated were deposited onto a thin buffer layer of pure Al. The film surface morphology was investigated by Atom Force Microscopy (AFM) (SPM-9500J3 from Shimadzu Co), and was found to depend distinctively upon the different deposition conditions. Generally, two kinds of structures were found—a columnar one, which was densely packed or organized in planar parallel sheets, and a flat structure, (typical for mono-crystals), with rms roughness below 0.2 nm. In this paper, the influence of argon added to the sputtering gas environment on the film properties is investigated and discussed. The depth elemental distributions were calculated using 2.4 MeV 4He + Rutherford Backscattering Spectrometry (RBS). Finally, the mechanical characteristics were described using hardness tests.

Mechanical property measurement of titanium/titanium nitride and aluminium–magnesium/magnesium freestanding multilayer foils

The advent of the closed field unbalanced magnetron sputtering (CFUBMS) system has allowed a novel method for the production of ultra-thick (above 50 μm) multilayer coatings, which form freestanding foils when removed from the substrate. Applications for this method range from the production of complex metal/ceramic probe tips to an alternative route for the production of axisymmetric high precision-machined components. In this study the CFUBMS system was developed to grow 50 μm aluminium–magnesium/magnesium (Al–Mg/Mg) and titanium/titanium nitride (Ti/TiN) multilayer combinations. The Ti/TiN foils were deposited using opposing magnetrons, with the TiN layers produced by reactive sputtering. The Al–Mg/Mg foils were deposited from pure Al and Mg targets in a co-planar configuration, conditions having been initially found that produced high hardness/high strength amorphous Al–Mg alloy foils. Both multilayer systems benefit mechanically from the combination of a high strength component (TiN; Al–Mg) and a ductile component (Ti; Mg). Conditions were found that limited the stresses induced in these ultra-thick coatings such that once removed from the substrate, the foils remained flat. Experimental arrays were then constructed to investigate the effect of relative percentage volume fraction, substrate bias and interlayer wavelength against the Young's modulus, tensile strength, ultimate tensile strength and other mechanical properties of the foils. These properties were determined using a modified Hounsfield tensometer. The study found that when in tension, the interlayer wavelength has no effect upon the tensile strength of the foil. However, as expected, tensile strength was strongly dependent upon the relative percentage volume fraction of the high strength component of the foil. The substrate bias was found to have a limited influence upon mechanical properties. Conditions were found that produced a tensile strength-to-film density ratio of 244, approaching that of tool steel.

Fabrication of AlN thin films on different substrates at ambient temperature

Aluminium nitride (AlN) is very useful as a barrier in superconductor–insulator–superconductor (SIS) device or as an insulating layer in many other applications. At ambient temperature, we deposit AlN thin films onto different substrates (such as MgO, LaAlO3 and Si) by using radio-frequency magnetron sputtering and pure Al target. X-ray diffraction (XRD) and Φ-scan patterns show that the films grown on MgO substrates are excellent epitaxial films with (101) orientation of a hexagonal lattice. A possible structure of the interface between the film and the substrate is suggested and discussed.

MD simulation of atomic displacements in pure metals and metallic bilayers during low energy ion bombardment at 0 K

Molecular Dynamics (MD) simulations of 100 eV Ar ion bombardment of (1 0 0) Ni and Al crystals, of bilayer crystals consisting of an Al (or Ni) layer on a (1 0 0) Ni (or Al) substrate, as well as pseudo-isotope bilayer crystals have been performed at 0 K using tight-binding potentials. For these systems sputtering yields, energy deposition with depth, atomic relocations, production of ad-atoms, depth distributions of vacancies and interstitials per ion impact were studied for times up to 7 ps. We observed that both the mean square displacement of atoms and defect production (vacancies, interstitials and ad-atoms) are larger in pure Al than in pure Ni. In addition, we observed for the bilayer systems Al/Ni and Ni/Al a high number of the near surface atomic relocations; especially ion bombardment induced exchange processes between atoms of the 1st (Al or Ni) and of the 2nd (substrate) layer. Potential energy calculations indicate that such relocations between the 1st and the 2nd layer are in both bilayer crystals energetically favourable. Both Al/Ni and Ni/Al bilayers show considerable higher production of ad-atoms as the pure Al and Ni targets. Typically ad-atoms are from the first layer, but in the Ni/Al bilayer system we found a substantial amount of Al ad-atoms from the 2nd layer (first Al layer). They contribute more to the ad-atom number than 1st layer Ni atoms. The mean square displacement of atoms in Al/Ni and Ni/Al crystals increases considerably during the thermal stages of the cascade evolution while it is almost constant in the case of the pure Al and Ni. Finally we observed that the maximum kinetic energies of atoms in the cascade volume after 4 ps are lower in the Ni and Al/Ni crystals than in Al and Ni/Al crystals, reflecting the lower cohesive energy of Al as compared to Ni. Calculations with pseudo-isotope bilayer crystals were performed to elucidate the influence of mass or potential on the observed effects.

Continuum x-ray source as a calibration system for charge coupled devices

We present x-ray spectra obtained by a charge coupled device (CCD) from an electron impacting x-ray source using several kinds of electron targets: Au, Al–bronze, Al, and pure Al. The x rays from the source are dispersed by a grating and the dispersed x rays are focused on the CCD. Owing to the fine spatial and moderate energy resolutions of the CCD, fine spectra with 2 eV energy resolution up to 2.2 keV are obtained. X rays from the pure Al target (99.999% purity) provide good continuum x rays except for Al K x rays. This continuum source is useful as a calibration source for low energy x-ray detectors.

He + scattering from Ni, Al, and their alloy. Model calculation of the charge exchange

The changes in the He + neutralization probability when scattered from pure Al and Ni targets and from a NiAl alloy are analyzed. The neutralization probability is calculated using a time-dependent quantum formalism which allows incorporation of several electronic bands of localized and extended nature in the description of the target band structure. The parameters of the interaction Hamiltonian are obtained from an ab-initio model based on a pair-bonds superposition. We find that for He + scattering from Al atoms in NiAl the neutralization is less probable than for He + scattering from pure Al, while for the scattering from Ni atoms there is no change in the neutralization probability when going from pure Ni to the alloy target. These results are in agreement with the experimental trends which show a matrix-dependent signal only for the scattering from Al. The marked difference in the neutralization behavior of He + can be explained by taking into account the differences in the electronic structure between pure Al and NiAl alloy, and the presence of the corelike Al-2p state which promotes the charge exchange process at low primary He + energies.

An interferometric investigation of ignition of a laser-supported detonation wave and its propagation

In this paper, the LSD wave ignition process is analyzed. Interaction of an Nd:YAG laser and a pure Al target is investigated synchronously with a Mach-Zehnder interferometer, and series of interferograms of the ignition of an LSD wave and its propagation are obtained first. The propagating speed of the LSD wave and the pressure behind the LSD wave are obtained.

Transformation de phase dans l'aluminium induite par implantation ionique de nickel à haute énergie

Implantation of Ni into a pure Al target leads to the formation of amorphous zones. Their formation is studied by transmission electron microscopy (TEM). The present results were obtained in samples implanted with ions having energies between 22 and 40 MeV and fluences between 1.68×10 15 and 2.5×10 17 ions/cm 2 . In order to observe the profile of the ion implantation in the TEM, cross-sectional samples were thinned with a specially modified ion bombardement. Measurements of the atomic concentration have been carried out with energy dispersive spectroscopy (EDS). In spite of the Ni concentration (up to 3 at. %) in the implanted layer, there is no observable nuclei of the Al 3 Ni phase after implantation at 120 K and room temperature. In contrary, amorphous zones with a diameter of about 10 nm are present together with a high density of dislocation loops and dislocations. The Ni concentration in the amorphous zones is about 25 at. %. An implantation conducted at 520 K shows only crystalline precipitates of Al 3 Ni. We conclude that the Ni implanted in Al agglomerates in zones having composition identical to that of the Al 3 Ni phase

Fabrication of microlaminated Al/Al2O3 composites by magnetron sputtering for tribological applications

Abstract Microlaminated composites consisting of alternating layers of Al and Al 2 O 3 have been produced using a radiofrequency triode magnetron sputtering unit equipped with metallic and oxide target sources. Composite films up to 25 μm thick with 100 Al/Al 2 O 3 layers were fabricated in the form of square coupons 20 mm × 20 mm, which were suitable for wear testing using a miniature pin-on-disc tribometer. To measure the strength and the wear resistance as a function of the interlaminate spacing, composites with Al layers 100–500 nm thick were fabricated. The thicknesses of the Al 2 O 3 layers were in the range 20–100 nm. Transmission electron microscopy and selected area electron deffraction studies showed that every Al layer consisted of polycrystallites with very fine grain size (20 nm on a average), whereas the Al 2 O 3 layers had an amorphous structure. Microhardness measurements showed that monolithic nanocrystalline Al produced using sputtering had a hardness of 1700 MPa (eight times higher than that of a pure Al target with a grain size of 5 mm) and the incorporation of Al 2 O 3 layers increased the microhardness to 2300 MPa. Tribological tests revealed that the dry sliding wear resistance of Al/Al 2 O 3 composites increased by a factor of two compared with that for monolithic nanocrystalline Al.

Energy distributions of sputtered metal Al-clusters

The energy distributions of neutral clusters escaping from metal targets under ion bombardment have been measured by nonresonant laser post-ionization and a time-of-flight (TOF) technique. Measurements of various Al- and Sn-atoms, dimers and trimers from pure Al and AlSn alloy targets show that the ionization process is crucial for the interpretation of the measured spectra. In particular, fragmentation of large clusters can easily mask and disturb the measured energy distribution of clusters with fewer atoms and of monomers, if the ionization probability is low, as it is the case for multiphoton ionization. The results obtained for the energy distribution of Al-atoms, dimers and trimers show that simple theories for the cluster formation cannot predict the correct energy distributions, but molecular dynamics simulations agree well with the experiments.