Showing papers on "Annealing (metallurgy) published in 1992"

Tantalum as a diffusion barrier between copper and silicon: Failure mechanism and effect of nitrogen additions

Abstract: The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross‐section transmission electron microscopy. Ta prevents Cu‐silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η‘‐Cu3Si precipitates at the Ta‐Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal‐TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta‐Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen‐alloyed Ta is a very similar...

Effect of growth conditions on the properties and morphology of chemically derived epitaxial thin films of Ba2YCu3O7−x on (001) LaAlO3

Abstract: Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single‐crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high‐temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low‐oxygen partial pressures. Superconducting films of 70 nm thickness with zero‐field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c‐axis normal BYC near the film/substrate interface with the overlying mater...

Non-linear properties of metallic cellular materials with a negative Poisson's ratio

Abstract: Negative Poisson's ratio copper foam was prepared and characterized experimentally. The transformation into re-entrant foam was accomplished by applying sequential permanent compressions above the yield point to achieve a triaxial compression. The Poisson's ratio of the re-entrant foam depended on strain and attained a relative minimum at strains near zero. Poisson's ratio as small as -0.8 was achieved. The strain dependence of properties occurred over a narrower range of strain than in the polymer foams studied earlier. Annealing of the foam resulted in a slightly greater magnitude of negative Poisson's ratio and greater toughness at the expense of a decrease in the Young's modulus.

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

Abstract: This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10−3 to 10.4× 10−3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10−3 to 11.6 × 10−3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. ...

Oscillations in giant magnetoresistance and antiferromagnetic coupling in [Ni81Fe19/Cu]N multilayers

Abstract: We report giant magnetoresistance in [Ni81Fe19/Cu]N multilayers. Saturation magnetoresistance values exceeding 16% for saturation fields of only 600 Oe are found at 300 K. In addition, we show evidence for well‐defined oscillations in saturation magnetoresistance as a function of Cu spacer layer thickness at 4.2 K, with an oscillation period and phase similar to that in Co/Cu multilayers. However, the temperature dependence of the magnetoresistance, while weak for thin Cu layers, is much stronger for thicker Cu layers. Consequently at 300 K only a single oscillation in magnetoresistance for thin Cu layers is found. We show that the properties of the Ni81Fe19/Cu multilayers are very sensitive to annealing at moderate temperatures, which may limit the possible technological applications of such structures.

Characterization of hydrothermal barium titanate

Abstract: Hydrothermally prepared powders of BaTiO 3 show a number of structural peculiarities which are closely connected with a considerable content of water, incorporated in the perovskite lattice. On annealing the powders to 500°C the water is gradually released and the normal structural properties of BaTiO 3 recur. A defect chemical model has been derived for hydrothermal BaTiO 3 showing a loosely packed perovskite structure with large numbers of protons in the oxygen sublattice and vacancies in the sublattices of Ba and Ti.

Comment on: Fluid distributions in two‐phase random media: Arbitrary matrices

Abstract: It is pointed out that the Ornstein–Zernike equations recently used by Madden in treating quenched‐annealed mixtures are approximate. The exact equations are given and briefly discussed.

Single‐crystal diamond plate liftoff achieved by ion implantation and subsequent annealing

Abstract: We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well‐defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well‐established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline dia...

Theoretical prediction and direct observation of the 9R structure in Ag.

Abstract: Molecular-dynamics simulations of the \ensuremath{\Sigma}3〈110〉(211) twin boundary in Ag predict a thin (1 nm) boundary phase of the 9R (\ensuremath{\alpha}-Sm) structure. High-resolution electron microscopy shows the presence of the predicted structure. We also calculate the energy ab initio for several hypothetical structures of Cu and Ag. Low energies of the 9R structure and other polytypes, low experimental stacking-fault energies, and the hcp-fcc energy difference are correlated and explained in terms of an effective nearest-neighbor Ising interaction.

The structure of NiN and PdN clusters: 4≤N≤23

Abstract: Stable geometrical structures of NiN and PdN clusters (N=4–23) are identified using a corrected effective medium (CEM) theory. Structural optimization is accomplished by simulated annealing using analytic derivatives to determine the interatomic forces. Unique structural features of these metal clusters are noted, especially in relation to the bulk and surface phases of these metals and to structures commonly associated with rare gas clusters. Elucidation of the general features of cluster growth leads to the principle that transition metal clusters generally maximize the minimum coordination of any atom. By contrast, rare gas clusters maximize the number of interatomic distances close to the optimal distance for the pairwise interaction between rare gas atoms. The latter can be interpreted as the packing of hard balls. Structural transformations between isomers of similar energy are also examined for selected sizes.

Crystallization of Fe73.5Cu1Nb3Si13.5B9 structure and kinetics examined by X-ray diffraction and Mossbauer effect spectroscopy

Abstract: Changes in the structure of the amorphous alloy Fe73.5Cu1Nb3Si13.5B9 were investigated after annealing for 1 h in a temperature range from 450-800 degrees C using X-ray diffraction scattering and Mossbauer effect spectroscopy. Between 520 and 550 degrees C nanocrystalline Fe80Si20 grains with the DO3 structure (diameter of about 10 nm) are embedded in an amorphous grain boundary phase. Above 650 degrees C the grain size increases and the amorphous grain boundary phase disappears. The Fe-B phases form and a new paramagnetic phase is observed. Furthermore the kinetics of the amorphous-to-nanocrystalline phase transition of this alloy was examined by X-ray diffraction observing the development of crystallization with time at a fixed annealing temperature of 520 degrees C. The beginning of crystallization appears at times less than 2 min, most grains developing in the first 10 to 20 min while after about 5 min the grain size remains constant with a diameter of about 10 nm.

Process effects on structural properties of TiO2 thin films by reactive sputtering

Abstract: We have been investigating the growth of crystalline titanium dioxide films at deposition temperature between room temperature and about 400 °C. The films were prepared by a dc magnetron reactive sputtering on glass and Si(100) substrates. The structural properties of the films were analyzed by x‐ray diffractometry. The influence of total pressure, oxygen mole fraction in the mixture of Ar–O2, discharge current, and substrate temperature on the structural properties were studied. In addition to higher substrate temperature, low total pressure, high discharge current, and small oxygen mole fraction were shown to be preferable for growing anatase–rutile mixture films. Annealing of the films in air at 850 °C showed that anatase–rutile transformation strongly depends on the deposition temperature; the films deposited at temperature below 400 °C were converted to the anatase–rutile mixture films, and the films deposited at 400 °C to complete rutile films.

Correlation of the electrical properties of metal contacts on diamond films with the chemical nature of the metal-diamond interface. I. Gold contacts: A non-carbide-forming metal.

Abstract: The I-V characteristics of titanium contacts on polycrystalline diamond have been correlated with x-ray-photoelectron-spectroscopy (XPS) and Auger-electron-spectroscopy (AES) characterizations of the interface. As-deposited titanium contacts were rectifying in nature because of minimal interaction between as-deposited titanium and diamond as confirmed via XPS and AES. Once annealed, however, these contacts became Ohmic. The change was related to the formation of a carbide at the interface as observed by XPS. The Schottky-barrier height of the titanium contacts, which was determined by valence-band XPS, decreased from 1.3 to 0.8 eV as a result of the postdeposition annealing. It is believed that the carbide formation at the interface creates a diamond surface layer rich in electrically active defects which lower the barrier height of the metal and increase the leakage current. The interface between titanium and an argon-sputtered diamond surface was also characterized. Titanium formed as-deposited Ohmic contacts on the sputtered surface. A high density of ion-radiation-induced defects and a formation of a carbide during deposition both contributed to the Ohmic-contact formation. These contacts remained Ohmic after postdeposition annealing despite the fact that the annealing did not increase the carbide formed at the interface. It is believed that the carbide formed by the deposition of titanium behaved as a diffusion barrier to prevent the damaged layer from being annealed out into the titanium overlayer. It is concluded that most materials will yield rectifying contacts on a clean diamond surface. Ohmic contacts can be obtained by modifying the interface in some way (i.e., carbide formation, sputtering, etc.).

Structural and electrical studies on rapid thermally processed ferroelectric Bi4Ti3O12 thin films by metallo‐organic solution deposition

Abstract: Thin films of Bi4Ti3O12 that were pinhole free with uniform composition and thickness were prepared by the metallo‐organic solution deposition technique on platinum coated silicon and bare silicon substrates. Crack free and crystalline films of 5000 A thickness were fabricated by spinning and post deposition rapid thermal annealing treatment at 500 °C. The films exhibited good structural, dielectric, and ferroelectric properties. The effects of annealing temperature and time on the structural and electrical properties of the films were evaluated. The measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 184 and 0.039, respectively for a film rapid thermally annealed at 700 °C for a time of 10 s. Room temperature resistivity of 108 Ω cm and leakage current density of less than 10−7 A/cm2 were obtained for a 0.5‐μm‐thick film at an applied electric field of 100 kV/cm; establishing good insulating behavior. Ferroelectricity was confirmed by P–E hysteresis loops with ...

Molecular dynamics simulation of silica liquid and glass

Abstract: A molecular dynamic computer simulation of the cooling of liquid silica to form an amorphous solid (glassy) phase was performed using the potential of Tsuneyuki, Tsukuda, Aoki, and Matsui, which was found to be consistent with the structure of several crystalline phases of silica. In the simulations, at low temperatures the atoms formed an almost perfect random tetrahedral network, and on subsequent annealing the material formed a perfect network, with each silicon having four oxygen neighbors and each oxygen having two silicon neighbors. The simulated material at low temperatures has a structure that is in close agreement with experimental neutron scattering measurements on amorphous silica. Several properties of the material were calculated and compared with experiment, and the nature of the ‘‘inherent structure’’ of the material as a function of temperature was investigated. The potential of Tsuneyuki et al. provides an excellent model for amorphous silica as well as crystalline silica.

Wettability and interfacial energies in SiC-liquid metal systems

Abstract: The sessile drop technique is used to measure the contact angles of molten Si, Sn, Cu and Ni in contact with mono- and polycrystalline α-SiC as well as CVD β-SiC in purified argon atmosphere and at various temperatures. The contact angle of silicon, near its melting point, is about 38° on a mono- as well as polycrystalline α-SiC substrate and about 41.5° on β-SiC. Tin does not wet the SiC. Using data from the available literature, the work of adhesion and the interfacial energy between SiC and Si or Sn were calculated. In the α-SiC-Sn system, both quantities are linearly dependent on temperature in the investigated temperature range 523–1073 K. The metals copper and nickel react with silicon carbide. The silicon content of the copper drop depends on the annealing temperature. The nickel drop after cooling forms the compound Ni3Si2. The interferometric measured groove angle of SiC (thermal etching) in vacuum at 2020 K gives a mean value of 157.6±5.8°.

Resistance and structural stabilities of epitaxial CoSi2 films on (001) Si substrates

Abstract: The resistance and structural stabilities of the epitaxial CoSi2 films, grown on (001) Si substrates using sequentially deposited Ti‐Co bimetallic layer source materials, have been investigated by further anneals under extended conditions. In contrast to reported polycrystalline silicide film cases, the epitaxial CoSi2 films are very stable under the additional rapid thermal annealing treatment at 1100 °C for times from 10 to 60 s. This means that such CoSi2 films are able to stand the further heat treatment required in the ultralarge‐scale integration regime of Si integrated circuit fabrication. The quality of the further annealed films has been actually improved: The film resistivity has decreased to reach a value as low as 10 μΩ cm, and the film structure has become more perfect, e.g., the densities of antiphase domains and film‐Si interface facets have been decreased. For technological applications, it is necessary to remove the Ti‐Co‐Si alloy layer formed concomitantly on top of the as‐grown CoSi2 fi...

Annealing studies of low-temperature-grown GaAs:Be

Abstract: The isochronal and isothermal annealing characteristics of acceptor‐doped GaAs:Be grown at low substrate temperatures (300 °C) by molecular‐beam epitaxy (LTMBE) have been studied. The Be was introduced in a range of concentrations from 1016 to 1019 cm−3. Electrical measurements of as‐grown material up to the highest Be concentration of 1019 cm−3 show that no free holes are contributed to the valence band even though Raman spectroscopy of the Be local vibrational mode indicates that the majority of the Be impurities occupy substitutional sites. It is proposed that Be acceptors are rendered inactive by the high concentration of AsGa‐related native donor defects present in LTMBE material. The concentration of AsGa‐related defects in the neutral charge state was estimated from infrared absorption measurements to be as high as 3×1019 cm−3. A distinct annealing stage at 500 °C, similar to that found in irradiation‐damaged and plastically deformed GaAs, marks a rapid decrease in the concentration of AsGa‐related...

Rapid thermal annealing of sol‐gel derived lead zirconate titanate thin films

Abstract: Sol‐gel derived ferroelectric thin films of lead zirconate titanate have been annealed through the rapid thermal annealing (RTA) technique to investigate the effect of various annealing temperature‐time combinations. Crystallization of the film into the perovskite phase required 10 s at 600 °C and a mere 1 s at 700 °C. Rapid thermally annealed films recorded weak‐field permittivities greater than 1000, dissipation losses of 0.02–0.05, maximum remanent polarization of 29 μC/cm2, and coercive field around 40 kV/cm. RTA films are distinguished by superior breakdown strengths, and morphologically smoother surfaces. The frequency dependent dielectric constants have been discussed in terms of a lumped circuit model.

Effects of thermal annealing on porous silicon photoluminescence dynamics

Abstract: Photoluminescence (PL) spectra and decay dynamics were studied for the spontaneously oxidized porous Si with subsequent various thermal annealing procedures. The PL decay was highly nonexponential and well described by the stretched‐exponential function. The PL lifetime was shorter for the higher PL photon energy, but at the same photon energy it decreased by an order of magnitude by the thermal annealing in N2 gas, in parallel with the large PL intensity decrease. This PL quenching upon the annealing is presumably ascribable to both the structural changes and dangling bond formations in porous Si, as suggested by ESR measurements and the annealing experiments in H2 gas.

Production bias and void swelling in the transient regime under cascade damage conditions

Abstract: Molecular dynamics (MD) studies of collision cascades have firmly established that, in addition to clusters of vacancies, clusters of self-interstitial atoms (SIAs) are formed within the cascade volume during the thermal spike phase of a cascade. These clusters are formed in a segregated fashion such that the vacancy-rich core is surrounded by SIA clusters. At temperatures above stage V the vacancies evaporate from the vacancy cluster and diffuse into the medium whereas the SIA clusters remain thermally stable at temperatures even above the peak swelling temperature. This asymmetry in the production of free and mobile vacancies and SIAs gives rise to a production bias. Some of the vacancies evaporating from the vacancy-rich core annihilate at the SIA clusters surrounding it and others escape into the medium. It is this escaping fraction of vacancies which determines the strength of the production bias. Diffusion calculations have been performed to estimate the magnitude of this escaping fraction ...