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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 3 • Date May 2007

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Displaying Results 1 - 25 of 40
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Passivation layer on polyimide deposited by combined plasma immersion ion implantation and deposition and cathodic vacuum arc technique

    Page(s): 411 - 414
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    A thin passivation layer of aluminum oxide was deposited on polyimide by using the combined plasma immersion ion implantation and deposition (PIII&D) and cathodic vacuum arc technique. X-ray photoelectron spectroscopy C 1s spectra showed that the carbonyl bond (CO) and ether group (C–O–C and C–N–C) presented in pristine polyimide were damaged by implantation of aluminum ions and deposition of an aluminum oxide passivation layer. O 1s and Al 2p spectra confirmed the formation of a thin aluminum oxide passivation layer. This passivation layer can be implemented in aerospace engineering where polyimide may suffer degradation from fast atomic oxygen in the low-earth-orbit environment. To test the protection of this passivation layer to energetic oxygen ions, a plasma-enhanced chemical vapor deposition system was used to simulate the oxygen-ion irradiation, and the results showed that a higher weight occurred for passivated samples compared to pristine ones. X-ray diffraction showed that Al peaks were presented on the surface region, but no aluminum oxide peak was detected. The authors then concluded that Al clusters were formed in polyimide besides aluminum oxide, which was in an x-ray amorphous state. Furthermore, contact-angle measurements showed a reduced contact angle for passivated polyimide from a pristine value of 78° to 20° by using deionized water. Several discussions have been made on the surface chemical and structural property changes by using the combined PIII&D and cathodic vacuum arc technique. View full abstract»

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  • Reduction of thin oxidized copper films using a hot-filament hydrogen radical source

    Page(s): 415 - 420
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    This article aims to provide practical information on the performance of a hot-filament radical source, with which it becomes feasible for metallization in ultralarge-scale integrated circuits, which has not been studied in detail thus far. A very simple arrangement using this technique allows the highly efficient generation of hydrogen radicals and a quick recovery of oxidized Cu surfaces to their original metallic state. The amount of CuO reduction was evaluated by measuring sheet resistance and also by transmission microscopy. The reduction started when the specimen temperature exceeded 100 °C, and several tens of nanometers Cu of film was formed without resulting in a serious increase in the specimen temperature. The amount of reduction was found to increase almost proportionately to the hydrogen radical flux. The Cu layer had a very flat surface topography showing no trace of self-agglomeration of Cu. The reduction of a thermally oxidized Cu specimen was also demonstrated. View full abstract»

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  • Thermal stability of nonhydrogenated multilayer amorphous carbon prepared by the filtered cathodic vacuum arc technique

    Page(s): 421 - 424
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    Through discrete modulation of the deposition biasing conditions, multilayered nonhydrogenated diamondlike amorphous carbon films were prepared by the filtered cathodic vacuum arc technique. Films deposited under different conditions were divided into two groups in order to study how the modulation as well as sublayer content affect various mechanical and material properties as deposited and after annealing in vacuum. A 30% decrease in the residual stress of the multilayer films from 4.3 to 2.8 GPa was observed with only marginal (5%) changes in the hardness. The frictional characteristics of the multilayer films were also studied and shown to be excellent, having a coefficient of friction of 0.1 and stable with annealing. A larger decrease in the resistance to wear was observed in multilayer films richer in soft sublayers which was linked to the decreased in sp3 content in the films. View full abstract»

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  • Influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO3 films in Ar/SF6 plasmas

    Page(s): 425 - 431
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    Langlois etal [Appl. Phys. Lett. 87, 131503 (2005)] have demonstrated that the etch yield of SrTiO3 films in Ar/SF6 plasmas decreases as the concentration fraction of molecular ions in the plasma increases. Introducing the concept of effective mass for both ions and SrTiO3, these experimental results have quantitatively been explained in the framework of a well-established model originally developed to describe the sputtering of single-atom materials by nonreactive monoatomic ions. This model has, however, ignored the dissociation of molecular ions occurring as these particles impact the material surface. In the present article, the influence of the positive ion composition on the ion-assisted chemical etch yield of SrTiO3 films in Ar/SF6 plasmas is reexamined to the light of this consideration. A rate model accounting for the dissociation of the various molecular ions is proposed and validated using experimental data. It is found that even though a specific ion species may not be the most important charge carrier in the plasma, its contribution to the plasma etching dynamics may still be the most significant. View full abstract»

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  • Reactive and anisotropic etching of magnetic tunnel junction films using pulse-time-modulated plasma

    Page(s): 432 - 436
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    Reactive and anisotropic etching of magnetic tunnel junction (MTJ) stacked films has been achieved using pulse-time-modulated (TM) plasma. While corrosion and delamination of MTJs are observed in continuous wave discharge plasma, a chlorine pulse-time-modulated plasma achieved a high MTJ etching rate without corrosion or delamination. The authors think that the negative ions enhance the chemical reactions on the surface of magnetic films. The magnetic characteristics are also significantly improved by using TM plasma because of reduced residues and improved tapered profiles. Accordingly, TM plasma etching is a promising candidate for high-rate and damage-free MTJ etching for magnetoresistive random access memory devices. View full abstract»

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  • Infrared absorber for pyroelectric detectors

    Page(s): 437 - 440
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    A quarter-wavelength absorber structure was developed for pyroelectric detector applications in the 2.5–3.5 μm range. The absorber consisting of Pt and plasma-enhanced chemical vapor deposited SiO2 layers was fabricated using standard clean-room processes. It exhibited a minimum reflectance of 2%. View full abstract»

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  • Identification of important growth parameters for the development of high quality Alx≫0.5Ga1-xN grown by metal organic chemical vapor deposition

    Page(s): 441 - 447
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    High quality Alx≫0.5Ga1-xN layers were grown on (0001) sapphire substrates by metal organic chemical vapor deposition utilizing an AlN nucleation layer. The growth conditions of the nucleation layer were observed to have a large impact on both the surface morphology and the crystalline quality of the AlxGa1-xN layers. Low temperature nucleation layers with an optimum thickness of ∼15 nm gave the best quality AlxGa1-xN layers. Additionally the annealing of the nucleation layer was seen to have a dramatic effect on the crystalline quality of the overgrown AlxGa1-xN layers. The quality of the films as measured by atomic force microscopy and x-ray diffraction was largely independent of the V/III ratios of the AlxGa1-xN layers, although Al incorporation and growth rate were affected. Two distinct regimes were identified for the Al incorporation in the overgrown AlxGa1-xN as a function of ammonia flow rate; the Al incorporation first decreases with increase in the ammonia flow rate and then increases with a continued increase in the ammonia flow rate. It is shown that the residence time of the species in the growth system controls the amount of the precursor prereaction independently of the actual flow rates and V/III ratio affecting the Al incorporation in the solid phase. View full abstract»

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  • Fluorine content of SiOF films as determined by IR spectroscopy and resonant nuclear reaction analysis

    Page(s): 448 - 454
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    In this article, the authors compare the fluorine concentrations obtained from the strength of the infrared-absorption band due to Si–F bonds, with the absolute concentrations determined from 19F(p,αγ)16O resonant nuclear reaction analysis, for a series of fluorinated silicon oxide (SiOF) films prepared by remote plasma-enhanced chemical-vapor deposition with different flow rates of H2 in SiF4/O2/He mixtures. The authors use this comparison to calibrate the proportionality constant between the strength (integrated absorption) of the infrared-absorption band due to Si–F bonds and the concentration of these bonds in the films. The authors found that (under the Gentzel and Martin approach [Surf. Sci. 34, 33 (1973)]) this calibration requires the correction of the “fudge” factor, to a new value, γ=1.28, which is more consistent with the small correction to the local field expected for porous SiOF films. The authors also found that the changes in the refractive index and density of the films introduce less significant corrections in the quantification process of fluorine by the infrared method. View full abstract»

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  • Electron and ion kinetics in magnetized capacitively coupled plasma source

    Page(s): 455 - 463
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    One-dimensional particle-in-cell Monte Carlo collision simulations of magnetized argon plasmas in an asymmetric capacitively coupled plasma reactor are presented. At low pressure (10 mTorr), electron kinetics are strongly affected by the magnetic field and transitions from nonlocal to local kinetic property occur with increasing magnetic field which are reflected in spatially resolved calculations of the electron-energy probability function. For high-energy electrons, the transition takes place when the energy-relaxation length is smaller than the system length. For low-energy electrons, however, the transition occurs when the electron-diffusion time scale in the energy space is shorter than the spatial-diffusion time scale in coordinate space. These observations are in agreement with experimental data and theoretical calculations deduced from the Boltzmann equation. The ion energy distribution function (IEDF) on the driven electrode changes from the ion-neutral collisional type to the ion-neutral collisionless type with increasing magnetic field strength. The maximum ion energy in the IEDF decreases and the angular spread in the ion angle distribution function slightly increases with increasing magnetic field strength. These changes are explained in terms of the ratio of the ion-transit time to rf frequency, the sheath length, and the mean potential difference between the driven electrode and the plasma. At high pressure (218 mTorr), electron-neutral collisions disrupt electron gyromotion so that the effects of the magnetic field on electron and ion kinetics are greatly reduced. View full abstract»

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  • Structural and electrical characteristics of microcrystalline silicon prepared by hot-wire chemical vapor deposition using a graphite filament

    Page(s): 464 - 467
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    Intrinsic hydrogenated microcrystalline silicon c-Si:H) films were prepared on Corning glass substrates by hot-wire chemical vapor deposition using a graphite filament. The advantage of the graphite filament is its longer lifetime and greater chemical stability as compared to the commonly used Ta and W wires, particularly at lower filament temperatures at which silicides are known to form on Ta and W. This study examines the deposition of μc-Si:H at the lower filament temperature of 1525 °C. A low substrate temperature of 210 °C was used for all μc-Si:H depositions with resulting deposition rates of up to 2.0±0.2 Å/s. Raman spectroscopy and electrical conductivity measurements showed that μc-Si:H growth occurred only for silane concentrations below 1.5% dilution in hydrogen. The average grain size was found to be 25 nm measured by transmission electron microscopy. View full abstract»

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  • NiCr etching in a reactive gas

    Page(s): 468 - 473
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    The authors have etched NiCr through a resist mask using Cl/Ar based chemistry in an electron cyclotron resonance etch system. The optimum gas mixture and etch parameters were found for various ratios of Ni to Cr, based on the etch rate, redeposits, and the etch ratio to the mask. The introduction of O2 into the chamber, which is often used in the etching of Cr, served to both increase and decrease the etch rate depending explicitly on the etching parameters. Etch rates of ≫50 nm min-1 and ratios of ≫1 (NiCr:Mask) were achieved for NiCr (80:20). Pattern transfer from the mask into the NiCr was achieved with a high fidelity and without redeposits for a Cl/Ar mix of 10% Ar (90% Cl2) at an etch rate of ≈50 nm min-1 and a ratio of 0.42 (NiCr:ZEP 7000 e-beam mask). View full abstract»

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  • Zinc deposition experiments for validation of direct-simulation Monte Carlo calculations of rarefied internal gas flows

    Page(s): 474 - 479
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    Specially designed experiments were performed for the validation of direct simulation Monte Carlo calculations of rarefied internal gas flows. Hot zinc vapor was released into a cold-wall deposition chamber filled with a background gas at low pressure in which two silicon wafers were mounted. The deposited zinc layers on these wafers have been measured in four different experiments, with varying background gas species (argon and helium) and background pressures (0.031–0.25 Pa). The background gas conditions were chosen such that the Knudsen numbers based on the zinc mean free path range from 0.34 to 2.8. The experimental results have been compared to simulation results. View full abstract»

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  • Mass fractionation of carbon and hydrogen secondary ions upon Cs+ and O2+ bombardment of organic materials

    Page(s): 480 - 484
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    A phenomenon known as mass fractionation has been probed in organic materials using secondary ion mass spectrometry (SIMS). Mass fractionation occurs because two isotopes of a particular species (i.e., identical number of protons, but different number of neutrons) do not have identical secondary ion yields in a constant chemical environment. Two primary ion probes, Cs+ and O2+, have been utilized with detection of negative and positive secondary ions, respectively, using a magnetic sector mass spectrometer. These two analysis conditions have been found to yield considerably different mass fractionation effects as a result of different sputtering and ionization mechanisms. Also, as determined previously with SIMS analysis of inorganic materials, the lower molecular weight species carbon and hydrogen are particularly susceptible to mass fractionation effects. Because organic materials are primarily composed of carbon and hydrogen, and because isotopic labeling is often utilized to accurately analyze such materials, knowledge of these effects in organic materials is essential for quantitative SIMS analysis. View full abstract»

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  • Effects of the deposition parameters on the growth of ultrathin and thin SiO2 films

    Page(s): 485 - 491
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    SiO2 ultrathin and thin films have been deposited on single-crystal Si substrates by means of nonreactive radio frequency magnetron sputtering. The temperature of the substrate and the deposition times have been varied in the range of 200–500 °C and 60–14 400 s, respectively. The average deposition rate has a range of 0.5–5 nm/min and tends to decrease with the increase of the substrate temperature. Two different growth regimes may be observed for ultrathin and thin films, the transition taking place in the range of 5–10 nm depending on the substrate temperature. The roughness of the film surface and the grain dimensions do increase with the substrate temperature for short deposition times (t≤300 s), whereas their behavior is less defined for intermediate ones (300 s≪t≪1800 s). Finally, for long deposition times (t≫1800 s) the roughness increases again with T, and its slope is higher, the higher the substrate temperature is. View full abstract»

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  • Sputter deposited electroluminescent zinc sulfide thin films doped with rare earths

    Page(s): 492 - 499
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    The effects of deposition conditions on the physical properties and threshold voltages of ZnS alternating current thin film electroluminescent (ACTFEL) phosphors are reported. The ZnS thin films were deposited by rf magnetron cosputtering of both a pure ZnS and a ZnS target doped with either 1.5 mol % ErF3, NdF3, or TmF3, and EL peaks in both the visible and near infrared (NIR) were observed. The substrate temperature during deposition was varied between 140 and 190 °C, and the highest NIR EL intensity was measured from as-deposited films at 140 °C. Energy dispersive x-ray analysis was used to determine the rare earth concentrations between 1.0 and 2.6 at. %, and the maximum emission was at ∼0.8–1 at. %. The EL intensity decreased at higher concentrations due to poor crystallinity and decreased at lower concentrations due to lower rates of excitation. The threshold voltage and phosphor thickness for these ACTFEL devices both decreased as the deposition temperature was increased due to re-evaporation of the incongruently sputter transported zinc and sulfur. Electrical data confirmed that the optical threshold voltage for both NIR and visible emission were equal to one another and to the electrical breakdown voltage, indicating that at breakdown the energies of ballistic electrons are sufficient to excite both visible and infrared emissions. View full abstract»

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  • Coverage dependent reaction of yttrium on silicon and the oxidation of yttrium silicide investigated by x-ray photoelectron spectroscopy

    Page(s): 500 - 507
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    The reaction of yttrium (Y) on (001) silicon (Si) with low temperature annealing is investigated for different coverages of Y using in situ x-ray photoelectron spectroscopy. The authors have also performed oxidation studies for Y on Si in the formation of yttrium silicate by a two-step process. This consists of an ex situ oxidation of Y–Si film, which is formed from low temperature annealing in vacuum. These films were then probed with depth profiling x-ray photoelectron spectroscopy. They report on three general reaction phases of Y on Si that are coverage dependent. Different coverages show differences in Si mixing and selective ultrahigh vacuum oxidation. They also report on the self-limiting formation of yttrium silicate at room temperature and low annealing temperature, which is insensitive to the annealing ambient. They also highlight the importance of oxygen partial pressure in both initial silicate formation and the extent of oxidation at different annealing temperatures. Finally, the authors also show that a high oxygen diffusion barrier prevents the oxidation of the entire Y–Si film. View full abstract»

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  • Radiative wafer heating during plasma deposition process

    Page(s): 508 - 513
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    Wafer heating with visible and infrared radiation is a well established method used in plasma deposition reactors used for solar cell production. A detailed study on radiative heat transfer as presented in this article gives a quantitative description by considering the spectral absorption of radiation in optical components, contamination of these components during plasma growth, the spectral emissivity of the silicon solar cell, and the effect of heat buffer components. Even with a clever implementation of heaters the net power incident on the wafer is shown to decrease to 60%. The wafer temperature ramp up time is shown to be dependent on the surface roughness and dopant level of the silicon solar cell, whereas the steady-state temperature during plasma growth is independent on these properties. Due to contamination during plasma growth, the wafer temperature decreases by 80 K within one production shift, but this decrease can be minimized to 10–20 K by implementing heat buffer components. View full abstract»

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  • Femtomolar isothermal desorption using microhotplate sensors

    Page(s): 514 - 526
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    The authors describe a technique that utilizes the fast heating rates (106 K/s) of a microhotplate sensor along with a calibrated thermal desorption system to determine the initial coverage and kinetic parameters using isothermal desorption on a millisecond time scale. Models for isothermal desorption including both pumping and desorption rate effects are presented for zero, first, and second order kinetics. Analysis of the first order model illustrates the domain of the desorption, pumping speed, and heating rate time constants that permit the desorption parameters to be estimated from the mass spectrometer signal. The technique is demonstrated using isothermal temperature programed desorption of benzoic acid from a single SnO2 covered microhotplate at surface temperatures ranging from 296 to 347 K. The data indicate that desorption is best represented by first order kinetics. The first order preexponential factor and the desorption energy in the zero coverage limit are determined to be 1×1017 s-1 and 97 kJ/mol, respectively, from desorption of 108 molecules which corresponds to an initial coverage of 1012 cm-2 (≤0.005 ML). View full abstract»

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  • Improvement of corrosion resistance of transparent conductive multilayer coating consisting of silver layers and transparent metal oxide layers

    Page(s): 527 - 531
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    An optical filter for plasma display panel (PDP) requires an electromagnetic shield with very high ability. The authors investigated a transparent conductive multilayer coating consisting of silver (Ag) layers and transparent metal oxide layers. The durability of the multilayer sputter coating, including the silver layer, is very sensitive to the surrounding atmosphere. For example, after an exposure test they found discolored points on the multilayer sputter coatings, possibly caused by migration of silver atoms in the silver layers. In their investigation, they modified the top surface of the multilayer sputter coatings with transition metals to improve the corrosion resistance of the multilayer coating. Specifically, they deposited transition metals 0.5–2 nm thick on the top surface of the multilayer coatings by sputtering. They chose indium tin oxide (ITO) as the transparent metal oxide. They applied the multilayer sputter coatings of seven layers to a polyethylene terephthalate (PET) film substrate. A cross-sectional structure of the film with the multilayer coatings is PET film/ITO/Ag/ITO/Ag/ITO/Ag/ITO. They evaluated the corrosion resistance of the films by a salt-water immersion test. In the test, they immersed the film with multilayer coatings into salt water, and then evaluated the appearance, transmittance, and electrical resistance of the multilayer coatings. They investigated several transition metals as the modifying material, and found that titanium and tantalum drastically improved the resistance of the multilayer coatings to the salt-water exposure without a significant decline in transmittance. They also investigated the relation between elapsed time after deposition of the modifying materials and resistance to the salt water. Furthermore, they investigated the effects of a heat treatment and an oxide plasma treatment on resistance to the salt water. View full abstract»

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  • Enhancement of thermal stability of Ta/Si(100) film by a Ta–Si interlayer

    Page(s): 532 - 535
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    Thermal stability of Ta films grown on Si(100) was investigated by in situ x-ray scattering and ex situ cross-sectional transmission electron microscopy. As a Ta/Si(100) film was annealed at around 500 °C, a uniform Ta–Si interlayer was formed at the interface. This interlayer acts as a diffusion barrier. The Ta film with the interlayer is thermally stable up to 700 °C. Meanwhile, Ta films directly annealed to above 640 °C exhibit no interlayer formation and transform to randomly nucleated tantalum-silicide phases. Maintaining a uniform interlayer is a critical factor for enhancing thermal stability of Ta/Si(100) films. View full abstract»

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  • Compound semiconductor bonded to AlN heat spreader substrate using graded intermediate layer

    Page(s): 536 - 542
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    The present work illustrates a novel method of bonding compound semiconductor wafers to AlN or AlN/diamond heat spreaders using a graded intermediate layer. The procedure is illustrated using In–Ga solder to bond GaSb (111) wafer to commercial AlN substrate. Thermal conductivity of three bonded structures was evaluated using the 3-ω method. The experimental measurements of thermal conductivity of the multilayer were simulated using the analysis applicable to a layered structure. The results illustrate that the thin intermediate graded layer has a thermal conductivity above that of GaSb and therefore does not form an insulating layer. Bonding ZnO (002) wafer to commercial AlN substrate using zinc film that is subsequently oxidized is illustrated. The advantages of the graded intermediate layer to bond the heat spreaders such AlN or AlN/diamond are highlighted. View full abstract»

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  • Combined filtered cathodic arc etching pretreatment–magnetron sputter deposition of highly adherent CrN films

    Page(s): 543 - 550
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    CrN films were prepared on steel substrates by a hybrid method utilizing filtered cathodic arc for Cr ion pretreatment and magnetron sputtering for coating deposition. During pretreatment the substrates were biased to -1200 V and exposed to filtered chromium plasma. The substrate-coating interface formed during the pretreatment contained a Cr-enriched modified layer with composition that was strongly influenced by the temperature of the substrate as observed by scanning transmission electron microscopy—energy dispersive spectroscopy. The modified layer had a nanocrystalline morphology and thickness of 15 nm. The path of formation of the layer is linked to the combined action of implantation, diffusion, and resputtering. The resulting adhesion of 3 μm thick CrN films was very high with scratch test critical load values of 83 N. The morphology of the films was smooth without large scale defects and the microstructure was columnar. The coatings behaved well in dry sliding tests with very low wear coefficients of 2.3×10-16 m3 N-1 m-1, which can be linked to the high adhesion and defect-free microstructure. The smooth coatings also had a high resistance to corrosion as demonstrated by potentiodynamic tests with particularly high pitting potentials of +800 mV. View full abstract»

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  • Residence times of water molecules on stainless steel and aluminum surfaces in vacuum and atmosphere

    Page(s): 551 - 556
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    The adsorption and desorption phenomena of water molecules on stainless steel and aluminum surfaces have been studied by means of tritium tracer technique (TTT) with special emphasis on potential differences in the residence times in atmosphere and vacuum. Samples with a geometrical surface area of about 2 cm2 have been exposed in an atmospheric environment loaded with a vapor pressure of HTO (tritium-labeled water) of known specific activity, and the adsorbed amount of water has been determined by liquid-scintillation counting technique. In previous studies it was found that, in atmosphere, adsorbed water quantities and their reproducibility depend significantly on the cleanliness of the surfaces. Furthermore, it was observed that desorption into atmosphere (or exchange with atmospheric humidity) is a rather slow process with a few percent of the adsorbed water molecules staying even for several days and with the water coverage versus time t characterized approximately by a 1/tα law with α≈0.4. In this work, TTT measurements of water desorption have been extended into high vacuum. HTO-covered specimens have been transferred into a vacuum chamber soon after HTO exposure and have been kept under high vacuum for a certain vacuum desorption time which was varied from minutes to several days. It was found that water desorption from stainless steel and aluminum surfaces in vacuum is slower than in atmosphere with the residual coverage again described approximately by a 1/tα law but now with α≈0.14 (stainless steel) and α≈0.17 (Al). Water desorption rates calculated from coverage versus time are within the range of outgassing data reported in literature, indicating that the TTT method can be a powerful tool for the characterizat- - ion of potential new vacuum materials even if just small specimens are available. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Meet Our Editors

Editor
G. Lucovsky
North Carolina State University