bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Tb at the interface of SiN/TbFeCo film by Auger electron spectroscopy
Authors: Hirasaka Masao , Sekiya Masahiko , Miki Tetsurou
Published: July 2002

The characterization of Tb at the interface of SiN/TbFeCo layers was carried out by Auger electron spectroscopy. The Auger spectrum of Tb in the TbFeCo layer was the same as that of Tb metal. Although oxygen was not detected at the interface, the Auger spectrum of Tb at the interface was similar to that of Tb oxide. Tb nitride was prepared by ion implantation of nitrogen onto Tb metal, and the Auger spectrum of Tb nitride was found to be similar to that of Tb oxide. Therefore, it was confirmed that Tb reacted with nitrogen of SiN layer and Tb nitride was formed at the interface. The thickness of the Tb nitride layer was estimated to be about 5 nm. Further, the spectra of Gd nitride and Dy nitride are also reported.
Observation of umklapp and surface bands in photoemission experiment on II–VI materials: A study of Cd0.6Hg0.4Te
Authors: Lévêque G. , Banouni M. , Jouanin C. , Bertho D. , Bonnet J.
Published: July 2002

Normal and off-normal photoemission are performed in the 16–27 eV range on Cd0.6Hg0.4Te mixed crystal. The umklapp bands, well recognized on normal incidence energy distribution curve, can be followed in off-normal data, with continuous variations not previously observed. A tight binding calculation of the energy dispersion of the umklapp bands confirms that most secondary emissions are in fact related to umklapp bands. The surface states appear partly masked by these bulk derived umklapp bands. Only one surface state, in an inner gap of the valence band, appears distinct from other bulk features, which indicates that some of the previously mentioned experimental surface states in II–VI compounds should be revised.
Effects of processing on electrical properties of YBa2Cu3O7 films. I. Postdeposition anneal process
Authors: Sheats James R. , Taber Robert C. , Merchant Paul , Amano Jun
Published: July 2002

The effects of several patterning process steps on the critical current density Jc and microwave surface resistance Rs of a-axis oriented films of YBa2Cu3O7 on LaAlO3 are described. The films were prepared by cosputtering from Y, BaF2, and Cu targets, followed by annealing in water-saturated O2. Jc and Rs parameters were measured by mutual inductance and parallel plate resonator techniques, respectively, so that the films did not require patterning for the measurement. Application of a polymer film followed by stripping in acetone caused modest degradation, while stripping with an O2 plasma resulted in no change in the parameters. Brief ion milling, as well as baking at 185 °C with polymer film present, caused severe degradation; other treatments had intermediate effects. The degree of degradation suggests that the surface damage results in secondary effects that penetrate well into the film. A formula is derived for the change in Rs due to a surface layer, providing a quantitative comparison to experiment.
Fabrication of NbN thin films by reactive sputtering
Authors: Maung Win Naing , Butler Donald P. , Huang Cheng-Liang
Published: July 2002

We have fabricated NbN thin films by reactive rf magnetron sputtering. Critical temperatures above 15 K have been achieved by carefully monitoring the deposition parameters of total chamber pressure, rate of Ar and N2 injection, partial pressures of Ar and N2 in the chamber and deposition rate. We found the deposition rate and partial pressure ratios of Ar:N2 to be the key parameters in reliably obtaining high critical temperature thin films. The critical temperature dependence upon total chamber pressure was found to be in general agreement with the scaling law. High quality NbN thin film microstructures were obtained by plasma etching without the degradation of the superconducting properties of the film.
Selective regrowth of III–V epitaxial layers by low pressure organometallic vapor phase epitaxy using CCl4
Authors: Hobson W. S. , Pearton S. J. , Lopata J. L.
Published: July 2002

The use of carbon tetrachloride was examined as a means of suppressing deposition on the dielectric mask during the selective regrowth of III–V epitaxial layers by organometallic vapor phase epitaxy. Highly anisotropic dry etching was used to form narrow (∼1 μm wide) trenches and mesas. Reentrant mesas were formed by wet chemical etching. Under conventional growth conditions, polycrystalline GaAs was deposited over the mask adjacent to the trenches. By adding CCl4, selectivity could be greatly enhanced; however the growth rate in the trenches was significantly increased due to lateral diffusion of the reactants upon desorption from the mask thereby making acceptable control of the growth rate difficult. Addition of CCl4 during the growth of InP and AlGaAs significantly improved the selectivity in the case of growth around etched mesas.
Low temperature growth of ZnTe by synchroton radiation using metalorganic sources
Authors: Ikejiri Makoto , Ogata Toshihiro , Ogawa Hiroshi , Nishio Mitsuhiro , Yoshida Akira
Published: July 2002

The use of synchrotron radiation to convert diethylzinc and diethyltelluride molecules into ZnTe has been employed for ZnTe growth. The formation of ZnTe epitaxial layer on (100) oriented GaAs substrate at room temperature is experimentally demonstrated. It is shown by x-ray photoelectron spectroscopy that no carbon is included in the film.
Properties of polysilicon films deposited on amorphous substrates using reactive plasma beam deposition technique
Authors: Moradi Behnam , Dalal Vikram L. , Knox Ralph
Published: July 2002

We report on the growth and properties of high mobility polycrystalline silicon films grown at low temperatures (400–500 °C) on amorphous substrates using a controlled reactive plasma beam deposition. The technique consists of carefully controlling the H radical flux from an electron cyclotron resonance (ECR) plasma to promote both nucleation and grain boundary passivation during growth. Using electrical and optical spectroscopy of the ECR plasma, we find that the density of H radicals impinging on the surface is one of the most important parameter controlling crystallinity of the film, and that by changing this flux, we can controllably alter the structure of the film from amorphous to polycrystalline. Unlike traditional deposition techniques for polysilicon, which requires either high deposition temperatures (650 °C) or a low temperature deposition followed by a post deposition anneal to achieve good mobilities, our technique produces films with mobilities of the order of 30–40 cm2/V s in as grown films at considerably lower temperatures. We have produced undoped and highly doped films using this technique.
Investigation about the incorporation of hydrogen into amorphous carbon
Authors: Schelz S. , Kania P. , Frauenheim Th. , Stephan U. , Oelhafen P.
Published: July 2002

Amorphous carbon and hydrogen containing amorphous carbon films have been prepared by evaporating polycrystalline graphite in hydrogen-free atmosphere (pH2<10−8 mbar) and in the presence of hydrogen at different pressures (3×10−4–1.7×10−2 mbar), respectively. After deposition, the films have been characterized by in situ photoelectron spectroscopy. The composition of the gas phase during graphite evaporation in the presence of hydrogen was measured with a quadrupole mass spectrometer. The gas phase data have been correlated to the hydrogen content in the film. It is found that hydrogen is incorporated preferably into amorphous carbon when already bound to carbon in the form of CHx (x=1,2,3) in the gas phase. In addition, the bombardment of a growing amorphous carbon film with high energy hydrogen ions has turned out to be a quite effective means of incorporating hydrogen into a-C.
Modeling of deposition and resputtering rate profiles in planar face to face sputtering systems
Authors: Hamerich A. , Wunderlich R. , Müller J.
Published: July 2002

A model of the sputtering process for multiconstituent materials which accounts for variations in the deposition rate profiles of thin films sputtered with planar sputtering systems in the common face to face geometry has been developed. Excellent agreement between calculated and measured profiles resulting from various process parameters was obtained. The model accounts for resputtering of the growing film by high energy particles or reevaporation occurring during deposition. The experimental results demonstrated that the deposition rate and the resputtering rate profiles of sputtered films can be tightly predicted. Various films (Ti, Pyrex, MgO, YBaCuO, ZnO) were deposited in different sputtering apparatuses and at different process parameters. When resputtering effects occur, a direct correlation between the predicted local strength of resputtering and the observed variations of physical properties across the deposited material (stoichiometry and index of refraction) was found.
Preventing vacuum leaks in the Continuous Electron Beam Accelerator Facility cavity pair bellows
Authors: Henkel Daniel P. , Doolittle Lawrence R.
Published: July 2002

Occasional vacuum leaks have occurred in bellows assemblies of helium pressure vessels at the Continuous Electron Beam Accelerator Facility. The flanged stainless steel bellows assemblies are used to connect the niobium rf cavity pairs to the surrounding liquid helium pressure vessels. An investigation of the source of these leaks has revealed a through-thickness network of microcracks in the cuff weld zones. The cuff material contained a mixture of soft and very hard elongated intermetallic inclusions that were oriented parallel with the weld fusion line; these inclusions served as crack initiation sites. Surface-exposed inclusions, in contact with a chlorine residue from a postweld machining process, induced crevice corrosion during a year of storage. Residual stresses in the weld led to a combination of lamellar tearing and stress corrosion cracking. Propagation of the cracks from one inclusion to another resulted in continuous vacuum leakage paths from the primary (2 K) helium circuit to the vacuum insulation space. Additional vacuum leaks were prevented by reconfiguring the weld geometry and avoiding any processing with chlorinated substances.
Clean ultrahigh vacuum system with single-structure diffusion pumps
Authors: Gay T. J. , Brand J. A. , Fritts M. C. , Furst J. E. , Khakoo M. A. , Mell E. R. , Sieger M. T. , Wijayaratna W. M. K. P.
Published: July 2002

A practical example of the use of single-structure diffusion pumping groups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was ‘‘clean,’’ i.e., which had no residual pump-oil contamination to a partial pressure below 10−8 mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard ‘‘UHV-surface science’’ processes. We discuss our vacuum system in detail, and present a review of the literature on the production of clean vacua with diffusion pumps.
Influence of the ratio of the electron temperatures at the electrodes on the current oscillations in a radio-frequency plasma reactor
Authors: Deutsch R. , Erz U. , Pohle M. , Räuchle E. , Schwarz J.
Published: July 2002

Based on electric circuits for radio-frequency plasma reactors it is shown numerically that not only the mean electron density and the mean electron temperature can be determined from the discharge current as described in R. J. Seeböck, R. Deutsch, and E. Räuchle, J. Vac. Sci. Technol. A 11, 682 (1993), but also the ratio of the mean electron temperatures in the electrode boundary sheaths can be estimated.
Fabrication of cylindrical, microcellular foam-filled targets, containing aluminum spheres, for sphere drag experiments
Authors: Falconer John W. , Nazarov Wigen , Horsfield Colin J. , Sutton Douglas W. , Rothman Stephen D. , Freeman N. J.
Published: July 2002

Hollow cylindrical fusion targets of 200–300 μm diam and 500–600 μm length, were fabricated and fitted at one end with a metallic ablator plate. The cylinders were then filled with a solution of polyfunctional acrylate monomer, which was subsequently polymerized to a gel using ultraviolet initiated polymerization. Either one or two aluminum spheres of diameter between 10 and 30 μm were placed in the gel at defined locations, before the gel was precipitated to give, on drying by critical point dryer, a foam of the required density (about 100 mg cm−3). The final targets had the sphere or spheres embedded in the foam at specified locations. Several techniques for placing the spheres were examined and the relative merits of the techniques are discussed.
Improved determination of the ultrathin structural parameters of Co/Pd multilayered film, and its magnetic and magneto-optical properties
Authors: Lee Y. P. , Kim S. K. , Kang J. S. , Jeong J. I. , Hong J. H. , Koo Y. M. , Shin H. J.
Published: July 2002

Co/Pd multilayered films with ultrathin layers of Co were prepared by alternating deposition in an ultrahigh-vacuum physical-vapor-deposition system. The individual layer thicknesses of the samples were estimated making use of the angular positions of x-ray diffraction peaks. The magnetic and magneto-optical properties were found to vary depending on Pd buffer layer and Pd sublayer thicknesses, as well as Co sublayer thickness. Some of the films showed good properties for magneto-optical medium, such as large perpendicular magnetic anisotropy and Kerr rotation, and perfect squareness of the magnetic hysteresis loop. The Pd-predeposited films were found to have a remarkably high coercivity of 4723 Oe and a greatly enhanced interfacial magnetic anisotropy of 0.72 mJ/m2. The transition from in-plane to perpendicular magnetic anisotropy took place at a Co sublayer thickness of 8.2 Å for the multilayer with Pd predeposition. Kerr rotation was inversely proportional to the Pd/Co sublayer thickness ratio, showing the maximum value of 0.12°. The magnetic and magneto-optical properties were correlated systematically to the structural parameters of the multilayered films.
Growth of Er-doped Si films by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Rogers Jim L. , Varhue Walter J. , Adams Edward , Lavoie Mark A. , Frenette Robert O.
Published: July 2002

Epitaxial Si films doped with Er have been grown at low substrate temperatures by plasma enhanced chemical vapor deposition. The Er gas source is a sublimed organometallic compound fed into the process chamber. High doping concentrations without silicide precipitation are possible because of the low deposition temperatures. The process relies on the beneficial effects of low energy ion bombardment to reduce the growth temperature. The ions as well as reactive chemical species are produced by an electron cyclotron resonance plasma stream source. A hydrogen/argon plasma is used to perform an in situ predeposition clean to remove oxide from the Si surface. Film quality and impurity concentration are determined by Rutherford backscattering spectrometry and secondary ion mass spectrometry.
Direct dimer-by-dimer identification of clean and monohydride dimers on the Si(001) surface by scanning tunneling microscopy
Authors: Wang Yajun , Bronikowski Michael J. , Hamers Robert J.
Published: July 2002

Atomic resolution images of clean Si(001)-(2×1) and the monohydride phase, Si(001)-(2×1)H were investigated using scanning tunneling microscopy at various sample-tip bias voltages. At a sample-tip bias of −1.9 V, each dimer of the monohydride phase shows two protrusions 3.3 Å apart separated by a minimum 0.12 Å deep, while clean dimers show a single protrusion per unit cell. Monohydride dimers appear lower than ‘‘clean’’ dimers, with apparent height differences ranging from 1.9 Å at −1.6 V to 0.65 Å at −3.0 V sample bias. An analysis of the apparent height and spatial distribution of tunneling current within each dimer can be used to unambiguously discriminate between clean dimers, monohydride dimers, and vacancy defects. This methodology is applied to study the distribution of hydrogen on Si(001) surfaces during chemical vapor deposition using disilane, revealing segregation of the monohydride into nearly isotropic islands.
Effects of processing on electrical properties of YBa2Cu3O7 films. II. In situ deposition processes
Authors: Sheats James R. , Newman N. , Taber Robert C. , Merchant Paul
Published: July 2002

The effects of several patterning process steps on the critical current Jc and surface resistance Rs of YBa2Cu3O7 films are described. Included are two off-axis sputtering processes and a metalorganic chemical-vapor deposition (MOCVD) process, all producing in situ superconducting films with c-axis epitaxial orientation. Jc and Rs parameters were measured by mutual inductance and parallel plate resonator techniques, respectively, so that the films did not require patterning for the measurement. Applying a polymer film and stripping, either with acetone or with an O2 plasma, resulted in no change in Rs. Brief ion milling, as well as baking at 185 °C with polymer film present, caused moderate degradation (∼25 μΩ) for films deposited on MgO (both sputtered and MOCVD). The damage caused by ion milling sputtered films on LaAlO3 was considerably greater (∼100 μΩ); photoresist developer also had a significant effect. The degree of degradation in Rs for these films suggests that the surface damage results in secondary effects that penetrate well into the film. This damage was not removed by annealing in O2; in fact it was made substantially worse. Jc was increased slightly by all processes, by an amount ranging from 5% to 50%.
Small ultrahigh vacuum compatible hyperthermal oxygen atom generator
Authors: Outlaw R. A. , Davidson Mark R.
Published: July 2002

The development of a compact, ultrahigh vacuum (UHV) compatible instrument for generating a flux of pure hyperthermal oxygen atoms for NASA applications has been achieved. The instrument combines the mechanisms of O2 dissociation and transport through a hot Ag membrane to provide a continuous source of O atoms to a vacuum interface where they are subsequently emitted into the vacuum space by electron-stimulated desorption (ESD). A flux of neutral O atoms 4.5×1013 cm−2 s−1 (3P) with a mean ion kinetic energy of approximately 5 eV and a full width at half maximum of 4 eV was detected at a quadrupole mass spectrometer located 10 cm away. The geometry of the instrument is such that it is mounted on a 7-cm flange and can be tailored in length and orientation to fit most UHV systems. The data presented here are for ESD-controlled conditions where increases in the flux are strictly linear with electron bombardment current. Calculation shows that transport-controlled conditions can be achieved at temperatures as low as 350 °C with membrane thicknesses on the order of 10 μm.
Interface studies of the diamond film grown on the cobalt cemented tungsten carbide
Authors: Pan F.-M. , Chen J.-L. , Chou T. , Lin T.-S. , Chang L.
Published: July 2002

The diamond film deposited on the cobalt cemented tungsten carbide substrate by the hot filament assisted chemical vapor deposition (CVD) method was studied by scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy. Surface pretreatment for the substrate is essential to the film quality and adhesion strength of the CVD grown diamond film. The presence of cobalt on the substrate surface is detrimental to the film growth. According to Auger studies, a carbon layer, possibly amorphous carbon, with a thickness less than 120 Å was present at the interface between the diamond film and the cobalt cemented tungsten carbide substrate. Cross-sectional transmission electron microscopy revealed that the diamond crystals can be grown directly from a polycrystalline tungsten carbide substrate without forming the interfacial carbon layer. The cobalt in the cemented tungsten carbide may be ascribed to the formation of the interfacial amorphous carbon layer for the hot filament assisted CVD grown diamond film.
Relative importance of bombardment energy and intensity in ion plating
Authors: Fancey K. S. , Porter C. A. , Matthews A.
Published: July 2002

For ion plating and similar plasma assisted physical vapor deposition processes, the relative significance of bombardment energy and intensity during film growth is poorly understood in relation to their effects on certain coating properties. In this article, we report on the results of a study on the microstructural properties of copper coatings deposited by a thermionically supported ion plating system with an electon beam evaporation source. By carefully selecting the deposition conditions, analysis of the coatings has provided the following conclusions: First, provided that a critical bombardment energy is exceeded, increasing bombardment intensity is more important than increasing the energy at the growing coating surface to attain maximum coating densification for minimum bombardment power. For copper coatings, the critical energy is approximately 200 eV. Second, we have identified sputtering as the main mechanism responsible for material redistribution during coating growth. We suggest that coating densification resulting from energetic bombardment may be characterized in a structure zone model by a parameter representing the proportion of arriving material which is sputtered during deposition.
Modeling of reactive sputtering of compound films in the presence of bias sputtering
Authors: Wautelet M. , Debal F. , Dauchot J. P. , Hecq M.
Published: July 2002

In many applications, reactive sputtering of compound films takes place in the presence of a bias voltage at the anode. In order to discuss fundamental processes involved in reactive sputtering, a model is given in which bias sputtering is introduced. It is assumed that no reaction takes place in the gas phase. Nevertheless, it turns out that the theoretical system involves 15 parameters that depend on the reactor design, the pumping system, the gas supply, the processing conditions, and the plasma–surface interactions. General equations taking all these parameters into account are given. Starting from these equations, many calculations can be performed. In order to show several possibilities for the model, we discuss the behavior of hysteresis in the pressure versus reactive gas flow curves.
Radio frequency electric-mirror sputtering deposition
Authors: Matsuoka Morito , Tohno Shun-ichi
Published: July 2002

The electric-mirror sputtering system involves the use of a planar and a cylindrical target in a special configuration that is useful for depositing high-quality films at low gas pressure (below 0.1 Pa). This article describes how a radio-frequency-mode (rf-mode) operation is combined with high-density plasma generation in electric-mirror sputtering for film deposition. To generate a high-density plasma by confining high-energy secondary electrons emitted from the targets between them, rf voltages must be applied to both targets with a phase difference of no more than 30°. Thin films are deposited at high rates, an order of magnitude higher than in a system with only a cylindrical target, in a low gas pressure atmosphere below 0.1 Pa, without extremely high-energy ion bombardment during deposition. Uniform films can be obtained over almost the same area as the internal area of the cylindrical target by optimizing the substrate location.
Synchrotron-radiation-excited etching and total electron yield measurement of silicon and silicon nitride
Authors: Kitamura Osamu , Terakado Shingo , Suzuki Shigeo , Nakao Masao , Sekitani Tetsuji , Tanaka Kenichiro
Published: July 2002

Photochemical etching of silicon and silicon nitride using synchrotron radiation (SR) was studied in the presence of reactive species produced by a 2.45-GHz microwave discharge in a mixture of SF6 and Ar. SR irradiation enhanced the etching reaction. The difference in patterning was investigated by using two kinds of SR that have different energy dispersions. It was found that the effect of SR irradiation is to achieve area-selective etching on the sample surface and SR with shorter wavelength is useful for achieving a clear pattern transfer. The increments of the etched depth due to monochromatic SR irradiation depended on the photon energy and were compared with the total electron yield (TEY) spectra. The etch rate for the increments was found to be almost proportional to the light absorption of the sample fully exposed to reactive species. It was suggested by TEY measurements that a fluorinated overlayer is formed on the sample surface during etching.
DIPLOMA: An experimental system to study MeV and keV particle- and photon-induced desorption of molecules
Authors: Brinkmalm G. , Håkansson P. , Kjellberg J. , Sundqvist B. U. R.
Published: July 2002

A high resolution time-of-flight mass spectrometer that analyzes secondary ions produced when samples are bombarded with MeV and keV ions and ultraviolet photons is described. The flexibility of the system is demonstrated by showing results from several varied experiments including high resolution mass spectra of molecular ions desorbed from a renin substrate sample by MeV and keV ions, a multiphoton ionization spectrum of gas-phase benzene, and a matrix assisted laser desorption spectrum of a glycoprotein. The keV ion source is useful for secondary ion mass spectrometry work, for imaging, and for micromachining of surfaces. By using the attached electrostatic ion reflector metastable decomposition of various molecular and fragment ions can be studied.
Hydrogen in thin films of CuInS2 solar cell material
Authors: Dzionk C. , Hessler S. , Lewerenz H. J. , Mahnke H.-E. , Metzner H. , Steiger J.
Published: July 2002

The production of thin films of CuInS2 by the reactive annealing process in H2S atmosphere leads to the incorporation of hydrogen. Hydrogen concentrations of up to 5×1020 cm−3 were measured by means of a nuclear reaction analysis method. No negative influence on the electrical properties of the films containing hydrogen was observed. Instead, hydrogen, when incorporated in situ, seems to help to passivate electrically active lattice defects.
Structure of stacking fault pyramids in silicon-on-insulator material
Authors: Twigg M. E.
Published: July 2002

Using transmission electron microscopy (TEM), we have analyzed stacking fault pyramids found in multiple implant silicon-on-insulator material. From a comparison of computer simulations with weak-beam TEM images, and from the constraints imposed by crystallography, we have found that the Burgers vectors of the pyramidal stair-rod dislocations are edge dislocations with the Burgers vector 1/3〈100〉. We have also determined that the stacking faults in these pyramids are intrinsic, and therefore probably formed through vacancy condensation.
Etching of InP surface oxide with atomic hydrogen produced by electron cyclotron resonance
Authors: Hofstra P. G. , Robinson B. J. , Thompson D. A. , McMaster S. A.
Published: July 2002

The plasma output of an electron cyclotron resonance source operating with hydrogen has been characterized using optical emission spectroscopy to observe neutral excited atomic hydrogen H* and a Langmuir probe to observe H+ as a function of currents to the two electromagnets producing the magnetic field. The rate at which the hydrogen plasma etches the surface oxide on InP substrates has been measured as a function of substrate temperature over the range 250–485 °C for two operating conditions, one that maximizes H* and the other for which a combination of high H+ and minimal H* occurs. The results indicate that the plasma stream with maximum H* etches approximately five times faster than the plasma stream with high H+ and low H* content. However, the activation energy of the etching reaction, Ea∼0.45 eV, is the same for the two plasma conditions. Considering the oxide as InPO4, produced by exposing the substrates to ozone generated by ultraviolet light, the proposed reaction for the etching is InPO4+7.3H→2H2O+0.5PH2 +0.5PH3+0.8InH+0.2In.
Role of oxygen partial pressure on the properties of doped silicon oxycarbide microcrystalline layers produced by spatial separation techniques
Authors: Martins R. , Vieira M. , Ferreira I. , Fortunato E.
Published: July 2002

The aim of this work is to present experimental data concerning the role of the oxygen partial pressure during the production process on the properties (structure, morphology, composition, and transport properties) exhibited by doped microcrystalline silicon oxycarbide films. The films were produced by a two consecutive decomposition and deposition chamber system, where a spatial separation between the plasma and the growth regions is achieved. The films produced by this technique are highly conductive and highly transparent with suitable properties for optoelectronic applications requiring wide band-gap and low-conductivity materials.
Structures of Fe/TiC multilayers prepared by ion beam sputtering at room temperature
Authors: Liu C. H. , Li Wen-Zhi , Li Heng-De , Li Y. H.
Published: July 2002

Multilayered films composed of bcc Fe and fcc TiC ceramic layers, with their thickness on the nanometer scale, have been synthesized by ion beam sputtering at room temperature. The structures of the individual layers and the interfaces were investigated by reflection x-ray diffraction at both low and high angles, and by transmission electron microscopy on the cross section. Results show that flat and smooth TiC and Fe layers with abrupt and incoherent interfaces were formed. Parallel growth between the TiC and Fe crystal plane and uniform lattice expansions were observed in the multilayers.
Simulation and sensitivity analysis of the heterogeneous oxidation of methane on a platinum foil
Authors: Behrendt F. , Deutschmann O. , Maas U. , Warnatz J.
Published: July 2002

The heterogeneous oxidation of methane–air mixtures in a stagnation point flow onto a platinum foil is investigated numerically and results are compared with experiments. The analysis includes detailed reaction mechanisms for the gas phase as well as the surface. Gas-phase transport and its coupling to the surface is described using detailed multicomponent models. The heterogeneous ignition, extinction, and autothermal behavior are interpreted in terms of elementary steps at the gas–surface interface. A sensitivity analysis of the surface reactions is performed to identify crucial steps in the mechanism, thus pointing to those reactions for which better kinetic and thermodynamic data are needed urgently.
Local density of states analysis by Auger electron spectroscopy
Authors: Zhou Huijian , Wang Yuqi , Ho Wei
Published: July 2002

In order to measure the local density of states (LDOS) on each depth profile of the GaAs/Si interface by Auger electron spectroscopy, the Auger line shapes are carefully processed and the Auger line shape analysis is performed with the help of factor analysis. A series of corrections to remove the distortions of the peak shape are carried out. There are two chemical states coexisting in the interface. Some of the Si atoms will bond with As and transfer 0.3 p electrons per Si atom to As, and the others will keep the chemical state of pure Si with Si–Si bond. The top of the valence band of Si has a slight shift due to the bonding between Si and As, and the amplitude of the LDOS has a significant decrease.
Surface dielectric function of CdTe(110) obtained by polarized surface differential reflectivity data
Authors: Cricenti A. , Felici A. C.
Published: July 2002

We present a determination of the complex surface dielectric function (SDF) of CdTe(110) obtained by using polarized surface differential reflectivity (SDR) data. The analysis of SDR data is done in the framework of a macroscopic three-layer model in which the media involved (vacuum, surface, and substrate) are assumed to have definite anisotropic functions. A relation between SDR data and the complex SDF is obtained under the assumption that the oxide layer is nonabsorbing in the range explored. From the experimental data SDF has been computed for light electric vector along [11̄0] and [001] directions, i.e., parallel and perpendicular to the natural chains of the unreconstructed (110) surface. In the energy range below 3.3 eV the imaginary part of SDF (εs″) and SDR data are very similar while above 3.3 eV they differ markedly because of the effect of bulk contribution. Three mainly isotropic structures are clearly visible in the deconvolved ε″ spectra at the following photon energies: 2.7, 3.3, and 3.7 eV. Such structures are interpreted in terms of optical transitions between surface state bands as derived from direct and inverse photoemission. The transition at 2.7 eV is assigned at the Γ point in the surface Brillouin zone, the one at 3.3 eV at the Γ and X while the one at 3.7 eV at the X and X′. The effective number of electrons per atom participating in the optical transitions is calculated for energies up to 4.0 eV resulting in slightly more than 0.5.
Scanning Auger microscopy and x-ray photoelectron spectroscopy studies of Roman bronzes
Authors: Paparazzo E. , Moretto L. , Northover J. P. , D’Amato C. , Palmieri A.
Published: July 2002

Scanning Auger microscopy and x-ray photoelectron spectroscopy (XPS) techniques are used to study the surface and interface microchemical composition of a series of Roman leaded bronzes of the third century B.C. The materials’ surface composition, as obtained from large-area XPS analysis, compares fairly well with that of the bulk, except for a significant surface lead segregation observed in one case. We find that, in the sample with the highest tin content, tin plays a sacrificial role in preventing the corrosion of copper. The tin is present mainly in the oxidized form, even at a depth of about 100 Å, whereas the copper is virtually all in the metallic form. Evidence is given for the presence of ‘‘white lead’’ [2PbCO3⋅Pb (OH)2] at the surface of the sample with the highest lead content. Auger point analysis evidences significant lateral inhomogeneities in the microchemistry of the materials, as well as sulfur segregation in the original patina. Auger images bring to light tin and lead lateral segregations with spatial resolutions of about 0.5 and 0.1 μm, respectively.
Optical temperature measurement by grating expansion for rotating semiconductor wafers
Authors: Huang C. , Lang M. , Brueck S. R. J.
Published: July 2002

A noncontact temperature measurement technique, diffraction-order analysis, based on monitoring the change in diffraction angle from a grating as a result of thermal expansion, is described and results for both Si and GaAs are presented. Two incident beams are used to provide a differential measurement, independent of wafer tilt. Image processing techniques are used to calculate the relative temperature in near real time from the optical signals. Good agreement between optical and the thermocouple temperature measurements is obtained, with an accuracy and precision of ±0.3 °C demonstrated over a 20–600 °C temperature range for a GaAs sample. Analysis of the effects of all six rigid-body motions of the wafer on the measurement is presented. The measurement is independent of all translational motions; rotational motions (pitch, roll, and yaw) can all be monitored with the same measurement scheme and the temperature measurement corrected for their effects. In many applications in semiconductor manufacturing, wafers are rotated to ensure uniformity. The diffraction-order analysis technique is demonstrated for a rotating wafer with a 3σ precision of 1.95 °C.
Effects of oblique energetic bombardment on the morphology and microstructure of triode ion plated titanium films
Authors: Gunasekhar K. R. , Krishna M. Ghanashyam , Raju A. R. , Krishna K. N. , Mohan S.
Published: July 2002

The effect of angle of incidence of ions, varied between 45° and 90°, generated in a triode ion plating system on the morphology and microstructure of titanium films, has been investigated. It has been found that intensity of reflections, lattice parameters, stress, and grain size are strong functions of the angle of incidence of the ions. The same properties were studied for their variation with bias voltage between 0 and 2 kV at a constant substrate bias current of 10 mA. It was found that the intensity of the (002) reflection increases with an increase in angle of ion incidence up to 60°. The lattice parameter and stress reach a minimum while the grain size goes through a maximum at this value. All the films show a tensile stress independent of deposition parameters. To isolate the effects due to ion bombardment the films have been coated in high vacuum, in a diode mode, and finally the triode configuration. It has been conclusively found that the angle of incidence of ions is very important in controlling properties and growth of the films.
Curve fitting in surface analysis and the effect of background inclusion in the fitting process
Authors: Sherwood Peter M. A.
Published: July 2002

An overview is presented of data analysis methods that can be used in surface analysis, especially those that can be used in x-ray photoelectron spectroscopy (XPS). The paper provides illustrations of the application of data analysis methods to real systems, and discusses practical problems that can arise when working with real data sets. The paper focuses upon curve fitting of core XPS data, and discusses the importance of combining curve fitting information with other supporting information and experiments. The effect of different backgrounds incorporated into the fitting process is discussed.
Contribution of short lifetime radicals to the growth of particles in SiH4 high frequency discharges and the effects of particles on deposited films
Authors: Watanabe Yukio , Shiratani Masaharu , Fukuzawa Tsuyoshi , Kawasaki Hiroharu , Ueda Yoshio , Singh Sanjay , Ohkura Hiroshi
Published: July 2002

Particle growth processes and the contribution of short lifetime radicals to the processes in SiH4 high frequency plasmas for a moderately high power above 0.25 W/cm2 are studied using polarization-sensitive laser light scattering, a newly developed Langmuir probe, a novel photodetachment, transmission electron microscopy, atomic force microscopy, and intracavity laser absorption methods together with a discharge modulation method. Particles are generated and grow from their nucleation phase principally around the plasma/sheath boundary near the powered electrode. Spatial profiles of the particle amount are very similar to those of production rates and densities of short lifetime radicals. The SiH2 density is low in spite of its high production rate. While the SiH2 density in the early discharge stage for 28 MHz is about one order higher than that for 6.5 MHz, the particle density for 28 MHz is two orders higher than that for 6.5 MHz. These results suggest that short lifetime radicals, in particular SiH2 radicals, not only participate mainly in the particle nucleation but also contribute numerous times to the nucleation and subsequent initial growth reactions of one particle. Moreover, photodetachment measurements showed that clusterlike particles exist even in the bulk plasma; some of them are considered to be neutral and hence they are likely to be transported to the substrate on the grounded electrode.
Reactor modeling for radio frequency plasma deposition of SiNxHy: Comparison between two reactor designs
Authors: Caquineau H. , Dupont G. , Despax B. , Couderc J. P.
Published: July 2002

Plasma deposition processes involve complex phenomena which make the design and optimization of industrial equipments difficult. In the particular case of silane-ammonia plasmas to produce silicon nitride (at very low silane percentage), two flow arrangements, i.e., (i) a longitudinal flow reactor and (ii) an axisymmetric showerhead electrode reactor were studied by two-dimensional modeling of momentum and mass transport. First, a kinetic scheme which enables us to reproduce experimental results for both reactor configurations was selected enlightening an unusual behavior of Si(NH2)3 radicals. Then, the way silane is consumed and its consequences on active species production was outlined as playing the leading parts in the processes. As silane concentration decreases along the flow direction, the modeling of the longitudinal flow reactor shows a steep decrease of the deposition rate and a significant composition variation of the deposit. In the axisymmetric reactor, the film thickness and composition uniformities considerably improve due to the distributed gas feed.
H2O pumping by sputter discharge with a LaB6 cathode
Authors: Funato Y. , Miyoshi M. , Akaishi K. , Kubota Y. , Mushiaki M.
Published: July 2002

Properties of H2O water vapor pumping by glow discharge sputtering with a LaB6 cold cathode are studied experimentally. For the purpose of developing a new type of sputter ion pump, lanthanum hexaboride (LaB6) is applied as the cathode material on the basis of a preliminary study. The application of LaB6 as the cathode of sputter discharge was proposed at first to obtain a low outgassing wall for a plasma vacuum chamber. The experiments showed that the vacuum chamber with the LaB6 sputter coating reached a lower ultimate pressure than that without the coating. LaB6 coating by glow discharge on a stainless steel wall is effective to reduce the H2O outgassing rate of a vacuum wall as shown by mass spectrometric analysis. The pumping speed of H2O by the coated wall is estimated experimentally. Characterization of the LaB6 coated films is also made by x-ray photoelectron spectroscopy measurements.
Particle formation in the remote plasma enhanced chemical vapor deposition of Si films from Si2H6–SiF4–H2
Authors: Kim Dong-Hwan , Rhee Shi-Woo
Published: July 2002

SiF4 was added to Si2H6–H2 to enhance the crystallinity of Si films deposited at low temperatures around 400 °C in a remote plasma enhanced chemical vapor deposition reactor. A grid was inserted to detect the extent of powder formation as a function of operating variables. It was found that the fluorine chemistry reduced the amount of powder formation in the gas phase and helped crystallization at low temperatures.
Cooling by dust in levitation experiments and its effect on dust cloud equilibrium profiles
Authors: Brattli A. , Havnes O.
Published: July 2002

The thermophoretic force on dust particles is caused by a temperature gradient in the background gas. This force can be important in experiments or production processes and in other environments where dust occurs. We discuss the local cooling of the neutral gas by levitated dust clouds and how this affects the temperature gradient and the equilibrium dust density profile. Dust is heated through neutral gas particle impacts while it loses energy by either reemitting impacting particles or by thermal radiation at the particle temperature. The dust particle temperature can be considerably lower than that of the ambient gas and can therefore lead to a local cooling of the gas. Changes in the temperature gradient and the thermophoretic force can be large enough to affect the equilibrium density profile of levitated dust. We find that the equilibrium profile with the thermophoretic force calculated from the temperature profile without dust cooling is closer to the electrode but with much the same shape as the profile calculated without the thermophoretic force. The profile where local cooling is included in the thermophoretic force is more compressed compared to the profile without local cooling and it often has a pronounced peak closest to the electrode. Since radiation cooling of a dust particle is proportional to the fourth power of its temperature, the cooling effect is largest at comparatively high gas (and dust) temperatures. We show examples of levitated dust layer profiles with and without the dust cooling effect.
Optical emission spectroscopy from arc-like Ti vapor plasma and effects of self-ion bombardment on Ti and TiN film deposition
Authors: Kajioka H. , Higuchi K. , Kawashimo Y.
Published: July 2002

Arc-like Ti vapor plasma is formed on the electron beam evaporation source by applying low dc voltage to the anode near the source in high vacuum. This plasma spectrum consists of Ti I (neutral) and Ti II (Ti+) lines. However no emission lines of nitrogen are observed with nitrogen gas inflow up to 1.3×10–1 Pa. This suggests that the dominant ion species is Ti+. Ti and TiN films are deposited on the water-cooled and non-cooled substrates at anode current 60 A. When negative substrate voltage (Vs) increases from 0 to 1000 V, substrate current density at 0.34 m from the source increases from 60 to 90 A/m2. Ion-to-Ti impinging flux ratio is estimated to be ∼1.35 at Vs=0 V. Deposition rates of 4 nm/s (Ti film) and 3 nm/s (TiN film) at Vs=0 V decrease largely in the former case and slightly in the latter case with increasing Vs. That is, self-sputter yield of the former is larger than that of the latter. The former varies with, and the latter is independent of substrate temperature. N/Ti ratio in TiN film is close to unity for the noncooled substrate. On the other hand, N/Ti ratio decreases from 0.9 to 0.7 with δ TiN single phase for the water-cooled substrate with increasing Vs. These results are different from the reported results from low energy-ion assisted deposition and reactive bias sputtering. This is attributed to the fact that self-ion bombardment differs from N+2 and/or Ar+ bombardment.
Aspects of nitrogen surface chemistry relevant to TiN chemical vapor deposition
Authors: Schulberg Michelle T. , Allendorf Mark D. , Outka Duane A.
Published: July 2002

NH3 is an important component of many chemical vapor deposition (CVD) processes for TiN films, which are used for diffusion barriers and other applications in microelectronic circuits. In this study, the interaction of NH3 with TiN surfaces is examined with temperature programmed desorption (TPD) and Auger electron spectroscopy. NH3 has two adsorption states on TiN: a chemisorbed state and a multilayer state. A new method for analyzing TPD spectra in systems with slow pumping speeds yields activation energies for desorption for the two states of 24 kcal/mol and 7.3 kcal/mol, respectively. The sticking probability into the chemisorption state is ∼0.06. These results are discussed in the context of TiN CVD. In addition, the high temperature stability of TiN is investigated. TiN decomposes to its elements only after heating to 1300 K, showing that decomposition is unlikely to occur under CVD conditions.
New aspects of K promoted nitridation of the InP(100) surface
Authors: Huang Lei , Zhao Texiu , Duan Yiwei , Wang Xiaoping , Lu Erdong , Xu Pengshou , Hsu C. C.
Published: July 2002

The effect of molecular nitrogen exposure on the InP(100) surface modified by the alkali metal K overlayer is investigated by core-level photoemission spectroscopy using synchrotron radiation. The alkali metal covered surface exhibits reasonable nitrogen uptake at room temperature, and results in the formation of a P3N5 nitride complex. Flash annealing at 400 °C greatly enhanced the formation of this kind of nitride complex. Above 500 °C, the nitride complex dissolved completely.