bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo-oxidation of σ-conjugated Si–Si network polymers
Authors: Kunz R. R. , Horn M. W. , Bianconi P. A. , Smith D. A. , Freed C. A.
Published: July 2002

The ultraviolet-induced photooxidation of polyalkylsilyne network polymers has been examined. Infrared and x-ray photoelectron spectroscopies indicate a higher oxygen coordination about the Si atoms following photolysis than observed for the linear polysilanes. A photochemical pathway leading to cleavage of the alkyl groups from the Si backbone has been observed, the products of which then desorb as the respective alkanes or 1-alkenes via a thermally activated process. Finally, the photooxidation rate at 193 nm of thin polyalkylsilyne films is photon limited at fluences less than 1–5 mJ/cm2 per pulse; whereas above this fluence, the photooxidation is oxygen limited. For the latter, the amount of oxygen chemically incorporated into the Si–Si network per laser pulse is dictated by the solubility level of oxidant in the film.
Carbon and oxygen removal from silicon (100) surfaces by remote plasma cleaning techniques
Authors: Thomas R. E. , Mantini M. J. , Rudder R. A. , Malta D. P. , Hattangady S. V. , Markunas R. J.
Published: July 2002

A hydrogen plasma-based technique for carbon removal has been combined with a modest anneal for oxide desorption at 720 °C to produce atomically clean Si(100)2×1 surfaces. Carbon and oxygen contamination can be removed from silicon surfaces by a 30 s hydrogen plasma exposure at 480 °C (for carbon removal) followed by a 5 min anneal in molecular hydrogen at 720 °C (for oxygen removal). Surface hydrocarbon removal is thought to occur by volatilization through hydrogenation. The mechanism for oxygen removal is believed to be more straightforward and consist of thermal desorption of SiO at approximately 700 °C. Hydrogen plasma exposures on the order of 5 min are seen to induce microscopic surface roughness without complete oxygen elimination. Samples which are devoid of oxygen following the 720 °C anneal are found to reoxidize upon re-exposure to the hydrogen plasma. The origin of the oxygenating species is unclear, but likely sources include, SiO or OH from tube wall erosion, or contamination produced by interactions of atomic hydrogen with the chamber walls. A subsequent anneal at 720 °C effectively removes any surface reoxidation. Anneals at 720 °C with carbon present on the surface results in a surface reaction which complexes the carbon and oxygen on the surface, rendering the surface contamination resistant, under nominal conditions, to subsequent plasma processing or annealing.
First-principles calculations of electronic subband structure and elementary excitations of a quantum wire
Authors: Yu R. H.
Published: July 2002

Self-consistent calculations of the subband electronic structure of semiconductor quantum wires are reported. The Schrödinger and Poisson equations were solved simultaneously in a rectangular waveguide geometry, using Fermi statistics for electrons at finite temperature. Calculated energy levels, wave functions, charge density, and potential differ from the predictions of the simple square well and harmonic oscillator models because of the influence of accumulation and depletion regions. The subband energies depend on the free-carrier density and the temperature as well as the band bending. Based on the self-consistently determined subband structure, the dynamical structure factor was evaluated using a nonlocal description of dielectric response theory in the random-phase approximation at finite temperature. We obtain intersubband as well as intrasubband plasmons and discuss their dispersion relations, localization, and line shapes. The dynamical structure factor of our model quasi-one-dimensional electron gas displays unique line shapes and dispersion relations which are in sharp contrast with the results expected for higher-dimensional electron gas.
New ways of using tests on statistical properties of randomly real rough surfaces
Authors: Varnier F. , Rasigni G. , Llebaria A.
Published: July 2002

Randomly rough real surfaces are characterized by their profile which is described by its statistical moments. A common assumption is that the distribution functions for these profiles are shaped Gaussianly. This article presents some statistical tests to characterize real rough surfaces in a quantitative way, and to assess how and what percent of these probability functions depart from Gaussian functions. Results of several tests are given on various thin films with rough surfaces.
Deposition of indium nitride by low energy modulated indium and nitrogen ion beams
Authors: Bello I. , Lau W. M. , Lawson R. P. W. , Foo K. K.
Published: July 2002

Indium nitride deposition on Si(100) using modulated In+ and N+2 has been carried out in a mass-separated low energy ion beam system. In+ and N+2 were generated in a Colutron ion source loaded with pure indium and fed with nitrogen, and were focused into a Wien filter. The mass analyzer was switched manually or by a computer for modulating the selection of In+ and N+2. After passing through the Wien filter, the selected ion beam was focused to the target chamber and was decelerated by a five-element deceleration lens in front of the target. In situ x-ray photoelectron spectroscopy (XPS) was used for film characterization. The spectral data confirmed the formation of InNx but the x value was less than unity for films prepared using ion energies of 5–100 eV and In/N dose ratios of 2–6. For example, the film prepared with an In/N ratio of 1/6 at a beam energy of 5 eV showed a composition of InN0.4. It was found that argon ion sputtering of this film at 1 keV and at a polar angle of 80° further depleted the nitrogen content and changed the composition to InN0.17. The argon bombardment result suggests that nitrogen depletion in the indium nitride films prepared by ion beam deposition in this study may be induced by ion bombardment during the film growth. In addition to this problem, it was also found that nitrogen bombardment in the early stage of film deposition led to the nitridation of the substrate. The damage of the crystallinity of the substrate is likely to prevent heteroepitaxial growth of InN on Si.
Electron beam patterning of SiO2
Authors: Allen P. E. , Griffis D. P. , Radzimski Z. J. , Russell P. E.
Published: July 2002

Maskless or ideally ‘‘resistless’ patterning of semiconductors is essential for in situ processes which require regrowth of semiconductor layers. If a practical method of patterning SiO2 were viable, many processing problems related to tasks currently utilizing organic resists could be eliminated. With the knowledge that etching selectivity can be induced in SiO2 by electron beam exposure, experiments were performed with the goal of gaining an understanding of some of the practical aspects of electron beam exposure and etching of SiO2. Electron beam energy optimization considerations for dose minimization were addressed followed by e-beam exposure and etching of 100 nm films of thermal and remote plasma enhanced chemical vapor deposition SiO2. The etching characteristics of the respective oxides are presented and discussed.
Ion beam analysis of Li diffused Ge–Li interfaces
Authors: Jen Causon K. C. , Kegel Gunter H. R. , Jen Kei-Peng
Published: July 2002

Lithium was evaporated onto 0.012 in.-thick high purity germanium substrates and was diffused into these samples at temperatures ranging from 175 to 260 °C for periods of several weeks in a vacuum of 5×10−8 Torr. The Ge–Li interface thus obtained was examined by 3-MeV proton backscattering coupled with the 7Li(p,α)4He reaction and also by scanning electron microscopy (SEM). The lithium-to-germanium ratio at the interface was measured by comparing the α yield of the 7Li(p,α)4He reaction to the proton backscattered yield from germanium. A Li2GeO3 sample was used as a standard in verifying the analysis approach. SEM micrographs indicate that lithium deposit on the germanium surface at 200 °C forms a 13-μm thick layer possibly in the form of an intermetallic compound.
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4,5 Auger transitions and valence hole screening of the 4d metals
Authors: Kleiman G. G. , Landers R. , de Castro S. G. C. , Nascente P. A. P.
Published: July 2002

High kinetic energy (2000–3000 eV) L3M4,5M4,5 Auger transitions (excited by Bremsstrahlung) are reported for the 4d series. The valence electron contribution to the measured Auger parameters was extracted from the data by exploiting systematics predicted theoretically. The systematic dependence on atomic number clearly manifests the effect of the nature of the screening charge and agrees remarkably well with independent theoretical calculations of metallic renormalization. Corresponding valence contributions for the 3d and 5d metals exhibit similar screening systematics.
Surface and interface properties of superconducting YBa2Cu3O7−x thin films on GaAs using yttrium stablized ZrO2/Si3N4 as a buffer layer
Authors: Jia Q. X. , Lee S. Y. , Shi Z. Q. , Anderson W. A. , Shaw D. T.
Published: July 2002

High temperature superconducting YBa2Cu3O7−x (YBCO) thin films have been deposited onto III–V semiconductor GaAs substrates. The deposition temperature of the YBCO layer could be increased to as high as 650 °C without apparently degrading the GaAs substrate due to the use of Si3N4 as a subbottom buffer on the GaAs surface. The growth of highly c-axis oriented YBCO films on GaAs was enhanced by using yttrium stabilized ZrO2 (YSZ) as a subtop buffer between YBCO and Si3N4. Surface and cross-sectional scanning electron microscopy revealed excellent surface and interface properties. The good interfaces were further confirmed using Auger electron spectroscopy depth profiling of the samples. The preservation of the GaAs surface due to the use of a dual buffer layer of YSZ/Si3N4 after YBCO deposition was demonstrated by photoreflectance measurement on the GaAs surface after removing YBCO, YSZ, and Si3N4 layers.
Evaluation of the arsenic dimer structure of an arsenic stabilized gallium arsenide surface by coaxial impact collision ion scattering spectroscopy
Authors: Sugiyama Naoharu , Hashimoto Akihiro , Tamura Masao
Published: July 2002

Coaxial impact collision ion scattering spectroscopy (CAICISS) has been applied to an analysis of As-stabilized GaAs surfaces. CAICISS spectral changes were observed, depending on the incident beam angle to the crystal surface. The shadow cone radius of Ga atoms in the GaAs crystal was obtained from the angular dependence of the signal intensities. The atom positions of As atoms on the top surface are also discussed on the basis of the result that the distance between the dimer atoms is shortened by less than 10% from the normal lattice constant.
Hydride cracker nozzle design for gas source molecular beam epitaxy
Authors: Shiralagi K. T. , Choi K. Y. , Droopad R. , Maracas G. N. , Quinn W. E.
Published: July 2002

The design of a tantalum nozzle for group V hydride cells in gas source molecular beam epitaxy is presented. The nozzle, which determines the flux distribution from the group V cell is optimized for uniformity and maximum flux utilization. Arsine cracking efficiency and relative concentrations of various gas species are measured by a quadrupole mass analyzer. The operating temperature for the source cell is determined as the region where maximum dimeric arsenic is available for growth.
Homojunction band discontinuities induced by dipolar intralayers: Al–As in Ge
Authors: Marsi M. , La Rosa S. , Hwu Y. , Margaritondo G.
Published: July 2002

The possibility of inducing a band offset in the electronic structure of Ge homojunctions has been recently demonstrated using Ga–As double layers. A photoemission study is presented in which it is proved that a similar effect can be induced using Al–As as an intralayer. Specifically, an offset of 0.4 eV has been obtained. It is found that the cation–anion intralayer deposition sequence produces the same dipole as the anion–cation sequence. This result is similar to that found for large overlayer coverages in the case of Ga–As intralayers; but contrary to the Ga–As intralayers the present system does not exhibit a reversed discontinuity for small thicknesses.
Amorphization of c-Si by the sputter deposition of Au studied by x-ray photoelectron diffraction
Authors: Lamontagne B. , Sacher E. , Wertheimer M. R.
Published: July 2002

It is well known that Si atoms can be dislodged from a silicon matrix and diffuse through a thin Au overlayer. In the course of studying this phenomenon, we have found x-ray photoelectron diffraction (XPD) to be a particularly powerful investigative tool: XPD, a relatively new surface analytical technique, is very sensitive to the surface quality of crystalline materials. We have avoided surface contamination by depositing very thin (<5 nm) Au films onto a (100) Si surface, both by sputtering and by thermal evaporation within the surface instrument. XPD reveals that the c-Si surface is amorphized by the former process and much less damaged by the latter, a fact we attribute to the higher average kinetic energy of incident Au atoms during sputtering. This interpretation is supported by related studies; for example, by the reaction of adventitious carbon to form Si–C bonds on c-Si during sputter cleaning and sputter deposition. The study illustrates the important role of even relatively low particle energies and fluxes in ion-assisted processing.
Flow and transport modeling of a low pressure plasma etching system
Authors: Bradley Stephen G. , Chen Ching-Hwa , Jasinski Thomas J.
Published: July 2002

Plasma etching of aluminum–copper alloys is performed at high densities and low pressures (10 mTorr) in a modified parallel plate plasma etching system with a Cl2/BCl3 gas chemistry. In this study, flow modeling is used to characterize the etching environment. The flow distribution and transport of chemical species within the reactor is modeled by the commercially available fluid dynamic software package, fluent, to predict metal etch rate and uniformity patterns on 6 in. aluminum wafers. Flow velocity vectors and chemical species distributions are presented. Cl2 is considered as the primary etchant by the single step surface reaction 3Cl2+2Al=2AlCl3. [D. Smith and R. Bruce, J. Electrochem. Soc. 129, 2045 (1982).] A good fit is achieved between the measured etch pattern and the predicted pattern. The etching is determined to be primarily transport limited, with diffusion as the dominant transport mechanism. Theoretical comparisons diffusive to convective transport in this pressure region are made.
Reactive ion etching of polyimidesiloxanes in fluorine-containing discharges
Authors: Jeng S. , Kwok H. S. , Tyrell J. A.
Published: July 2002

There is great interest in polyimides as dielectric insulators in high density circuits due to their high thermal stability and excellent dielectric properties. The newly developed polyimidesiloxanes (SIMs) offer several additional advantages over conventional polyimides in applications to microelectronic packaging. However, there are only a few studies on the reactive ion etching (RIE) behavior of SIMs in fluorine-containing discharges. Previously reported RIE results of SIMs showed a very low etching rate in a pure oxygen plasma. In this study, we investigated the etching behavior of SIMs in discharges of CF4/O2 and SF6/O2 mixtures. Actinometric optical emission spectrometry was used to monitor the relative densities of F and O atoms. The highest etching rates were found in SF6/O2 RIE due to the greatly increased concentrations of both F and O atoms. The maximum etching rate in each mixture appeared near the same IF(703.5 nm)/IO(844.6 nm) ratio, which is directly related to the F to O atom concentration ratio. The IF/IO ratio for the maximum etching rate was found to be invariant despite the different etching conditions of reactive gases, loading effects, and vacuum conditions. By comparing the etching rates of nonsiloxane polyimide and SIMs with different siloxane content in various discharges, we observed preferential etching behavior of SIMs in fluorine-rich environments.
Modeling the uniformity in a magnetron etching system
Authors: Paranjpe A. P. , Moslehi M. M. , Davis C. J.
Published: July 2002

Magnetically enhanced reactive ion etch (MERIE) systems are increasingly popular for etching applications which demand high anisotropy and high etch rates without sacrificing etch selectivity. Conventional planar magnetron etch systems in which the magnetic fields are radial, exhibit a nonuniform race track etch. We report on an adjustable, rotating field, planar MERIE system. An etch uniformity of ±5% (6 in. wafer diameter) for resist etching in an O2 plasma has been obtained over a wide range of conditions. The impact of magnetic field adjustment and contoured electrodes on resist etch uniformity is characterized. An equivalent circuit model coupled with a diffusion model, and a Monte Carlo simulation of secondary electron transport have been used to predict the spatial distribution of plasma parameters in an Ar plasma sustained between planar electrodes. The measured magnetic field distribution, radio-frequency power, current, and voltage are used as inputs to the model. The spatial distribution of the magnetic field has a profound influence on the plasma parameters. The calculated spatial distribution of the ion flux in an Ar plasma is in qualitative agreement with the resist etch rate distribution across the wafer in an O2 plasma.
Self-consistent numerical model for analyzing thermal layering of liquid mixtures of hydrogen isotopes inside a spherical inertial confinement fusion target
Authors: Simpson E. M. , Kim K. , Bernat T. P.
Published: July 2002

A self-consistent numerical model has been developed to describe the thermally induced behavior of a liquid layer of hydrogen isotopes inside a spherical inertial confinement fusion (ICF) target and to calculate the far-field temperature gradient which will sustain a uniform liquid layer. This method is much faster than the trial-and-error method previously employed. The governing equations are the equations of continuity, momentum, energy, mass diffusion–convection, and conservation of the individual isotopic species. Ordinary and thermal diffusion equations for the diffusion of fluxes of the species are included. These coupled equations are solved by a finite-difference method using upwind schemes, variable mesh, and rigorous boundary conditions. The solution methodology unique to the present problem is discussed in detail. In particular, the significance of the surface tension gradient driven flows (also called as Marangoni flows) in forming uniform liquid layers inside ICF targets is demonstrated. Using the theoretical model, the values of the externally applied thermal gradients that give rise to uniform liquid layers of hydrogen inside a cryogenic spherical-shell ICF target are calculated, and the results compared with the existing experimental data. For targets containing a mixture of hydrogen and deuterium the agreement between the theoretical predictions based on either the binary or ternary mixture model and the experimental data is shown to be excellent.
Poly-Si etching using electron cyclotron resonance microwave plasma sources with multipole confinement
Authors: Gorbatkin S. M. , Berry L. A. , Swyers John
Published: July 2002

In this study, mirror field and single coil 2.45 GHz electron cyclotron resonance microwave plasma sources were coupled to a multipole, multicusp plasma confinement system and used to produce chlorine plasmas for poly-Si etching. Scanning Langmuir probes were used to study the effect of process parameters on plasma potentials, plasma density, plasma density uniformity, and electron temperature, while poly-Si etching experiments on 150 mm diam wafers were used to relate process parameters and Langmuir probe results to etch rate, SiO2 selectivity, photoresist selectivity, and etch uniformity. Radio-frequency substrate bias at 13.56 MHz was used for ion energy control, and the addition of a third coil below the substrate plane was found useful for fine-tuning the radial plasma uniformity. Undoped poly-Si etch rates ≳3000 Å/min, Si/SiO2 etch selectivities ≳25 and 150 mm diam etch uniformities <2% at 1 σ were obtained, but not simultaneously. Tradeoffs in choosing operating conditions for optimum poly-Si etch performance will be discussed.
Interaction of cesium and barium on partially oxygen covered Nb(110)
Authors: Magera Gerald G. , Davis Paul R.
Published: July 2002

We present results of investigations of the adsorption and desorption of Cs and Ba on clean and oxygenated Nb(110) surfaces. The experiments were conducted under ultrahigh vacuum conditions using the techniques of line-of-sight thermal desorption mass spectrometry, Auger electron spectroscopy, and retarding potential work function measurement. The room temperature work function was found to increase from 4.62 eV for clean Nb(110) to 5.63 eV for Nb(110) with a saturated chemisorbed layer of oxygen. For a 4.8 L (1 L=1 Langmuir=1×10−6 Torr s) oxygen exposure, corresponding to about 70% of saturated oxygen coverage, minimum work functions of 2.21 and 1.42 eV were found with the adsorption of Ba and Cs, respectively. The minimum work function tends to increase with further adsorption of oxygen. The adsorption of Cs on the Ba/Nb(110) surface yielded a minimum work function of 1.47 eV. The results of the thermal desorption studies showed an initial (low coverages) binding energy of 3.72 eV for Ba on Nb(110) and 2.42 eV for Cs on Nb(110). We also present desorption energy data for Cs on the Ba/Nb(110) surface.
Influence of electronic structure on XeF2 etching of silicon
Authors: Lo C. W. , Shuh D. K. , Yarmoff J. A.
Published: July 2002

The work function and Fermi level pinning position of Si(111) exposed to XeF2 are measured with soft x-ray photoemission spectroscopy. The exposures range from the chemisorption of F on Si(111)-7×7 to steady-state etching. The work function increases monotonically with XeF2 exposure. The Fermi level is pinned near midgap after each exposure, but moves upwards towards the conduction band as the exposure is increased. The results are discussed in terms of the electronic structure of the surface reaction layer, and a chemical etching mechanism is proposed.
Photoirradiation-charge compensation for secondary ion mass spectrometers analysis of semiconductors
Authors: Hayashi Shun-ichi , Hashiguchi Yoshihiro
Published: July 2002

For secondary ion mass spectrometry (SIMS) analysis a photoirradiation-charge compensation technique has proven to be very effective and useful in the analysis of semiconductor samples. The mechanism of charge compensation was also studied. Monochromatized visible light was applied to the SIMS analysis of narrow band gap semiconductors. UV synchrotron radiation was used to irradiate a wide band gap semiconductor studied using ion induced Auger electron spectroscopy as well as SIMS. It was confirmed that photoirradiation at a photon energy greater than the band gap of the sample induces photoconductivity through electron–hole pair creation at the top surface.
Photoelectron spectroscopy studies of Tm silicide films on Si(111)
Authors: Wigren C. , Andersen J. N. , Nyholm R. , Karlsson U. O.
Published: July 2002

The formation of TmSi2−x on Si(111) by means of solid phase epitaxy has been studied with low-energy electron diffraction (LEED) and photoelectron spectroscopy (PES). PES shows that metallic TmSi2−x is formed and that the Tm of the silicide is trivalent. It is also found that this Tm silicide has Tm in the surface layer. Very good (√3×√3)R30° patterns were seen in LEED showing that the Tm silicide can be formed epitaxially. The optimum annealing temperature used in order to form the epitaxial TmSi2−x silicide was around 750 °C. When temperatures below 500 °C were used as reaction temperatures, LEED showed diffuse patterns and PES showed that the reacted film consisted of several different types of Tm-Si compounds.
Scanning tunneling microscopy study of carbon and hydrogen reactions with Si(111) in ultrahigh vacuum
Authors: Rogers D. , Tiedje T.
Published: July 2002

Carbon is deposited onto a Si(111) surface in ultrahigh vacuum by three methods: hydrocarbon exposure of a heated sample, contamination by the residual gases in the chamber and carbon evaporation by resistively heating carbon fibers. The scanning tunneling microscope shows that for all three methods the result of heating the sample with deposited carbon to 1000 °C is a surface covered by identically shaped objects which we interpret as tip images formed by sharp clusters of β-SiC on the surface. The SiC crystallites and the Si surface can be etched by exposure to atomic hydrogen. After large exposures the Si surface becomes rough and possibly porous.
Effects of substrate bias frequency in an electron cyclotron resonance plasma reactor
Authors: Caughman J. B. O. , Holber W. M.
Published: July 2002

The effects of varying the substrate bias frequency on both substrate and plasma parameters have been studied in an electron cyclotron resonance plasma reactor. The frequency was varied between 13.56 and 76.0 MHz. The plasma density at the substrate was in the mid-1011/cm3 range. It was generally found that as the frequency was increased, less rf power was coupled to the ions accelerated across the sheath to the substrate, and more rf power was coupled to the plasma bulk. Thus, more power was needed to achieve the same self-bias voltage as the bias frequency was raised. The same trend was seen as the plasma density increased—i.e., more rf power was needed to achieve the desired self-bias voltage at higher densities. These effects are analyzed in terms of a simple sheath model of the reactor.
Ion deflector of an ionization gauge for extreme high vacuum
Authors: Otuka A. , Oshima C.
Published: July 2002

An ion deflector of an ionization pressure gauge for an extreme high vacuum use has been developed. On the basis of the calculated ion trajectories, the optimum deflection angles of the electrostatic cylindrical deflector have been determined versus the electrode gap: an excellent focusing of ion beam has been established at the optimum angles. This is important in order to use the channeltron and to remove the electron stimulated desorption (ESD) noise from the signals. We have realized a high efficiency of ion collection together with a large reduction of the two noises of soft x-ray photoemission current and ESD ions by using the ion deflector.
Dielectric behavior of O2/CF4 plasma etched polyimide exposed to humid environments
Authors: Wu Shien-Yang , Denton Denice D. , De Souza-Machado Ressano
Published: July 2002

The influence of moisture on plasma etched polyimide (PI) films is reported. Reactive ion etching plasmas with different CF4/O2 ratios (0%–30% CF4) are used to etch metal–polyimide–metal parallel plate capacitors. Plasma etching leads to a geometrical modification of the capacitor structures studied. This results in a reduction of the device capacitance which is modeled using a three-dimensional Poisson solver (seses). A Debye type dielectric relaxation is observed in O2/CF4 plasma treated capacitors when measured at 85% relative humidity. The location of the loss peak is found to be dependent on CF4/O2 ratios. Wet capacitors do not exhibit this loss peak prior to etching. The observed relaxation in plasma treated PI capacitors can be removed by reheating to the cure temperature. A Debye model is used to extract a RC equivalent circuit for the etched capacitor structures. In parallel, x-ray photoelectron spectroscopy (electron spectroscopy for chemical analysis) is used to monitor the chemical changes in PI due to plasma treatment, and the observed chemical and dielectric changes are correlated.
Redistribution of solid fuel in inertial confinement fusion target by plasma
Authors: Chen C. M. , Norimatsu T. , Tsuda Y. , Yamanaka T. , Nakai S.
Published: July 2002

A new technique of applying a high frequency discharge for redistribution of solid deuterium–deuterium (D2) or deuterium–tritium (DT) fuel in a laser fusion target is proposed for future reactor-class targets. This technique can enhance the beta decay technique which has a long time constant for redistribution of the fuel far below the triple point. A plasma initiated in the central void of the target by glow discharge uniformly heats the inner surface of the fuel ice, and the target is located in an isothermal cooling medium. Resultant higher temperatures at a thicker fuel ice area induce sublimation of the thick fuel ice and condensation of the vapor on a thinner, cold area. This technique is applicable to deuterium fuel in a shell for current implosion experiments. A proof of principle was demonstrated by using krypton gas and liquid nitrogen as substitutes for the D2 or DT fuel and liquid helium, respectively. A smooth solid krypton layer was formed in a glass shell with a gas feeder.
Measuring the depth of fluorine incorporation in high and low density polyethylene by Rutherford backscattering spectrometry
Authors: Karwacki Eugene J. , Bauman Scott M.
Published: July 2002

We report on our efforts to apply Rutherford backscattering spectrometry (RBS) for measuring the permeation of fluorine into low (LDPE) and high density polyethylene (HDPE) that have been exposed to gas atmospheres containing fluorine. To address the issue of sample damage during RBS analysis, experimental conditions were chosen using polytetrafluoroethylene as a standard. Our studies of LDPE and HDPE containers exposed to 1% fluorine in nitrogen atmospheres show the depth of fluorine penetration to be approximately 400 Å. Though the depths of treatment for both materials are quite similar, we find that the amount of fluorine uptake per unit volume is significantly higher for LDPE. The information yielded by RBS (depth of treatment and uptake per unit volume) shows it to be a powerful method for evaluating surface and near surface treatments of polymeric materials.
Influence of clearance on the pumping performance of a molecular drag pump*
Authors: Liqun Shi , Yue Zhu , Xiaozhen Wang , Shijing Pang
Published: July 2002

The pumping performance of a molecular drag pump of the disk type has been studied using a three-dimensional dynamic model based on leakage flow through the clearance between the rotating and the stationary disks of the pump and the Monte Carlo method. The relationship between the theoretical values of the pumping performance and the structural parameters of the pump has been studied. The results showed that clearance has no big effect on the pumping speed, but dramatically affects the compression ratio of the pump, especially in cases of high rotation speed and heavy element gases. The amount of leakage through the clearance is determined not only by the amount of clearance, but also by its ratio to the depth of pumping channels.
Transmission ion channeling facility for structural studies of monolayer films on clean semiconductor surfaces
Authors: Seiberling L. E. , Lyman P. F. , Grant M. W.
Published: July 2002

Transmission ion channeling is a powerful analytical tool for determining surface structure, but involves special equipment and sample preparation considerations. We describe an ultrahigh vacuum structural analysis and sample preparation facility for transmission ion channeling studies of monolayer films on clean semiconductor surfaces. After samples are cleaned and films deposited, they can be moved under vacuum and investigated using low energy electron diffraction, Auger electron spectroscopy, atomic resolution scanning tunneling microscopy, or, using an ion scattering chamber attached to a beamline of a 3.5 MeV Van de Graaff accelerator, transmission ion channeling. Transmission channeling can determine the bonding position of adatoms to typically 0.1 Å resolution, and is one of the few techniques able to measure reconstruction at a buried interface or to detect the presence of order in the midst of disorder. These aspects of the technique are illustrated by a site determination of a monolayer of Sb deposited on Si(100) and by a determination of the pseudomorphic fraction of thin Ge films deposited on Si(100) at low growth temperatures.
Miniature multitarget sputtering system for the in situ x-ray study of high T
c multilayer film growth
Authors: Williams S. M. , Yang H. Q. , Ketterson J. B.
Published: July 2002

A miniature sputtering system equipped with mylar windows allowing for normal and grazing incidence x-ray studies to be performed in real time during film growth is described herein. The system incorporates multitarget sputtering guns which allow for the deposition of up to four different materials. In this way multilayer structures can be studied in situ without changing the substrate environment or alignment between layers.
Epitaxial growth and characterization of Ni films grown on MgO(001) by biased direct-current sputter deposition
Authors: Qiu Hong , Nakai Hisashi , Hashimoto Mituru , Safran Gyorgy , Adamik Miklos , Barna Peter B. , Yagi Eiichi
Published: July 2002

Ni films thinner than 180 nm are deposited on MgO(001) substrates at a temperature Ts of 190 or 280 °C by dc sputtering at 2.5 kV in Ar gas. A dc bias voltage Vs between 0 and -140 V is applied to the substrate during the deposition. A study of structural and physical properties of the Ni film is made by the use of reflection high-energy electron diffraction (RHEED), cross-sectional transmission electron microscopy (XTEM), x-ray reflection diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and by measuring (TCR) in the temperature range from 35 to 135 °C. When Ts=190 °C the Ni film retains a polycrystalline structure at any Vs. When Ts=280 °C, as Vs increases from 0 to −140 V the film transforms from the polycrystal to the single crystal with the orientation as Ni(001)∥MgO(001) and Ni〈010〉∥MgO〈010〉, indicating that an optimal value of Vs for the epitaxial growth ranges from −80 to −110 V. Besides, an analysis of RBS spectra in comparison with XTEM images explains that the atomic density of the Ni film is the highest at Vs=−80 V. The optimal condition for the epitaxial growth is also confirmed by the change of TCR as a function of Vs. In conclusion, the epitaxial growth of the Ni film with the lower defect density is dominated at Vs=−80 to −110 V by the bombardment of both energetic ions and fast neutrals of Ar to increase the mobility of Ni adatoms and to resputter impurities during the film formation. This effect is pronounced at Ts≥280 °C.
Hydrogen uptake into silicon from an electron cyclotron resonance plasma
Authors: Wampler W. R. , Barbour J. C.
Published: July 2002

The concentration of hydrogen in solution near the surface of silicon exposed to an electron cyclotron resonance (ECR) plasma was determined by measuring the flux of hydrogen permeating to subsurface microcavities. The energy and flux of hydrogen impinging onto the surface from the plasma was also measured. A model is described which predicts the concentration of hydrogen in solution from the energy and flux of the impinging hydrogen. The measured solution concentrations were ∼10−9 H/Si at 600 °C and ∼10−8 H/Si at 400 °C, in fairly good agreement with the model. The absence of accumulation of immobile hydrogen near the surface indicates that lattice defects, which strongly trap hydrogen, were not produced by the ECR plasma. This study establishes a connection between the properties of the ECR plasma and the concentration of mobile hydrogen in silicon samples exposed to the plasma, which allows improved control over passivation of defects and dopants.
Surface analysis by photoionization at very high laser intensities
Authors: Becker C. H. , Hovis J. S.
Published: July 2002

Photoionization at high laser intensities (∼1014 W/cm2) has been used to examine gaseous and sputtered atoms and molecules together with reflecting time-of-flight mass spectrometry. Light from a 35-ps Nd:YAG laser pulse was focused with a 10-cm focal length lens. The wavelengths used were 1064, 532, 355, and 266 nm, at nominal pulse energies of 70, 40, 18, and 10 mJ, respectively. Significant amounts of multiple ionization were observed even for high ionization potential (IP) atoms. For open-shell heavy transition metal atoms, the amounts of multiple ionization exceed single ionization. Relative elemental sensitivity factors were determined for the compounds SiO2, GaAs, and GaN which cover a wide range of IPs. 532-nm light gave the largest amounts of multiple ionization and also relative sensitivity factors most approaching unity, for the conditions studied. From these observations it is concluded that such high intensity laser beams lead to saturation of photoionization as well as sharply defined ionization volumes, both of which can advance surface analytical quantitation under high sensitivity conditions.
Enhancement of the deposition rate of TiO2 film in radio frequency reactive sputtering
Authors: Sekiguchi Hidetoshi , Kanzawa Atsushi , Imai Takahiro , Honda Takuya
Published: July 2002

Titanium oxide thin films were prepared using rf reactive sputtering in which a titanium target was sputtered in a mixture of Ar and reactive O2 gas. The flow modulation of reactive gas was proposed to enhance the deposition rate of the film which is generally low in continuous flow reactive sputtering. The experimental results indicated that the deposition rate could be enhanced maintaining the film stoichiometric ratio of TiO2. The enhancement occurred because the modulated flow appeared to reduce the formation of compounds on the target surface which inhibit sputtering under continuous flow conditions. The effects of the flow modulation were understood by adapting a reactive sputtering theoretical model.
Monte Carlo simulation of ion transport through radio frequency collisional sheaths
Authors: Ardehali M.
Published: July 2002

Ion transport in collisional sheaths is simulated with a Monte Carlo method. The simulation results indicate that the length scale over which the horizontal component of the electric field is significant scales with the trench width. Thus the degree of ion deflection by the horizontal component of the electric field at the trench opening does not depend on the trench width.
Evaluation of the background signal for mass spectrometry under high ambient hydrogen pressures in plasma discharges
Authors: Nakashima Y. , Tsuchiya K. , Ohtoshi K. , Shoji M. , Yatsu K. , Tamano T.
Published: July 2002

The background signal of a quadrupole mass spectrometer (QMS) has been evaluated under high ambient hydrogen pressures. Hydrogen gas is injected into a vacuum chamber and the resultant change of the QMS signal is investigated for dominant gaseous impurities with mass numbers from M=1 to M=50. The partial pressures of impurity gases (H2O, CO, CH4) are observed to increase with the quantity of the hydrogen gas injected. It is found that each increase of partial pressure is in proportion to the hydrogen pressure in the range 4×10−6–4×10−5 Torr. A method to compensate for suppressing the background signal is considered on the basis of experimental results and is applied to mass spectrometry of residual gases in plasma discharges. The partial-pressure measurements in the GAMMA 10 tandem mirror device, which is used for fusion plasma studies, were performed and it was confirmed that this method substantially improves the accuracy of the measurement. A production mechanism of the impurity gases inside the QMS is modeled and is discussed with respect to the transient state of hydrogen pressure due to gas puffing.
On-line studies of plasma surface interactions between a radio frequency plasma jet and 3 w/o boron doped graphite samples
Authors: Avni R. , Erin J. , Morvan D. , Mabille-Rouger I. , Amouroux J. , Winter J. , Nickel H.
Published: July 2002

The aim of this study was to provide insights into the mechanisms governing the plasma–surface interactions (PSIs) between a doped graphite with 3 w/o boron and an oxidizing plasma jet (Ar/O2 and Ar/H2O) or a reducing (Ar/H2) plasma jet. The PSI was studied on line by optical emission spectroscopy and quadrupole mass spectrometry. A mechanism for the PSI is proposed and related to the PSI at TEXTOR (the fusion reactor at Jülich FZ).
Magnetic field in two-dimensional magnetrons
Authors: Murphy M. J. , Cameron D. C. , Hashmi M. S. J.
Published: July 2002

An equation in integral form has been derived which in principle enables the calculation of the magnetic field associated with any simple magnetron whose geometry may be regarded as being two dimensional. Some approximations are necessary in the course of the analysis but these are not unduly restrictive. The equation is arrived at using conformal mapping techniques. It is used to find analytic expressions for the magnetic stream function and the magnetic field for the ‘‘standard’’ rectangular magnetron geometry. Theoretical results are given for a commercial planar magnetron system. These are then compared with experimental observations.
Growth of chalcopyrite Cu(In,Ga)Se2/CuIn3Se5 absorbers by radio frequency sputtering
Authors: Hernández-Rojas J. L. , Mártil I. , Santamaria J. , González-Diaz G. , Sánchez-Quesada F.
Published: July 2002

We have characterized rf sputtered films from a CuIn3Se5 single target. We find that films deposited at growth temperatures (Tg) below 400 °C are homogeneous with a composition close to the target and no secondary phases detected. These films have a band gap of 1.25 eV and a much stronger 112 orientation than Cu(In,Ga)Se2 (CIGS) thin films. For Tg above 400 °C, film composition in a ternary phase diagram approaches the line that joins CuInSe2 and InSe. X-ray diffraction shows the presence of InSe, and optical measurements indicate a band gap of 1.0 eV with a high subband-gap absorption. It is found that in the Cu-poor side of the phase diagram, film formation takes place from the selenide binaries analogously to CIGS. Nevertheless, for high Tg, Cu2Se and In2Se3 do not react completely, leaving unreacted In2Se3 that decomposes into InSe(s)+Se2(g). On the other hand, absorbers grown by the sequential deposition of high-Tg Cu-rich CIGS and CuIn3Se5 films show complete intermixing of the elements, and an improved performance with respect to devices fabricated on films that are rf sputtered from a single target.
Optical emission spectroscopy of H2–CO and H2O–CH3OH plasmas for diamond growth
Authors: Manukonda R. , Dillon R. , Furtak T.
Published: July 2002

Optical emission spectroscopy (OES) was used as a diagnostic tool to determine diamond growth in our rf plasma chemical vapor deposition systems. Diamond was grown with a conventional H2–CO source gas and in a low pressure system using a water–methanol source. Optical emission spectra were recorded between the wavelengths of 2000 and 8000 Å for both the systems. The OES spectral peak ratios of Hα to certain carbon radicals are an indicator of diamond growth in H2–CO plasmas. In particular, both the growth rate and morphology showed a correlation with Hα to certain carbon radical ratios in H2–CO discharges. The OES spectra in the water–methanol plasma are quite different than in the H2–CO plasma. Different species are represented and the intensity of the common peaks is much higher than in the H2–CO plasma.
Surface type conversion of CuInSe2 with H2S plasma exposure: A photoemission investigation
Authors: Nelson Art J. , Frigo Sean P. , Rosenberg Richard
Published: July 2002

Surface type conversion of CuInSe2 by H2S plasma exposure was studied by synchrotron radiation soft x-ray photoemission spectroscopy. The low power H2S plasma was generated with a commercial electron cyclotron resonance plasma source using pure H2S with the plasma exposure being performed at 400 °C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H2S plasma exposure type converts the n-type CuInSe2 surface to a p-type surface at this elevated temperature and that the magnitude of the band bending is 0.5 eV, resulting in a homojunction interface.
Preparation of cubic boron nitride films by radio frequency bias sputtering
Authors: Tsuda Osamu , Yamada Yukiko , Fujii Tsuyoshi , Yoshida Toyonobu
Published: July 2002

Cubic boron nitride films were successfully prepared on Si(100) substrates by radio frequency (rf) bias sputtering of a hexagonal boron nitride target in pure Ar discharge with the aid of a magnetic field and with the phase regulation of the rf voltages applied to the target and substrate electrodes. Above the threshold of the negative substrate bias voltage (VS), the infrared (IR) absorbance corresponding to the cBN TO mode showed a linear increase proportional to deposition time, while that of the sp2 phase kept a nearly constant value. The resulting dependency indicated that the cBN films consisted of a double-layered structure caused by an initial deposition of the sp2 phase and the subsequent growth of a cBN single phase, and did not consist of a two-phase mixed layer. The layered structure was also confirmed by observing the depth dependence of the IR spectra. The growth rate of the cubic phase and the thickness of the initial sp2 bonded layer were estimated to be approximately 1 nm/s and 40 nm, respectively, for cases where VS ranged from 250 to 300 V at p=16 m Torr. This rate was relatively high compared with those of other techniques used for cBN deposition.
Thermal behavior of carbon nitride and TiN/NbN superlattice films
Authors: Lopez Sébastien , Wong Ming-Show , Sproul William D.
Published: July 2002

Hard coatings are commonly used today to enhance the life of numerous tools and wear parts. As carbon nitride and TiN/NbN superlattice films prepared by reactive sputtering were being evaluated for such tribological applications, it appeared necessary to test their thermal behavior to determine their stability at high temperatures. The coatings were reactively sputtered on silicon, M1 steel, or cemented carbide substrates. Two deposition conditions were used for the carbon nitride films producing either soft or hard films. The effect of a metal interlayer, either chromium or titanium, has also been studied. Two modulation periods were used for the TiN/NbN films with the same deposition conditions. Thermal annealings were performed up to 700 °C under vacuum in the 10−6 Torr range. Several properties of the coatings before and after these annealings were evaluated and compared, including hardness (nano-indentation), adhesion/cohesion (scratch test), structure x-ray diffraction, and composition Auger electron spectroscopy. The carbon nitride coatings lost part of their nitrogen, and both the hardness and the critical load dropped as the annealing temperature was increased. Carbon nitride films deposited on silicon wafers peeled off after treatment at 400 °C, while films deposited on an M1 steel remained adhered. A critical temperature for both chemical and physical properties around 600 °C was observed. For the TiN/NbN superlattice films, annealing up to 700 °C caused almost no intermixing, while the nitrogen content, the hardness, the adhesion/cohesion, and the structure remained unaffected.