bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial growth and characterization of CuCl(110)/GaP(110)
Authors: Chen W. , Dumas M. , Ahsan S. , Kahn A. , Duke C. B. , Paton A.
Published: July 2002

Epitaxial layers of the ionic zinc blende compound CuCl are grown on the (110) surface of GaP. The growth is performed by congruent evaporation from a single CuCl source. Surface and interface properties of CuCl/GaP are studied with Auger electron spectroscopy, ultraviolet and x-ray photoemission spectroscopy, electron energy-loss spectroscopy, and low-energy electron diffraction. The interface formed at 100 °C is abrupt, but undergoes a massive chemical reaction which leads to the formation of a copper phosphide layer at high temperature (≥300 °C). The valence band discontinuity is 0.85 eV ±0.15 at the abrupt CuCl/GaP interface. The CuCl(110) surface is atomically ordered and exhibits a (1×1) unit cell. Its atomic geometry is determined by multiple scattering analysis of low-energy electron diffraction intensities. The surface is found to be relaxed in a way which is entirely compatible with the ‘‘universal’’ structure of cleavage surfaces of tetrahedrally coordinated III–V and II–VI compound semiconductors.
Time-resolved measurements of electron and ion concentrations in low-frequency sulfur hexafluoride discharges
Authors: Utagikar Ajit , Thompson Brian E.
Published: July 2002

Electron and ion concentrations in low-frequency SF6 discharges were measured with an impedance technique in which a small high-frequency power perturbation is added to the low-frequency powering signal. The impedances for the high frequency signals are measured and interpreted with an electrical analog of the plasma that gives bulk ion concentration and electron concentration with time within the low frequency cycle. Ion concentrations, which are about 5×1011 cm−3 at 0.3 W/cm2, 2 cm electrode spacing and 350 mTorr, increase approximately with (power)0.8 but change little with pressure from 250 to 450 mTorr. Electron concentrations change from essentially 0 to about 109 cm−3 during the low frequency cycle and increase approximately with (power).1.5 An overall negative ion balance in which the creation of negative ions by electron attachment equals loss by ion–ion recombination is used to compare the ion and electron concentrations. The calculated ion concentrations as determined from measured electron concentrations and literature-reported rate constants are within 25% of the measured concentrations without using any adjustable fitting parameters.
Correlative imaging in scanning near-field optical microscopy
Authors: Vaez-Iravani M. , Toledo-Crow R. , Chen Y.
Published: July 2002

Operational aspects of a newly developed simultaneous near-field optical and force microscope are considered. Using a glass probe, the technique is capable of monitoring the sample topography, through its force microscopy capability, as well as the sample’s optical parameters, using the light guiding properties of the tip. In addition, the force signal can be used reliably as a feedback signal, thus allowing a crash-free detection of optical fields in the vicinity of opaque steps on the sample. Results are presented on imaging a variety of samples including biological and nonbiological objects and thin film structures. In each instance, results obtained with different modalities are compared. It is shown that the simultaneity of the images obtained with different modalities can be very useful in, and sometimes necessary for, sample identification.
Surface characterization of fluorinated polyimide films grown by vapor deposition polymerization
Authors: Maruo Yasuko Yamada , Andoh Yasuko , Sasaki Shigekuni
Published: July 2002

Vapor deposition polymerization (VDP) was used to prepare fluorinated polyimide films. The process utilizes the coevaporation of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) monomers. We characterized the surface by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The XPS analysis showed that the film stoichiometry greatly depended on the ratio of source effusion rates, and that a 6FDA/TFDB pressure ratio of 1:10 was best for obtaining stoichiometric 6FDA/TFDB polyimide. The surface structure image obtained by AFM was clearly different from that of spin-cast films. The surface morphology of the VDP films was characterized by an accumulation of parallel rod shaped structures, whereas that of the spin-cast one was a rough structure. The surface morphology of the VDP grown films at the initial growth state was also found to be a vertical stripe structure according to STM results.
Thin gold film strain gauges
Authors: Li Chunshien , Hesketh P. J. , Maclay G. J.
Published: July 2002

Gold thin films, of thickness 30, 60, 100, and 300 Å were studied for use as miniature strain gauges. The thin metal films were thermally evaporated onto silicon dioxide coated silicon wafers and patterned into strain gauges with dimensions of 100 μm×70 μm and annealed at a maximum temperature of 400 °C. The silicon substrate was cut into cantilever beams to calibrate the strain gauges by loading the beams. The impedance, Z, was measured over a frequency range from 5 kHz to 1 MHz. For the 30, 60, and 100 Å thick films the magnitude of the impedance was typically 1 MΩ at 5 kHz and the gauge factor ([Δ‖Z‖/‖Z‖]/ε) was 24–48 at small strain (ε<2.8×10−6). The gauge factor was independent of frequency but decreased at larger strains. The 300 Å thick films were typically 110Ω with a gauge factor of 2.6. The conduction process for the island-like film was modeled with activated tunneling. The sensitivity [Δ‖Z‖/‖Z‖]/ε versus strain response model included a contribution from the strain energy in the activated tunneling.
Real-time in situ epitaxial film thickness monitoring and control using an emission Fourier transform infrared spectrometer
Authors: Zhou Z. H. , Yang I. , Kim H. , Yu F. , Reif Rafael
Published: July 2002

An emission Fourier transform infrared (E/FT-IR) technique for epifilm thickness measurement will be reported. The E/FT-IR technique takes advantage of the heated wafer as the source of IR radiation. It is a noncontact, nondestructive, real-time, and in situ epifilm thickness monitoring tool that we demonstrated to be useful for observing real-time growth rates and incubation times. In addition, this method is especially applicable to precise end point control when critical film thicknesses are required. Moreover, we have identified some limitations to this method, and found the operable temperature ranges. Furthermore, we have demonstrated, for the first time, a closed-loop feedback control of epitaxial silicon film thickness in a multichamber single-wafer chemical vapor deposition reactor.
Surface alloying in metal-on-metal epitaxial growth
Authors: Engdahl C. , Stoltze P. , Jacobsen K. W. , No/rskov J. K. , Skriver H. L. , Aldén M.
Published: July 2002

Energies relevant for metal-on-metal heteroepitaxial growth are calculated for a few selected systems using the effective-medium theory and a Green’s function technique within the tight-binding linear muffin-tin orbitals method. The two methods show good agreement with each other, lending support to the accuracy of the effective-medium modeling. The energetics of surface segregation and surface alloy formation are investigated and compared to simple estimates often used in this context. Quantitative as well as qualitative deviations from the simplest picture are found showing that more accurate models are necessary.
Electron beam evaporator constructed from aluminum alloy and the gettering effect of chromium films
Authors: Nakada S. , Yamaguchi M. , Yamamoto M. , Ishimaru H.
Published: July 2002

We developed a new ultrahigh vacuum (UHV) electron beam evaporator. The vacuum chamber was constructed from aluminum alloy to minimize the chamber baking temperature and baking time. A new electron gun was developed to minimize the desorption of gas. Chromium (Cr), titanium (Ti), molybdenum (Mo), and copper (Cu) thin films were deposited by this evaporator. We can hold the pressure under 1×10−8 Torr to evaporate Cr and Cu. After evaporation of Cr, the lowest pressure, 2×10−10 Torr, is achieved. The pressure after the baking of the vacuum chamber is 3×10−9 Torr. The pressure after Cr evaporation is about one-tenth of that after the baking of the chamber. This is due to the gettering effect of the deposited Cr films, which has ten times the pumping ability of the turbomolecular pump. The pumping power of Cr films is stronger than that of Ti films.
Early vacuum systems and process descriptions used to deposit optical coatings
Authors: Alexander C.
Published: July 2002

A review will be given of the equipment and evaporative processes used to manufacture optical coatings prior to the formation of the Committee on Vacuum Techniques in 1953. Processes to be covered: sealed beam headlights; antireflection films (using hot substrates and electron beamed substrates); German SiO coated mirrors; coating of Schmidt mirrors using a record changer in system; the Mt. Palomar astronomical mirror; hot and cold filters. Present day sputtering of large architectural windows will be described.
Investigation of the energy transfer to the substrate during titanium deposition in a hollow cathode arc
Authors: Steffen H. , Kersten H. , Wulff H.
Published: July 2002

During titanium layer deposition with a hollow cathode arc discharge the integral energy influx to the substrate has been monitored by measuring temperature gradients. Discharge power and substrate voltage have been varied. Simultaneously, the plasma parameters in front of the substrate were determined by means of Langmuir-probe measurements. From the integral energy influx and the plasma parameters the contributions of the charge carriers and the heat radiation to the substrate heating were calculated. The contribution of the titanium condensation heat could be estimated by means of Rutherford backscattering and ellipsometrical measurements. It was found that heat radiation and charge carriers mainly contribute to the integral substrate heating. The contribution of condensation can be neglected.
Synchronization in oscillatory surface reactions on single crystal surfaces
Authors: Imbihl R. , Veser G.
Published: July 2002

In oscillatory surface reactions on single crystal surfaces the partial pressure variations that accompany the oscillations in the reaction rate represent a global interaction between the local oscillators. The NO+CO reaction on Pt(100) exhibits both synchronized and unsynchronized oscillatory behavior depending on the substrate phase. Unsynchronized oscillations occur on the 1×1 phase but on the hex phase one finds synchronized oscillatory behavior. The mechanism leading to synchronization in the oscillations on Pt(100)-hex can be traced back to a critical dependence of the 1×1⇄hex phase transition on the partial pressures of NO and CO. At both ends of the temperature window for rate oscillations one finds well-defined transitions to a stationary reaction rate. These bifurcations are discussed in terms of a transition from synchronized to unsynchronized behavior. In particular, the occurrence of deterministic chaos in connection with a Feigenbaum scenario is interpreted as being due to such a transition.
Layer-by-layer growth of Hg on W(110)
Authors: Zhang Jiandi , Li Dongqi , Dowben P. A.
Published: July 2002

Using photoelectron spectroscopy, the overlayer electronic structure was observed to be modulated by the Hg growth mode for Hg adsorbed on W(110) at 200 K. The Hg layer-by-layer growth was also characterized by variations in the ratio between the Hg 5d shallow core level and W 4f photoemission intensities. This layer-by-layer growth occurs in spite of surprisingly weak electronic interactions between the adatoms and the substrate.
Image-potential-induced resonance on Al(111) observed by two-photon photoemission spectroscopy
Authors: Bulović V. , Quiniou B. , Osgood R. M.
Published: July 2002

Using the technique of two-photon photoemission we have observed the peak in the density of states of an image-potential resonance on Al(111). Image-potential resonances have a short, bulklike lifetime, resulting in a very weak, but observable, two-photon photoemission signal. We find the peak of the density of states for Al(111) n=1 resonance at 0.46±0.1 eV below the vacuum level. Our measurement is in agreement with previous inverse photoemission measurements as well as with several theoretical treatments of image resonances on metal surfaces. This investigation provides further confirmation of the existence of such a resonance level on Al(111).
Dependence of x-ray absorption magnetic circular dichroism on layer periodicity in iron–platinum multilayers
Authors: Jankowski A. F. , Waddill G. D. , Tobin J. G.
Published: July 2002

Magnetic circular dichroism in x-ray absorption is observed in Fe/Pt multilayers. The magnetization and helicity are both in the plane of the Fe/Pt multilayers which are prepared by planar magnetron sputter deposition. Lattice and layer pair spacings are measured using grazing incidence and high-angle x-ray scattering. The film composition and lattice growth are confirmed using Auger depth profiling and cross-section transmission electron microscopy, respectively. The state of the film magnetization is found to be dependent on the layer pair spacing as well as the relative thickness of the Fe to Pt layer. The maximum magnetic moment is measured for a (Fe 9.5 Å/Pt 9.5 Å)92 multilayer.
Role of Ge in SiGe epitaxial growth using silane/germane gas-source molecular beam epitaxy
Authors: Suemitsu M. , Kim K-J. , Miyamoto N.
Published: July 2002

Precise measurements on the growth rate and the hydrogen coverage on the growing surface of SiGe epitaxial film by silane/germane gas-source molecular beam epitaxy (GSMBE) have been performed for the germane mixing ratio Xg of 0%–6%. For all Xg, the growth-rate Arrhenius plot showed a distinct separation into the high-temperature region with a lower activation energy and the low-temperature region with a higher activation energy, similar to silane GSMBE. The growth rates in the low-temperature region increased with Xg, while those in the high-temperature region peaked at Xg=0.8% and decreased thereafter. As a result the transition temperature shifted towards lower temperatures. The activation energy in the low-temperature region stayed almost unchanged or increased with Xg, which is quite contrary to the previous understandings and is thus discussed. A model is presented to describe the hydrogen desorption process from SiGe surfaces, which explains both the growth rate in the low-temperature region and the temperature-programed-desorption (TPD) spectra obtained from the quenched growing surface. The role of Ge in the low-temperature region is concluded to enhance processes involved in hydrogen desorption from Si atoms.
Nonthermally driven surface chemistry of phosphine on GaAs(100)
Authors: Sun Y.-M. , Huett T. , Sloan D. , White J. M.
Published: July 2002

Photon driven surface reactions of PH3 on GaAs(100) have been studied by x-ray photoelectron spectroscopy, temperature programmed desorption, and high resolution electron energy loss spectroscopy. Nonthermal excitation was achieved with an excimer laser producing 193 nm (ArF) and 248 nm (KrF) photons. Photons induce both desorption and dissociation of PH3 at 100 K. Phosphine coverage decreased monotonically with increasing photon fluence. Two dihydrogen desorption peaks at 500 and 600 K, found after irradiation with photons, were attributed to the desorption of hydrogen from Ga and P sites. The appearance of Ga–H stretches in the high resolution electron energy loss spectra following irradiation confirms that H is transferred from P to Ga during the irradiation process. The cross sections of the overall PH3 loss were 1.9×10−18 and 2.9×10−20 cm2 for 193 and 248 nm photons, respectively. X-ray photoelectron spectra of P(2p) show that some gallium phosphide was formed after photon irradiation. The observed reactions were attributed to both direct photon absorption by the adsorbate and to substrate mediated hot electron attachment processes.
Surface reactions of tetraneopentyl zirconium on zirconium carbide thin films
Authors: Parmeter John E. , Smith David C. , Healy Matt D.
Published: July 2002

Interest has arisen recently in the use of metal alkyl compounds as precursors in the chemical vapor deposition of metal carbides. This paper presents results of a study of the surface chemistry of one such precursor, tetraneopentyl zirconium (ZrNp4), on zirconium carbide thin films. Decomposition of the precursor leads to the desorption of both methane and a larger hydrocarbon species that is tentatively identified as neopentane. The desorption of large amounts of methane may help to explain the fact that ZrC films grown to date with this precursor are not stoichiometric but rather contain excess carbon.
Multiphonon scattering of thermal energy He atoms from the LiF(001) surface
Authors: Bishop G. G. , Gillman E. S. , Hernández J. J. , Baker J. , Skofronick J. G. , Safron S. A.
Published: July 2002

Results from the scattering of nearly monoenergetic (ΔE/E≊2%) thermal energy He atoms from the LiF(001) surface are presented and discussed with particular emphasis on multiphonon interactions. These experiments represent the next step in a series of experiments exploring the multiphonon scattering of He from alkali halides in that previous work [G. G. Bishop et al., Phys. Rev. B 47, 3966 (1993)] has now been extended to include nonspecular angles. The LiF surface was prepared as in the previous experiments by cleaving the crystal in air and cleaning it by sublimation in the ultrahigh vacuum system. The measurements consist of time-of-flight spectra of the scattered He atoms taken for a number of incident angles as a function of the surface temperature ranging from 290 to 720 K and for He incident wave vectors ranging from 7 to 11 Å−1. Analysis of the data was carried out using a theoretical model developed by Manson [Phys. Rev. B 43, 6924 (1991)], which allows the determination of the interaction potential between the incident atoms and the LiF surface by isolating the scattering form factor. The good representation of the multiphonon scattering found from the model allows this background to be subtracted from the time-of-flight spectra to enhance the single-phonon He atom scattering signal, which in turn permits improved surface phonon dispersion measurements and interpretation.
Comparison of two epitaxial formation mechanisms in the SiGe system and the subsequent defect generation
Authors: Prokes S. M. , Rai A. K.
Published: July 2002

Two epitaxial growth mechanisms have been examined, and the resulting defect generations will be discussed. The first growth process involved molecular-beam epitaxy (MBE), while the second employed wet oxidation to form a Ge-rich epilayer from an initially amorphous film. The MBE-grown high Ge content layers evolved by island coalescence, while the oxidation-produced high Ge content layers formed by a Ge exchange mechanism below a contamination layer, leading to a more uniform epitaxial layer. Due to the very different growth modes, the resulting dislocation, stacking fault, and twin densities were reduced, along with a reduction in the surface roughness.
Geometrical structure of the Bi/GaP (110) interface: An x-ray standing wave triangulation study of a nonideal system
Authors: Herrera-Gómez A. , Kendelewicz T. , Woicik J. C. , Miyano K. E. , Pianetta P. , Southworth S. , Cowan P. L. , Karlin A. , Spicer W. E.
Published: July 2002

The locally ordered structure formed by one monolayer of Bi on GaP (110) is studied by x-ray standing wave triangulation applied to three Bragg planes. This system has a larger lattice mismatch than other V/III–V interfaces (e.g., Sb/GaAs, Sb/InP, and Bi/InP), and does not grow epitaxially as those other systems. Prior scanning tunneling microscopy studies of the Bi/GaP interface show that Bi grows in chains along the (11̄0) direction interrupted by vacancies. The large difference in the atomic radii induces the formation of vacancies to allow relaxation. Nevertheless, our results indicate that the interface structure resembles the epitaxial continued layer structure, as in the better matched systems.
Effects of corrosion and recovery processes on chloride-ion-selective electrode surfaces
Authors: Young Vaneica Y. , Schoenfeld Dean W. , Weaver Jason F. , Hoflund Gar B. , Hoke S.
Published: July 2002

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS) and secondary-ion-mass spectrometry (SIMS) have been used to examine the composition of the visible corrosion layer formed on a chloride-ion-selective electrode (ISE) during exposure to a simulant solution containing dissolved Halon fire suppression by-products such as HBr. ISS depth profiling indicates that the Cl− is replaced by Br− forming a corrosion layer about 75 Å thick. Surface recovery of the ISE by aqueous hydrochloric acid etching has also been studied as a function of acid concentration and etchant contact time. Based on XPS data, the optimum etching parameters have been found to be 0.5 mol L−1 aqueous HCl and a contact time of 290 s. XPS, AES, ISS, and SIMS data indicate that the HCl etch removes most of the Br− in the near-surface region, thus providing an in situ means of regenerating chloride-ion-selective electrodes.
Diagnostics and control of radio-frequency glow discharge
Authors: Mutsukura N. , Fukasawa Y. , Machi Y. , Kubota T.
Published: July 2002

The diagnostics of 13.56 MHz planar radio-frequency (rf) plasma were carried out using spatially resolved optical emission spectroscopy between the parallel electrodes. Plasma sheath thickness d evaluated from the optical emission profiles depends on gas pressure P, and a relationship of Pnd=const. was obtained for CH4, CF4, and O2 plasmas with n≥1/3, and for He and Ar plasmas with n≥1/2. The etching rate and the etching profile of silicon in CF4 plasma were also examined as a function of gas pressure. A novel technique for controlling rf plasmas using the optical sheath thickness and maximum optical emission intensity is presented. This technique was applied to dry etching of silicon in CF4 plasma. When this novel control technique was used, the deviation in the etched depth for a constant etching time became smaller than that obtained using conventional power control methods.
Super-wide electron cyclotron resonance plasma source excited by traveling microwave as an efficient tool for diamondlike carbon film deposition
Authors: Ishii A. , Amadatsu S. , Minomo S. , Taniguchi M. , Sugiyo M. , Sakaguchi Y. , Kobayashi T.
Published: July 2002

An electron cyclotron resonance (ECR) plasma source which generates 500-mm-wide plasma has been developed. A divergent magnetic field sufficient for ECR is generated by permanent magnets and a solenoid coil. A 2.45-GHz traveling microwave is supplied through a long slot antenna prepared in the sidewall of the waveguide and excites ECR plasma. This apparatus is applied to the diamondlike carbon (DLC) films deposition and DLC films were deposited in a wide zone 320 mm in width.
Examination of hydrogen etched mercury cadmium telluride by spectroscopic ellipsometry
Authors: Orloff Glennis J. , Smith Patricia B.
Published: July 2002

The incorporation of dry etch processes for mercury cadmium telluride (HgCdTe) infrared device fabrication is becoming critical for the infrared community as we advance toward the production of high-density devices. Dry etch processes are cleaner than wet etch processes. In addition, dry etches are highly anisotropic and are capable of producing the small features required by the more advanced device architectures. However, the incorporation of dry etch processes into device fabrication often affects the surface quality, producing roughened surfaces and variations in composition. Consequently, the identification of suitable dry etch processes to produce high quality infrared devices is essential. In this investigation, three different plasma etching tools (reactive ion etching, electron cyclotron resonance, and remote microwave) were used to etch HgCdTe with hydrogen. The hydrogen interaction with HgCdTe at similar etch depths was examined with spectroscopic ellipsometry and atomic force microscopy. Variations in surface roughness and composition obtained when etching with the three plasma etching tools are reported and the significance of energetic ions on surface quality is discussed.
Operation of DIII-D with all-graphite walls
Authors: Holtrop K. L. , Jackson G. L. , Kellman A. G. , Lee R. L. , Hollerbach M. A.
Published: July 2002

Recently, additional graphite coverage has been installed in the DIII-D tokamak, increasing the graphite tile coverage from 45% to ∼90% (limited only by openings for ports). Due to a problem with copper impurity bursts during tokamak discharges, copper foam sheets between the graphite tiles and the Inconel wall have been replaced with Grafoil gaskets (a compressible graphite material), which further increases the surface area of the graphite inside the DIII-D torus. Although additional graphite has the potential for improving DIII-D performance, if not properly conditioned it can also degrade tokamak discharges by contributing to increased low Z impurity influx (C and O) and higher particle fueling (D). To address these concerns, improvements were implemented both in tile preparation and wall conditioning techniques. All previously installed tiles were grit blasted with boron–carbide grit to remove codeposited metal impurities and all tiles were outgassed to 1000 °C prior to installation. The only conditioning techniques used were baking and helium conditioning (glow and Taylor discharge cleaning) to avoid producing loosely bound carbon. Previously, H2 or D2 Taylor discharge cleaning was used extensively during the vent recovery phase. The glow discharge system used for wall conditioning was modified to include a large area electrode (0.32 m2). Recovery from the recent 7 month machine opening was extremely rapid with improved modes of energy confinement (H-mode) transitions observed on the fourteenth plasma discharge. In addition, very high confinement (VH-mode) discharges were obtained without boronization, which is further indication of the rapid vent recovery. Lower recycling/lower fueling efficiency was also observed during operation with all-graphite walls. We will also discuss the use of neon and argon glow, and qualification of the new graphite, including outgassing tests of the Grafoil material.
Laser fusion target shell wall thickness from interference fringe shape analysis
Authors: Stephens R. B. , Wittman M. D.
Published: July 2002

We have developed an analytic expression to describe the shape of interference fringes produced by transparent shells using plane-wave front dual-beam interferometry. Using this expression, one can calculate the wall thickness of the shell from a few simple measurements of the curvature or separation of fringes relative to its size. It is feasible to calculate wall thickness to within a few percent, the limit being the ability to accurately locate the center of the interference fringes. One of our approaches has been incorporated into an image analysis program. We will discuss the usefulness of this approach as a first step toward an automated image analysis program.
Low-temperature plasma-assisted oxidation combined with in situ rapid thermal oxide deposition for stacked-gate Si–SiO2 heterostructures: Integrated processing and device studies
Authors: Misra V. , Hattangady S. V. , Yasuda T. , Xu X-L , Hornung B. , Lucovsky G. , Wortman J. J.
Published: July 2002

We have fabricated stacked-gate structures with (i) thin Si–SiO2 heterostructures formed by a combination plasma-assisted and rapid thermal processing, and (ii) polysilicon gate electrodes deposited by rapid thermal chemical-vapor deposition (RTCVD). All processing was performed in situ and sequentially in a single chamber reactor, which provided for independent control of the interface formation and oxide deposition steps. The predeposition, low-temperature, 300 °C, remote-plasma-assisted Si-cleaning/passivation/oxidation (i) removed residual C-atom contamination, (ii) created a device-quality Si–SiO2 interface, and (iii) generated ∼0.5–0.6 nm of oxide, which served as a platform for the subsequent SiO2 deposition. Deposition of the SiO2 film, ∼10.0 nm thick, was performed in situ by an 800 °C RTCVD process. This study emphasizes the interface formation process, and its effect on electrical properties of stacked-gate structures in metal–oxide–semiconductor capacitors and field effect transistors.
In situ measurement of thin-film conductivity during and after energetic condensation
Authors: Mausbach Michael , van Kronenberg Guido , Ehrich Horst
Published: July 2002

An anodic vacuum arc served as a source for a pure, gas-free Cu-vapor plasma. This source enables the independent control of important plasma parameters like degree of ionization (1%–14%) and energy of the Cu ions (2–100 eV) arriving at a substrate surface. Time-resolved in situ measurements of the electrical conductivity of the growing films show no significant dependence of the onset thickness of conductivity on ionization and ion energy for ion energies exceeding about 10 eV. For ion energies below 10 eV, a tendency to higher onset thicknesses can be observed. The onset of electrical conductivity, i.e., the formation of continuous films, occurs between 1.5 and 4.5 nm film thickness. The film conductivity decreases with increasing ion energy and increasing ionization. After film condensation, a long time drift showing increasing film conductivity was observed. This increase follows approximately a simple exponential lifetime dependence with a typical meanlife of several hours increasing towards higher ion energy and ionization. This behavior can be explained in terms of point defects being induced during energetic condensation, creating a transient metastable state followed by a recrystallization process.
(Ti1−xAlx)N coatings by plasma-enhanced chemical vapor deposition
Authors: Lee Sang-Hyeob , Ryoo Ho-Joon , Lee Jung-Joong
Published: July 2002

(Ti1−xAlx)N was deposited on high-speed steel using a radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) process from the gas mixture of TiCl4, AlCl3, NH3, H2, and Ar. The composition of the coated layer could be controlled from TiN to (Ti0.17Al0.83)N by the ratio of source gases, TiCl4 and AlCl3. At the same ratio of AlCl3 and TiCl4, the Al content in the coated layer was changed by the rf power employed. According to x-ray diffraction and transmission electron microscopy, the PECVD-(Ti1−xAlx)N coating with x≤0.77 was found to have a NaCl-type structure with Ti atoms substituted by Al atoms and a strong crystallographic texture of (200), but (Ti0.17Al0.83)N had a mixed phase of TiN+AlN. It was also found that the hardness, the adhesion, and the surface morphology of the coated layer were affected by the Al content as well as by the rf power employed.
Hollow foam microshells for liquid-layered cryogenic inertial confinement fusion targets
Authors: Schroen-Carey Diana , Overturf George E. , Reibold Robert , Buckley Steven R. , Letts Stephan A. , Cook Robert
Published: July 2002

Future U.S. inertial confinement fusion (ICF) targets will use capsules, 1–2 mm in diameter, with uniform 100 μm thick, cryogenic fuel layers. Research is currently underway to identify optimal methods for producing these thick, uniform layers. One method is to use a spherical polymer foam layer within a full density polymer overcoat to support the fuel. Targets of this type, 0.4–0.8 mm in diameter, with 10–30 μm walls, have been developed by the Institute of Laser Engineering at Osaka University, Japan. Reported here are the results obtained from work to extend the method to the future ICF target design. Overcoated foam shells of the proper dimensions were produced, but their optical properties precluded the use of current diagnostics to determine the amount and uniformity of the fuel fill. Briefly outlined are options for improving the optical properties.
Electron cyclotron resonance plasma generation using a planar ring-cusp magnetic field and a reentrant coaxial cavity
Authors: Yasui Toshiaki , Tahara Hirokazu , Yoshikawa Takao
Published: July 2002

An electron cyclotron resonance (ECR) plasma source 16 cm in diameter using a planar ring-cusp magnetic field and a reentrant coaxial cavity was developed. The planar ring-cusp magnetic field produces a large-area ECR surface. The reentrant coaxial cavity forces microwaves to be introduced into the ECR surface from an annular window of a discharge chamber sidewall. This plasma source generated large-area, uniform, and stable plasmas. At 0.079 Pa of discharge chamber pressure for Ar, the plasma uniformity was 11.1% within a 12-cm-diam plane. Above 184 W of forward power, overdense plasmas were produced on the center axis at 0.079 Pa. The maximum Ar plasma density of 1.14×1011 cm−3 was achieved on the center axis at a discharge chamber pressure of 0.079 Pa with a forward power of 437 W.
Creation of extreme high vacuum with a turbomolecular pumping system: A baking approach
Authors: Cho Boklae , Lee Sangtae , Chung Sukmin
Published: July 2002

Pressures in the low 10−12 Torr range are produced by a 200 °C bakeout with a turbomolecular pumping system. A small molecular drag pump in conjunction with the membrane pump turns out to be an effective means of achieving low backing pressures. The stainless-steel test chamber of 6800 cm2 surface area has been prebaked to 450 °C. An ultimate pressure of 1×10−12 Torr is obtained on the extractor gauge and to date this is the lowest pressure attained with turbomolecular pumps only. This system offers simplicity of arrangement, ease of operation, rather low cost, and fast pumpdown to ultrahigh vacuum. The pressure reaches 2×10−9 and 4×10−11 Torr at 2 and 83 h, respectively, after startup without bakeout when vented to atmospheric pressure using extremely dry nitrogen.
Unstable arc operation and cathode spot motion in a magnetically filtered vacuum-arc deposition system
Authors: Zhitomirsky V. N. , Boxman R. L. , Goldsmith S.
Published: July 2002

Arc discharges were established on a Ti cathode in vacuum in an arc deposition system with a toroidal macroparticle filter. A magnetic field with a radial component of up to 3 mT on the cathode surface at the distance of 20 mm from the cathode center was applied in order to drive the cathode spots in an azimuthal motion on the front surface of the cathode, and an axial component of the field of up to 30 mT was applied parallel to the walls of the plasma ducts leading from the cathode region to the substrate in order to collimate the plasma beam. Cathode spot motion was observed by means of a television camera and VCR via a window installed at the substrate holder flange and a mirror located in the quarter torus. Ion current convected by the plasma beam was measured with a negatively biased probe. It was shown that the magnetic field of the coils located on the plasma duct has a strong influence on cathode spot behavior. If they produce a field stronger than 4 mT at the cathode surface, the spots move off the cathode surface, and the probability of their return decreases with stronger fields. The spots moving off the cathode surface cause an increase of the arc voltage and its fluctuations, and the arc becomes unstable and tends to extinguish. Location of the cathode spots on the side of the cathode becomes increasingly likely with increasing duct magnetic field, and results in a decrease in the plasma flux through the plasma duct. An optimal duct field of 16 mT maximized the plasma output flux.
Characterization of amorphous carbon thin films
Authors: Capano M. A. , McDevitt N. T. , Singh R. K. , Qian F.
Published: July 2002

The objective of this study is to develop improved procedures for characterizing amorphous carbon films. Raman spectroscopy is used to characterize amorphous carbon thin films grown by pulsed laser deposition at temperatures between 293 and 873 K. The amount of bond-angle disorder is shown to decrease with increasing substrate temperature. However, a shift of the Raman D peak to higher wave numbers is not observed to coincide with the presumed decrease in sp3 bonding as the deposition temperature increases. The graphitic domain size is shown to initially decrease, pass through a minimum, and then increase as temperature increases. Mass densities, measured independently by x-ray specular reflectometry, are seen to decrease from a maximum of 2.4 g/cm−3 as deposition temperature increases. The trend in the observed density measurements correlates well with the Raman spectroscopy data. The importance of x-ray specular reflectometry as part of a strategy to completely characterize amorphous carbon films is discussed in terms of these data.
Plasma etch modeling using optical emission spectroscopy
Authors: Chen Roawen , Huang Herb , Spanos C. J. , Gatto Michael
Published: July 2002

Plasma etching is often considered a yield limiter in the manufacturing of submicron integrated circuit devices. Much effort has been devoted to developing reliable models that relate the process outputs to variations in real-time sensor signals. These models, called chamber state models, allow semiconductor manufacturers to predict etch behavior. In this article, we propose to use optical emission spectroscopy (OES) as a real-time sensor to quantify and predict the etching performance in an integrated circuit manufacturing line. This method is especially useful in plasma processing because it provides in situ and real-time analysis without disturbing the plasma or interfering with the process. This study is based on an OES system that has been installed on an Applied Materials 5300 Centura dielectric etcher with a single optical fiber connected from the reactor viewport to a spectrograph. A designed experiment was performed on oxide test wafers. Several etch characteristics, including etch rate, within-wafer uniformity, and aspect-ratio dependent etching (ARDE), were modeled in this study. Various modeling techniques such as multivariate principle component analysis, and partial least squares were employed to relate the various OES signatures to etching performance. The results show that 87% of etch rate variation and more than 95% of the variation in within-wafer uniformity can be explained by these models, although the OES signals can only explain 65% of the variation in ARDE.
Comparison of dry etch chemistries for SiC
Authors: McDaniel G. , Lee J. W. , Lambers E. S. , Pearton S. J. , Holloway P. H. , Ren F. , Grow J. M. , Bhaskaran M. , Wilson R. G.
Published: July 2002

SiC has generally been plasma etched in polymer-forming chemistries such as CHF3/O2 or CF4/O2, often with addition of H2 to achieve acceptable surface morphologies. We find that under high ion density conditions gases such as SF6, NF3, IBr, and Cl2 produce smooth surfaces that are free of hydrogen passivation effects. Etch rates in excess of 1500 Å/min are achieved in electron cyclotron resonance (ECR) NF3 or Cl2/Ar discharges with low additional rf chuck powers (100–150 W); dc bias of −120 to −170 V. The rates are somewhat lower (factors of 2–4) with IBr and SF6 chemistries. Ion-induced damage is evident from Hall measurements for SiC exposed to rf powers >150 W (dc bias >−170 V) under ECR conditions and >250 W (dc bias >−275) under reactive ion etch conditions. Efforts to anneal damage at these higher powers reveals a major annealing stage is evident at ∼700 °C, with an activation energy of ∼3.4 eV, but there is significant damage remaining even after 1050 °C annealing. Hydrogen passivation is a problem only in p-type SiC, and is removed at similar temperatures to ion-induced damage by annealing at ∼700 °C under N2 ambients. This is strongly correlated with secondary ion mass spectrometry measurements on deuterated samples annealed at different temperatures.
Surface reaction probabilities and kinetics of H, SiH3, Si2H5, CH3, and C2H5 during deposition of a-Si:H and a-C:H from H2, SiH4, and CH4 discharges
Authors: Perrin Jérôme , Shiratani Masaharu , Kae-Nune Patrick , Videlot Hervé , Jolly Jacques , Guillon Jean
Published: July 2002

The relations between the surface reaction probability β of an atom or a radical in a reactive gas discharge, its diffusive flux to the wall, spatial density profile and temporal density decay during the postdischarge, are examined. Then, the values of β for H, SiH3, and Si2H5 on a growing a-Si:H film, and CH3 and C2H5 on an a-C:H film are derived from the temporal decay of radical densities during the discharge afterglow by using time-resolved threshold ionization mass spectrometry. For SiH3 on a-Si:H, β=0.28±0.03 in excellent agreement with previous determinations using other experimental approaches, and for Si2H5, 0.1<β<0.3. For H on a-Si:H, 0.4<β<1 and mostly consists of surface recombination as H2, while the etching probability of Si as SiH4 is only ε≈0.03 at 350 K in good agreement with other studies of H reaction kinetics on crystalline silicon. At high dilution of SiH4 in H2 the sticking probabilities of Si hydride radicals are affected by the flux of H atoms of hydrogen ions which enhances surface recombination at the expense of sticking. For CH3 or C2H5 on a-C:H it is shown that β is not constant during the discharge afterglow, decreasing from about 0.01 down to 0.001. This reveals that chemisorption of these radicals on the H-saturated a-C:H surface is entirely governed by the competition between desorption and creation of active sites by ion bombardment or H atoms. The differences between the surface reaction kinetics of SiH3 on a-Si:H and CH3 on a-C:H are discussed within a unified model of precursor-mediated chemisorption.
Magnetic field optimization in a dielectric magnetically enhanced reactive ion etch reactor to produce an instantaneously uniform plasma
Authors: Lindley R. A. , Björkman C. H. , Shan H. , Ke K.-H. , Doan K. , Mett R. R. , Welch M.
Published: July 2002

The effect of magnetic field on plasma uniformity was investigated for a capacitively coupled plasma in a dielectric etch chamber and a tool to measure the dc bias uniformity across the high-powered cathode (e.g., 1200 W) was developed. At that power, the dc bias can be as high as 1500 V at 50 mT. A 5% variation in the dc bias across the cathode corresponds to a 75 V potential drop across the wafer, which may in turn cause degradation or breakdown of gate oxide structures. Therefore control of the instantaneous plasma uniformity is important to minimize device damage. The primary effect of the magnetic field on instantaneous plasma uniformity is through the E×B drift force which, because of the strong electric field at the cathode surface at high powers, dominates the other magnetic field effects on the plasma. dc bias measurements show that the plasma nonuniformity can be optimized by adjusting the gradient of the magnetic field, and thus the E×B drift force, across the cathode over a wide range of magnetic field strengths (10–90 G), process pressures (50–250 mT), and cathode powers (750–1100 W), for a CF4/Ar chemistry and 13.56 MHz rf power. Finally, the data analysis method used to improve signal-to-noise is discussed.
Selective inductively coupled plasma etching of group-III nitrides in Cl2- and BCl3-based plasmas
Authors: Shul R. J. , Willison C. G. , Bridges M. M. , Han J. , Lee J. W. , Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Donovan S. M. , Zhang L. , Lester L. F.
Published: July 2002

High-density plasma etching has been an effective patterning technique for the group-III nitrides due to ion fluxes which are two to four orders of magnitude higher than more conventional reactive ion etch systems. GaN etch rates exceeding 0.5 μm/min have been reported in inductively coupled plasma (ICP) etch systems at relatively high dc-biases (>200 V). However, under these conditions, the etch mechanism is dominated by ion bombardment energies which can induce damage and minimize etch selectivity. Development of etch processes with high selectivity has become relevant with recent interest in high power, high temperature electronic devices. In this study, we report ICP etch rates and selectivities for GaN, AlN, and InN in Cl2/Ar, Cl2/N2, Cl2/H2, Cl2/SF6, BCl3/Ar, BCl3/H2, BCl3/N2, and BCl3/SF6 plasma chemistries.
Atomic force microscopy study of the faceting on MgO(110) surface
Authors: Chern G. , Huang J. J. , Leung T. C.
Published: July 2002

Using atomic force microscopy, we have studied the morphologies of the MgO(110) surface. After annealing at 650 °C, this surface facets into elongated triangular mesoscale islands along the [001] direction. A statistical counting of both the widths and the heights of these islands can be well fitted by a Gaussian normal distribution. The most popular island width and height are ∼1200 and 140 Å, respectively, indicating that these faces are roughly (350). The formation of (350) plans, instead of (100), is believed due to a kinetic reason. Besides, both Gaussian distributions are much narrower than predicted for the microscopic terrace-step-kink model. This result may suggest that an island–island interaction is fundamentally different from a step–step interaction.
Growth and characterization of epitaxial fcc Fe wedges on diamond (100)
Authors: Li Dongqi , Keavney D. J. , Pearson J. , Jiang J. S. , Bader S. D. , Keune W.
Published: July 2002

Epitaxial Fe wedges with a thickness gradation from 0 to 20 Å were grown on diamond (100) at room temperature, subsequently annealed, and investigated with reflection high-energy electron diffraction and the surface magneto-optical Kerr effect. The results indicate that for <5 monolayer thicknesses the Fe grows on C(100) as smooth, epitaxial fcc films, which are not ferromagnetic, but that thicker films undergo a transition to become rough and the ordinary bcc ferromagnetic phase.
Pulsed electron-beam technology for surface modification of metallic materials
Authors: Proskurovsky D. I. , Rotshtein V. P. , Ozur G. E. , Markov A. B. , Nazarov D. S. , Shulov V. A. , Ivanov Yu. F. , Buchheit R. G.
Published: July 2002

This article concerns the foundations of a new technology for surface modification of metallic materials based on the use of original sources of low-energy, high-current electron beams. The sources contain an electron gun with an explosive-emission cathode and a plasma anode, placed in a guide magnetic field. The acceleration gap and the transportation channel are prefilled with plasma with the use of spark plasma sources or a low-pressure reflected discharge. The electron-beam sources produce electron beams with the parameters as follows: electron energy 10–40 keV; pulse duration 0.5–5 μs; energy density 0.5–40 J/cm2, and beam cross-section area 10–50 cm2. They are simple and reliable in operation. Investigations performed with a variety of constructional and tool materials (steels, aluminum and titanium alloys, hard alloys) have shown that the most pronounced changes of the structure-phase state occur in the near-surface layers quenched from the liquid state, where the crystallization front velocity reaches its maximum. In these layers partial or complete dissolving of second phases and formation of oversaturated solid solutions and ordered nanosized structures may take place. This makes it possible to improve substantially the electrochemical and strength properties of the surface layers. It has been established that the deformation processes occurring in the near-surface layers have the result that the thickness of the modified layer with improved strength properties is significantly greater than that of the heat-affected zone. Some examples of the use of low-energy, high-current electron beams for improving the performance of materials and articles are given.