bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective reactive ion etching of silicon nitride on oxide in a multifacet (‘‘HEX’’) plasma etching machine
Authors: Stocker Hans J.
Published: July 2002

A two-step process using CHF3 /CO2 and CHF3 /O2 gas mixtures for the reactive ion etching (RIE) of silicon nitride, which allows stopping on thin oxides, is described and analyzed. Taking into account the etch rate of silicon nitride, oxide, and photoresist, the etch rate nonuniformity, and the nonuniformity of the silicon nitride and oxide layers, the etching times can be chosen to insure three conditions: (i) complete removal of all silicon nitride, (ii) a finite fraction of the oxide remaining, and (iii) small linewidth losses. The process has been implemented in an AME 8110 ‘‘HEX’’ plasma etching machine. By controlling the uniformity of the HEX etch rates, it has been possible to etch 1200 Å of silicon nitride on 175 Å of pad oxide with an average of 108-Å oxide remaining (σ=10 Å). The number of stacking faults generated after B implantation and reoxidation is significantly reduced for samples etched with the two-step process as compared with RIE etches in which the pad oxide is removed completely and the Si therefore exposed to the reactive ions during the overetch.
Geometric characterization of macroshell targets
Authors: Alway Peter C. , Scott Larry A. , Martin Alfred J.
Published: July 2002

We are investigating methods to produce and characterize large diameter, uniform shells for beta-heating experiments. A highly spherical cavity fabricated in a glass matrix is processed into a high aspect ratio shell (diameter/wall) by removing the excess glass surrounding the cavity. High silica glass is the preferred material because of its high permeation rates, which reduces the deuterium–tritium fueling time. It also provides great strength and a high degree of chemical durability. Cavity sphericity is a critical parameter for these macroshell targets. Although we do not have a direct method to measure cavity sphericity, it can be inferred by comparing the circularity of multiple planar images. Photographic prints or direct optical images are digitized and evaluated by a computer. Each image is fit to a circle and analyzed using fast Fourier transforms. The output data specify type, magnitude, and position of each nonuniformity. We will discuss the characterization instrumentation and procedures, focusing on instrumentation capabilities and accuracy.
Fundamental aspects of film nucleation and growth
Authors: Tiller William A.
Published: July 2002

At real surfaces, atomic reconstruction generates a surface stress tensor that influences all subsequent surfaces processes like roughening, cluster formation, nucleation, adsorption layer characteristics, and layer flow kinetics. Here, computer simulation results using semiempirical potential energy functions for the Si–Ga–As and Al–Ga–As systems are used to illustrate some important long-range effects on ledge/ledge interaction and cluster excess energy that would not have been anticipated using the conventional dangling bond viewpoint. New insight has also been added to adsorption layer isotherm considerations and an equation for crystal growth velocity, which incorporates gas phase transport, surface transport, ledge attachment kinetics, plus ledge trapping of adsorbate species, is given.
Nanometer-scale roughness study and indentation test with a scanning tunneling microscope
Authors: Yokohata Toru , Kato Koji , Ohmura Kenji
Published: July 2002

The surface roughness of four gold surfaces mechanically finished, three by diamond cutting and one by mechanical polishing, were measured with a scanning tunneling microscope (STM) and with a conventional stylus profilometer. The roughness measurements revealed that the maximum height and the center line average of each profile varied with its representative wavelength. The relationship between roughness parameters and wavelength was almost linear on a logarithmic graph. The indentation tests were done on the best gold surface with a Pt STM probe tip. STM images and profile curves between, before, and after indentation were compared. Most of the valleys around the indentation point changed in depth after contact: some valleys became shallow and other became deep. The tip may become blunt during contact, but the variation of change in depth of valleys is not explained only by the damage of the tip.
Correlation between scanning tunneling microscopy/spectroscopy images and apex profiles of scanning tips
Authors: Nishikawa Osamu , Tomitori Masahiko , Iwawaki Fumikazu , Hirano Nobuo
Published: July 2002

Variations of topographic and current images with bias voltages were examined utilizing the current imaging tunneling spectroscopy (CITS) and dual-polarity tunneling imaging (DPTI) techniques. While the CITS and DPTI images of the Si(111)-(7×7) reconstructed structure at the specimen voltage of +2 V and the DPTI image at −2 V are reliably reproducible exhibiting bright Si adatoms and dark corner holes, the CITS current image at −2 V often showed reversed contrast grey-scale images with bright corner holes. The observed reversed image is explained as the result of the difference in the effective tunneling barrier and the surface state density of the tip apex and specimen, and also as the effect of the atomic arrangement and composition and profile of the tip apex.
Surface defects, gap states, and low-energy modes of degenerately doped n-GaAs(110)
Authors: Kilday D. G. , Margaritondo G. , Lapeyre G. J.
Published: July 2002

We show that information about gap states at semiconductor surfaces and interfaces can be obtained from high-resolution electron energy-loss spectroscopy. This novel approach is based on a careful analysis of low-energy (<0.1 eV) modes, using theoretical spectra derived from a layered spatially dispersive model of the dielectric response.
Ion scattering studies of clean Nb(110) surfaces before and after exposure to hydrogen
Authors: Mingde Xu , Whang C. N. , Smith R. J.
Published: July 2002

The Nb(110) surface was studied using high-energy ion backscattering and channeling (HEIS) to determine the structure of the clean surface, and to measure changes in structure induced by H2 adsorption at the surface and absorption into the bulk material. Measurements with He+ ions channeling in the [1̄1̄0] and [1̄1̄1] directions were made as a function of ion energy (0.6 to 1.8 MeV) and H2 exposure. Computer simulations of the experiment for the clean surface show good agreement with the data using negligible enhancement (≤2%) of the surface-atom vibration amplitudes, and negligible surface relaxation. To obtain agreement with experiment does require that the simulations include reduced bulk atom vibration amplitudes, which simulate the effect of correlated vibrations. Our conclusions are in good agreement with calculations based on experimental phonon frequencies. As the surface is exposed to H2, the Nb surface peak area increases by ∼12% (1 MeV ion energy) in the chemisorption regime (0 to 20 L), followed by a more gradual increase as the H is absorbed into the bulk Nb. We discuss possible explanations for these increases in ion yield in the context of recent models for hydrogen uptake kinetics.
Characterization of electron beam damage in oxidized silicon using thermally stimulated exoelectron emission
Authors: Xiong-Skiba P. , Carroll D. L. , Doering D. L.
Published: July 2002

Silicon dioxide thin films grown on p-type Si(111) wafers were exposed to electron beam irradiation ranging from 1 to 4 keV in energy. Subsequent heating of the samples resulted in thermally stimulated exoelectron emission (TSEE) with several peaks in the emission intensity as a function of temperature. Peaks with temperatures below 450 °C occurred at a fixed temperature for a given oxide, but varied as a function of oxide thickness. This emission is thought to be related to electron desorption from shallow trap states or energetic defects in the near surface region of the oxide and some impurity trap states in the bulk. A high temperature peak was observed which varied in time during heating as a function of sample temperature. This suggests a diffusion limited process where physical defects such as vacancies or interstitials must migrate to the surface to produce emission. The energy and thickness dependence of these emission states are related to the creation of defects and excited states in the thin film and the interaction of these states with the Si substrate.
Spectroscopic studies of carbon impurities in PISCES-A
Authors: Ra Y. , Pospieszczyk A. , Hirooka Y. , Leung W. K. , Conn R. W.
Published: July 2002

The graphite used for the limiter of the tokamak reactor produces carbon-containing molecular impurities as a result of the interactions with the edge plasma. The behavior of these molecular impurities has been studied using emission spectroscopy. The present work includes: (1) finding molecular bands and atomic lines in the visible spectral range, (2) studying the breakup processes of the molecular impurities on their way from the source into the plasma, and (3) developing a spectroscopic diagnostic method for the absolute measurement of the carbon influx resulting from graphite erosion. For these, carbon-containing molecules such as CH4, C2H2, C2H4, CO, and CO2 were injected into the tokamak-boundary-like plasma generated by PISCES-A. Spectrograms of these gases were taken. Many useful bands and lines were determined from the spectrograms. The breakup processes of these gases were studied by observing the spatial profiles of the emission of the molecules and their radicals for different plasma conditions. For the absolute measurement of the eroded molecular impurity flux, the photon efficiency of the lines and bands were found by measuring the absolute number of the emitted photons and injected gas molecules. The chemical sputtering yield of graphite by hydrogen plasma was spectroscopically measured using the previously obtained photon efficiencies. It showed good agreement with results obtained by weight loss measurements.
An accel-mode einzel lens with through-lens energy analyzer for electron beam testing
Authors: Saito Kenichi , Wada Kou , Okubo Tsuneo
Published: July 2002

An accel-mode einzel lens with through-lens energy analyzer is developed to apply a purely electrostatic optical column in low-voltage electron beam testers. A purely electrostatic optical column, enabling use of the accel-mode einzel lens as an objective lens, is also designed. Lens aberration is lowered by reducing focal length. Energy analyzer performance is improved by calculating secondary electron trajectories for the lens. The purely electrostatic optical column provides a 100 nm beam diam and a 0.23 eV energy resolution at beam voltage of 0.5 kV and beam current of 1 nA.
Hydrocarbon coating by laser-induced chemical vapor deposition onto microsphere target levitated by a viscous gas jet
Authors: Katayama H. , Norimatsu T. , Nakai S. , Yamanaka C.
Published: July 2002

A hydrocarbon ablator was uniformly deposited by means of laser-induced chemical vapor deposition (CVD) onto a spherical glass microsphere target, which was levitated by a viscous gas jet flow. The maximum deposition rate was 18.4 nm/min and the uniformity of the coating layer was 98%. The deposition rate was independent of the back pressure ranging from 1×10−2 to 2×104 Pa. The deposition rate increased with the flow rate of the coating gas and with the laser intensity irradiating the microsphere. Optimum condition of the gas flow for stable levitation is also suitable for laser-CVD coating. These characteristics are preferable to coatings on future targets of larger sizes. Characterizations of the coating layer obtained in this work with a scanning electron microscope, a contact x-ray microradiograph, and an optical interference microscope are presented.
Distinguishing thin film and substrate contributions in microindentation hardness measurements
Authors: Feldman Charles , Ordway Fred , Bernstein Jean
Published: July 2002

Microhardness measurements were carried out on silicon, boron, boron nitride, and nickel films deposited on polished stainless steel substrates. A titanium diboride film on a sapphire subsubstrate was also examined. It is shown that a log–log plot of indentation size versus applied load (the Meyer plot) reveals the point at which the substrate begins to influence the hardness measurements. The ratio of indentation depth to film thickness at the critical point varied from 0.06 to 0.4 depending on both film and substrate hardness. The microhardness numbers differ from those calculated from data in the composite (film plus substrate) region by proposed formulas.
Corrugation of Si surfaces and profiles of tip apexes
Authors: Tomitori Masahiko , Iwawaki Fumikazu , Hirano Nobuo , Katsuki Futoshi , Nishikawa Osamu
Published: July 2002

Si(111) surfaces heated at 1300 °C show many steps and terraces exhibiting the (√3×√3) R 30°, c(4×2), (5×5), (7×7), and (9×9) reconstructed structures. A detailed study of the surface corrugation indicates that the observed maximum depth of the corner hole is 2.4 Å and the trace of a scanning tip is close to the profile of the [111]-oriented W tip with a single atom at the apex and the most desirable cone angle of ∼120°. Occasionally, anomalous, ordered structures appeared and were explained as the result of the scanning with two apex atoms 4.5 Å apart, the distance between the nearest surface atoms of the W(111) plane.
Thermal desorption of InSb surface oxides
Authors: Klem J. F. , Tsao J. Y. , Reno J. L. , Datye A. , Chadda S.
Published: July 2002

We have investigated methods of chemical preparation and thermal treatments of InSb substrates to produce InSb surfaces suitable for subsequent molecular beam epitaxy. Etching in a solution of lactic acid: HNO3:HCl was shown to produce an oxide surface layer which could be thermally desorbed. Growth on surfaces prepared in this manner produced precipitate-free substrate–epilayer interfaces.
Sputter deposition of precision Si/Si3N4 Bragg reflectors using multitasking interactive processing control
Authors: Babic D. I. , Dudley J. J. , Shirazi M. , Hu E. L. , Bowers J. E.
Published: July 2002

High quality Si/Si3N4 Bragg reflectors have been fabricated using magnetron sputter deposition. The individual layer characterization and process control were performed using multitasking processing control software that we have designed and implemented onto the sputter-deposition equipment. The experimentally determined Bragg reflector characteristics match very closely with the theoretical model which includes both loss and dispersion in the films. The multitasking processing control software system enables real-time monitoring and control for in-depth process characterization and sequencing. Individual layers, as well as the full structure of ten alternating layers of Si and Si/Si3N4, have been optimized to produce 99.4% reflective mirrors at wavelength of 1300 nm.
Structural transformations in adsorbed oxygen layers on Al surfaces observed using optical second-harmonic generation
Authors: Janz S. , Pedersen K. , van Driel H. M. , Timsit R. S.
Published: July 2002

Optical second-harmonic generation is used in conjunction with Auger electron spectroscopy and low-energy electron diffraction to study the evolution with temperature of oxygen adsorbed on Al (111), (100), and (110) surfaces. For O2 exposures ranging between 34 and 450 L, the adsorbed oxygen undergoes two distinct transformations. As the specimen is heated in vacuum to 350 °C after exposure to oxygen, the adsorbed oxygen reacts with the metal to form an oxide (Al2O3) phase. Above 350 °C the oxide overlayer breaks up into oxide islands. We propose that the island formation mechanism is triggered by the transformation of amorphous Al2O3 to crystalline Al2O3.
Ordering of ethylidyne on clean and adsorbate covered Pd(111): Influence of the coadsorption of oxygen
Authors: Nascente Pedro A. P. , Van Hove M. A. , Somorjai G. A.
Published: July 2002

The adsorption and ordering of acetylene on clean and on oxygen-covered Pd(111) at low temperature (150–170 K) and at room temperature were studied by low-energy electron diffraction and high-resolution electron energy-loss spectroscopy. At low temperature a poorly ordered overlayer of molecularly chemisorbed C2H2 was formed on both clean and O-covered Pd(111). At room temperature C2H2 converted to ethylidyne (C2H3), which weakly ordered in a ((3)1/2×(3)1/2) R30° structure. However, preadsorption of oxygen was found to induce better ordering of C2H3 on Pd(111) by (a) possibly removing the free hydrogen atoms on the surface and (b) interacting with the hydrocarbon species via the coadsorbate induced ordering mechanism. It is proposed that the Pd(111)-((3)1/2×(3)1/2) R30°–O+C2H3 ordered overlayer can arise from a combination of dipole–dipole interaction and charge transfer through the substrate.
Preparation, characterization, and chemical properties of ultrathin MgO films on Mo(100)
Authors: Wu Ming-Cheng , Corneille Jason S. , He Jian-Wei , Estrada Cesar A. , Goodman D. Wayne
Published: July 2002

Ultrathin MgO films have been synthesized under ultrahigh vacuum conditions by evaporating Mg onto Mo(100) in various background pressures of oxygen. Low-energy electron diffraction and surface spectroscopic studies show that the MgO films, prepared under optimum oxidation conditions, grow epitaxially in the 200–600 K substrate temperature range and have an essentially one-to-one stoichiometry. The nature of the near-surface defects of the MgO films grown at low oxygen pressures has been explored using electron energy-loss spectroscopy. Finally, the chemical properties of the stoichiometric MgO films have been investigated using high-resolution electron energy-loss spectroscopy.
Low energy ion beam interactions with electronic polymer surfaces
Authors: Jeong Hyo-Soo , White Robert C.
Published: July 2002

The surfaces of polyimide films have been treated by exposure to low energy ion beam and electron cyclotron resonance plasma prior to metallization in order to understand the effects of ion treatment on adhesion of metallized plastics. Thin metallized structures were tested by the blister test for adhesion measurement. A nonlinear analysis for the test was developed based on local energy balance. Our data show the processed polymer surfaces exhibit one order of magnitude stronger adhesion to metal overlayers than the untreated surfaces, indicating that controlled interphase engineering is important between the two dissimilar materials.
Low temperature oxidation and reduction of ceria particles on Rh(111)
Authors: Belton David N. , Schmieg Steven J.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) was used to study the oxidation and reduction of Ce vapor deposited onto a Rh(111) single crystal in a system which couples a moderate pressure reactor to an ultrahigh vacuum (UHV) analysis chamber. This article compares the behavior of thick (≥50 Å) ceria layers to that of thin (4–8 Å) ceria islands. Using variable takeoff angle XPS and difference spectra we find that the interior of both the thick Ce layers and the thin Ce islands oxidize completely to CeO2 with 1 Torr of oxygen at 475 K; however, the surfaces of both of the cerias are a mixture of Ce+3 and Ce+4. As for reduction, under our conditions (≤525 K) both the thick layers and the thin islands undergo a surface reduction that generates Ce+3. This Ce+3 surface is quite stable and no reduction of the bulk of the material occurs. Whereas the thick ceria layers require high pressures (8 Torr) of CO in order to reduce the surface, the thin islands reduce under UHV conditions—CO adsorbed at 300 K forms CO2 at 475 K during desorption. Further reduction of the thin ceria islands does not occur if they are treated with 8 Torr of CO at 525 K. We conclude that intimate contact with Rh can enhance ceria reduction via reaction with CO which initially adsorbs on Rh. Further, these two cerias are in fact very similar in that the amount of oxygen that they store is proportional to their surface area.
Growth and reactivity of ZnOx on Cu(111)
Authors: Onsgaard J. , Bjo/rn J. A.
Published: July 2002

The oxidation of the Zn/Cu(111) interface has been investigated by the methods of thermally programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). The process has been studied for zinc coverages, θZn, in the 0≤θZn≤3 monolayer (ML) range and for oxygen exposures up to 6000 L O2. It was found that a zinc oxide film formed at 103 K changes its composition to islands of ZnOx, with x≤1, by annealing to 410–523 K with loss of oxygen. The new phase is characterized by three Zn states in the TPD spectra. The sequence of states, ranging from a zinc state at 820 K to Zn++ in ZnO at 978 K, can be correlated with different O(1s) binding energies. One of the three zinc components, positioned at the boundary of the ZnOx islands, reacts with oxygen and is transformed to a state with a higher oxidation step. A model for the zinc oxide formation at the Zn/Cu(111) interface is proposed.
Cyanogen iodide adsorption on Ni(100)
Authors: Marshall K. R. , Jones Robert G.
Published: July 2002

Low energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy have been used to study ICN on Ni(100). On adsorption at room temperature, a poor p(2×1), then a p(2×2), and finally a sharp c(2×2) with a high background were formed with the I, C, and N coverages saturating after ∼2×10−5 mbar s. This surface is thought to consist of adsorbed iodine atoms and CN groups. On annealing to ≊500 K, the CN group dissociated and carbon diffused into the bulk leaving a sharp c(2×10) structure. Further heating caused this structure to transform gradually into sharp p(2×2) after annealing to 650 K with very little change in the coverage of I or N. At T≊800 K, the iodine coverage began to fall rapidly reaching zero coverage by 1000 K, but still with some nitrogen on the surface. Adsorption at 110 K proceeded as for room temperature with dissociation of the molecule in the first layer, but then continued to form multilayers of ICN. On warming back to room temperature the multilayers desorbed by 173 K leaving a molecular monolayer which cracked and/or desorbed on further heating to room temperature. The surface formed in this way had a higher coverage than that formed by direct room temperature adsorption. The chemistry of this adsorption system is discussed, in particular the remarkable ability of the Ni(100) surface to crack the CN bond in the presence of iodine, and the structure of the different surface phases.
Comparative characteristics of plasma etched GaAs and InP
Authors: He L. , Anderson W. A.
Published: July 2002

Plasma etching was performed on GaAs and InP to prepare the surface before Schottky metal deposition. A comparative study was carried out for the two materials to study the influence of CF4 plasma etching on material properties and device characteristics. Photoreflectance (PR) and electroreflectance (ER) spectroscopy measurements were conducted to study the effect of plasma etching on the material surface. The PR and ER spectra showed the introduction of considerable radiation damage by dry etching. Current–voltage (I–V) and deep level transient spectroscopy (DLTS) were used for device characterization and defect level identification. Rapid thermal annealing (RTA) effectively removed the damage which was evident by all test techniques. The Schottky diodes on the GaAs control wafer, the plasma etched wafer, and the wafer after RTA showed barrier heights φB of 0.82, 0.65, and 0.86 eV, respectively. For InP, the plasma etched sample showed such serious damage that no Schottky contact was achieved. For the control wafer and the plasma etched wafer after RTA, the barrier heights obtained were 0.50 and 0.49 eV. The DLTS results showed two trap levels in GaAs with activation energy below the conduction band of 0.634 and 0.397 eV introduced by plasma etching. For both GaAs and InP, the control wafer and plasma etched sample after RTA showed very similar DLTS spectra which indicated the effectiveness of the RTA treatment.
Effect of bulk doping on scanning tunneling microscopy images of GaAs(001)2×4 surfaces
Authors: Gallagher M. C. , Kim J. , Willis R. F.
Published: July 2002

Scanning tunneling microscopy (STM) and tunneling I–V measurements of n and p-type GaAs(001)2×4 surfaces are reported. These substrates were prepared using both migration enhanced epitaxy and conventional molecular-beam epitaxy techniques. A puzzling feature of this surface is that, while it is difficult to obtain empty state images with n-type samples, images can be obtained at positive and negative sample bias on p-type substrates equally well. Neglecting the contribution from states at the surface, we demonstrate that providing the Fermi level remains pinned midgap, the tunnel current should be independent of the bulk dopant. Using the method of dual voltage STM imaging, we verify that, unlike GaAs(110), both the filled and empty state images of p-doped samples are dominated by As related states. We also observe kink defects on the p-type surfaces that have been reported on n-doped samples. We find the number density of kinks is decreased by terminating the epitaxial growth with a layer of intrinsic material, which supports the view that the surface forms these kink defects to accept charge from the dopant atoms in the bulk, acting to pin the Fermi level.
Dynamics of adsorbate-induced restructuring and reaction between adsorbates on Cu and Ni surfaces studied by scanning tunneling microscopy
Authors: Besenbacher F. , Klink C. , Lægsgaard E. , Nielsen L. P. , Ruan L. , Stensgaard I.
Published: July 2002

The interaction of adsorbates such as hydrogen, carbon, oxygen, and sulphur with Cu and Ni surfaces has been studied by scaning tunneling microscopy. The results are briefly reviewed, and it is shown that atomistic scanning tunneling microscopy studies are important for deepening the mechanistic understanding of dynamic surface processes such as adsorbate induced restructuring and surface reactions.
Surface step density oscillation during the growth of YBa2Cu3O7−x and DyBa2Cu3O7−x superconducting thin films
Authors: Chandrasekhar N. , Achutharaman V. S. , Goldman A. M.
Published: July 2002

Intensity oscillations of the specular reflection high-energy electron diffraction (RHEED) beam observed during the growth of YBa2Cu3O7−x and DyBa2Cu3O7−x thin films on (100) SrTiO3 substrates have been analyzed within the framework of an analytical model. Monte Carlo studies have also been carried out. Results of both of these studies are in agreement with experimental data and support the proposition that the RHEED intensity oscillations in these systems are a consequence of changing surface step density, caused by cycles of nucleation and coalescence. Differing time periods for RHEED oscillations of the Dy and Y compounds are shown to be the consequence of differing vapor pressures at the substrate temperature.
Adsorption of Au on InSb(100): A scanning tunneling microscopy study
Authors: Schweitzer M. O. , Leibsle F. M. , Jones T. S. , McConville C. F. , Richardson N. V.
Published: July 2002

The growth of thin films of Au on InSb(100) has been studied by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Adsorption of increasing amounts of gold (up to 6.5 ML) results in gradual disappearance of the LEED pattern. At 0.5 ML coverage, STM images show an even distribution of gold clusters on the well ordered InSb (100)-c(8×2) surface. At higher coverages, the gold layer forms parallel ridges. Upon annealing to 625 K, the LEED pattern changes to a (2√2×2√2)R45° structure. Previous Auger spectroscopy measurements suggest that this is a result of the migration of the Au into the near-surface region of the InSb sample leaving an excess of Sb on the surface. A relatively large sized (≳500 Å × 500 Å) ordered region of this surface is also observed by STM. The local translational symmetry, however, differs from that corresponding to the LEED measurements reflecting the different spatial sensitivities of the two structural probes.
Dual-function remote plasma etching/cleaning system applied to selective etching of SiO2 and removal of polymeric residues
Authors: Yasuda T. , Lucovsky G.
Published: July 2002

A dual-function chamber integrating (i) remote rf plasma-enhanced etching with low energy, <100 eV, ion bombardment and (ii) in situ Si surface cleaning and passivation is described. This plasma-assisted processing system is applied to the etching of SiO2 layers on Si(100) wafers, followed by the removal of the polymeric residues and the passivation of the exposed Si surface. A SiO2 etch rate of ∼5 nm/min was obtained at a CF4 partial pressure as low as 0.25 mTorr. An etching yield with respect to a single ion bombardment was estimated to be 0.38 (SiO2 unit/ion) at a substrate bias of −100 V. Combining in situ mass spectroscopy for end-point detection via the SiF+3 signal, and on-line Auger electron spectroscopy, we have followed the changes in the sample surface as the SiO2 layer was first removed, and the exposed Si surface was eventually contaminated with polymeric residues comprised of C and F. We discuss the effectiveness of in situ exposures to plasma-generated atomic H and/or reactive O in removing these polymeric residues.
Aluminum oxide thin film deposition by reactive ion plating using the cathode system composed of LaB6 disc and Ta pipe
Authors: Takahashi Y. , Nitobe K. , Uramoto J. , Momose T. , Ishimaru H.
Published: July 2002

New type reactive ion plating with the pressure gradient plasma gun is used to deposit aluminum oxide thin films. The plasma gun has a cathode system composed of a LaB6 disc and a tantalum pipe. The 650 ℓ process chamber is made of an aluminum alloy. A 1800 ℓ/s compound molecular pump is used for the main pump. The ultimate pressure of the process chamber is 7.8×10−9 Torr. Argon is used for the carrier gas for the plasma, and oxygen is introduced to the process chamber to produce the oxygen plasma. The electron beam in plasma concentrated with magnetic field is applied to aluminum pellets in the hearth to vaporize the pellets. Aluminum vapor and oxygen radicals interact to make aluminum oxide thin films. The typical deposition rate of an aluminum oxide thin film is 60 Å/s. This film is regarded as a nonequilibrium phase of oxide or hydroxide film. The aluminum oxide thin film deposited on an aluminum alloy plate with constant contents of aluminum and oxygen was locally corroded in wet chlorine gas, but the film with the gradient in oxygen concentration was not corroded. The outgassing of an aluminum oxide thin film with gradient in oxygen concentration deposited on an aluminum plate was one order of magnitude lower than a conventional anodic oxide film formed on an aluminum alloy in sulfuric acid.
Deposition by glow discharge sputtering of thin epitaxial films of Ib–VIII alloys (AgPd, CuPd, CuRh)
Authors: Delplancke M. P. , Reniers F. , Asskali A. , Jardinier-Offergeld M. , Bouillon F.
Published: July 2002

Thin films of CuRh, CuPd, and AgPd were deposited by glow discharge sputtering onto (100) magnesium oxide single crystals. The rhodium and palladium content ranged from 0% to 100% of precious metal and the film thickness was usually between 10 and 100 nm. The composition, epitaxial relationship, crystallinity, and phase diagram were investigated as a function of substrate temperature and target composition. A comparison of the three systems was realized. Conditions of epitaxy were determined for the pure metals and their alloys. The temperature of epitaxy of the alloys, even at very low precious metal concentrations, is close to that of the group VIII elements. The parallel epitaxial relationship between the deposit and the substrate is identical for the three systems, namely (001)[110]d∥(001)[110]s. Various techniques were used to characterize the deposits: grazing incidence x-ray diffraction, electron probe microanalysis, Auger electron spectroscopy, scanning Auger microscopy, pulse polarography, reflection high-energy electron diffraction, transmission high-energy electron diffraction, transmission electron microscopy, and inductively coupled plasma.
Thermal effects on the growth of SiO2 on GaAs(100) by reduction of native oxides
Authors: Jiménez I. , Palomares F. J. , Avila J. , Cuberes M. T. , Soria F. , Sacedón J. L. , Horn K.
Published: July 2002

The reactivity of Si with oxidized GaAs surfaces has been recently proposed as a new pathway to form SiO2/GaAs interfaces. In this work, we study the maximum amount of native oxides which can react with evaporated Si atoms, leading to a complete reduction of the GaAs–oxides. Photoemission techniques, using synchrotron radiation and conventional x-ray sources, were used to monitor in situ the interface formation. The completion of the native oxides reduction is limited to layers around 5 Å thick at room temperature, though substrate heating at 550 K during Si deposition allows this limitation to be overcome. This temperature seems to be high enough to activate the diffusion of the Si monomers to the inner interface so that the reduction process can continue. The reduction process stops when Si monomers cannot diffuse through the Si–oxide layer and Si–Si bonds are formed on top of the oxide layer.
Charging effects in measurements of high-temperature superconductors with high-resolution electron-energy-loss spectroscopy
Authors: Akavoor P. , Phelps R. B. , Kesmodel L. L.
Published: July 2002

We report observations of charging effects in measurements of high-temperature superconductors with high-resolution electron-energy-loss spectroscopy. The source of the charging was found to be a nominally conductive, silver-filled epoxy, such as is commonly used for mounting samples to be cooled in ultrahigh vacuum. The tests performed to confirm the presence of the charging effects and the methods used to overcome these effects are discussed.
Electron cyclotron resonance plasma source for metalorganic chemical vapor deposition of silicon oxide films
Authors: Popov O. A. , Shapoval S. Y. , Yoder M. D. , Chumakov A. A.
Published: July 2002

An electron cyclotron resonance (ECR) plasma source was employed for low-temperature (50–300 °C) metalorganic plasma-enhanced chemical vapor deposition of silicon oxide films. The plasma was excited in mixtures of oxygen and tetraethylorthosilicate vapor, and oxygen and tris(trimethylsiloxy)boron (TTMSB) vapor. The operation pressure range was 1–50 mTorr; oxygen and metalorganic vapor flow rates varied from 10 to 100 sccm. Microwave power (f=2.45 GHz, P=100–1500 W) was introduced into a 15-cm-diam ECR chamber via a microwave quartz introduction window. A static magnetic field in the plasma chamber was generated by two Helmholtz coils. It had intensity near the microwave window, Bvw=875–935 G in a narrow plasma mode, and Bvw=1000–1100 G in a uniform plasma mode. Silicon dioxide films were deposited onto a 10-cm-diam silicon wafer located at 16 cm from the source output. A line-averaged plasma density N̄e was measured with a microwave interferometer (35 MHz) at 11 cm from the source output. In the mixture of TTMSB vapor and oxygen (20 mTorr), N̄e was 1.5–1.7×1011 cm−3 and then decreased as pressure grew. The film deposition rate increased with TTMSB flow rate; it had a maximum value of 1200 Å/min at total pressure of 15–20 mTorr.
Thickness determination of thin oxide layers at the bottom of contact holes of semiconductor devices by Auger electron spectroscopy
Authors: Pamler W. , Mathuni J.
Published: July 2002

Fabrication of electrical contacts in semiconductor device technology can be hampered by the presence of thin oxide layers that may form at the bottom of the contact or via holes as a consequence of the reactive ion etching process. In order to achieve low contact resistances after metallization this oxide thickness must be below some critical value. This article describes a method based upon Auger electron spectroscopy for the thickness determination of such thin oxide films at the bottom of micron-sized contact holes prior to metallization. In this technique, the different Si KLL line shapes of elemental and oxidized silicon are utilized for fitting the measured spectrum with a superposition of Si and SiO2 spectra; the oxide thickness follows from the fitting coefficients. The method is applicable to oxide thicknesses up to ∼10 nm and to contact holes with aspect ratios below ∼1. Systematic errors due to scattering and shadowing effects, and to electron-beam induced damaging are discussed. The method has proven to be extremely important in optimizing reactive ion etching processes.
Vacuum characteristics of an oxygen-free high-conductivity copper duct at the KEK Photon Factory ring
Authors: Hori Y. , Kobayashi M. , Takiyama Y.
Published: July 2002

Oxygen-free high-conductivity copper is a more suitable material than aluminum alloy and stainless steel, which are used in many electron storage rings, because the former has a higher thermal conductivity, a larger shielding power for high-energy synchrotron radiation, and a lower photodesorption coefficient. A copper beam duct was fabricated and an aluminum alloy duct was replaced by the copper duct in the Photon Factory (PF) ring to receive intense synchrotron radiation (SR) from a super-conducting wiggler which can emit radiation with 20 keV critical energy. This installation can also help us verify whether or not the experimental results concerning photodesorption obtained in the beamline can be re-obtained in a practical ring. The copper duct exhibited good vacuum characteristics, and the surface treatment that we adopted in both the experimental duct and real duct has been demonstrated to be suitable for reducing the photodesorption yields. The final photodesorption yields of the copper duct have been less than 10−6 molecules/photon.
Static secondary ion mass spectrometry and x-ray photoelectron spectroscopy for the characterization of surface defects in paper products
Authors: Istone William K.
Published: July 2002

In many cases the surface chemistry of paper plays an important role in the performance of the paper in its end use. Differences in surface chemistry of paper can result from both intentional and unintentional changes in chemical additives and manufacturing processes. Examples of the impact of surface chemistry on end use performance include: ink or toner wetting and adhesion in printing, polymer adhesion in lamination and extrusion, slip due to changes in coefficient of friction, and visual defects. While paper represents a less than ideal specimen for classical surface analysis, x-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) are two techniques that can be used successfully to characterize defects in paper that are due to changes in surface chemistry. In this presentation, some of the problems associated with the surface analysis of paper by XPS and SIMS will be discussed along with several examples detailing successful characterization of surface defects in paper utilizing these techniques.
W nucleation on TiN from WF6 and SiH4
Authors: Lantz S. L. , Bell A. E. , Ford W. K. , Danielson D.
Published: July 2002

The chemical reactions of WF6 and SiH4 with reactive ion sputtered TiN surfaces have been studied in ultrahigh vacuum. Auger electron spectroscopy was used in situ to study the surface reactions from 300 to 550 °C. The effects of O and C surface contamination due to atmospheric exposure are characterized and comparisons are made to substrates sputter cleaned in vacuo. The WF6+TiN reaction exhibits linear growth rates over the range of temperatures studied. TiN surface oxidation reduces the initial WF6 reaction probability from ∼0.8 to <0.1, and increases the effective activation energy from 0.04 to 0.62 eV. Surface C has no effect on the reaction. A simple kinetic model is presented that describes the uptake of W on either clean or oxidized TiN surfaces. The exposure of TiN to SiH4 results in the deposition of Si with a reaction probability of ∼10−4. Auger peak shapes indicate that Si is bonded to O on oxidized TiN surfaces and elementally or as SiN on sputter cleaned TiN. When the TiN was exposed first to WF6 the SiH4 reaction probability for subsequent exposure increased to 0.06.
Model of an 80 K liner vacuum system for the 4.2 K cold bore of the Superconducting Super Collider 20 TeV proton collider
Authors: Turner W. C.
Published: July 2002

In this article we discuss a model for an 80 K liner system for the beam tube vacuum of the Superconducting Super Collider (SSC). The liner is a coaxial perforated tube fitting inside the ∼4.2 K bore tube of the SSC magnet cryostats. A liner of this type is useful for pumping the gas desorbed by synchrotron radiation out of the view of the synchrotron radiation and for decoupling the beam current from the 4.2 K refrigeration plant capacity. Addition of cryosorber on the bore tube, e.g., charcoal, greatly increases the H2 sorption capacity compared to the bare metal surface, thus lengthening the time between beam tube warmups. The model equations are useful for estimating the performance of the beam tube vacuum and for defining the experimental information necessary to make a prediction. Some analysis is also presented for 4.2 and 20 K liners and a simple 4.2 K beam tube without a liner.
Simultaneous dual-element analyses of refractory metals in naturally occurring matrices using resonance ionization of sputtered atoms
Authors: Calaway W. F. , Wiens R. C. , Burnett D. S. , Pellin M. J. , Gruen D. M.
Published: July 2002

The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed.
Probing the interfacial properties of poly(vinyl acetate-ethylene) copolymer/poly(vinyl chloride) laminations by time-of-flight secondary ion mass spectrometry
Authors: Cornelio Clark Paula A. , Gardner Sharon A. , Horwat David
Published: July 2002

A better understanding of polymer interfaces is being driven by the need to develop new materials for coating and adhesive applications. Poly(vinyl acetate-ethylene) copolymers (VA-E) are a class of water-based adhesives which find wide application in the wood products industry. Here, we report on our efforts to understand how poly(vinyl chloride) (PVC) composition can impact adhesive performance when the PVC is laminated to particle board using a VA-E adhesive. We find that high levels of plasticizer and lubricants on the surface of the PVC adversely affect adhesive performance. We believe these compounds form a weak boundary layer at the interface between the PVC and the adhesive and contribute to adhesive failure between the PVC and adhesive. Time-of-flight secondary ion mass spectrometry is a very powerful analytical tool for identifying these additives, particularly when the compounds are present at or below the detection limits of either attenuated total reflectance-infrared spectroscopy or x-ray photoelectron spectroscopy.
High rate–low temperature deposition of silicon dioxide films by remote plasma enhanced chemical vapor deposition using silicon tetrachloride
Authors: Alonso J. C. , Ramírez S. J. , García M. , Ortiz A.
Published: July 2002

Silicon dioxide films have been deposited at rates as high as 1100 Å/min and substrate temperatures as low as 200 °C by a remote plasma enhanced chemical vapor deposition (RPECVD) process using mixtures of silicon tetrachloride, oxygen, hydrogen, and argon. The films were characterized by ellipsometry, chemical etch rate, infrared transmittance, and electrical measurements. Infrared transmittance, refractive index, and etch rate measurements reveal that these oxides are free of Si–OH and Si–H bonds, and their structural quality is close to that of thermal CVD oxides. The electrical quality of the as-deposited oxides, incorporated in metal–oxide–semiconductor structures, is equivalent to that reported previously for RPECVD oxides deposited from the same mixture at significantly lower deposition rates. The application of these oxides in the fabrication of some multilayer devices such as alternating current electroluminescent devices is briefly described.
15N hydrogen depth profiling measurements of candidate superconducting supercollider beam pipe materials
Authors: Ruckman M. W. , Strongin Myron , Lanford W. A. , Turner W. C.
Published: July 2002

Photodesorption of gas, particularly H2, by synchrotron radiation in the proposed next generation of superconducting proton colliders is a critical issue confronting the design of the vacuum system. As an initial step in understanding the source of this hydrogen, we report measurements of the surface and bulk concentrations of hydrogen in candidate beam tube materials and compare the surface concentration to the amount of H2 desorbed in photodesorption experiments. Hydrogen profiling measurements using the 6.4 MeV H(15N,αγ) 12C resonant nuclear reaction were performed on representative vacuum system materials including stainless steel, stainless steel electroplated with copper, and high purity bulk copper. All of the Cu samples examined had a hydrogen-rich surface layer <100 Å thick containing 2–5×1016 H atoms/cm2 and a bulk concentration of approximately 1% atomic hydrogen.
Resonant photoemission studies of the thickness dependence of the unoccupied Gd 5d bands
Authors: Dowben P. A. , Li Dongqi , Zhang Jiandi , Onellion M.
Published: July 2002

Ultrathin Gd films have been studied with constant initial-state spectroscopy (CIS) of photoemission utilizing linearly polarized light of synchrotron radiation. The photoemission cross section of the 5d surface state near EF shows strong photon energy dependence, i.e., sharp peaks in CIS spectra near the Gd 5p1/2 absorption edge. These peaks originate from resonant photoemission processes involving the occupied 5p and unoccupied 5d levels of the surface atoms. The symmetry of the unoccupied states were determined experimentally by changing the polarization of light, where p-polarized light excites only to the unoccupied dz2 or dxz,yz states and s-polarized light to all the d states including dx2−y2 and dxy states. Based on the symmetry assignments, the lower bound of the exchange splitting of the Gd 5dz2 surface state can be abstracted, which increases when the thickness of Gd film decreases and reach maximum at the monolayer limit.