bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonant inductive plasma etching evaluation of an industrial prototype
Authors: Henry D. , Francou J. M. , Inard A.
Published: July 2002

The development of the resonant inductive plasma etcher was undertaken in order to satisfy the ultra large scale integrated manufacturing requirements. We present in this article an evaluation of this equipment, based upon test processes as support for pointing out the specific advantages and limitations of the reactor. Plasma chemistries such as SF6 and HBr have been studied. Silicon trench etching and polysilicon gate etching results are reported. Studies have been made at both low-pressure range (1 μbar), and at higher pressure range (7 μbar), even though the equipment was not optimized for this operating pressure range. We present successful results for polysilicon gate etching at low pressure; whereas for trench etching, we show that a higher pressure is more suited to satisfying the requirements of such a process.
Electrochemical and in situ atomic force microscopy and scanning tunneling microscopy investigations of titanium in oxalic acid solution
Authors: Brown Gilbert M. , Thundat T. , Allison D. P. , Warmack R. J.
Published: July 2002

The growth of an oxide film and the dissolution of the metal were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for titanium electrodes which had been pretreated by a chemical polishing procedure. Images were obtained with a gas–solid interface and under an aqueous solution containing 0.1 M oxalic acid. The electrochemical polarization of titanium in 0.1 M oxalic acid is qualitatively the same as observed in chloride or sulfate medium, and the dissolution reaction in oxalic acid appears to follow the same monolayer coverage mechanism as in the other media. The titanium specimen is polycrystalline and the presence of grain boundaries between individual crystallites is observed by AFM. In situ microscopy indicates that both the rate of growth of oxide and the dissolution of the metal are dependent on the crystallographic face of the titanium. AFM and STM show that the growth of titanium (IV) oxide or hydrous oxide has the appearance of hemispherical domes which grow together to form peaks on the surface. Dissolution of the metal in the active region occurs first in areas between the peaks where the oxide is thin, and later the oxide coverage of the small peaks appears to coalesce to a smaller number of large peaks.
Interaction of aliphatic acids and alcohols with aluminum surfaces
Authors: Underhill R. , Timsit R. S.
Published: July 2002

The present work examines the interaction of propanoic acid and 1-propanol, 1-butanol, 1-ethanol, and 1-hexanol with clean, oxidized, and anodized aluminum to identify the nature of the chemical bond on these surfaces. The investigations were carried out by x-ray photoelectron spectroscopy, at temperatures ranging from ∼20 to 500 °C. Initially at room temperature, chemisorbed acid molecules break up on clean Al, leading to attachment of aliphatic chain fragments to the surface via carbon atoms. As adsorption continues, acid molecules react with Al via the functional group to oxidize the surface. In contrast, aliphatic alcohols chemisorb on clean Al via the functional group alone. At elevated temperatures, the acid and alcohols dissociate on the clean surface along similar reaction paths. On oxidized and anodized surfaces, the acid and alcohols chemisorb via the functional group and desorb at elevated temperatures without molecular dissociation.
Testing of turbomolecular pumps
Authors: Basford James A.
Published: July 2002

Turbomolecular pumps (TMPs) are used to provide clean pumping to attain pressures down into the 10−10 Torr range. Some of our data indicated that the pumping speeds and compression ratios claimed by some manufacturers of TMPs were greatly overstated. To measure these parameters, an apparatus was constructed following AVS recommended practices. Hydrogen, helium, nitrogen, and argon were used as test gases, with their flow rates controlled to provide inlet pressures over the range 10−6–10−2 Torr for pumping speed measurements and exhaust pressures over the range 0–1 Torr for compression ratio measurements. Ten pumps from eight manufacturers were tested, all with 6 in. o.d. Conflat flanges at their inlets. Wide variations were found between the pumps, with the specifications of the manufacturers met by only a few pumps. Pumping speeds varied from 0.3 to 1.1 times those specified by the manufacturers. Compression ratios were frequently exaggerated by a factor of 10 or more. As expected, four of the pumps, equipped with coaxial molecular drag pumping sections, had much larger compression ratios than conventional pumps, particularly for the light gases.
Manifestation of electric dipole selection rules in angle resolved photoemission spectra from zinc blende semiconductors
Authors: Niles David W. , Höchst Hartmut
Published: July 2002

We use angle resolved photoemission spectroscopy to determine critical point energies of the Γ7, Γ8, and X6 levels and the valence band dispersion E(k) along the [100] direction of Cd0.8Zn0.2Te. The experimental analysis is carried out without assuming any specific form of the final state bands. Normal emission valence band spectra provide clear evidence of a band gap opening in the final state bands. The crystal potential, which perturbs the final states, causes the conduction band Γ point at ∼12.5 eV to split by ≥0.60 eV. In addition to this very pronounced band gap, we find smaller gaps in the final states at k vectors ∼1/3 and 2/3 towards the X point. Relying on structural arguments, we also deduce the symmetries of the final state bands.
Plasma-enhanced metalorganic chemical vapor deposition of BaTiO3 films
Authors: Van Buskirk Peter C. , Gardiner Robin , Kirlin Peter S. , Krupanidhi Salora
Published: July 2002

BaTiO3 films have been grown by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) for the first time. The BaTiO3 films were grown on Pt-coated Si substrates in an inverted vertical reactor with a remote O2 plasma at 450 mTorr. Plasma powers exceeding 10 W reduced or eliminated the presence of CO3 in the as-grown films at 525 and 600 °C, respectively. Films deposited at 600 °C by PE-MOCVD were polycrystalline BaTiO3 with perovskite structure and partial texture in the [100] direction; films grown at 525 °C were amorphous. The polycrystalline BaTiO3 films had dielectric constants as large as 300, loss tangents of 0.02, and resistivities exceeding 109 Ω cm at room temperature.
A high resolution electron energy loss spectroscopy study of trimethylgallium decomposition on gallium rich GaAs(100)
Authors: Zhu X.-Y. , White J. M. , Creighton J. R.
Published: July 2002

The adsorption and decomposition of trimethylgallium (TMGa) on the gallium rich (4×6) and (1×6) GaAs(100) surfaces have been studied by high resolution electron energy loss spectroscopy (HREELS), in conjunction with temperature-programmed desorption, x-ray photoelectron spectroscopy, and low energy electron diffraction. TMGa adsorbs molecularly at 108 K and dissociates above 200 K to form monomethylgallium (MMGa) and, possibly, some dimethylgallium surface species. Above 400 K, MMGa dominates. Surface MMGa remains stable until 650 K, above which temperature methyl radicals desorb. HREELS results showed unambiguously that methyl groups remain intact throughout the thermal decomposition of TMGa on GaAs(100). The effect of UV photons on both surface TMGa and MMGa has also been investigated, but no photochemistry was observed at wavelengths longer than 230 nm.
Cosputtered films of mixed TiO2/SiO2
Authors: Laird R. , Belkind A.
Published: July 2002

A series of experiments to develop thin films composed of mixed oxides by reactive cosputtering from two different C-MAG (C-MAG is Reg. U.S. Pat & Tm. Off) cathodes (titanium, silicon) is discussed. The depositions were produced in a production scale coating machine capable of coating substrates of one meter square and larger. The optical, mechanical, structural, and chemical properties are also presented in this paper.
Lubrication by molecular monolayers at Ni–Ni interfaces
Authors: Gellman Andrew J.
Published: July 2002

An ultrahigh vacuum (UHV) tribometer has been used to study the frictional properties of sulfided Ni(100) surfaces modified by molecular films of ethanol ranging in thickness from submonolayer to multilayer. The instrument has been designed to allow preparation and characterization of the surfaces of pairs of metal single crystals under UHV conditions. Friction (shear) and adhesion (tensile/compressive) forces can then be measured between the two while in sliding contact. We observe very high and erratic friction forces between two Ni(100) surfaces with c(2×2) overlayers of sulfur. Adsorption of ethanol at coverages of greater than one monolayer results in a decrease in the coefficient of friction and sliding of one surface over the other with a well defined coefficient of friction.
Internally detected electron photoexcitation spectroscopy on heterostructures
Authors: Coluzza C. , Margaritondo G. , Neglia A. , Carluccio R.
Published: July 2002

We applied the internal photoemission technique to the direct observation of deep levels together with barrier heights and band discontinuities at different semiconductor heterostructure interfaces. Its performances and capabilities are superior to those of established techniques: the energy resolution is excellent and it can be applied to ‘‘real’’ device interfaces under bias. The technique was successfully tested for the Pd/n–GaAs and Pd/a-Si:H Schottky barriers as well as for the a-Ge/n-GaAs and a-Ge/p-GaP heterojunctions. We found a Pd/n-GaAs Schottky barrier height of 0.78 eV and an a-Ge/n-GaAs valence band discontinuity of 0.42 eV; in both cases the Fermi level was ‘‘pinned’’ at an averaged value of 0.76±0.03 eV above the top of the GaAs valence band. Furthermore we directly measured a feature at 1.09 eV, due to Pd-induced empty states ∼1.1 eV above the valence band. The Pd/n-GaAs Schottky barrier also exhibits a feature at 1.36 eV, explained by transitions from the valence band to a localized state, made possible by the band bending. In the case of a-Ge/n-GaP we found a ΔEV = 0.88 ± 0.05 eV and a ΔEC = 0.68 ± 0.05 eV. Finally, in the Pd/a-Si:H Schottky barrier, we demonstrated the contribution of resonant tunneling through localized states of the conduction band.
Secondary ion mass spectrometry for characterizing photopatterned, self-assembled monolayers on gold
Authors: Frisbie C. Daniel , Wollman Eric W. , Martin John R. , Wrighton Mark S.
Published: July 2002

Secondary ion mass spectrometry (SIMS) can be used to determine the lateral distribution of molecular photoproducts in a photopatterned, self-assembled monolayer (SAM) on Au. The photosensitive SAMs, Au-I, are made by immersing evaporated Au films into a solution of a disulfide with a pendant aryl azide. Near-UV irradiation (λ≳320 nm) of these SAMs through a Cr-on-glass mask and a thin film of N-(2,2,2-trifluoroethyl)-N-(2-ferrocenylethyl) amine, II, results in the photoattachment of II to the Au surface where irradiated. Cyclic voltammetry establishes the presence of 2.8×10−10 mol/cm2, or about one monolayer, of ferrocene centers on the irradiated substrate. Positive SIMS survey spectra of the photosensitive Au-I SAMs show several peaks assigned to the aryl azide functionality. Survey spectra of Au-I substrates irradiated in the presence of II show peaks assigned to ferrocene fragments. Importantly, the high lateral resolution imaging capability of SIMS is used to map the lateral distribution of molecular and elemental species in a SAM photopatterned with II. The lateral resolution demonstrated was 10 μm. The chemical maps for C12H12Fe+ (m/z 212) and F− (m/z 19) reproduce the pattern of the mask. An important manifestation of the exceptional sensitivity of SIMS is the speed of image acquisition. Maps are generally acquired in less than 30 s with total ion doses of ∼1013 ions/cm2. A damage study was made showing counts for ions with m/z 27, 56, 197, and 212 as a function of primary ion dose. The half-life for the C12H12Fe+ (m/z 212) fragment was approximately 8.5 min at 45 nA/cm2 primary beam current density. This is ≳15 times longer than it takes to acquire a well-resolved image of m/z 212 distribution in a patterned SAM.
Deposition of Y2O3 by plasma enhanced organometallic chemical vapor deposition using an electron cyclotron resonance source
Authors: Varhue W. J. , Massimo M. , Carrulli J. M. , Baranauskas V. , Adams E. , Broitman E.
Published: July 2002

Deposition of Y2O3 films on Si is of interest due to its use as a heteroepitaxial dielectric material to obtain Si-on-insulator or as an epitaxial buffer layer for the growth of YBa2Cu3Ox, high temperature superconductors on Si. In this investigation, Y2O3 films have been deposited in the downstream location in an electron cyclotron resonance oxygen plasma using an organometallic Y source. The reactor pressure was varied which resulted in changes in the ionic and atomic oxygen flux as well as the energetic ion bombardment of the substrate. The deposited material has been characterized by reflected high-energy electron diffraction, x-ray diffraction, Rutherford backscattering spectrometry, and atomic force microscopy. The majority of the films appear to be highly oriented, textured films. Deposition of the (111) phase is preferred, even on the (100) substrate.
Gas porosity formation in epitaxial TiN films deposited by reactive magnetron sputtering in mixed Ar/N2 discharges
Authors: Kazansky P. R. , Hultman L. , Ivanov I. , Sundgren J.-E.
Published: July 2002

Transmission electron microscopy (TEM) has been used to study gas porosity in epitaxial TiN films grown on MgO (001) by reactive magnetron sputtering in mixed Ar/N2 discharges at a total Ar+N2 pressure of 1 mTorr while varying the Ar partial pressure PAr from 0 to 0.9 mTorr. During film growth the substrate temperature Ts was kept at 750 °C, and an applied negative substrate bias Vs of 350 V was used to obtain a flux of Ar+ and N+2 ions impinging on the growing film surface. The size distributions of gas bubbles formed during deposition were obtained from TEM analysis of TiN films grown at different PAr. It was found that an increase in PAr, while changing the relative amount of trapped Ar and N which precipitate into bubbles, also leads to a decrease in mean bubble diameter from ∼8 nm at PAr=0 to ∼2 nm at PAr=0.5 mTorr and to ∼1 nm at PAr=0.9 mTorr. Such a strong dependence of bubble diameters on the composition of the gas trapped within the bubbles suggests that gas solubility is an important factor responsible for differences in bubble nucleation and growth kinetics. It is shown that gas dissociation controlled resolution and reabsorbtion of nitrogen is the dominating mechanism responsible for the growth of large N2 bubbles. Surface diffusion controlled migration and coalescence of bubbles only provides a limited coarsening of predominantly the Ar-containing bubbles.
Electrical and optical properties of ion beam sputtered ZnO:Al films as a function of film thickness
Authors: Qu Y. , Gessert T. A. , Ramanathan K. , Dhere R. G. , Noufi R. , Coutts T. J.
Published: July 2002

Electrical and optical properties of as-deposited, ion beam sputtered, Al-doped ZnO films have been studied as a function of film thickness and carrier concentration. Hall effect measurements reveal that the bulk electrical resistivity of the film generally decreases with increasing film thickness. Additionally, it is observed that the rate of decreasing resistivity depends on the particular film thickness regime. For thinner films (100–200 nm), the resistivity decreases rapidly with increasing film thickness and is due to increases in both carrier concentration and Hall mobility. However, for thicker films, the resistivity decreases more slowly with increasing film thickness and approaches a nearly constant value at a thickness of 1100 nm. In this thickness regime, the slight decrease in resistivity with increasing film thickness is found to be due to an increase in carrier concentration alone. The above observations suggest the presence of at least two scattering mechanisms. It is speculated that grain boundary and ionized impurity are the most likely mechanisms. These issues, together with observed optical properties of the films, are discussed.
Growth mechanism and surface alloy formation of Ni on Pt(110) surface
Authors: Fu T. I. , Liao P. C. , Shern C. S.
Published: July 2002

Low-energy electron diffraction (LEED) and Auger electron spectroscopy were used to observe the growth mode of a nickel thin film on a Pt(110)-(1×2) surface at room temperature. The Auger uptake curve of this system shows a premonolayer break and a monolayer break with an initial linear growth. The LEED pattern changes from (1×2) to (1×1) after half a monolayer of Ni is deposited on the substrate. The LEED pattern then shows a gradual diminishing of all spots when more layers of the Ni thin film are deposited on the Pt(110) surface. These results demonstrate that the initial growth of Ni on the Pt(110)-(1×2) surface follows the Stranski–Krastanov mode; growth of 11/2 monolayer followed by agglomeration into three-dimensional islands. The growth mechanism is discussed. A surface alloy film then forms by heating this surface at T=350 °C.
Flux measurement of a hyperthermal atomic oxygen beam
Authors: Davidson Mark R. , Hoflund Gar B. , Outlaw R. A.
Published: July 2002

A method has been developed and is described for measuring the flux of a beam of hyperthermal oxygen atoms using a quadrupole mass spectrometer. The accuracy of this method has been assessed by adsorbing the O atom flux on a Au surface for a specified period of time and quantifying the adsorbed amount using ion scattering spectroscopy and by estimating the oxygen-atom flux from the electron stimulated desorption parameters used to produce the oxygen-atom beam.
Surface reactivity of Zr–V–Fe getter alloys exposed to H2O, CO, and O2 at 300 and 700 K
Authors: Vedel I. , Schlapbach L.
Published: July 2002

The surface analysis of Zr–V–Fe getter alloys by means of x-ray photoelectron spectroscopy shows that the H2O and CO dissociation to form metal oxides and carbides is less important than the O2 dissociation at 300 K. These results are well correlated with theoretical and experimental dissociation energies for the molecules on metal surfaces. A thin passivated layer formed on the metal surface after 1 L CO exposure prevents further CO molecules from dissociating, but O2 dissociation continues. Heating the Zr–V–Fe getter up to 700 K yields an increase of H2O and CO dissociation. The metal surface is less oxidized after O2 exposure at 700 K than at 300 K because oxygen atoms diffuse from the surface into the bulk.
Linear thermal expansion coefficient and biaxial elastic modulus of diamondlike carbon films
Authors: Blech Ilan A. , Wood Peter
Published: July 2002

Diamondlike carbon films were deposited on silicon, gallium arsenide and aluminum substrates using ion-assisted chemical vapor deposition. The stress of these films was measured as a function of temperature between 25 and 150 °C. Using the stress-temperature measurements, the average linear thermal expansion coefficient was found to be 2.3 ppm/°C, while the biaxial elastic modulus 1.74×1011 Pa.
Electron and hole spin lifetimes in Zn1−xMnxSe and Zn1−yFeySe based heterostructures
Authors: Jonker B. T. , Warnock J. , Fu L. P. , Yu W. Y. , Chou W. C. , Petrou A.
Published: July 2002

We have studied carrier spin relaxation in diluted magnetic semiconductor (DMS) epilayer and spin superlattice samples using polarization and magnetic field dependent photoluminescence. The giant Zeeman splitting of the DMS materials permits unambiguous identification of electron and hole excitonic spin relaxation times. We find that the heavy hole spin lifetime τhs is comparable to the radiative recombination time τr, and substantially longer than the electron spin lifetime τes, with τhs/τr≊4 and τes/ τr≊0.06. We attribute these long spin lifetimes to the strain induced splitting of the bulk degenerate light and heavy hole bands, which inhibits mixing of the hole spin states and subsequent heavy hole spin flip relaxation processes. In the regime of weak confinement, the spin relaxation times are independent of the degree of quantum confinement, the number of interfaces, the magnetic ion concentration, and the magnetic species. We conclude that spin flip via exchange scattering between the carriers and magnetic ions is not the dominant excitonic spin relaxation mechanism.
Infrared absorption spectroscopy for monitoring condensible gases in chemical vapor deposition applications
Authors: O’Neill James A. , Passow Michael L. , Cotler Tina J.
Published: July 2002

In situ infrared absorption spectroscopy is used to monitor the delivery of condensible gases in chemical vapor deposition (CVD) systems. A Fourier transform infrared (FTIR) spectrometer has been configured to enable simultaneous measurements of the concentrations of multiple gases which are critical to the performance of CVD processes. In the deposition of silicon dioxide (SiO2) films using tetraethylorthosilicate (TEOS) and ozone (O3), IR measurements of the concentration of gas-phase TEOS closely track the deposition rate of SiO2. In doped oxide deposition processes, the percentage of phosphorous in the film is predicted from infrared measurements of the concentration of the dopant precursor gas [trimethylphosphene (TMP)]. These capabilities provide improved control of the delivery of condensible gases in CVD systems without the use of test wafers, and they enable the detection of failures in the gas delivery system in real time.
Influence of an external axial magnetic field on the plasma characteristics and deposition conditions during direct current planar magnetron sputtering
Authors: Ivanov I. , Kazansky P. , Hultman L. , Petrov I. , Sundgren J.-E.
Published: July 2002

The magnetic field distribution between substrate and target in a dc magnetron sputtering system was altered by superimposing an axially symmetric external magnetic field Bext to the original field of the magnetron source. The magnetron was operated with a Mo target and Ne, Ar, and Kr discharges were investigated. The plasma parameters in the substrate vicinity were measured as a function of Bext using both cylindrical and flat Langmuir probes. It was found that the variation of the magnetic field strength caused large changes in the plasma parameters, such as charge carrier density, plasma and floating potentials, electron temperature, and electron energy distribution function while the cathode discharge processes remained unchanged. The Mo deposition flux was found to be independent of Bext, but the ion saturation current to the negatively biased substrate holder could be changed by a factor of ∼50 by varying Bext. In addition to the ion flux, the two other sources of energetic species arriving at the substrate—the sputtered Mo atoms and the reflected Ne, Ar, and Kr neutrals from the target were calculated using a trim computer code and taking into account gas phase scattering en route between target and the substrate.
Aligned Au–Si eutectic bonding of silicon structures
Authors: Shoaf S. E. , Feinerman A. D.
Published: July 2002

A technique for precisely aligning structures before a Au–Si eutectic bond has been developed. A (100) silicon wafer is anisotropically etched to create v grooves around the periphery of the structure to be bonded. Gold is then deposited onto one of the wafers prior to dicing into individual die. Optical fibers are used as precision locating keys and align the structure when it is assembled. The entire structure is then placed onto a hot chuck at 400 °C. An ultrasonic transducer is used to aid the Au–Si bond. The fibers may be removed after bonding. Current results have shown a maximum misalignment of 5 μm for a 1 cm×1 cm die. This accuracy is achieved with the entire assembly being done by hand without the aid of a microscope or micropositioners. This technique allows a sensor die to be precisely bonded to an electronics die.
Metastable argon beam source using a surface wave sustained plasma
Authors: Bannister M. E. , Cecchi J. L.
Published: July 2002

A new source of metastable argon atoms in the thermal energy range is reported. The source is based on expanding a plasma sustained by electromagnetic surface waves in a quartz tube through a converging nozzle and extracting a beam from the supersonic free-expansion jet. The beam was characterized by time-of-flight measurements which yielded the absolute intensity and velocity distribution of the argon metastables. The source produced a maximum intensity of 6.2×1014 metastables per second per steradian, the highest time-averaged intensity of thermal argon metastables of any source reported to date. A simple picture of an expanding plasma in a recombination regime is used to explain the dependence of the metastable intensity on absorbed power.
Deposition of gallium oxide and indium oxide on GaAs for in situ process use by alternating supply of TEGa, TMIn, and H2O2 as surge pulses
Authors: Ozasa Kazunari , Ye Tianchun , Aoyagi Yoshinobu
Published: July 2002

Deposition of gallium oxide and indium oxide on GaAs (001) was investigated by the alternating supply of triethylgallium (TEGa) or trimethylindium (TMIn), and hydrogen peroxide (H2O2). A pressure-control method was newly developed to produce precisely controlled surge pulses of source gases. Strong temperature dependence of the growth rate per source cycle obtained for the oxide deposition was caused by the decomposition of metalorganics, and by the thermal desorption of the oxide during the deposition. A critical thickness of 20 nm for the thermal desorption of gallium oxide was observed, which gives the upper limit of the promotive effect of underlying GaAs on thermal desorption of gallium oxide. With implications for in situ process use, deposition of GaAs on gallium oxides and on indium oxides was performed by chemical beam epitaxy, and the differences between the two oxides were discussed from the viewpoint of gallium-atom-induced desorption and selectivity for GaAs deposition.
DNA nanoconstructions
Authors: Seeman Nadrian C. , Zhang Yuwen , Chen Junghuei
Published: July 2002

The control of structure on the nanometer scale is central to nanotechnology. We are pursuing this end with synthetic DNA, whose sequence is selected by sequence symmetry minimization algorithms, so that it can form branched junctions. These structures can be ligated together in the same way that linear DNA is ligated in molecular cloning. Ligating branched structures generates stick figures whose edges consist of double helical DNA and whose vertices are branch points. We have built a DNA molecule whose helix axes have the connectivity of a cube. The vertices are separated by two helical turns of DNA; hence the plectonemic nature of DNA makes this molecule a hexacatenane, each of whose cyclic strands corresponds to a face. We have developed a solid-support-based procedure to implement these constructions. Using the solid-support-based methodology we have constructed a molecule whose helix axes have the connectivity of a truncated octahedron. This figure contains 14 faces, of which six are ideally square and eight are hexagonal; this Archimedean polyhedron contains 24 vertices and 36 edges. Control of topology is strong in this system, but control of three-dimensional (3D) structure remains elusive. Our key aim is the formation of prespecified two-dimensional and 3D periodic structures. Applications envisioned include nanomanipulators and scaffolding for molecular electronic devices.
Scanning tunneling microscopy studies of thin film AgBr on Au(111)
Authors: Mason M. G. , Hansen J. C.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to determine the surface structure of thin evaporated AgBr films on Au(111). Two structurally different regions are observed. One shows a complex moiré structure due to the long-range commensurability of the Au and AgBr lattices. This structure implies that the thin AgBr films are (111) oriented without any significant reconstruction. The second region appears to have the (√3×√3)R30° structure that has been previously observed in AgBr grown on Ag(111) single crystals.
Sulfur passivation of AlxGa1−xAs for ohmic contact formation
Authors: Fischer Verlyn , Ristolainen E. , Holloway P. H. , Lampert W. V. , Haas T. W.
Published: July 2002

The use of sulfur to passivate Al0.3Ga0.7As surfaces to aid in the formation of Au and Al–Ni–Ge ohmic contacts has been studied using current–voltage measurements, Auger electron spectroscopy, and scanning electron microscopy (SEM). After cleaning the surfaces with solvents, the surfaces were passivated using (NH4)2S. The samples were exposed to laboratory air, then placed in a vacuum for evaporation of Au or Al–Ni–Ge. The samples were then analyzed as deposited or after heat treatment in forming gas at temperatures and times up to 500 °C and 30 min. Current–voltage measurements indicate that S passivation reduced the specific contact resistance for Au contacts but not for Al–Ni–Ge contacts. The Au films were stripped from the surface and SEM used to study the reaction ‘‘pits’’ on the Al0.3Ga0.7As surface. Presumably sulfur passivation assisted in ohmic contact formation with Au by preventing the formation of surface native oxides.
Electron cyclotron resonance plasma source for conductive film deposition
Authors: Ono Toshiro , Nishimura Hiroshi , Shimada Masaru , Matsuo Seitaro
Published: July 2002

We have developed an electron cyclotron resonance (ECR) plasma source for conductive film deposition. In this source, 2.45 GHz microwaves are divided into two directions by an E-plane divider and pass through a quartz window into the composer, where the microwave electric field is parallel to the external magnetic field. The quartz windows are set in the blind space from the ECR plasma and in a region of higher magnetic field than that of the ECR condition (875 G). The composed microwaves are transported from the higher magnetic field region to the ECR magnetic field region in the plasma source. Highly ionized plasma of over 10 mA/cm2 has been generated by preventing plasma generation in the composer. A good uniformity of ±5% over a 6 in. diameter has been obtained. TiN films and Al films have been deposited with high reliability over an extended operation time.
Influence of a heteroepitaxial interface with large lattice mismatch on the low temperature growth of a film
Authors: Zeng Hong , Vidali Gianfranco
Published: July 2002

We report on the influence of a heteroepitaxial interface Pb/Cu(100) on the growth of a Pb film at 150 K using helium beam scattering, low-energy electron diffraction (LEED), and Auger electron spectroscopy. The large lattice mismatch, the difference in bonding strengths, and symmetry between substrate and film produce a rather complex growth pattern. The growth mode in the very early stage is strongly influenced by the Pb/Cu interface, evolving from ordered growth (first layer) to disordered growth (second and third layers) and ordered quasi-layer-by-layer growth (from the fourth to the sixteenth layers). The LEED pattern shows the presence of Pb(111) exposed surfaces with domains rotated by 90°. The envelope of helium beam intensity reveals evidence of quantum size effects and of increasing interface width. The broadening of in-phase diffraction profiles indicates formation of mosaic surface structures. Better layer-by-layer growth is achieved by annealing the disordered second layer. Depending on substrate temperature, first layers with different structures are obtained. These first layer structures dramatically affect the subsequent growth at low temperature.
Epitaxial growth of ultrathin MgO films on Fe(001) seed layers
Authors: Park Yongsup , Fullerton Eric E. , Bader S. D.
Published: July 2002

Ultrathin films of MgO (5–300 Å ) were grown epitaxially onto 150-Å-thick Fe(001) seed layers on MgO(001) at 700 K using electron beam deposition. Reflection high-energy and low-energy electron diffraction and x-ray photoelectron diffraction show that the films have good crystalline quality that improves with thickness.
Ion beam epitaxy of silicon films in an ultrahigh vacuum using a sputtering-type metal ion source
Authors: Matsuoka Morito , Tohno Shun-ichi
Published: July 2002

Ion beam epitaxy (IBE) of silicon films in an ultrahigh vacuum is carried out using a specially developed electric-mirror sputtering-type metal ion source. Silicon films with 2×1 reconstructed surface structures are homoepitaxially grown on silicon wafers above 320 °C, and contamination by oxygen and carbon is suppressed below the level of bulk Czochralski silicon (<1×1018 cm−3). Argon entrapment from sputtering discharge in the film is suppressed by controlling the ion energy during film growth, and metal contamination is suppressed below the detection limit (<1×1016 cm−3) of the conventional secondary ion mass spectroscopy system used. The IBE films exhibit bulklike perfect crystallinity, as examined by electron microscopy, etch-pit observation, Raman spectroscopy, and Rutherford backscattering spectroscopy. Precise and steep control of dopant profile is demonstrated in situ. Heavily doped (B:5×1018 cm−3, As: 1×1019 cm−3) silicon films are grown and the dopants are ideally activated in the films. These films exhibit bulklike carrier mobility.
Surface morphology of Si(111)-(7×7) under an external isotropic tensile stress
Authors: Wei Y. , Li L. , Tsong I. S. T.
Published: July 2002

A special strain stage was designed for a scanning tunneling microscope (STM) to apply an isotropic tensile stress on a Si(111) surface at elevated temperatures. After straining, the surface was allowed to cool to room temperature and STM images of the strained surface were taken. Glide steps along 〈1̄10〉 directions with single atom-layer height of 3.1 Å were observed. The glide steps were caused by the propagation of a dislocation of the type (a/2) [110] due to the slip of {111̄} planes occurring in the bulk. Despite the application of up to 1% isotropic strain, the anticipated (7×7)→c(2×8) phase transition was not observed on the Si(111) surface probably because the strain was taken up by the slippage of {111̄} planes. However, large (5×5) monolayer islands were found on the largest terraces of the strained surface.
Scanning photoelectron microscope with submicron lateral resolution using a Wolter-type x-ray focusing mirror
Authors: Ninomiya Ken , Hasegawa Masaki
Published: July 2002

The scanning photoelectron microscope is operated at a soft x-ray beamline (BL-8A) at the Photon Factory in the National Laboratory for High Energy Physics. The microscope uses a Wolter-type x-ray mirror as an x-ray focusing device for probe beam formation. The lateral resolution of the microscope is evaluated based on total photoyield imaging of Al stripes patterned on a SiO2 film. The 0.6- and 0.7-μm-wide stripes are detected with a modulation of 0.07–0.08 when a 150 eV soft x-ray microbeam with a sagittal beam size of 1.8 μm scans the stripes one dimensionally. The experimental results agree well with the changes in the photoelectron count rate expected from the beam intensity profile and from the arrangement of the stripe pattern. The highest lateral resolution attainable under current instrumental conditions is also predicted.
Interplay between step velocity and morphology during the dissolution of CaCO3 surface
Authors: Liang Yong , Baer Donald R. , McCoy James M. , LaFemina John P.
Published: July 2002

The interplay between the velocity and morphology of steps during the dissolution of the cleaved CaCO3(101̄4) surface in aqueous solution has been studied using atomic force microscopy (AFM). The experimental results were analyzed based on the terrace-ledge-kink model. Real-time AFM images show that, in the surface reaction regime, steps not only retreat at constant velocities which depend only on the atomic structure of the step, but also preserve a straight-edge morphology during the course of dissolution. The straight step morphology suggests that the nucleation of kinks is balanced by the annihilation of the kinks at the step during the dissolution. This result, along with the constant step velocity, can be explained in terms of a kink-kink annihilation process.
Conductance and leakage in superconducting tunnel junctions
Authors: Goodchild M. S. , Barber Z. H. , Blamire M. G.
Published: July 2002

We report an analysis of data from Nb/AlOx/Nb tunnel junctions. We show that both conductance and subgap leakage follow simple scaling laws as a function of oxidation conditions. The leakage effects are discussed in terms of a simple physical model of tunnel barrier inhomogeneity that is also applicable to directly deposited barriers on NbN. We demonstrate that an improvement in barrier properties can be achieved by the use of a buffer layer overlying the barrier, and that this improvement is consistent with a model based on resputtering effects.
SiOxNy films deposited by remote plasma enhanced chemical vapor deposition using SiCl4
Authors: Sanchez O. , Aguilar M. A. , Falcony C. , Martinez-Duart J. M. , Albella J. M.
Published: July 2002

Silicon oxynitride films have been deposited by remote-plasma enhanced chemical vapor deposition using SiCl4 as a silicon source at a substrate temperature of 250 °C. Different mixtures of O2 and NH3 were used to obtain different oxynitride compositions ranging from SiO2 to a stoichiometry close to that of silicon nitride. Also the effect of a hydrogen flow added during the deposition process on the structural characteristics of the deposited films was studied. The behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the stoichiometry of the films as well as the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si–O–Si bonds toward lower wave numbers as the relative concentration of ammonia was increased with respect to oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of a homogeneous alloy. The IR absorption spectra for these films did not show any presence of O–H or Si–H related peaks. Atomic force microscopy measurements on these films show that the hydrogen flow added during deposition results in a reduction of the film roughness.
Simulation of microloading in aluminum etching
Authors: Aoki Masahiko , Sasamura Yoshitaka
Published: July 2002

A simulator for aluminum etching was developed in order to analyze the microloading effect. We have adopted the procedure that the flux rates (gas particles, ions, and sputtered mask fragments) are calculated independently as a function of trench aspect ratio; then the etching rate is calculated with these flux rates at each aspect ratio. The simulator can be operated on a personal computer by this simple procedure and the characteristics of aluminum etching can be obtained quickly. The surface reaction parameters were determined by fitting the calculated result to the basic experimental etching rate data. By using these surface reaction parameters the simulator can predict the characteristics of aluminum etching such as etching rate, selectivity, etc. The difference of the microloading effect between photoresist and oxide mask was also analyzed. It was confirmed by this simulator that the microloading effect was affected by the sputtered photoresist fragments.
Extraction of oxygen from CO2 using glow-discharge and permeation techniques
Authors: Wu D. , Outlaw R. A. , Ash R. L.
Published: July 2002

A promising method to extract oxygen from CO2, which constitutes more than 95% of the Mars atmosphere, is by using glow-discharge dissociation of CO2 combined with the permeation of the generated oxygen through a Ag membrane. Quadrupole mass spectrometry was utilized to measure the oxygen flux through a 0.35-mm-thick, 2.01 cm2 area membrane separating a two-chamber system. On the upstream side of the membrane, a dc glow discharge was established with 350 V and 5 mA current. It was found that as much as 75% of the CO2 was dissociated to form CO and O (part of which recombined to form O2). The atomic and molecular oxygen generated were adsorbed on the membrane surface, subsequently dissolved into the Ag, and diffused through the membrane thickness to the downstream surface where it desorbed as molecular oxygen. The resulting oxygen flux was studied as a function of upstream CO2 pressure, discharge current, discharge probe to membrane distance, and membrane temperature. It was found that the atomic oxygen generated a much higher concentration gradient across the membrane than did the molecular oxygen which resulted in a correspondingly higher oxygen flux through the membrane. The total oxygen flux through the membrane with a CO2 glow-discharge pressure of 5 Torr and a membrane temperature of 450 °C was found to be greater than 1014 cm−2 s−1. This method can be used to continuously and efficiently supply oxygen for astronauts in a future manned mission to Mars.
Filament replacement for ‘‘nude’’ Bayard–Alpert ion gauges
Authors: Cox Michael E. , Panitz J. A.
Published: July 2002

A simple method for producing inexpensive, replacement filaments for a ‘‘nude’’ Bayard–Alpert ion gauge is described. Replacement filaments in the form of a ten-turn coil fabricated from 6-mil tungsten wire are identical in performance to their commercial counterparts.
Determination of chemically active species in a novel microwave plasma source by laser-induced fluorescence
Authors: Brockhaus A. , Yuan Y. , Behle St. , Engemann J.
Published: July 2002

The downstream zone of a new type of plasma source was investigated. Microwave power is fed to the plasma by an annular waveguide ring with slotted line radiators on the inner side. In a pure oxygen plasma the conditions for the generation of atomic oxygen were studied by laser-induced fluorescence. Excitation from the ground state is achieved by two-photon absorption (3p 3P1,2,0←2p 3P2,1,0 transitions) of 226 nm laser radiation. Fluorescence is observed at 845 nm. From the Doppler-broadened absorption line profile a temperature of 350 K is determined. A rate equation model combined with a measurement of laser properties and a calibration of the detection system by Raman scattering in hydrogen gas enabled an absolute calculation of the atomic oxygen ground state density. In the downstream zone values in the range of 1013–1014 cm−3 are obtained. The scaling of the atomic oxygen density with external parameters was investigated.
Determination of diamond growth rate in a flow tube geometry as a function of measured atomic hydrogen density
Authors: Gardner W. L.
Published: July 2002

Present diamond deposition reactors have been very successful in furthering our understanding of how diamond grows at low pressures. However, their primary disadvantage is that changes in reactor conditions (e.g., filament temperature or microwave power, substrate temperature, and CH4:H2 concentration ratio in methane-based reactors) change all chemical species and their relationships. Changes in diamond growth created by independent changes to a single species are not directly accessible. For example, it is known that making atomic hydrogen is required for the growth of diamond films. However, changes to film growth rate have not been tied quantitatively to changes in the amount of atomic hydrogen available. A high-yield atomic hydrogen source was fabricated and pretested in a diamond growth setup. A previously developed atomic hydrogen sensor was used to measure atomic hydrogen density output as a function of both power and pressure. Diamond was then grown as a function of atomic hydrogen density, and growth rate was shown to be linear with density with a lower bound relationship of 0.27 μm/h/1016 cm−3. Since the magnitude and trend of the data appear to be inconsistent with other reported results, they are analyzed with respect to a simplified growth model. Based on reasonable assumptions, we conclude that the data are consistent with growth rate being independent of surface atomic hydrogen concentration and linear with methyl radical concentration. Because sufficient methyl radical density is produced through the interaction of atomic hydrogen with methane with correspondingly negligible reduction in total atomic hydrogen density, it is inferred that growth rate linearity with atomic hydrogen enters only through the production of methyl radical.
Preparation of low-temperature fluorinated oxides by anodic oxidation in dilute hydrofluosilicic acid (H2SiF6) solution
Authors: Jeng Ming-Jer , Hwu Jenn-Gwo
Published: July 2002

Anodic oxidation at room temperature in dilute H2SiF6 solution is proposed as a method to grow the low-temperature fluorinated oxides. It was found that two competing mechanisms exist in anodization. One is the growing mechanism due to constant current anodization and the other is the etching mechanism due to the existing HF solution. It was observed that fluorine atoms are incorporated into the anodic oxides. A growth rate of about 1 μm/h was found that is much higher than by liquid phase deposition (LPD) techinques reported nowadays. Also, the anodic oxides show less leakage current and higher breakdown field properties than the conventional LPD oxides. An excellent breakdown field strength of 10 MV/cm was found in this work.
Root cause determination of particle contamination in the tungsten etch back process
Authors: Uritsky Y. , Chen L. , Zhang S. , Wilson S. , Mak A. , Brundle C. R.
Published: July 2002

Blanket tungsten deposition is used in the wafer processing industry to make via interconnects. The W etch back (WEB) process subsequently removes the W blanket film by an SF6 plasma treatment. WEB is a “dirty” process because, though the major etch product is gaseous WF6 (harmless), F• radicals and process by products attack chamber hardware, producing particles. In this study, these particles were characterized by using scanning electron microscopy/energy dispersive x-ray and Auger spectroscopy. A low-level, general surface contamination was also discovered using Auger. From this work, it was established that a major particle generation process involved etch by-product redeposition on, and attack of, Al chamber hardware. Based on this information, adjustment could be made to process conditions and chamber hardware which resulted in particle reduction to below specification levels.
Experimental approach to a biological characterization of materials
Authors: Nygren Håkan , Eriksson Cecilia
Published: July 2002

Titanium oxide surfaces with thin (4 to 5 nm) or thick (30–40 nm) TiO2 layers and rough (Rrms 1.9 μm) or smooth (Rrms 0.45 μm) surface structure were exposed to capillary blood for 5 s through 64 min. The adsorption of main plasma proteins (albumin, IgG, fibrinogen), binding of cascade enzymes (serine proteases) and adhesion and activation of blood cells was measured with immunofluorescence techniques using specific antibodies, the binding of which was quantitated by computer-aided image analysis. The activation of cascade enzymes was detected with antibodies against prothrombin/thrombin (terminal step in the coagulation cascade), C1q and C3c (initial complement activation), terminal complement complex (TCC), and plasmin (terminal step in fibrinolysis). The activation of cells was measured by expression of selectin (platelet CD62), expression of integrins (neutrophil CD11b), or respiratory burst (NBT test) of peritoneal leucocytes adhering to the surfaces after in vivo exposure. The results show different profiles of protein adsorption at the four surfaces. Fibrinogen was the dominating protein on all surfaces, significant amounts of IgG was found on the rough surfaces only. Prothrombin/thrombin and C1q were found initially on the thick-rough surface only. No TCC or plasmin levels were detected during the exposure time studied. Platelets and neutrophils were activated to a significantly higher degree on rough surfaces than on smooth, and neutrophils more on the rough surface with a thin oxide layer than on the thick one. The ensemble of antigens and enzyme activity detected shows a fingerprint which is unique for each material investigated.