bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrations of CO chemisorbed on metal surfaces: Cluster model studies
Authors: Müller W. , Bagus P. S.
Published: July 2002

The molecular orbital cluster model has been used to study the vibrations of CO interacting with metal surfaces. In all cases the equilibrium CO geometry is taken normal to the surface with C directly above a metal atom; SCF and correlated CI wave functions have been obtained. For CO/Cu(100), we have studied the C–O and Cu–C stretch modes. The C–O frequency ωe and effective charge e* have been analyzed in terms of σ and π contributions; the adsorption site metal π, 3dπ, and 4pπ, donation to CO 2π* contributes in a major way to e*. The ωe and e* for the C–O stretch have been compared for one metal atom–CO clusters of Cu, Ni, and Fe. The ωe decrease in the order Cu, Ni, and Fe; the e* increase in the same order. This is to be expected from the order of the metal dπ to CO 2π* donation and bonding which is Fe>Ni>Cu.
Sputter depositions of silicon film by a planar magnetron cathode equipped with three targets
Authors: Serikawa T. , Okamoto A.
Published: July 2002

This paper discusses the effects on uniformity of a newly developed planar magnetron cathode with three targets. The cathode is comprised of permanent magnets placed under the targets. Silicon films with a phosphorus concentration of up to 0.3 wt. % are successfully deposited from three phosphorus-doped, 4-in.-diam silicon targets, using the cathode in rf system. Surfaces of the three targets are equally sputter etched and doughnut shaped erosion patterns are formed. Sputter deposition by the cathode exhibits the advantage of improving film thickness uniformity. Moreover, it is experimentally demonstrated that low resistivity silicon films with an excellent uniformity are obtained. The cathode is very useful in fabricating films in advanced devices.
Characterization of diamondlike carbon films and their application as overcoats on thin-film media for magnetic recording
Authors: Tsai Hsiao-chu , Bogy D. B.
Published: July 2002

This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin-film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin-film properties.
Adsorption of H2O on planar and stepped Si(100): Structural aspects
Authors: Larsson C. U. S. , Johnson A. L. , Flodström A. , Madey T. E.
Published: July 2002

The adsorption of water on two silicon surfaces [reconstructed planar (100)2×1 and single domain stepped (100)2×1 cut 5° towards (011)] was studied using low-energy electron diffraction and digital imaging electron stimulated desorption ion angular distributions (ESDIAD) as a function of temperature (145–700 K) and coverage. Water has been shown previously to chemisorb dissociatively to form surface OH groups. At 300 K the H+ ESDIAD pattern for the planar surface is a nearly symmetric halo, indicating that OH is oriented with its bond vector inclined away from the surface normal, while at low temperatures (≤200 K) a four-lobed pattern that preserves substrate symmetry is observed. This reversible temperature dependence is related to librations and rotations of the OH complexes. ESDIAD from the stepped surface exhibits a two-lobed pattern, with enhanced emission towards the steps, consistent with bonding of OH to single-domain terrace sites. An interpretation is presented based on the dimer model of the Si(100) reconstruction in which the OH bond axis azimuths are oriented nearly perpendicular to the dimer azimuths.
Ion beam sputter deposition and epitaxy of CdTe and HgCdTe films
Authors: Krishnaswamy S. V. , Rieger J. H. , Doyle N. J. , Francombe M. H.
Published: July 2002

A preliminary study has been made of ion beam sputter deposition as a technique for the epitaxial growth of CdTe and HgCdTe films suitable for use in infrared detector fabrication. A specially designed UHV dual ion gun system, equipped with cryogenic cooling for targets, was used to investigate epitaxial growth on CdTe substrates. High-quality epitaxial CdTe has been achieved at temperatures down to 140 °C. Conditions for the growth of stoichiometric HgCdTe at temperatures in the range below 100 °C were explored using single-crystal alloy targets. Epitaxial structures free from twinning were obtained at substrate temperatures below 70 °C, and it was found possible to sustain epitaxy down to room temperature. These findings indicate that ion beam sputter deposition may be well suited to the low-temperature growth of infrared heterojunctions and superlattice structures.
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u scanning tunneling microscopy of platinum (111) surface with the observation of monatomic steps
Authors: Itaya K. , Sugawara S. , Sashikata K. , Furuya N.
Published: July 2002

I n situ scanning tunneling microscopy was applied to single-crystal platinum (111) surfaces both before and after electrochemical potential cycling in an aqueous sulfuric acid solution. Steps observed on a Pt(111) facet were usually located on nearly parallel straight lines or on the directions forming an angle of close to 60°, as expected for a surface with threefold symmetry. The height of each step was in accord with the monatomic step height of 0.238 nm on the Pt(111) surface. Randomly oriented islands a few atoms in height were clearly observed on the terraces after five potential cyclings. It was suggested that Pt adatoms produced by the reduction of the oxide are coagulated on the terraces.
Theory of magnetic force microscopy
Authors: Hartmann U.
Published: July 2002

A theory is presented describing the fundamentals of contrast formation in magnetic force microscopy (MFM). In particular, effects due to the finite MFM probe size are taken into account. As a result, complete MFM images can be simulated in good agreement with experimental data employing only minimum information about the actual probe configuration. As an example, the 180° Bloch wall in iron is considered.
Observation of two-temperature electrons in a sputtering magnetron plasma
Authors: Sheridan T. E. , Goeckner M. J. , Goree J.
Published: July 2002

We experimentally find that there are hot and cold electron components present in a sputtering magnetron plasma. The density of the hot component is greatest in the magnetic trap and decreases with the distance from the cathode. The cold electron density is negligible inside the trap and is approximately constant outside. The largest cold electron density is nearly as great as the hot electron density inside the magnetic trap.
Electron cyclotron resonance plasma experiment for in situ surface modification, deposition, and analysis
Authors: Nowak S. , Gröning P. , Küttel O. M. , Collaud M. , Dietler G.
Published: July 2002

An electron cyclotron resonance plasma source which allows in situ surface modification and thin film deposition combined with surface analysis by x-ray photoelectron spectroscopy (XPS) is presented. This experiment enables well defined surface modification studies to be performed. We discuss the experimental details of this plasma source as well as the main discharge characteristics as a function of gas, pressure, and geometry. Using plasma diagnostics, a Langmuir probe and an ion energy analyzer, the ion density, the electron temperature, and the ion flux were determined. Two examples of applications analyzed by XPS, one for surface modification and one for thin film deposition, confirm the ability to produce well defined and contamination-free surfaces.
Polycrystalline TiN films deposited by reactive bias magnetron sputtering: Effects of ion bombardment on resputtering rates, film composition, and microstructure
Authors: Petrov I. , Hultman L. , Sundgren J.-E. , Greene J. E.
Published: July 2002

Transmission electron microscopy, x-ray diffraction, and Rutherford backscattering have been used to investigate the effects of ion irradiation during growth on the deposition rate, composition, and microstructure of single-phase polycrystalline NaCl-structure TiNx films deposited by reactive magnetron sputtering with a negative substrate bias voltage Vs. The layers were deposited on thermally oxidized Si(001) substrates in mixed Ar+4% N2 discharges at a total pressure of 4.2 mTorr. Varying Vs between 0 and 1800 V resulted in incident ion-to-Ti atom flux ratios of 0.3 to 0.6 at the film growth surface and increases in the substrate temperature Ts (initially Ts=300 °C) of 40 to 200 °C. The Ti resputtering yield increased from ≤0.02 (Vs≤100 V) to 0.30 (Vs=1800 V) Ti atoms per incident ion (primarily Ar+), while the N/Ti ratio in as-deposited films increased from 1.03 for Vs=0 V to 1.12 for 100 V≤Vs≤400 V and then decreased to ≂0.95 as Vs was raised to 1800 V. Trapped Ar concentrations ranged from ≤0.5 at.% (Vs=0) to ≂5.5 at.% (Vs=1800 V). However, the Ar was not randomly dispersed in films grown with Vs≳1000 V and gas bubbles were observed. Film lattice parameters a0 were found to vary from the bulk value of 0.4240 nm at Vs=0 to a maximum of 0.4295 nm at Vs=800 V and then decrease to 0.4265 nm at Vs=1800 V. Voided grain boundaries were observed in films grown with Vs≤120 V. The use of higher substrate biases initially resulted densification of grain boundaries with a corresponding decrease in average grain size. However, with Vs≥800 V, the films again became less dense and increased intragranular defect densities were observed.
Spirals and propagating reaction fronts during catalytic CO oxidation on a cylindrical Pt single crystal
Authors: Sander M. , Veser G. , Imbihl R.
Published: July 2002

The spatiotemporal patterns that are associated with kinetic oscillations in the catalytic CO oxidation have been investigated on a Pt single crystal of cylindrical shape whose axis is oriented in the [001] direction. The experiments were conducted in the 10−5 and 10−4 Torr range between 450 and 550 K using a photoemission electron microscope for imaging the spatial adsorbate distribution during the reaction. The cylinder surface exhibits all orientations of the [001] zone including (100), (110), and (210) whose oscillatory behavior has been studied before. On Pt(110) rotating spirals, target patterns, and ordered arrays of reaction fronts are observed, but these regular patterns were confined to a narrow orientational range of ±2° around (110). Further away fluctuating irregular patterns are found which finally merge into the oxygen-covered surface characteristic of the more active orientations around (210). Under appropriate conditions kinetic oscillations can be found on (210) which are again associated with spatial pattern formation. The transition from a CO-covered to an oxygen-covered surface proceeds via a propagating reaction front, while the transition in the reverse direction takes place through the growth of small CO islands distributed randomly across the surface. Finally, an oscillation mode has been found in which the phase boundaries separating the oxygen-covered active zone from the inactive CO-covered zone on the cylinder surface periodically shifts thus causing an expansion/contraction cycle of the active zone. The phase boundary in between (210) and (100) can also act as a source for oxygen islands which are detached from the phase boundary and then shrink while traveling as a whole towards (100).
Magnetically enhanced etching of sub-0.5 μm polysilicon gates
Authors: Bui S. , Sasserath J. , Ghanbari E.
Published: July 2002

We have compared Cl2 and HBr for etching polysilicon lines in a band magnetron cathode reactor. The experiments were designed utilizing response surface methodology. Our study shows a significantly wider operating window with the HBr chemistry. Typical results obtained are a polysilicon etch rate of 1500–2000 Å/min, selectivities 100:1 poly:SiO2 and 10:1 poly:photoresist. Direct-current bias values were under 100 V, and operating pressures were less than 6 mTorr. The results for 0.25 μm lines indicate that etching was free of undercut, oxide trenching, and polysilicon notching over steps. No evidence of polymer formation was observed using scanning electron microscopy and optical emission spectroscopy.
In situ surface vibrational spectroscopy of the vapor/solid and liquid/solid interfaces of acetonitrile on ZrO2
Authors: Hatch S. R. , Polizzotti R. S. , Dougal S. , Rabinowitz P.
Published: July 2002

Infrared-visible sum-frequency generation (SFG) is employed in an internal reflection geometry to investigate, in situ, the adsorption of acetonitrile on ZrO2 from liquid and vapor. This configuration induces large field enhancements near the critical angle that increase signal levels by more than 100-fold compared with reflection from the liquid or vapor side of the interface. Acetonitrile is a widely used, highly polar, chromatographic solvent that has simple structure and strong stretching modes with large frequency separation, making it an ideal liquid for SFG studies. The C≡N and C–H stretching modes are observed at submonolayer and neat liquid coverages on ZrO2. The relative polarization dependent SFG oscillator strengths are determined providing estimates of the binding energy, 4.7±0.2 kcal/mol, and the mean orientation of the molecular axis to the surface, 22±2°. Spectra of CD3CN show resolvable structure in the C≡N and C–D stretching regions, suggesting the presence of aggregates on the surface. SFG measurements as a function of CH3CN concentration in CCl4, at equilibrium, is shown to be consistent with the formation of dimers and higher order surface species.
Nature of active sites in the oxidative coupling of methane to ethane over Li/MgO catalysts
Authors: Wu Ming-Cheng , Truong Charles M. , Coulter Kent , Goodman D. Wayne
Published: July 2002

The partial oxidation of methane to ethane over a model Li/MgO catalyst has been studied using combined surface science techniques/elevated pressure kinetic measurements. The results indicate that [Li+O−] centers are not likely directly involved in the methane activation step. Rather, addition of lithium promotes the production of F centers which are considered to be responsible for this key step in the methane coupling reaction.
Cryogenic trick for enhanced cooling using liquid nitrogen
Authors: Xu Jiazhan , Jänsch Heinz J. , Yates John T.
Published: July 2002

The thermal transpiration method has been employed to replace the temperature of liquid nitrogen by ∼12 K. This is done by bubbling He (g) through the liquid nitrogen.
Reactive evaporation of potassium in CO2 and the formation of bulk intermediates
Authors: Axelsson O. , Paul J. , Weisel M. D. , Hoffmann F. M.
Published: July 2002

Potassium vapor condensed in CO2 has been studied by transmission infrared spectroscopy and by total pressure thermal desorption spectroscopy. The results are compared with surface spectroscopic data for CO2 adsorbed on alkali metal overlayers. Both systems show the formation of bulk coordinated oxalate species at cryogenic temperatures and the conversion to carbonate intermediates upon annealing.
Mass and energy resolved detection of ions and neutral sputtered species incident at the substrate during reactive magnetron sputtering of Ti in mixed Ar+N2 mixtures
Authors: Petrov I. , Myers A. , Greene J. E. , Abelson J. R.
Published: July 2002

The fluxes of ions and neutral sputtered particles incident at the growth surface during the deposition of TiN by reactive magnetron sputtering from a Ti target in mixed Ar+N2 discharges were determined using a combination of in situ double-modulation mass spectrometry, Langmuir probe, discharge, deposition rate, and film composition measurements. The N2 fraction fN2 in the discharge was varied from 0 to 1 with the total pressure maintained at 3 mTorr (0.4 Pa). Target nitridation, observed directly through the detection of sputter-ejected TiN molecules, was found to occur over the narrow fN2 range between ≂0.035 and 0.06. With fN2<0.1, more than 94% of the ion flux incident at the substrate is Ar+ while for pure N2 discharges, N+2 accounts for more than 95% of the incident ions. Both the incident Ar+ and N+2 ion fluxes are highly monoenergetic with energies corresponding to eVs, where Vs is the applied negative substrate bias with respect to the plasma potential. However, the energy distributions of incident Ti+ and N+ ions are extended due to the high-energy tails in their sputter-ejection energy distributions. The primary sputter-ejected particles are Ti and N atoms. TiN, TiN+, and Ti+ do not contribute significantly to film growth kinetics.
Sputtering of neutral and ionic indium clusters
Authors: Ma Z. , Coon S. R. , Calaway W. F. , Pellin M. J. , Gruen D. M. , von Nagy-Felsobuki E. I.
Published: July 2002

Secondary neutral and secondary ion cluster yields were measured during the sputtering of a polycrystalline indium surface by normally incident ∼4 keV Ar+ ions. In the secondary neutral mass spectra, indium clusters as large as In32 were observed. In the secondary ion mass spectra, indium clusters up to In18+ were recorded. Cluster yields obtained from both the neutral and ion channel exhibited a power law dependence on the number of constituent atoms n in the cluster, with the exponents measured to be −5.6 and −4.1, respectively. An abundance drop was observed at n=8, 15, and 16 in both the neutral and ion yield distributions, suggesting that the stability of the ion (either secondary ion or photoion) plays a significant role in the observed distributions. In addition, our experiments suggest that unimolecular decomposition of the neutral cluster may also play an important role in the measured yield distributions.
Effects of ion-induced electron emission on magnetron plasma instabilities
Authors: Hendricks M. B. , Smith P. C. , Ruzic D. N. , Leybovich A. , Poole J. E.
Published: July 2002

Some magnetron sputtering systems experience rapid oscillations in the current and voltage of the plasma discharge after several hours when equipped with certain targets. These oscillations often lead to the plasma becoming extinguished, a condition known as ‘‘flame-out.’’ This article details the study of two 90% W–10% Ti magnetron targets which differed in density. The higher density targets sometimes experienced flame-out after approximately 3 h of sputtering. The less dense material could be sputtered for the entire 15 h life of the target. Scanning electron microscopy pictures and atomic composition depth profiles were obtained using Auger electron spectroscopy. In addition, a Colutron-based ion source with a high vacuum system was used to measure ion-induced secondary electron emission coefficients as a function of energy, ion specie, and gas coverage. Analysis of the sample from the group that suffers flame-out showed large regions of pure titanium in the interior of the sample and higher levels of oxygen contamination. These oxide regions act as insulators in the material which cause the secondary electron emission to decrease, the plasma current to drop and the voltage to rise. The less dense targets had a surface topography which helped overcome these decreases is electron emission. Experiments showed that an increase in the voltage with respect to the surface significantly increased electron emission, for the less dense targets, counteracting any drops in plasma current.
An actinometric study of C2H2 plasma polymerization and film properties
Authors: Mota Rogério Pinto , Shiosawa Tadashi , Durrant Steven Frederick , Bica de Moraes Mário Antônio
Published: July 2002

Thin polymer films were grown in radio frequency discharges containing C2H2. Actinometry revealed the trend in the plasma concentration of the CH species as a function of the operating pressure. The C–H bond density in the films, revealed by infrared analysis, was found to increase with the pressure of C2H2 in a similar way to that of the concentration of the CH species in the discharge. From transmission ultraviolet-visible spectroscopy data, optical parameters of the polymers, namely, the refractive index and the optical gap, were calculated. For the range of pressure studied, the refractive index decreased from 1.73 to 1.63 and the optical gap increased from 2.4 to 3.3 eV. Finally, measurements of the residual stress of the polymer films were carried out by the bending beam method, using a He–Ne laser, yielding values from 0.05 to 0.3 GPa.
Deposition on mica and scanning force microscopy imaging of DNA molecules whose original B structure is retained
Authors: Muzzalupo I. , Nigro C. , Zuccheri G. , Samorì B. , Quagliariello C. , Buttinelli M.
Published: July 2002

The supercoiling of topologically constrained DNA molecules is altered by modifications of their original B structure. Contact mode, scanning force microscope (SFM) imaging requires a fairly tight binding of the DNA molecules to a flat surface, generally mica, and is often accomplished using divalent or trivalent cations and dehydrating the sample thoroughly immediately upon deposition, following procedures known to cause at least a partial B-DNA to A-DNA transition. We report a modification of the DNA deposition method presented by Koller et al. [Biopolymers 13, 995 (1974)] that is suitable to SFM imaging of DNA and allows complete control of the conditions of deposition (ionic strength, temperature). We have measured the contour length of linear DNA molecules in SFM images of depositions prepared with the reported method. Our data show that the B structure is preserved.
Fundamental leak calibration system for gas leaks with a defined pressure difference over the leak element
Authors: Wälchli U. , Stöckli A. L. , Rapp F. , Bösch M. A. , Schmid A.
Published: July 2002

The principal concern in the calibration of leaks is the calibration of leaks to be used under vacuum. With a growing number of sniffing applications and the change from permeation leak to physical leak elements due to reasons of stability and reproducibility, the study focuses on the calibration of physical leaks under application conditions. The calibration of these test leaks must be carried out at atmospheric pressure. To get an accurate calibration independent of the filling gas for these sniffing test leaks a PΔV/Δt calibration system was built according to DIN28417. The linear displacement of a piston gives the change in volume, ΔV. The smallest ΔV that can be set is 3 nl, which corresponds, at a pressure of 1000 mbar, to 3×10−6 mbar l. The systematic errors in ΔV are determined by the diameter and tolerances of the piston, 0.6±0.0015 mm or 0.25%, and the measurement of the displacement of the piston h and its error Δh, which could be maintained at less than 0.01 mm or 2% for h=0.5 mm. The overall systematic errors are below 2.5%. With this leak calibration apparatus, sniffing test leaks with leak rates of 2×10−5 mbar l/s at room temperature can be calibrated with an accuracy of better than ±10% within several minutes. In such a calibration the ΔV is performed 20 times to get 20 individual determinations of the leak rate. The comparison of this method with a capillary measurement tube method shows very good agreement.
Diamond-like carbon film synthesized by ion beam assisted deposition and its tribological properties
Authors: He Xiaomimg , Li Wenzhi , Li Hengde
Published: July 2002

Ion beam assisted deposition offers a novel and unique process to prepare diamond-like carbon (DLC) films at room temperature with particularly good interface adhesion. This advantage is explored to deposit highly wear resistant DLC coating on AISI 52100 steel. Various bombarding species and energy are examined to optimize the process. Infrared, Raman, Auger electron spectroscopy spectra, and hardness measurements are used to characterize the structure and properties of DLC films. The friction and wear behavior of DLC films are systematically investigated by performing extensive experiments in different testing styles. It is disclosed that by means of a dynamic mixing of atoms in interfaces, a pure metal intermediate layer can tremendously improve the tribological properties of DLC films on 52100 steel. The results are optimistic and may lead to useful applications.
A simple optical emission method for measuring percent dissociations of feed gases in plasmas: Application to Cl2 in a high-density helical resonator plasma
Authors: Donnelly V. M.
Published: July 2002

Optical emission was used to determine absolute Cl2 number densities in a Cl2 high-density, helical resonator plasma that was used to etch Si. Emission from Cl2 at 306 nm was monitored, and rare-gas actinometry was used to correct for changes in the electron energy distribution. This emission band of Cl2 is ascribed in this study to a state at 8.4 eV, or possibly to one at 9.2 eV. A state of Xe at 9.8 eV, emitting at 823.2 nm, was chosen as a suitable match to the energy of the emitting state of Cl2. Absolute number density measurements were obtained by extending the measurement to extremely low powers where little dissociation occurs. This simple self-calibration method has advantages over other more complicated techniques such as laser induced fluorescence that rely on external calibrations. It is also much easier to carry out than mass spectrometry and is more sensitive than optical absorption. It is applicable to feed gases with optical emission from states with energies above about 8 eV. In this study it was found that a Cl2 helical resonator discharge is nearly completely dissociated (95%) at a power density of 0.4 W/cm3 in the glass tube source region. The percent dissociation drops to 85% below the source and above the Si substrate. Near the stainless-steel walls, fast Cl-atom recombination reduces the dissociation to ∼10% (determined by line-of-sight mass spectrometry). The high degree of dissociation in the source and near-downstream region is in agreement with recent model predictions for high-density discharges.
High resolution electron energy loss spectroscopy of MnO(100) and oxidized MnO(100)
Authors: Langell M. A. , Hutchings C. W. , Carson G. A. , Nassir M. H.
Published: July 2002

Single crystal MnO(100) substrates can be selectively oxidized to produce Mn2O3- and Mn3O4-like surfaces under mild oxidation/reduction conditions readily accessed under ultrahigh vacuum (UHV). MnO(100) yields a characteristic Mn 2p x-ray photoelectron spectroscopy (XPS) satellite structure and appropriate O/Mn concentrations from O 1s/Mn 2p XPS intensity ratios. Its high resolution electron energy loss (HREEL) spectrum shows a series of Fuchs–Kliewer multiple phonon excitations with a single loss energy of 70.9 meV, characteristic of the cubic manganese monoxide structure. However, the HREEL spectral (HREELS) background is high and the phonons are not as well resolved as those typically observed on comparable metal monoxides. Annealing the MnO(100) substrate at 625 K and 5×10−7 Torr O2 slowly forms Mn2O3, as indicated by O 1s and Mn 2p XPS, and does so without significantly altering the symmetry of the MnO(100) low energy electron diffraction pattern. The MnO(100)-Mn2O3 surface can be selectively reduced to Mn3O4-like composition by heating under UHV to 775 K and to MnO(100) at 1000 K. HREEL spectra for the UHV annealed surfaces are well-resolved, and for the MnO(100)-Mn3O4 substrate a second fundamental phonon loss is observed at 55.6 meV as a result of the lower symmetry of the Mn3O4 spinel structure. The UHV-annealed MnO(100) surface appears to be more highly ordered since its HREELS phonon loss peaks are better resolved. It is also somewhat reduced, however, resulting in a less intense phonon spectrum with a fundamental loss energy of only 65.1 meV.
Reordering at the gas-phase polysulfide passivated GaAs(110) surface
Authors: So B. K. L. , Kwok R. W. M. , Jin G. , Cao G. Y. , Hui G. K. C. , Huang L. , Lau W. M. , Wong S. P.
Published: July 2002

The structural and chemical changes of the GaAs(110) surface induced by sequential processes of UV/O3 exposure, HF etching, and gas-phase polysulfide passivation were investigated by x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and thermal desorption. Prior to any annealing, no samples showed any LEED patterns, and XPS indicated the presence of both As–S and Ga–S bonds. When the polysulfide-passivated surface was annealed to 400 °C, a sharp oblique LEED pattern started to emerge, which was accompanied by the desorption of S–As species. At the same time, XPS indicated that only a single type of sulfide (S–Ga) remained on the surface. Further annealing of the sample to 600 °C resulted in a complete removal of sulfur species from the surface and the appearance of a (2×1) LEED pattern. In contrast, no LEED pattern was observed from samples that had only been subjected to UV/O3 treatment and HF etching up to an anneal temperature of 600 °C, thus indicating the absence of any kind of ordered structure on these surfaces. The results suggest that sulfide assisted the reordering of the GaAs(110) surface; this is most likely a crucial factor in the improvement of the electrical properties of the devices based on this surface.
Angular dependence of the polysilicon etch rate during dry etching in SF6 and Cl2
Authors: Hedlund C. , Jonsson L. B. , Katardjiev I. V. , Berg S. , Blom H.-O.
Published: July 2002

The angular dependence of the etch rate in reactive ion etching (RIE) and inductively coupled plasma (ICP) systems for polysilicon etching with SF6 and Cl2 is determined using a recently developed direct measurement method. The latter utilizes specially patterned silicon groove structures consisting of 7–10 μm wide planar surfaces which form various angles with respect to the wafer normal. The structures are produced by highly anisotropic wet chemical etching of Si through a gratinglike mask pattern aligned along specific crystallographic orientations of the wafer which results in the development of planar surfaces of various orientations. These surfaces are then coated with the materials to be studied—polysilicon in this case. The deposited polysilicon is then etched under a variety of conditions in a RIE and an ICP reactor and the etch rates determined by interferometric measurements. Since only standard Si wafers are used and the size of the pattern is only a few μm the method is fully IC production compatible, which means that one can measure the angular dependence of the etch rate directly in production etching systems. The results for RIE of polysilicon with SF6 show that the process becomes more isotropic with increasing pressure. The angular dependence of the RIE and ICP polysilicon etch rates in Cl2 atmosphere were found to vary with the substrate bias. Specifically low substrate bias resulted in an under cosine distribution whereas bias higher than 240–250 V led to over cosine distributions.
Studies of the low-pressure inductively-coupled plasma etching for a larger area wafer using plasma modeling and Langmuir probe
Authors: Collison Wenli Z. , Ni Tom Q. , Barnes Michael S.
Published: July 2002

As semiconductor wafer size increases (from the current 200 to 300 mm), scaling up a process chamber to meet the same or even more stringent requirements becomes difficult due to complexity of the nonequilibrium plasmas. Designing 300 mm etching reactors can be costly and time consuming for developers without an understanding of fundamental physical and chemical processes. To expedite development and reduce cost, plasma modeling and plasma diagnostics are used to gain insight and assist the 300 mm etching reactor development. In this article, it is demonstrated that plasma modeling and Langmuir probe measurement can be used to study various plasma properties including the effects of inductively coupled power, chamber pressure, aspect ratio, and coil configuration, for a planar inductively-coupled plasma. The results from these studies are used to optimize an inductively-coupled plasma R&D chamber capable of etching 300 mm wafers.
Interface formation between metals (Cu, Ti) and low dielectric constant organic polymer (FLARE™ 1.0)
Authors: Du M. , Opila R. L. , Case Carlye
Published: July 2002

The continuing trend toward miniaturization of integrated circuits is driving the development of low dielectric constant materials (k<3) and their integration with copper metallization. In this work, the interface formed between copper or titanium and low dielectric constant polymer was explored. Fluorinated poly(arylene ether) (FLARE™ 1.0) was studied as an example of fluorinated organic polymers. X-ray photoelectron spectroscopy (XPS) was used to study the chemical interactions between the metal and FLARE™ 1.0 during interface formation. XPS revealed that copper is relatively unreactive with FLARE™ 1.0 compared to titanium. However, depositing the copper by rf sputtering caused significant defluorination of the FLARE™ 1.0 surface, which was not evident for thermally evaporated copper. No copper fluoride formation was observed for either deposition. Evaporation of titanium does cause defluorination of the polymer, with subsequent formation of titanium fluoride. Titanium is more reactive than copper and forms bonds of T–C, Ti–O, and Ti–F at the interface.
Friction-reducing mechanisms of molybdenum dithiocarbamate/zinc dithiophosphate combination: New insights in MoS2 genesis
Authors: Grossiord C. , Martin J.-M. , Le Mogne Th. , Inoue K. , Igarashi J.
Published: July 2002

The friction-reducing properties of the Modtc/Zndtp combination were studied using a ultrahigh vacuum (UHV) analytical tribometer. The friction tests were performed on a previously formed tribofilm. Transmission electron microscopy observation shows that this tribofilm is composed of a mixture of zinc phosphate zones containing molybdenum and carbon-rich zones containing zinc and MoS2 single sheets. After UHV friction, the wear scars of both the sliding surfaces were characterized by in situ analytical tools like Auger electron spectroscopy, scanning Auger spectroscopy, and microspot x-ray photoelectron spectroscopy. Low friction is associated to the transfer of a thin MoS2 film to the pin. Zinc, phosphorous, and oxygen are localized in the wear debris surrounding the pin wear scar. The friction-reducing phenomena is explained on the basis of the hard and soft acids and bases principle.
Optimization of plasma density and radial uniformity of a point-cusp magnetic field applied capacitive plasma
Authors: Wickramanayaka Sunil , Nakagawa Yukito , Sago Yasumi , Numasawa Yoichiro
Published: July 2002

A feasibility study in the development of a large area high-density plasma source with a higher radial plasma uniformity for large area wafer processing was carried out. Experiments were performed for 200 mm diameter wafers using parallel plate capacitively coupled plasma excited by 60 MHz radio frequency current. Point-cusp magnetic fields that can be easily expanded for 300 mm diameter wafer processing reactors without any technical difficulties are applied to the upper electrode. The point-cusp magnetic fields are generated by arranging 115 permanent magnets on a 266 mm diameter upper electrode with alternate polarity and equal distance. This arrangement of magnets produces a strong magnetic field at the surface of upper electrode and almost a magnetic field-free environment at around 40 mm below the upper electrode. This magnetic field also causes no polarization of the plasma due to the E×B drift of electrons where E and B are the direct current electric and magnetic field strengths, respectively. Application of the point-cusp magnetic field increases the plasma density by a factor of 2 and decreases the radial nonuniformity by a factor >1.5. The radial nonuniformity of the plasma at 58 mm below the upper electrode is further reduced to ±3.5% across the central 200 mm region by the application of a bucket magnetic field to the reactor sidewall and removing 16 magnets from the central region of the upper electrode. This latter change, however, slightly reduces the earlier explained plasma density increment. The radial uniformity of large area plasmas can be controlled with considerable ease by removing selected magnets from the central region of the upper electrode or reducing the magnetic field strength at the central region.
A new polyimide membrane for x-ray masks
Authors: Huang J. B. , Gong B. M.
Published: July 2002

In the fabrication of polyimide x-ray masks, the degradation problem of the prepolymer of polyimide (polyamic acid) has been successfully solved by using a new prepolymer, polyamide acid methyl ester. This new polymer is very stable at room temperature whether it is stored in solid state or dissolved in proper solvents. Conversion into polyimide is carried out in a 300 °C oven or in a 200 °C far infrared oven. The behavior of polyamide acid methyl ester, some properties of the polyimide converted from it and the performance of x-ray masks fabricated from it have been investigated.
Cavernous undercuts appearing in reactive ion etched submicron-wide deep trenches
Authors: Ohki Shigehisa , Oda Masatoshi , Akiya Hideo , Shibata Toshitaka
Published: July 2002

The mechanism for the cavernous undercuts appearing on submicron-wide Si trench sidewalls etched in Cl2 plasma is investigated. Etching with the inclined Si substrate implies that the ions scattered from the opposing mask edge plane are responsible for the undercut. Angular and energy distributions of ions scattered from the mask edges are simulated with a Monte Carlo method. The number and energies of the scattered ions are calculated as being high enough to etch sidewalls. Etching profile simulation incorporating the ion scattering effect shows good agreement with experimental results concerning the amount and the location of the undercut. These results apparently show that ion scattering at a sloped mask edge is the dominant origin of the cavernous undercut.
Point exposure distribution measurements for proximity correction in electron beam lithography on a sub-100 nm scale
Authors: Rishton S. A. , Kern D. P.
Published: July 2002

The exposure distribution function in electron beam lithography, which is needed to perform proximity correction, is usually simulated by Monte Carlo techniques, assuming a Gaussian distribution of the primary beam. The resulting backscattered part of the exposure distribution is usually also fitted to a Gaussian term. In this paper we demonstrate a technique, using a very high contrast resist, whereby the normalized point exposure distribution can be measured experimentally, both on solid substrates which cause backscattering, and on thin substrates where backscattering is negligible. The data sets so obtained can be applied directly to proximity correction and represent the practical conditions met in pattern writing. Results are presented of the distributions obtained on silicon, gallium arsenide, and thin silicon nitride substrates at different beam energies. Significant deviations from the commonly assumed double Gaussian distributions are apparent. On GaAs substrates the backscatter distribution cannot adequately be described by a Gaussian function. Even on silicon a significant amount of exposure is found in the transition region between the two Gaussian terms. This deviation, which can be due to non-Gaussian tails in the primary beam and to forward scattering in the resist, must be taken into account for accurate proximity correction in most submicron lithography, and certainly on the sub-100 nm scale.
Soft x-ray reduction lithography using multilayer mirrors
Authors: Kinoshita H. , Kurihara K. , Ishii Y. , Torii Y.
Published: July 2002

A soft x-ray lithograpy using multilayer mirrors for demagnifying optics and a reflecting mask has been designed and studied experimentally. In this system, a wavelength of 45–130 Å has been selected based on the optical characteristics, the exposed depth of the resist film, and the reflectivity of the multilayer mirror. To obtain a replication pattern resolution of 0.2 μm, the numerical aperture required is estimated to be greater than 0.0125 or 0.0325 for a wavelength of 50 or 130 Å, respectively. These values show that the multilayer optics using two mirrors can be realized to replicate a 0.2 μm pattern. The experiments were performed on the SR beamline BL-1 of the KEK-PF storage ring. The Schwarzschild demagnifying optics with a ring field were designed and fabricated. Demagnified exposure patterns of less than 0.5 μm have been obtained using a reflecting mask. The feasibility of the soft x-ray reduction method using multilayer mirrors has been confirmed. Furthermore, new telecentric optics are proposed to realize a practical reduction lithography system.
Direct electron-beam patterning for nanolithography
Authors: Lee K. L. , Hatzakis M.
Published: July 2002

An experimental high resolution e-beam system has been developed for direct deposition of microstructures with feature size ≂0.1 μm and below. This system is used to study various aspects of high resolution direct e-beam deposition process, i.e., physical factors which govern the resolution of the process, film characteristics and properties, nucleation of film growth, and pattern aspect ratio capability. For direct e-beam deposition of Au, using organometallic complexes, features with minimum linewidth of ≂30 nm and center-to-center feature spacing as small as 50 nm have been achieved. These represent the finest and densest features yet fabricated using the organometallic Au complexes. Potential applications of the technique for high resolution mask repair, fabrication of two- or three-dimensional nanometer scale devices, sensors and transducers for a variety of fundamental physics studies will be discussed.
Fast silicon etching using an expanding cascade arc plasma in a SF6/argon mixture
Authors: Beulens J. J. , Wilbers A. T. M. , Haverlag M. , Oehrlein G. S. , Kroesen G. M. W. , Schram D. C.
Published: July 2002

An expanding cascaded arc is used as a fluorine atom source for fast etching of silicon. Extremely high etch rates up to 1.3 μm/s have been obtained. A reactor parameter study has been performed. The obtained selectivity Si/SiO2 is ∼11 for substrate temperatures of 600 °C, increasing to ∼20 at 100 °C. The etching proces is fully isotropic.
Monte Carlo-fluid model of chlorine atom production in Cl2, HCl, and CCl4 radio-frequency discharges for plasma etching
Authors: Sommerer Timothy J. , Kushner Mark J.
Published: July 2002

Chlorine chemistries are often used for the radio-frequency (rf) discharge plasma etching of compound semiconductors, metals, and silicon. A variety of gas mixtures are used as Cl atom donors, many of which have different electron transport coefficients. In this article we computationally investigate 13.56 MHz rf discharges sustained in He/Cl2, He/HCl, and He/CCl4 gas mixtures in the context of plasma etching. The study is performed using a Monte Carlo-fluid hybrid model of rf discharges. We find that the Cl atom production efficiency is surprisingly similar in these mixtures, while the details of the electron transport (sources of ionization, locations of attachment, electronegativity) dramatically differ. We also find that even at the low pressures of interest (0.25–1 Torr) attachment in He/HCl mixtures is dominated by vibrationally excited HCl, in analogy to high-pressure discharge devices.
Submicron patterning of thin cobalt films for magnetic storage
Authors: New R. M. H. , Pease R. F. W. , White R. L.
Published: July 2002

We are investigating the feasibility of a recording medium in which each bit of information is stored in a single-domain magnetic particle. To this end we have developed a procedure for high-resolution patterning of magnetic recording films using direct write electron-beam lithography and a multistep sputter etching process. We have used this procedure to define small islands of polycrystalline magnetic thin film with feature sizes down to 0.1 μm. The patterning process is suitable for many different kinds of magnetic films, including single-crystal epitaxially grown films, and is designed to minimize physical and chemical damage to the magnetic material being patterned. Both atomic force microscopy and x-ray photoemission spectroscopy have been used to establish that the magnetic islands patterned using this process are physically isolated from each other.
Optimization of interfaces in InGaAs/InP heterostructures grown by gas source molecular-beam epitaxy
Authors: Mozume T. , Kashima H. , Hosomi K. , Ouchi K. , Sato H. , Masuda H. , Tanoue T. , Ohbu I.
Published: July 2002

A novel source switching procedure in gas source molecular-beam epitaxy achieves abrupt interfaces in lattice-matched InGaAs/InP. In this procedure, the source supply is interrupted at each interface to reduce excess residual As or P atoms on the InGaAs or InP surfaces. The interruption time is optimized by characterizing the heterointerfaces by Auger electron microscopy and photoluminescence spectroscopy. High-resolution transmission electron microscopy reveals that each heterointerface of single quantum wells grown by this optimized switching procedure has no transition region. To our knowledge, this is the first successful growth of a perfectly abrupt InGaAs/InP heterointerface.
H2O enhanced focused ion beam micromachining
Authors: Stark T. J. , Shedd G. M. , Vitarelli J. , Griffis D. P. , Russell P. E.
Published: July 2002

The use of H2O vapor as a chemical adjunct for focused ion beam micromachining has been investigated. The presence of H2O vapor during micromachining with a 25 keV Ga+ beam increases the removal rate of carbon-containing materials such as polyimide, PMMA, and other resists by a factor of 20 (relative to physical sputtering), and that of diamond by a factor of 10. In addition, H2O causes a decrease in the removal rate of some other materials (e.g., Si and Al) by as much as a factor of 10, effectively increasing the selectivity of polymers over these other materials by as much as a factor of 200. The dependence of the removal rate on H2O pressure at the sample, pixel dwell time, pixel size, pattern frame time (corresponding to pattern size), and current density has been investigated utilizing PMMA. PMMA removal rates were calculated by measuring the depth of rectangular pits micromachined into PMMA films under the various experimental conditions. In addition to investigating the effect of H2O on material removal rates, the change in removal rate of PMMA in the presence of selected gases including O2, H2, and CH3OH, has been measured.
Electronic properties of ideal and interface-modified metal-semiconductor interfaces
Authors: Mönch Winfried
Published: July 2002

The electronic properties of metal-semiconductor or Schottky contacts are characterized by their barrier heights. At ideal contacts, they are determined by the continuum of metal-induced gap states. Extrinsic interface defects and dipoles as well as interlayers may be present in real contacts and will modify the barrier heights. The zero-charge-transfer barrier height and a slope parameter describe the chemical trends of the barrier heights of Schottky contacts on a specific semiconductor. The zero-charge-transfer barrier heights may be calculated by using the empirical tight-binding method with universal parameters and the width of the dielectric band gaps and the slope parameters are given by the optical dielectric constants of the semiconductors. This is verified by comparison with numerical data from well-established theoretical approaches. Hydrogen doping of metal–diamond and metal–silicon interfaces changes their barrier heights with opposite sign. This is explained by a different orientation of H–C and H–Si interface dipoles. Ag and Pb/Si(111) contacts may be prepared with a ‘‘7×7’’ and a 1×1 interface structure. The difference of their barrier heights is explained by the electric dipole correlated with the stacking fault which is a characteristic of 7×7 reconstructions. Interlayers will also alter the barrier heights of Schottky contacts. Typical examples are SiO2 and Si3N4, i.e., MOS and MNS structures. Previous investigations found their barrier heights to vary as a function of the metals used. The chemical trends of these two data sets are described by the slope parameters predicted from the optical dielectric constants of SiO2 and Si3N4.