bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of ion energy flux on the properties of hydrogenated amorphous carbon films
Authors: Vandentop G. J. , Kawasaki M. , Kobayashi K. , Somorjai G. A.
Published: July 2002

In this study the effect of varying ion energy flux on the properties of amorphous hydrogenated carbon films produced by plasma-assisted chemical vapor deposition from methane was investigated. The ion current, used to calculate the apparent ion energy flux, was measured through an orifice in one of the electrodes of the parallel plate system, using a Faraday cup. The film properties investigated include hardness, stress, methyl and methylene concentrations, and optical gap. All the observed properties vary significantly with ion energy flux and are strongly correlated with each other. As ion energy flux increases, the hardness increases, the compressive stress increases, the concentration of methyl and methylene groups decrease, and the optical gap decreases. The results demonstrate how the ion energy flux on to the film surface controls the final properties of the films.
Enhanced chemical bonding between lubricants and magnetic coatings by high energy irradiation and its application to tape durability
Authors: Lee Ting-Ho Dan
Published: July 2002

Metal particle and metal evaporated tapes topcoated with perfluoropolyether (PFPE) were irradiated with either x rays, electron beams or ion beams in an effort to understand the process for enhancing tape durability. The species formed were studied by x-ray photoelectron spectroscopy. Dissociation of PFPE and formation of a chemical bond involving fluorine and metal occurred with all three types of irradiation. The stability of different types of PFPE were compared. Certain species were found to be more reactive with the metal upon high energy radiation. Increased durability of the magnetic tapes after radiation exposure is believed to be the result of radiation-enhanced chemical bonding of lubricants to the tape surface.
Ion-induced topography, depth resolution, and ion yield during secondary ion mass spectrometry depth profiling of a GaAs/AlGaAs superlattice: Effects of sample rotation
Authors: Cirlin Eun-Hee , Vajo John J. , Doty Robert E. , Hasenberg T. C.
Published: July 2002

Effects of sample rotation and sputtering conditions on the depth resolution and ion yield during secondary ion mass spectrometry (SIMS) sputter depth profiles have been studied on bulk GaAs and a GaAs(5 nm)/Al0.3Ga0.7As (5 nm) superlattice. Profiles without sample rotation with 1.0–7.0 keV O+2 show a rapid degradation of the depth resolution with increasing sputter depth. Profiles with Ar+ show only slight degradation. Scanning electron microscope (SEM) studies indicate that degradation is associated with development of periodic surface ripples. The wavelength of the ripples is energy dependent and increases with increasing ion impact energy. With sample rotation, no degradation of the depth resolution is observed and SEM micrographs indicate that surfaces sputtered with rotation are smooth. In addition, with 3.0 keV O+2 significant changes in the secondary ion yield of AsO+ from bulk GaAs are observed at a depth of ∼200 nm. No changes are observed with sample rotation. Our results demonstrate that sample rotation during SIMS depth profiling prevents and can reverse the development of surface topography that both degrades depth resolution and changes secondary ion yield. Thus, interpretation and quantitation of SIMS analysis is facilitated.
Reactivity of a fluorine passivated silicon surface
Authors: Haring Ruud A. , Liehr Michael
Published: July 2002

Fluorine-terminated Si(100) surfaces have been prepared by dosing with XeF2. The reactivity of these surfaces towards reoxidation by water vapor or molecular oxygen has been analyzed in situ using x-ray photoelectron spectroscopy. Whereas the fluorine-terminated surface is quite stable in dry oxygen, significantly stronger reactivity is observed with water vapor. Reaction with water molecules creates Si–OF surface species, presumably via an insertion reaction, and leads to loss of fluorine and to growth of a thin oxide. It is inferred that the hydrogen-terminated, HF-cleaned surface, which exhibits some surface fluorine, is oxidatively attacked in water or air at Si–F defect sites.
Atomic force microscopy of deoxyribonucleic acid strands adsorbed on mica: The effect of humidity on apparent width and image contrast
Authors: Thundat T. , Warmack R. J. , Allison D. P. , Bottomley L. A. , Lourenco A. J. , Ferrell T. L.
Published: July 2002

We have investigated the effect of relative humidity on the apparent width and contrast of isolated strands of deoxyribonucleic acid (DNA) imaged with atomic force microscopy (AFM). Due to convolution of the tip with DNA, the apparent width of DNA molecules observed with AFM was broader than the known width of DNA. Also, the apparent width of DNA increased with increasing humidity while the contrast of the DNA images decreased with increasing humidity. This phenomenon is completely reversible and can be attributed to non-normal forces causing a buckling of AFM cantilever.
Pumping performance of a new type of hybrid molecular pump
Authors: Ba Dechun , Yang Naiheng , Wang Xiaodong , Pang Shijin , Zhu Yu , Wang Xiaozhen
Published: July 2002

A new type of hybrid molecular pump of high performance and reliability has been developed. The pump’s rotational speed is 18 000 rpm. The pump is constructed with eleven stages of a turbomolecular pump and a drum multigroove drum molecular pump in which the clearance between rotor and stationary part is 0.35 mm; the rotor’s deformation forms a cuneiform channel of the proper working clearance to ensure the pump’s performance and working reliability. The pump can operate within the pressure range of 5×102–10−6 Pa for a oil-free vacuum with the maximum speed of 400 ℓ/s. The maximum compression ratio for H2 is over 4000. It can be widely used in vacuum processes, and is suitable for the higher pressures in dry etching, chemical vapor deposition, etc. This article describes the design considerations and structure of the pump and gives the structural parameters of the pump and the curves relating to the performance.
Growth of sodium clusters at the surface of Na β″-alumina crystals induced by electron bombardment
Authors: Achete C. A. , Freire F. L.
Published: July 2002

The growth of sodium metallic clusters on the edge face of Na β″-alumina single crystals was observed by scanning Auger microscopy. Even using low current densities it is possible to observe the growth of these clusters. The changes in the elemental concentration of the irradiated surfaces are investigated as a function of the irradiation time for two different beam parameters: current density and focalization conditions.
Variation of the lead content in sputtered copper–lead films due to resputtering effects
Authors: Eisenmenger-Sittner Christoph , Bergauer Anton , Wagendristel Alfred , Gärtner Walter
Published: July 2002

Soft tribological coatings deposited by magnetron sputtering are used as protective layers of sliding bearings in high-performance diesel engines. They consist of a tough component with a high melting point and a soft component with a low melting point. The tough component gives mechanical stability while the soft component provides the capability to embed contamination particles. The components are immiscible to prevent the formation of intermediate brittle phases. One system under investigation is copper lead. Although the chemical composition of a sputter-deposited film should generally be equal to target composition this does not hold for Cu with a small amount of Pb. The experiments showed that the Pb content of films deposited by magnetron sputtering with Ar+ ions from a planar-cast Cu 4 wt % Pb target strongly depends on the process parameters of working gas pressure and substrate temperature. Gas pressure and substrate temperature were varied from 0.3 to 5 Pa and 100 to 260 °C, respectively. The Pb content of the films was measured by energy-dispersive x-ray (EDX) analysis and compared to the actual Pb content of the target (3.7 wt % measured by AAS and EDX). Low substrate temperature or low working gas pressure yields a low Pb content. Increasing either temperature or gas pressure increases the Pb content up to target composition. These effects are explained semiquantitatively by taking into account the gas-phase transport mechanism of the sputtered particles and the adsorption mechanisms of Pb atoms on the surface of the forming film. Mechanical and structural film properties, which are also influenced by the Pb content, are evaluated by fracture, microhardness testing, and examination of microtome cuts.
Hydrogen and CO spillover at Cu/Rh(100) bimetallic surfaces studied by high-resolution electron energy-loss spectroscopy
Authors: Estrada C. A. , He J.-W. , Goodman D. W.
Published: July 2002

Hydrogen and CO spillover at Cu/Rh(100) interfaces has been studied using high-resolution electron energy-loss spectroscopy (HREELS). Upon hydrogen exposure to 0.33 ML of Cu on Rh(100) and subsequent annealing to 250 K, hydrogen atoms migrate from Rh to Cu as evidenced by the appearance of the HREELS loss feature corresponding to a H–Cu vibration at 866 cm−1. In addition, deposition of ∼3 ML of Cu onto a H-preadsorbed Rh(100) surface induces the hydrogen atoms to spillover from the Rh(100) surface onto the Cu overlayers. Likewise, CO is found to diffuse from Cu sites to Rh sites as CO-covered Cu/Rh(100) surfaces are heated to ∼250 K. Furthermore, depositing Cu onto a CO-precovered Rh(100) surface at 90 K results in spillover of CO from Rh to Cu overlayers leading to a CO/Cu/Rh(100) structure.
Pumping behavior of sputtering ion pump
Authors: Chou T. S. , Bittner J. , Schuchman J.
Published: July 2002

To optimize the design of a distributed ion pump (DIP) for the superconducting x-ray lithography source, the stability of the rotating electron cloud at very high magnetic field beyond transition [W. Schuurman, Physica 43, 513 (1969)] must be re-examined. In this work the pumping speed and frequency spectrum of a DIP at various voltages (1–10 kV) and various magnetic fields (0.1–4 T) are measured. Three cell diameters 10, 5, and 2.5 mm, each 8 mm long, and with 3 or 4 mm gaps between anode and cathode are investigated. In this study both the titanium cathodes and the stainless steel anode plates are perforated with holes comparable in size to the anode cell diameters. Only the partially saturated pumping behavior is under investigation. The ultimate pressure and conditioning of the pump will be investigated at a later date when the stability criterion for the electron cloud is better understood.
Complementary scanning tunneling microscopy and scanning electron microscopy studies of electroplated gold surfaces
Authors: Siperko L. M. , Hurban S. S. , Spalik J. M. , Katnani A. D.
Published: July 2002

The surface topography of gold electroplated as a function of current density has been studied by two topographical imaging techniques. Scanning tunneling microscopy (STM) was used to extend the magnification regime of scanning electron microscopy (SEM). STM micrographs of a 1×1-μm scan area compare well with high resolution (50 000×) SEM micrographs. The surface of the gold was found to exhibit a distinct trend from an amorphous, porous appearance to a closely packed granular structure with decreasing current density. Surface roughness values extracted from STM data indicate a logarithmic dependence of roughness on the plating density.
Chemical vapor depositing of metal fluorides
Authors: Sarhangi A. , Power J. M.
Published: July 2002

High Purity BeF2 and BeF2–AlF3 glasses have been deposited by the chemical vapor deposition technique using beryllium and aluminum 1,1,1,5,5,5 hexafluoroacetylacetonate, M(hfa)x, as source compounds. Be(hfa)2 and Al(hfa)3 provided the source for both metal and fluorine. Thermal decomposition of M(hfa)x forms two exclusive products, MFx and a volatile organic byproduct, 2,2-difluoro-2,3-dihydro-5-trifluoromethylfuran-3-one. This unique intramolecular fluorine transfer from the ligand to the metal provides a method for depositing various high purity metal fluorides. Optically clear BeF2 and BeF2–AlF3 glass samples have been made with the correct stoichiometry and a very low level of impurities.
Surface structure of the disordered Cl/Ti(0001) system determined by diffuse low-energy electron diffraction
Authors: Ri C.-S. , Watson P. R.
Published: July 2002

Molecular chlorine adsorbs dissociatively on the clean Ti(0001) surface to form a disordered overlayer that only orders after high-temperature annealing. We have made measurements of the diffuse low-energy electron diffraction (DLEED) from a disordered chlorine layer at 20% of a monolayer coverage. After substraction of the DLEED intensities from the clean surface, the Pendry Y function was calculated using (78,82) and (90,94)-eV energy pairs. These experimental functions were then compared with calculated Y functions for several plausible adsorption sites on the Ti(0001) surface: on-top, bridge and the two types of threefold hollow sites (with or without an atom directly under the site). The calculations also allowed the Ti–Cl interlayer distance to vary, but fixed other structural parameters. Using the Pendry R factor (RP) the on-top and bridge sites are easily rejected, but the two types of threefold sites cannot be distinguished. The analysis produces a best fit for a threefold site with a Ti–Cl interlayer spacing of 2.48±0.07 Å with a value of Rp = 0.45. This structure has a Ti–Cl bond length of 2.96 Å that is in good agreement with a value of 2.94 Å predicted from solid-state chemistry considerations.
Photoemission studies and outgassing-rate measurements on aluminum-alloy surfaces lathed with various alcohols
Authors: Suemitsu M. , Shimoyamada H. , Matsuzaki N. , Miyamoto N. , Ishibe J.
Published: July 2002

X-ray photoemission spectroscopy measurements have been carried out for aluminum surfaces lathed with various kinds of alcohols. Through analysis of the surface chemistry of each surface, the formation mechanism of the surface oxide layer during the lathing was clarified. All the alcohols tested in this study showed equivalently thin oxide layer on the treated surface, suggesting their possibilities for the use in ultrahigh vacuum. Validity of this suggestion was confirmed by extremely low outgassing rates and a rapid evacuation curve obtained for the ethanol-lathing or the isopropanol-lathing treated aluminum-alloy chambers.
Ferroelectric lead zirconate titanate thin films by radio frequency magnetron sputtering
Authors: Ramakrishnan E. S. , Howng Wei-Yean
Published: July 2002

Ferroelectric thin films of lanthanum modified lead zirconate titanate (PLZT) were deposited on platinum and fused quartz substrates by rf magnetron sputtering. Cold pressed powder was used as the target with excess PbO in the target composition. The PLZT films were deposited at different substrate temperatures and the thickness of the sputtered films were in the 1–2 μm range. The effect of post-deposition anneal on the structure and ferroelectric properties are discussed. The structure and composition of the films were determined by x-ray diffraction and energy dispersive x-ray analysis and found to be strongly dependent on the excess PbO content in the target, and on the deposition parameters. Films deposited on platinum have (111) or (110) orientation depending on the deposition temperature and the oxygen content in the sputter gas. Film Pb/(Zr+Ti) ratios were determined from energy dispersive x-ray spectra as a function of the sputtering geometry. Electrical properties were evaluated in terms of the dielectric constant, K, from capacitance measurements. Ferroelectric hysteresis characteristics were measured using a modified Sawyer–Tower circuit. The values of the remanent polarization, Pr, was in the range 5–15μC/cm2 and the coercive field, Ec, between 17 and 35 kV/cm depending on the process parameters.
Amorphous Si as an interfacial control layer for SiNx/InP
Authors: Kwok R. W. M. , Lau W. M. , Ingrey S. , Landheer D.
Published: July 2002

The use of an ultrathin amorphous silicon layer at the interface between silicon nitride and InP has been studied. The objective was to reduce the interface state density of the dielectric-semiconductor structure. Amorphous silicon and silicon nitride were deposited sequentially in the same remote plasma chemical vapor deposition chamber with a base pressure in ultrahigh vacuum. Less than 2 nm of amorphous silicon was deposited on InP by decomposing silane in a remote plasma. Three different plasmas, argon, helium, and hydrogen were tried. Silicon nitride was deposited by reacting silane with atomic nitrogen from a remote nitrogen plasma. Most of the processing steps were monitored by x-ray photoelectron spectroscopy (XPS) with sample transfer in ultrahigh vacuum. The degree of Fermi level pinning of InP at the resultant interface was studied by surface charge spectroscopy (SCS). It was found that the deposition of amorphous silicon in the nanometer thickness range could be readily controlled. The amount of native oxide on InP under the amorphous silicon layer was below the detection limit of XPS. Moreover, a 1 nm amorphous silicon layer was thick enough to protect the underlying InP from oxidation even with an exposure to ultraviolet/ozone for 15 min. SCS analysis also showed that the deposition of amorphous silicon significantly reduced the degree of Fermi level pinning of InP.
NF3 plasma treatment of polymeric dielectrics
Authors: Lu Hsueh Yi , Petrich Mark A.
Published: July 2002

Polyimide and polyphenylquinoxaline are important dielectric materials used in microelectronics fabrication. These polymers could be used even more extensively if they had greater moisture resistance. We demonstrate that plasma processing techniques can be used to improve the moisture resistance of polyimide and polyphenylquinoxaline films. Films are exposed to nitrogen trifluoride plasmas to introduce fluorine into the surface of the polymers. Fluorination is monitored with x-ray photoelectron spectroscopy and Fourier-transform infrared absorption spectroscopy. Water-contact angle measurements are used to assess the hydrophobicity of the treated surfaces. The polyimide and polyphenylquinoxaline film surfaces are quickly fluorinated during plasma exposure, and the moisture resistance improves consequently. The water-contact angle of our best film, 102°, compares favorably with polytetrafluoroethylene (109°). Plasma conditions can be controlled to minimize polymer degradation. The polyphenylquinoxaline films are etched by less than 0.01 μm/min in these experiments. Spectroscopic studies show that the aromatic carbons in the polymers are more readily fluorinated than carbonyl group carbons, and that the fluorination is restricted to the surface.
Characterization of the electrical bias induced strain variation in metal–oxide–semiconductor field effect transistors using x-ray double crystal topography
Authors: Ma David I , Qadri Syed B. , Peckerar Martin C. , McCarthy Daniel
Published: July 2002

N-channel metal–oxide–semiconductor field effect transistors (n-MOSFETs) were biased under different operating conditions. Superficial silicon strain patterns were recorded by reflection mode double crystal topography. Stress redistributions caused by various applied electrical field (E) biases were observed. A comparison of the electrical field induced stress and mechanically induced stress was made. Based upon this result, the amount of bias induced stress was measured. X-ray peak reflection intensity, the diffraction angle of this peak, and the full width at half-maximum (FWHM) of the x-ray double crystal rocking curves under various biases were also analyzed. All of these measurements indicate that a weak piezoelectric effect (WPE) exists in the superficial layers of MOS devices. A quantitative analysis of WPE modulus is also presented.
X-ray diagnostics for electron cyclotron resonance processing plasmas
Authors: Castagna T. J. , Shohet J. L. , Ashtiani K. A. , Hershkowitz N.
Published: July 2002

Electron cyclotron resonance processing plasmas have been shown to produce low-energy x rays. X radiation was detected in nitrogen plasmas from energies of 1 to 17 keV for microwave input powers of 800 and 1000 W. The x-ray flux decreased with increasing pressure over the range of 0.5 to 3.5 mTorr. Temperatures corresponding to the component of the electron velocity distributions responsible for creating the x rays were estimated from the slopes of the tails of the x-ray spectra and also decreased with increasing pressure. The x-ray flux measured by the detector could be decreased substantially by changing the magnetic field configuration. In general, it was found that measurable x radiation was produced whenever the surface described by the value of magnetic field which corresponds to that for cyclotron resonance intersects the vacuum chamber walls and/or other solid surfaces inside the chamber.
Residual stress and the effect of implanted argon in films of zirconium nitride made by physical vapor deposition
Authors: Perry A. J. , Sartwell B. D. , Valvoda V. , Rafaja D. , Williamson D. L. , Nelson A. J.
Published: July 2002

Zirconium nitride films made by reactive cathodic arc evaporation at high bias have been dual energy ion implanted with argon. It is found that the x-ray elastic constants of the unimplanted films differ from those measured under simple biaxial compressive elastic stress conditions. The effect of 1% argon implantation is to reduce both the lattice parameters and the compressive residual stress. It is considered that the argon resides on substitutional lattice sites following a softening of the implanted layers caused by the energy accompanying the implantation process. As the amount of argon implanted is increased (6% or 12%), the lattice continues to contract, but less rapidly, and the residual stress is hardly affected. It is suggested that the lattice softening continues and is accompanied by precipitation of the argon as bubbles.
Vapor transport epitaxy, a novel growth technique for compound semiconductors
Authors: Gurary A. , Tompa G. S. , Nelson C. R. , Stall R. A. , Liang S. , Lu Y.
Published: July 2002

An advanced vapor transport epitaxy (VTE) technique for depositing compound semiconductors is described. The technique operates in the 10−1–10−6 Torr range using elemental, gas, or metalorganic sources. We have previously demonstrated elemental VTE oval defect-free growth of several microns of GaAs at growth rates exceeding one micron per hour, on GaAs (100) and (111) 2° off toward 〈110〉 substrates. Elemental VTE is reviewed, and the effects of hydrogen on elemental VTE are discussed. The deposition process for GaAs films using metalorganic sources is described and results are presented. Electrical characteristics, as measured by Hall and sheet resistivity, show that films deposited using monoethylarsine and triethylgallium are n type as deposited. The resolving of several problems common to molecular-beam epitaxy, chemical-beam epitaxy, and metalorganic chemical vapor deposition systems has been the motivation for investigation of this technique.
Measurement of electron swarm parameters in GeH4–Ar mixtures
Authors: Soejima H. , Nakamura Y.
Published: July 2002

The drift velocity W and the product of the longitudinal diffusion coefficient of electrons and the gas number density NDL were measured in the 0.210% and 0.980% monogermane (GeH4)–argon mixtures by using a double-shutter (four-gauze) drift tube with variable drift distance. The measurements were carried out over the E/N range 0.04–20 Td and over the N-values 7.1×1016–3.6×1019 cm−3. All measurements were carried out at room temperature. No apparent dependence of W and NDL on the gas number density was observed throughout the present measurement. The measured E/N dependence of these electron swarm parameters showed very similar features to those observed in our recent measurements in monosilane (SiH4)–argon mixtures. The present swarm parameters were analyzed to derive a set of electron collision cross sections for GeH4 molecule. Derived vibrational cross sections showed a threshold peak and a resonance peak at about 2.5 eV.
Effects of aluminum silicon copper sputtering target processing methods on thin film uniformity and process control during very large scale integrated device fabrication
Authors: Dunlop J. A. , Pouliquen B. Y. , Drinnon T. J. , Wilcoxen D. T. , Huneke J. C. , Ivanov I. C. , Knorr D. B. , Tracy D. P.
Published: July 2002

The relationship between AlSiCu target manufacturing technique and sputtered-deposited film quality was examined with an emphasis on film uniformity and process control. Targets with the following attributes were evaluated: standard grain size (0.5 mm)—random orientation, standard grain size (1.4 mm prior to orientation)— 〈110〉 orientation, small grain size (0.15 mm)—random orientation, and small grain size (0.2 mm prior to orientation)— 〈110〉 orientation. A Varian 3290 sputtering system and Al 0.8%Si 0.5%Cu (weight percent) targets was used to deposit thin films under standard production conditions. Deposition uniformity, thin film microstructure and analytical results are reported. Beneficial synergism was noted when the combination of small grain size and grain orientation was produced in the target manufacturing process. These targets displayed significantly better sputtered film thickness uniformity, more consistent target erosion through target life and increased target lifetime. A mechanism for these enhancements, uniform target erosion, is discussed. Other critical properties of films deposited from the four target types were found to be equivalent for device production.
Interfacial reactions between aluminum and BPDA-PDA
Authors: Chenite A. , Selmani A. , Lamontagne B. , Yelon A.
Published: July 2002

Interaction of evaporated aluminum with BPDA-PDA polyimide surfaces have been studied using x-ray photoelectron spectroscopy. At low coverage, aluminum reacts primarily with carbonyl groups as in the PMDA-ODA and also diffuses into the polyimide substrate to react with inner carbonyls. No trace of metal clusters are detected in the initial metallization. When the covering rate becomes somewhat higher, additional interfacial reactions occur, involving the formation of N–Al and C–Al bonds. In general, the chemical interactions of Al at BPDA-PDA and PMDA-ODA are similar. It is suggested that the observed difference in adhesion strength between the two polyimides comes from the diamine moiety (PDA and ODA). In the PMDA-ODA the macromolecules can rotate around the ether function which is not the case in the BPDA-PDA where the conjugation makes the macromolecule more rigid. Thus the difference in adhesion may be attributed to the chain conformation of polyimide.
Correlation of plasma and surface chemistry during electron cyclotron resonance hydrogen etching of native silicon oxide
Authors: Tsai W. , Delfino M. , Day M. E. , Sheng T. , Chung B. C. , Salimian S.
Published: July 2002

Downstream electron cyclotron resonance H2 plasma etching of native silicon oxide was studied in a multichamber integrated cluster tool. H (656.3 nm), OH (306.4 nm), SiO (266.9 nm), SiH (412.8 nm) and Si (288.2 nm) emission lines were monitored and correlated with surface atomic O/Si ratios measured by in situ x-ray photoelectron spectroscopy. Two distinct regimes of oxide etching were observed by plasma emission with the removal of the interfacial oxide to be four times slower than the bulk oxide. Concentration of H, OH, SiO radicals, native oxide etch rate, and ion density near the surface were maximized at 2.5 mTorr, which confirms that the downstream plasma process is driven by an ion-assisted removal mechanism. The ion density varies from 7.5 to 0.6×1010 cm−3 at a distance from substrate of 20 and 1.5 cm, respectively.
Surface characterization of GaAs after the reactive ion etching of GeMoW ohmic contact in radio frequency SF6–O2 plasma
Authors: Campo A. , Cardinaud Ch. , Turban G. , Dubon-Chevallier C. , Amarger V. , Etrillard J.
Published: July 2002

A characterization of monocrystalline GaAs surfaces after reactive ion etching of a GeMoW contact in SF6–O2 is presented. Scanning electron microscopy (SEM), monochromatized x-ray photoelectron spectroscopy (XPS), and Auger spectroscopy are used as means of investigation. Irregular 0.1 μm structures are observed by SEM on the surface while the XPS analysis reveals the existence of a gallium oxyfluoride superficial layer which composition is typically GaOF. Contributions in the As 2p and As 3d spectra at 1.8 eV with respect to As (GaAs) are identified as arsenic sulfides. Moreover, they have been localized on top of the GaAs substrate, and in the lowest part of the gallium oxyfluoride layer. An annealing at 800 °C for 10 s partly removes the SEM observed structures which can be assigned to the AsxSy and As2O3 species. The XPS analysis reveals the decomposition of the interface As–species when the temperature increases and the concomitant Ga–S bonds formation. Concurrently, the GaOF layer could be degraded by fluorine evaporation to yield a Ga2O3 oxide phase.
In situ observation of growing surface of oxide films by reflection high-energy electron diffraction beam excited Auger electron spectroscopy
Authors: Nonaka Hidehiko , Shimizu Takashi , Ichimura Shingo , Arai Kazuo
Published: July 2002

The reflection high-energy electron diffraction beam excited Auger electron spectroscopy (AES) was applied to in situ and real time observation of the growing surface of films during molecular-beam epitaxy deposition. A compact electron energy analyzer assembly which consists of an einzel lens, sector-type energy analyzer, microchannel plate detector, and magnetic shielding case was built to enable the measurement close to the substrate without disturbing the deposition. The system was checked by the in situ AES measurement of crystals surface during cleaning with ozone. The technique is applicable to analyze in situ the growing surface of more complicated materials such as oxide superconductors whose microstructures at an atomic level must be well controlled for better quality and for use in microelectronic devices such as the Josephson junction.
Tungsten and tungsten–carbon thin films deposited by magnetron sputtering
Authors: Gouy-Pailler Ph. , Pauleau Y.
Published: July 2002

Tungsten and tungsten–carbon thin films have been produced from a W target sputtered in argon and argon–methane mixtures, respectively. The deposition rate of W films was measured as a function of the sputtering power and argon pressure varying in the range of 0.3–3 Pa. The crystallographic structure and composition of W films deposited on silicon and carbon substrates were investigated by x-ray diffraction and Rutherford backscattering spectroscopy. The electrical resistivity of the W films was minimum (12 μΩ cm) when the internal stresses in the films were negligible. The carbon concentration in the W–C films determined by nuclear reaction analyses and Rutherford backscattering spectroscopy was varied from 10 to 95 at. % with increasing CH4 content in the gas phase. The crystallographic structure of the W–C films was found to be dependent on the carbon concentration. Below 25 at. % of carbon, the structure of the W–C films was that of the cubic α-W phase with a dilated lattice parameter. For higher carbon concentrations, the bcc α-W phase disappeared and the structure was that of the nonstoichiometric cubic β-WC1−x phase. The structure of W–C films with a carbon content greater than 65 at. % was nearly amorphous. Internal stresses and electrical resistivity of W–C films were determined as functions of the carbon concentration. The experimental parameters suitable to produce W and W–C films with low resistivities and reduced internal stress level are reported in this article.
Selective reactive ion etching of phosphorus-doped oxide over undoped SiO2
Authors: Vender David , Oehrlein Gottlieb S. , Schwartz Geraldine C.
Published: July 2002

Experiments on reactive ion etching of plasma enhanced chemical vapor deposition (PECVD) phosphorus-doped oxide [phosphosilicate glass (PSG)] and thermal oxide films have revealed significant differences which allow highly selective etching of PSG over SiO2. Samples were etched in a diode reactor with a Teflon-covered cathode in a mixture of CF4 and H2, and the proportion of hydrogen was varied over the whole range of 0%–100%. The plasma chemistry is significantly affected as the proportion of hydrogen in the mixture is increased leading to a transition from etching of oxide to deposition of a fluorocarbon film on the oxide surface. This transition occurs near 50% H2 under our experimental conditions. In contrast to thermal oxide, PSG films with 7% phosphorus continue to etch in mixtures with as much as 80%–90% H2 under the same conditions, and the etch rate is insensitive to the proportion of hydrogen. This effect is most likely due to the presence of phosphorus in the doped oxide film since PECVD borosilicate films etch similarly to thermal oxide. Furthermore, the transition from etching to deposition depends on the phosphorus concentration in the doped film.
Model of differential electrical network for the blades of turbomolecular pumps*
Authors: Chu J. G.
Published: July 2002

Models of differential electrical networks are introduced as analogs of the pumping action and the leakage effects. A concept of synthetic modified compression ratio is suggested to refine the analysis. The theoretical expectations are verified by the experimental results. The design work of turbomolecular pumps can be simplified by using this method.
Treatment of the wall materials of extremely high vacuum chamber for dynamical surface analysis
Authors: Tsukui Katsuyuki , Hasunuma Ryu , Endo Kazuhiko , Osaka Toshiaki , Ohdomari Iwao
Published: July 2002

In order to investigate the surface structure dynamically reducing the influence of the residential molecules upon the surface, the way to observe the surfaces under the extremely high vacuum (XHV; <10−12 Torr) condition has been discussed. We proposed to combine the two processes, electrochemically polishing and high temperature baking, in order to reduce the outgassing rate of the wall material. We have characterized the inner surfaces of the stainless steel chamber processed by two optimum ways to minimize outgassing rate, by means of surface analysis and measurements of gas emission rate. We have found that in order to accomplish the XHV condition, the inner surface should be electrochemically polished after the complete baking of the material itself at 1300 K. These processes made the degassing rate of the wall lowest.
Electronic properties of ionic insulators on metal and semiconductor surfaces: RbCl on Si(100) and W(110)
Authors: Souda R. , Hayami W. , Aizawa T. , Otani S. , Ishizawa Y.
Published: July 2002

The nature of bonding of RbCl on the Si(100) and W(110) surfaces has been investigated on the basis of neutralization and inelastic scattering of low-energy D+ ions. It is found that RbCl is dissociatively adsorbed on both substrates in a low coverage regime (<0.4 ML). The resultant Rb and Cl adatoms are covalently bonded to the W(110) surface while, on the Si(100) surface, Cl reacts preferentially with the dangling bond and Rb is ionically adsorbed on the surface. The hydrogenation of the Si(100) surface prevents dissociative adsorption and enables the growth of an ionic RbCl film from the low-coverage limit.
Growth of DyBa2Cu3O7−x thin films on vicinal (100) SrTiO3 substrates
Authors: Chandrasekhar N. , Agrawal V. , Achutharaman V. S. , Goldman A. M.
Published: July 2002

We report studies of the initial stages of epitaxial growth of DyBa2Cu3O7−x films on vicinal (100) SrTiO3 substrates using in situ reflection high energy electron diffraction (RHEED), transmission electron microscopy, and atomic force microscopy. Two sets of substrates, with misorientations of 2.2° and 4.4° off (100) towards (110) were used. These substrates were prethinned and annealed prior to deposition. DyBa2Cu3O7−x films were grown by ozone-assisted molecular beam epitaxy. The annealed substrates were reconstructed and had stepped surfaces. Films nucleating preferentially at the steps giving rise to an interconnected network of islands, as observed in plan view transmission electron microscopy. In situ RHEED showed intensity oscillations of the specular spot consistent with such an interpretation, and exhibited behavior dominated by surface diffusion. The higher density of nucleation sites on vicinal surfaces appears to reduce the fraction of a-axis outgrowths. The films grown on vicinal substrates also exhibit a high degree of orthorhombicity. No relationship between RHEED oscillation time periods and the completion of a unit cell of film was found, contrary to observations reported in the literature.
Atomic release of hydrogen from pure and boronized graphites
Authors: Franzen P. , Vietzke E.
Published: July 2002

The release of implanted hydrogen from pure and boronized graphites was investigated with reemission and thermal desorption (TDS) experiments. In both experiments the release of hydrogen atoms is observed. At low temperatures the release of hydrogen occurs only in the form of molecules. Above temperatures of about 900–1100 K an increasing fraction of the implanted hydrogen is released as atoms. For pure graphite, the reemission of hydrogen atoms starts at about 900 K, whereas the onset of the atomic remission is shifted to higher temperature for the boronized graphite. In the TDS experiments the release of hydrogen molecules peaks around 1000 K, the release of atomic hydrogen around 1100–1200 K. From a comparison of the reemission with the TDS data the conclusion is drawn, that the atomic release of hydrogen from graphite after hydrogen implantation is a thermal process.
C49/C54 phase transformation during chemical vapor deposition of TiSi2
Authors: Engqvist Jan , Jansson Ulf , Lu Jun , Carlsson Jan-Otto
Published: July 2002

The initial stages of chemical vapor deposition of TiSi2 from TiCl4, H2, and Si(100) have been investigated with respect to the phase formation sequence. The result showed that the metastable C49 TiSi2 phase was formed prior to the equilibrium C54 TiSi2 phase. As the growth continued, the C49 phase was transformed to the C54 phase. X-ray diffraction analyses showed that both TiSi2 phases exhibited an epitaxial-like growth with respect to the substrate. Moreover, the transformation from the C49 phase to the C54 phase was favored by increased film thickness rather than high-temperature annealing. The results could be explained by an interfacial stabilization effect where the metastable C49 phase is stabilized by epitaxy. In addition, the influence of oxygen and carbon on the process was investigated by adding O2and C2H4 to the reaction gas mixture. Oxygen had no effect while a minor stabilization of the C49 phase was observed when carbon was introduced during deposition.
Control of purple membrane adsorption to a glass surface using self-assembled monolayers
Authors: Brizzolara Robert A. , Beard Bruce C.
Published: July 2002

There is a considerable interest in the use of biological materials in electronic device applications. For example the purple membrane, a photoactive biological material, may have an application in artificial retinas. To fabricate devices such as artificial retinas from the purple membrane, a means of patterning the biological material on the substrate surface is needed. We have explored the use of self-assembled monolayers to achieve the control of the adsorption of the purple membrane to a glass surface. By changing the terminal group of the self-assembled monolayer, the affinity of the surface for the purple membrane is controlled. The adsorbed purple membrane films have been examined with x-ray photoelectron spectroscopy and fluorescence microscopy. The x-ray photoelectron spectroscopy data reveal that the purple membrane adsorbs to a clean glass surface in the amount 0.84 μg/cm2. Modifying the glass surface with a fluorocarbon-based self-assembled monolayer reduces the amount of purple membrane adsorbed by a factor of 9.3, to 0.09 μg/cm2. In the future, these results combined with one of the existing methods for patterning self-assembled monolayers, will provide a means of spatially controlling the adsorption of the purple membrane on a substrate. Thus, this work represents an important first step in the patterning of purple membrane structures and devices on a surface.
Buried reconstruction inhibition of solid phase epitaxy of Ge on Si (111)
Authors: Hellman Olof
Published: July 2002

We study the epitaxial crystallization of a thin film of amorphous Ge deposited at room temperature on Si (111). Silicon surface features which are buried beneath the Ge film are seen to affect the rate of crystallization. In particular, solid phase growth is observed to be enhanced at surface steps and defects in the surface reconstruction. We demonstrate that control of Ge crystallization morphology is possible through manipulation of Si surface structure.
Observation of cryopump fluorescence during operation of electron-beam evaporator
Authors: Erck R. A.
Published: July 2002

A blue-green glow was observed in the cold-plate section of a conventional cryogenic pump used in a vacuum-deposition chamber. The fluorescence is associated with operation of an electron-beam evaporator and is present at all gas pressures and evaporator voltages used, but cannot be made to occur during operation of a 1 kV Kaufman-type ion source or a 3 kV electron source.
Simple pulsed-plasma-beam gun for ultrahigh vacuum applications
Authors: Yamada Chikashi , Kimura Takahiro
Published: July 2002

A simple pulse-operated plasma gun, which is a combination of a pulsed-solenoid valve and an electrode to induce an electric discharge in gas at the outlet is described. The performance of the pulsed-plasma-beam gun was tested by carrying out hydrogen-plasma deoxidization of a GaAs wafer.
Characteristics of extremely fast pump-down process in an aluminum ultrahigh vacuum system
Authors: Miki M. , Itoh K. , Enomoto N. , Ishimaru H.
Published: July 2002

Characteristics of an extremely fast pump-down process were studied in an aluminum ultrahigh vacuum system, using super-dry nitrogen. The system is constituted of a roughing pump line, a main pump line, a venting gas line and a main chamber with vacuum gauges. The venting gas line has two types of water traps in series. Experiments were done after achieving 10−11 Torr range following a bake. Experimental results were the following: (1) using only the moisture trap in venting (case A), the pressure reached, from 760 Torr, was 1×10−5 Torr in 0.7 min, 1×10−8 Torr in 4.2 min, 1×10−10 Torr in 1000 min; the pressure was proportional to exp(−St/V) down to the 10−5 Torr range; here, V, S, and t are the chamber volume, the pumping speed, and the pumping time, respectively; (2) using both the moisture trap and the ‘‘MonoTorr’’ in venting (case B), the pressure reached from 760 Torr was 1×10−5 Torr in 0.7 min, 1×10−8 Torr in only 2.5 min, 1×10−10 Torr in only 170 min; the pressure was proportional to exp (−St/V) to the 10−5 Torr range. The difference of results between (1) and (2) is mainly due to the difference of the amount of water and hydrogen content in vent-gas; the moisture trap can reduce the H2O content of vent-gas to 200 ppb after 2 h of operation, on the other hand, the MonoTorr can reduce other contents (H2O, H2, CO, CO2, etc.) of vent-gas, except N2, to a few ppb after 2 h of operation.
Electrochemical study of ultrathin silica films supported on a platinum substrate
Authors: Xu Xueping , Bojkov Hristo , Goodman D. Wayne
Published: July 2002

The aqueous electrochemistry of ultrathin silica films supported on metal substrates has been investigated in an apparatus that combines an ultrahigh vacuum analysis chamber with an electrochemical cell. The silica films were prepared in vacuum by evaporating silicon in oxygen ambient onto a platinum substrate. It is established that the silica films completely cover the substrate and isolates it from the solution. The silica films on platinum are stable under electrochemical conditions of cycling. It is shown that the thin silica films (15–100 Å) are electrically conductive, with a conductivity several orders of magnitude larger than bulk silica. The silica/Pt electrodes behave over a wide range of potentials as ideally polarizable, which facilitate electrochemical studies of supported metal particles of Pd and Pt. The under-potential deposition of copper onto silica-supported palladium particles and methanol oxidation on platinum particles have also been demonstrated.
Effects of target polycrystalline structure and surface gas coverage on magnetron I–V characteristics
Authors: Leybovich A. , Kuniya T. , Smith P. C. , Hendricks M. B. , Ruzic D. N.
Published: July 2002

The effects of Al target surface grain structure and surface gas coverage on sputtering magnetron I–V characteristics have been investigated to reveal the net effect of variations in the ion-induced electron emission yield (IIEEY) on I–V characteristics. One (110) single-crystal and three polycrystalline Al–1 wt % Cu targets with the similar (110) crystallographic orientations and grain sizes of 0.25, 0.95, and 5.5 mm were studied. The partial pressures were monitored before, during, and after sputtering. The direct IIEEY was measured under 600–900 eV Ar+ and He+ beam bombardment as a function of grain size and gas coverage at specimen temperatures of 19 and 74 °C. The IIEEY measurements demonstrated that both the surface grain structure and the gas coverage affect the electron emission. The direct IIEEY was highest in the small grain size and lowest in the large grain size specimens. An increase in specimen temperature raised the emission yield due to increased chemisorption of residual gas species. In contrast magnetron I–V characteristics suggested the highest IIEEY for medium grain size target. This difference is explained by the combined effect of residual gas adsorption and plasma sheath distortion around surface relief which results in IIEEY increase.
Proposed warm bore beam-pipe assemblies and associated vacuum systems for the worlds two largest particle detectors
Authors: Chapman G. R. , Zhou J. X.
Published: July 2002

In Ellis County, 35 miles south of Dallas, Texas, the Superconducting Super Collider is being constructed. The dominant element is the 54-mile underground collider ring, which is oval in shape with a major axis of 19 miles and a minor axis of 15 miles. When completed, opposing beams of protons at maximum energies of 20 TeV will be brought into collision at each of four experimental areas. This paper describes the long warm beam pipe assemblies and vacuum systems proposed for the two massive detectors [Gammas Electrons, and Muons (GEM) Collaboration and Solenoidal Dector Collaboration (SDC)] which will occupy the two underground experimental halls (each 300 ft long and 100×180 ft cross section) situated on the east side of the collider ring. The driving factors which influence the beam pipe geometry and vacuum system are discussed together with presentations of graphic average pressure profiles of the interaction regions. Pressure requirements are identified and the influence of the synchrotron-radiation-induced gas desorption, ion-induced pressure instability, and electron multipactoring are examined.