bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical reactivity between Teflon surfaces subjected to argon plasma treatment and atmospheric oxygen
Authors: Momose Y. , Tamura Y. , Ogino M. , Okazaki S. , Hirayama M.
Published: July 2002

Surface modification of two Teflon polymers, PFA (tetrafluoroethylene and perfluoroalkoxyvinyl ether copolymer) and PTFE (polytetrafluoroethylene), induced by argon plasma treatment using a radio frequency generator and subsequent air exposure has been investigated by x-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Chemical species assigned to peroxy radicals were produced with the development of a heavily cross-linked or branched structure at the surfaces. The dependence of the XPS and ESR spectra on the plasma treatment conditions (treatment time and power) indicated that the formation of the peroxy radicals was closely parallel to the incorporation of oxygen at the surfaces. The analysis of the XPS and ESR spectra suggested that the peroxy radicals can be attributed to two types of oxygen: one bonded to carbon in the multiply cross-linked structures, and the other bonded to carbon arising from the scission of the main chain of the polymer. The former is the most abundant radical and localized near the surface, but the latter in the bulk region. The relative contribution of the two peroxy radicals for PFA differed from that for PTFE, while the surface chemical structures of both polymers were almost the same. The oxygen of the peroxy radicals was eliminated by UV irradiation in vacuum. For PFA UV irradiated in air for a certain time the chain scission peroxy radical was produced without a change in the surface chemical structure.
Langmuir probe measurements of a radio frequency induction plasma
Authors: Hopwood J. , Guarnieri C. R. , Whitehair S. J. , Cuomo J. J.
Published: July 2002

In this work a planar, radio frequency induction plasma source is characterized in terms of ion density, electron temperature, and plasma potential using a single Langmuir probe in oxygen and noble gases. Probe measurements of density were also verified using microwave interferometry. Measured argon ion densities increase nearly linearly with power from 1×1011 cm−3 at 300 W rf power to 6×1011 cm−3 at 1.2 kW at 1×10−3 Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2×1012 cm−3 at 1×10−3 Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26×10−3 Torr to 7 eV at 0.3×10−3 Torr. Plasma potentials are typically 15–30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5×10−3 Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. Ion generation energy cost in argon is 100–250 W/A.
Scanning tunneling microscopy studies of nucleation and growth in a reactive, epitaxial system: Co/Si(111)
Authors: Bennett P. A. , Parikh S. A. , Cahill D. G.
Published: July 2002

We present scanning tunneling microscopy observations of the reaction of cobalt with Si(111)-(7×7). For deposition at 320 °C (reactive epitaxy), flat-topped monolayer islands of triangular shape with vertices along 〈1̄1̄2〉Si nucleate on the faulted side of the 7×7 structure then grow in size attaining edge lengths that are quantized to integer multiples of the 7×7 unit cell. A 2×2 reconstruction with large corrugation occurs on some of the islands, and is believed to be an ordered array of silicon adatoms. The shape and orientation of the islands appears to be determined by energetics, not growth kinetics. They coexist with the 7×7 structure, implying that metal atoms readily diffuse through the silicon matrix before attaching to an existing island. From the areal density of islands we estimate an activation energy for ‘‘surface diffusion’’ of 0.8 eV, and argue that the process involves metal atom transport through near-surface silicon interstitials. At lower temperatures, no ordered silicide forms, while at higher temperatures, multilayer islands form with a predominant layer spacing of 3.1 Å suggesting that they are (111)CoSi2. For postdeposition annealing at 600 °C (solid phase epitaxy), large, multilayer islands of CoSi2 form, in coexistence with a √7 submonolayer phase. General aspects of the nucleation, growth, and coarsening in this reactive, epitaxial system are discussed.
In situ internal reflection infrared study of aqueous hydrofluoric acid and ultraviolet/ozone treated silicon (100) surfaces
Authors: Zazzera L. , Evans J. F.
Published: July 2002

An internal reflection infrared cell has been employed to study aqueous hydrofluoric acid (HF) and ultraviolet (UV)/ozone processing of Si(100) surfaces in situ. The useful range of the infrared experiment was extended below 1500 cm−1 to examine the Si–O–Si asymmetric stretching region by using a thin (75 μm) silicon single crystal in optical contact with a germanium internal reflection element. UV/ozone cleaning produces hydrophilic surfaces by oxidative removal of adventitious hydrocarbon on SiO2 or by oxidation of hydrogen terminated silicon to SiO2. Hydrophobic Si–H terminated surfaces are produced using dilute aqueous HF and are characterized by an increase in the intensity of the Si–H stretching mode and a concomitant decrease in the intensity of the Si–O–Si mode. UV/ozone oxidation of the HF treated surface produces oxidized silicon hydrides while removing Si–H and growing SiO2. Where appropriate, comparisons will be made between the corresponding XPS and infrared spectra to demonstrate the complementary information provided by these spectroscopies.
Wear resistant sulfur films on hard ball bearing steel studied by Auger electron spectroscopy and sputter profiling, including factor analysis
Authors: Jansson C. , Nielsen G. T. , Jakobsen J. , Morgen P.
Published: July 2002

Tribological procedures with hard SAEb) 52100 steel elements (hardness of 850 Vickers or above) leading to scoring resistant surfaces with sulfur films have been monitored with Auger electron spectroscopy and sputter profiling. For hard SAE 52100 steel with clean and dry surfaces, a criterion for scoring resistance is a static friction coefficient of 0.73–0.76. These surfaces are found to consist of an approximately 30-Å-thick upper region of oxide and sulfur. Sulfur was added to the lubricant in one of the steps of the procedure, after the end of which the majority of it (85%) was found to be bound to iron as in FeS. The formation of this sulphide film is the key to scoring resistance. For other, nonscoring resistant surfaces resulting from various unsuccessful procedures, only oxide films were formed, and no sulfur had been taken up by those surfaces. The sulfur film on a scoring resistant surface was shown to slow initial oxidation compared to a surface stripped of this film. Wear of hard steel surfaces in sliding contacts, without any sulfur in the surface region, was shown to occur through oxidation, with a release of oxide debris. Thus, oxides are not beneficial to scoring resistance.
Chemical and morphological changes on silver surfaces produced by microwave generated atomic oxygen
Authors: Bhan Mohan K. , Nag Pallob K. , Miller George P. , Gregory John C.
Published: July 2002

Silver surfaces, useful in space applications because of their high conductivity and reflectivity, can be corroded by the gases and ultraviolet radiation present in the earth’s upper atmosphere. At shuttle altitudes (200–700 km), the atmosphere mainly consists of neutral atomic oxygen whose flux is about 1015 atoms/cm2 sec. On exposure to such a high flux, silver surfaces are strongly oxidized, and after prolonged exposure, the oxide layer formed is flaked off. A real-life time characterization of the oxidation of silver in space is not practical. To understand this process, it is necessary to study it under controlled laboratory conditions. In the present work, an attempt has been made to examine and understand the influence of atomic oxygen on the amount of erosion/corrosion of silver surfaces. A special emphasis has been given to studying the formation of oxides of silver, when exposed to atomic oxygen. Thin films and high purity foils of metallic silver were exposed in a microwave powered atomic oxygen generator for various powers and time intervals. X-ray photoelectron spectroscopy and x-ray diffraction results indicate the presence of only Ag2O in all samples. Scanning electron microscopy investigations confirm that the oxidation process starts as soon as silver comes under the bombardment of atomic oxygen. The oxide layer swells on formation, and becomes saturated when the oxygen concentration reaches a critical limit of 35 (± 5) at. %. Stresses and strains are developed due to volume expansion of the oxide layer, causing it to crack and spall away. This brings a fresh surface in contact with atomic oxygen and on further exposure, the process repeats itself.
Low temperature radio frequency sputter deposition of TiN thin films using optical emission spectroscopy as process monitor
Authors: Pang Z. , Boumerzoug M. , Kruzelecky R. V. , Mascher P. , Simmons J. G. , Thompson D. A.
Published: July 2002

TiN films were deposited onto various substrates including InP by rf sputtering in an N2/Ar ambient at room temperature. The rf power, the ratio of gas flows, and the total pressure were systematically varied. To optimize the deposition conditions, the plasma excitation processes were examined by optical emission spectroscopy using a calibrated crystal thickness monitor to determine the corresponding deposition rates. At pressures below 15×10−3 mbar, the deposition rate is linearly proportional to the intensity of the optical emission at 364.2 nm, I(Ti), associated with excited Ti. Although I(Ti) increases with the total pressure, at a given rf power, the resulting deposition rate decreases at pressures above 20×10−3 mbar due to greater gas-phase scattering. The [N]/[Ti] ratio in the deposited films, as determined by Rutherford backscattering and Auger electron spectroscopy, is found to be linearly correlated with the ratio of the optical emission intensities of excited N+2(391.4 nm) and Ti at 364.2 nm, I(N+2)/I(Ti).
Ga–CH3 bond scission by atomic H: The depletion of surface carbon from a gallium alkyl film on silicon dioxide
Authors: Lucas S. R. , Partlow W. D. , Choyke W. J. , Yates J. T.
Published: July 2002

It is shown that atomic hydrogen is an effective reagent for the extraction of CH3 groups from an adsorbed monolayer produced from trimethylgallium adsorption on SiO2. The reaction is first order in CH3 surface concentration and proceeds with zero activation energy in the 100 K temperature region. The efficiency for the extraction process is about 10−2 per atomic H collision with the surface. These results show that the Ga–CH3 bond may be broken by insertion of hydrogen atoms and that either CH3 or CH4 is eliminated by the process. The results indicate that atomic hydrogen is an effective agent for removal of carbon (present as CH3) during III–V film growth processes. The extraction of CH3 by atomic H occurs on the surface, but in metalorganic chemical vapor deposition processes a similar reaction with metal alkyl species may also occur in the gas phase. Excellent agreement with the theoretical calculations of Hiraoka and Mashita for the interaction of atomic H with AlH2(CH3) molecules is found.
Low-energy ion-induced electron emission from gas-covered surfaces
Authors: Smith P. C. , Hu B. , Ruzic D. N.
Published: July 2002

Measurements of ion-induced electron emission have been performed with helium and argon ions with energies between 300 and 900 eV on W, W with 10% Ti, Al, Al with 1% Cu, Al with 1% Si, Si, and Be. This article describes many of the important surface characteristics that influence the ion-induced electron emission. For low-energy ions, the substrate material was found to be less important as the velocity of the incident ion decreased. In the case of incident Ar+ the substrate material had a negligible effect on the emission for this energy range. The presence of an adsorbed layer enhanced emission in all cases. Heating the substrates resulted in oxidation of the surfaces and a subsequent increase in emission. The electron emission from aluminum samples with smaller grain sizes was higher than samples of identical composition with larger grains. This effect is due to the greater number of adsorption sites resulting from the higher grain boundary area.
Altered layer as sensitive initial chemical state indicator*
Authors: Dementjev A. P. , Ivanova O. P. , Vasilyev L. A. , Naumkin A. V. , Nemirovsky D. M. , Shalaev D. Y.
Published: July 2002

XPS techniques are used for a comparative study of ion induced effects in simple oxides (ZrO2, SiO2, TiO2) and complex oxides (ZrSiO4, CaTiSiO5, La2TiO5, PbTiO3). We have found that reduction effects in simple and complex oxides differ. The interpretation of altered layer composition has been qualitatively considered in terms of the preferential loss of oxygen and reverse chemical reactions.
Surface free energies for diamond growth from hydrogen–hydrocarbon mixtures
Authors: Zhang Yafei , Chen Guanghua
Published: July 2002

The surface free energies of diamond crystals under different chemical vapor deposition conditions have been comprehensively calculated. The calculations are based on a model where a fraction of carbon dangling bonds on the growth surface are saturated by hydrogen atoms. The results show that the surface free energies increase with the increasing substrate temperature or the decreasing hydrocarbon concentration in hydrogen and intersect each other at a critical point when the surface coverage fraction is equal to 0.83 monolayers. The results are excellent in theoretically interpretating the changes of predominant facets in the surface morphology from {100} to {111} with the increasing substrate temperature or the decreasing hydrocarbon concentration in hydrogen.
Simulations of real-time control of two-dimensional features in inductively coupled plasma sources for etching applications
Authors: Ventzek P. L. G. , Yamada N. , Sakai Y. , Tagashira H. , Kitamori K.
Published: July 2002

Design of a real-time control scheme to provide an optimal etch rate and uniformity in reactive plasmas is not easy because of the complexity of the plasma and surface chemistries, and because it is difficult to choose a measurable and controllable variable that directly represents etch rate and uniformity. In this article, a feedback control system is proposed in which two independently powered and controlled coils are used to control a density measurement based uniformity in an inductively coupled plasma reactor. Stability limits and the utility of this control system are investigated using a simplified two-dimensional hybrid model.
Development of neutral-beam-assisted etcher
Authors: Yunogami Takashi , Yokogawa Ken’etsu , Mizutani Tatsumi
Published: July 2002

Advanced neutral-beam-assisted etching machines have been developed for very low-damage SiO2 etching. The etching reactions are enhanced by a neutral beam and neutral radicals. This enhancement effect was first demonstrated by a prototype etcher equipped with independent sources for the neutral beam and neutral radicals. Next, a simple co-axial type etcher was developed. Only one co-axial discharge tube generates two cylindrical plasmas: the inner one is a neutral beam source; the outer one is a neutral radical source. The typical SiO2 etch rate was 60 nm/min. To further increase the etch rate, the beam and etching characteristics were studied in detail. We found that the neutral radical density had to be increased. To achieve a high etch rate, a tandem type etcher was designed and developed. It generates two plasmas side by side in only one discharge tube. This etcher can supply high-density uniform neutral radicals from one of the tandem plasmas very close to the specimen. This new etcher is expected to be a significant advance toward the development of a practical, low-damage, high rate etcher.
Core-level shifts in trimetallic systems
Authors: Rainer Darrell R. , Corneille Jason S. , Goodman D. Wayne
Published: July 2002

Trimetallic systems prepared by the deposition of monolayers of two different metals (Cu, Pd, Ag, and Au) on a Mo(110) single crystal have been studied using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). Because the dissimilar second layer can be resolved from the bulk substrate with XPS, this approach allows the core-level shifts (CLSs) for the first and second layers in the trimetallic system to be measured. ISS was employed to measure the relative surface composition of the sample in order to identify those systems in which no significant mixing of the admetals takes place at room temperature. The Cu/Pd/Mo(110), Au/Pd/Mo(110), and Ag/Cu/Mo(110) systems were determined to exist as segregated monolayers at room temperature. Initial ISS studies showed that a He+ ion beam with an energy of 475 eV was sufficient to induce alloying between Cu and Pd monolayers. The CLSs for the Au/Pd/Mo(110) and Cu/Pd/Mo(110) systems indicate changes in the d-electron populations of Au, Pd, and Cu. In the case of the Cu/Pd/Mo(110), the CLSs cannot be explained in terms of a simple charge transfer between metals.
Growth of InxGa1−xN and InxAl1−xN on GaAs metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , MacKenzie J. D. , Bharatan S. R. , Jones K. S. , Pearton S. J.
Published: July 2002

InxGa1−xN (x=0.07–1.0) and InxAl1−xN (x=0.16–1.0) layers were grown on GaAs substrates by metalorganic molecular beam epitaxy. The films display strong n-type conductivity (n≳1020 cm−3) for a wide range of InGaN compositions but only a limited range for InAlN films. The use of a H2 rather than a He carrier gas produces a lower carrier concentration in the as-grown InGaN material. The surface morphology of the ternary layers is improved by the addition of Al to the surface while it is degraded by the addition of Ga. Nonetheless, the InxGa1−xN is single crystal at low Ga concentrations with the lattice mismatch accommodated by a high density of stacking faults and microtwins. The InN layers contain only the cubic phase, while the ternaries contain both cubic and hexagonal phases.
Atomic force microscopy of amorphous hydrogenated carbon–nitrogen films deposited by radio-frequency-plasma decomposition of methane–ammonia gas mixtures
Authors: Prioli R. , Zanette S. I. , Caride A. O. , Franceschini D. F. , Freire F. L.
Published: July 2002

Atomic force microscopy was used for the surface characterization of hard amorphous hydrogenated carbon–nitrogen films deposited by plasma enhanced chemical vapor deposition. The films were deposited onto silicon substrates by rf-plasma decomposition of methane–ammonia mixtures. The film roughness and the friction coefficient between the silicon nitride tip and the film surface were determined. The results indicate that the surface roughness increases with the amount of nitrogen incorporated in the film. The friction coefficients, measured in air, are almost constant for nitrogen incorporation up to 11 at. %.
Fluorocarbon high density plasmas. VII. Investigation of selective SiO2-to-Si3N4 high density plasma etch processes
Authors: Zhang Ying , Oehrlein Gottlieb S. , Bell Ferdinand H.
Published: July 2002

A comparison of the plasma etching characteristics of SiO2 and Si3N4 in high-density fluorocarbon discharges with the goal of identifying an etching chemistry with a very high SiO2-to-Si3N4 etch selectivity has been initiated. High-density plasmas were excited in an electron cyclotron resonance apparatus equipped with a cooled rf powered electrostatic chuck. Gas mixtures of either CF4/H2, CHF3/H2 (low carbon/fluorine ratio fluorocarbon gases), or C2F4/H2, C2F6/H2, and C3F6/H2 (high C/F ratio) were used in this work. We will show that a carbon-rich fluorocarbon gas like C2F4 and a modest amount of H2 are useful in achieving high SiO2/Si3N4 etch selectivity (≳28). On the other hand, hydrogen-rich fluorocarbon gas mixtures which contain less carbon, e.g., CHF3/H2, are not useful for achieving SiO2 over Si3N4 etch selectivity although they will enable SiO2/Si etch selectivity. The gas phase and surface chemical aspects of the different gas mixtures were studied by optical emission spectrometry and line of sight mass spectrometry and by post plasma x-ray photoelectron spectroscopy. The results of these measurements can explain the etch rate data by selective deposition of fluorocarbon films on Si3N4 and Si surfaces.
Reduction of outgassing rate from residual gas analyzers for extreme high vacuum measurements
Authors: Watanabe Shu , Aono Masakazu , Kato Shigeki
Published: July 2002

One problem associated with partial pressure measurement in an extreme high vacuum region is outgassing from the residual gas analyzer (RGA) itself. In order to reduce the outgassing rate from the RGA, the temperature of the filament should be lowered, and the heat generated around the ion source of the RGA should be dissipated in the atmosphere. We modified a RGA and reduced its outgassing rate to 1.5×10−12 Pa m3/s. We also determined the partial outgassing rate from the ion source and chamber quantitatively and found that hydrogen constituted more than 99% of the outgassing from the stainless steel.
Epitaxial growth of TiSe2 thin films on Se-terminated GaAs(111)B
Authors: Nishikawa Hiroyuki , Shimada Toshihiro , Koma Atsushi
Published: July 2002

Epitaxial growth of TiSe2 films on Se-terminated GaAs(111)B substrates were carried out at different growth temperature by molecular beam epitaxy. Grown films have been investigated by reflection high energy electron diffraction, Auger electron spectroscopy, and measurements of resistivity parallel to the surface. TiSe2 epitaxial films have been obtained at various temperatures, but the optimum growth temperature was determined to be 400 °C. A charge density wave transition has been observed in the resistivity of the film grown at 400 °C, indicating that it has a good quality comparable to a bulk single crystal.
Role of substrates for heteroepitaxial growth of low room-temperature resistivity RuO2 thin films deposited by pulsed laser deposition
Authors: Jia Q. X. , Wu X. D. , Song G. , Foltyn S. R.
Published: July 2002

Conductive RuO2 thin films were grown on different substrates by pulsed laser deposition. Films deposited on MgO are of (110) orientation and of polycrystalline nature, while highly crystalline RuO2 films can be heteroepitaxially grown on LaAlO3 and yttria-stabilized zirconia (YSZ) substrates under proper processing conditions. The crystalline RuO2 thin films show metallic resistivity versus temperature characteristics and have a room-temperature resistivity of 35±2 μΩ cm. A residual resistivity ratio (ρ300 K/ρ4.2 K) of around 5 has been achieved for the RuO2 thin films grown at a substrate temperature of 700 °C on both LaAlO3 and YSZ.
Mechanisms affecting kinetic energies of laser-ablated materials
Authors: Chen K. R. , Leboeuf J. N. , Wood R. F. , Geohegan D. B. , Donato J. M. , Liu C. L. , Puretzky A. A.
Published: July 2002

A dynamic source effect was found to accelerate the plume expansion velocity much higher than that from a conventional free-expansion model. A self-similar theory and a hydrodynamic model are developed to study this effect, which may help to explain experimentally observed high front expansion velocity. Background gas can also affect the kinetic energies. High background gas may cause the ablated materials to go backward. Experimentally observed plume splitting is also discussed.
Optical emission diagnostics for contact etching in Applied Materials Centura HDP 5300 etcher
Authors: Guinn Keith , Tokashiki K. , McNevin S. C. , Cerullo M.
Published: July 2002

This article reports the use of an optical emission diagnostic as an in situ monitor of the photoresist etch rate during contact etch in a commercial, hot wall high density plasma reactor. The chamber was conditioned by prior photoresist etch and postetch oxygen clean to achieve reproducible conditions. The etch rate of photoresist and thermal oxide was measured, along with the optical emission observed for Si, SiO2 and photoresist wafers. With the rf bias power fixed at 600 W (125 mm wafers), the chamber roof temperature (240–260 °C) and source power (2350–2800 W) were varied in an experimental array to produce a range of photoresist etch rates (700–2800 Å/min). C2 and SiF optical emissions were measured for blanket Si, SiO2 and photoresist wafers. A procedure which ratioed the C2 to SiF emissions of a blanket photoresist wafer and normalized this ratio to the C2 to SiF emission ratio of a Si wafer, measured under the same conditions, was used. A strong correlation observed between the amount of C2 optical emission, and the removal rate of photoresist in the etching plasma was observed. This correlation provides a real time diagnostic that can be used for monitoring and controlling the contact etching process conditions.
Interaction of CO with Pd clusters supported on a thin alumina film
Authors: Sandell A. , Libuda J. , Brühwiler P. A. , Andersson S. , Maxwell A. J. , Bäumer M. , Mårtensson N. , Freund H. J.
Published: July 2002

The adsorption of CO on Pd particles supported on a thin alumina film has been studied employing high resolution x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS), and of special interest was the CO–Pd interaction as a function of island size and CO coverage. CO saturation at 90 K leads to an overlayer characterized by a rather weak CO–Pd hybridization as manifested by the core ionized and core excited states. The interaction strength gradually increases with island size. Desorption of parts of the overlayer results in CO more strongly interacting with the Pd islands. A comparison between the XPS and XAS energies yields a behavior indistinguishable from metallic systems for islands larger than 15 Å, i.e., the XPS binding energy appears near the x-ray absorption onset. For the smallest islands (5 Å), a CO coverage dependent reversal of the XPS–XAS energy relation was observed, indicating a drastic change in the screening ability of the CO–Pd complex.
Strain relief in metal heteroepitaxy on face-centered-cubic(100): Cu/Ni(100)
Authors: Müller Bert , Nedelmann Lorenz , Fischer Bjo/rn , Fricke Alexander , Kern Klaus
Published: July 2002

Strain relaxation is very important for the fabrication of smooth heteroepitaxial films with abrupt interfaces. At fcc(111) surfaces, strain is very efficiently relieved through the formation of fcc-hcp stackings, which are usually arranged in mesoscopically ordered networks. At fcc(100) surfaces, however, fcc-hcp stacking faults are symmetrically impossible. We report here on a novel mechanism—internal (111) faceting—of strain relief at heterointerfaces with square symmetry. The mechanism has been revealed for thin Cu films on Ni(100) by variable temperature scanning tunneling microscopy. In the first monolayer, monatomic chains of Cu atoms are shifted laterally from the fourfold hollow configuration to the twofold bridge configuration and thereby protrude from the surface layer. The gain in lateral freedom of expansion of the protruding atoms overbalances their lowered binding energy. With each Cu layer added the relaxed stripes grow in width by one atom, forming internal {111} interfaces in the Cu film. In this mode the film grows layerwise up to about 20 monolayers where bulk dislocations are formed through merging stripes.
Materials processing with intense pulsed ion beams
Authors: Rej D. J. , Davis H. A. , Olson J. C. , Remnev G. E. , Zakoutaev A. N. , Ryzhkov V. A. , Struts V. K. , Isakov I. F. , Shulov V. A. , Nochevnaya N. A. , Stinnett R. W. , Neau E. L. , Yatsui K. , Jiang W.
Published: July 2002

We review research investigating the application of intense pulsed ion beams (IPIBs) for the surface treatment and coating of materials. The short range (0.1–10 μm) and high-energy density (1–50 J/cm2) of these short-pulsed (⩽1 μs) beams (with ion currents I=5–50 kA, and energies E=100–1000 keV) make them ideal in flash heating a target surface, similar to the more familiar pulsed laser processes. IPIB surface treatment induces rapid melt and solidification at up to 1010 K/s causing amorphous layer formation and the producing nonequilibrium microstructures. At higher energy density the target surface is vaporized, and the ablated vapor is condensed as coatings onto adjacent substrates or as nanophase powders. Progress towards the development of robust, high-repetition rate IPIB accelerators is presented.
Orientation and order in microcontact-printed, self-assembled monolayers of alkanethiols on gold investigated with near edge x-ray absorption fine structure spectroscopy
Authors: Fischer Dorothee , Marti Andreas , Hähner Georg
Published: July 2002

Near edge x-ray absorption fine structure spectroscopy (NEXAFS) was used to investigate contact-printed (CP), self-assembled monolayers (SAMs) of alkanethiols on gold. We studied the influence on order and orientation of the alkyl chains of both the chain length of the thiols and the concentration of the inking solution that was used for stamping. The results are compared to those for monolayers prepared by the conventional technique of immersing the substrate into solution. Our study shows that the CP process, when performed with a sufficiently concentrated solution of the thiol, can result in monolayers indistinguishable from those established by immersion into solution, independent of the thiol chain length. For lower concentrations, however, CP monolayers show a significant deviation from well-ordered films and have to be classified as mainly disordered. As with SAMs prepared from solution, shorter chains (dodecanethiol) lead to a lower degree of order compared to longer ones (hexadecanethiol), which can be attributed to their relatively higher percentage of gauche conformations at room temperature. Nevertheless, with lateral force microscopy a slight contrast is still observable between immersed and microcontact-printed (μCP) areas of well-ordered films, as has been previously reported by other groups and attributed to slight differences in the packing density of the chains in the differently prepared regions of the final layer. On the basis of our NEXAFS data the difference of gauche defects due to different average packing densities in the resulting layers can be estimated to be less than 30%.
Sculptured thin films and glancing angle deposition: Growth mechanics and applications
Authors: Robbie K. , Brett M. J.
Published: July 2002

Sculptured thin films with three dimensional microstructure controlled on the 10 nm scale were fabricated with an evaporation technique. Glancing angle deposition (GLAD) and substrate motion were employed to “sculpt” columnar thin film microstructure into desired forms ranging from zigzag shaped to helical to four-sided “square” helical. Computer control of substrate motion was used to accurately position the substrate and to achieve the desired film structures. The growth mechanics of this novel thin film deposition technique are investigated with density measurements, scanning electron microscopy analysis, and measurements of effective refractive index. Adatom diffusion and atomic shadowing are the dominant growth mechanisms with glancing angle deposition conditions creating extreme shadowing. With controlled rotation of the substrate about two axes during deposition, a dense capping layer can be produced on top of the porous sculptured films. The success of the capping process was found to be strongly dependent on the technique used, with an exponential decrease (θ∝[1−A⋅eB⋅t]) with time of incident flux angle found to be the best to reduce filling of the porous film and fracturing of the capping film. The GLAD technique was found to have potentially promising application in optical, biological, and chemical devices and materials.
Early nitriding stage of evaporated-Ti thin films by N-ion implantation
Authors: Kasukabe Y. , Takeda S. , Fiujno Y. , Yamada Y. , Nagata S. , Kishimoto M. , Yamaguchi S.
Published: July 2002

The early growth stage of epitaxial titanium nitride (TiN) films, formed by implanting nitrogen ions (N2+) with 62 keV into 100-nm-thick evaporated-Ti films, was studied by transmission electron microscopy, Rutherford backscattering spectrometry and elastic recoil detection analysis. Evaporated-Ti films spontaneously absorb hydrogen (H) from the interior of the NaCl substrate, and then TiHx partially grows in addition to the hcp-Ti. The implantation of N into evaporated-Ti films expands the hcp-Ti lattice and reduces the H concentration in the evaporated-Ti film. The former induces the hcp–fcc transformation and then leads to the growth of (001)-oriented TiNy by the occupation of N in octahedral (O) sites in the fcc-Ti sublattice. The latter induces contraction of the fcc-Ti sublattice by the escape of H from (110)-oriented TiHx and then leads to the growth of (110)-oriented TiNy by the occupation in O sites of the H-escaped metastable fcc-Ti lattice by N. The nitriding mechanism of epitaxial Ti thin films is discussed.
Polysilicon-germanium gate patterning studies in a high density plasma helicon source
Authors: Vallon S. , Monget C. , Joubert O. , Vallier L. , Bell F. H. , Pons M. , Regolini J. L. , Morin C. , Sagnes I.
Published: July 2002

High density plasma etching processes using halogen based chemistries have been studied for 0.2 μm polysilicon-germanium gate patterning. Bilayer gate stacks consisting of 80 nm polycrystalline Si on 120 nm polycrystalline Si1−xGex (x was varied between 0.55 and 1) were grown on 4.5 nm SiO2 covered 200 mm diameter p-type silicon wafers. The bilayer gates were masked with oxide patterns. The wafers were etched in a low pressure, high density plasma helicon source. Various mixtures, based on Cl2, HBr, and O2 gases, have been used to investigate the etching of the Si/SiGe bilayer gates. The gas mixture and the plasma operating conditions have been optimized to obtain anisotropic etching profiles for features down to 0.2 μm, and to minimize the gate oxide consumption. Real time process control was achieved using HeNe ellipsometry in blanket areas, allowing the SiGe/oxide transition to be easily detected. A two step etching process using a Cl2/O2–He mixture was developed. The first step uses a high energy ion bombardment in order to obtain a high etch rate, and the second step uses a lower ion energy to achieve high SiGe/oxide selectivity. The second step is started 40 nm before reaching the SiGe/SiO2 interface in order to reduce gate oxide consumption and structural defects formation at the edges of the gate.
Plasma etching of III-nitrides in ICl/Ar and IBr/Ar plasmas
Authors: Vartuli C. B. , Pearton S. J. , Lee J. W. , MacKenzie J. D. , Abernathy C. R. , Shul R. J.
Published: July 2002

Two new plasma chemistries, ICl/Ar and IBr/Ar, were investigated for dry etching of III-nitrides. Under electron cyclotron resonance conditions, we examined the effect of plasma composition, and source and chuck power on etch rates and surface morphology. The etch rate of InN proved to be the most sensitive of the materials investigated to the plasma composition and ion density in ICl plasmas. The GaN, InN, and InGaN etch rates reached ∼13 000, 11 500, and 7000 Å/min, respectively, at 250 W rf chuck power and 1000 W microwave source power for ICl discharges. The etch rates in IBr plasmas were somewhat slower than in ICl. The etched surface of GaN was found to be smooth, with no significant preferential loss of N from the surface at low rf powers in either chemistry. There was no significant residue on the GaN surfaces after etching in IBr/Ar, and only slight chlorine contamination on the surfaces etched in ICl/Ar. Selectivities of 5–10 for GaN over InN, AlN, or InAlN were achieved in ICl/Ar, but were <4 under all conditions with IBr/Ar.
Calculated physical adsorption isotherms of neon and radon on a heterogeneous surface
Authors: Hobson J. P.
Published: July 2002

The physical adsorption isotherms on a heterogeneous surface of neon (Ne) have received limited attention, and those of radon (Rn) virtually none. The other inert gases, helium, argon, krypton, and xenon have been explored extensively, both theoretically and experimentally. The purpose of the present article is to calculate the physical adsorption isotherms of Ne and Rn on a heterogeneous surface over wide ranges of temperature, pressure, and coverage. The model used is the same as that used recently for hydrogen, wherein the isotherm was carried to the vapor pressure at the higher pressures, and to Henry’s Law at the lowest pressures, with the intermediate range being described by the Dubinin–Radushkevich (DR) equation. All that is needed for this model is a knowledge of the vapor pressures of the adsorbates as a function of temperature, and the DR constant B. By comparison with measured values of B−1/2 for the other inert gases, values of B−1/2 of 440 cal/mol for Ne and of 2685 cal/mol for Rn were obtained. Using these values, calculations were carried out for Ne at temperatures of 7, 10, 15, 20, 27.2 (normal boiling point), 40, 77.4, 300, and 500 K, and for Rn at temperatures of 60, 77.4, 100, 150, 211.4 (normal boiling point), 300, and 500 K. In all, the pressure range extended from 10 exp−18 to 10 exp 7 Torr (about 10 exp−16 to 10 exp 9 Pascals), and the relative coverage range from 10 exp−15 to 10 exp 3 monolayers. Experimental data for the physical adsorption of Ne on a number of adsorbents are compared to the calculations and give reasonable agreement considering the simplicity of the model. No experimental data for Rn are available.
Gas permeation and leakage through reusable seals
Authors: Johnson M. L. , Manos D. M. , Provost T.
Published: July 2002

This article describes a study of outgassing and permeation of high vacuum seal materials for use in multichamber deposition tools and other production tools to make electronic materials and devices. The study compares the performance between all metal, single use seals (copper knife edge and aluminum spring-loaded seals), elastomer O-rings, and a “compound seal.” The compound seal consists of an outer baked elastomer O-ring surrounding an inner compressible aluminum seal with rough pumping (40 mTorr) on the interspace. Conceptually, this seal should perform like an elastomer because of its ability to seal repeatedly, yet should be useful in environments that are corrosive to elastomers, such as etch, chemical vapor deposition, or plasma chambers. This study focuses on measurements of quantitative gas influx, including mass-resolved measurements of permeation and outgassing, for various O-ring materials and conditioning sequences. The study compares the outgassing, leakage, and permeation of baked and unbaked elastomer seals in single ring configurations to baked and unbaked configurations of double O-rings with either an elastomer or an aluminum inner seal.
Transition metal cleaning using thermal beams
Authors: Chang Jane P. , Zhang Zhe , Xu Han , Sawin Herbert H. , Butterbaugh Jeffery W.
Published: July 2002

The cleaning of transition metals including copper, nickel and iron from silicon surfaces at ambient temperature was demonstrated using various thermal beams. Sputter-deposited copper was found in two forms on silicon surfaces: uniformly dispersed copper and copper islands. At room temperature, a ClF3 beam removed the uniformly dispersed copper, but not the copper islands. Since copper–halides are not volatile at room temperature, the observation of uniformly dispersed copper removal suggested the formation of a volatile silicon–copper–halogen species. To remove the copper islands, a hot thermal dichlorosilane SiCl2H2 (DCS) beam which pyrolytically produces SiCl2 was used as a reactive silicon source. The DCS beam alone deposited SiClx on wafer surfaces suppressing complete copper removal. Exposure of this surface to ClF3 removed the SiClx deposition and copper islands from the wafer surface at room temperature. Beams containing DCS+Cl2 or DCS+F2 in which the F2 or Cl2 was also pyrolytically dissociated at 1000 °C to form F and Cl atoms, were tested. The combination of DCS with Cl2 at a beam temperature of 1000 °C reduced the deposition rate, but did not remove all of the copper islands from the wafer surface. A F2 beam at 1000 °C alone did not remove the SiClx deposition as ClF3 did; however, the mixed DCS+F2 beam at 1000 °C removed copper to below the detection limit of x-ray photoelectron spectroscopy without any observable deposition. These results validated the proposed copper removal mechanism in which a volatile copper–halogen–silicon compound was formed. The mixed DCS+F2 beam was also capable of removing other transition metals such as nickel and iron at room temperature.
Na impurity chemistry in photovoltaic CIGS thin films: Investigation with x-ray photoelectron spectroscopy
Authors: Niles David W. , Ramanathan Kannan , Hasoon Falah , Noufi Rommel , Tielsch Brian J. , Fulghum Julia E.
Published: July 2002

Thermal processing of Cu(In1−xGax)Se2 thin-films grown as part of photovoltaic devices on soda-lime glass leads to the incorporation of Na impurity atoms in the Cu(In1−xGax)Se2. Na contamination increases the photovoltaic efficiency of Cu(In1−xGax)Se2-based devices. The purpose of this investigation is to develop a model for the chemistry of Na in Cu(In1−xGax)Se2 in an effort to understand how it improves performance. An analysis of x-ray photoelectron spectroscopy data shows that the Na concentration is ∼0.1 at. % in the bulk of Cu(In1−xGax)Se2 thin films and that the Na is bound to Se. The authors propose a model invoking the replacement of column III elements by Na during the growth of Cu(In1−xGax)Se2 thin films. Na on In and Ga sites would act as acceptor states to enhance photovoltaic device performance.
Hydrazine cyanurate as a nitrogen source for thin nitride film growth
Authors: Kropewnicki Thomas J. , Kohl Paul A.
Published: July 2002

The use of liquid hydrazine (N2H4) as a nitrogen source for nitridation reactions has been restricted because of safety, purity, and difficulties in using a liquid source. Hydrazine cyanurate (HC) is a stable solid complex of N2H4 which can be easily handled and purified before use and which evolves pure N2H4 upon heating, thus making it a promising source of N2H4 for nitridation reactions. In this article, a process for the synthesis of HC has been developed which decreases the H2O content of the evolved N2H4 from 10% when H2O was used as the solvent in the synthesis of HC to 0.7% by replacing H2O with dimethylsulfoxide as the solvent in the synthesis of HC. The use of the purified HC is demonstrated as a solid source in the nitridation of (100) GaAs substrates at 200 °C in a low pressure chemical vapor deposition reactor. The nitridated GaAs surfaces were analyzed by x-ray photoelectron spectroscopy and were found to be primarily comprised of GaN, GaAs, and Ga2O3. The ratio of the constituent peak heights in the Ga 3d peak of GaN to Ga2O3 was 2.25 in the grown nitride films. The oxide impurities were most likely due to incomplete removal of the native substrate oxide formed prior to growth and were not a product of the nitridation.
Plasma-surface kinetics and feature profile evolution in chlorine etching of polysilicon
Authors: Chang Jane P. , Mahorowala Arpan P. , Sawin Herbert H.
Published: July 2002

Chlorine-based plasma etching of polysilicon was characterized as a function of the impinging Cl+, Cl–to–Cl+ flux ratio, ion bombardment energy, ion bombardment angle, and the flux of etching by-products (SiCl2) using a multiple beam scattering apparatus. The ion-enhanced etching yield was a strong function of the neutral-to-ion flux ratio, and scaled linearly with the square root of the ion energy. The ion-enhanced etching yield was independent of the ion bombardment angle at near normal ion incidence angles, but decreased almost linearly above 40° off-normal angles. The presence of SiCl2 greatly suppressed the etching of polysilicon by either Cl+ or Cl+ with Cl. A Monte Carlo based profile simulator was constructed which incorporated the dominant reaction mechanisms of surface chlorination under ion bombardment, surface re-emission, and ion reflection. The profile evolution of patterned samples etched by Cl and Cl+ beams were simulated. Quantitatively good agreement was found between the simulated profiles and the measured profiles. A sensitivity analysis of the recombination probability of Cl on photoresist suggested that the recombination of atomic chlorine on the photoresist had a significant impact on the profile evolution.
Near-surface interactions and their etching-reaction model in metal plasma-assisted etching
Authors: Tachi Shinichi , Izawa Masaru , Tsujimoto Kazunori , Kure Tokuo , Kofuji Naoyuki , Suzuki Keizo , Hamasaki Ryoji , Kojima Masayuki
Published: July 2002

Reactive interactions in plasma etching have been investigated. Simple gas-phase transport of etchants and the reaction by-products in the wafer near-surface area are discussed. A new reincidence parameter, determined with a proposed near-surface model, was used to formulate metal etch rates. The experimental results obtained from an electron cyclotron resonance microwave plasma etching system revealed that the measured etching rate agreed well with those obtained by the near-surface model. It was found that reaction by-products repeatedly arrived at the surface depending on the reincidence numbers for the metal etching. The reincidence is the result of the diffusional transport in the vicinity of the wafer and is given by the expression {(one-half of the wafer radius)/(mean-free path)}. The ratio of the by-product flux is expressed by the product of the etching-rate flux times the reincidence number. Then, the resulting ratio of the reaction products in the flux becomes very high when we compare it to those obtained by the residential time model. Based on the near-surface model, the reactive interactions between the wall near-surface and the wafer near-surface make it possible to relate the etching of the wall materials to side-etching width control. The effects of wall etching on the feature profile control are clarified through the inter-near-surface mechanism in metal etching. The use of an oxygen-free reactor inner wall and a C additive to the source gas are found to be effective for enabling highly selective metal etching with fine features.
Competing strain relaxation mechanisms in organometallic vapor-phase epitaxy of strain-compensated GaInP/InAsP multilayers on InP(001)
Authors: Desjardins P. , Isnard L. , Marchand H. , Masut R. A.
Published: July 2002

The strain relaxation of strain-compensated GaInP/InAsP multilayers grown on InP(001) has been studied as a function of misfit strain f, number of periods N, and growth temperature Ts. X-ray reciprocal lattice maps indicate globally fully strained structures while transmission electron microscopy observations show coherent buffer-layer/multilayer interfaces. The full width at half maximum intensity of the superlattice peaks in high-resolution x-ray diffraction 004 ω–2θ scans (Γω–2θ) decreases with increasing N (up to N=50) for structures with |f|=0.50% grown at Ts=620 °C as expected for multilayers of high crystalline quality. In contrast, Γω–2θ increases with N for structures with |f|=0.75% due to interface nonhomogeneities when N=20 and dislocations when N=50. Structures with |f|=0.75% and N=20 grown at Ts=650 °C showed long-wavelength thickness modulations of very small amplitude with no evidence of extended defects. For Ts=680 °C, strong thickness undulations with peak-to-cusp amplitude of ≃50 nm after 20 periods and lateral wavelength of ≃550 nm lead to dislocation nucleation in highly strained regions.