bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of sulfur and bimetallic surfaces: Fe-promoted sulfidation of Mo(110)
Authors: Rodriguez José A. , Kuhn Markus
Published: July 2002

Iron promotes the interaction between S2 and Mo(110). The exposure of Mo(110) to large amounts of S2 produces only a chemisorbed layer of sulfur, without forming molybdenum sulfides. The sulfidation of Mo occurs after exposing Fe/Mo(110) surfaces to S2 gas. Fe promotes the rate of formation of molybdenum sulfides by transferring charge to Mo (favoring in this way an electrophilic attack of S on Mo) and by changing the structure of the surface (making the penetration of S into the bulk of the sample easier). The thermal stabilities of the MoSx/Mo(110) and FeSy/MoSx/Mo(110) systems are comparable, with the bimetallic sulfide showing a somewhat lower decomposition temperature (∼1200 K). The behavior of FeMoS catalysts in hydrodesulfurization processes is discussed in light of these results.
Chemical effects of biofilm colonization on 304 stainless steel
Authors: Pendyala J. , Avci R. , Geesey G. G. , Stoodley P. , Hamilton M. , Harkin G.
Published: July 2002

Changes in the surface concentrations of the main alloying elements of an as-received 304 stainless steel, exposed to a mixed culture of biofilm-forming bacteria under flowing conditions, were observed using Auger electron spectroscopy. In the oxide film close to the bulk stainless steel, there was an enrichment in the relative concentration of Cr with a corresponding decrease in the relative Fe concentration as compared to a control coupon exposed only to sterile media. There were no changes observed in the relative Ni concentration.
Self-assembled films of alkyl halides on alkali halides
Authors: Hernández J. J. , Li J. A. , Baker J. , Safron S. A. , Skofronick J. G.
Published: July 2002

Monolayer films of four different alkyl halides were prepared by exposing freshly cleaved alkali halide (001) surfaces via immersion for at least 48 h to dilute benzene solutions of these compounds. The thickness and orientation of each film were inferred from the variation with take-off angle of the characteristic atomic peak heights in x-ray photoelectron spectroscopy spectra. For each of these compounds on each alkali halide surface, the spectra indicate that the halogen end of the molecule lies at the substrate interface and the other end points away from the interface. Films of BrCH2(CH2)4CH3 were formed by deposition in vacuum on a cleaved KBr(001) target at ∼140 K. The growth and evolution with thermal cycling of the film up to its desorption temperature at ∼180 K were followed by monitoring the specular reflection of a helium atomic beam from the surface. Films heated above ∼170 K appear to anneal to a more ordered structure; helium diffractive scattering from the deposited film taken at ∼50 K without annealing yielded broad diffraction peaks at the KBr positions, while similar measurements taken after annealing produced sharp diffraction peaks at these angles and at half-order angles as well. Consistent with helium diffraction measurements over a range of azimuths, the structure of this annealed film could be interpreted as one of mixed (1×2) and (2×1) domains. Specular intensity measurements as a function of surface temperature yielded a Debye temperature of the annealed film ∼95 K.
Atomic hydrogen adsorption on Si(100)-(2×1) with preadsorbed acetylene: Structure, bonding, and chemical reactions
Authors: Yi S. I. , Widdra W. , Yan C. , Weinberg W. H.
Published: July 2002

The adsorption of atomic hydrogen on acetylene-saturated Si(100)-(2×1) was studied using high-resolution electron energy loss spectroscopy, temperature programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction (LEED). With saturation coverage of preadsorbed acetylene, the initial adsorption probability of atomic hydrogen on Si is reduced to 40% of the initial adsorption probability of atomic hydrogen on clean Si(100)-(2×1), and the uptake of hydrogen to form the Si monohydride up to 0.65±0.05 of a monolayer is observed. Although the hydrogenation of acetylene is substantially slower than the chemisorption of hydrogen as the Si monohydride, molecular desorption of ethylene is observed in temperature programmed desorption following the hydrogenation of chemisorbed acetylene. With further postexposures of atomic hydrogen, the LEED pattern changes from (2×1) to (1×1) and the Si dihydride forms, confirming the conversion of ethylene to ethyl.
Charge issues in high oxygen gas ratio tetraethylorthosilicate plasma enhanced chemical vapor deposition films
Authors: DeCrosta D. A. , Hackenberg J. J.
Published: July 2002

The effect of multilayered silicon dioxide films on reflective charge, Nss, and flatband voltage, Vfb, was investigated using plasma enhanced chemical vapor deposition. Parameters investigated included the thickness and type of oxide film layers, as well as dopant type. Deposition of a high oxygen gas ratio film [4:1, oxygen:tetraethylorthosilicate (TEOS)] as the first layer of a multilayer film resulted in a statistically lower Nss and a smaller shift in flatband voltage, Vfb, than films deposited with lower oxygen gas ratios (1:1, oxygen:TEOS). Multilayer films were deposited to a thickness of 18 kÅ using a high oxygen gas ratio as the initial layer. These films exhibited Nss and Vfb values of 1.28×1011 cm−2 and −11.5 V, respectively. In contrast, those films with a lower oxygen gas ratio initial layer exhibited statistically higher Nss and Vfb values of 1.70×1011 cm−2 and −15.4 V, respectively. Film compositional changes in subsequent layers did not display any statistically significant change in either Nss or Vfb. The deposition of 4:1 gas ratio films occurs at a slower rate than the 1:1 gas ratio films. The use of 4:1 gas ratio films as the initial layer of a multilayer film allows for lower Nss and smaller shifts in Vfb without significantly affecting throughput.
Temperature-dependent Raman scattering in PT and PMN-PT thin films
Authors: Ching-Prado E. , Cordero J. , Katiyar R. S. , Bhalla A. S.
Published: July 2002

Raman spectroscopy was used to investigate PbTiO3 (PT) and 0.7Pb(Mg1/3 Nb2/3)O3-0.3PbTiO3 (PMN-PT) thin films prepared by the sol–gel technique and deposited on platinum-coated silicon, and Al2O3. The PT spectra reveal that the films are polycrystalline in nature and the frequencies of most of the modes are decreased as compared to those in single crystal or powder material. This result is due to grain under stress, which is caused by nonequilibrium defects. Temperature dependence (290–60 K) of the Raman half-width bands in PT/Al2O3 is discussed in terms of anharmonic processes involving three phonons, however, the main contribution to line broadening appears to be due to presence of defects. In the case of PMN-PT films the temperature dependence study indicates strong disorder in the system, predominantly, in the B sites of the ABO3 perovskite structure. The bands are, therefore, interpreted as due to a breakdown in the phonon momentum conservation within the Brillouin zone. Micro-Raman measurements at different film positions indicate that PT/Al2O3, and PMN-PT/Pt/Si films are homogeneous, while PT/Pt/Si films show different microstructure in the middle and edge positions. Scanning electron microscopy, Fourier transform infrared spectroscopy, and x-ray diffraction techniques have been used for the structural characterization.
Surface processing by gas cluster ion beams at the atomic (molecular) level
Authors: Yamada I. , Matsuo J. , Insepov Z. , Takeuchi D. , Akizuki M. , Toyoda N.
Published: July 2002

Gas cluster ion beam techniques have been developed for atomic and molecular level surface modification processing. Shallow implantation, high yield sputtering, surface smoothing, and low damage surface cleaning have been demonstrated experimentally. This article reports recent results concerning surface treatments that are distinctly different from those produced by conventional monomer ion irradiation. Possible applications of gas cluster ion beam processing to new areas of surface modifications are suggested.
Tetraethylorthosilicate reaction rates on SiO2 at 1000 K: Zero-order dependence on hydroxyl coverage and implications for reactions with three-membered siloxane rings
Authors: Bartram Michael E. , Moffat Harry K.
Published: July 2002

We have determined key kinetic parameters for the reaction of tetraethylorthosilicate (TEOS) on SiO2. This was accomplished under conditions (20–500 mTorr at 1000 K) that pertain directly to TEOS-based chemical vapor deposition processes. TEOS reactions were carried out using deuterated silanols (SiOD) on the initial SiO2 surface. This allowed Fourier transform infrared spectroscopy measurements to distinguish the consumption of SiOD by TEOS from the concurrent formation of SiOH which results from TEOS decomposition at 1000 K. While SiOD consumption did exhibit a first-order dependence on SiOD coverage, TEOS decomposition exhibited a zero-order dependence on the total coverage of hydroxyl groups. This suggests that reactions with hydroxyl groups alone cannot account for all of the TEOS decomposition reactions at 1000 K. Since the low coverage of two-membered siloxane [(Si–O)2] rings was consumed during the initial TEOS exposure, siloxane (Si–O–Si) bridges in three-membered siloxane [(Si–O)3] rings may be the additional species responsible for the constant rate of TEOS decomposition. However, it is not conclusive that this type of site-specific mechanism controls the chemistry. The data may also be explained with a site-independent mechanism in which intramolecular decomposition of TEOS on the surface provides a common rate-determining step for subsequent consumption of hydroxyls and siloxane bridges on SiO2. Regardless of the specific mechanism, our results predict that deposition rates will be insensitive to the relative coverages of siloxane bridges and hydroxyls on SiO2. Therefore, a precise knowledge of the coverages of these species on SiO2 is not essential for modeling thermal TEOS decomposition rates.
Simple equipment tolerant reflectometry for monitoring of molecular beam epitaxy and metalorganic chemical vapor deposition growth
Authors: Bean J. C. , Peticolas L. J. , Lum R. , McDonald M. L.
Published: July 2002

We describe simple interferometric reflectometry systems that have been applied to real-time monitoring of epitaxial growth in a variety of crystal growth systems. These include molecular beam epitaxy (MBE) systems from Vacuum Generators and Varian, and metalorganic chemical vapor deposition reactors from Aixtron and Emcore. The reflectometry systems are composed entirely of off-the-shelf hardware, including charge-coupled-device-based spectrometers and light bulb white light sources. These fixed modules are connected by simple fiber optic links. Input and output lenses are matched to the crystal growth systems such that unmodified viewports and rotating sample stages/platens are fully accommodated. The systems are driven by a WindowsTM-based program operating on a conventional PC. This program permits display of the time-dependent spectra as either line graphs or grayscale converted ‘‘fingerprints’’ that may be overlaid, in real time, on data from reference growth runs. It also includes provision for full simulation of complex layered structures in the GeSi, AlGaAs, and InGaAsP materials systems, along with corrections for elevated growth temperature. For the MBE-based GeSi system, vertical resonant cavity photodiode structures were monitored. The reflectometry system easily revealed growth rate deviations of less than 1% and permitted termination of growth at precise resonance conditions.
Dependence of microstructure and thermochromism on substrate temperature for sputter-deposited VO2 epitaxial films
Authors: Jin P. , Yoshimura K. , Tanemura S.
Published: July 2002

A systematic study on the epitaxial growth of VO2 films deposited on sapphire by sputtering at various substrate temperatures (Ts) was carried out. The deposited films were characterized by x-ray diffraction, high energy electron diffraction, Rutherford backscattering spectrometry, atomic force microscopy, and spectrophotometry. Epitaxial VO2 was obtained from a Ts of 300 °C which is the lowest reported yet. Two epitaxial relationships, i.e., a dominant VO2(010)//sapphire (110), (001)//(001) and a secondary VO2(100)//sapphire (110), (010)//(001), were confirmed. The epitaxial films show strong dependence of the morphology and thermochromism on Ts. Films deposited at above 400 °C exhibit changes in resistivity of ΔR>104 upon switching, while those deposited at Ts=300 °C have reduced ΔR of 102. The film obtained at Ts=300 °C exhibits novel transition properties, i.e., a largely reduced τc (45 °C) even without any doping, and very little thermal hysteresis.
Microstructure, composition, and optical properties of PbTiO3 thin films prepared by the sol-gel method
Authors: Lu C. J. , Ren S. B. , Shen H. M. , Liu J. S. , Wang Y. N.
Published: July 2002

Crack-free and transparent PbTiO3 thin films with a perovskite structure were deposited on NaCl (100), Si(111), and fused quartz substrates by the sol-gel method. The crystal structure, morphology, domain structure, composition, and optical properties of the films were characterized by means of x-ray diffraction, transmission electron microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and optical transmission spectrum. The films on Si and fused quartz substrates exhibit slight a axis preferred orientation, while the films on NaCl substrates show slight c axis preferred orientation. From XPS analysis, no residual carbon or other impurity element was detected on the films after 3 keV Ar+ cleaning. The chemical composition of the films was found to be stoichiometric. A great amount of absorbed oxygen exists on the surfaces of the films. In the fine-grained (≈150 nm) films, no 90° domains are present in most of the grains, while some grains show lamellar 90° domains. A large number of pores exist in the films and their sizes are in the range of 5–30 nm. The packing density of the film fired at 600 °C was estimated to be about 89.3% from its optical transmission spectrum. The film has a surface roughness Δd≈37.5 nm. The refractive index of the film is approximately 2.43 at 630 nm, and the absorption edge is at 321 nm.
Effect of oblique sputtering on microstructural modification of ZnO thin films
Authors: Lee Yong Eui , Kim Soo Gil , Kim Young Jin , Kim Hyeong Joon
Published: July 2002

The effects of oblique sputtering on microstructural modification of ZnO films were investigated. Surface morphologies of the films were profoundly modified with an incidence angle. By using pure Ar gas, etch pits, pyramids, ridge, and ledgelike structures were developed on the film surface. By using Ar/O2 mixture gas, large elongated grains, which aligned perpendicular to the direction of incidence vapor at incidence angle above 80°, were formed on the fine columnar matrix. The x-ray Schulz method showed that the (002) pole located away from the direction of incoming vapor at low incidence angles, while the (101) pole uniformly distributed as a concentric ring. For films deposited at high angles, the (002) pole inclined toward an incoming vapor, while the (101) pole moved to the central region. In this case, (110) poles had a tendency to align biaxially. The topological modification and crystallographic orientation change could be explained with an adatom mobility and crystallographic geometry contribution.
High resolution electron energy loss spectroscopy study of vapor-deposited polyaniline thin films
Authors: Plank R. V. , DiNardo N. J. , Vohs J. M.
Published: July 2002

Vapor deposited polyaniline films on Cu(110) have been characterized using high resolution electron energy loss spectroscopy. Ultrathin films (⩽100 Å) were found to exist in an oxidation state close to that of the starting emeraldine powder. After doping with HCl, the films exhibited plasmon excitations in the far-ir, suggesting that they are highly crystalline and possess electrical conductivities higher than those of HCl doped emeraldine films produced by wet-chemical deposition techniques. In contrast, thicker vapor-deposited films (⩾1000 Å) were found to be highly reduced, less crystalline, and exhibited electrical conductivities lower than those of the thinner films upon doping. These results suggest that the interactions of emeraldine with a metal surface can play an important role in determining the chemical, structural, and electronic properties of polyaniline films near the polymer-substrate interface.
Anisotropic etching of InP with low sidewall and surface induced damage in inductively coupled plasma etching using SiCl4
Authors: Etrillard J. , Ossart P. , Patriarche G. , Juhel M. , Bresse J. F. , Daguet C.
Published: July 2002

We report on the sidewall and surface characterization of InP etched patterns obtained by inductively coupled plasma (ICP). The fabrication of InP based optoelectronic integrated circuits requires dry etching processes, normally using CH4/H2 gas mixtures, with low induced damage, high and reproducible etch rate, and controlled etch direction. These requirements imply the use of a high-density plasma source, which reduces the energy of ions impinging on the wafer surface while keeping a sufficient etch rate. We introduce here the use of an ICP to etch InP. We show that one can obtain anisotropic processes in SiCl4 chemistry avoiding the carrier compensation due to the H+ bombardment. The surface morphology and the pattern profiles are observed by scanning electron microscopy and by atomic force microscopy. Auger electron spectroscopy and secondary ion mass spectroscopy are used to obtain the elemental composition in the top 30 nm of the etched surface and to evaluate contamination. Transmission electron microscopy is used to observe the sidewall damage on patterns delineated by e-beam lithography. The effects of ion density, ion energy, pressure, reactor environment, and surface temperature are observed. Finally, surface damage induced on InP etched substrates are characterized through photoluminescence intensity. We observed the destructive effects of high ion energy etching processes, already reported in CH4/H2 chemistry. Some very low bias voltage processes (as low as 5 V) have been studied in the ICP equipment. It is found that extremely low surface damage and very low sidewall amorphization can be obtained in such processes while keeping high etch rate and anisotropy.
Low energy cathodoluminescence spectroscopy of SiO2 nanoparticles
Authors: Yang X. , Law K.-Y. , Brillson L. J.
Published: July 2002

We have performed low energy cathodoluminescence spectroscopy (CLS) measurements on nanometer scale particles of SiO2. We investigated both hydrophobic and hydrophilic SiO2 specimens under ultrahigh vacuum (UHV) conditions in order to control surface chemical adsorption. CLS yielded evidence for energy levels deep in the band gap of these materials. Specifically, a set of spectral peaks appeared at ∼1.2–1.3, 1.6–1.9, and ∼2.7 eV in both hydrophobic and hydrophilic SiO2. The appearance of these features at energies well below the band edge of SiO2 (8.9 eV) is indicative of traps in the band gap which may play a role in the charge transfer process. We observed a strong intensity dependence of the features on incident electron beam energy with 1 (more surface) versus 2 keV (more bulk) excitation. This feature also displayed an increase with hydrophobicity, with particle size, as well as with additional surface chemical treatment. The 2.75–2.95 eV feature increase with larger hydrophobic particle size suggests that chemical conditions as well as surface area contribute to the peak intensity. Furthermore, particle size also affects peak energies as well, indicative of quantum size effects. In addition, they provide significant evidence for deep levels in wide band gap insulating SiO2 playing a role in triboelectric contact charging.
Transmission through the quadrupole mass spectrometer mass filter: The effect of aperture and harmonics
Authors: Voo A. C. C. , Ng R. , Tunstall J. J. , Taylor S.
Published: July 2002

This article considers the effect of initial ion energy and quadrupole rod length on transmission percentage of ions through the mass filter for a computer simulation of the quadrupole mass analyzer. It also examines the effect of aperture for the mass filter with sinusoidal rf ac and rf ac with harmonics.
Ion energy, ion flux, and ion species effects on crystallographic and electrical properties of sputter-deposited Ta thin films
Authors: Ino Kazuhide , Shinohara Toshikuni , Ushiki Takeo , Ohmi Tadahiro
Published: July 2002

The effects of ion bombardment conditions on the crystallographic and electrical properties of tantalum thin films grown on SiO2 and Si have been systematically investigated in Ta thin film formation process employing low-energy (<100 eV) inert-gas ion bombardment on a growing film surface. It is demonstrated that the properties of Ta films are strongly dependent upon ion energy and ion flux as well as substrate materials. The bcc-Ta can be formed on SiO2 by controlling impinging ion energy and normalized ion flux defined as the ratio of ion flux to Ta flux ranging lower than 20 eV and higher than 13, respectively, for Ar plasma. Based on these results, low-resistivity bcc-Ta thin films (14.8 μΩ cm at 300 K) have been successfully formed. It is also experimentally shown that the irradiation by ions with different mass numbers has different effects on growing film properties, even if the energy or momentum of the ions is the same. When normalized ion flux is 26, bcc-Ta films can be grown on Si at ion energy lower than 30 eV for Ar ions and at ion energy ranging from 30 to 90 eV for Xe ions. The results also suggest that there are two cases where the phase transition from bcc to β occurs. One is caused by defects induced by the recoil implantation of Ta atoms due to the excessive higher-energy ion bombardment and the other is induced by defects due to insufficient total energy input to a growing film surface by ion irradiation and resulting poor film quality.
Empirical and numerical calculations in two dimensions for predicting the performance of a single stage turbomolecular pump
Authors: Schneider T. N. , Katsimichas S. , de Oliveira C. R. E. , Goddard A. J. H.
Published: July 2002

Empirical formulae for the compression ratio and speed factor of a single stage turbomolecular pump operating in the molecular flow regime are developed for blade speeds lower than the most probable molecular velocity. These formulae are based on Becker’s compression formula derived from drag theory and on Bernhardt’s pumping speed formula but are modified and extended to take account of the full range of parameters in the two dimensional infinite blade row model of Kruger. Numerical constants are determined using the direct simulation Monte Carlo method. Results from the latter method are presented as contour plots of transmission probabilities intended to cover cases of interest for design calculations.
The recombination of chlorine atoms at surfaces
Authors: Kota Gowri P. , Coburn J. W. , Graves David B.
Published: July 2002

Chlorine atom recombination coefficient (γCl) measurements are reported for a variety of surfaces and at a range of surface temperatures. The surfaces include crystalline silicon, quartz, anodized aluminum, tungsten, stainless steel, polycrystalline silicon, and photoresist. Surface temperatures ranged from about −90 °C up to 85 °C. Measurements were made in a vacuum chamber with chlorine atoms and molecules effusing from an external discharge source as a molecular beam and impacting a selected surface. The incident and reflected beam compositions calculated using a modulated beam mass spectrometer were used to infer the recombination coefficient. At room temperature, the values of γCl ranged from below the detection sensitivity (about 0.01) for crystalline silicon to ∼0.85 for stainless steel. Other surfaces displayed intermediate values between these extremes. For example, γCl for polycrystalline silicon is about 0.2–0.3 at room temperature. All surfaces, except stainless steel, displayed increasing values of γCl as surface temperature was lowered below room temperature, down to the freezing temperature of chlorine (−101 °C). The γCl for stainless steel appeared to saturate at 0.85 as temperature was lowered. All surfaces displayed decreasing values for the recombination coefficient as surface temperature was raised above room temperature. The γCl data as a function of temperature were fit to a phenomenological model. The phenomenological model assumes Cl atoms adsorb into a weakly bound physisorbed, state on at least 1 monolayer of strongly bound, chemisorbed chlorine. After adsorption, the model assumes that thermally activated diffusion and atomic recombination occur with a rate that is first order in physisorbed chlorine. Thermal desorption competes with diffusion and reaction, and is also thermally activated. Fits to the data were made, and the physical interpretation of the model parameters is discussed.
Evaluation of plasma charging damage during polysilicon gate etching process in a decoupled plasma source reactor
Authors: Ma Shawming , Jain Mohit , Chinn J. D.
Published: July 2002

Charging induced damage of thin gate dielectric during polysilicon gate etching in a high density decoupled plasma source was investigated for 0.16 and 0.24 μm gates on 30 Å nitrided gate oxide. The undoped polysilicon gates were etched with a HBr/He/O2 based process recipe. The optimized process recipe resulted in vertical profiles (89°–90°) with microloading of <1°. No notching of the polysilicon or punch through of the thin gate oxide was observed. Gate leakage and breakdown voltage measurements after gate formation were made on metal-oxide-semiconductor capacitor structures with antenna ratios ranging from 100:1 to 1000:1. These measurements did not exhibit any damage to the thin gate dielectric. In addition, no significant change in the damage characteristics was observed over a wide process window around the optimized recipe, i.e., increased over etch (OE) time, increased source power, or reduced bias power in the OE step. A soft landing scheme was used for the etching of poly gates. This scheme provides vertical profiles without punch through and with minimum damage to the thin gate oxide and the substrate.
Secondary ion mass spectroscopy characterization of the deuterium sintering process for enhanced-lifetime complementary metal–oxide–semiconductor transistors
Authors: Lee Jinju , Aur Shian , Eklund Robert , Hess Karl , Lyding Joseph W.
Published: July 2002

We have investigated the lifetime improvements in complementary metal–oxide–semiconductor transistors with nitride sidewalls by the deuterium sintering process. We report the incorporation of deuterium (D) at the gate SiO2/Si interface (overcoming the diffusion barrier of nitride sidewalls) and mean lifetime improvements by a factor of 15. Sintering temperatures ranged from 400 to 480 °C, and the D concentration inside the furnace varied from 10% (in ultra-high purity nitrogen) to 100% with sintering times between 30 and 150 min. We performed secondary ion mass spectrometry to obtain the depth profiles of hydrogen (H) and D in the sintered transistors. The measured D/H concentration ratio at the SiO2/Si interface correlates directly with the sintering parameters and the measured transistor lifetime improvements.
Preparation of nearly oxygen-free AlN thin films by pulsed laser deposition
Authors: He Maoqi , Cheng Naiqun , Zhou Peizhen , Okabe Hideo , Halpern Joshua B.
Published: July 2002

For preparation of oxygen-free AlN thin films by pulsed laser deposition (PLD), emission spectra of the ablation plume of an AlN target were measured to search for oxygen impurity sources during the growth process. A very sensitive 777 nm emission line of oxygen was found to be a good process monitor. A new source of oxygen impurity in AlN thin films was found to be the oxidation of the AlN target surface. Its mechanism is discussed and it is shown that simple mechanical abrasion can renew the AlN target. With careful attention paid to preventing all oxygen impurity sources, nearly oxygen-free and stoichiometric AlN thin films were grown for the first time by (to the best of our knowledge) PLD.
Delamination mechanism in relation to adhesion of cubic boron nitride
Authors: Kim Ig-Hyeon , Kim Seon-Hyo , Kim Kyoung-Bo
Published: July 2002

The growth and delamination mechanism of cubic boron nitride (c-BN) film on silicon substrate was investigated with Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). c-BN films were prepared by the helicon wave plasma chemical vapor deposition process on (100) Si. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. It is found that moisture in the air, as well as severe compressive stress in the film, contribute to film delamination. From FTIR and TEM characterization, a model for the delamination mechanism of c-BN film is suggested. Based on the delamination mechanism, several kinds of remedies such as post-annealing and post-N2 plasma treatment were carried out to improve the adhesion. The effects of these respective remedies on the adhesion of c-BN film are also discussed.
Holographic imaging of macromolecules
Authors: Gölzhäuser A. , Völkel B. , Jäger B. , Zharnikov M. , Kreuzer H. J. , Grunze M.
Published: July 2002

The low energy electron point source microscope (kendroscope) is used to acquire in-line holograms of rodlike macromolecules of phthalocyaninato polysiloxane (PcPS). The molecules were placed on a new class of substrates, thin microstructured silicon membranes that have slits about 100 nm wide which can be “bridged” by the molecular chains. The resulting in-line holograms of PcPS were recorded digitally and reconstructed numerically via a Kirchoff–Helmholtz transform. The mechanisms of image formation and uncertainties relating to the interpretation of the holograms are discussed.
Synthesis and characterization of highly textured polycrystalline AlN/TiN superlattice coatings
Authors: Wang Y. Y. , Wong M. S. , Chia W. J. , Rechner J. , Sproul W. D.
Published: July 2002

AlN/TiN multilayer coatings were synthesized by sputtering Al and Ti metal targets simultaneously in an Ar+N2 plasma using a dual-cathode unbalanced dc magnetron sputtering system. Two different power sources, rf and pulsed-dc, were employed for substrate bias. It was found that under a critical thickness for the AlN layer, the AlN/TiN coating with the AlN layers below a critical thickness exhibit a highly textured [111]-oriented superlattice structure. However, the rf-biased films have poor mechanical properties. Transmission electron microscopy (TEM) studies of the rf-biased films show columnar structure of large grains with weak links (amorphous-like material) between different columnar grains. In the pulsed-dc-biased films, however, we noticed a twofold increase in hardness, when the bilayer thickness is under ∼5 nm. The increase of the hardness coincides with the structure phase transition from a randomly oriented polycrystalline AlN/TiN thin film to a highly [111]-textured AlN/TiN thin film. X-ray diffraction and TEM studies indicate that in the highly [111]-textured multilayer films, AlN is in a nanostabilized cubic form. The critical thickness for AlN to form a nanostabilized cubic structure along [111] is less than about 2.5 nm. TEM studies on the highly textured films deposited with pulsed-dc bias showed a coherent growth of an AlN/TiN layered structure across the film and highly dense grain boundaries, which was achieved by using the low-energy ion bombardment induced by the pulsed-dc bias. The high hardness value of the coating with small bilayer thickness deposited with pulsed-dc bias is not only due to the formation of the nanometer-scale multilayer structure and nanometer-stabilized cubic form of AlN, but also due to the strongly bonded high-angle grain boundaries between different columnar grains.
Investigation of electron-beam-induced phase transitions in amorphous aluminum trifluoride thin films using transmission electron microscopy
Authors: Chen G. S.
Published: July 2002

In this study we employ an electron probe of a current density ∼104 C m−2 from a conventional transmission electron microscope to examine in situ the electron-beam-induced crystallization behavior of thermally evaporated amorphous aluminum trifluoride (a-AlF3) thin films. Under the electron beam, the self-developing a-AlF3 material undergoes an extremely complicated crystallization process, subsequently forming crystalline Al, AlF3, and Al2O3 substances. The crystallization process of a-AlF3 relies heavily on the amount of H2O absorbed into the films, thereby reducing the dose required to crystallize a-AlF3, inhibiting radiolytic dissociation of AlF3 into aluminum and fluorine, and further activating a chemical reaction between AlF3 and the absorbed H2O, forming oriented Al2O3 crystallites. Dry a-AlF3 thin film material, evaporated from anhydrous AlF3 powder under a base pressure of 10−4 Pa, follows a clear sequence sequentially transforming itself into aluminum, crystalline AlF3 (c-AlF3) and textured Al2O3 at a threshold dose of approximately 1×105, 1×106, and 1×107 C m−2, respectively. However, a-AlF3 thin film material, deposited from hydrous AlF3•3H2O powder under a relatively wet vacuum ambient of a base pressure of 10−2 Pa, has a reduced threshold dose of about 2×105 C m−2 to transform itself simultaneously into c-AlF3 and aluminum. Monitoring the oxygen 534 eV and fluorine 685 eV energy-loss spectra during the irradiation of AlF3 films indicates that: (a) c-AlF3 is far more resistant to radiolysis than a-AlF3 and (b) H2O is gradually absorbed into the films, ultimately initiating the transformation of AlF3 into Al2O3. Finally, the statistic variation toward less sensitivity of developing a-AlF3 resists found in previous investigations is attributed to the higher ability of the beam-crystallized AlF3 against radiolysis.
Influence of crucible material and source alloy composition on thermally evaporated indium tin oxide layers
Authors: Kerp H. R. , van Cleef M. W. M. , Wit A. B. , Schropp R. E. I. , Galloni R. , Lazzeri P.
Published: July 2002

Indium tin oxide layers were deposited by reactive thermal evaporation of an In:Sn alloy in an oxygen ambient. The films were evaporated from tungsten (W) and tantalum (Ta) crucibles using a large range of tin concentrations. The influence of the crucible material and the tin concentration on the optoelectrical and electrical properties was studied. A minimum film resistivity of (2.8±0.5)×10−4 Ω cm and a maximum optical transmittance of 91% were obtained for the films evaporated from a tantalum crucible containing 70% tin [deposition rate of (0.6±0.3) Å/s and oxygen partial pressure of 1×10−3 mbar]. The atomic tin concentration in these films is (0.4±0.06)% at maximum. The resistivity decreases monotonically with increasing tin concentration in the source alloy up to 70 at. %. The films deposited from a tungsten crucible showed similar low resistivity, (3.4±0.2)×10−4 Ω cm, using only 10 at. % Sn in the source alloy. It was found that this low resistivity obtained by using a W crucible is not the result of tin doping (<0.05 at. %), but is caused by the incorporation of tungsten impurities (∼0.8 at. %) into the film. The presence of W in these films can be explained by oxidation of the tungsten crucible. The resulting WO3 has, unlike W, a much higher vapor pressure than Sn, which implies a higher evaporation rate. No traces of Ta were found in films evaporated from a Ta crucible.
Plasma-enhanced metal organic chemical vapor deposition of high purity copper thin films using plasma reactor with the H atom source
Authors: Jin Hong Jie , Shiratani Masaharu , Kawasaki Takashi , Fukuzawa Tsuyoshi , Kinoshita Toshio , Watanabe Yukio , Kawasaki Hiroharu , Toyofuku Masaharu
Published: July 2002

In situ Fourier-transform infrared measurements have been carried out to study the effects of H atoms on removing impurities in Cu thin films during plasma enhanced metal organic chemical vapor deposition (PEMOCVD) using bis(hexafluoroacetylacetonato) copper (II), Cu(hfac)2 as a source material. The results show that H atoms are very effective in removing impurities in the film, as well as on its surface. Based on such knowledge regarding the effects of H atoms, a PEMOCVD reactor equipped with an H atom source is developed to control both densities of H atoms and Cu-contained radicals independently. High purity (≈100%) Cu films of a low resistivity of 2 μΩ cm can be deposited for a H2 gas volume fraction of 50%–67% by using the H atom source, while the high purity films were obtained only for a very high H2 gas volume fraction above about 90% in the case of no H atom source as reported previously. This feature opens up a possibility of deposition of high quality Cu films at a high rate using the reactor equipped with the H atom source, since a gas volume fraction of Cu metal organic material can be increased by more than five times.
Novel approach to collimated physical vapor deposition
Authors: Kools J. C. S. , Paranjpe A. P. , Heimanson D. H. , Schwartz P. V. , Song K. , Bergner B. , McAllister S. , Van Ysseldyk R. W.
Published: July 2002

In some applications of physical vapor deposition (PVD), it is desirable to have the atoms arriving at the substrate at angles close to the normal (collimation). Applications of collimated PVD include continuous coverage of high-aspect ratio vias, as used in multilevel integrated circuit metallization, or high resolution shadow masking as used in lift-off technology. Several approaches to collimation have been proposed in recent years: natural (or long throw) collimation, physical collimation, ion beam deposition, ionized PVD cathodic arc deposition and hollow cathode collimation. In this article, we introduce a novel approach to collimation. According to simulations of target-to-substrate atom transport using the SIMBAD program this approach provides narrow angular distribution functions of the sputtered flux at the substrate surface. Furthermore, it is shown experimentally that this approach leads to a strongly improved degree of collimation when compared to the conventional methods based on either physical or natural collimation, through formation of abutted junction permanent magnet stabilization and metallization layers as in applied magnetoresistive thin film recording heads, using a lift-off process.
Structure and electronic properties of the novel semiconductor alloy Cd1−xCuxTe
Authors: López-López S. , Torres-Delgado G. , Jiménez-Sandoval S. , Jiménez-Sandoval O. , Castanedo-Pérez R. , Meléndez-Lira M.
Published: July 2002

In this work an investigation of the structural and electronic properties of the novel semiconductor alloy Cd1−xCuxTe is presented. The samples were prepared as thin films by rf sputtering on substrates made of Corning glass. X-ray diffraction patterns showed that the incorporation of Cu into CdTe did not significantly affect the lattice parameters and that the incorporation of copper favors the growth of films preferentially oriented parallel to the (111) planes of cubic CdTe. Due to its sensitivity to local atomic order, the samples were studied by micro-Raman spectroscopy. The transverse and longitudinal optic modes regularly observed in CdTe were also found in the Cd1−xCuxTe samples with frequencies variations of less than 2 cm−1. The appearance of second and third harmonics of the longitudinal optic mode is indicative of high crystalline quality. The Raman bands become broader as a consequence of the disorder induced by the random incorporation of copper. From the Raman experiments it was also determined that the incorporation of Cu precluded the formation of Te clusters, which are commonly detected in CdTe thin films and bulk samples. The band gap of the alloys measured by optical transmission and photoreflectance spectroscopies tends to decrease with increasing copper content. The smallest band gap values were lower by approximately 60 meV compared to those of pure CdTe.
Si dopant site within ion implanted GaN lattice
Authors: Kobayashi H. , Gibson W. M.
Published: July 2002

We have investigated the Si dopant site in the GaN lattice using ion channeling in combination with Rutherford backscattering spectrometry (RBS), particle induced x-ray emission (PIXE), and nuclear reaction analysis (NRA). Metalorganic chemical vapor deposition grown GaN on a c-plane sapphire substrate implanted with Si28 at a dose of 7×1014 cm−2 with postimplant annealing was investigated. Channeling measurements were performed by taking angular scans around the 〈0001〉 and 〈101̄1〉 axes and recording RBS, PIXE, and NRA yields for Ga, Si, and N, respectively. The channeling results indicate that almost 100% of Si goes into the Ga site when the samples are annealed at 1100 °C for 30 min while for annealing at 1050 °C and below, Si is distributed almost randomly. This suggests that a drastic change of Si substitutionality takes place in a narrow temperature region near 1100 °C. Our results directly indicate that the electrical activation of Si implanted GaN with postimplant annealing is due to the formation of substitutional Si at this temperature.
Pattern shape effects and artefacts in deep silicon etching
Authors: Kiihamäki J. , Franssila S.
Published: July 2002

Deep silicon etching in an inductively coupled plasma (ICP) reactor offers a high etch rate (7 μm/min), nearly vertical profile with simple oxide masking. Test structures with patterns of different sizes (from a few microns to over 100 μm) and shapes (square and circular holes and trenches of variable width/length) have been etched to depths up to 500 μm. Long narrow features are etched faster than wide short features, indicating the three-dimensional nature of the reactive ion etching lag. Experiments have been done for many different etch times in order to understand aspect ratio dependence of deep etching. Simple flow conductance model explains most of the observed aspect ratio and feature size dependence.
Carbon incorporation in SiGeC alloys grown by ultrahigh vacuum chemical vapor deposition
Authors: Mocuta A. C. , Greve D. W.
Published: July 2002

We report on incorporation of carbon in Si1−x−yGexCy alloys by ultrahigh vacuum chemical vapor deposition and on thermal relaxation properties of Si1−x−yGexCy alloys with low carbon levels. Si1−x−yGexCy alloys have been grown at temperatures between 550 and 650 °C using silane, germane and methylsilane as precursor gases. For levels of less than 1% total C the layers are of excellent quality. The total carbon level was found to be independent of the Ge fraction and growth temperature. However, the Ge fraction in the alloys was observed to increase when carbon was added to the alloys, suggesting that C alters the sticking probabilities of silane and germane. We also studied the thermal stability of Si1−x−yGexCy alloys with low levels of carbon and found that adding even 0.2% C significantly improves the thermal stability when compared to SiGe alloys of similar strain and thickness.
Fermi surface study of pseudomorphic Fe1−xNix and Co1−xNix thin films on Cu(100)
Authors: Hochstrasser M. , Schumann F. O. , Willis R. F. , Cummins T. , Waddill G. D. , Mishra S. R. , Tobin J. G. , Rotenberg E.
Published: July 2002

We report angle resolved photoemission studies of the electronic behavior of ultrathin epitaxial layers of fcc structured binary alloys, Fe1−xNix and Co1−xNix, deposited by molecular beam epitaxy on Cu(100) substrates. In particular, we have used Fermi surface mapping to monitor changes in the Fermi surface with increasing magnetization density. Fe1−xNix and Co1−xNix binary alloys show a different behavior in the bulk. Co1−xNix is structurally and magnetically well-behaved. In particular, the magnetic moment varies linearly as a function of concentration. This is in sharp contrast to fcc Fe1−xNix which displays a magnetic instability at ∼65% Fe content. An extended regime of fcc stability is possible via epitaxy on Cu(100). The changes in the Fermi surfaces of Fe1−xNix and Co1−xNix pseudomorphic film alloys depending on various concentrations of Ni have been investigated in a large photon energy regime. We address the following question: To what degree is the Fermi surface sharply preserved in substitutional alloys?
Complete solvent free stripping of via structures using NF3/H2O/O2 ashing chemistry
Authors: Au Wing kei , Solis Randy , Bersin Richard , Xu Han , Boumerzoug M.
Published: July 2002

The objective of this study is to develop a via post-strip cleaning process which would utilize non-hydroxylamine (HDA) based solvent, thereby reducing possibility of corrosion in the via and also reducing the cost of chemicals and waste disposal expenses. The work resulted in the development of a 100% solvent-less process which matches the performance of HDA-based solvents but totally eliminates chemical costs and waste-disposal expenses; removes the hazards of working with hot hazardous solvents; avoids corrosion which is common with HDA-based solvents; and thereby facilitates more efficient utilization of costly clean-room space. The new ash process in combination with a post-ash DI water rinse has been demonstrated to be effective at removing polymer inside vias and achieving via resistances comparable to standard oxygen ash + HDA wet solvent stripping.
Substrate effects on electronic properties of atomic chains
Authors: Yamada Toshishige
Published: July 2002

A substrate for future atomic chain electronics, where adatoms are placed at designated positions and form atomically precise device components, is studied theoretically. The substrate has to serve as a two-dimensional template for adatom mounting with a reasonable confinement barrier and also provide electronic isolation, preventing unwanted coupling between independent adatom chains. For excellent structural stability, we demand chemical bonding between the adatoms and substrate atoms to secure the positions (chemical bonding scheme), but then good electronic isolation is not always guaranteed and necessary conditions are clarified. The substrate influences fundamental chain properties through chemical bonds. A chain with group IV adatoms having two chemical bonds each, or a chain with group III adatoms having one chemical bond each, is semiconducting. Charge transfer from or to the substrate across the chemical bonds brings about unintentional doping for semiconducting chains. The electronic properties have to be considered for the combination of the adatom and substrate systems in this scheme, even though the adatom modes are well localized in the adatom chains.
Effect of tensile strain on B-type step energy on Si(001)-(2×1) surfaces determined by switch-kink counting
Authors: Heller E. R. , Jones D. E. , Pelz J. P. , Xie Y. H. , Silverman P. J.
Published: July 2002

Scanning tunneling microscopy (STM) images of unstrained Si(001) and Si(001) grown under tensile strain have been analyzed to determine whether the SB step energy increases with applied tensile strain, as predicted by Xie et al. [Phys. Rev. Lett. 73, 3006 (1994)]. We did this using “kink counting” of STM images, using a new “switch-kink” counting method that is better suited for analysis of STM images in which the local azimuthal miscut angle changes. Our measurements indicate that the SB step energy does increase with tensile strain, in qualitative agreement with the predictions of Xie et al., although not as strongly as their calculations suggested.