bluuebunny/crossref_metadata_2025 huggingface dataset:
Protection of In0.25Ga0.75As/GaAs structures during lateral oxidation using an amorphous InGaP layer
Authors: Pickrell G. W. , Chang K. L. , Epple J. H. , Cheng K. Y. , Hsieh K. C.
Published: July 2002

Using very-low-temperature molecular beam epitaxy growth techniques, an amorphous InGaP layer was deposited to protect the surface during lateral oxidation of an underlying AlGaAs layer. For comparison, other oxidation protection layers such as SiNx and SiO2 were also studied. The oxidized structure consisted of single crystal In0.25Ga0.75As grown on the underlying AlGaAs layer, and then capped with an oxidation protection layer. The oxidation rate of the amorphous InGaP was investigated and compared to the oxidation rates of both single crystal InGaP and GaAs. In addition, the effects of the InGaP layer thickness on the threading dislocation density of the In0.25Ga0.75As layers were investigated. It was found that the amorphous InGaP layers allowed for threading dislocation reduction in the underlying In0.25Ga0.75As layers, while the dielectric protection layers caused an increase in dislocation densities. Atomic force microscopy was also used to investigate the surface after removal of the InGaP protection layers.
Electroplating copper in sub-100 nm gaps by additives with low consumption and diffusion ability
Authors: Lin Kun-Cheng , Shieh Jia-Min , Chang Shih-Chieh , Dai Bau-Tong , Chen Chia-Fu , Feng Ming-Shiann
Published: July 2002

This work presents a novel leveler with low consumption and low diffusion that achieved defect-free filling in vias as small as 0.1 μm and generated as-deposited films with low resistivities. Experimental results indicate that the additive, 2-aminobenzothiazole (2-ABT), with benzyl and amino (–NH2) functional groups, is a desirable leveler. It produced a highly selective concentration gradient between the opening and the bottom of the feature. This novel leveler, with weaker adsorption, also reduced the consumption during copper electroplating, and eventually deposited a film with a high conductivity.
Selective wet etching of AlGaAs in HF/CrO3 solutions: Application to vertical taper structures in integrated optoelectronic devices
Authors: Huang Hui , Huang Yongqing , Ren Xiaomin
Published: July 2002

The etch rate and surface morphology of AlxGa1−xAs (x=0.3, 0.5, 0.65) versus composition of CrO3/HF solutions were studied using the dynamic etch mask technique. The selectivity, defined as a ratio of the etch rates, decreases from 179 to 8.6 for Al0.8Ga0.2As/Al0.3Ga0.7As with the volume ratio of HF (48 wt %)/CrO3(33 wt %) increasing from 0.01 to 0.138. The selective etching was experimentally applied to the fabrication of the vertical taper structures with angles ranging from 0.32° to 6.61° on an Al0.3Ga0.7As epitaxial layer. The surface roughness of AlxGa1−xAs (x=0.3, 0.5, 0.65), which was etched by CrO3/HF at a volume ratio of 0.028, were 1.8, 9.1, and 19.3 nm, respectively. The dependence of etch rate for AlxGa1−xAs (x=0.8, 0.85, 0.9) on composition of CrO3/HF has also been obtained. This technique has proven to be very useful in integrated optoelectronic device fabrication.
Approach to structure determination of compound semiconductor surfaces by kinematical LEED calculations: GaAs(110) and ZnSe(110)
Authors: Mark P. , Cisneros G. , Bonn M. , Kahn A. , Duke C. B. , Paton A. , Lubinsky A. R.
Published: July 2002

Because of the expense of dynamical low-energy electron diffraction (LEED) computational analyses, a more economical approach to the comparison between measured and computed LEED intensity profiles of nonpolar compound semiconductor surfaces consists of determining an initial estimate of surface atomic position coordinates via comparison of experimental data with kinematical calculations. Once an acceptable region of position parameter space has been identified, further refinements can be obtained by dynamical LEED analyses. This paper presents the results of the kinematical portion of such an analysis applied to GaAs(110) and ZnSe(110) surfaces. It is found that both materials exhibit similar surface atomic rearrangements characterized by bond length distortions and vertical displacements of the two sublattices in the uppermost atomic layer. These rearrangements differ from the ’’rotated’’ rearrangement reported earlier for GaAs(110) principally in that the structures identified herein involve small changes in bond lengths.
Fine-focus ion beams with field ionization
Authors: Orloff J. , Swanson L. W.
Published: July 2002

The applicability of the field ionization source for microprobe use is under investigation with a differentially pumped high-pressure source and an electrostatic optical column. Resolution of 6500 Å with greater than 50 pA hydrogen current and approximately 2000 Å with 20 pA Ar current have been achieved, using polycrystalline Ir emitters. Single-crystal 〈110〉 Ir emitters can be built up in a manner similar to 〈100〉 oriented W to reproducibly yield high current on axis with good angular confinement of the ion beam, as opposed to the poor confinement and difficult-to-reproduce results obtained with polycrystalline Ir.
Low-temperature annealing and hydrogenation of defects at the Si–SiO2 interface
Authors: Johnson N. M. , Biegelsen D. K. , Moyer M. D.
Published: July 2002

Characteristic defects at the Si–SiO2 interface are strongly influenced by specific low-temperature treatments. Annealing aluminum thin films on thermal oxides removes both characteristic interface states and the interfacial paramagnetic defect center. However, the anneal processes occur at significantly different temperatures. Since the spin center has been previously identified as a trivalent silicon defect bonded to three silicon atoms at the interface, it appears that this defect center is not directly responsible for the characteristic interface states. Hydrogen is generally believed to be involved in the removal of interface states, although the microscopic processes have not been established. The effect of hydrogen was investigated by using deuterium as a readily traceable isotope which simulates hydrogen chemistry. Anneals in atomic deuterium annihilated the interface spin center. The physical presence of deuterium in the SiO2 layer was established with secondary ion mass spectrometry, which revealed an accumulation of deuterium at the Si–SiO2 interface for deuteration temperatures in the investigated range of 25 to 230°C; postdeuteration anneals above 500°C (in vacuum) were required for its removal. Annihilation of the spin center is therefore explained by the conversion of trivalent silicon defects to nonparamagnetic Si–D bonds.
Sputtered Bi2Te3 and PbTe thin films
Authors: Shing Y. H. , Chang Y. , Mirshafii A. , Hayashi L. , Roberts S. S. , Josefowicz J. Y. , Tran N.
Published: July 2002

Thin films of Bi2Te3 and PbTe were produced by sputtering using targets of stoichiometric compounds. The compositions of these sputtered thin films were analyzed by the electron microprobe; the Bi2Te3 film showed nonstoichiometric compositions of Bi=44.5 at.%, Te=55.5 at.%, whereas the compositions of PbTe films were stoichiometric. The morphology of these sputtered films was established to be polycrystalline by x-ray diffraction (XRD). XRD peaks of Bi2Te3 films revealed the existence of nonstoichiometric crystalline phases; PbTe films have a single cubic phase with (200) preferred orientation. X-ray photoelectron spectroscopy chemical state analysis on both Bi2Te3 and PbTe films showed that Bi, Pb, and Te have one chemical state consistent with the valence state in the compounds. Room temperature carrier concentration and Hall mobility of BiTe3 film were measured to be 7.2×1020 cm−3 and 15 cm2/V-s respectively; the corresponding values of PbTe films are 5.6×1019 cm−3 and 38 cm2/V-s, respectively. Doping experiments on Bi2Te3 and PbTe films using a single target sputtering system are reported. Sputtered PbTe films doped with Sn have shown promising thermoelectric properties.
Optical properties and grain boundary effects in CuInSe2
Authors: Kazmerski L. L. , Hallerdt M. , Ireland P. J. , Mickelsen R. A. , Chen W. S.
Published: July 2002

The optical properties of CuInSe2 thin films and single crystals are reported. The wavelength dependence of the refractive index and extinction coefficient is measured using multiple angle-of-incidence ellipsometry. Absorption coefficients as high as 6×105/cm are reported—the highest for any semiconductor. CuInSe2 is confirmed to have a room temperature, direct-bandgap transition near 0.96 eV for the single crystals, and 1.02 for the thin films. The difference is proposed to be due to nonuniformity in composition of the polycrystalline material. Additional absorption in the low absorption-coefficient regime is likely due to transitions associated with phonon absorptions for the single crystals. The effects of heat treatments in Ar, N, and O are shown to improve the optical properties of the thin films due to improvement in film compositional uniformity. Heating in high vacuum causes Se desorption near the film surface, causing a related degradation in the absorption characteristics.
Early applications of vacuum, from Aristotle to Langmuir
Authors: Madey Theodore E.
Published: July 2002

Highlights of the development of vacuum science and technology from ancient times to the early 20th century are reviewed. The view of the Greek philosophers that vacuum was an impossibility hampered understanding of the basic principles of vacuum until the mid-17th century. Verifiable vacua were first produced in Italy by Berti and Torricelli; von Guericke’s dramatic experiments vividly demonstrated atmospheric pressure. Pistonlike ‘‘air pumps’’ were widely used in England and the European continent through the 18th and early 19th centuries to produce and characterize the properties of vacuum (lack of sound transmission, inability to support life, gas discharges, etc.). The Industrial Revolution was made possible through the genius of Newcomen, who designed huge atmospheric engines (based on condensation of steam to form a vacuum beneath a piston, which was then driven by the pressure of the atmosphere). A system of ‘‘atmospheric railways’’ propelled by vacuum pistons was built in England in the mid-19th century. Serious scientific developments of the 19th century which necessitated vacuum included Crookes’ and Faraday’s gaseous discharge measurements, the first sputtering experiments by Grove, the isolation of the rare gases by Ramsay, the standards work of Miller, the discovery of the electron by Thomson, and of x-rays by Röntgen. The development of the incandescent light by Edison provided a background for the remarkable achievements of Langmuir in vacuum and surface science at the dawn of the 20th century. An Appendix is included which lists museums containing vacuum-related exhibits.
Production of large vaporized metal clusters and their applications to functional metallurgical coatings
Authors: Takaoka Hiroshi , Yamada Isao , Takagi Toshinori
Published: July 2002

Cluster formation mechanism with large vaporized metal clusters is discussed, and several specific applications of ionized cluster beam (ICB) to films of metallurgical interest are described. In the ICB deposition and epitaxy, the crystallographic, mechanical, electrical, optical, and magneto-optical properties of the metal and intermetallic compound films can be controlled by adjusting the acceleration voltage and the electron current for ionization. Metal-based and intermetallic compound-based films with characteristic advantages are reported; Cu films with strong adhesion and high packing density, Cu–Ni alloy films with controllable crystal structure and high strain gage, CdTe–PbTe superlattice with very thin and multilayered structures, and Cd1−xMnxTe films with large Faraday rotation and controllable composition and crystallinity. Thus, the ICB technique is found to have a high potential and unique features as an emerging technique for functional film formation and surface modification.
Structural and electrical characteristics of vacuum-evaporated erbium fluoride thin films
Authors: Ramanujam R. , Radhakrishnan M. , Balasubramanian C.
Published: July 2002

Thin-film capacitors of erbium fluoride were fabricated by thermal evaporation. The film structure was analyzed by x-ray diffractogram and confirmed by the x-ray small-angle surface reflection technique. The current–voltage characteristics of these films were studied at different temperatures in the range of 300–390 K. It was observed that at high electric fields the current increases linearly with the square root of the field. The conduction mechanism was found to be predominantly by Poole–Frenkel emission in these films and is an activated process with the activation energy decreasing with increasing electric field.
Partial pressure control of reactively sputtered titanium nitride
Authors: Hmiel A. F.
Published: July 2002

The production of reactively sputtered films under mass flow control is complicated by transitions in pressure upon exceeding a critical value of flow. Stable operation of a dc magnetron, reactive sputtering process in the critical region where TiN is created has been demonstrated when partial pressure control is employed. Equilibrium flow values that decrease with increasing nitrogen pressure are found in the region where the pressure transitions had occurred. A mechanism supporting these observations under partial pressure control in this region is proposed.
Dynamics of dissociative adsorption and vibrational excitation in molecule–surface collisions
Authors: Gadzuk J. W.
Published: July 2002

Collisions between diatomic molecular beams and solid surfaces are here simulated through classical trajectory calculations over model potential-energy surfaces. Insights into the conditions responsible for dissociative adsorption versus vibrationally excited scattering are provided.
Structural studies of (331) GaAs surface
Authors: Horng S. , Young K. , Kahn A.
Published: July 2002

The atomic structures of (331)-A and (331)-B GaAs surfaces, prepared by ion bombardment and annealing (IBA) or by molecular-beam epitaxy, are investigated with low-energy electron diffraction, electron energy-loss spectroscopy, and Auger electron spectroscopy. The IBA (331)-A surface exhibits double-layer steps at rather low temperature, and develops large (110) and (111) facets after further annealing at ∼420 °C; the (331)-B surface is flat up to annealing temperatures ∼600 °C, and exhibits large {110} and (111) facets after further annealing. When prepared by molecular-beam epitaxy, the (331)-A surface exhibits double-layer steps after annealing up to ∼550 °C, and develop (110) and (111) facets after further annealing; the (331)-B surface is flat up to annealing at 550 °C, and exhibits double-layer steps after further annealing at 600 °C; it then develops large {110} and (111) facets after further annealing.
Growth and electronic structure of Nb and Ta films on Pd and their interaction with CO
Authors: Jiang L. Q. , Ruckman M. W. , Strongin Myron
Published: July 2002

The growth of Nb and Ta films on Pd(111) and their modification of CO chemisorption are studied using ultraviolet photoelectron spectroscopy (UPS), low-energy electron diffraction, and low-energy ion scattering (LEIS). At 300 K, LEIS shows significant amounts of Pd in the top layer even after more than a monolayer of Nb or Ta is deposited. This is in contrast to Pd on Nb or Ta(110) where a Pd monolayer completely covers the substrate. UPS shows that the surface electronic structure at monolayer Nb or Ta coverage resembles that of a Pd monolayer on Nb or Ta(110) and is characterized by strong Pd 4d emission 1–4 eV below Ef and a low density of states at Ef. Molecular CO adsorption is observed at submonolayer coverage; there is little CO adsorption at monolayer coverage and dissociative CO adsorption starts at greater than monolayer coverage. It is concluded that the deposited Nb or Ta monolayers intermix with the Pd(111) substrate and it is also shown that this behavior can be understood by examining the energetics of the system.
Image processing of multispectral x-ray photoelectron spectroscopy images
Authors: King P. L. , Browning R. , Pianetta P. , Lindau I. , Keenlyside M. , Knapp G.
Published: July 2002

A new direct imaging photoelectron microscope has been demonstrated at the Stanford Synchrotron Radiation Laboratory. Data are obtained in the form of spectrally resolved images with a lateral resolution of <5 μ. The microscope produces a series of projected images with 64×64 picture elements. These images are recorded digitally and represent a very large data set. Image statistical methods have been used to reduce and present the image information.
Electron spectroscopic identification of carbon species formed during diamond growth
Authors: Belton David N. , Schmieg Steven J.
Published: July 2002

Carbon deposits formed during filament assisted diamond film growth were characterized with x-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The samples were transferred between the growth chamber and the ultrahigh vacuum analytical chamber without exposure to air. These results are presented with an emphasis on data analysis for carbon chemical state identification. By comparison of the C(1s) binding energies to a highly oriented pyrolytic graphite standard, we are able to distinguish pure carbon species, such as diamond and graphite, from compounds, such as SiC and CxHy. For substrates with Z≤30, the loss electrons from the C(1s) core level are free from overlap with the substrate core levels; therefore, EELS spectra can be obtained by x-ray excitation of the C(1s) level. These EELS data can then be used as a fingerprint for distinguishing between diamond, graphite, and carbides. For samples with mixed deposits of diamond and graphite, or carbide and diamond, curve fits of the EELS data can qualitatively determine which species are present.
Influence of barriers on charge transport across HgCdTe heterojunctions
Authors: Kosai K. , Radford W. A.
Published: July 2002

This paper is a discussion of the influence of heterojunction barriers on minority-carrier hole transport in wide band gap p+ on narrow gap n HgxCd1-xTe diodes that are illuminated from the n side. We have simulated detectors with 10.5 μm cut off wavelengths at 80 K by numerically solving the coupled transport and continuity equations for electrons and holes with Poisson’s equation. Parameters in the modeling include the composition of the p+ cap layer, the composition grading width, the doping of the base layer, temperature, and detector bias. The modeling predicts that the ratio of the quantum efficiency in a device with a barrier height of 2kT to that of a detector with no barrier is 0.95, while a 4.5kT barrier gives a value of 0.5. The model calculations have been qualitatively confirmed by experimental measurements of x=0.42/0.22 and 0.30/0.22 heterojunctions in which the doping in the low band gap n layer was varied to adjust the height of the heterojunction barrier.
Large-area sputtering of i
n s
i
t
u superconducting YBa2Cu3O7 films
Authors: Ballentine P. H. , Allen J. P. , Kadin A. M. , Mallory D. S.
Published: July 2002

High-temperature superconducting thin films of YBa2Cu3O7 are deposited on 2 in. MgO and LaAlO3 substrates by radio frequency magnetron sputtering from an 8 in. diam powder target. By locating the substrate above the center of the magnetron erosion ring and by placing a ‘‘negative ion shield’’ between the target and the substrate, negative ion resputtering is avoided and high quality films are grown in situ, and are superconducting on removal from the vacuum chamber without a high-temperature post anneal. Stoichiometric films on LaAlO3 and MgO have critical temperatures up to 88 K and critical currents above 5×105 A/cm2 at 77 K. Uniformity in thickness of ±5%, and in room temperature resistivity of ±7% were measured on 2 in. diam substrates. Microwave surface resistance measurements at 1.2 GHz and 4.2 K showed Rs≊0.1 mΩ for YBCO ground planes and ≊0.3 mΩ for patterned YBCO strip lines on MgO.
K-edge absorption analysis of hyrogenated diamond-like carbon films
Authors: Wang Yaxin , Chen Hsiung , Hoffman R. W.
Published: July 2002

K-edge absorption features of hydrogenated diamond-like carbon films (a-C:H) are analyzed with reflection electron energy loss spectroscopy. The a-C:H films were prepared by a plasma-enhanced chemical vapor deposition from methane. Hydrogen in these films ranges from 28 to 44 at.%. The π and σ electron absorption edges are measured for the films with different hydrogen contents. The π absorption edge, which corresponds to the transitions of 1s electrons to the anti-π (π*) states, shifts about 1 eV with hydrogen increasing about 16 at. % in the films. The σ absorption features corresponding to the transitions of 1s electrons to the anti-σ (σ*) states is not affected much by different C–H bonding. The σ absorption peak is scattered around 291 eV for all samples.
Quantitative surface analysis with elemental standards: Surface roughness limitations
Authors: Dawson P.T. , Petrone S.A.
Published: July 2002

The dependence of the detected Auger signal on crystal orientation and surface morphology has been investigated for a pure elemental standard of Mo. Two large adjacent grains with orientations close to (100) and (1, 4, 11) were used for this study. After polishing to a uniform surface topograpy the sample was sputtered with 2 keV argon ions at glancing incidence, typical of the conditions used in surface analysis. The initial line scan across both crystal surfaces showed an essentially constant detected Auger current. However, under continued ion bombardment up to a fluence of 5×1019 ions cm−2, the Auger current changed until the (100) crystal showed an 18% larger signal than the high index grain. This large difference is attributed to changes in surface roughness that develop quite differently for different crystal orientations. The surface morphology changes have been characterized using scanning electron microscopy and surface profile measurements. The implications of these results for quantitative surface analysis are discussed.
Homoepitaxial growth investigated by high-resolution He atom scattering: NaCl onto NaCl(001)
Authors: Duan J. , Bishop G. G. , Gillman E. S. , Chern G. , Safron S. A. , Skofronick J. G.
Published: July 2002

The homoepitaxial growth of NaCl vapor deposited onto the cleaved (001) surface of NaCl was studied with a nearly monoenergetic (ΔE/E≂2%) He atom beam. In comparison with reflection high-energy electron diffraction, the He atom is unique for epitaxial studies in that it is uncharged, nondestructive, and sensitive only to the outer surface layer. The oscillations in the scattered intensities of the specular and Bragg peaks due to the layer-by-layer growth were examined by measuring the angular distributions as a function of coverage, surface temperature (150–400 K) and incident He atom wave vector (6–8 Å−1). The periodic variation in the relative heights of the specular and Bragg peaks with Δkz=‖kfz−kiz‖ showed that under these conditions the growth is two-dimensional with a terrace height of 2.8 Å or half the bulk face-centered-cubic lattice spacing. In addition, scattering cross sections for adsorbed NaCl at low coverages were determined with respect to these same parameters. The cross sections for substrate temperatures above 250 K decline rapidly, which suggests that surface diffusion becomes much more rapid above this point. Previous studies had reported high mobilities down to temperatures considerably lower.
Powder dynamics in very high frequency silane plasmas
Authors: Dorier J.-L. , Hollenstein Ch. , Howling A. A. , Kroll U.
Published: July 2002

Particulate contamination produced during plasma-assisted deposition of amorphous silicon devices can be responsible for reduced quality and yield. The threshold for powder formation imposes an upper limit on the radio frequency (rf) power and hence the deposition rate. In this work, the parallel-plate capacitor discharge volume is illuminated and global, spatio-temporal powder dynamics are recorded by CCD camera for analysis. The onset of powder production is determined visually and from observed modifications to the discharge electrical properties such as the matching condition, the direct current self-bias and the rf power transfer efficiency. A systematic study has been made of the powder-free operational space as a function of rf power, rf frequency (13.56–70 MHz) and substrate temperature.
Comparative effects of gauge-wall materials on the outgassing rate of a hot-cathode ionization gauge
Authors: Watanabe Fumio
Published: July 2002

Using a newly developed spherical-grid Bayard–Alpert gauge, a comparative test of gauge-wall material (stainless steel, gold on stainless steel, aluminum, gold on aluminum, and copper) on the outgassing rate and pumping speed of a hot-cathode ionization gauge has been carried out. (1) Outgassing was primarily related to electron emission and, in the ultrahigh vacuum (UHV) range, the existence of the hot-cathode filament was a small factor, compared to electron emission. (2) At a low emission of 1 mA, an aluminum gauge wall had a very high pumping speed at UHV after degassing by electron bombardment. (3) At a high emission of 10 mA, the lowest outgassing rate was obtained with a vacuum-cast oxygen-free copper gauge wall. (4) Using low emissivity metals such as gold, copper, and aluminum for the gauge wall, the filament heating power was reduced to approximately half the power required with a stainless-steel gauge wall for the same emission. (5) The outgassing rate of the spherical grid gauge with a low emissivity metal wall was of the order of 10−11 (mbarℓ/s), which is about 1/10–1/100 that of an ordinary stainless-steel nude UHV gauge.
X-ray photoelectron spectroscopy analysis of aluminum and copper cleaning procedures for the Advanced Photon Source
Authors: Rosenberg R. A. , McDowell M. W. , Noonan J. R.
Published: July 2002

The Advanced Photon Source (APS), presently under construction, will produce x rays of unprecedented brightness. The storage ring where the x rays will be produced will be constructed from an extruded 6063 aluminum alloy, while transition pieces (flanges, etc.) will be made from a 2219 aluminum alloy. In addition, cooled photon absorbers will be placed in strategic locations throughout the ring to intercept the majority of the unused high power-density radiation. These will be made of either CDA-101 (OFHC) copper or glidcop (a dispersion strengthened copper alloy). Before any of these components can be assembled they must be cleaned to remove surface contaminants so that the ultrahigh vacuum (<0.1 nTorr) necessary for successful operation can be achieved. Many recipes for cleaning aluminum and copper exist; however, most of them involve the use of chemicals that present safety and/or environmental concerns. We have undertaken an x-ray photoelectron spectroscopy study of the effects of a variety of commercially available cleaners on the surface cleanliness of aluminum and copper. Several important results have been identified in this study. A simple alkaline detergent in an ultrasonic bath cleans aluminum alloys as effectively as the more aggressive cleaning solutions. The detergent can be used at 65 °C to clean the 6063 alloy and at 50 °C to clean the 2219 alloy. A citric acid based cleaner was found to be effective at cleaning copper, although the surface oxidizes rapidly. To date, we have been unable to find a universal cleaning procedure, i.e., one that is optimal for cleaning both Al and Cu.
Reactive-sputter deposition and structure of RuO2 films on sapphire and strontium titanate
Authors: Wang Q. , Gladfelter Wayne L. , Fennell Evans D. , Fan Yue , Franciosi Alfonso
Published: July 2002

Metallic films of RuO2 were deposited by reactive-sputtering deposition on single crystal substrates of Al2O3 (0001) and SrTiO3 (100) at room temperature and 450 °C. Measurement of the characteristic hysteresis loop revealed that the target’s transition from a metal to a metal oxide surface occurred at a very high O2/Ar ratio (88%) under our experimental conditions. The hysteretical behavior of the transition was evaluated experimentally and was modeled. Resonance-enhanced Rutherford backscattering spectrometry established that the films deposited at 450 °C had an oxygen to ruthenium ratio of 1.97, while a slightly higher value of 2.08 was observed for the films grown at room temperature. The latter films were amorphous, whereas those grown at 450 °C exhibited a highly oriented polycrystalline microstructure. On SrTiO3 (100), the RuO2 (100) plane is parallel to the substrate surface, but no in-plane orientation was found. The same face, RuO2 (100), was also parallel to the surface of Al2O3 (0001), and the [001] direction of individual grains of RuO2 aligned with the three 〈1̄010〉 directions of the substrate to produce a threefold mosaic microstructure.
Nanometer-scale lithography on H-passivated Si(100) by atomic force microscope in air
Authors: Lee Hai Tai , Oh Jae Seuk , Park Seong-Ju , Park Kang-Ho , Ha Jeong Sook , Yoo Hyung Joun , Koo Ja-Yong
Published: July 2002

We report on the mechanical friction method for a fabrication of a Si nanostructure on a H-passivated Si(100) substrate using an atomic force microscope (AFM) in a contact mode in air. The bare Si surface region exposed by the mechanical friction between a silicon nitride tip and Si surface was fully oxidized by ambient oxygens. The oxide mask patterns could withstand a selective wet etching process for pattern transfer. The width of the oxide layer formed by an AFM tip was about 200 Å. As the etching time and scan rate were decreased, the oxide line shape was improved. This study also showed that there exists a critical tip force in the removal of a H-passivating layer.
High density fluorocarbon etching of silicon in an inductively coupled plasma: Mechanism of etching through a thick steady state fluorocarbon layer
Authors: Standaert T. E. F. M. , Schaepkens M. , Rueger N. R. , Sebel P. G. M. , Oehrlein G. S. , Cook J. M.
Published: July 2002

For various fluorocarbon processing chemistries in an inductively coupled plasma reactor, we have observed relatively thick (2–7 nm) fluorocarbon layers that exist on the surface during steady state etching of silicon. In steady state, the etch rate and the surface modifications of silicon do not change as a function of time. The surface modifications were characterized by in situ ellipsometry and x-ray photoelectron spectroscopy. The contribution of direct ion impact on the silicon substrate to the etching mechanism is reduced with increasing fluorocarbon layer thickness. Therefore, we consider that the silicon etch rate is controlled by a neutral etchant flux through the layer. Our experimental data show, however, that ions play an import role in the transport of silicon etching precursors through the layer. A model is developed that describes the etch kinetics through a fluorocarbon layer based on a fluorine diffusion transport mechanism. The model is consistent with the data when one or two of the following roles of the ions on the etching process are assumed. The first role is an enhancement in the diffusivity of fluorine atoms through the fluorocarbon layer and an enhancement in the reaction probability of fluorine in the fluorocarbon layer. In this case the fluorine is assumed to originate from the gas phase. The second role includes ion fragmentation and dissociation of the fluorocarbon surface molecules.
Oxygen adsorption and oxide formation on Ni3Al (111)
Authors: Becker C. , Kandler J. , Raaf H. , Linke R. , Pelster T. , Dräger M. , Tanemura M. , Wandelt K.
Published: July 2002

The interaction of oxygen with the ordered Ni3Al (111) surface has been investigated in the temperature range from 300 to 1000 K using high-resolution electron-energy-loss spectroscopy (HREELS) and low-energy electron diffraction (LEED). The “2×2” LEED pattern of the clean Ni3Al (111) surface indicates a bulklike termination. After oxygen adsorption at 300 K the LEED pattern is diffuse suggesting the formation of an amorphous overlayer. The HREELS spectra show evidence for oxygen interaction with both aluminum and nickel atoms. At 600 K adsorption temperature the fcc surface order is restored, however, the observed (1×1) LEED pattern indicates the loss of chemical order. Again HREELS spectra suggest interaction of oxygen with both aluminum and nickel. For an adsorption temperature of 800 K LEED shows an unrotated oxygen induced superstructure with a lattice spacing of 2.93 Å in addition to the (1×1) substrate spots. The HREELS spectra exhibit an intense loss at 81.9 meV, which is also known from oxygen in threefold hollow sites on Al (111). Since such sites are not available on the Ni3Al (111) surface, we conclude the buildup of an oxygen covered aluminum overlayer. Finally, during oxygen exposure at 1000 K we observe the growth of a γ′-Al2O3 structure on the reordered Ni3Al (111) substrate surface. This structure has been identified by means of the characteristic vibrational losses in HREELS at 54.6, 80.3, and 112.8 meV together with the emergence of overlayer spots in LEED exhibiting the lattice spacing of γ′-Al2O3 (3.02 Å). For oxygen exposures at 800 and 1000 K an island growth of the overlayer has been found.
Radial profile of energetic particles bombarding the substrate in a glow discharge
Authors: Moreno-Marı́n Juan Carlos , Abril Isabel , Garcia-Molina Rafael
Published: July 2002

We have analyzed in an interrelated way the main processes that occur in a glow discharge system: generation of the energetic particles that strike the cathode, emission of sputtered and reflected atoms from the cathode, and transport of these particles through the plasma, until their eventual arrival to the substrate. As an output of our calculations we have obtained the radial profiles of the energy and the number of particles that reach the substrate, as a function of the geometrical characteristics and pressure of the discharge. Our results show that the main part of the energy deposited in the substrate comes from the reflected gas atoms, in spite of the larger number of sputtered cathode atoms.
Field-induced manipulation of Ag clusters for tailoring of nanostructures on a silicon surface
Authors: Park Kang-Ho , Ha Jeong Sook , Yun Wan Soo , Lee El-Hang
Published: July 2002

We devised new nanofabrication methods using a manipulation of self-organized Ag clusters on Sb-terminated Si(100) surfaces by a scanning tunneling microscope (STM) tip. Various kinds of nanostructures could be manufactured by dot-by-dot manipulation. We found that two methods could be used for those fabrications; (1) Ag clusters could be detached and redeposited by a field-induced manipulation using an STM tip and (2) Ag clusters could be also detached from the surface via the formation of mechanical point contact between the tip and clusters. These fabrication methods were systematically investigated with variation of manipulation conditions such as a bias voltage and a tip-sample distance.
Properties of a-Si:H films deposited from silane diluted with hydrogen and helium using modified pulse plasma technique
Authors: Mukherjee C. , Anandan C. , Seth T. , Dixit P. N. , Bhattacharyya R.
Published: July 2002

Hydrogenated amorphous silicon films were deposited in a modified square wave modulated pulsed plasma discharge at 13.56 MHz using silane diluted with hydrogen, helium, and their mixtures at two different modulation frequencies. The deposition rate is found to be higher in helium diluted plasmas and also at 10 Hz modulation. Increasing the modulation frequency from 2 to 10 Hz increases the deposition rate at all dilutions with helium or helium and hydrogen. At 2 Hz modulation, the deposition rate in helium diluted silane is higher and tends to saturate with increasing dilution whereas with hydrogen dilution it decreases. In helium diluted discharge with 10 Hz modulation the material properties deteriorate. However, the addition of hydrogen to helium diluted silane improves the film properties. The decrease in the deposition rate in hydrogen, and hydrogen and helium diluted plasmas is attributed to atomic hydrogen mediated etching of the growth surface which also explains the improvements in optoelectronic properties of these films. Hydrogen content, hydrogen bonding configurations, and the defect density also depend on the dilution ratio and modulation frequency.
Low-energy Ar+ ion induced angularly resolved Al(100) and Al(110) sputtering measurements
Authors: Smith P. C. , Ruzic D. N.
Published: July 2002

An apparatus and analysis method to obtain both the angular distribution of sputtered atoms and the total sputtering yield for materials of interest to physical vapor deposition (PVD) has been created. Total yield is determined by collecting the sputtered material on a quartz crystal oscillator (QCO) microbalance. The sputtered material is also collected on a pyrolytic graphite witness plate. By mapping the concentrations of the sputtered material on this plate, both polar and azimuthal angular distributions of the sputtered material can be determined. Utilizing this setup, data have been obtained for (200–500 eV) Ar+ normally incident on polycrystalline aluminum sputtering targets with strong (100) and (110) crystallographic orientations. The overall yields of these samples compare well to the available data as well as empirical formulas. Crystallographic effects in the angular distributions are clearly seen. The Al(100) sample shows 12% enhanced sputtering along the 〈110〉 direction at all energies.
Problems of determining true equilibrium pressures of hydrogen getters over a wide range of getter temperature and hydrogen sorption
Authors: Ghezzi F. , De Angeli M.
Published: July 2002

We have assessed a conventionally configured apparatus to measure hydrogen equilibrium pressures of getter alloys over the temperature range of 25 to 400 °C and hydrogen concentration range of 0.02 to 1 H/A. An in situ approach has been proposed to correlate the measurements of different gauges using one of the precisely calibrated gauges as a standard reference. The pressure range of interest was 10−7–105 Pa and was covered using a Bayart–Alpert gauge, a spinning rotor gauge, and different capacitance gauges. The approach involves measuring the characteristic response of these instruments prior to determining hydrogen equilibrium pressures over the relevant range of wall and getter bed temperature. To evaluate the accuracy of the measurements, we performed an error propagation analysis. The use of a porous filter to avoid fines contamination and the adsorption/desorption kinetics of the walls of the system were both addressed.
A low-temperature atomic force/scanning tunneling microscope for ultrahigh vacuum
Authors: Giessibl F. J. , Gerber Ch. , Binnig G.
Published: July 2002

We have built an ultrahigh vacuum atomic force/scanning tunneling microscope that works at 4.2 K. The microscope is incorporated into a very small chamber (100 ml) which can be evacuated and baked to UHV within a few hours by a specially designed valve. The instrument is about 20×20×70 mm3 in size and sturdy enough to operate without vibration isolation. The deflection of a microfabricated cantilever is detected by electron tunneling. Preliminary results show atomic resolution of HOPG in the STM mode and steps in KBr that range from one to four lattice constants in height at UHV conditions and 4.2 K.
Uniform-stress tungsten on x-ray mask membranes via He–backside temperature homogenization
Authors: Mondol Mark , Li Huiying , Owen Gabrielle , Smith Henry I.
Published: July 2002

When x-ray absorbers such as W are sputtered directly onto x-ray mask membranes a large temperature gradient is set up due to the power input from the plasma, and the very inefficient thermal conduction in the plane of the thin membrane. To obtain absorber stresses sufficiently low that pattern distortion is negligible, the temperature gradient across the membrane must be no greater than a few degrees. To achieve this we introduce He at about 665 Pa (5 Torr) between the back surface of the membrane and an Al heat sink heated to 200 °C, separated by 1 mm. Uniform stress is easily achieved. The He gas also allows one to implement an in situ stress control feedback system based on an array of optically based gap sensors which can determine stress of the deposited film from the change in the pressure-induced bulge of the membrane.
Plasma polymerized all-dry resist process for 0.25 μm photolithography
Authors: Joubert O. , Weidman T. , Joshi A. , Cirelli R. , Stein S. , Lee J. T. C. , Vaidya S.
Published: July 2002

Plasma-polymerized resist films (PPMS) based on methylsilane have high sensitivity to short wavelength radiation. The photoinduced oxidation of PPMS films exposed in air forms siloxane network material, allowing dry development by selective rapid etching of the unexposed regions upon treatment with chlorine based plasmas. Negative-tone patterns of oxidized methylsilane thus formed can be transferred through an underlying organic planarizing layer (0.7 μm) with excellent selectivity (≳100) to give high resolution patterns. This provides a versatile, dry photolithographic process usable with current exposure and etching tools that can be integrated into future cluster tool technologies. This article details the process tolerances and lithographic performance of PPMS under 248 nm exposure. Structures as small as 0.2 μm were printed with exposures ranging from 50 to 200 m cm−2 on a GCA XLS DUV stepper. Promising results are also obtained over topography.
Scanning tunneling microscopy study of S adsorption on Ni(111)
Authors: Ruan L. , Stensgaard I. , Besenbacher F. , Lægsgaard E.
Published: July 2002

The chemisorption of sulfur on Ni(111) has been studied by scanning tunneling microscopy. At initial adsorption individual S atoms appear as protrusions 0.3–0.4 Å high, forming a local p(2×2) structure near step edges. The p(2×2) structure is found to be a simple S overlayer structure. After further H2S exposure the surface undergoes a reconstruction to a (5√3×2) structure, accompanied by a homogeneous nucleation of small islands resulting from an ejection of Ni atoms from terraces. The Ni density of 0.80±0.03 ML in the (5√3×2) structure has been determined by measuring the amount of Ni atoms used to build the islands.
Vertical etching of thick SiO2 using C2F6-based reactive ion beam etching
Authors: Dutta Achyut Kumar
Published: July 2002

Anisotropic etching of deep SiO2 has been obtained using electron cyclotron resonance–reactive ion beam etching with C2F6 gas. The influence of total gas pressure and gas flow rate on the profile control and the roughness due to the etching have been determined. The sidewall angle of etched profile can be tailored by adjusting the processing conditions, and it is found that a sidewall angle of 90° for an etching of deepness around 18 μm is obtained at a pressure of 1.0 mTorr and a gas flow rate of 35 sccm. Low roughness has also been achieved for a pressure of 1.0 mTorr with the gas flow rate ranging from 25 to 40 sccm. Here, the scanning electron microscope and the scanning tunneling microscope have been used to study the etched profile and the roughness, respectively.
Capacitive effects on quantitative dopant profiling with scanned electrostatic force microscopes
Authors: Hochwitz Todd , Henning Albert K. , Levey Chris , Daghlian Charles , Slinkman James
Published: July 2002

A force-based scanning Kelvin probe microscope has been applied to the problem of dopant profiling in silicon. Initial data analysis assumed the detected electrostatic force couples the sample and only the tip at the end of a force sensing cantilever. Attempts to compare measurements quantitatively against device structures with this simple model failed. A significant contribution arises from the electrostatic force between the sample and the entire cantilever, which depends strongly upon the relative size of the tip, cantilever, and lateral inhomogeneities in the surface topography and material composition of the sample. Actual and simulated measurements which demonstrate the characteristic signature of this effect are presented.
Siamese cell for group V flux measurements, uniform arsenide phosphide alloys, and quaternary lasers
Authors: Wood C. E. C. , Johnson F. G.
Published: July 2002

We have used an effusion cell with independently valved solid arsenic and red phosphorus sources and a common cracking zone to prepare extremely uniform composition GaAs(1−x)Px epitaxial films on 3 in. diam substrates. Mass spectrometry and ion gauge measurements of dimer species allowed determination of ionization sensitivities for phosphorus and arsenic species in good agreement with the relationship of Flaim and Ownby [J. Vac. Sci. Technol. 8, 661 (1971)]. From the mass spectrometer data, it was possible to determine the thermodynamic equilibrium constant 1.9+/−0.4, and hence free energy −0.55 eV molecule−1 for the process As2+P2■2 AsP. Finally double heterojunction GaInAsP/InP lasers grown with this cell and operating at room temperature have transparency threshold currents below 800 A cm−2.
Modified DNA immobilized on bioreactive self-assembled monolayer on gold for dynamic force microscopy imaging in aqueous buffer solution
Authors: Hegner M. , Dreier M. , Wagner P. , Semenza G. , Güntherodt H. J.
Published: July 2002

Recent advances in DNA specimen preparation techniques for dynamic scanning force microscopy based on terminal anchoring of the DNA segments on bioreactive self-assembled monolayers on ultraflat gold surfaces or on the gold surfaces themselves are presented DNAs of well-defined lengths and sequences carrying amino- or thiol-modified nucleotides at each end have been prepared. DNA imaging in the ac mode has been reproducibly achieved in buffer solution. Since the DNA segments are anchored at their ends only, their backbones are lying free on the self-assembled monolayer and are accessible to DNA–protein interaction. These procedures are suitable to follow in real time biological processes involving DNA.
Morphological stability of strained-layer semiconductors
Authors: Wessels B. W.
Published: July 2002

The morphological stability of strained-layer semiconductors is analyzed for the case where strain relaxation occurs by formation of isolated, coherent islands. In the model, partial strain relaxation in the underlying strained-layer is taken into account. Using a mean-field approximation, the interaction energy is taken to be linearly proportional to the strain energy in the film. The model predicts that the critical thickness for island formation depends inversely on the square of the misfit. The predicted dependence of critical thickness on the misfit is in quantitative agreement with recent experimental studies on island nucleation for heteroepitaxial III–V compounds.
Removing drift from scanning probe microscope images of periodic samples
Authors: Woodward John T. , Schwartz Daniel K.
Published: July 2002

Thermal drift is frequently encountered when imaging with scanning probe microscopes. The drift skews real space images and distorts the reciprocal space lattice vectors. A settling time of up to 2 h is generally required to achieve relatively drift free images at the high magnifications needed for molecular or atomic resolution. We demonstrate a simple method to extract accurate lattice parameters from periodic samples which compensates for drift to first order (approximately constant drift rate), dramatically shortening the necessary waiting time. The method is based on averaging the apparent reciprocal lattice vectors corresponding to consecutive scans obtained in opposite scanning directions.