bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy of passivated gallium arsenide under ambient conditions
Authors: Dagata J. A. , Tseng W. , Silver R. M.
Published: July 2002

Scanning tunnel spectroscopy of n- and p-type GaAs (110) and (100) surfaces, prepared with a novel electrically transparent surface oxide, reveals that the current–voltage (I–V) characteristics of these surfaces obtained in air exhibit transport properties typical of the bulk band structure, a result which was previously obtained only on (110) GaAs surfaces cleaved in ultrahigh vacuum. The passivation technique has been used to obtain stable images of cleaved, molecular-beam epitaxy grown GaAs pn junctions in air as well. The results of this study demonstrate that quantitative doping information over the range of 1015<NA,ND<1019 cm−3 can be extracted from scanning tunneling microscopy data on passivated GaAs surfaces under ambient conditions.
Chemical and electrochemical treatments of GaAs with Na2S and (NH4)2S solutions: A surface chemical study
Authors: Yota J. , Burrows V. A.
Published: July 2002

Chemical treatments of GaAs with sulfur containing media have been shown to improve GaAs surface electronic properties. There is still considerable controversy, however, regarding the chemical nature of the surface film which results from the sulfidation. We have investigated the surface chemistry of GaAs after chemical and electrochemical treatments with Na2S and (NH4)2S solutions using surface infrared reflection spectroscopy and x-ray photoelectron spectroscopy. We have found that these sulfidation treatments removed the GaAs oxide and deposited a film on the surface which includes various arsenic sulfide and sulfur–oxygen species. No arsenic oxide, nor gallium oxide or sulfide after the treatments is detected. The arsenic sulfide observed after chemical (NH4)2S treatment is more stable against oxidation in air than the one observed after chemical Na2S treatment. Both of these sulfides, however, are removed with water rinsing. The arsenic sulfide phases formed after electrochemical sulfidation with both Na2S and (NH4)2S solutions are not removed with water rinsing. This anodic sulfidation treatment may be promising as a new method to passivate and improve the GaAs surface electronic properties.
Cracking and debonding of microlaminates
Authors: Suo Z.
Published: July 2002

Materials layered together for their electronic properties and chemical stabilities are typically subjected to residual stresses induced by thermal expansion mismatch, epitaxy, phase transition, or other mechanisms specific to deposition procedures. Interacting with preexisting defects, these stresses can cause brittle layers to crack, or solid–solid interfaces to debond, which may be assisted by chemical reactions between atoms at the crack tip and species in the environment. Recent developments of fracture mechanics for layered materials are reviewed. Included are representative crack patterns, safety design criteria, crack driving force, and the physical origins of fracture resistance. The last section discusses unique mechanical properties of microlaminates.
Development and fabrication of thin-film BaTiO3 capacitors using radio-frequency magnetron sputtering
Authors: Shi Z. Q. , Jia Q. X. , Anderson W. A.
Published: July 2002

BaTiO3 thin films were deposited by radio-frequency magnetron sputtering. The electrical and dielectric properties of the films were investigated as a function of substrate temperature and sputtering gas. The performance of the thin-film capacitors was studied as a function of the capacitor structure and electrode materials. The film formed at room temperature, with Ar+O2 gas, showed an amorphous structure and had very good insulating properties. The films formed at high temperature (700 °C) had a polycrystalline structure, yielded a high dielectric constant up to 330, and lead to a large dc leakage current. By using Ar+H2+O2 as the sputtering gas, the leakage current was reduced from 6.2×10−6 to 2.5×10−9 A/cm2 for the amorphous film, and from 7.7×10−1 to 7.7×10−7 A/cm2 at 4.0 V for the polycrystal films, respectively. Single and double layer capacitors were developed and fabricated using the above amorphous and polycrystalline films with Pd and RuO2 as the electrodes. The temperature dependence of the capacitance was found to be very small even at the Curie temperature. This can be explained by the modifications of composition and microstructure.
Investigation of the kinetics of digermane chemisorption and reaction product desorption in thin film growth of germanium
Authors: Eres Gyula , Sharp J. W.
Published: July 2002

The kinetics of the elementary reaction steps in surface-limited thin film growth of germanium from digermane was investigated by utilizing surface differential reflectance. Separation of the elementary reaction steps of chemisorption and reaction product desorption was achieved by using a pulsed molecular beam to modulate the digermane delivery to the heated substrate. Both elementary reaction steps were found to be single exponential first-order processes. The chemisorption reaction on Ge(100) was rapid (k1=500±50 s−1), and independent of the substrate temperature between 680 and 810 K. On the other hand the desorption step in the same substrate temperature range is strongly temperature dependent with an activation energy of 1.7±0.1 eV and a prefactor of 2×1013±1 s−1. A simple kinetic model comprised of two opposing first-order elementary steps is found to be consistent with the experimental results. It is concluded that the kinetic data are compatible with the pairing mechanism for molecular hydrogen desorption, but no (thermal) decomposition mechanism of digermane is found to provide a unique interpretation for the first-order adsorption kinetics.
Gas adsorption studies of sputtered amorphous hydrogenated carbon films
Authors: Pigram P. J. , Lamb R. N. , Collins R. E. , Pailthorpe B. A.
Published: July 2002

A temperature limitation mechanism for solar evacuated tubular collectors (ETCs) has been developed which is centered around the reversible adsorption of benzene by the spectrally selective cermet film in the collector vacuum space. Benzene desorption behavior of microporous amorphous hydrogenated carbon films (the adsorbing component of the cermet) has been investigated using thermal desorption spectroscopy (TDS). Desorption spectra show two peaks which vary in intensity and line shape with film thickness and coverage. Gas adsorption studies undertaken using a Kelvin probe are presented which show changes in contact potential difference (CPD) of a-C:H films in response to a variety of adsorbates. Strong surface adsorption of oxygen and nitrogen species was detected. A comparison TDS and CPD results has shown that benzene is adsorbed exclusively in the pore volume.
X-ray diffraction analysis and x-ray photoelectron spectroscopy of α- and β-W thin films grown by ion beam assisted deposition
Authors: Shah S. I. , Doele B. A. , Fincher C. R. , Unruh K. M. , Weerasekera I.
Published: July 2002

Thin W films have been deposited by dual ion beam sputtering using a sputtering ion gun and an assisting ion gun. The crystal structure of the deposited films was strongly dependent on the energy of the assisting ions, substrate temperature, and the thickness of the film. All these variables were found to affect the oxygen concentration of the film which in turn, determines whether the film will have an A-2 body-centered-cubic α-W phase, an A-15 face-centered-cubic-like β-W phase, or a mixture of the two. Assisting ions and substrate temperature both increase the diffusivities of W and O resulting in a decreased oxygen concentration in the film which makes the α-W phase more stable. Films deposited at low substrate temperatures and without any ion bombardment show only the β-W phase.
Surface type conversion of InP by H2S plasma exposure: A photoemission investigation
Authors: Nelson Art J. , Frigo Sean P. , Rosenberg Richard
Published: July 2002

The surface chemistry and the electronic structure of InP(100) before and after exposure to a H2S plasma was investigated by synchrotron radiation soft x-ray photoemission spectroscopy. The low power H2S plasma was generated with a commercial electron cyclotron resonance plasma source using H2S with the plasma exposure being performed as a function of incident angle and temperature. Plasma species were identified with optical emission spectroscopy. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence band electronic structure as well as changes in the In 4d, P 2p, and S 2p core lines. The results were correlated in order to relate the plasma species and characteristics to changes in surface chemistry and electronic properties. These measurements indicate that the H2S plasma exposure type converts the p-type InP(100) surface to an n-type surface resulting in a shallow homojunction interface.
Effect of anode bias on the index of refraction of Al2O3 thin films deposited by dc S-Gun magnetron reactive sputtering
Authors: Clarke Peter J.
Published: July 2002

Using direct-current anode bias in an S-Gun magnetron sputtering system during the reactive deposition of Al2O3 increases the index of refraction from 1.52 to 1.70. This effect takes place at less than 75% of the O2 flow rate necessary to convert the sputter cathode from the metal mode to the oxide mode. A second effect of sputtering in the linear portion before the ‘‘knee’’ of the voltage versus O2 flow rate curve (hysteresis curve) is a stable and noise-free deposition.
Tribochemistry at lubricated interfaces
Authors: Novotny V. J. , Pan Xiaohe , Bhatia C. S.
Published: July 2002

High resolution mass spectrometry is used to monitor in situ gaseous wear products that are generated during sliding of lubricated carbon–carbon interfaces in a vacuum. During the initial stages of sliding, significant amounts of polyperfluoroether lubricant fragments are detected, which resemble the mass patterns of scissioned lubricant in the thermal desorption experiment. The intermediate stage of sliding characterized by lower rate of lubricant fragmentation is followed by higher rate before wear of hydrogenated carbon overcoat occurs, which is accompanied by hydrogen emission and friction increase. Lubricant loss, removal, and alteration are precursors of the wear of solids and are determined by scanning microellipsometry. The amount of altered lubricant that is left on the disk and slider surfaces is quantified by x-ray photoelectron spectroscopy and the chemical structure of altered lubricant is evaluated by time-of-flight mass spectrometry. It is found that the dominant process, before the wear of solids occurs, is tribochemical scission of fluorocarbon polymers. Some fragments desorb from the interface, while others containing carboxylic end groups attach by strong physisorption to solid surfaces.
Influence of charge exchange on ion/neutral arrival rates in an ion-assisted deposition system
Authors: Kim J-K. , Kheyrandish H. , Colligon J. S.
Published: July 2002

During ion-assisted deposition of TiN using Kaufman sources the pressure in the substrate chamber can rise to about 10−2 Pa. This leads to charge-exchange collisions and as a result, a component of fast neutral atoms in the energetic beam. This paper considers the transport of 100–500 eV Ar+ or N+2 ions through a gas mixture of argon and nitrogen of known composition. Charge exchange cross sections for N+2→N2, Ar+→Ar, Ar+→N2, and N+2→Ar reactions have been used to calculate the neutral component of the beam. The results show that the neutral component is only weakly dependent on the primary ion energies and ion species. The magnitude of this component for a constant total pressure of 3×10−2 Pa varies between 10% and 60% as the partial pressures of nitrogen (and argon) vary between 1 and 3×10−2 Pa.
Preparation of in-plane textured Y2O3-doped ZrO2 thin film on polycrystalline metallic tape by modified bias sputtering
Authors: Aoki S. , Fukutomi M. , Komori K. , Maeda H.
Published: July 2002

Yttria-stabilized zirconia (YSZ) thin films with in-plane texturing were successfully deposited on polycrystalline metal tape (Hastelloy) by modified bias sputtering. Two specially devices electrodes installed in a sputtering system generated a characteristic plasma with a parabolic shape. A directionally aligned argon ion flux extracted from this plasma appeared to impinge obliquely on the growing film. X-ray measurements revealed that the resulting YSZ films exhibited clear in-plane grain texturing as well as a strong (001) orientation. The best YSZ films grown on Hastelloy substrates had Δφ [full width at half-maximum (FWHM) of a peak in φ scan]=20° and Δω (FWHM of a peak in the rocking curve)=5°. An advantage of this new bias sputtering technique was pointed out in its applicability to the growth of YSZ as a buffer layer on a relatively long metal tape for deposition of YBa2Cu3Oy superconducting thin films.
Erbium-doped indium oxide films prepared by radio frequency sputtering
Authors: Kim Hong Koo , Li Cheng Chung , Barrios Pedro Jose
Published: July 2002

Er doping of conducting oxide films has been investigated. Erbium-doped indium oxide films were prepared by rf magnetron sputtering. The deposited films were characterized in terms of electrical, optical, and structural properties. The Er-doped indium oxide films are highly (222)-oriented normal to the substrate surface and show a resistivity in the range of 10−3–103 Ω cm. The Er-doped conducting (or semiconducting) oxide films are optically active, i.e., show a clear room-temperature photoluminescence at 1.54 μm, corresponding to intratransitions in Er3+ ions. Compared with the undoped indium oxide films, the erbium doping is found to have the effect of increasing the resistivity (up to two orders of magnitude) of the films, mainly via a reduction of carrier concentration. Post-deposition annealing in air ambient significantly enhances both the Er3+ luminescence and Hall mobility (up to 60 cm2/V s), and reduces the carrier concentration. The enhancement of Hall mobility is attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by the x-ray diffraction measurement results. Post-deposition annealing in reducing ambient (N2/H2) decreases the resistivity dramatically, mainly via an increase of carrier concentration (up to 1020 cm−3), and also enhances the Er3+ luminescence.
Study of the epitaxial growth of GaAs(110) films by molecular beam epitaxy
Authors: Fawcett P. N. , Neave J. H. , Zhang J. , Joyce B. A.
Published: July 2002

The epitaxial growth of GaAs(110) films by molecular beam epitaxy has been investigated in situ by reflection high-energy electron diffraction (RHEED). In comparison to the GaAs(001) surface it is necessary to grow GaAs(110) at much lower temperatures to obtain films with good surface morphology. The period of the RHEED oscillations shows a transition from monolayer to bilayer growth as the temperature is reduced and growth occurs under more arsenic rich conditions. At high temperatures (≳500 °C), oscillations show a continuous increase in period to a value several times that expected for monolayer growth. This behavior is explained in terms of a decrease in the sticking coefficient of As2 with increasing temperature which leads to Ga-rich growth and a growth rate which is limited by the incident As2 flux.
Infrared absorption and nuclear magnetic resonance studies of carbon nitride thin films prepared by reactive magnetron sputtering
Authors: Li Dong , Chung Yip-Wah , Yang Shengtian , Wong Ming-Show , Adibi Farshid , Sproul William D.
Published: July 2002

Carbon nitride thin films were prepared by dc magnetron sputtering of a graphite target in a nitrogen containing gas mixture onto Si(100) substrates held at ambient temperatures. All CNx coatings grown to a thickness of 1.5 μm are adherent and smooth. Infrared absorption and isotropic nitrogen labeling indicate that carbon and nitrogen are chemically bonded together. Both solid-state 13C and 15N magic angle spinning nuclear magnetic resonance (NMR) analyses were performed. NMR measurements indicate the presence of sp2 bonded C and N.
Effects of surface structures of MgO(100) single crystal substrates on ferroelectric PbTiO3 thin films grown by radio frequency sputtering
Authors: Kim Sangsub , Baik Sunggi
Published: July 2002

Effects of surface structures of MgO(100) single crystal substrates on the growth of PbTiO3 thin films by radio frequency magnetron sputtering have been investigated. First, the surface structures of the substrates prepared by cleaving, polishing, and annealing were characterized using Rutherford backscattering spectroscopy combined with channeling, surface sensitive x-ray scattering, and atomic force microscopy. We found a strong correlation between the surface structures and the growth of the thin films. The film on the cleaved substrate was not uniform and its crystallinity was poorer than that on the polished or the annealed substrates due to the presence of large cleavage steps, whereas better epitaxiality was found on the annealed substrate than on the polished substrate. Favorable effects of thermal annealing after polishing have been explained based on surface step rearrangements, damage removal, and improvement in surface flatness by the thermal annealing treatment.
Beam and decomposition properties of copper-containing metalorganic precursors and their use for CuO thin film preparation in chemical beam epitaxy
Authors: Willmott P. R. , Felder P. , Lingenauer M. , Huber J. R. , Fritsch E. , Bidell W. , Berke H. , Mächler E. , Williams E. J. , Locquet J.-P. , Bednorz J. G.
Published: July 2002

The 2,2,6,6-tetramethyl-3,5-heptanedionato and pivaloato precursors of copper have been investigated for their thermodynamic and gas-phase properties. More specifically, time-modulated mass spectroscopy has been used to determine the chemical compositions of the effusive beams of metalorganic precursors under various conditions, and to identify the thermal decomposition products resulting from breakdown of the effusive beam on a heated MgO(001) single-crystal surface. From these results, their relative suitability for use in chemical beam epitaxy is compared. Also, copper oxide films have been grown in a chemical beam epitaxy system and their properties are discussed.
Photoelectron spectroscopy from atomic layer epitaxially grown ZnTe/ZnSe heterostructures
Authors: Link P. , Grobbel G. , Wörz M. , Bauer S. , Berger H. , Gebhardt W. , Paggel J. J. , Horn K.
Published: July 2002

Photoelectron spectra have been taken from ZnTe/ZnSe and ZnSe/ZnTe heterostructures grown in situ by atomic layer epitaxy. Synchrotron radiation within the photon energy range of 70–80 eV was used for excitation. The extent of the interface region was determined by an analysis of the Te 4d and Se 3d core-level shifts. The valence-band offset was determined as a function of layer thickness. After a critical thickness is reached the lattice relaxes and the valence-band offset becomes +0.50±0.05 eV for ZnTe/ZnSe and −0.55±0.05 eV for ZnSe/ZnTe. Obviously the commutativity rule is well fulfilled within the limits of the experiment.
Thermal desorption spectroscopy study of HF/DF-treated Si(100) surfaces
Authors: Kinoshita Keizo , Nishiyama Iwao
Published: July 2002

Hydrogen (H)- and deuterium (D)-terminated Si (100) surfaces are investigated by thermal desorption spectroscopy (TDS). The H/D exchange reaction, using 1.6% DF, creates partially D-terminated Si surfaces from passively H-terminated Si by using 1.6% or 49% HF. The H/D exchange reaction rate, determined from TDS intensity changes, follows natural-logarithmic equations. The half-exchange time is 12.8 min. The 49% HF pretreated samples show rapid surface roughness changes in the initial stage of the 1.6% DF treatment; these changes are detected by rapid TDS H2 intensity decreases. SiFx and F2 peaks are detected by TDS. F/D exchange occurs on the 49% HF pretreated samples along with H/D exchange. The activation energy for deuterium termination is 8.7 kcal/mol.
Defect production and recombination during low-energy ion processing
Authors: Kellerman B. K. , Floro J. A. , Chason E. , Brice D. K. , Picraux S. T. , White J. M.
Published: July 2002

Low-energy ion processing produces damaged, microroughened semiconductor surfaces due to the production of point defects. We present a study of point defect production and annealing on the Ge(001)-2×1 surface during low-energy inert ion bombardment as a function of ion energy, ion mass, and substrate temperature. Ion-induced surface point defect production was quantified experimentally in real time using in situ reflection high-energy electron diffraction. The observed surface defect yield decreased abruptly around room temperature as the substrate temperature was increased from 175 to 475 K. We have developed Monte Carlo simulations of defect diffusion to model defect recombination both in the bulk and on the surface. Bulk defect production statistics generated by our binary collision simulator, TRIMRC, were coupled with our bulk diffusion simulator to predict the number of ion-induced surface defects. A comparison between the experimental results and the simulation predictions indicated that defects produced in the bulk may represent a significant contribution to the observed surface defect yield and suggested that TRIMRC may overestimate the depth of the defects. The simulations further indicated that the abrupt drop in the experimental yield with increasing substrate temperature does not arise from bulk defect recombination. Our Monte Carlo simulations of surface diffusion (applicable to any crystalline surface) support a defect annealing mechanism (at low ion fluxes) that involves surface recombination of defects generated within a single cascade.
Molecular beam epitaxial growth of ZnMgSSe and its application to blue and green laser diodes
Authors: Ikeda M. , Ishibashi A. , Mori Y.
Published: July 2002

ZnMgSSe alloys lattice-matched to GaAs substrates have been successfully grown by molecular beam epitaxy. The band gap energy and refractive index at a wavelength of 500 nm for ZnMgSSe at room temperature were given as a function of the lattice-matching alloy composition of Mg and S. Conductive n- and p-type epitaxial layers were produced using ZnCl2 and plasma-excited N2 as doping sources. The maximum net acceptor concentration attainable in p-ZnMgSSe decreased below 5×1016 cm−3 as the band gap energy increased above 2.91 eV, which is currently limiting the useful range of ZnMgSSe as a cladding layer in laser diodes. Room temperature continuous-wave (cw) operation of ZnCdSe/Zn(S)Se/ZnMgSSe single strained quantum well separate confinement heterostructure lasers has been achieved for emission in the range from 490 to 524 nm. More than 0.38 eV energy difference between the band gap of the ZnMgSSe cladding layer and the effective band gap of ZnCdSe strained quantum well was required to obtain cw operation. Employing a ZnTe/ZnSe resonant tunneling superlattice as the p-type contacting scheme, the threshold voltage of II–VI laser diodes could be reduced to 4.9 V. The device lifetime was significantly dependent on the dislocation density in the II–VI layers.
Buffer layer–modulation-doped field-effect-transistor interactions in the Al0.33Ga0.67As/GaAs superlattice system
Authors: Pellegrino J. G. , Richter C. A. , Dura J. A. , Amirtharaj P. M. , Qadri S. B. , Roughani B.
Published: July 2002

The correlation between the structural and transport properties for a series of high-quality modulation-doped field-effect-transistor (MODFET) structures was made for various growth temperatures. X-ray reflectivity, x-ray diffraction, and magnetotransport measurements were used to assess structural quality and transport parameters. Four samples with growth temperatures in the range 500–630 °C were examined. The results show a correlation exists between the measured electron mobility and the quality of the interface width, as measured from satellite peaks of the buffer layer. In addition, these results show, for the first time to the best of our knowledge, that a direct correlation can be made between x-ray reflectivity structural measurements and the measured electron mobility of high-quality gallium–arsenide-based MODFETs. Both x-ray and transport results suggest a higher-quality structure was obtained at higher growth temperatures.
Processing of PbTiO3 thin films. I. In situ investigation of formation kinetics
Authors: Li Chen C. , Desu Seshu B.
Published: July 2002

A novel in situ stress measurement technique to study the formation kinetics of multicomponent oxide thin films was developed and was applied to PbTiO3. Single phase PbTiO3 thin films were formed from the reaction between films in the deposited PbO/TiO2 multilayer. The film stoichiometry was accurately controlled by depositing individual layers with the required thickness. The development of film stresses associated with the formation of the product layer at the PbO/TiO2 interface of the multilayers was used to monitor the growth rate of the PbTiO3 layer. It was found that growth of the PbTiO3 phase obeyed the parabolic law, and the effective activation energy was estimated to be 108 kJ/mole. It is believed that the mechanism of this reaction was dominated by grain boundary diffusion of the participating cations.
Detection of tribochemical reactions using photoelectron emission microscopy
Authors: Montei Eric L. , Kordesch Martin E.
Published: July 2002

The thermal decomposition of trifluoroacetic acid on a Mo(100) is studied using high resolution electron energy loss spectroscopy. It is found that trifluoroacetic acid (CF3COOH) exposed to the Mo(100) surface at room temperature deprotonates to form a trifluoroacetate species (CF3COO–). Further decomposition of the acetate species is observed resulting in the formation of an intermediate species and possibly ionic fluorine adsorption at elevated temperatures. Dynamic photoelectron emission microscopy images are obtained from a rotating, cylindrical molybdenum sample. This real-time imaging of a rotating sample lays the foundation for imaging various tribo-induced reactions in real time. First experiments employing the rotating cylindrical sample, the adsorption of trifluoroacetic acid and how such experiments may clarify the mechanisms for lubricant degradation are discussed.
Isothermal hydrogen desorption from the diamond (100)2×1 surface
Authors: McGonigal M. , Kempel M. L. , Hammond M. S. , Jamison K. D.
Published: July 2002

Isothermal desorption experiments to study the kinetics of the desorption of hydrogen from the diamond (100)2×1 surface are described. The surface hydrogen concentrations are measured using direct recoil spectroscopy, an ion spectroscopy in which ions and neutral species recoiled from the surface are detected by time-of-flight measurements. Results indicate that the desorption of hydrogen from diamond (100) is zeroth order at temperatures below 800 °C and changes to first order above 825 °C. In the first-order region, the measured activation barrier is 39 kcal/mol and the pre-exponential factor is 3.2×105 s−1.
Magnetron reactive ion etching of group III-nitride ternary alloys
Authors: McLane G. F. , Monahan T. , Eckart D. W. , Pearton S. J. , Abernathy C. R.
Published: July 2002

Magnetron reactive ion etching of the group III-nitride ternary alloys InxGa1−xN and InxAl1−xN was investigated in BCl3 plasmas and also in SF6/BCl3, H2/BCl3, and Ar/BCl3 gas mixtures. Etch rates were determined as a function of cathode power density, flow rate, pressure, and gas composition. Etch rates were achieved that were four to six times greater than previously reported for these materials, and at low cathode bias voltages (<100 V). The addition of H2 and Ar to concentrations of 60% in BCl3 increased In0.25Ga0.75N etch rates by 35% and 90%, respectively. Auger electron spectroscopy measurements on In0.75Al0.25N showed a reduction in the surface In/Al ratio upon etching, but essentially no change in the surface composition of etched In0.25Ga0.75N.
Ion–surface interactions in low temperature silicon epitaxy by remote plasma enhanced chemical–vapor deposition
Authors: Habermehl S. , Lucovsky G.
Published: July 2002

Epitaxial Si thin films have been deposited by remote plasma enhanced chemical–vapor deposition at temperatures below 450 °C and at pressures between 50 and 500 mTorr. Growth rate data reveal the presence of two pressure dependent regimes for deposition process activation. Sampling of the plasma afterglow by mass spectrometry indicates a correlation between enhanced rates for single crystal film formation and the onset of an ion-induced surface H abstraction processes below pressures of ∼200 mTorr. The role of low energy ions in the abstraction of chemisorbed H and its effects on the growth kinetics are discussed.
Ion implantation for silicon device manufacturing: A vacuum perspective
Authors: Current Michael I.
Published: July 2002

Ion implantation systems rely on a diverse vacuum environment to accomplish the goals of doping of Si materials for formation of electronic devices. Failure to manage the gas flows and contaminants in this complex vacuum system can lead to severe penalties for integrated circuit processing. Examples of vacuum control issues in ion sources, beam transport, dosimetry, wafer charging, and contamination are discussed. Contamination issues involve a mix of ion and vapor transport of dopants and metals, charge exchange and molecular breakup collisions, and particle generation associated with electrode arcing. Additional factors in good vacuum design include operation of contamination-free, rapid-cycle loadlocks and safety issues, such as management of potentially explosive gas mixtures during regeneration of cryopumps.
An ion beam vapor deposition technique for epitaxial growth of Si-Ge films on Si substrates
Authors: Mohajerzadeh S. , Selvakumar C. R. , Brodie D. E. , Robertson M. D. , Corbett J. M.
Published: July 2002

We are reporting a new ion beam vapor deposition technique for epitaxial growth of Si-Ge alloys on 〈100〉 Si substrates at temperatures as low as 285 °C. The growth of Si films involves beam assisted dissociation of SiH4 gas while the incorporation of Ge is achieved through thermal evaporation of elemental Ge. We have used transmission electron microscopy, electron diffraction analysis and Rutherford backscattering to study the quality of the grown films. The results of this study show that a beam energy of 40 to 50 eV yields optimum growth.
Development of a multilayer thin-film solar control windshield
Authors: Finley J. J.
Published: July 2002

The trend in automotive glazing design has been towards more steeply sloped windshields with larger glass areas, resulting in greater transmission of solar radiation. Driver comfort, air conditioning load, and fabric deterioration are some of the challenges manufacturers of automotive glazing face because of these new designs. Ultraviolet and solar infrared radiation must be effectively reduced while visible light transmission must be maintained above 70% (the legal limit). The windshield surface, which receives up to 60% of the solar irradiation incident upon the vehicle glazing, is traditionally tinted, resulting in absorption and reradiation. The most effective means of reducing the solar heat load, however, is by using a multilayer coating which reflects the solar energy. The coating consists of two layers of silver sandwiched between antireflective dielectric metal oxide layers. The coating is applied to the inner surface of the outer glass light of the laminated windshield using the dc magnetron sputtering process. For the coating process to be both cost effective in manufacturing, and suitable for a variety of complex shaped windshields, the glass is first coated flat, and subsequently bent and laminated. The coating process can then be integrated into the windshield manufacturing process without limiting throughput. This multilayer coating, specifically developed to be bent on soda–lime–silicate glass, remains stable and uniform for complex, and small radius of curvature bends. The development of this coating in the laboratory, transfer into production, and integration into the windshield manufacturing process is described.
Optical approaches to determine near-surface compositions during epitaxy
Authors: Aspnes D. E.
Published: July 2002

Various algorithms have been proposed for determining the near-surface dielectric function εo of depositing materials from kinetic complex reflectometric or ellipsometric data, even under conditions where the underlying sample structure is unknown. These capabilities are essential for sample-driven closed-loop feedback control of epitaxy, since they allow compositional fluctuations to be detected over nominally vanishingly small thicknesses without the instability inherent in conventional Fresnel analysis. The accuracy of earlier derivative approaches was improved significantly with the development of virtual-interface (V-I) theory, which is based on exact equations instead of exponential-spiral approximations that are valid only for optically thick films. I summarize previous relevant work, assess the accuracy of these derivative methods analytically for the complex normal-incidence reflectance, develop new algorithms by combining earlier approaches, develop a geometric construction that allows relative sensitivities, accuracies, and applicabilities of these algorithms for determining the composition of ternary alloys to be conveniently assessed, and propose a new hybrid V-I–Fresnel method that retains the stability of the V-I approach yet is exact. For ellipsometry the virtual-substrate approximation still represents the best combination of simplicity, speed, and acceptable accuracy.
Hydrogen desorption from ion-roughened Si(100)
Authors: Hess G. , Russell M. , Gong B. , Parkinson P. , Ekerdt J. G.
Published: July 2002

Low energy Kr+ ions were used to create rough Si(100) surfaces. Hydrogen adsorption and desorption on these surfaces were studied using high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). A comparison of hydrogen TPD data from smooth and ion-roughened Si(100) surfaces showed no significant shift for the dihydride and monohydride related desorption features, revealing that ion impact roughening does not change the activation barriers for hydrogen desorption. In contrast to smooth Si(100), HREELS spectra from rough Si(100) surfaces with different hydrogen coverages showed a dihydride scissor mode at 0.8 ML and dihydride desorption below monolayer coverage in the corresponding TPD experiment. The vibrational spectra of hydrogen covered rough surfaces generally showed a smaller ratio of the scissor mode/bending mode intensity than the smooth Si(100) surfaces, suggesting a lower dihydride/monohydride coverage ratio. The corresponding TPD results on the other hand showed increased dihydride desorption and higher total coverages up to 2 ML. Although different dihydride units on terrace sites and at edge sites could not be unambiguously identified in the vibrational spectra, they provide a reasonable explanation for this inconsistency.
High-selectivity pattern transfer processes for self-assembled monolayer electron beam resists
Authors: Carr D. W. , Lercel M. J. , Whelan C. S. , Craighead H. G. , Seshadri K. , Allara D. L.
Published: July 2002

Novel processes have been developed for transferring patterns using self-assembled monolayer (SAM) electron beam resists. Because the SAMs are very thin, high-selectivity processes are required for effective substrate modification. Two separate techniques have been studied for patterning intermediate layers for use as reactive ion etch (RIE) masks. A bilayer process using the native oxide as an intermediate etch mask has been used to etch into both crystalline and polycrystalline silicon. The native oxide is patterned with the SAM resist and the oxide is then used as a mask in an electron cyclotron resonance RIE. This process has been used to produce ∼25 nm etched features in silicon. Instead of its selective removal, an alternative technique for forming the intermediate etch mask layer is the selective deposition of the layer. Thin nickel layers have been formed with an electroless plating technique on silicon. The electroless deposition is highly selective for producing nickel plating on silicon as opposed to the silicon oxide. These novel high-selectivity techniques demonstrate the ability for ultrathin SAM resist layers to pattern silicon and other materials.
Atomic and mesoscopic scale characterization of semiconductor interfaces by ballistic electron emission microscopy
Authors: Lee E. Y. , Bhargava S. , Chin M. A. , Narayanamurti V.
Published: July 2002

Ballistic electron emission microscopy (BEEM) is a powerful new low energy electron microscopy in materials physics for nondestructive local electronic characterization of semiconductor heterostructures. In this article, low energy electron imaging of buried semiconductor heterostructures will be explored, with particular emphasis on BEEM imaging of buried objects in metal–GaAs based heterostructures.
Simulation of pressure effects in a multipulsed nitrogen plasma source ion implantation system
Authors: Bear Michael J. , Guillory John U.
Published: July 2002

Plasma source ion implantation is typically performed at low pressures (10−4 Torr), but pressure plays an important role in the control of the deposited ion energies and the location of the time dependent sheath edge. At high pressures (10−2 Torr) with energy-dependent secondary electron production rate, the sheath edge advances to a nearly fixed position for most of the voltage pulse, and the deposited ion energy spectrum appears collisional, consistent with the ion-mean-free path being shorter than the sheath length. This results in high TiN surface concentration with a broad tail into the sample. Nitrogen dissociation increases the amount of monatomic N gas and its ions with each system pulse. At low pressures (10−3 and 10−4 Torr) the sheath edge advance into the bulk plasma throughout the pulse, instead of reaching a quasistatic limit as it does at 10−2 Torr. The energy spectrum of ions arriving at the cathode shows a larger proportion of high energy ions, which produces a deep TiN subsurface band. In this one-dimensional implantation system simulation (N2 plasma and Ti target), we have shown that pressure can be used to tailor the desired TiN profile and that the TiN deposition rate drops as the number of voltage pulses increases.
Planar magnetron sputtering discharge enhanced with radio frequency or microwave magnetoactive plasma
Authors: Musil J. , Mišina M. , Hovorka D.
Published: July 2002

The dc discharge of an unbalanced planar magnetron was enhanced by a rf or microwave plasma generated by a helical antenna. An array of permanent magnets around the discharge chamber was used for the plasma confinement. The discharge current-voltage characteristics, substrate ion current densities is and ionized fraction of the flux of sputtered metal atoms are reported. The substrate ion current density is was found to depend strongly on the type and orientation of the permanent magnets with order-of-magnitude differences between different configurations. The rf or microwave enhancement of the sputtering discharge resulted in (i) increased substrate ion current densities is up to 7 mA/cm2 even for low pressures <0.1 Pa, (ii) control of is independently on the discharge current, (iii) sputtering at low pressures down to 7×10−3 Pa, (iv) well controlled dc discharge at small cathode voltages, i.e., at small sputtering rates. These features enable a low pressure sputter deposition of thin films grown under an intensive ion assistance.
Diamond films grown by hot filament chemical vapor deposition from a solid carbon source
Authors: Woo H. K. , Lee S. T. , Lee C. S. , Bello I. , Lam Y. W.
Published: July 2002

Continuous diamond films have been grown on mirror-polished silicon, polycrystalline copper, SiC and high oriented pyrolytic graphite substrates using hot filament assisted chemical vapor deposition. Instead of using conventional gaseous carbon source, a graphite plate was used as the carbon source with hydrogen as the only feeding gas. No substrate pretreatment such as diamond powder scratching or negative biasing was needed. When carbon-13 was used as the carbon source, only diamond-12 was detected on carbon-13 indicating that deposition rather than direct conversion of carbon to diamond occurred. High nucleation density and conversion efficiency were obtained for the present growing process. Diamond films grown by this method were found to be particularly pure in diamond content.
Ion-induced chemical vapor deposition of high purity Cu films at room temperature using a microwave discharge H atom beam source
Authors: Chiang T. P. , Sawin H. H. , Thompson C. V.
Published: July 2002

Films deposited via ion-induced chemical vapor deposition (II-CVD) typically contain high percentages of carbon and exhibit poor electrical conductivities. The role of atomic H in the removal of carbonaceous impurities was investigated using quartz crystal microbalance mass deposition rate measurements, x-ray photoelectron spectroscopy compositional analysis, and laser-induced thermal desorption coverage measurements. A surface kinetic model for the ion-enhanced etching of C with H is formulated based upon experiments conducted on carbon substrates. Simultaneous Ar ion and H atom bombardment lead to high etching yields of ∼15 C/Ar+ at H atom to Ar ion flux ratios of ∼3000:1. During H-assisted II-CVD, the H serves to enhance the removal of C through ion-enhanced chemical sputtering in addition to physical sputtering with ions alone. The primary products detected with the addition of H were CH4 and CH3. High purity (∼99 at. %) Cu films with resistivities of ∼5 μΩ cm were achieved at room temperature with use of the H atom beam. The Cu content represents the highest purity ever reported using II-CVD at room temperature.
Piezoelectric properties of sputtered PbTiO3 films: Growth temperature and poling treatment effects
Authors: Cattan E. , Jaber B. , Tronc P. , Remiens D. , Thierry B.
Published: July 2002

Thin films of lead titanate (PbTiO3) were prepared on silicon substrates by sputtering. Two processes have been developed; (a) the in situ process (the growth temperature was 440 °C) and (b) the deposition at room temperature followed by a conventional annealing at 680 °C. The dielectric constant, the ferroelectric, and the piezoelectric properties were evaluated and compared. The dielectric constant of films deposited in situ was higher than those of postannealed films likely due to the dense microstructure with fine and homogeneous grains. The embedded beam method and the Berlincourt piezometer were used to measure the e31 and the d33 piezoelectric coefficients, respectively. The PbTiO3 films were naturally polarized, in particular the films grown in situ have large piezoelectric constants: e31=−0.49 C/m2 and d33=20 pC/N. These values agree broadly with data of bulk ceramics, however, with bulk material a poling treatment is necessary to attain these values. The poling of the postannealed films leads to a substantial increase of their piezoelectric properties; e31=−0.26 C/m2 and d33=8 pC/N for virgin film and e31=−0.41 C/m2−d33=18 pC/N for an applied electric field of 110 kV/cm (close to saturation) and a poling time of 30 min. The piezoelectric response was found to depend on the direction of the poling field. Note d33 and e31 decreased when the poling field was applied against the preferred polarization direction; the polar domains were oriented from the film surface to the substrate.
Epitaxial growth of (001)-oriented titanium nitride thin films by N implantation
Authors: Kasukabe Y. , Ito A. , Nagata S. , Kishimoto M. , Fujino Y. , Yamaguchi S. , Yamada Y.
Published: July 2002

The epitaxial growth process of titanium nitride (TiN) films, formed by implanting nitrogen ions (N2+) with 62 keV into 100-nm-thick Ti films grown on NaCl substrates held at 250 °C, has been studied by transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. It has been revealed that the (001)-oriented TiNy is epitaxially grown by N implantation into the as-grown (03⋅5)-oriented hcp Ti. The TiNy is formed by the transformation of the hcp Ti to (001)-oriented fcc Ti during the N implantation, partially inheriting the atomic arrangement of the square and/or the octahedron of the hcp Ti, as well as the occupation of N in octahedral sites of the fcc Ti. Strain due to the expansion of the lattice and/or the volume of hcp Ti by N implantation can be considered as one of the driving forces for the hcp–fcc transformation of the Ti lattice. The nitriding mechanism of epitaxial Ti thin films is discussed.
Lateral selectivity of ion-induced quantum well intermixing
Authors: Haysom J. E. , Poole P. J. , Feng Y. , Koteles Emil S. , He J. J. , Charbonneau S. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

Quantum well (QW) intermixing using high-energy ion implantation is a promising technique for laterally selective, post-growth modification of a quantum well structure. In this work, we investigate the lateral selectivity of the technique, which is a function of the ion straggling during implantation and of the lateral diffusion of defects during post-implantation annealing. We have used photoluminescence and a specially designed mask to monitor the intermixing of QWs under masked regions. A significant amount of intermixing, resulting in a blueshift of the QW band-gap energy, was observed when the mask stripe width was less than 5 μm, thus giving a lateral selectivity of 2.5 μm.
Bakable, all metal burst diaphragm for ultrahigh vacuum applications requiring low pressure venting
Authors: Todd R. J. , McIntyre G. T.
Published: July 2002

A bakable, all metal burst diaphragm for low pressure venting is described. The device incorporates a bellows which, under pressure, drives a piece of copper foil into a stationary blade. The spring constant of the bellows allows for a puncturing pressure of 8 psi, while complete rupture occurs at 15 psi. The copper foil can be replaced at minimal cost, and the device can be reliably baked at temperatures up to 300 °C.
Biaxially oriented conductive La0.5Sr0.5CoO3 thin films on SiO2/Si
Authors: Jia Q. X. , Arendt P. N. , Kwon C. , Roper J. M. , Fan Y. , Groves J. R. , Foltyn S. R.
Published: July 2002

We have grown biaxially textured La0.5Sr0.5CoO3 (LSCO) thin films on technically important SiO2/Si substrates by pulsed laser deposition, where a biaxially oriented yttria-stabilized zirconia (YSZ) produced by ion-beam-assisted deposition (IBAD) is used as a seed layer to enhance the texture of LSCO on SiO2/Si. The degree of in-plane texturing of LSCO is directly related to the quality of IBAD-YSZ. The smaller the value of full width at half maximum of the IBAD-YSZ (220) diffraction peak, the higher the crystallinity of the LSCO film. The biaxially oriented LSCO film deposited at 700 °C on SiO2/Si shows metallic resistivity versus temperature characteristics and has a room-temperature resistivity of around 110 μΩ cm.
Microstructure-dependent ferroelectric properties of SrBi2Ta2O9 thin films fabricated by radio frequency magnetron sputtering
Authors: Cho Kwang-Jun , Lee Jeon-Kook , Jung Hyung-Jin , Park Jong-Wan
Published: July 2002

Microstructure dependencies on the ferroelectric properties of SrBi2Ta2O9 (SBT) thin films were observed by changing the sputtering pressure in the rf magnetron sputtering technique. The microstructure and the crystal orientations were determined by the compositional change of the films, which was controlled by the scattering behaviors during sputter depositions. The good ferroelectric hysteresis loop behavior was due to the stoichiometric composition and the layered perovskite structure of the SBT thin films. On the other hand, nonstoichiometric SBT films had small grains of pyrochlore structure and linear dielectric behavior.