bluuebunny/crossref_metadata_2025 huggingface dataset:
Outgassing mechanism after the current decaying phase in disruptive and normal discharges in a tokamak
Authors: Ogiwara N. , Maeno M.
Published: July 2002

Outgassing from the first wall made of graphite has been investigated with a newly developed pressure gauge. This gauge can measure the pressure near hydrogen plasmas in a short response time (<10 ms). Large amounts of gases are released suddenly in two stages during a disruption of the plasma. The first gas release occurs at the same time as the soft x-ray crash. This is ascribed to the heat flux due to the loss of the plasma thermal energy (thermal quench). The second appears during the current decay phase. This is caused by the heat flux due to the loss of plasma magnetic energy. The disruption of a 1 MA plasma outgases a surface area of ∼10 m2 . A typical disruption releases 30–80 Pam3 of gases in ∼30 ms. Then three-quarters of them return to the wall. Nevertheless, the evacuated gas quantity after a typical disruption is almost equal to or greater than the input. On the other hand, the evacuated quantity after a normal discharge is less than the input. The outgassing occurs after the end of the plasma with a gradual current decay. This lasts for ∼30 s with rates decreasing gradually from 1–2 to 0.1–0.2 Pam3 /s. The hydrogen atoms probably diffuse from the bulk of the graphite after ions and charge-exchange fast neutrals from the plasma impinge on the wall during the decay of the plasma current. The activation energy of the bulk diffusion is estimated to be less than 1.5 eV. Finally, the use of the disruption in reducing the content of fuel particles in the first wall is discussed.
Investigation of In contacts on atomically clean GaAs(110) surfaces
Authors: Cao R. , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

We have examined In–GaAs(110) contacts fabricated in situ both by depositing In at room temperature followed with annealing and by depositing In on heated surfaces [n- and p-type GaAs(110) surfaces (250 and 300 °C, respectively) using synchrotron radiation photoemission. It is found that In deposition on GaAs(110) surfaces with temperature below room temperature does not induce measurable reaction, whereas reaction takes place with InAs as product when the room-temperature-formed interface is annealed or when In is deposited on the heated substrate. However, there is no evidence of InxGa1−xAs graded heterojunction formation at the interface in either case. Outdiffusion of the excess As from the substrate is suggested to provide a source for InAs formation instead of the previously proposed In–GaAs replacement reaction. Electrical measurements were also performed on in situ In/n-GaAs(110) contacts before and after annealing. Reproducible high-barrier heights were recorded (1.02±0.02 eV) with good ideality factors (1.05±0.01) for the unannealed contacts, which is significantly different from the previously published values (0.76 and 0.78 eV). No dramatic change has been recorded in terms of barrier height upon annealing up to 375 °C although the ideality factor increases to around 1.2±0.1. The implication of this study to ohmic contact formation mechanisms will be discussed.
Minority carrier diffusion length of p-GaAs determined by time-of-flight
Authors: Keyes B. M. , Dunlavy D. J. , Ahrenkiel R. K. , Asher S. E. , Partain L. D. , Liu D. D. , Kuryla M. S.
Published: July 2002

A diffusion time-of-flight (TOF) technique is described and analysis is performed on four different p-GaAs heterostructure devices. These p/n junction devices were grown by metal organic chemical vapor deposition (MOCVD). Both Zn and Mg were used as dopants with concentrations ranging from 1×1018 to 1×1019 cm−3. We have been able to determine the diffusivity (D) along with upper and lower estimates of the diffusion length (LD). The results imply the presence of a mechanism such as photon recycling.
Passivation with II–VI compounds
Authors: Nemirovsky Y.
Published: July 2002

The physical, chemical, and electrical properties of II–VI compounds used for the passivation of HgCdTe are briefly reviewed. Practical passivation technologies for present and next generation infrared focal plane arrays (IRFPAs) are outlined as well as suggested processing methods to improve the current native oxide and sulfide films. Finally, various ways of assessing the quality of the passivating films are discussed.
Laser-induced selected area epitaxy of CdTe and HgTe
Authors: Irvine S. J. C. , Hill H. , Hails J. E. , Mullin J. B. , Barnett S. J. , Blackmore G. W. , Dosser O. D.
Published: July 2002

The enhancement of growth rate of epitaxial CdTe on GaAs(100)2°→(110) substrates is investigated. Photolytic decomposition of the precursors dimethylcadmium with either dimethyl telluride or diethyl telluride is brought about by absorption of 257 nm radiation from an intra cavity doubled argon ion laser. Growth rate was studied as a function of ultraviolet (UV) intensity by the time resolved reflectivity method to monitor CdTe film thickness. Evidence for enhancement of growth rate from surface absorption of uv radiation is discussed together with the factors that can affect pattern definition. The photoenhancement factor depends primarily on the ratio of photolytic to pyrolytic growth rates, the more stable dimethyl telluride yielding higher photoenhancement factors than diethyl telluride. Results on photopatterned bar and mesa structures are presented with feature sizes down to 50 μm. Preliminary experiments on HgTe photopatterning indicate similar kinetic mechanisms to those for CdTe but slow desorption of reaction products might be responsible for lower growth rates. Possible surface reaction mechanisms are discussed and the prospects for selected area epitaxy of mercury cadmium telluride (MCT) considered.
Large-area HgTe–CdTe superlattices and Hg1−xCdxTe multilayers on GaAs and sapphire substrates grown by low-temperature metalorganic chemical vapor deposition
Authors: Pain G. N. , Bharatula N. , Elms T. J. , Gwynn P. , Kibel M. , Kwietniak M. S. , Leech P. , Petkovic N. , Sandford C. , Thompson J. , Warminski T. , Gao D. , Glanvill S. R. , Rossouw C. J. , Stevenson A. W. , Wilkins S. W. , Wielunski L.
Published: July 2002

Specular HgTe–CdTe superlattice epilayers have been obtained on two 2-in. diam GaAs or sapphire wafers per growth run using a horizontal metalorganic chemical vapor deposition (MOCVD) reactor in which the pyrolysis of the organometallics is induced by a cracking susceptor suspended above the substrates. This enables growth of superlattices below 300 °C using the standard precursors dimethyl cadmium, diethyl telluride, and elemental mercury. Annealing the superlattices at 350 °C converts them to homogeneous Hg1−xCdxTe. Compositional profiles obtained by Rutherford backscattering, sputter Auger depth profiling, and e-beam analysis of ultramicrotomed thin cross sections, were used to study interdiffusion of the CdTe and HgTe layers during growth and annealing. Arrays of metal–semiconductor field effect transistors (MESFETS) and photoconductive detectors with room temperature peak responsivity between 1.3 and 1.6 μm have been prepared from incompletely interdiffused material grown on semi-insulating GaAs without thick buffer layers. Device processing used mesa technology and a KI:I2:HBr etchant developed for its selectivity with respect to Hg1−xCdxTe . Capping layers of CdTe and HgTe deposited at low temperatures have been investigated as dielectric and ohmic contacts, respectively. Electrical analyses by Hall and C–V measurements are presented. Room temperature electron mobilities up to 27 500 cm2 /V s and resistivities of 1–2 Ω cm have been observed for the HgTe layers. Information on crystallinity and defect structure of the epilayers was obtained by selected area electron channeling patterns, high-resolution transmission electron microscopy (HRTEM), Rutherford backscattering spectroscopy (RBS) and four-circle, double-crystal, and triple-crystal x-ray diffraction. Compositional profiles in the 100 cm2 deposition area were obtained by wavelength dispersive x-ray analysis (WDX), Fourier transform infrared (FTIR) spectrometry and inductively coupled plasma atomic emission spectrometry (ICPAES).
Growth of CdTe and Hg-based alloys by chemical-beam epitaxy
Authors: Benz R. G. , Wagner B. K. , Summers C. J.
Published: July 2002

A chemical-beam epitaxial system designed specifically for the growth of Hg-based materials is described. Preliminary results on CdTe, HgTe, and HgZnTe growth are presented.
Electron trapping and chemical composition in radio frequency glow discharge a-SiN:H
Authors: Varhue W. J. , Manglore R. B. , Pandelisev K. A. , Pastel P. W.
Published: July 2002

The electron trapping phenomenon in a-SiN:H films deposited by radio frequency (rf) glow discharge has been studied as a function of rf power and gas feed ratio. The chemical composition of the films was determined with Fourier transform infrared spectroscopy. The nitrogen content of the films increased with rf power level if the feed ratio of silane to ammonia was sufficient, 1:10. A gas ratio of 1:5 lacked sufficient ammonia fraction to yield nitrogen rich films despite an increase in rf power level. The electrical resistivity increased and in general electron trapping decreased with increasing nitrogen content in the a-SiN:H films. There is weak experimental evidence that an electron trapping minimum is obtained at a film composition similar to stoichiometric silicon nitride. The measured coordination number of 2.4 for films at this stoichiometric ratio corresponded to the optimum coordination number for a random covalent network. This conceivably should yield the lowest trap density material. At this time, however, it is safer to conclude that electron trapping decreases with increasing nitrogen content in the material.
Growth process of wrinkles generated in deposited films
Authors: Kinbara A. , Baba S.
Published: July 2002

High compressive stresses usually observed in carbon films prepared by physical vapor deposition (PVD) method often form wrinkles in them. The change of the wrinkle pattern and the shape of its cross section were investigated by optical microscope. The moving rate of the peeling front in the wrinkle pattern was measured and analyzed on the assumption that the wrinkling is the activation process. The energy of the activation was considered to be supplied from the strain energy which is originally equivalent to the internal compressive stress in the film. It was found that in order to interpret the wrinkling of the carbon film, stress concentration at the peeling front is necessary and most of the stored strain energy is converted into the surface free energy of the film and the substrate surface. For the determination of the shape of the wrinkle cross section, buckling equation was solved and the shape is approximated by a part of a sinusoidal curve.
The origins and elimination of oval defects in GaAs layers grown by molecular beam epitaxy
Authors: Takahashi Kazue , Kawada Hiroki , Ueda Shinjiro , Furuse Muneo , Shirayone Shigeru
Published: July 2002

Oval defects in GaAs layers are serious impediments to GaAs device fabrication. Of particular importance is the relationship between the droplets deposited on the crucible walls and the number of oval defects. These droplets previously believed to be gallium oxides are shown to consist of GaAs shells covering the Ga particles. By increasing the wall temperature of the crucible orifice, and reducing the arsenic beam intensity, the density of droplets is reduced, thus decreasing oval defects. Using a uniform-heated Ga effusion cell and adjusting the cell configuration, the droplets can be reduced substantially and the defect density can be reduced from >104 cm−2 to less than 200 cm−2.
The role of surface microstructure in the sputtering of graphite
Authors: Youchison D. L. , Nahemow M. D. , McGrath R. T. , Baratta A. J.
Published: July 2002

Extensive exposure to tokamak plasmas may result in significant alterations to the surface microstructure of graphite plasma-facing components. A change in microstructure from a commercial isotropic graphite to an amorphous carbon film may produce a significant change in the total sputtering yield and the level of plasma contamination. To investigate this sensitivity to surface microstructure, sputtering experiments on a variety of graphites with various surface structures were performed using the ion–surface interaction system (ISIS).1 ISIS is a computerized ion beam sputtering system equipped with twin quartz crystal microbalances capable of simultaneously monitoring both sputtering and redeposition of the beam target material. ISIS was used to obtain sputtering data on two orientations of pyrolytic graphite at seven energies between 100 eV and 10 keV. Helium bombardment perpendicular to the prism plane produced yields 2 to 7 times higher than on the basal plane. Proton bombardment perpendicular to the prism plane produced yields 45% higher than those on the basal plane. Amorphous graphite films produced from Poco AXF-5Q and Union Carbide ATJ graphites using an argon radio-frequency (rf) plasma discharge were also irradiated. Sputtering yields on the amorphous films were as much as 50% to an order of magnitude higher than those measured on commercial bulk samples. Pre and post-irradiation scanning electron microscopy of selected targets was performed to monitor surface microstructure. A structural mechanism responsible for the magnitude of physical sputtering is suggested, and an effective surface binding energy is introduced to quantify this structural dependence.
Initial stages of heterojunction formation: Si on GaAs(100)
Authors: Palomares F. J. , Méndez M. A. , Cuberes M. T. , Soria F.
Published: July 2002

Si/GaAs(100) interfaces grown at 300, 600, and 770 K on c(8×2)-Ga surfaces prepared by simultaneous argon bombardment at 600 V and annealing cycles at temperatures lower than 800 K have been studied by Auger electron spectroscopy and low-energy electron diffraction (LEED). Si deposition at room temperature up to 8 monolayers (ML) results in disordered Si surfaces. At 600 K the first 2 Si ML grow pseudomorphically to the substrate with the formation of an ordered 1×1 structure at about 0.75 ML. At 770 K Si follows a Stranski–Krastanov mechanism. Up to 0.25 Si ML a (4×2) structure, never reported before, is detected. From 0.25 to 0.75 ML a (1×2) pattern develops which coexists with (2×1) domains above 0.75 ML. This alternation of domains indicates Si dimerization in two orthogonal surface directions. At about 1 ML the (1×2) and (2×1) structures have equal intensities. Above 1.25 ML streaks features appear following the Bragg spot directions. This LEED pattern can be seen even at coverages greater than 4 ML, though with an increasing diffuse background.
Current research problems and opportunities in the vapor phase synthesis of diamond and cubic boron nitride
Authors: Yarbrough W. A.
Published: July 2002

Current research problems in the chemical-vapor deposition (CVD) of diamond and cubic-boron nitride (c-BN) include efforts to rationalize the formation of well-crystallized diamond as part of efforts to achieve several important goals. Among these is well-crystallized c-BN by CVD, improved diamond crystal perfection important to many applications, the large-area heteroepitaxial growth of diamond (or c-BN), and possibly, new composites and superlattice materials not heretofore thought possible. It is argued that the synthesis of diamond is not inconsistent with thermodynamic analysis, provided the influence of relevant surface chemistries and the nonequilibrium nature of materials synthesis are taken into account, and that the phase composition of the solid is determined in large measure by the lowest free-energy structure of its surface during growth. From linear irreversible thermodynamics it follows that crystal perfection and the nature of the growth surface during deposition will be determined by how far from equilibrium the system is held and whether or not a locally stable stationary state is maintained during deposition. The greater the departure from equilibrium, the higher the defect levels expected, implying that the growth of relatively defect-free diamond will require a close approach to equilibrium. Much of the experimental data available are shown to be consistent with this approach, including difficulties with using methods successful for diamond to grow c-BN. Although the diamond growth surface can be stabilized by the chemisorption of hydrogen, a similar stabilization of the surfaces of c-BN is at best problematic, and new chemistries may be needed to achieve its synthesis. Similarly, the heteroepitaxial growth of diamond may require not only the provision of a suitable surface template or lattice match but, also, a compatible interfacial chemistry for the stabilization of sp3 hybridized carbon.
The air-exposed surface of sputter deposited silicon carbide studied by x-ray photoelectron spectroscopy
Authors: Lee Ray C. , Aita Carolyn Rubin , Tran Ngoc C.
Published: July 2002

X-ray photoelectron spectroscopy analysis of the air-exposed surface of sputter deposited amorphous silicon carbide films shows three dominant features: (1) Si–C bonding characteristic of SiC, with Si 2p electron binding energy at 100.4–100.7 eV and C 1s electron binding energy at 282.7–283.2 eV, (2) Si–O bonding characteristic of SiO2, with Si 2p electron binding energy at 102.1–102.5 eV, O 1s electron binding energy at 532.0 eV, and the O 1s-Si 2p electron binding energy difference equal to 429.5–429.9 eV, and (3) a strong adventitious C signal. The spectral features are consistent with a model for the surface of SiC powder consisting of several monolayers of hydrocarbons over several nm of SiO2 that overlays the bulk SiC. The oxidation behavior of the film surface was found to depend upon the cathode voltage at which the film was deposited.
Infrared spectroscopy of hydrogen-terminated gallium arsenide (100)
Authors: Gee P. E. , Hicks R. F.
Published: July 2002

The surface structure of gallium arsenide (100) has been examined by infrared spectroscopy of adsorbed hydrogen and deuterium. The GaAs crystal was etched in 1:1:10 H3PO4/H2O2/H2O and 1:1 HCl/H2O, then annealed to 580 °C in 5 × 10−10-Torr vacuum. The resultant surface contains nearly equal amounts of Ga and As, ∼5-at. % carbon, and no oxygen. The infrared spectrum of adsorbed hydrogen and deuterium at 50 °C exhibits 4 bands for arsenic hydride (and deuteride) from 1950 to 2150 (1425 to 1575) cm−1, and 7 bands for gallium hydride (and deuteride) from 1700 to 1950 (1225 to 1400) cm−1 and at 1610 (1165) cm−1. All the arsenic hydride vibrations are p-polarized. This is consistent with hydrogen bonding to the arsenic along the [1̄10] crystal direction, i.e., parallel to the arsenic dimer bonds. The Ga–H vibrations between 1700 and 1950 cm−1 are both s- and p-polarized, while the vibration at 1610 cm−1 is only s-polarized. The higher frequency bands are tentatively assigned to three-coordinate, sp2 gallium monohydrides and dihydrides, whereas, the low frequency band may be due to four-coordinate, sp3 gallium hydride. Schemes for hydrogen bonding to gallium and arsenic are proposed which can account for the observed infrared spectrum.
Reduction in diffusion of copper in parylene by thermal pretreatment
Authors: Yang G.-R. , Dabral S. , Wu X. M. , Lu T.-M. , McDonald J. F. , Bakhru H.
Published: July 2002

A thermal preannealing technique for limiting diffusion of Cu into parylene-n (PA-n) in an interconnection application has been demonstrated. These thermal pretreatments enhance fabrication latitude for PA-n. The Cu was deposited by partially ionized beam technique and the PA-n was vapor deposited. Diffusion was investigated using the Rutherford backscattering (RBS) technique. Cu was found to diffuse into as-deposited PA-n at temperatures of about 623 K. It was also found that with certain thermal pretreatment of PA-n, this diffusion could be stopped for temperatures as high as 623 K. Pretreatment at temperatures of 523 and 623 K were successful in stopping diffusion. The microstructure has been investigated using scanning electron microscopy and RBS. The annealing causes formation of lengthy grainlike structures perpendicular to the surface. Under some preanneal conditions, the grain structure reaches the surface and diffusion is observed for these samples. The preannealing technique has been successful in reducing diffusion caused at soldering temperatures (623 K) in a Cu/PA-n interconnection scheme. It must be noted that pretreatments at temperatures of 573 K were generally not effective, except for one case where the temperature was ramped down over a 2 h period.
Closed-loop control of growth of semiconductor materials and structures by spectroellipsometry
Authors: Aspnes D. E. , Quinn W. E. , Tamargo M. C. , Gregory S. , Schwarz S. A. , Pudensi M. A. A. , Brasil M. J. S. P. , Nahory R. E.
Published: July 2002

Using closed-loop ellipsometric feedback control, we have grown a variety of epitaxial AlxGa1−xAs structures by chemical beam epitaxy where compositions x vary continuously with thickness according to a given input function. Present limits are exemplified by a 200 Å parabolic quantum well structure grown using compositions determined from the outermost running ∼3 Å (∼1 monolayer) of depositing material.
Fabrication of superconducting YBa2Cu3O7−δ submicron structures
Authors: Barth R. , Spangenberg B. , Langheinrich W. , Albrecht W. , Kurz H. , Gieres G. , Holzapfel B.
Published: July 2002

Submicron structures of superconducting YBa2Cu3O7−δ (δ<0.1) are fabricated by high-energy electron-beam lithography in combination with Ar/O2 ion-beam etching. A novel three-level resist system of platinum/titanium/PMMA is developed to minimize the process-induced loss of superconductivity. Bridges as narrow as 150 nm with lengths between 0.3 and 4 μm have been fabricated, retaining their superconductivity without reloading with oxygen. Possible reasons for process-induced deterioration of superconducting properties are discussed.
Study of fluorine (XeF2) adsorption and of oxygen/fluorine coadsorption on silicon using infrared reflection absorption spectroscopy
Authors: Bermudez V. M.
Published: July 2002

Infrared reflection absorption spectroscopy has been used to study the chemisorption of fluorine (by exposure to XeF2) on polycrystalline Si surfaces in ultrahigh vacuum and under low-pressure steady-state conditions. Adsorption at 300 K leads to the sequential formation of mono-, di-, and trifluoride SiFx groups. Annealing at successively higher temperature forms more ≡SiF by decomposition of =SiF2 and –SiF3. After a 770 K anneal, only the 890 cm−1 ≡SiF band remains and is removed by F desorption at ∼820 K. Similar results are obtained in a continuous XeF2 flux with, in addition, the appearance near 300 K of a weak feature possibly due to adsorbed SiF4. Based in part on these results, an estimate can be made of the rate-limiting step in the reaction. In the high-temperature limit (T≥650 K) it appears to be the conversion of ≡SiF to =SiF2; whereas, near 300 K, it is the formation of SiF4 from –SiF3. The effects on fluorination of pre- and postexposure to O2 have also been observed. Preadsorbed O stabilizes F, shifting the F desorption temperature higher by at least 100 K. In the presence of coadsorbed F, the Si–O–Si antisymmetric stretch appears at 1150 cm−1, significantly higher than on a similar, F-free surface. Preadsorbed F impedes subsequent chemisorption of O2, and the O that is adsorbed has no apparent effect on SiFx bonding as reflected in the Si–F stretching vibrations.
Stress and microhardness in sputter deposited molybdenum and chromium films
Authors: Window B. , Harding G. L. , Horrigan C. , Bell T.
Published: July 2002

The stresses in magnetron sputtered chromium and molybdenum films produced with various energies of ion bombardment and at various substrate temperatures have been measured using x-ray diffraction. The results confirm earlier work on the dependence of stress production on temperature and ion energy, and show that the maximum stress which can be supported in chromium films is reduced by increasing the temperature. Above the plastic flow transition, the lattice strain decreases rapidly with further bombardment. Results for the microhardness of chromium and molybdenum films show a close correlation with measured stress. The films deposited in a state of plastic flow have a rough surface.
Silicon nitride/silicon oxynitride/silicon dioxide thin film multilayer characterized by variable angle spectroscopic ellipsometry
Authors: Xiong Yi-Ming , Snyder Paul G. , Woollam John A. , Krosche Eric R.
Published: July 2002

Variable angle spectroscopic ellipsometry (VASE) was used to nondestructively characterize a silicon nitride (Si3N4)/silicon oxynitride (SiOxNy)/silicon dioxide (SiO2) thin film multilayer structure, in which Si3N4 and SiOxNy layers were deposited by plasma enhanced chemical vapor deposition and low-pressure chemical vapor deposition, respectively. The measured VASE spectra (3500–8200 Å) were analyzed with an appropriate multilayer fitting model, in which the SiOxNy layer was modeled, in the Bruggeman effective medium approximation (EMA), to be a physical mixture of two distinct phases, SiO2 and Si3N4. Remarkably good agreement between the measured spectra and the model calculations was obtained, indicating that the EMA and the fitting model were appropriate for the data analysis. As a result, the three layer thicknesses, compositions, and the optical constants of SiOxNy layer at several spots across the sample were determined. The thickness values obtained by VASE were in very good agreement with those measured by cross-sectional transmission electron microscopy.
I–III–VI2 compound semiconductors for solar cell applications
Authors: Başol Bülent M.
Published: July 2002

I–III–VI2 compounds in general and CuInSe2 (CIS) in particular are important photovoltaic materials. Among the various thin film deposition techniques that have been employed for CIS film growth, so far only three-source evaporation and the two-stage method have yielded films that could be used for high efficiency solar cell fabrication. In this paper we briefly review some of these thin film deposition techniques and describe a two-stage method that gives high quality CIS films with uniform morphology and stoichiometry.
New generation solar control coated products
Authors: Nikodem Robert B.
Published: July 2002

The mandate for high performance solar control coated glass in the automotive, commercial, and residential markets has presented significant challenges to thin film scientists and engineers. Products are required which provide more efficient control and utilization of solar energy. Implementation of innovative advances in coating deposition and design technology, materials science, research and development experimental techniques, and systems engineering has facilitated development of a new generation of products. These new solar control products are specifically designed to meet both today’s and tomorrow’s high performance requirements in coated glass. A few of the principal achievements in energy conservation provided by these products are (1) minimization of solar heat gain and/or of heat loss, (2) minimization of ultraviolet effects, (3) improved daylight opening visibility, and (4) compatible aesthetics. These advancements in technology and engineering have been incorporated into large scale production. The spectral properties and applications of several products manufactured on large float systems will be presented.
Enhanced structural and electronic properties of strained Ge(100) films grown by molecular-beam epitaxy with a Sb surfactant layer
Authors: Rioux Dennis , Höchst Hartmut
Published: July 2002

Reflection high-energy electron diffraction and angle-resolved photoemission spectroscopy with synchrotron radiation were used to investigate the effect of a Sb surfactant layer on the growth and electronic properties of strained Ge(100) films. The Ge epilayers were grown by molecular-beam epitaxy on highly ordered InP(100) substrates. The Ge/InP interface was found to be nonreactive yet extensive with outdiffusion of In into the overlayer. With a Sb surfactant layer the critical thickness for a coherently strained Ge film was increased to 5 ML, which is 2.5 times larger than the critical thickness for Ge films grown without a surfactant. The experimental values for the valence-band offsets for epilayers under 2.9% tensile strain were found to be ΔEv = −0.94 ± 0.1 eV and ΔEv = −0.97 ± 0.1 eV for films grown with and without a surfactant layer, respectively. These results are in agreement with the model-solid theoretical prediction of ΔEv = −1.00 eV for this strained heterostructure.
High-power fast-atom beam source and its application to dry etching
Authors: Shimokawa Fusao
Published: July 2002

We have developed a new high-power fast-atom beam (FAB) source by modifying a McIlraith-type ion source. The beam current density emitted from a source with an electromagnet and multiaperture grid is about ten times higher (up to 1 mA/cm2) than that emitted from a conventional source. Silicon dioxide can therefore be etched at 60 nm/min when CF4 gas is used, or about six times faster than by using a conventional source with the same discharge current. The beam neutralization coefficient of the new FAB source is nearly 100%. We have used this FAB source to etch Si, SiO2, GaAs, and other compound materials. We could easily etch an anisotropic profile (nearly vertical with an aspect ratio of more than 10 for a 0.6 μm L&S pattern), etch at a high rate (0.3–0.5 μm/min), and etch with high selectivity (GaAs:resist =30:1). We also fabricated a SiO2 fine pattern in 0.6 μm L&S by using CF4 reactive-fast-atom beam etching. The uniformity of the etch depth is about ±5% over a 4-in. wafer. Surface radiation damage (total oxide charge) caused by FAB bombardment of the SiO2/Si structure is very close to that of reference (not etched) samples. This damage is significantly less than that caused by ion beam bombardment under almost the same radiation conditions.
Vapor deposition of parylene-F by pyrolysis of dibromotetrafluoro-p-xylene
Authors: You L. , Yang G.-R. , Lang C.-I. , Moore J. A. , Wu P. , McDonald J. F. , Lu T.-M.
Published: July 2002

Structural characteristics of poly(tetrafluoroparaxylylene) (PA-F) films deposited directly from C6H4(CF2Br)2 precursor have been studied using Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Zn was used as the catalyst and the vapor pyrolysis of precursor was carried out between 350 and 400 °C. It is shown that the FTIR and XPS spectra of the PA-F films deposited from the precursor are comparable to those made from the conventional dimer route. Dissociation of the PA-F films does not occur up to an annealing temperature of 500 °C. Both Zn and Br contaminants were observed in the XPS spectra. However, we found that the Br contamination disappears after annealing to an elevated temperature (≥350 °C), while Zn impurities still remain in the film.
Atomic force microscopy of single- and double-stranded deoxyribonucleic acid
Authors: Thundat T. , Allison D. P. , Warmack R. J. , Doktycz M. J. , Jacobson K. Bruce , Brown G. M.
Published: July 2002

The atomic force microscope (AFM) was used to image double-stranded DNA and single-stranded DNA adsorbed onto mica modified by Ba (II). Images of double-stranded DNA show an open circular shape without drastic contortions, and contour lengths that measure within 7% of the calculated length. Images of single-stranded DNA show two distinct forms; compact open circles with ‘‘nodes’’ or lumps almost uniformly distributed are the most frequently observed while less abundant are highly elongated circles with a few nodes. Heating the single-stranded DNA sample and altering the solvent conditions prior to adsorption was found to increase the number of elongated circular molecules observed in the AFM images.
Model calculations of optical properties for disordered GaAs/AlAs superlattices
Authors: Strozier J. , Zhang Y. A. , Horton C. , Ignatiev A. , Shih H. D.
Published: July 2002

We have investigated the role of disorder in effecting the optical properties of short period superlattices. A one-dimensional, two atoms per unit cell, tight binding model of a superlattice is solved exactly for the ordered structure and for a given disorder in the growth direction. A difference vector and the resulting disorder structure factor are proposed to characterize the disorder. The density of states, participation number, and optical absorption for both the ordered and disordered superlattice models are calculated as a function of energy. The results show that introduction of disorder into an indirect band gap material enhances the optical transitions near the indirect band edge.
Applications of in situ ellipsometry to microwave electron cyclotron resonance plasma processes
Authors: Hu Y. Z. , Joseph J. , Irene E. A.
Published: July 2002

In situ static spectroscopic ellipsometry used during a process is a powerful method for characterizing the optical properties and structure of multilayered thin films. However, the commonly practiced rotating element ellipsometry takes about 10 min for each spectral measurement. Using only a single wavelength gives less information, but each measurement time reduces to about 5 s. It is shown that a combination of the techniques was adequate to investigate the plasma processes. Spectroscopic ellipsometry measurements for Si, Ge, InP, InSb, and GaAs showed that for properly selected photon energy ranges, the dependence of the dielectric functions on temperature is minimum while the sensitivity to surface modifications is high. The electron cyclotron resonance (ECR) plasma oxidation of Si is discussed first, since it is the simplest case, and then attention is given to more complex example of ECR plasma ion bombardment induced oxidation and damage in single crystal Ge.
Mesh pattern of Ge islands grown using solid phase epitaxy
Authors: Hibino H. , Shimizu N. , Shinoda Y.
Published: July 2002

We present mesh patterns of Ge islands grown on a Si(111) surface using solid phase epitaxy. Typical experimental conditions for the formation of these mesh patterns are substrate temperatures of 300–500 °C and a Ge thickness of about 10 Å. The mesh pattern is due to preferential crystallization of a-Ge films at steps and at out-of-phase boundaries of 7×7 structures.
Method to calculate substrate temperature during intermittent radiant heating in vacuum
Authors: Larsson M. I. , Hansson G. V.
Published: July 2002

We have developed a method to determine the time dependent temperature of intermittently radiation-heated substrates for epitaxial growth of Si in ultrahigh vacuum. The method is particularly useful during the time intervals of growth when a pyrometer cannot be relied on, e.g., due to light reflection from the substrate surface. The use of a thermocouple is not possible due to slow response and risk for contamination. The model has been derived by applying Stefan–Boltzmann’s law and the fact that heat radiation is the dominating energy transport mechanism in the studied system for the actual substrate temperatures and time constants. The vertical temperature gradient through the substrate was estimated to be at most of the order of 100 K m−1.
Photoemission study of evaporated CuInS2 thin films. I. Surface stoichiometry and phase segregation
Authors: Scheer R. , Lewerenz H. J.
Published: July 2002

The surfaces of evaporated CuInS2 films were investigated by photoelectron spectroscopy (XPS) with respect to stoichiometry dependent features. The surface composition of In-rich CuInS2 films drastically exceeds the respective bulk value determined by energy dispersive x-ray fluorescence and displays the formation of an In-rich surface layer with a cation ratio of In/(In+Cu)=0.75(2). Sputter profiles obtained by Auger electron spectroscopy confirm the effect of In enrichment and Cu depletion on the surface. The altered surface region is estimated to extend approximately 0.1μm into the film. Films with a Cu-rich bulk composition also exhibited In-rich surfaces, but in addition the segregation of a CuS phase is concluded from XPS investigations. The interrelation of these observations is discussed using simple model considerations.
Initial metal fluoride formation at metal/fluorocarbon interfaces
Authors: John P. J. , Liang J.
Published: July 2002

The interaction of several perfluoroalkyl ethers [CF3OCF3, CF2OCF2OCF2 , and CF3OCF2OCF3] and an acyl fluoride [CF3OCF(CF3)CFO] with iron and aluminum surfaces has been studied with x-ray photoelectron spectroscopy. The perfluoroalkyl ethers were found to not interact with either the clean iron surface or the clean aluminum surface. In contrast, the acyl fluoride compound was observed to readily decompose when in contact with the clean aluminum surface. The same molecule formed a surface carboxylate structure when in contact the clean iron surface. Interactions were also observed on native oxides of aluminum and iron exposed to acyl fluoride. For the aluminum surface, the degradation of the acyl fluoride molecule is not limited to the carbonyl group as it is for the iron surface. Rather, the entire molecule dissociates on the surface.
Adhesion durability of tantalum BPDA-PDA polyimide interfaces
Authors: Callegari A. C. , Clearfield H. M. , Furman B. K. , Graham T. G. , Neugroschl D. , Purushothaman S.
Published: July 2002

Adhesion durability of dc magnetron sputtered tantalum to in situ radio frequency (rf) plasma treated biphenyl tetracarboxylic acid dianhydride–para phenylene diamine (BPDA-PDA) polyimide films was determined as a function of repeated 400 °C thermal exposure cycles and 85 °C/80% temperature/humidity (T/H) exposures. rf plasma treatments in Ar, oxygen and a sequential combination of oxygen followed by Ar were evaluated. Using 90° peel testing, it was found that all the plasma treatments resulted in high peel strengths (greater than 60 g/mm) initially and after high temperature thermal exposures, but structures fabricated with rf oxygen plasma treatment rapidly degraded in peel strength during T/H exposure. It is proposed that this hydrothermal degradation is a result of the instability of the nonstoichiometric tantalum oxide present at the metal/polyimide interface which transforms to stoichiometric Ta2O5 during the T/H exposure. Supporting evidence for this model is presented based on failure analysis of peeled strips by Auger electron spectroscopy as well as in situ x-ray photoelectron spectroscopy observations of the Ta bonding chemistry to the rf plasma treated polyimide.
Unique hydride chemistry on silicon–PH3 interaction with Si(100)-(2×1)
Authors: Colaianni M. L. , Chen P. J. , Yates J. T.
Published: July 2002

The dissociative adsorption of phosphine (PH3) on Si(100)-(2×1) and its high temperature thermal behavior have been studied by high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy, and by temperature programmed desorption (TPD). Phosphine adsorbs dissociatively onto Si(100)-(2×1) at 100 K as PH2 and H species, as revealed by vibrational bands at 1050 cm−1 [δsc(PH2)] and 2100 cm−1 [ν(Si–H)]. The PH2(a) undergoes thermal decomposition to adsorbed P and H near 650 K, as determined by HREELS. TPD measurements reveal two PH3 desorption processes at 485 and 635 K. The 635 K desorption is shown to result from PH2+H recombination, while the mechanism for the 485 K desorption cannot be definitely identified. Additionally, two H2 desorption states were observed at 685 and 770 K.
Improved epitaxial layer design for real-time monitoring of dry etching in III–V compound heterostructures with depth accuracy of ±8 nm
Authors: Vawter G. Allen , Klem John F. , Leibenguth Ron E.
Published: July 2002

Etching structures for state-of-the-art electronic and optoelectronic devices such as heterojunction bipolar transistors, optical waveguide modulators, gratings, and vertical-cavity surface-emitting lasers often requires nonselective etching with depth accuracy on the order of ±8 nm. We disclose the application of in situ optical reflectance monitoring during chlorine reactive-ion-beam etching of III-V compound heterostructure devices for real-time determination of etch depth to ±8 nm independent of total etch depth. High-vertical-resolution etching of thick, layered structures is achieved through use of a resonant periodic set of reflective interfaces, greatly enhancing the reflected amplitude oscillations without detrimental effects on device performance. This method demonstrates that slight modifications of material structure to optimize monitor response greatly enhance the accuracy of nonselective dry etching.
Growth and energetics of Ga and Al chains on Si(112)
Authors: Jung Timothy M. , Prokes S. M. , Kaplan R.
Published: July 2002

We present a low-energy electron diffraction and Auger electron spectroscopy (AES) study of the growth of Al and Ga chains on Si(112) substrates. For substrate temperatures between 500 and 650 °C growth proceeds first by the creation of metal atom chains along the step edges of the (112) surface. Once the step-edge sites have been occupied, a state defined here as ‘‘saturation coverage,’’ excess deposition leads to island formation with no further increase in the metal AES signal intensity. The clean Si(112) (1×2) surface reconstruction is removed upon the formation of the metal chains so that the equivalence of adjacent single-layer-height steps is restored. At the saturation coverage both the Al and Ga chains exhibit a sixfold periodicity along the step edge, or [11̄0], direction. Below the saturation coverage these chains can also exhibit a fivefold periodicity along the same direction. We propose a model in which the periodicities of the chains are determined by the density of dimerized Si edge atoms, i.e, metal atom vacancies, whose presence balances the tensile stress imposed by the larger metal atoms. We investigate the relative binding energies of Al and Ga to the step-edge sites and find that Al atoms are more strongly bound. At substrate temperatures near 600 °C the deposition of Al on a Ga saturated surface leads to the complete substitution of Ga by Al atoms at the step-edge sites.
Electron interference effects in electron projection microscopy
Authors: Shedd G. M.
Published: July 2002

This article discusses manifestations of wave interference phenomena in electron projection microscopy (EPM), and how these effects may explain the existence of what appear to be atomic resolution details in EPM images of very thin Au films. It has been pointed out that the projected shadow image can be considered to be an in-line hologram of the object, and that it is possible to reconstruct high resolution information about an object from a hologram. Theories of EPM hologram formation and atomic resolution image reconstruction have been put forth, however, they do not predict that atomic scale defects will be visible in the direct shadow image, only in the reconstructed image. The work presented here suggests an alternative explanation of the EPM images, one based on considering holes in the Au film to be point sources of spherical waves. Actual EPM images of Au(100) films are compared to simulated images that result from calculations based on the model. The model provides a simple explanation of latticelike image features, including such details as apparent lattice dislocations.
Historical perspective of oriented and epitaxial thin films
Authors: Francombe M. H.
Published: July 2002

Over the years, vacuum techniques for both oriented and epitaxial film growth, and also for device processing, have played a critical role in the evolution of advanced solid-state components. The American Vacuum Society, through its symposia and publishing activities, has contributed greatly to this progress. The history of organizational and technical factors that have impacted on these developments is summarized, and selected examples of unique epitaxial metallic, semiconductor and ferroelectric device structures are discussed.
Comparison of Ar electron-cyclotron-resonance plasmas in three magnetic field configurations. I. Electron temperature and plasma density
Authors: Junck Kevin L. , Getty Ward D.
Published: July 2002

Optical emission spectroscopy, Langmuir probe, and microwave interferometry measurements have been used to characterize the electron temperature and plasma density of electron-cyclotron-resonance (ECR) heated Ar plasmas in a magnetic-mirror plasma tool. The magnetic field was operated in a symmetric mirror, asymmetric mirror, and minimum-B configuration. The dependency of the plasma parameters upon microwave power, pressure, and magnetic field configuration have been examined. Plasma densities up to 2×1012 cm−3 at the midplane and 5×1012 cm−3 at the ECR zone for a symmetric mirror configuration of the magnetic field have been measured. Operation of the minimum-B magnetic field configuration was found to increase the plasma stability with comparable plasma density while an asymmetric mirror magnetic field configuration, similar to other devices recently studied, yielded densities in the 2–8×1011 cm−3 range. Radial uniformity was found to be ±25% over the 4 cm radius of the microwave window.
Chemisorption of hydrogen on the Ag(111) surface
Authors: Lee Geunseop , Sprunger P. T. , Okada M. , Poker D. B. , Zehner D. M. , Plummer E. W.
Published: July 2002

The interaction of atomic hydrogen/deuterium with the Ag(111) surface was investigated with high-resolution electron loss spectroscopy (HREELS), thermal desorption spectroscopy, low-energy electron diffraction (LEED) and the results correlated with the work function change and an absolute coverage measurement. Dissociation of molecular hydrogen is an activated process on Ag(111) but atomic hydrogen chemisorbs and at a temperature of ∼185 K, recombines and desorbs as H2. Upon the adsorption of atomic hydrogen at 100 K, a sharp (2×2) LEED pattern is observed in the coverage range 0.25∼0.5 ML and is followed by combined (2×2)+(3×3) patterns with an increase in coverage of 0.1 ML. The saturation coverage is determined to be Θsat=0.6±0.1 ML. In contrast to other H/fcc(111) systems, the intensities of the fractional order diffraction beams are quite large, suggesting an H-induced reconstruction. The work function increases monotonically with H-exposure to a maximum value of Δφmax=+0.32 eV at saturation. Specular HREELS vibrational data show a single loss at 106 meV for hydrogen (76 meV for deuterium), similar to the normal vibrational mode observed for the H/Ag(110) system. A rather low activation energy (8.7±1.0 kcal/mol) for recombinative desorption is obtained from the low coverage thermal desorption spectra (Θ<0.1 ML).
Surface chemistry of polycarbonate film and adhesion of ultraviolet-cured inks
Authors: Burrell Michael C. , Tilley Mark G.
Published: July 2002

One of the primary uses of polycarbonate film is in screen-printing applications, with ultraviolet (UV)-cured inks becoming increasingly popular due to environmental concerns. During multicolor printing operations, regions of the polycarbonate film surface are unavoidably exposed to UV irradiation during the cure of adjacent regions. Subtle changes in the polycarbonate surface chemistry affect subsequent printing on the UV-exposed surface, primarily manifest as a decrease in the ink adhesion level. In this study, static secondary-ion-mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), and contact angle measurements were used to show that the surface becomes oxidized and water wettable. The degree of photo-oxidation, nature of the photoproducts, and ink adhesion characteristics were measured as a function of the UV wavelength window. Filtering out the short wavelengths (λ<300 nm) from a medium pressure Hg lamp resulted in significantly less photo-oxidation compared to identical exposures from the unfiltered UV. The ink/polymer interfaces were also examined by transmission electron microscopy (cross section) and by peeling followed by XPS and static SIMS analysis. Based on these results, mechanisms for ink/polycarbonate interface adhesion are proposed.