bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutral molecule emission from the fracture of crystalline MgO
Authors: Dickinson J. T. , Jensen L. C. , McKay M. R.
Published: July 2002

We present further measurements of the neutral molecule emission accompanying the fracture of single-crystal MgO. Comparison is made of the intensities and species of this emission for basically two types of MgO: optically clear and so-called ‘‘cloudy’’ MgO. The latter material contains voids and precipitates of micron and submicron dimensions. In addition to time resolved mass selected measurements of the released neutral species we also examine the fractrography of the fracture surfaces and infrared spectroscopy of the bulk material. These measurements strongly support a correlation between O2, CO, H2O, and CH4 emission intensities and the presence of dissolved H2O, microscopic voids, and precipitates in the MgO. Segregation of gases in zones near precipitates may be the major source of O2 emission.
Photoemission studies of the room-temperature Si/Hg1−xCdxTe, Si/HgTe, and Si/CdTe interfaces
Authors: Carey G. P. , Friedman D. J. , Lindau I. , Spicer W. E.
Published: July 2002

The room-temperature interface between Si and Hg1−xCdxTe (x=0, 0.30, 0.39, 1.0) was investigated using the surface sensitive techniques of photoemission spectroscopy and low-energy electron spectroscopy (LEED). Elemental Si was electron beam evaporated onto atomically clean cleaved (110) surfaces in ultrahigh vacuum and the chemistry and morphology of the interface was monitored as a function of Si overlayer growth. The LEED pattern disappeared at ∼1 monolayer (ML) coverage Si for all substrates, indicating that the overlayer coverage was fairly uniform. At submonolayer Si coverages on the Hg containing alloys, the substrates exhibited Hg loss with Te coming out of the substrate into the overlayer. At moderate coverages (<6 ML), Te continued to come to the surface. Chemical shifts of the Si and Te core levels suggest that Te interacts with Si in the overlayer, with the possible formation of Si–Te phases in the overlayer. At thicker coverages of Si, Hg and Cd are seen to intermix within the Si overlayer, but stay away from the surface. For the Si/CdTe case, there is much less interaction between the Si overlayer and the substrate. Therefore Si appears to disrupt the surface of the Hg containing alloys much more than that of CdTe and hence the weaker Hg–Te bond in the lattice is seen to play a central role in dictating the surface chemistry and morphology in this alloy system. These findings have possible implications into Si-based passivation layers on HgCdTe.
Far-infrared analysis of alloy structure in HgTe–CdTe superlattices
Authors: Perkowitz S. , Sudharsanan R. , Yom S. S.
Published: July 2002

Far-infrared reflectivity measurements have been made on eight molecular-beam epitaxy (MBE)-grown HgTe–CdTe superlattices from two sources. The spectra at 300, 77, and 6 K display the phonon modes of pure HgTe, pure CdTe, and alloy Hg1−xCdxTe . Analysis shows that two of these microstructures contain layers of pure HgTe and CdTe separated by abrupt or graded alloy interfaces, whereas the others are more nearly HgTe–Hg1−xCdxTe structures with x=0.65 to 0.90. Details of the alloy models are discussed. Our analysis appears to be a first test of long-wavelength superlattice dielectric response theory.
Chemical sputtering of sintered diamond compacts and diamond film
Authors: Yamada R.
Published: July 2002

The chemical sputtering of sintered diamond compacts and diamond film have been measured as a function of target temperature and incident energy of protons. The C2 hydrocarbon production yields were 25%–55% smaller for the diamond compacts and the diamond film as well as the CH4 production yields 12%–14% smaller for the diamond compacts than for graphite, depending on incident energy, whereas the diamond film had the similar CH4 yields of graphite. The Raman spectroscopy shows that the bombarded surfaces of diamond compacts and film still had sp3 configuration of diamond structure even though they were irradiated up to a high fluence of more than 1020 H/cm2, whereas the bombarded graphite surface changed into microstructure domains. These results are considered to be the reasons why the yields are lower for the diamond compacts and film than for graphite and also why the steady yields of graphites differently fabricated have the similar values after prolonged irradiation.
Surface chemical shifts and photoelectron diffraction in CoSi2
Authors: Leckey R. , Riley J. D. , Johnson R. L. , Ley L. , Ditchek B.
Published: July 2002

An angle resolved study of the Si(2p) photoelectron line from bulk-grown CoSi2(111), (100), and (110) surfaces has been performed using synchrotron radiation. A surface shifted component has been observed from annealed (111) and (100) faces, the surface/bulk intensity ratio being a strongly modulated function of polar emission angle and of photoelectron kinetic energy. Surface emission has been found to be significantly stronger from (111) faces than from (100) faces. We adopt a model in which the (100) face is terminated in a single Si layer, whereas we suggest that in the (111) surface, two Si layers exist above the first layer of Co atoms, thereby forming a Si (111)-like template for the further growth of epitaxial Si. We consider that the interfacial Co atoms are sevenfold coordinated. Fractured CoSi2(111) surfaces are found to exhibit no surface Si.
Interaction of atomic hydrogen with cleaved InP. II. The decomposition stage
Authors: Proix F. , M’hamedi O. , Sébenne C. A.
Published: July 2002

Auger electron spectroscopy, electron energy-loss spectroscopy, low-energy electron diffraction, and photoemission yield spectroscopy have been used to study the interaction of atomic hydrogen with cleaved InP(110) upon heavy hydrogenation. Beyond the initial adsorption stage, the substrate dissociates into In metal and possibly two hydrogenated compounds of P, among which most likely phosphine PH3, which remain adsorbed on the surface. This interaction stage is characterized by the existence of the ‘‘black hole’’ phenomenon in photoemission yield spectroscopy, i.e., the complete disappearance of the photoemission signal at 5.3 and ∼5 eV, photon energies specific of the adsorbed species. The hydrogenated compounds desorb upon heating at 525 °C leaving a surface close to its H-adsorbed state. From there on, the properties of the surface can by cycled by, alternately, introducing a new heavy dose of H and annealing.
The interaction of excimer laser ultraviolet radiation with Kapton-H in vacuum and under mechanical stress
Authors: Tonyali K. , Jensen L. C. , Dickinson J. T.
Published: July 2002

We examine the response of highly stressed polyimide films to excimer laser radiation (20-ns pulses at 248-nm wavelength) in vacuum. We present changes in surface topography due to surface/near-surface damage, crack initiation, and eventually crack growth over a wide range of applied stress. We show that the morphology of the stressed material has a significant influence on the resulting damage and suggest that the regions of highest damage are those experiencing the highest local stress. Finally, we present initial results on the effect of mechanical stress on yields of the photoablation products ejected from the polymer surface.
Growth of Al and Al nitride films in N2–Ne and N2–(Ne+Ar) discharges: Construction of a ternary gas phase diagram
Authors: Siettmann James R. , Aita Carolyn Rubin
Published: July 2002

An Al target was sputtered in N2, N2–Ne, and 5% N2–(Ne+Ar) discharges. The resulting films were studied by x-ray diffraction, Rutherford backscattering spectroscopy, and resistivity measurements. The results were combined with data previously obtained for the N2–Ar system. A three-gas composition diagram was constructed onto which phase evolution in the films was mapped. In general, phase evolution proceeded as follows: Al→microcrystalline cermet→microcrystalline AlN→multiorientation AlN→single basal orientation AlN. For the same nominal discharge N2 content, the use of Ne in place of Ar as the rare-gas component of the discharge suppressed the formation of the Al, cermet, and microcrystalline AlN phases, and enlarged the region over which basal orientation AlN was formed. In situ optical emission spectroscopy data suggested that this result is related to an increased N+2 /Al0 flux in the discharge when Ne rather than Ar gas was used.
Characteristic electron-barrier interaction times
Authors: Leavens C. R. , Aers G. C.
Published: July 2002

Büttiker and Landauer derived characteristic times describing the interaction of a particle with a potential barrier, using a variety of approaches that give identical results within the Wentzel–Kramers–Brillouin approximation. Without resorting to this approximation, we generalize their two basic approaches to an arbitrary barrier and find that they can lead to significantly different characteristic times, particularly at very low energies. Hence, the results of Büttiker and Landauer should not be used uncritically outside the context in which they were originally derived. This is illustrated for the tunneling of electrons through a barrier containing a transverse magnetic field. A further generalization is made for transmission to any point within an arbitrary barrier. Finally, some of the conceptual difficulties that arise when the characteristic times are regarded as actual particle propagation times are discussed very briefly.
Chemical shifts of silicon and titanium in titanium silicide studied by Auger electron spectroscopy, slow electron energy-loss spectroscopy, and internal x-ray photoelectron spectroscopy
Authors: Sharma J. K. N. , Chakraborty B. R. , Shivaprasad S. M.
Published: July 2002

This paper describes the study of Auger and core-level energy shifts measured for pure Si, Ti, and TiSi2 by Auger electron spectroscopy (AES), slow electron energy-loss spectroscopy (SEELS), and internal x-ray photoelectron spectroscopy (IXPS). The Auger line-shape changes in TiSi2 are noted and the chemical shifts measured. The deep-core-level loss energies of the silicon K- and L-shell electron and the titanium L- and M-shell electrons are determined using SEELS technique. The collective surface and bulk plasma excitations in Ti, Si, and TiSi2 are also observed. Using a high-energy beam Si(Kα) x rays are generated to produce titanium photoelectrons by the IXPS L-shell electrons in TiSi2. The core level shifts observed from AES, SEELS, and IXPS are compared and this confirms the already established metallic nature of the silicide.
The role of chlorinated surface films in excimer laser etching of Cu at low Cl2 pressures
Authors: Baller T. S. , van Veen G. N. A. , Dieleman J.
Published: July 2002

Mass spectroscopy combined with time of flight (TOF) is used to study the products ejected from a Cu surface exposed concurrently to nanosecond excimer laser pulses at 308 nm and a low Cl2 pressure (p). Starting with a clean surface the etch rate increases with the number of pulses (n) until a steady state level (S) is reached. For various values of the laser pulse fluence F (0.14–0.82 J cm−2), of p (3×10−4–10−2 Pa), at a pulse repetition rate (r) of 4 Hz, and for irradiation along the surface normal, the main products are Cu3Cl3 and CuCl. All TOF distributions can be simulated well with Maxwellians (MB). At each set of values of F, p, r, and n the temperature (T) corresponding to the MB’s of the different products is the same. Starting with a clean Cu surface, T increases with n until S is reached. In S, T increases with p, but the dependence on F shows a maximum. T values of up to 6000 K may be reached. Rutherford backscattering analysis of the etched Cu samples reveals that Cl is incorporated during etching up to several tens of atom percentages and to depths of a few hundred nm. The increase in etch rate with n in the buildup to S is correlated to the gradual laser-assisted formation of a chlorinated Cu surface film. In S the Cl profile remains constant. The magnitude of the Cl concentration in and the thickness of the chlorinated Cu surface film are correlated to T and the etch rate. It is proposed that this behavior can be related to the lower heat conductivity of the chlorinated surface film.
Cathodoluminescence spectroscopy of metal–semiconductor interface structures
Authors: Brillson L. J. , Viturro R. E. , Shaw J. L. , Richter H. W.
Published: July 2002

Low-energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of semiconductor surfaces and ‘‘buried’’ metal–semiconductor interfaces. This extension of a more conventional electron microscopy technique provides information on localized states, deep-level defects, and band structure of new compounds at interfaces below the free solid surface. Specifically, CLS provides direct identification of metal-induced interface states which evolve in energy and density with multilayer metal coverages of the particular metal, extrinsic surface states due to lattice disruption, as well as bulk defect levels—all of which can play a role in Schottky barrier formation. From the energy dependence of spectral features, one can distinguish interface versus bulk state emission and assess the relative spatial distribution of states below the free surface. From the dependence of spectral intensity on injection level, one can spatially resolve large differences in recombination dynamics and band bending across semiconductor surfaces, depending on their detailed morphology. Unlike surface-science techniques sensitive to only the outer few monolayers, low-energy CLS reveals the electronic structure of buried interfaces and their changes with thermal processing at overlayer thicknesses which permit bulk chemical interactions to occur. For metal–semiconductor interfaces, these CLS spectral features provide a new perspective on physical mechanisms of Schottky barrier formation.
Combined surface analysis by synchrotron radiation photoemission spectroscopy and surface extended x-ray absorption fine structure of oxidation features of metal-deposited GaAs
Authors: Oshima Masaharu , Kawamura Tomoaki , Maeyama Satoshi , Miyahara Tsuneaki
Published: July 2002

Synchrotron radiation photoemission spectroscopy (SRPES) was used to study the oxidation processes of metal-covered GaAs(100) surfaces in order to understand the catalytic effect of metal overlayers on the oxidation of GaAs with an eye towards possible practical applications. It is found that Au-covered GaAs surfaces show strongly enhanced oxidation rates compared to bare GaAs and Al- or Cu-deposited GaAs surfaces for unexcited oxygen exposure and dc plasma oxidation. From an analysis of the chemically shifted peaks, this enhancement effect is attributed to the formation of an interfacial AuGa alloy and free As. A sandwich structure of GaAs oxide/Au/GaAs is confirmed based on x-ray photoelectron spectroscopy, SRPES, and Auger electron spectroscopy in-depth profiling, while oxidation of Al/GaAs results in an Al oxide/GaAs oxide/GaAs structure. Furthermore, in situ analysis of heavily oxidized surfaces by a dc plasma using SRPES and surface extended x-ray absorption fine structure above the O K edge revealed that dc plasma oxidation results in heavily oxidized As2O5 with an oxygen double bond which may have some correlation to an ‘‘intermediate O 2p state’’ at binding energy (BE)=11 eV in the valence band.
Diffusion of Si into Ge studied by core level photoemission
Authors: Hoeven A. J. , Aarts J. , Larsen P. K.
Published: July 2002

Ge(3d) and Si(2p) core level photoemission intensities were measured to monitor the coverage of Ge(001) and Ge(111) surfaces during the interrupted deposition of a thin Si film at room temperature and upon annealing. Annealing treatments were performed at temperatures up to a maximum of 880 K and interrupted a few times to allow for core level measurements. The Ge(3d) core level intensity was found to almost recover to its initial value upon annealing while the Si(2p) intensity decreased ∼60%. Intensity changes were observed at temperatures from 680 K upwards. It is concluded that above 680 K a significant diffusion of Si into Ge occurs, although at higher temperatures island formation or surface roughening also takes place.
Dense plasma production and film deposition by new high-rate sputtering using an electric mirror
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

Production of a dense plasma for new high-rate sputtering using an electric mirror has been achieved. The plasma, whose density is over 1012 cm−3, is generated by reciprocating an electron beam between two targets. Microwave excitation is detected in the dense plasma. Nonlinear interaction between the electron beam and the plasma plays an important role in dense plasma production. High deposition rates of over 3000 Å/min have been realized for Al, Mo, Fe, etc. Low-frequency instability, corresponding to E×B drift wave, also occurs in the plasma.
High-efficiency CdTe thin-film solar cells using metalorganic chemical vapor deposition techniques
Authors: Nouhi A. , Stirn R. J. , Meyers P. V. , Liu C. H.
Published: July 2002

Energy conversion efficiency of metalorganic chemical vapor deposited CdTe as an intrinsic active layer in n-i-p solar cell structures is reported. Small-area devices with efficiencies over 9% have been demonstrated. I–V characteristics, photospectral response, and the results of Auger profiling of structural composition for typical devices will be presented. Also presented are preliminary results on similar photovoltaic devices having Cd0.85Mn0.15Te in place of CdTe as an i layer.
Characterization of surface oxides and oxide desorption on InGaAs
Authors: Ingrey S. I. J. , Lau W. M. , Sodhi R. N. S.
Published: July 2002

In0.53Ga0.47As layers grown on InP substrates by metalorganic chemical vapor deposition were oxide ‘‘capped’’ using a UV ozone treatment. Oxide removal was accomplished by thermal desorption in vacuum and by remote hydrogen plasma treatments carried out in reaction chambers attached to a high spectral resolution x-ray photoelectron spectrometer (XPS). The XPS spectral results showed the oxide layer to be composed of a mixture of oxides. Subsequent desorption occurred over a range of temperatures. Desorption of As and In oxides, oxygen transfer from oxidized to nonoxidized sites and the formation of the suboxides occurred as intermediate stages. Complete removal of all oxides was observed at a temperature above the decomposition temperature of the In0.53Ga0.47As. The use of atomic H, generated in a remote plasma system, to enhance oxide removal was found to be a more effective procedure; the complete removal of all oxides was achieved at a substrate temperature of 192 °C. The resulting surface composition was In0.60Ga0.46As and the surface band bending was estimated to be <0.2 eV.
Standard relationships in the properties of Hg1−xCdxTe
Authors: Higgins W. M. , Pultz G. N. , Roy R. G. , Lancaster R. A. , Schmit J. L.
Published: July 2002

There have been significant variations in the reported properties of the Hg1−xCdxTe family of materials prepared at different laboratories since the discovery of its infrared detecting properties in the late 1950s. Such variations can be a result of the growth processes, the measurement techniques, and the standard relationships used. The objective of this paper is to present selected standard relationships that can be used to interrelate Hg1−xCdxTe material and device properties. High-quality Honeywell melt-grown bulk Hg1−xCdxTe was used as the standard reference material for several of the relationships. The specific relationships discussed are 1% absolute transmission cut-on versus alloy composition x, electron mobility (77 and 300 K) versus x, electron concentration (77 and 300 K) versus x, electrical resistivity (300 K) versus x, energy gap versus x and temperature, cutoff wavelength versus x and temperature, lattice constant versus composition, and density versus x.
Laser induced effects in HgCdTe photovoltaic devices
Authors: DeWames R. , Bajaj J. , Yao E. S. , Williams G. M.
Published: July 2002

In this paper we report on induced persistent dark currents in HgCdTe photodiodes induced with lasers, and relationships of these effects with those observed with γ rays and high-energy electron irradiations. Front side laser illumination with relatively small photon flux induces changes in the dark currents with thermal recovery characteristics similar to those observed from irradiation experiments with Co60 gammas and high-energy electrons. The induced currents produced by these alternative sources are mostly of tunneling origin. The degree of susceptibility to irradiation and illumination observed on devices of different structures is found to be similar, i.e., devices with relatively hard characteristics when exposed to irradiation with γ rays or high-energy electrons also are observed to be hard to laser illumination. Our results indicate that these metastable effects produced by lasers, γ rays, and high-energy electrons are of a common origin. The laser experiments suggest that these effects are associated mostly with changes in the electronic properties in the vicinity of the semiconductor junction at the insulator interface. The magnitude of the change in the dark current decreases with increasing wavelength of light and band-gap light produces no notable changes. This observation suggests a threshold energy for producing the effects and suggests that the physical processes are excitation of carriers from the semiconductor into the insulator/interface region. Junction parameters and the material features of the insulator/semiconductor interface are shown to be important factors in determining the susceptibility of devices to irradiation and illumination.
Particle bombardment effects on thin-film deposition: A review
Authors: Mattox D. M.
Published: July 2002

In many atomistic film deposition processes, concurrent energetic particle bombardment (ions, atoms, molecules, atom clusters) may occur inadvertently and uncontrollably or bombardment may be used to deliberately modify film properties. These energetic particles can arise from (i) the acceleration of charged particles, (ii) high-energy neutrals from reflection from bombarded surfaces, or (iii) charge exchange processes. Particle bombardment effects that can affect film formation and growth include (a) modifying the substrate surface (cleaning, defect formation), (b) momentum transfer processes in the surface region (sputtering, desorption, recoil implantation, defect formation), (c) addition of heat to the surface region, and (d) formation of secondary elelctrons that can affect chemical reactions. These in turn affect film properties such as adhesion, residual film stress, film morphology, density, grain size and orientation, surface coverage, pinhole density, and surface area. The understanding of these effects and how to use them advantageously is important to those utilizing processes where concurrent energetic particle bombardment is occurring or can be made to occur.
Effects of low-energy low-flux ion bombardment on the properties of VO2 thin films
Authors: Case Francine C.
Published: July 2002

An ion-assistance technique for deposition of VO2 thin films has been reported to influence the phase transition properties of the material [F. C. Case, J. Vac. Sci. Technol. A 5, 1762 (1987); 6, 2010 (1988)]. Films in those series were deposited as VOx (x<2) under high-energy (350–750 eV), high-flux (0.4–1.0 mA/cm2) ion bombardment and required annealing in flowing oxygen to bring the material into the VO2 phase. In this study, VOx (x∼2) thin films were reactively evaporated during simultaneous bombardment by either 200- or 350-eV oxygen ions at fluxes of <0.32 mA/cm2 and at two values of oxygen background pressure. The films underwent no further processing. Ion energy is observed to exert a strong influence over the resulting VO2 electrical properties and optical constants. A comparison of these as-deposited VO2 films to those prepared without ion bombardment, under otherwise identical conditions, is presented.
Structural characterization of Zn1−xCoxSe epilayers on GaAs(001)
Authors: Jonker B. T. , Qadri S. B. , Krebs J. J. , Prinz G. A. , Salamanca-Young L.
Published: July 2002

We have grown a Co-based diluted magnetic semiconductor, the wide-gap compound Zn1−xCoxSe, by molecular-beam epitaxy on GaAs(001) substrates. We report here a detailed study of the structure and crystalline quality of these epilayers as obtained from a variety of x-ray diffraction and transmission electron microscopy (TEM) techniques. The films grow as (001) single-crystal zinc-blende epilayers which exhibit some degree of tetragonal distortion for the full range of Co concentrations (x≲0.1) and thicknesses (0.1–2.6 μm) studied. X-ray double-crystal rocking curve and topography measurements show that the crystalline quality of the thinner films (0.3 μm) approaches that of the GaAs substrates. Cross-sectional and plane-view TEM results indicate a low dislocation density and the absence of twin formation within the epilayers. High-resolution lattice images show that the interface between the epilayer and substrate is coherent and atomically abrupt.
The effect of vapor incidence angle upon thin-film columnar growth
Authors: Mazor A. , Bukiet B. G. , Srolovitz D. J.
Published: July 2002

We present a generalized theory for the growth of columnar microstructure in vapor-deposited thin films under the joint influence of a constant uniform deposition flux coming down with an arbitrarily chosen incidence angle, and surface diffusion. The dependences of the zone I to zone II transition temperature, and the characteristic length scales associated with the unstable modes on the deposition angle are predicted. The surface morphology is obtained as a function of vapor incidence angle. For a specific deposition angle, there is a one-parameter family of steady-state surface profiles that corresponds to a range of possible columnar orientation angles, among which only one angle is associated with the tangent rule. These results agree with experimental observations.
A study of voids in sputtered SiO2
Authors: Logan Joseph S. , Hait Mitchell J. , Jones Harris C. , Firth Gerald R. , Thompson David B.
Published: July 2002

Voids have been observed in sputtered SiO2 films when deposited over substrate topographies with high aspect ratios (depth/width). This report describes experimental results which show the conditions under which voids are found, and the response of void formation to available deposition parameter variations, such as resputtering bias, power, and frequency. A simple model for void formation is used to predict quantitatively the limits of the process with respect to void formation. The results show that it is possible to obtain void-free coatings up to an aspect ratio of ∼2.0, and that the controlling factor is the sputtering yield versus angle of incidence curve. Data suggest that 40-MHz conditions are slightly more favorable than 13 MHz.
Surface roughness of rubbed polyimide film for liquid crystals by scanning tunneling microscopy
Authors: Suzuki M. , Maruno T. , Yamamoto F. , Nagai K.
Published: July 2002

The surface roughness of the rubbed polyimide (PI) film for the liquid crystals (LC) is studied by means of scanning tunneling microscope (STM). The PI films are fabricated on indium–tin–oxide (ITO) coated glasses, and are rubbed by a nylon roller. The just-spin-cast PI film surface shows that all the grains stick together. The lightly rubbed PI surface has a highly aligned grain structure along the rubbing direction. A ferroelectric LC fabricated on this lightly rubbed PI substrate has a high aligning coefficient, which corresponds to the higher quality in the LC cells. The STM images of the more rubbed PI films show that a spherical grained surface follows the paste-like state.
Scanning tunneling microscopy observation of sliding charge-density wave in blue bronze
Authors: Nomura Kazushige , Ichimura Kôichi
Published: July 2002

We investigated the sliding motion of charge-density wave (CDW) in K0.3 MoO3 with scanning tunneling microscopy (STM). With fixed position of the tunneling tip, a sharp peak was found in the spectra of tunneling current for sample bias current exceeding the threshold for the CDW depinning. The peak frequency increased with the extra current carried by the CDW condensate. This peak is understood to be generated by the modulation of gap distance between the tunneling tip and sample atom due to the sliding motion of CDW. The velocity of CDW at the surface was obtained directly: vs =5.7×10−3 cm/s just above the threshold. The corresponding sliding velocity in the interior of the same sample was obtained as vb =6.3×10−4 cm/s from the narrow band noise frequency. It was confirmed that the CDW is easily depinned at the surface and begins to slide with much higher velocity than the interior of sample. Tunneling spectroscopy was also measured and the CDW gap structure was obtained as a preliminary result.
The effect of Sr and Bi on the Si(100) surface oxidation: Auger electron spectroscopy, low energy electron diffraction, and x-ray photoelectron spectroscopy study
Authors: Fan W. C. , Mesarwi A. , Ignatiev A.
Published: July 2002

The effect of Sr and Bi on the oxidation of the Si (100) surface has been studied by Auger electron spectroscopy, low electron diffraction, and x-ray photoelectron spectroscopy. A dramatic enhancement, by a factor of 10, of the Si oxidation has been observed for Si(100) with a Sr overlayer. The SR-enhanced Si oxidation has been studied as a function of O2 exposure and Sr coverage. In contrast to the oxidation promotion of Sr on Si, it has been also observed that a Bi overlayer on Si(100) reduced Si oxidation significantly. Sr adsorption on the Si(100) with a Bi overlayer enhances Si oxidation only at Sr coverage θSr >0.3 ML.
Time-resolved electric probe techniques in radio frequency plasmas
Authors: Ruzic D. N. , Wilson Jeffrey L.
Published: July 2002

Time-resolved cross-sectional variation of plasma potential and electron energies were measured in a parallel-plate capacitively coupled argon discharge at 400 mTorr. Movable capacitive and shielded Langmuir probes were scanned between the plates and used to obtain I–V characteristics at the plasma potential minima and maxima. The variation of plasma potential was sinusoidal at the center of the discharge producing a sheath at both electrodes. During the plasma potential minima and maxima an electron beam component of the electron energy distribution at 5–26 eV was seen. The energy of the beam increased, and its magnitude decreased, traversing through the sheath region. Electron beam energy variations with pressure (200 mTorr–1 Torr) are also discussed.
Integrated thermal chemical vapor deposition processing for Si technology
Authors: Liehr M.
Published: July 2002

A multichamber integrated ultrahigh vacuum processing and analysis facility is described that addresses issues of chemical growth processes in terms of fundamental chemical reaction mechanisms, as well as the correlation of process parameters and specific materials properties. Examples for research using and related to ultraclean and integrated processing are given. (1) Impurities left at Si(100) surfaces as a result of wafer preclean with HF and UV/O3 are characterized with in situ analysis equipment, such as x-ray photoemission spectroscopy and high resolution electron energy loss spectroscopy. (2) Electrical figures of merit are determined by fabricating simple test structures [metal–oxide semiconductor (MOS) capacitors] in situ. They show electrical properties (breakdown field, interface state densities) comparable to wafers processed in standard tools. (3) Particle creation and particle size distribution on wafers after handling in the integrated processing tool are shown. (4) An example of basic research on the chemical equilibrium on the wafer surface during chemical vapor deposition film growth is shown for Si epitaxy using SiH4.
Reactive sputter etching in axial magnetic fields
Authors: Davies K. E. , Gross M. , Horwitz C. M.
Published: July 2002

Magnetic fields are often applied to radio-frequency discharges in order to obtain high rate operation at low target voltages and low discharge pressures. It is known that discharge ionization is improved due to retention of electrons by magnetic fields. Here, a detailed comparison of axial magnetic enhancement and hollow cathode enhancement is made. Also included is the performance of a diode system. Our comparison criteria are (i) etch rate and (ii) surface power efficiency, for a given applied target voltage and gas pressure. High power efficiency is related to low substrate heating, which is important in high-rate semiconductor wafer processing. The axial configuration used here is one of three types of magnetic enhancement in common use (the others being magnetron and multipolar). It has the advantage of simple experimental design due to the uniform magnetic field across the target surface. Most of the results given here describe SiO2 etching in CF4 gas; however, some results for Si etching in SF6 are also given. Diode uniformity and reproducibility is poor in axial magnetic fields. This is not the case with the hollow cathodes, and we ascribe this difference to the difference in energy of typical electrons that are approaching target sheaths in the two cases. The rate enhancement available from axial magnetic fields in simple diode and target confined hollow cathode geometries is a factor of 2–3, for a given target voltage and at 1 Pa pressure of CF4. An even larger improvement of 16 times is obtained in the unconfined hollow cathode at low pressures. However, power efficiency is not improved by magnetic fields in any of the systems. These results can be understood in terms of the relative loss rates of electrons and neutrals from the discharge. Electron retention increases ionization, which raises both etch rates and input power. Neutral retention can increase rates, with little effect on input power. Thus, axial magnetic fields seem to be most appropriate where rate is not limited by the availability of active neutral species, and where electron energies approaching the target sheath are high.
Submicron two-layer metal system of selective tungsten and TiW cap metallization
Authors: Mattox R. J. , Wilson S. R. , Sellers J. A.
Published: July 2002

The processing options available to fabricate multilevel metal interconnects are becoming greatly reduced as circuit dimensions enter the submicron regime. Advanced lithography techniques are required, such as x ray, electron-beam, or monochromatic steppers. The choice of metal materials is small, due to resistivity and interconnect dimension requirements. Sputter deposition equipment has difficulty in depositing the metal into the high aspect ratio vias and new processes with superior stepcoverage are required. Other processing technologies are also experiencing difficulties as dimensions shrink. This paper discusses the utilization of certain advanced processing technologies, namely: stepper lithography, TiW capped AlCu metallization, chemical vapor deposition (CVD) tungsten, plasma deposited oxide (tetraethylorthosilicate source), and etchback planarization to successfully fabricate a submicron two-layer metal structure. The test vehicle had via chains increasing in length from 10–8000 vias with dimensions from 0.75–1.5 μm. Serpentine metal patterns ranged from 0.001–1.1 m in length with pitch of 1.75–3.0 μm. Fabrication issues and potential solutions, as well as electrical data obtained from the test vehicle are presented. The electrical data includes metal serpentine yield and via chain data, comparing: (1) warm deposited AlCu, (2) hot deposited AlCu, and (3) CVD tungsten filled vias.
Surface passivation of HgCdTe photodiodes
Authors: Zimmermann P. H. , Reine M. B. , Spignese K. , Maschhoff K. , Schirripa J.
Published: July 2002

At higher temperatures HgCdTe photodiode dark currents are usually limited by bulk material properties exhibited as diffusion currents. As the temperature is decreased diode the dark currents transition to a region of smaller temperature dependence consistent with generation recombination in the space charge region, whereas at yet lower temperatures diode dark currents are limited by interband tunneling. The latter two effects are often of a surface origin. Two classes of surface passivation insulators are discussed: (1) the classical dielectric insulator in which the space charge width far exceeds the insulator thickness; and (2) the heterostructure passivation in which doping and/or thickness of the ‘‘insulator’’ are high enough for space charge layers and associated barriers to fully develop.
Temperature and composition dependence of the energy gap of Hg1−xCdxTe by two-photon magnetoabsorption techniques
Authors: Seiler D. G. , Lowney J. R. , Littler C. L. , Loloee M. R.
Published: July 2002

Accurate determinations of the energy gap Eg at liquid helium temperatures in alloys of 0.24≤x≤0.30 have been made by two-photon magnetoabsorption techniques. They are shown to help verify the use of the Hansen–Schmit–Casselman (HSC) relation over the range 0<x<0.30 at these temperatures. In contrast, the observed temperature dependence of Eg below 77 K is nonlinear and thus cannot be described accurately by the HSC relation. Analysis of Eg (T) data for three samples with 0.24≤x≤0.26 has allowed the deduction of a new relationship for Eg (x,T) that more properly accounts for the nonlinear temperature dependence below 77 K and the linear behavior above 77 K, while still accurately describing the x dependence Eg(x,T) =−0.302 +1.93x +5.35(1−2x)(10−4) [(−1822+T 3)/(255.2+T 2)] −0.810x2 +0.832x3, for Eg in eV and T in K. This relation should apply to alloys with 0.2<x<0.3. The maximum change from the HSC relation in this range is 0.004 eV for x=0.2 at ∼10 K.
The excess carrier lifetime in vacancy-  and impurity-doped HgCdTe
Authors: Fastow R. , Nemirovsky Y.
Published: July 2002

The excess carrier lifetimes of numerous vacancy- and impurity-doped bulk p-type HgCdTe crystals are measured using the techniques of steady-state photoconductivity and photoconductive decay. It is shown that the steady-state minority carrier lifetimes of impurity-doped crystals can be significantly larger than those of vacancy-doped crystals. However, the transient and steady state lifetimes differ by as much as an order of magnitude at 77 K due to minority carrier trapping, and appear to be uncorrelated. For Hg1−xCdxTe wafers with x∼0.225 and Na∼1×1016/cm3, the steady-state minority carrier lifetimes of impurity-doped crystals ranged from 1.6 to 62 ns, while those of vacancy-doped crystals ranged from 1.4 to 28 ns.
Island and step structures on molecular beam epitaxy grown Si(001) surfaces
Authors: Hoeven A. J. , Dijkkamp D. , van Loenen E. J. , Lenssinck J. M. , Dieleman J.
Published: July 2002

Initial stages of Si molecular beam epitaxy (MBE) on Si(001) substrates, misoriented 0.5° towards [110], were investigated using scanning tunneling microscopy (STM). Images from samples grown at 750 K and subsequently quenched to room temperature indicate that after deposition of more than about 0.5 monolayers both step flow and island growth occur. The islands have an anisotropic shape while in-between islands antiphase boundaries can be seen.
Intrinsic stress and mechanical properties of hydrogenated silicon carbide produced by plasma-enhanced chemical vapor deposition
Authors: Windischmann Henry
Published: July 2002

Hydrogenated SiC films were deposited by radio frequency plasma chemical vapor deposition in a silane–ethylene gas mixture. In the as-deposited condition the films are in compression with absolute values as high as 2×1010 dyn/cm2 (2 GPa). The origin of the stress is attributed to hydrogen incorporation, as evidenced by C–H and Si–H bands observed in infrared transmission measurements of as-deposited films. The hydrogen content was measured directly by 15N nuclear reaction analysis. Values as high as 40% (at.) were observed. Annealing the films in vacuum above 400 °C eliminated the hydrogen-related bands, accompanied by a simultaneous stress reversal from compressive to tensile. It is shown that the stress magnitude and sign can be modulated, depending on the annealing conditions. The ultimate tensile strength and elastic modulus were measured using the bulge test on free-standing membranes. Their values are close to bulk values. Raman spectroscopy and x-ray diffraction show that the films are amorphous. SiC membranes 3 μm thick and 50 mm in diameter were produced with 75% transmission at 632.8 nm, uncorrected for reflection losses.
Etch characterization of an electron cyclotron resonance process reactor
Authors: Fortuño-Wiltshire Guadalupe
Published: July 2002

An electron cyclotron resonance (ECR) etching reactor has been studied for its potential utility in plasma processing of thin films and semiconductor substrates. An ASTeX ECR source was installed on a conventional reactive ion etching reactor. Etch rates, etch uniformities, selectivities, etch profiles and dc bias voltages were measured as a function of many equipment and process parameters. Both the etch rates and the etch uniformity exhibited a strong dependence on the magnetic field strength and field profile at the wafer. The addition of a third electromagnet at the wafer for plasma collimation provided the greatest enhancement to the etching characteristics. Etch rates of Si for radio-frequency (rf)-biased ECR were on the order of 1 μm/min. The dc bias voltages in the ECR case were less than 100 V. SiO2 films were etched anisotropically with good selectivity to photoresist. The etch rate of SiO2 was found to increase monotonically with bombardment energy from a threshold of 36 eV in agreement with a sputtering model, suggesting that the reaction occurs via ion-induced chemical processes. Anisotropic profiles were observed for Si using pure SF6 in low pressure rf-biased ECR conditions. Clean vertical profiles were etched at high rates in polyimide using pure O2 with very high selectivity to a Si3N4 mask and the underlying Si substrate.
Electrical and optical measurements of electron cyclotron resonance discharges in Cl2 and Ar
Authors: Oomori Tatsuo , Tuda Mutumi , Ootera Hiroki , Ono Kouichi
Published: July 2002

Electron cyclotron resonance (ECR) discharge plasmas in Cl2 and Ar have been investigated over a pressure range of 0.2–10 mTorr, using microwave interferometry, optical emission spectroscopy, electrostatic probes, and charge collectors. The plasma parameters measured were spatially nonuniform along the magnetic field. The plasma electron density and the plasma potential had their maxima around the ECR region and decreased in going forward the position of the substrate, giving rise to a broadened energy distribution of positive ions incident on the substrate. The plasma density in Ar increased monotonously with increasing pressure, while the density in Cl2 had its maximum around 0.3–0.4 mTorr.
The influence of low-energy particle–surface interactions on the initial stages of thin film formation
Authors: Stone C. A. , Ghoniem N. M.
Published: July 2002

The initial stages of thin film formation by energetic particle deposition are modeled by a system of kinetic rate equations which describe atomic clustering phenomena. Specifically, a set of discrete kinetic rate equations, used to model small atomic clusters, is coupled to a set of kinetic moment equations which describe the size distribution function of large atomic clusters. These moments are derived from a Fokker–Planck equation which is an equivalent continuum limit of the discrete kinetic clustering equations. Low-energy particle–surface interactions and their impact on the growing film are considered by modeling surface defect production, sputtering, and cluster dissolution effects. Comparisons are made with thermal atom deposition to demonstrate the influence of energetic particle bombardment on the cluster size distribution, total cluster density, and nucleation rate.
The use of a direct current saddle-field plasma for the deposition of hydrogenated amorphous silicon
Authors: Harry M. , Zukotynski S.
Published: July 2002

The electrical characteristics of a saddle-field glow discharge were studied. The saddle-field electrode configuration consisted of a semitransparent anode sandwiched between two outer cathodes of similar diameter. The gases used were a mixture of silane and hydrogen, and pure nitrogen. The anode and cathode currents were correlated with anode voltage, pressure, and electrode separation. The use of a grounded enclosure as opposed to a floating enclosure, to confine the discharge, was shown to enhance the discharge currents for similar pressures and voltages. Data obtained from the variation of the discharge current with anode transparency, where the anode transparency is defined as the ratio of the sum of the area of the apertures in the anode to the area of a solid anode with the same diameter, shows that below 100 mTorr a dc saddle-field discharge gives rise to larger currents than those obtained using a conventional dc diode discharge. Hydrogenated amorphous silicon films were prepared and studied. Films exhibited a smooth surface morphology and good adhesion to the substrate. Growth rates as high as 10 Å/s were obtained for relatively low pressures (50–100 mTorr), flow rates (5–9 SCCM) and anode voltages (600–900 V). Preliminary studies indicated that the deposited films possessed good optoelectronic properties.
Preparation, properties, and characterization of thin ferroelectric films of lead titanate
Authors: Yoon Soon-Gil , Park Jong-Do , Choi Joon-Hoo , Kim Ho-Gi
Published: July 2002

Lead titanate thin films with a perovskite structure were successfully fabricated on titanium and borosilicate glass substrate by chemical vapor deposition. These films were characterized according to crystal structure, composition, and optical properties. Semiquantitative compositional analysis of the deposited films was carried out with x-ray photoelectron spectroscopy (XPS). From the XPS analysis, no other impurities can be detected on the film after 3.5 keV Ar+ cleaning. The lead titanate layer deposited onto the titanium substrate has a columnar structure and grows along the [001] preferred orientation. The stoichiometry of PbTiO3 has almost similar results regardless of deposition parameters. The optical transmittance of PbTiO3 film is influenced by the grain morphology of PbTiO3 deposit.
Phase selective deposition of boron achieved by crystallization control
Authors: Jansson U. , Boman M. , Markert L. C. , Carlsson J.-O. , Greene J. E.
Published: July 2002

The growth kinetics and phase composition of boron films deposited by chemical vapor deposition from H2/BCl3 mixtures depend strongly upon the choice of substrate material. We have demonstrated phase-selective deposition of amorphous boron (a-B) and crystalline α-rhombohedral boron (α-B) on a substrate patterned with Ti and Mo regions. a-B was obtained on Ti at growth temperatures up to 1500 K, well above the normal stability temperature of the amorphous phase, while at the same time α-B was obtained on the exposed Mo region of the substrate. The interface between the two phases remained abrupt and vertical for film growth to thicknesses >10 μm.
Regrowth of GaAs at the Au–Ge–Ga/GaAs interface under an As flux
Authors: Li Baoqi , Holloway Paul H.
Published: July 2002

Isothermal regrowth of doped GaAs at the Au/GaAs interface was studied using scanning electron microscopy and Auger electron spectroscopy. Electrical properties of the interface were characterized using I–V and C–V measurement. Multilayer films of AuGe(1500 Å) and Ga(200 Å) were evaporated on chemically cleaned GaAs surfaces and annealed in N2 or an As flux. An n-type, moderately doped, nonuniform regrown GaAs layer was formed at the interface of the substrate with little reaction between the metal films and the substrate even after annealing at 450 °C in an As flux. Current transport across the interface exhibited different behavior dependent upon whether regrowth had or had not regrown; (1) thermionic field emission(FET) through the grown GaAs/metal region, and (2) tunneling emission through the Au/original substrate interface area. Thicker Ga films result in nonuniform regrowth of GaAs both at the Au/air as well as the Au/GaAs interface.