bluuebunny/crossref_metadata_2025 huggingface dataset:
Auger electron spectroscopy studies of I–III–VI2 chalcopyrite compounds
Authors: Kazmerski L. L. , Sprague D. L. , Cooper R. B.
Published: July 2002

Auger electron spectroscopy (AES) spectra are presented for Cu ternary chalcopyrite compounds. CuInS2, CuInSe2, and CuInTe2 thin films, bulk polycrystalline, and single-crystal samples are examined and their AES spectra are compared. The validity of quantitative analysis methods [(1) calibration with Ag-standard, (2) utilization of sensitivity factors, and (3) calibration with specific ternary standards] is examined and the results are compared. Consistent results are obtained for polycrystalline (bulk and thin film) samples, but not for the single-crystal cases. It is found that peak width variations must be considered in the single-crystal data which vary due to diffraction channeling effects. Calculations, taking these variations into account, yield the expected results.
Auger and photoelectron study of codeposited sulfur and oxygen layers on silver (111)
Authors: Tibbetts Gary G. , Burkstrand James M.
Published: July 2002

When oxygen and sulfur are codeposited on a silver surface, the sulfur L2,3MM Auger spectrum is altered significantly from that obtained when sulfur alone is deposited. Besides a chemical shift due to the observed 6.6-eV sulfur L2,3 binding energy increase on coadsorption with oxygen, the oxygen L1 core level and a hybridized sulfur level in the valence band participate in the sulfur Auger process, introducing new Auger peaks similar to those present in surfaces containing SO4= groups. Electron bombardment of this film preferentially desorbs oxygen and alters the Auger spectrum back to one characteristic of films of sulfur alone on silver. These Auger spectra are analyzed on the basis of a model which uses experimentally determined initial states and small final-state effects.
ir study of molecules adsorbed on metal surfaces by surface electromagnetic wave spectroscopy
Authors: Chabal Y. J. , Sievers A. J.
Published: July 2002

The infrared spectra of monolayer coverages of two different molecules (KReO4 and SF6) physisorbed on metal surfaces have been measured in the 10-μm region by means of a new surface electromagnetic wave (SEW) coupling technique in conjunction with a CO2 laser. Coverages as low as two monolayers can be readily monitored in agreement with predictions based on an optical sum rule. The new coupling configuration is based on the principle of inhomogeneous wave coupling and allows the matching of both the propagation wave vector and the spatial profile of the SEW. Our method is both more efficient and more convenient for SEW spectroscopy than the conventional prism technique.
Effect of interface recombination at AlxGa1−xAs p–n junction perimeters on photoluminescence and current
Authors: Henry C. H. , Logan R. A.
Published: July 2002

The interfaces forming the perimeters of AlxGa1−xAs p–n junctions, such as cleaved surfaces or etched surfaces are regions of intense nonradiative recombination. Almost all of the p–n junction 2kT current is due to recombination at these nonradiative perimeters. When an uncontacted sample is studied in photoluminescence, these interfaces produce broad nonradiative regions known as large dark spots. The rate of interface recombination can be quantitatively evaluated from measurement of either the 2kT current or the large dark spot line shape. The 2kT current is usually explained in terms of the Sah, Noyce, and Shockley model of p–n depletion layer recombination. We develop an alternative model in which we show that recombination at a depleted surface will have 2kT charater. The rate of surface recombination is R=s0(np)1/2=s0ni exp(eV/2kT) where s0?4×105 cm s−1 for x=0.08 active layers with etched surfaces. This form of the recombination rate follows naturally from the requirement that the interface remain neutral.
Interfacial recombination in GaAlAs–GaAs heterostructures
Authors: Nelson R. J.
Published: July 2002

Photoluminescence time-decay measurements (300 K) are reported for Ga0.5Al0.5As–GaAs double heterostructures over a wide range of GaAs active layer thickness and doping levels. Decay times range from 10 to 650 ns in variously doped GaAs samples. Effects of self-absorption of luminescence and doping level on the decay times are observed for GaAs layer thickness d≳1 μm. For sufficiently thin GaAs layers, interfacial recombination is believed to determine the decay time. The interfacial recombination velocity is observed to vary from Si=300 cm s−1 for p=5×1015 cm−3 heterostructures to Si=500 cm s−1 for p=1.7×1017 cm−3.
Auger profiling studies of LPE n-AlxGa1−xAs–n-GaAs heterojunctions and the absence of rectification
Authors: Garner C. M. , Shen Y. D. , Su C. Y. , Pearson G. L. , Spicer W. E.
Published: July 2002

Grading of the heterojunction interface has previously been proposed to explain the absence of rectification for LPE n–n heterojunctions. In this study, Auger profiles were made of LPE n-AlxGa1−xAs–n-GaAs (doped 1015 to 1016 cm−3 in both layers) which had been grown to minimize any barrier lowering due to the grading width and high carrier concentration. In a specific case, the calculated interface widths necessary to eliminate the barrier was greater than 500 Å; however, the measured interface width was less than 150 Å. Ion profiling effects such as preferential sputtering, knock-on, and substrate surface roughness would only increase the measured interface width. Although the measured interface width was much less than that required by theory to remove the barrier in the conduction band, the samples did not exhibit rectification. This indicates that the present grading model may be insufficient to explain the lack of rectification of these samples.
Plasma anodization of GaAs in a dc discharge
Authors: Chesler L. A. , Robinson G. Y.
Published: July 2002

Thin oxide films have been grown by anodization of GaAs in the negative glow region of a dc oxygen discharge. As-grown and annealed films grown on both p- and n-type bulk GaAs were characterized by conventional electrical measurements and by Auger analysis. The anodic oxide displayed ohmic characteristics up to fields of 0.5×106 V/cm with a resistivity of 1014 Ω cm in the as-grown condition and over 1015 Ω cm after anneal. Capacitance–voltage measurements indicated a fixed positive charge in the insulator of 1.5×1012 cm−2 for p-type substrates and 4.0×1011 cm−2 for n-type substrates. Majority carrier trapping near the oxide/GaAs interface was reduced by annealing and a corresponding reduction of As at the interface was observed. The distribution of fast interface states on p-type substrates had a broad minimum of 7–10×1011 cm−2 eV−1 near midgap while the distribution of fast interface states displayed a peak of over 1013 cm−2 eV−1 near midgap on n-type samples. No corresponding difference in the Auger composition profiles were observed between n- and p-type samples.
Theoretical trends in the abrupt (110) AlAs–GaAs, Ge–GaAs, and Ge–ZnSe interfaces
Authors: Pickett Warren E. , Cohen Marvin L.
Published: July 2002

The self-consistent pseudopotential method has been applied to describe the electronic structure of the abrupt (110) interfaces of AlAs–GaAs, Ge–GaAs, and Ge–ZnSe system. These systems were chosen both for their technological interest as well as to study trends with ionicity. The method allows the study of existence, character, and density of interface states as well as allowing estimates of the conduction and valence-band discontinuities and the characterization of the bonding properties of the interface. The results indicate that the ideal structure may be stable for AlAs–GaAs, but the character of the bonds at the Ge–GaAs and Ge–ZnSe interfaces suggest unbalanced forces on the atoms which will lead to relaxation. It is suggested that, in addition to the change of ionicity, the change of crystal symmetry (diamond–zincblende) across the interface may be of central importance in these systems.
Amorphous metals and ion implantation
Authors: Grant W. A.
Published: July 2002

Amorphous metals lack the long-range atomic periodicity typically found in crystalline materials and their atomic arrangements are usually best described in terms of the random packing of hard spheres. Recent work has demonstrated that ion implantation can produce metastable, amorphous alloys. A brief review of the structure of noncrystalline metals is presented and recent data on ion-implanted amorphous alloys is reviewed. A discussion of the route by which ion-induced amorphization proceeds is also given together with some future prospects.
New advances in semiconductor implantation
Authors: Rupprecht H. S.
Published: July 2002

The objective of this review is to illustrate with some selected topics the advances made by ion implantation in modifying semiconductor materials, particularly silicon. The progress in obtaining extremely shallow impurity distributions, either by direct implants or by recoil methods, has led not only to better insights into the stopping phenomena of energetic particles in the low-energy range, but also to the capability of developing advanced Schottky barrier diodes. The application of radiation damage for gettering purposes is discussed in combination with the marked increase in the pipe-limited yield of bipolar devices. Another topic related to the generation of defects during implantation is the radiation-enhanced diffusion. Recent studies and advances in the understanding of these phenomena are presented.
Electrical properties of sputtered epitaxial films of GaAs
Authors: Soukup R. J. , Kulkarni A. K. , Mosher D. M.
Published: July 2002

Doped and undoped films of gallium arsenide have been sputter deposited onto single crystal GaAs substrates. The electrical properties of these films have been measured by two techniques. The first technique involved measurements of conductivity and mobility. Although Si and Mg doped films yielded fairly high conductivity films the carrier mobilities were quite low. A deep trap level appears to be present which limits the mobility. The second technique involves measurements of Schottky barrier contact properties as a means of deducting the film properties. The measurements made on these devices include capacitance–voltage, current–voltage, and electron-beam-induced currents in a scanning electron microscope. These measurements yielded data on barrier heights and minority carrier diffusion lengths. It has been determined that the doping level is controlled by the codeposition of an impurity material using pulsed sputtering techniques.
Relationship of optical degradation to surface morphology changes in solar absorbers
Authors: Zajac G. , Ignatiev A.
Published: July 2002

The physical basis for high-temperature optical degradation of electrodeposited black chrome coatings has been investigated via scanning electron microscopy and Auger electron spectroscopy coupled with inert gas depth profiling. Severe oxidation of the metallic chromium in the coatings has been observed and it is believed to result in shape changes of the particles comprising the film thereby decreasing their near-ir absorptance as is observed for air heat-treated coatings.
Simultaneous RHEED–AES–QMS study on epitaxial Si film growth on Si(111) and sapphire (1̄102) surfaces by partially ionized vapour deposition
Authors: Narusawa T. , Shimizu S. , Komiya S.
Published: July 2002

The role of simultaneous measurements of the chemical composition of a surface by AES, surface crystalline structure by RHEED, and released species by QMS are presented. A molecular beam of Si is effused from a partially ionized vapor deposition (PIVD) source consisting of a Kundsen cell and an electron-impact-type ionization chamber. The 7×7 structure of a Si(111) substrate at 1100 K changes into a broad 1×1 structure after vacuum deposition (VD) of 15 nm of Si while the epitaxial temperature can be lowered to 620 K (PIVD) in a 0.5% ionized atomic vapor with a typical deposition rate and acceleration energy of 0.3 nm/min and 100 eV, respectively. Epitaxial growth of Si on sapphire (11̄02) can be observed at 850 (VD) and at 700 K(PIVD), with a 1% ionized atomic vapor. The Auger spectra during deposition at 870 K remarkably shows that O and Al are reacted with Si on the film.
Emission of neutral particles from anodized aluminum surfaces during tensile deformation
Authors: Larson L. A. , Dickinson J. T. , Bräunlich P. F. , Snyder D. B.
Published: July 2002

Anodization of aluminum and other metals serves as surface preparation for a number of important applications including adhesive bonding of metal parts. We have been investigating the emission of several types of particles (commonly referred to as exoemission) from the surfaces of anodized aluminum during tensile deformation as a means of characterizing these oxides. Most recently, we have also observed relatively intense emission of neutral particles, primarily O2 and CO2, during deformation. From correlations with the growth of cracks in the oxide layer as the sample elongates, a model for tribostimulated neutral emission is suggested.
Performance of a directional detector of molecular density
Authors: Kobayashi M. , Tuzi Y.
Published: July 2002

A directional detector of molecular density was developed and applied to the measurements of angular distributions of desorbed molecules from Mo surfaces and outgassing rates from small test surfaces. The detector is composed of a mass spectrometer installed in a detector chamber and a collimator set on the entrance of the detector chamber. The collimator has two apertures and a pumping surface between them. The performance of the collimator is analyzed and compared with experiment data. The ratio of the incident flux intensities of molecules to the detector coming directly from a test surface to the one of chaotic background molecules, collimation efficiency, depends on the pumping speed of the collimator and the bell jar. When the pumping speed of the collimator is increased by cooling the inner wall and/or deposition of evaporated Ti on it, the collimation efficiency can be increased by the factor of 102.
Adhesive bonding of ion-beam-textured metals and fluoropolymers
Authors: Mirtich Michael J. , Sovey James S.
Published: July 2002

An electron bombardment argon ion source was used to ion etch various metals and fluoropolymers. The metal and fluoropolymers were exposed to 0.5–1.0-keV Ar ions at ion current densities of 0.2–1.5 mA/cm2 for various exposure times. The resulting surface texture is in the form of needles or spires whose vertical dimensions may range from tenths to hundreds of micrometers, depending on the selection of beam energy, ion current density, and etch time. The bonding of textured surfaces is accomplished by ion beam texturing mating pieces of either metals or fluoropolymers and applying a bonding agent which wets in and around the microscopic conelike structures. After bonding, both tensile and shear strength measurements were made on the samples. Also tested, for comparison’s sake, were untextured and chemically etched fluoropolymers. The results of these measurements are presented in this paper.
The American Vacuum Society: A multidisciplinary organization
Authors: Beavis L. C.
Published: July 2002

This presentation is based upon that which was to be given by the Society President at the 25th National Symposium of the American Vacuum Society, 29 November 1978, in San Francisco, California. The talk to the Society by its President was an innovation of the 1979 Program Committee. The intention is that such a presentation be given each year at the awards acceptance plenary session along with those of the Welch and, when appropriate, Gaede–Langmuir awards. To be discussed are the recent highlights of Society activity, the direction the Society is taking, and an example of the multidisciplinary activities of Society members.
Critical implantation temperature and annealing of indium phosphide
Authors: Rothemund W. , Fritzsche C. R.
Published: July 2002

This communication adds further data to the discussion of implantation temperatures for III–V compounds recently published by Gamo et al. Amorphization of InP by ion implantation can be avoided by heating the target to 150° C. Postimplantation annealing of amorphous layers can be done within 30 min at 500° C under phosphorus pressure but noticeable residual damage is left.
Steps on III–V(110) faces: A theoretical investigation
Authors: Lohez D. , Lannoo M.
Published: July 2002

A preliminary analysis of the nature of the defect causing Fermi-level pinning on the (110) faces of the (III–V) semiconductors is presented. Attention is focused on the cases of vicinal faces. Steps along the (110), (11̄1) and (001) directions are considered as well as clusters of steps. It is first shown that the high density of states observed on small disorientation angle faces can be understood only for steps along the (11̄0) direction. The absence of LEED patterns for steps on the (110) faces is discussed: it may suggest that clusters of steps must be chosen preferentially to single steps. One is then led to discriminate between steps with metallic and nonmetallic atom edges. To do this the energy dependent effective interactions method is applied to provide an estimation of the step levels of gallium arsenide for every configuration. The results are discussed: it is proposed that one of the most likely geometry might be a cluster of steps with nonmetallic atom edges, each atom bearing only one dangling bond.
Work function measurements on MBE GaAs(001) layers
Authors: Massies J. , Devoldere P. , Linh N. T.
Published: July 2002

For the first time, we report contact potential difference (CPD) measurements, using the Kelvin vibrating condensor method, on GaAs (001) layers in situ grown by molecular beam epitaxy (MBE). By using a tungsten rod [calibrated with a W(110) crystal] as reference, absolute determinations of the work function have been done on several surface structures. The MBE layers used for this study were n-type tin-doped 5×1016 cm−3 (μ300K∠4500 cm−2 V−1s−1) and p-type undoped 5×1014 cm−3 (μ300K∠380 cm−2 V−1  s−1) layers. For more than 20 layers tested, no significant work function differences were found between n-type and p-type layers of the same surface structure [c (4×4), c (2×8), (1×6). etc.]. However, important work function differences were observed between the different surface structures. The first result is interpreted as a Fermi level pinning by a high density surface state band (≳1012 cm−2) and compares with recent theoretical and experimental investigations, whereas possible changes in electron affinity due to surface dipole variation with the surface reconstruction are taken into account in the discussion of the second result.
Control of the VPE layer properties by the characteristics of the boundary layer
Authors: Duchemin J. P. , Bonnet M. , Beuchet G.
Published: July 2002

The surface of epilayers grown by chemical vapor deposition (CVD) cannot be characterized insitu by RHEED, LEED, or Auger spectroscopy methods used for molecular beam epitaxy. But, unlike the epilayers grown by molecular beam epitaxy, those grown by CVD method have their crystallographic and electric properties controlled by the characteristics of a 4–20-μm-thick motionless gas layer called boundary layer. Samples of the boundary layer can be probed as a function of the distance above the growth surface and analyzed by gas phase chromatography in the case of silicon epitaxy in order to measure concentration and concentration gradient of pertinent chemical species close to the growth surface. This analysis allows us to explain the behavior of the growth rate, the kinetics of the incorporation of impurities and the crystallographic quality of eqilayers as a function of the growth parameters. General results can be used to explain most cold wall reactor behavior. GaAs and InP materials grown by the organometallic method are treated as examples.
Interfacial reactions on anodized GaAs
Authors: Schwartz G. P. , Griffiths J. E. , Schwartz B.
Published: July 2002

Elemental arsenic generated via a thermally induced reaction between arsenic trioxide and GaAs has been observed to occur at the anodic oxide /GaAs interface using reflection Raman scattering. Chemical etching experiments have verified that the arsenic is indeed localized in the interfacial region. Both amorphous and crystalline allotropes were observed, with the amorphous arsenic lying closest to the substrate. No evidence for the existence of elemental arsenic as an intrinsic anodization product in unannealed samples was observed down to the detection limits of the technique.
High-speed, low-overhead electron beam direct slice writing system
Authors: Varnell G.L. , Spicer D. F. , Hebley J. , Robbins R. , Carpenter C. , Malone M.
Published: July 2002

Electron beam writing systems have been primarily used for photomask and reticle fabrication because of the limited throughput ahievable. A vector-scan beam writing system (EBSP) has been developed with a 1–1.25 μm resolution capability and ±0.25 μm pattern overlay accuracy and a potential throughput capability of 14 3-in. slices/h for 1–1.25 μm minimum pattern geometries and 20 3-in. slices/h for 2.5 μm minimum pattern geometries. This paper discusses the throughput factors for vector-scan e-beam systems and describes the new developments and improvements to tne major subsystems of the earlier photomask machine (EBM II) which were necessary to achieve this order of magnitude improvement in throughput.
Boron nitride mask structure for x-ray lithography
Authors: Maydan D. , Coquin G. A. , Levinstein H. J. , Sinha A. K. , Wang D. N. K.
Published: July 2002

Properties of a new boron nitride mask structure for x-ray lithography are described. Of particular importance is that this structure does not suffer from excessive mask distortion as did the Kapton x-ray mask. Average pattern distortions less than 0.2 μm are achieved routinely.
Fabrication of silicon oxynitride masks for x-ray lithography
Authors: Csepregi L. , Heuberger A.
Published: July 2002

The fabrication of optically transparent silicon oxynitride x-ray masks using CVD process on silicon is reported in this paper. The etch rate in the ethylenediamine, pyrocatechol, and water mixture used for substrate removal has shown a strong dependence on the layer composition. Because of the notable etch rate of SixOyNz films, it is of advantage to cover them with a thin (?500 Å) Si3N4 layer. Thin Si3N4/SixOyNz/Si3N4 composite membrane foils have been fabricated with a total thickness of 6000 Å and a window size of 2.5×2.5 cm2. Fizeau interference measurements showed that the window geometry has a significant influence on the total geometrical distortion of the thin mask membrane.
Epitaxial growth of Si on (1̄012) Al2O3 by partially ionized vapor deposition
Authors: Shimizu S. , Komiya S.
Published: July 2002

The epitaxial growth of silicon on (1̄012) sapphire by partially ionized vapor deposition is investigated with a RHEED–AES system. The measurement of the epitaxial temperature and the observation of the RHEED pattern during epitaxial growth are carried out under varying ionization conditions for the silicon ions; i.e., average ion energy of 30 and 180 eV and fractions of silicon ions mixed with silicon atoms ranging from 0 to 7%. When a silicon molecular beam is deposited without ionization for thickness from 2 to 10 nm, (100) oriented and two different {110} oriented islands are observed in the RHEED pattern at substrate temperatures between 870 and 1020 K. The RHEED pattern, however, shows no change for selective epitaxy when the silicon molecular beam is partially ionized up to 7%. A decrease in epitaxial temperature by as much as 150 K is observed at a fraction of silicon ions of 1%, but no further change is observed at higher fractions up to 7% for ion energies of either 30 eV or 180 eV.
Bonding of Al and Ga to GaAs(110)
Authors: Skeath Perry , Lindau I. , Su C. Y. , Chye P. W. , Spicer W. E.
Published: July 2002

The interfacial electronic states associated with Al and Ga overlayers on cleaved GaAs (110) surfaces are studied by ultraviolet photoemission spectroscopy (UPS) and low energy electron diffraction (LEED). Deposition of Al or Ga can produce valence-band spectra nearly devoid of new structure. Sb produces quite significant changes in the surface valence band and is shown as a contrasting example. Pseudopotential calculations from the literature for Al- and Ga-ordered overlayers are found to be in somewhat better agreement with the data than the corresponding tight-binding calculations, particularly in the adatom states which lie above the GaAs valence-band maximum (VBM), although neither calculation gives a good description of the observed overlayer states. It is shown that Al and Ga most likely form two-dimensional clusters or rafts on the surface at submonolayer coverage which are not in registry with the GaAs surface lattice. A comparison is made with results by other workers for Al, Ga, and In on GaAs and Si.
X-ray lithography — A review and assessment of future applications
Authors: Smith Henry I. , Flanders D. C.
Published: July 2002

The radiation used in x-ray lithography spans a rather broad range, from about 4 to 50 Å. At the short wavelength end, transmission through mask membranes and vacuum windows is high, and minimum linewidth is of the order of 1/2 μm. At the long wavelength end, mask selection is limited, exposure is done in vacuum and minimum linewidth is about 100 Å. At intermediate wavelengths, one can make numerous tradeoffs among resolution, system configuration, masks and resists. X-ray lithography at the AlK wavelength (8.34 Å) is compared with scanning electron beam lithography from the point of view of exposure time, assuming a step-and-repeat strategy. The use of gap adjustment to compensate for homogeneous substrate distortion may be an important advantage of x-ray lithography relative to other parallel exposure techniques.
Scattering of inversion layer electrons by oxide polar mode generated interface phonons
Authors: Moore B. T. , Ferry D. K.
Published: July 2002

The role of polar interface phonon scattering in determining mobility has been investigated in inversion layers of MOS structures on InAs and Si. The comparison between mobility measurements and transport calculations is found to provide an alternative method for determining interface properties. Transport at the Si/SiO2 interface is found to be dominated by several scattering mechanisms at various inversion densities. However, transport at the InAs/oxide interface is dominated entirely by surface roughness, because of the larger interface widths in this system. Interface phonon contributions are small.
Study of GaAs–oxide interface by transient capacitance spectroscopy: Discrete energy interface states
Authors: Kamieniecki E. , Kazior T. E. , Lagowski J. , Gatos H. C.
Published: July 2002

Interface states and bulk GaAs energy levels were simultaneously investigated in GaAs MOS structures prepared by anodic oxidation. These two types of energy levels were successfully distinguished by carrying out a comparative analysis of deep level transient capacitance spectra of the MOS structures and MS structures prepared on the same samples of epitaxially grown GaAs (n?1015 cm−3). The identification and study of the interface states and bulk levels was also pursued by investigating the transient capacitance spectra as a function of the filling pulse magnitude. It was found that in the GaAs–anodic oxide interface there are states present with a discrete energy (0.65 eV below the conduction band) rather than with a continuous energy distribution as previously reported. The value of the capture cross section of the interface states was found to be 1014 to 1015 cm2, which is far more realistic than the extremely large values of 10−8 to 10−9 cm2 reported on the basis of conductance measurements.
Surface studies on MBE-grown III–V compounds and alloys
Authors: Ludeke R.
Published: July 2002

We have examined electronic surface properties.
Is first compound nucleation at metal–semiconductor interfaces an electronically induced instability?
Authors: Bené R. W. , Walser R. M. , Lee G. S. , Chen K. C.
Published: July 2002

We present transmission electron microscopy (TED) and transport measurements on thin films of cobalt on (100) and (111) silicon substrates which show that first phase nucleation proceeds upon deposition past a critical thickness and is preceded by a semiconductor/metallic transition in the glassy, as-deposited phase. We have also performed electron diffraction measurements on thin cobalt films deposited on highly doped Si substrates. It is found that compound nucleation begins upon metal deposition for any thickness down to practical minimum depositions for our sputtering system on the order of 10 Å. We interpret these results to indicate that in these systems thin film nucleation is driven by an electronic two-dimensional instability of the interphase region.
Laser annealing and epitaxy
Authors: Leamy H. J.
Published: July 2002

Epitaxial reordering of disordered surface layers is accomplished during laser or electron beam annealing by growth from either the solid or the liquid phase. Both processes yield homoepitaxial layers of excellent quality on silicon. The solid-phase-epitaxial process (SPE) is analogous to that obtained by furnace heating and is applicable to implantation damaged surface layers. The process, however, is completed within milliseconds by beam processing, and impurity diffusion is insignificant. Liquid-phase-epitaxial growth (LPE) occurs during resolidification of the flash melted surface and is applicable to deposited overlayers as well as to implantation damaged layers. In this process, impurity diffusion within the liquid film and segregation at the crystallization front are responsible for impurity redistribution. Metastable solutions of extraordinary solute concentration may be fabricated by the (LPE) process.
Structural aspects of tunnel-junction coupled granular lead films
Authors: Vandenberg J. M. , Nakahara S. , Hebard A. F.
Published: July 2002

Granular lead films were deposited using the technique of reactive ion beam sputtering of a lead target with argon ions in the presence of an oxygen background. The superconducting properties of these films reveal that the primary means of electron transport is by tunneling across insulating lead oxide barriers separating clusters of lead grains. Results of x-ray and TEM studies confirm this interpretation and show that the films consist of randomly-oriented lead grains, less than 500 Å in diameter, embedded in an insulating matrix which contains at least two identifiable oxides of lead. These unique structural properties are most likely responsible for the excellent mechanical and electrical stability observed for these films.
Measurement of neutral gas density with ionization gauges in plasma physics research
Authors: Berman A.
Published: July 2002

The assessment of neutral gas density in the vicinity of a magnetically confined plasma is necessary for the consideration of atomic processes in fusion research experiments. Ionization gauges can be used provided that steps are taken to restrict the influence of the magnetic field on their sensitivity and to effect the differentiation of the true signal from the plasma produced background. In addition, the gauges must have a rather short time constant and a large signal-to-noise ratio. This paper presents an analysis of the features mentioned, based on a careful review of the literature to date. The results achieved by different research workers are discussed within the frame of the foregoing analysis. An attempt to correlate the design criteria underlying the operation of ionization gauges used in plasma machines is presented.
Overcompensated surface layer in n-GaAs due to anodic oxidation
Authors: Kamieniecki E. , Cooperman G.
Published: July 2002

The effect of defect states at a GaAs–oxide interface on the electronic properties of n-type MOS structures was investigated. It is shown that these 0.65 eV discrete energy interface states are of the same nature as the defect levels formed near the surface due to the deposition of foreign atoms in a vacuum. The spatial distribution of these states in a region extending about 2000 Å below the GaAs surface is responsible for the anomalously low value fo the high frequency accumulation capacitance in n-type GaAs MOS structures, as well as for the long characteristic filling time of these states observed in DLTS measurements.
Oxidation of silicon surfaces
Authors: Redondo A. , Goddard W. A. , Swarts C. A. , McGill T. C.
Published: July 2002

We have carried out theoretical studies (generalized valence bond) for chemisorbed O atom and O2 molecule on Si(111) surfaces using clusters of atoms to model the surface. For the perfect surface we find that O2 molecule binds to a single surface Si with an Si–O bond length of 1.68 Å (bulk SiO2RSi–O = 1.61 Å), an Si–O–O angle of 116 °, and an O–O bond distance of 1.32 Å. We have also calculated the shifts in the Si(2p) and O(1s) core level energies for chemisorbed O and O2 on the surface. The Si(2p) shift is +1.1 eV (higher binding energy) for the O atom and +1.5 eV for O2, in agreement with the shifts observed for low oxygen exposure by Spicer and co-workers.
Initial stage of formation of a metal-semiconductor interface: Al on GaAs(110)
Authors: Zunger A.
Published: July 2002

A re-examination of the experimental data and previous electronic structure calculations on the prototype system Al/GaAs(110), together with new calculations and models, indicates that at low coverages and temperatures neither a covalent bond nor a metallic bond is formed between Al and the substrate. Instead, the predominant species is likely to be Al clusters which interact only weakly with the substrate.
Simulation of ion-beam etched pattern profiles
Authors: Tsuge H. , Esho S. , Gokan H.
Published: July 2002

Profiles of fine patterns formed by ion-beam etching were simulated with a three-dimensional model on the basis of redeposition effect. First, a revolution ellipsoid format was assumed to represent angular distribution of sputtered atoms to simplify the simulation. Secondly, an experimentally obtained distribution was used. Consequently, the pattern width difference between mask and substrate decreases as the angular distribution changes from undercosine to overcosine. The pattern width difference, which shows a maximum value at the bottom of etched substrate patterns, is almost independent of pattern gap width. Pattern sidewalls become steeper with increasing gap width or with decreasing etched depth. These simulated pattern profiles are in good agreement with the experimental results.
X-ray photoelectron spectroscopy of sputtered platinum thin films containing large amounts of carbon
Authors: Delrue J. P. , Pireaux J. J. , Caudano R. , Robert T. , Hecq A.
Published: July 2002

Polycrystalline thin films of platinum containing amounts of carbon up to 17 at.% have been prepared by dc reactive sputtering. Although bulk properties were also investigated, emphasis is given here to the surface study of these films by x-ray photoelectron spectroscopy. The Pt and C core level intensities, the Pt 4f asymmetry, and the valence band spectra are consistent with the existence of a surface phase of the type Pt-Cx.
Chemical reaction at the Al–GaAs interface
Authors: Schwartz G. P. , Cho A. Y.
Published: July 2002

Interfacial chemical reactions between thermally aged films of aluminum on GaAs have been observed using surface reflection Raman scattering. The measurements provide identification of the chemical composition of the reacted interfacial layer. Under thermal aging conditions in which the aluminum overlayer is not totally reacted, AlAs was observed as the reaction product. Depletion of the aluminum overlayer followed by continued reaction leads to the observation of an interdiffused AlxGa1−xAs layer.
Generation and applications of finely focused beams of low-energy electrons
Authors: Yau Y. W. , Pease R. F. W. , Iranmanesh A. A. , Polasko K. J.
Published: July 2002

In electron-beam lithography, two well-known problems are proximity effects due to electron scattering and slow throughput because of limited exposure rate and resist sensitivity. We have investigated the generation of finely focused electron beams of low landing energy (?5 keV) and their application to materials processing. Lenses employing magnetic and retarding electric fields are found to have very low spherical and chromatic aberrations, thus facilitating the production of beams of low-energy electrons without seriously sacrificing current density. With such beams the power dissipated per unit volume at the surface of a bulk target is higher than with high-energy electrons, thus increasing the speed to exposure of very thin resists and dramatically reducing proximity effects. This compact volume of high-power dissipation is also attractive for selected area annealing.
Postirradiation polymerization of e-beam negative resists: Theoretical analysis and method of inhibition
Authors: Ohnishi Y. , Itoh M. , Mizuno K. , Gokan H. , Fujiwara S.
Published: July 2002

Many e-beam negative resists show postirradiation polymerization, i.e., even after e-beam irradiation termination, crosslinking reaction continues. This phenomenon shows an unfavorable effect in precise pattern fabrication; the first delineated portion of the resist undergoes a dimensional change with respect to the last-delineated portion. A method to inhibit postirradiation polymerization is presented based on a theoretical analysis of the postpolymerization mechanism. In the model used for analysis, active radicals are not extinguished in the vacuum and polymerization proceeds at a rate proportional to the radical concentration (first order reaction). A radical loses its activity due to collision with another radical (second-order reaction ). This model successfully explained experimental results. Postirradiation polymerization inhibition is achieved by adding a radical scavenger to resists. Active radical collision with a scavenger also extinguishes radical activity. Thus resist pattern width and thickness are freed from time dependence after irradiation. Resolution is also improved by postpolymerization inhibition as chain reactions in resists are suppressed. Although sensitivity is decreased, a highly sensitive negative resist can meet today’s requirement (around 1 μC/cm2), even after the addition of a scavenger. To demonstrate the benefit of postirradiation polymerization inhibition, a Cr mask was made with submicron features. It has 7-μm period Y-Y propagation patterns for a bubble memory, in which all gaps are designed as 0.5 μm. Adding a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and SEL-N resist, precise pattern fabrication was achieved, irrespective of the time after exposure.
Oblique deposition enhanced sensitivity in electron beam exposed g-GexSe1−x inorganic resist
Authors: Balasubramanyam K. , Ruoff Arthur L.
Published: July 2002

The enhancement of the electron beam sensitivity by a factor of ten has been achieved in silver adsorbed g−Ge0.25Se0.75 inorganic resist by oblique deposition of the amorphous chalcogenide films. The electron beam induced chemical and structural changes in obliquely deposited films, the lithographic performance, and the resolution limits are reported.
Verification of a proximity effect correction program in electron-beam lithography
Authors: Kratschmer E.
Published: July 2002

A new method for computing proximity effect corrections for submicron electron-beam lithography is introduced. It is based on a fast algorithm for shape partitioning to gain better control for resultant exposure intensity distribution across each shape in the pattern. By careful investigation of the intrashape and the intershape proximity effects the program supplies a means of controlling the submicron pattern delineation. Values for the parameters of the double Gaussian function used in the calculation of the dose variation factors are given for a variety of exposure conditions. Results of the application of the program to delineation of submicrometer patterns in PMMA and AZ 1350 resist on silicon substrate are presented.
Proximity effect correction in electron-beam lithography
Authors: Kato T. , Watakabe Y. , Nakata H.
Published: July 2002

Electron-beam fabrication offers several important advantages for lithography, including a capability of geometries smaller than one micrometer, a high adaptability to automation and the ability to write directly on a Si wafer without the need for a mask. However, for submicron patterns, a proximity effect is observed by the behavior of incident electrons in a resist. In electron-beam lithography the exposure intensity distribution (hereafter EID) is an essential physical quantity for implementing a proximity effect correction. There are many correction methods and several methods have been tried to correct for practical devices. However, the variation of the EID along the distance into the resist from the surface is neglected, and only a two-dimensional EID is presented in those articles. The present paper describes experimental and theoretical study on a correction method of the proximity effect which contains the consideration of the three-dimensional profile of a resist. It has been found from a Monte Carlo simulation that a cross-sectional profile can be controlled by an additional exposure at the vicinity of a pattern edge. With this method, for example, an undercut resist pattern, which is suitable for a lift-off process, can be obtained, avoiding as a whole the overdose on a pattern. A 0.5 μm line and space pattern with 1 μm thickness PMMA has been easily obtained, namely, when under-developed, the wall profile of the resist becomes rather steep, and when properly developed, the profile becomes undercut.
Lift-off of thick metal layers using multilayer resist
Authors: Lyman S. P. , Jackel J. L. , Liu P. L.
Published: July 2002

We have developed a modified multilayer resist technique which allows lift-off of very thick (≳2 μm) metal layers while retaining fine resolution. The trilayer structure consists of a thick (3 μm) lower layer of AZ 2430, the top of which is plasma-hardened in a CF4 discharge in order to render it impervious to solvents, an intermediate layer of SiO (∠1000 Å), and a thinner (1 μm) upper resist layer, typically AZ 1350 J. After standard patterning of the upper resist, the pattern is transferred to the SiO and lower resist layers by reactive ion etching in CF4 and O2 respectively. By varying the pressure of the O2 plasma, either vertical walls, or walls with controlled undercut were produced. Because the lower resist layer remains soluble in acetone, it is easily removed, making this method appropriate for lift-off. Using this technique, we have made 2 μm thick microwave electrodes of aluminum and of gold coated copper. This procedure is potentially useful for fabricating x-ray masks or other structures requiring thick high resolution metal patterns, as well as for these specialized electrodes.
High-sensitivity, high-resolution, high-thermal-resistant negative electron x-ray resist
Authors: Tan Z. C. H. , Petropoulos C. C. , Rauner F. J.
Published: July 2002

A novel negative-working electron/x-ray resist with high sensitivity, high resolution, and good dry etch resistance was obtained by the free radical copolymerization of an unsaturated methacrylate and a hydroxy alkyl methacrylate. Depending on the copolymer ratio, sensitivity of at least 0.2 μC/cm2 was achieved with 10 keV electrons in most cases with polymers with a ?w well below 100 000. Resolution of 1.0 μm line and space was obtained from a 0.95-μm-thick resist by either direct e-beam writing or by exposure to soft x-rays through a mask. The sensitivity to 7 Å tungsten M lines was 9 mJ/cm2 and the contrast was ∠1.3. An aspect ratio of ∠2 was obtained with isolated submicron lines 7000 Å thick. The resist had good resistance to both chemical and dry etching. The plasma etch resistance was at least twice that of PMMA.
Variation in the stoichiometry of thin silicon nitride insulating films on silicon and its correlation with memory traps
Authors: Bailey R. S. , Kapoor V. J.
Published: July 2002

Auger electron spectroscopy and the internal photoelectric-effect technique have been used to investigate the chemical structure of the thin Si3N4 film as a function of deposition conditions and its correlation with impurity/defect related memory traps in Al–Si3N4–SiO2–Si structures. The silicon content in the Si3N4 film showed an increase of 7% for a decrease of the NH3 to SiH4 gas ratio from 300:1 to 25:1 and a corresponding increase in the trapped electron density from 0.95×1018 to 2.1×1018/cm3. The film was stoichiometric for gas ratios greater than 300:1 and for the deposition temperature range of 700–950 °C. The results suggest an association of trapped electronic charge with some structural defects in addition to excess silicon incorporated in the Si3N4 film as explained by the valence alternation pair defect model.
Mechanism of anodic oxidation of Hg0.8Cd0.2Te
Authors: Ahearn J. S. , Davis G. D. , Byer N. E.
Published: July 2002

The initial stages of Hg0.8Cd0.2Te anodization have been studied by electrochemistry and x-ray photoelectron spectroscopy (XPS). Comparison of the polarization curves of HgCdTe, HgTe, and CdTe with XPS measurements of HgCdTe surfaces anodized to various potentials allows us to propose a possible model for the anodization. First the Hg-rich surface layer formed by the bromine–methanol etch is removed at a potential of ∠−0.1 V vs SCE (standard calomel electrode). Upon oxidation of the Te2− at ∠+0.35 V vs SCE in an aqueous solution (at ∠+0.6 V vs SCE in an ethylene glycol solution) the Cd2+ and Hg2+ ions are released, with the Cd2+ reacting with the Te4+ and O2− to form CdTeO3 and CdTe2O5. Some of the Hg2+ is incorporated into the oxide in analogous compounds, but most is driven into solution. The dissolution of Hg proceeds in advance of the Te4+/Te2− interface, resulting in a depletion of Hg from the interfacial region of the semiconductor.
He leak detection in the presence of deuterium background in tokamak vacuum systems
Authors: Blanchard W. R. , Krawchuk R. B. , Dylla H. F.
Published: July 2002

Helium leak detection systems for magnetic fusion devices present several unique design problems because of the large dynamic range required and the high partial pressures of D2 encountered. We describe the design and operation of a He leak detector system for the PDX tokamak. The system consists of a differentially-pumped, low resolution, He mass spectrometer which is interfaced to the foreline of one of the torus turbomolecular pump lines. The He detector has a minimum throughput sensitivity of 10−10 Torr⋅l/s, and the torus-integrated system has been designed for detection of torus leaks over the range of 10−7 to 10 Torr⋅l/s. Minimum leak-rates on the 38 m3 PDX vessel which have been quantified using this system are ∠3×10−8 Torr⋅l/s. When PDX is operated with D2 plasmas it is necessary to reduce the partial pressure of D2 by a factor of 100 within the mass spectrometer to maintain this sensitivity in the presence of the torus D2 outgassing. We have designed and incorporated a D2 filter which employs a Zr–Al getter assembly to affect the required D2 pressure reduction.