bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of de-ionized water parameters rinse on postmetal etch residue removal using semiaqueous cleaning chemistries
Authors: Small Robert , Kirk Simon , Cernat Mihaela
Published: July 2002

As the plasma etch processes have evolved, the wet cleaning process has included resist stripping, sidewall polymer removal, and also encompasses surface cleaning, which can include mobile ion reduction and damaged metal removal. This scenario has ushered in the recent popularity of fluoride based semiaqueous cleaning (SAC™) chemistries for postmetal etch cleaning. These chemicals can include low or room temperature operation and very short process times, are easily rinseable in water, and are easy to dispose of. This study looks at the effects of cleaning metal and via structures with SAC™ chemistries. The primary focus is on metal integrity when looking at: (1) process latitude of the cleaning chemicals; (2) the effect of de-ionized water rinsing; and (3) the effect of utilizing different intermediate rinses. This study shows that an emphasis should now be placed on total process optimization. This not only includes the cleaning chemistry, but also the rinsing process, which had historically not been a focus item.
Advanced transfer system for spin coating film transfer and hot-pressing in planarization technology
Authors: Sato Norio , Machida Katsuyuki , Kudou Kazuhisa , Yano Masaki , Kyuragi Hakaru
Published: July 2002

A film transfer system suitable for the spin coating film transfer and hot-pressing (STP) method was developed. The STP method consists of three steps: spin coating a base film with a dielectric, transferring it from the base film to a wafer by hot pressing in a vacuum, and peeling off the base film from the dielectric. STP is simple and cost effective for film deposition and planarization, since both processes can be performed simultaneously. Among the above steps, the transfer step is the most crucial in achieving stable and reproducible transfer of a dielectric. To improve this step, we devised an arrangement of the base film and wafer, and introduced a tension ring for stretching the base film and a press force equalizer. Each technique was individually evaluated and proved to be effective. A low-k material (k=2.9) was applied to the system and the overall effect of the three techniques working together was also investigated. The experimental results show that the system achieves better film transfer with the thickness variation of 1.8% on the wafer and that STP is a very promising key technology for planarization.
Electronic transport in perylenetetracarboxylic dianhydride: The role of In diffusion
Authors: Hudej Robert , Bratina Gvido
Published: July 2002

Electronic transport measurements of Ag/3,4,9,10-perylenetetracarboxylic dianhydride In/Si(001) heterostructures demonstrate that when the structure temperature approaches the In melting point a current-voltage characteristic changes from rectifying to ohmic. The synchrotron radiation photoemission investigation of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) layers of the same thickness grown on In in the same temperature range show strong In diffusion throughout the PTCDA layers as thick as 1 μm. The formation of In-related coordination compound appears to be limited to the region near the In/PTCDA interface.
Measurement of Vacuum in Nonuniform Temperature Environments
Authors: Moore Boude C.
Published: July 2002

If temperature gradients exist in a high-vacuum chamber, the residual gas may be of nonuniform density and pressure. If the gas is stationary and reflects according to Knudsen's cosine law, then the flux will remain uniform, despite the temperature gradients. Solutions for the density and pressure are given for parallel planes and for concentric spheres. When estimating pressure from a density observation, the maximum uncertainty is the temperature ratio a2. From a flux observation, the maximum uncertainty is only a. These uncertainties may be reduced by knowledge of the geometry and the accommodation coefficients. The variation of density with position is suggested as a method of measuring the kinetic accommodation coefficient.
High-Temperature Insulating Adhesives for Vacuum Applications
Authors: Kendall B. R. F. , Zabielski M. F.
Published: July 2002

Results of experiments with several types of adhesives that withstand bakeout temperatures of 300 °C in vacuum are given. The experiments included measurements of outgassing rates, mass spectra of evolved gases, and electrical and mechanical properties. Certain polyimide and silicone resins were found to have outgassing rates below 10−7 Torr liter sec−1 cm−2 at temperatures up to 155 °C. With the addition of trace amounts of uniform small glass spheres to obtain reproducible electrical characteristics, some of these materials also exhibited good insulating and bonding properties when used to join metal surfaces. Possible applications in the construction of experimental electron devices and other high-vacuum apparatus are discussed.
Factors Affecting the Adhesion of Titanium and Molybdenum Couples
Authors: Johnson K. I. , Keller D. V.
Published: July 2002

Metallic-adhesion experiments reported in the literature have shown that softer metal couples could weld more easily than harder, and that metal couples of hexagonal atomic structure are more difficult to weld than those of cubic structure. Because of the presence of contamination in all of these studies, however, it has not been clear whether these tendencies are intrinsic properties of the metals, or simply due to a difference in the sensitivity of these materials to such contamination. Previous studies by the authors have shown that the principal barrier to adhesion between soft metals at room temperature is due solely to contamination. This work is presently extended to a metal of high hardness, a molybdenum-molybdenum adhesion couple, and to a couple of hexagonal atomic structure, titanium-titanium. Both metal couples were found to be most difficult to prepare with ultraclean surfaces; however, when this was accomplished, cold welding was observed at room temperature to approximately one-half the bulk strength of titanium and one-quarter of the bulk strength of molybdenum, respectively. The greater difficulty encountered when pressure welding harder metals or couples of hexagonal atomic structures, was shown to be due to contamination effects, and is not an inherent property of these materials. A few atomic layers of contaminant are sufficient to prevent adhesion of these metals under lightly loaded conditions. Contact resistance has been demonstrated as a useful tool for the estimation of the degree of cleanliness of the metal surfaces.
Adsorption Of Nitrogen, Hydrogen, Oxygen, and Carbon Monoxide on a Beryllium Film
Authors: Hurd J. T. , Adams R. O.
Published: July 2002

Results of measurements of sticking coefficients of nitrogen, hydrogen, oxygen, and carbon monoxide on beryllium thick films at room temperature are described. Beryllium was vapor deposited onto glass substrates and the sticking coefficient of the impinging gas molecules was measured as a function of quantity adsorbed. No adsorption was observed with either nitrogen or hydrogen. A sticking coefficient of 0.4 for oxygen was measured with a total coverage of 8.4×1014 molecules/cm2. Carbon monoxide displayed some pressure dependence and the initial sticking coefficient was found to be roughly proportional to the square root of the pressure. In the 10−8 Torr range a sticking coefficient of 0.1 was measured with a total coverage of 4.0×1013 molecules/cm2; in the 10−7 Torr range a sticking coefficient of 0.5 was measured with a total coverage of 2.4×1014 molecules/cm2.
Studies on the Al2O3−Ti−Mo−Au metallization system
Authors: Harris J. M. , Lugujjo E. , Campisano S. U. , Nicolet M.−A. , Shima R.
Published: July 2002

The behavior of Ti−Mo−Au metallization on Al2O3 and C has been investigated by backscattering spectrometry. Results show that Mo−Au bimetal films typically mix during deposition. Diffusion of Ti in Mo film occurs at 600°C, but is inhibited by the presence of oxygen in the Ti film. Even 1000 Å of Mo is not a barrier against interdiffusion of Ti and Au during 20−min anneals at 600°C. The amount of mixing observed also depends on the nature of the substrate which supports the Ti−Mo−Au metallization.
Search for preferential sputtering in Ag/Au alloys
Authors: Nelson G. C.
Published: July 2002

Sputtering yields from AgxAu1−x alloys were obtained by 20Ne+ ion scattering spectroscopy in order to detect preferential sputtering effects. Selective sputtering and concomitant enrichment of the sputtered surface was not observed, implying that the ion yield does not change with alloy composition. (AIP)
Probing surface properties with adsorbed metal monolayers
Authors: Rhead G. E.
Published: July 2002

Many methods for investigating surfaces are sensitive to a layer several atoms deep. It is difficult to distinguish the separate contributions from successive layers. One approach to the study of a single atomic surface layer of a metal is to look at epitaxial adsorbed metal overlayers. Some results from this approach and the prospects for ’’two-dimensional metallurgy’’ are surveyed. The following topics are included: the existence of adsorbed metallic monolayers from thermodynamic and kinetic considerations; surface diffusion; the structure and composition of adsorbed metallic monolayers examined by LEED and AES; melting and solid–solid phase changes; surface alloying and binary monolayers; surface defects and implications for clean surface behavior.
Mechanism of high-temperature instability of CuO–Ag thin-film solar absorbers
Authors: Blattner R. J. , Evans C. A. , Braundmeier A. J.
Published: July 2002

The thermal instability of CuO–Ag tandem thin-film solar absorbers above 400°C has been investigated using Auger electron spectroscopy, scanning electron microscopy, energy-dispersive x-ray analysis, and optical reflectivity measurements. A Cu layer on a Ag film supported by a glass microscope slide and thermally oxidized at 380°C to form CuO is shown to be capable of reliably producing a solar absorber with a room-temperature ratio of solar absorptivity to infrared emittance (a/ε) of about 20. During oxidation, holes form in the Ag film resulting from the growth of precipitates in the Cu layer. During extended heat treatment at 540°C, Ag migrates toward the surface from where it vaporizes into the ambient. A heat treatment of ∠ 20 days at this temperature leads to the complete loss of Ag without an appreciable loss of CuO film adhesion, at which point the optical properties have degraded to those observed for CuO on glass. Sputtering artifacts, such as cone formation, observed during Auger depth profiling, are discussed. A qualitative mechanism describing the processes leading to changes in microstructure and composition is presented, along with a discussion of the impact of these chemical and morphological changes on the optical properties.
Chemisorbed phases of O2 on TiO2 and SrTiO3
Authors: Henrich Victor E. , Dresselhaus G. , Zeiger H. J.
Published: July 2002

We have investigated the chemisorption of O2 on TiO2 and SrTiO3 surfaces by using ultraviolet photoemission difference spectroscopy. Both nearly perfect surfaces and surfaces having a high density of defects associated with filled Ti(3d) surface states were studied. On all surfaces low O2 exposures produced an initial adsorbed phase, with a sticking coefficient of 0.2–1, that yields a difference spectrum consisting of two peaks separated by 2.5 eV. The location of these peaks corresponds closely to the valance-band photoemission structure of the substrate, suggesting that the chemisorbed phase consists of O2− ions. For surfaces having initially filled Ti(3d) surface states, formation of this phase is accompanied by charge transfer from the substrate. With increasing exposure, a second adsorbed phase, with a sticking coefficient of 10−3 or less, is formed on some surfaces. This phase exhibits a sharp peak about 2 eV below the bottom of the substrate valence band and a broad peak overlapping the valance band.
Atomic and electronic structure of semiconductor surfaces
Authors: Pandey K. C.
Published: July 2002

The electronic structure of surfaces, which can be determined by various electron/ion spectroscopies including ultraviolet photoemission spectroscopy (UPS), is dependent on the surface atomic geometry. Thus, it is possible to determine the surface atomic structure via structure-dependent theoretical analyses of these experimental spectra. Because of the complexity of such systems, a simple but accurate theoretical scheme is required. We show that the valence electronic states and atomic structures of semiconductor surfaces—both clean and with chemisorbed species as well as relaxed and/or reconstructed—can be determined using a tight-binding model. Such calculations together with UPS data show that the annealed Si(111)7×7 surface contains about 25% vacancies. For GaAs(110), we have found tha the Ga atoms move into, and As atoms move out of the surface with small bond length distortions so that a plane through them makes an angle of about 20° with the surface. We show that H chemisorbed on Si(111) has two distinct structural phases: a monohydride phase at low coverages, and a rather unexpected trihydride phase at high coverages.
Fabrication of integrated injection logic using e-beam lithography
Authors: Evans S. A. , Bartelt J. L. , Sloan B. J. , Varnell G. L.
Published: July 2002

Integrated injection logic (I2L) gates have been fabricated using electron-beam lithography, ion implanatation, and advanced I2L design technology. Minimum line widths of 1.25 μm were used to delineate structures five times smaller in area than obtained with conventional design rules. Improved geometry control was achieved by using shallow diffusions and thin epi (∠1.2 μm). PBS positive resist was used to pattern and etch oxides and TI309 negative resist was used to mask etching of Al/Si and Al/Cu metallizations. Thick PMMA was used as an implant mask for 300-keV p− intrinsic base implant. Chip-by-chip alignment of 2.5×2.5 mm2 fields yielded level to level registration accuracy of 0.2–0.4 μm. Using a 25-stage ring oscillator as a test vehicle, gate delays of ∠6 ns at 100 μA/gate have been measured on 5-collector, n+ guard ring device structures. These devices also yielded a speed–power product five times lower than that of similar conventionally sized devices.
Simultaneous measurement of weight and torque in controlled atmospheres by magnetic suspension
Authors: Gast Th. , Koppe K.
Published: July 2002

Experiments exist where a vertical force, for instance the weight of a sample, and a torque caused by a certain physical effect, have to be measured simultaneously. Examples are the determination of molecular weight according to Knudsen or the simultaneous measurement of permittivity and dielectric loss of very small samples. Such measurement may be carried out with the aid of free magnetic suspension in the following way: A horseshoe magnet with poles turned upward is suspended beneath a second one, whose poles point downward. The distance between the mutually attracting poles is kept constant by automatic control. The lower magnet carries two vanes of copper sheet, aligned in a horizontal plane, which are in the sensitivity range of four symmetrically arranged inductive sensors, fixed to the upper magnet. The sensors are connected in a Wheatstone bridge in such a manner, that the distance and angular position of the vanes can be measured simultaneously. The signal for the distance is compared with a reference signal and the deviation causes a controlling current through a winding on the upper magnet. In equilibrium, this current is a measure of weight or other vertical forces acting on a sample, which is attached to the lower magnet. Because of the quasielastic behavior of the magnetic lines of forces, the signal for angular deflection is a measure of torque. Preliminary results are shown.
Diffusion studies of Au through electroplated Pt films by Auger electron spectroscopy
Authors: McGuire G. E. , Wisseman W. R. , Holloway P. H.
Published: July 2002

Diffusion of gold through thin films of electroplated platinum was studied using Auger electron spectroscopy. Platinum is widely used for the Schottky barrier metallization on GaAs IMPATT and varactor diodes with gold being used to contact the platinum. The effects of gold diffusion through platinum into the active semiconductor region could lead to long term reliability problems for diodes operated at elevated temperatures. Diffusion anneals in the temperature range from 750 to 900 K were carried out in an ultrahigh vacuum system while the surface sensitivity of Auger spectroscopy was utilized to monitor surface compositional changes. A grain boundary mechanism is proposed for the diffusion of Au through the 0.55-μm electroplated Pt films. The effective grain boundary diffusion constant for Au in the thin Pt films, Db=0.18 exp  (−1.65 eV/kT) cm2/s, was determined by a time-of-penetration test which accounts for bulk diffusion. This diffusion coefficient differs from others in the literature due to K and Sb impurities in the grain boundaries.
Interfacial behavior of Cr–Au films in the 423–573-K temperature range
Authors: Hampy R. E. , Yost F. G. , Ganyard F. P.
Published: July 2002

Thin film layers of Cr–Au were subjected to temperatures in the range 423–573 K for various periods of time and the morphology of the Cr layer was examined with optical and scanning electron microscopy. A preferential depletion of Cr was found beneath the Au grain boundaries and intergranular spaces which was not fully compensated by diffusion of Au into the Cr. Since the Au grain boundaries intersect, this results in islands of remaining Cr surrounded by a labyrinth of voids or channels. This phenomenon renders the entire Cr–Au interface vulnerable to the entry of corrosives. By using transmission optical microscopy in conjunction with a photometer, the optical transmission of the Cr layer was measured and related to the Cr depletion as a function of time and temperature. From these measurements two mathematical models were devised to calculate the activation energy for the Cr diffusion resulting in values of 1.30 and 1.36 eV, respectively.
Influence of atomic mixing and preferential sputtering on depth profiles and interfaces
Authors: Liau Z. L. , Tsaur B. Y. , Mauer J. W.
Published: July 2002

Atomic mixing and preferential sputtering impose a depth resolution limit on the use of sputter sectioning to measure the composition of metal–semiconductor interfaces. Experimental evidence obtained with the Pt–Si system is used to demonstrate ion-induced atomic mixing and then its effect on sputter etching and depth profiling. Starting with discrete layer structures, a relatively low ion dose (≳3×1013 cm−2) first produced a mixed surface layer with thickness comparable to the ion range. Higher ion doses then result in successive sputter etching and continual atomic mixing over a constant surface layer thickness. A model is developed that is based on a sputter removal (including preferential sputtering) of atoms at the surface and a uniform mixing of atoms over a constant thickness. The model predicts the influences of atomic mixing and preferential sputtering on the depth profiling of thin-film structures and interfaces.
Oxide formation on ruthenium observed by TDS and ESCA
Authors: Klein Ralph , Siegel Roy , Erickson Nils E.
Published: July 2002

Oxygen adsorbed at room temperature on a Ru(101̄0) surface shows a single peak in its thermal desorption curve, the peak maximum shifting to lower temperature with higher initial concentration in accordance with second order kinetics. Additional peaks in the thermal desorption spectrum of oxygen from Ru(101̄0) were observed after exposure of the ruthenium above 600 K to oxygen. These peaks, desorbing with first order kinetics, are attributed to oxide formation. The change in the size of the peaks with respect to the temperature of the surface during oxygen exposure is correlated with an oxygen sticking coefficient that is constant up to 850 K and decreases thereafter. The ESCA spectrum of a surface with the ’’oxide’’ showed an increase in the height of the 0(1s) peak but no chemical shift. Sulfur adsorbed on Ru(101̄0) prevents the adsorption of oxygen.
Electronic surface resonance band structure and lineshapes
Authors: McRae E. G.
Published: July 2002

Electronic surface resonances are quasistationary surface states at energies above the vacuum level. They may be observed as narrow intensity fluctuations in LEED and other electron scattering experiments. A survey of recent developments in the measurement and interpretation of low-energy surface resonance band structure E (k∥ (E = resonance energy, k∥ = reduced surface-parallel momentum) is presented. The importance of analyzing resonance lineshapes for accurate determination of resonance levels is emphasized, and high-resolution LEED data for W(001) surface is analyzed as an example.
Preferential sputtering in gold–nickel and gold–copper alloys
Authors: Tompkins H. G.
Published: July 2002

The preferential sputtering of three alloys of gold and nickel and five alloys of gold and copper is studied. Binary alloys containing 6–26 at. % nickel and 6–57 at. % copper were used. Samples were scribed in situ to avoid the complication of a surface oxide film. For Ni/Au with an ion energy of 1 keV, the gold was sputtered preferentially leaving a nickel-enriched surface. For the 6% alloy the amount of enrichment was somewhat less than is predicted from pure element sputter yields, whereas for the other two alloys the enrichment is slightly higher than predicted. The thickness of the altered layer appears to be in the 50–75 Å range. For Cu/Au, very little preferential sputtering was observed.
Isothermal ramped field-desorption of benzene from tungsten
Authors: Panitz J. A.
Published: July 2002

The binding of molecular benzene on clean (field-evaporated) tungsten surfaces at 78 K has been investigated as a function of electric field strength using a new ramped field-desorption technique. The resulting spectra, analogous to total pressure thermal desorption spectra (which do not mass analyze the desorbing species), show a physisorbed structure below 0.36 V/Å which increases continuously in area with increasing benzene coverage, a peak at 0.36 V/Å which grows until a saturation coverage is reached (and is thought to represent a physically adsorbed transition layer between chemisorbed and multiple layer physisorbed benzene at the surface), and a series of poorly resolved chemisorbed peaks (between ?0.38 and 1.13 V/Å) whose detailed shape depends on the local morphology of the surface region being examined. By recording the image of the desorbing species over the narrow field ranges which define these distinct features, the crystallographic behavior of the physisorbed and chemisorbed layers on the surface has been visually determined with angstrom resolution.
Atomic structure of clean and arsenic-covered GaAs(110) surfaces
Authors: Mrstik B. J. , Tong S. Y. , Van Hove M. A.
Published: July 2002

During the past few years there have been several LEED studies to determine the atomic structure of the clean GaAs(110) surface. The LEED data have been analyzed by comparison to both kinematical and dynamical theories, and several different structures have been reported. These structures have ranged from a surface which is unreconstructed to a surface which has the As atoms tilted outward with a tilt angle of 34.8°. We have recently compared our data to results of dynamical calculations and have determined that the best structure has the As atoms rotated outward with a tilt angle of 27°, a Ga to second layer spacing of 1.452 Å, and back bonds which are slightly contracted. Differences between this structure and previously reported structures are discussed. We also present preliminary results of our LEED studies on the bonding of an As monolayer to the GaAs(110) surface. We find that the As atoms remove the reconstruction of the clean substrate and adsorb on sites which continue the bulk structure.
EXAFS studies of the bonding geometry of oxygen on Si(111) using electron yield detection
Authors: Stöhr J. , Johansson L. I. , Lindau I. , Pianetta P.
Published: July 2002

Surface extended x-ray absorption fine structure (EXAFS) measurements are reported above the O K absorption edge (∠535 eV) for oxygen chemisorbed on Si(111). For the investigated initial oxidation stage—characterized by a Si 2p chemical shift of 2.5 eV—we find the O–Si bond length to be closely the same (within 0.05 Å) as in bulk SiO2. Comparative analysis of the relative EXAFS amplitude with that for SiO2 provides information on the oxygen bonding geometry on the Si(111) surface.
Speed enhancement of PMMA resist
Authors: Moreau W. , Merritt D. , Moyer W. , Hatzakis M. , Johnson D. , Pederson L.
Published: July 2002

The enhancement of the electron beam sensitivity of PMMA from 10−5 C/Cm2 to the 10−6 C/cm2 range has been achieved by incorporation of 15 mol % methacrylic anhydride (MAN) groups into the polymer chain. The MAN group is introduced by cyclization of a copolymer of PMMA–MA (poly methyl methacrylate–methacrylic acid) into a terpolymer of PMMA–MA–MAN of 70/15/15 mol % composition. The terpolymer retains all of the exemplary properties of PMMA; high resolution, excellent adhesion, ease of processing and process versatility. The resist has been used for lift-off metallurgy deposition, chrome mask fabrication, and for wet and dry etching of insulators. The enhancement of the sensitivity is primarily due to the higher chain scission and gaseous product formation. The incorporation of the anhyride group also increases the thermal stability of PMMA from 135° to 175°C.
Photoemission method for the study of surface kinetics: CO on Mo(100)
Authors: Semancik S. , Estrup P. J.
Published: July 2002

Using a photoelectron spectrometer, a technique has been developed to continuously monitor changes that may occur in an adlayer when heated. After identifying adsorbate-induced features in UV photoemission (UPS) spectra from a chemisorption system, the intensities of individual features are recorded as a function of temperature and/or time. Kinetic parameters can be extracted from the rates of these intensity changes. The thermally activated decomposition of CO on Mo(100) has been used to demonstrate the technique here. Preliminary results show that this process does not obey simple first-order kinetics. Analysis of isothermal data gives a coverage-dependent dissociation activation energy with Edis?0.60 eV for 0?0.5, and a frequency factor near 1013 s−1.
Computer-automated measurement of high-temperature vapor pressures by the simultaneous Knudsen torsion-effusion method
Authors: Thompson H. Bradford , Edwards Jimmie G.
Published: July 2002

Data acquisition from high-temperature vapor-pressure measurements by the simultaneous mass-effusion, torsion-effusion method has been automated by interfaces to a laboratory computer. The apparatus consists of a torsion-effusion pendulum suspended from a vacuum semimicrobalance. Rate of mass effusion is monitored by an analog interface to a retransmitting potentiometer on the chart recorder of the semicrobalance. Torque is measured by a digital interface to an array of photodetectors which register the torsion-pendulum position by a reflected-light method. Output from the balance is handled by one channel of an analog multiplexer and an analog-to-digital converter (ADC). The output from the ADC and the output from the torsion pendulum are fed to two channels of a digital multiplexer. With stored information about the torsion pendulum and the effusion cell, the computer calculates real-time vapor pressures from both simultaneous measurements, and then the apparent molecular weight of the vapor. Early results from study of the vapor pressure over PbIn2S4(s)/Pb2In6S11(s) are presented.
Quantitative examination of individual atomic events on solids
Authors: Ehrlich Gert
Published: July 2002

The behavior of individual atoms on solids has long been of interest for understanding the physical and chemical properties of surfaces. Now, through the use of the field ion microscope, it is possible to directly image single atoms on metal surfaces and to examine their properties quantitatively. Such studies are reviewed, with special emphasis on: (1) surface structure and its effect on diffusion; (2) the details of the jump process; (3) interactions between atoms leading to cluster formation; and (4) the properties of clusters.
Glow discharge mass spectrometry of sputtered tantalum nitride
Authors: Aita C. R. , Myers T. A. , LaRocca W. J.
Published: July 2002

It is well known that the properties of reactively sputtered thin films of tantalum nitride are dependent upon the partial pressure of N2 in the sputtering gas. In this study, a Ta target was rf diode sputtered using various Ar/N2 gas mixtures. Glow discharge spectrometry was used to monitor the positive ions present in the sputtering plasma. Electrical and x-ray diffraction measurements on the resulting films related their crystallography and resistivity to the composition of the plasma, in particular to the relative number of Ta and TaN ions. The results are discussed in terms of the change in the target surface with increasing N2 partial pressure.
Optically enhanced oxidation of semiconductors
Authors: Schafer S. A. , Lyon S. A.
Published: July 2002

An increase in the oxidation rate of Si has been observed during thermal oxidation accompanied by optical excitation with visible laser light. The enhancement of the oxidation rate is approximately 60%, and is believed to arise from two sources: simple heating by the laser beam, and a direct nonthermal effect of the laser light. The calculated temperature rise is not large enough to fully account for the observed rate increase, and the experimental data are in agreement with calculations based upon a model of optical carrier generation and resultant bond breaking in the Si near the Si–SiO2 interface. An increase in oxidation rate has also been observed in GaAs and InP. The degree of enhancement obtained in these materials is greater than in Si, and provides further evidence of a nonthermal optically-excited process. The GaAs oxide contains a relatively high As2O3 concentration (∠10%) near the outer surface.
Mutual repulsion effects in a high throughput e-beam lithography column
Authors: Groves T.
Published: July 2002

A fundamental limit on the current obtainable in an electron beam writing system is set by the mutual repulsion of beam electrons. Computer Monte Carlo simulations of the electron beam take into account the essential physical properties, which are discreteness of the charge, the random nature of the problem, and the many-body aspect. A Monte Carlo simulation has been used as a design tool for a high throughput lithography system at Hewlett-Packard. The column, which is in successful operation, is capable of 0.6 μA of current in a 0.5 μm spot at 20 kV. This resolution is maintained over a 5 mm square deflection field. Beam broadening effects are described for both the field emission source region and the column. The energy broadening of 1.5 eV is determined mainly within the first 0.1 mm near the source, with less than 15 percent increase in the remainder of the column. The major beam broadening is caused by transverse repulsion, which acts over the entire 41.5 cm long column.
Electron energy loss spectroscopy of adsorbed atoms
Authors: Black J. E. , Rahman Talat S. , Mills D. L.
Published: July 2002

This paper explores the vibrational properties of atoms and ordered overlayers on the surface of nickel metal with emphasis on contact with recent studies of these systems by the method of electron energy loss spectroscopy (EELS). We obtain a good account of data on these systems, within the framework of a lattice dynamical model that is simple but which contains no adjustable parameters. The force constant which couples the adsorbate atoms to the substrate is deduced from the ab initio studies of adsorbate/substrate interactions reported by Upton and Goddard. We present results of studies of the spectrum of vibrational frequencies of isolated adatoms, and of the p(2×2) and c(2×2) overlayer of O on the Ni(100) surface.
Understanding core–valence–valence Auger line shapes
Authors: Jennison Dwight R.
Published: July 2002

Core–valence–valence (CVV) Auger spectroscopy can now be used as a local valence probe of molecular, chemisorbed and solid-state species. Analysis of Auger data has led to the discovery of localized multihole valence excitations in covalent systems, and there is evidence that these excitations may play a major role in the dissociation of large molecules and in stimulated desorption from semiconductor surfaces. The basic physics behind the CVV decay is summarized. The relative importance of factors that influence the decay amplitudes (local charge density, initial-state screening, valence nonorthogonality, and configuration mixing) and the Auger energies (independent vs coupled final-state holes) is explored.
Change in surface polarizability of Mo(100) with oxidation measured by XPS of physisorbed xenon
Authors: Henry R. M. , Fryberger T. A. B. , Stair P. C.
Published: July 2002

The polarizability of a Mo (100) surface has been characterized as a function of surface oxidation using XPS measurements of the extra-atomic relaxation energy EPER in physisorbed xenon. The clean and oxidized molybdenum surfaces as well as the physisorbed Xe were prepared and characterized in UHV by XPS. To unambiguously obtain the Xe relation shifts, we have measured the change in the Auger parameter, Δα, between gas phase and physisorbed Xe (α = Auger kinetic energy minus core level photoelectron kinetic energy). The Auger parameter allows a separation of initial state potential changes from final state relaxation changes. The xenon EPER decreases from 2.55 eV on the clean surface to 1.95 eV on a surface with 1.3 ML of oxygen atoms incorporated into the surface region to 1.8 eV on a MoO2 surface. The decrease in EPER is attributed to a decreased surface polarizability due to a reduction in the conduction band electron density. In contrast, the local electrostatic potential at the xenon adsorption site increases by 3.05 eV and most of the increase accompanies the incorporation of the first monolayer of oxygen atoms. This increase is attributed to a contraction of the surface dipole layer.
Estimation of surface charge densities for low-energy atom diffraction
Authors: Haneman D. , Haydock Roger
Published: July 2002

For purposes of comparing models of surface atomic structure with atom diffraction data, it is proposed that the surface of critical charge density for atom scattering be obtained from the superposition of atomic charge densities. The results of this method, which has the advantage of permitting fast calculation for many structures, including complex ones, are compared with the self-consistent calculations of Hamann for GaAs(110) and Ni(110). The method is then applied to the Si(111) surface and used to illustrate the effects of atom shifts on corrugations of the surface of critical charge density.
The fabrication and use of silicon and gallium arsenide ion source extraction grids
Authors: Speidell J. L. , Harper J. M. E. , Cuomo J. J. , Kleinsasser A. W. , Kaufman H. R. , Tuttle A. H.
Published: July 2002

This paper describes the fabrication and use of silicon ion source extraction grids. Ion beam processing is dependent upon the extraction grid design and materials since the stability of the beam characteristics depends upon the stability of the grids. Conventional ion source extraction grids are produced using mechanical methods and have several disadvantages, including cost and distortion. A procedure is presented here for fabricating silicon grids using microelectronic fabrication methods. Designs for producing collimated, diverging or focused beams, and a fine mesh single grid configuration suitable for low energy operation are described. Beam profiles and performance are presented. Extraction grids of gallium arsenide have also been prepared, and their fabrication is described.
The Si(111)/Cu interface studied with surface sensitive techniques
Authors: Rossi G. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

The formation of the Cu/Si interface is described on the basis of joint photoemission (valence band and Si 2p core levels) and Auger lineshape (SiL2,3VV) analysis. The system is characterized by an extended mixed phase where a silicidelike compound of average stoichiometry Cu3Si is formed and appears to be stable for an extended range of Cu coverages and annealing temperatures. The intermixing is strongly temperature dependent, but the chemical reaction between Cu and the top layers of Si can proceed even at 100 K.
The effects of adsorbed sulfur on the adsorption and reaction of CO and methanol on Ni(100)
Authors: Madix R. J. , Lee S. B. , Thornburg M.
Published: July 2002

The surface coverage of sulfur on Ni(100) was varied between 0 and 8.0×1014 atoms/cm2 in order to quantify its effect on both CO adsorption and CH3OH dehydrogenation as studied by temperature-programmed reaction spectroscopy. At a sulfur coverage of ns=4.8×104 atom/cm2 the CO desorption peak characteristic of clean Ni(100) was extinguished and was replaced by two distinct peaks at lower temperature (β1 and β2). Also at this coverage the methoxy intermediate became stable above room temperature, and the dehydrogenation selectivity shifted toward H2CO. At θs=0.38 only partial dehydrogenation of CH3OH to H2CO and H2 occured, and the amount of H2CO formed was maximized. It was found that CO preadsorbed into fourfold hollow sites poisoned the partial dehydrogenation in a one-to-one fashion by blocking formation of adsorbed methoxy intermediates. The results also indicate that short range interactions between adsorbed CO and S are not responsible for the sharp decrease in the saturation coverage of CO at low concentrations of adsorbed atomic sulfur.
The structure of atomic oxygen and carbon overlayers on the Mo(001) surface studied by low energy ion scattering
Authors: Overbury S. H. , Stair P. C.
Published: July 2002

The bonding geometry of atomic overlayers composed of submonolayer quantities of pure oxygen, pure carbon, and a mixture of carbon and oxygen on a Mo(100) surface has been studied for the first time by low energy angle-resolved K+ and Li+ ion backscattering. The surface composition and long range ordering of the clean and adsorbate-covered surfaces were also characterized by Auger and LEED. The overlayers were generated in UHV by dissociative adsorption of O2 or CO or by thermal cracking of C2H4 on the clean Mo(100) surface. The absence of double scattering along the [110] direction for the oxygen overlayer compared to the clean surface indicates that the oxygen atoms are located in fourfold hollows on the surface. This is confirmed by Monte Carlo simulations of the K+ scattering. Li+ scattering results corroborate this structural model. The K+ scattering energy distributions from pure carbon and mixed carbon/oxygen overlayers are very similar to the oxygen overlayer suggesting that carbon is also situated in the fourfold hollow.
New insights from electron spin polarization studies of surfaces
Authors: Pierce D. T. , Celotta R. J.
Published: July 2002

Examples of recent investigations in several laboratories, where measurement of effects due to electron spin polarization provided new insight into surface phenomena, will be reviewed. The results to be discussed include the use of spin dependent electron scattering to determine the surface potential barrier, the magnetic critical behavior of a semi-infinite solid, and the low temperature surface magnetization. Examples from spin-polarized photoemission include studies of the nature of the resonant 6 eV satellite in Ni and of oxygen-induced magnetism in a Cr(100) surface. The use of angle-resolved spin-polarized inverse photoelectron spectroscopy to obtain information on spin dependent band structure of unoccupied states will also be described. The rapid growth of measurements involving electron spin polarization, where previously only electron energy or momentum was measured, is explained by the development of new experimental techniques like the GaAs spin-polarized electron source and advances in spin polarization detectors.
Structural models for Si(111)-(7×7)
Authors: Himpsel F. J. , Batra Inder P.
Published: July 2002

A class of structural models is studied for the Si(111)-(7×7) surface which is consistent with scanning tunneling microscopy (STM) results. The hills observed with STM are identified with trimers that are formed by bond flipping. The valleys correspond to boundaries between differently stacked triangular areas. Atoms with broken bonds are removed along these boundaries. A modified Keating strain calculation is used to determine the orientation of the trimers and to obtain accurate atomic positions. The trimer models exhibit large atomic displacements perpendicular to the surface accompanied with small parallel displacements in qualitative agreement with Rutherford backscattering results. The structural changes upon hydrogenation of Si(111)-(7×7) are explained by a reversal of the bond flip whereby the stacking is not altered.
The electronic structure of c(2×2)S/Fe(100): S 3p-level dispersions and linewidths
Authors: DiDio R. A. , Plummer E. W. , Graham W. R.
Published: July 2002

The electronic structure of segregated c(2×2)S/Fe (100) has been determined using synchrotron radiation and angle-resolved photoemission. In addition to mapping the S 3p-derived energy bands, the line shapes of the S photoemission features were correlated to their surface Brillouin zone (SBZ) position. The dispersions of the bands derived from in-plane S 3pxpy levels are induced by S–S interactions, and are well described by a tight-binding model. The S 3pz-derived band is anomalously wide (1.2 eV) compared to the tight-binding width, which is a substrate-induced effect. The line shape variation of the S photoemission features along a particular band is a dramatic function of SBZ position, and is directly related to the presence of projected Fe sp levels at the same k∥. These linewidth variations match the predictions of Liebsch for c(2×2)O/Ni (100), and indicate that the S(3pz)–Fe(sp) interaction is a principal component of the S–Fe bond on Fe (100). Thus, the correlation of the k∥ dependence of adsorbate level dispersions and linewidths provides new information about the bonding character of chemisorption systems.
Rare gas titration studies of Si(111) surfaces
Authors: Demuth J. E. , Schell-Sorokin A. J.
Published: July 2002

Ultraviolet photoemission (UPS) measurements of the coverage-dependent electron binding energies of adsorbed argon and xenon atoms on Si(111) surfaces are used to obtain surface structural information. We distinguish three submonolayer types of adsorption sites on Si(111)-7×7 which fill sequentially and whose coverage relative to a full monolayer are determined with UPS: an initial site (∼4%), a majority site (∼76%), and another minority site (∼20%) which fills last. These results exclude most structural models for the 7×7 but are consistent with recent vacuum tunneling micrographs and the structure proposed by Binnig and Rohrer. The sensitivity of rare gas UPS binding energies to other structural differences induced by impurities, laser annealing, and sputtering are described.
Perspectives on residual gas analysis
Authors: Lichtman D.
Published: July 2002

The advent of ultrahigh vacuum in the late 1940’s led to the rapid development of specialized mass spectrometers for the analysis of the gas composition in high vacuum systems. These devices, generally referred to as residual gas analyzers or partial pressure analyzers, have now become almost as prevalent as ionization gauges, and in many instances much more important. A short review of the early types will be presented, and the reasons for the discontinued use of most of them will be discussed. Details of the two instruments currently in dominant use, namely the magnetic sector and the quadrupole, will be presented. Typical applications will be considered. The present status and future directions of partial pressure analyzers will be evaluated.
Water adsorption on cleaved silicon surfaces
Authors: Schaefer J. A. , Anderson J. , Lapeyre G. J.
Published: July 2002

High-resolution electron-energy-loss spectroscopy together with x-ray photoelectron spectroscopy and low energy electron diffraction are used to study water adsorption on the cleaved 2×1 surface of Si. Adsorption studies at both 100 and 300 K were performed. At 300 K and during initial adsorption at 100 K the water is adsorbed principally by forming a dissociated chemisorption structure containing hydroxyl and hydride groups. At 300 K this phase saturates at low coverages, with a (1×1) LEED structure while at 100 K the sample will adsorb additional water. For exposures from about 1/3 to 2 L at 100 K an intermediate transitional adsorption layer forms which contains both molecular water and chemisorbed lines. Larger exposures form multiple layers of water (ice) and exhibit the loss features that have been reported for ice on other faces of Si. Very high resolution, about 5 meV, was achieved during the 300 K adsorption studies, allowing the identification of a small amount of molecular water. These phenomena for the cleavage face are quite complex and are different than those previously observed for water adsorption on the (100) surface where the 300 K adsorption consists simply of the dissociation of the water into the hydroxyl and monohydride species with no evidence for molecular water adsorption. In the latter case the adsorption is attributed to bonding with the dangling bonds. The adsorption on the cleavage surface is more disruptive of the surface, as evidenced by the observation of the dihydride species and the relaxation of the π-bonded chain structure characteristic of the cleaved surface into a more bulklike (1×1) structure.
Film and interstitial formation of metals in plasma-sprayed ceramics
Authors: Hendricks R. C. , McDonald G. , Mullen R. L.
Published: July 2002

A method is described to electrodeposit noble metals such as platinum and ordinary metals such as copper on and within plasma-sprayed ceramic materials and ceramic fiber materials. Low-density ceramic fiber bodies were vacuum impregnated with plating solution and attached to an electrode. Light micrographs illustrating the density and location of deposited materials are presented and discussed. Voids in the plasma-sprayed ceramic were filled with deposits that vary from spherical to lens-shaped acircular and have particle size corresponding to the full range of void size. Multiple coatings of ceramic and metal can be sequenced.
Laser-induced chemical vapor deposition of titanium silicide films
Authors: West G. A. , Beeson K. W. , Gupta A.
Published: July 2002

Films of titanium silicide have been deposited from gas mixtures of SiH4 and TiCl4 using laser irradiation to initiate chemical vapor deposition. Two different laser excitation sources have been used. A CO2 laser initiates deposition through the thermal decomposition of silane, whereas an ArF excimer laser causes deposition by the photolytic dissociation of titanium chloride. Both methods permit control of the substrate temperature independently from the reactor gas temperature. The substrate temperature has been found to strongly influence the resulting titanium silicide film morphology and crystal structure. The different chemistries initiated by the CO2 and excimer lasers have much less influence on the final film properties. Smooth films with a resistivity of 20 μΩ cm are obtained with either method by depositing the films at a low substrate temperature (400 °C) followed by an annealing step at elevated temperature (650–800 °C).