bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and properties of dc-sputtered IrO2 and Ir thin films for oxygen barrier applications in advanced memory technology
Authors: Pinnow C. U. , Kasko I. , Dehm C. , Jobst B. , Seibt M. , Geyer U.
Published: July 2002

IrO 2 and Ir thin films have been deposited by dc sputtering in Ar/O2- and pure Ar atmospheres, respectively. The microstructural characterization of the films was done by x-ray diffraction and transmission electron microscopy and showed that (nano-)crystalline Ir and IrO2 films with different textures could be deposited. Stress analyses showed that the stress of the Ir films can be varied from about −3.5 GPa for a deposition temperature of 100 °C to nearly zero stress if deposited at 500 °C. However, IrO2 films generally exhibited a large compressive stress of about −1.5 GPa, which is nearly independent of substrate temperature, but changed with texture and stoichiometry of the films. Surface and roughness analyses of the cumulatively annealed samples were performed by various analysis methods, and stoichiometry was examined by Rutherford backscattering spectrometry. In situ stress measurements were used to investigate the stress relaxation behavior of the films up to 900 °C. We demonstrate that it is generally possible to optimize reactive IrO2 sputter deposition by a detailed study of plasma and deposition conditions via recording generic curves for the sputtering system used. At optimized conditions these fine grained IrO2 films exhibit very high thermal phase stability to at least 800 °C for several hours and a very low roughness. The aim of these investigations is to optimize stability of IrO2 films under high temperature conditions for oxygen barrier application in dynamic random access memory and nonvolatile Fe random access memory cells.
Fabrication of nanohole array on Si using self-organized porous alumina mask
Authors: Shingubara Shoso , Okino Osamu , Murakami Yasuhiko , Sakaue Hiroyuki , Takahagi Takayuki
Published: July 2002

Formation of the ordered array of nanoholes on Si was investigated by the use of the self-organized porous alumina nanoholes array etching mask that is directly formed on the Si substrate by sputtering and subsequent anodic oxidation. Reactive ion etching using chlorine plasma against a porous alumina/thin-SiO2(10 nm)/Si substrate with a high self-bias of rf plasma was revealed to be very effective for pattern transfer to Si. After pattern transference a significant reduction of hole size was observed. In fact, the initial porous alumina hole size of 45 nm is reduced to 13 nm Si holes when the higher aspect ratio of porous alumina nanoholes mask is used. The etching characteristics strongly suggest that not only chemical etching but sputtering occurred, and that redeposition of nonvolatile materials in nanoholes plays an essential role in the reduction of the hole size.
Current and future ferroelectric nonvolatile memory technology
Authors: Fox G. R. , Chu F. , Davenport T.
Published: July 2002

Ferroelectric random access memories (FRAMs®) are nonvolatile integrated circuit memories that store data by using the field switchable polarization state of a ferroelectric material. Besides allowing unique applications, FRAM memories are ideal replacements for standard random access memory, erasable programmable read-only memory, and Flash memories due to their fast access speed, low power consumption, extended read/write endurance, and ability to store data without the need for battery backup power. FRAM memories have been mass produced since 1992 and memory densities up to 256 kbit are currently available for purchase. Current applications include smart cards, data collection and storage (e.g., power meters), configuration storage, and buffers. The ferroelectric material at the core of FRAM is perovskite PbZr1−xTixO3 (PZT). Current FRAM cell designs utilize the PZT in a bistable capacitor structure that is integrated with a transistor or a complementary capacitor and two transistors. A review of ferroelectric performance in current memory products will be presented. Recent development has lead to capacitor performance with endurance beyond 1012 read/write cycles and operation at 1.8 V. A roadmap for future FRAM development will be presented.
Modeling and development of a deep silicon etch process for 200 mm election projection lithography mask fabrication
Authors: Dauksher W. J. , Clemens S. B. , Resnick D. J. , Smith K. H. , Mangat P. J. S. , Rauf S. , Ventzek P. L. G. , Ashraf H. , Lea L. , Hall S. , Johnston I. R. , Hopkins J. , Chambers A. , Bhardwaj J. K.
Published: July 2002

Gravitation toward a dry silicon etch process for electron projection lithography (EPL) mask fabrication is beneficial because of the concomitant increase in the available membrane area. In order to help understand the complex Bosch etch process and its dependence upon hardware design and process parameters for scattering with angular limitation in projection election beam lithography (SCALPEL) mask fabrication, a combined equipment and feature scale model has been employed. For case studies such as varying the deposition cycle time or ramping the bias power, computed sidewall profiles from the model deviate from experimental data by only about 5.5%. Given the extreme complexity of the Bosch process, this correlation is considered excellent. The best experimental Bosch etch conditions produce SCALPEL substrates with an effective silicon etch rate of 2.7 μm/min, 6.1% etch uniformity, selectivity to tetraethyl orthosilicate >240:1, and average strut sidewall angles of 87.4°. Introduction of hardware into the chamber results in partially blocking the transport of important etch and polymer deposition species to the wafer, thereby altering the etch and passivation rates. The provided learning is applicable to projection reduction exposure with variable axis immersion lenses format EPL masks as well.
Accuracy evaluation of the point diffraction interferometer for extreme ultraviolet lithography aspheric mirror
Authors: Otaki K. , Yamamoto T. , Fukuda Y. , Ota K. , Nishiyama I. , Okazaki S.
Published: July 2002

We evaluated the accuracy of the point diffraction interferometer, which has been completed at the Atsugi Research Center’s Association of Super-Advanced Electronics Technologies for the precise measurement of extreme ultraviolet lithography optics. To evaluate the absolute accuracy, more precision is required. A pinhole with 0.5 μm diameter was used to generate a near completely spherical reference wave front, and helium gas filled the inside of the chamber to suppress air turbulence. With this apparatus, precision of 0.04 nm root-mean-square (rms) was achieved. Absolute accuracy was evaluated from the measurement of mirror rotation and displacement and an absolute accuracy of 0.17 nm rms was obtained for a spherical mirror with numerical aperture of 0.145. Absolute accuracy was improved to 0.11 nm rms by limiting the numerical aperture to 0.08.
Dislocation structure and relaxation kinetics in InGaAs/GaAs heteroepitaxy
Authors: Lynch C. , Chason E. , Beresford R. , Chen E. B. , Paine D. C.
Published: July 2002

In situ real-time stress monitoring is used to study the kinetics of stress relaxation during molecular beam epitaxy growth of strained thin films of InxGa1−xAs/GaAs. We present measurements of the temperature-dependent relaxation behavior obtained at 443 and 469 °C. To study the relationship between the dislocation structure and the stress relaxation, samples were grown to different thicknesses for transmission electron microscopy (TEM) analysis. The combination of the information from the real-time stress monitoring and observations from TEM provides insight into the mechanisms of stress relaxation.
Annealing effects of aluminum silicate films grown on Si(100)
Authors: Cho M.-H. , Rho Y. S. , Choi H.-J. , Nam S. W. , Ko D.-H. , Ku J. H. , Kang H. C. , Noh D. Y. , Whang C. N. , Jeong K.
Published: July 2002

The annealing effects of the thin aluminum silicate films grown on Si(100) by sputtering method were investigated using various physical and electrical measurements. All the films grown at the temperature of 300 °C using sputtering Al2O3 target show an amorphous structure as examined by x-ray diffraction and transmission electron microscopy. The amorphous structure is maintained up to 700 °C and then transformed to crystalline Al1.7SiO0.15O2.85 or mullite phase above the annealing temperature of 800 °C. The conduction process, charge trapping and detrapping characteristics, and trap charge density in metal–oxide–semiconductor structure are influenced by the annealing temperature. The depth profiling data using x-ray photoelectron spectroscopy show that the properties are closely related to the change of the interfacial layer and chemical state under the high temperature annealing. The breakdown characteristics are degraded after the annealing temperature of 900 °C due to the rapid change of the interfacial layer thickness and chemical state of the silicate layer.
Chemical mechanical polishing of shallow trench isolation using the ceria-based high selectivity slurry for sub-0.18 μm complementary metal–oxide–semiconductor fabrication
Authors: Kim Sam-Dong , Hwang In-Seok , Park Hyung-Moo , Rhee Jin-Koo , Nam Chul-Woo
Published: July 2002

In this article we investigate the effects of chemical mechanical polishing using a CeO2-based high silicon-nitride/silicon-dioxide selectivity slurry on 0.18 μm complementary metal–oxide–semiconductor (CMOS) shallow trench isolation (STI). When high selectivity slurry (HSS) is employed for STI, within-die and lot-to-lot variations of the remaining pad nitride thickness and the field oxide erosion are significantly reduced to ∼150 and ∼400 Å, respectively, which are much smaller than for cases of conventional silica-based slurry. Scratches occupy ∼80% of the total defect in the case of HSS STI polishing, and are minimized by using an optimized in situ filtering method for the slurry. When in situ filtered HSS is used, the gate oxide integrity of 256 million isolated MOS capacitors improves compared to samples prepared by conventional unfiltered HSS slurry. In addition, the level of leakage current for n+/p-well junctions is not affected when in situ filtered HSS is used for STI polishing.
Patterning pentacene organic thin film transistors
Authors: Kymissis Ioannis , Dimitrakopoulos Christos D. , Purushothaman Sampath
Published: July 2002

Organic semiconductors have demonstrated excellent electrical performance, in some cases rivaling inorganic systems in use today. These materials, which are processed at or near room temperature, have attracted considerable interest because they would enable the creation of active circuitry on organic substrates leading to a new generation of displays, rf identification systems, and smartcards. Many of these materials are intolerant to wet processing, however. This has led to a major processing limitation: the lack of a subtractive photolithographic patterning process to define active regions of the semiconductor. This article presents a process which uses a dry organic encapsulant (parylene) as a boundary layer between an organic semiconductor (pentacene) and photolithographic chemicals. Traditional photolithography may then be performed to use a dry etch to pattern the material stack. This process, which is fully subtractive, opens the path to the use of these materials in a wide range of applications.
Comparison of the Trigger Discharge Gauge with an Ionization Gauge and a Partial Pressure Analyzer
Authors: Young J. R.
Published: July 2002

The trigger discharge gauge has been compared with a thoroughly processed Bayard-Alpert ionization gauge capable of measuring pressure to 2×10−11 Torr. Differences no greater than a factor of two were observed between the two gauges for pressures between 1×10−11 and 10−4 Torr. By subtracting the x-ray limit of 2×10−11 Torr, the ionization gauge readings were corrected and indicated fair agreement with the trigger discharge gauge down to 1×10−11 Torr. Comparison of these gauges with a partial pressure analyzer indicates the ionization gauge output decreased linearly down to 10−10 Torr and saturated at 2.6×10−11 Torr while the trigger discharge gauge current varied as P1.2 in the range between 10−7 Torr to 5×10−12 Torr—the lowest indicated pressure achieved while operating the partial pressure analyzer. It is concluded that slow and continued ion desorption and outgassing of the ionization gauge is responsible for differences of more than a factor of two in trigger gauge and ionization gauge readings.
Optimization of an electron-bombardment ion source for ion machining applications
Authors: Reader Paul D. , Kaufman Harold R.
Published: July 2002

A new 10-cm-diameter ion source has been designed specifically for ion machining applications. This source employs technology and experience from the development of ion engines for electron space propulsion and generates a highly uniform beam of 500-eV Ar+ at current densities exceeding 2 mA/cm2.
Upper bound to the pressure in an elementary vacuum system
Authors: Edwards D.
Published: July 2002

A vacuum system consisting of a volume V, a pump with speed S, and a surface area A on which there are initially adsorbed n (0) molecules in a first-order desorption state is considered and discussed. The essential result is that Pmax=1.146×10−5 A/St Torr is expected to provide a reasonably accurate estimate for the value the pressure should be strictly less than t seconds after the pumping has started, given that the pressure in the system is due to an adsorbed surface phase. Experimental tests of this relation have been performed and comparisons are made between this result and the pressure measured in an elementary vacuum system.
On the use of ring gap discharges for high-rate vacuum coating
Authors: Schiller S. , Heisig U. , Goedicke K.
Published: July 2002

The performance and features of ring gap discharges are described. A limited plasma of high density in the cathode region as well as magnetic and electrostatic focusing of the electrons on a given directrix are characteristic of this discharge type. In conformity with the shape of this curve, various ring gap discharges of different geometry can be put into being, e.g., planar type and torus type, just to cite an example. Based on ring gap discharges several ion-aided technologies may thus be used to advantage in the field of vacuum deposition. High-rate sputtering, for instance, permits deposition rates in the order of some micrometers per minute which, in turn, brought about entirely new coating arrangements. Against sputter cleaning in a glow discharge the energetic efficiency of substrate pretreatment is about seven times as high and the cleaning speed increases by approximately two orders of magnitude. Alternating ion plating results in very high ion rates. With plasma plating, on the other hand, a single energy source is sufficient to generate on the substrate a powerful stream of vapor particles, sputtered particles, and ions.
Quasisimultaneous SIMS, AES, and XPS investigations of the oxidation of Mo, Ti, and Co in the monolayer range
Authors: Benninghoven A. , Ganschow O. , Wiedmann L.
Published: July 2002

The oxidation of Mo, Ti, and Co at oxygen exposures up to several hundred Langmuirs has been investigated by combination of static SIMS, ’’static’’ AES (i.e. direct counting of the N (E) spectrum at low primary electron current), and XPS. The proportionally of the O(1s) and O(KLL) signals allows one to establish a coverage scale in the submonolayer range. For Mo and Ti, saturation of the Auger and O(1s) signals is reached after 4 and 9 L, respectively. The beginning surface oxidation is indicated by the successive appearance of the compound secondary ions MeO±n at about 2−20 L. For Ti, the in-depth growth of the ’’oxide’’ is indicated at exposures above 8 L by the chemical shift of the Ti 2p levels, whereas for Mo no shift of the Mo(3d) levels is present up to 1000 L. Co behaves similarly to Ti, except for the higher oxygen doses needed for saturation and an additional phase at 0−5 L, which is characterized by enhanced Co+, CoO+, and O− emission, a break in the O(1s)vs exposure curve, and an initial O(1s) level with different binding energy.
Chemisorption of CO on Pd particles supported on mica
Authors: Thomas M. , Dickinson J. T. , Poppa H. , Pound G. M.
Published: July 2002

A new UHV technique is presented for evaluating the adsorption–desorption properties of UHV vapor-deposited metal particles supported on insulating substrates. Desorption studies of CO from particulate and continuous Pd films supported on mica were performed. The desorption results indicate that (1) the CO desorption energies from the deposited metals are much lower than those from bulk single crystals. (2) two desorption states were found for the vapor-deposited films, and (3) the lower energy desorption peak of the vapor-deposited films is coverage dependent with an activation energy of 27.25–2.85σ kcal/mol. Possible reasons for the difference between previously reported CO desorption studies on bulk substrates and the present results are discussed.
Improvement of the diffusion barrier properties of rf-sputtered molybdenum
Authors: Nowicki R. S. , Wang I.
Published: July 2002

In a contact metallization employing Mo as a thin-film ’’diffusion barrier’’, we have observed that this refractory metal does not exhibit optimum barrier properties when rf sputtered in argon. It was found that the use of ∠1500 Å of rf-sputtered Mo between Si and Au results in extensive Si and Au intermixing in <30 min at 450°C. Auger depth profile analysis confirmed that both Si and Au had moved through the Mo. This would preclude subsequent processing involving elevated temperature, as in a Silox deposition. The intermixing appears to proceed via a grain boundary diffusion mechanism (Ea=0.21 eV). Significant improvement in the intermixing time was obtained by the controlled incorporation of N2 into the Mo via reactive rf sputtering. A possible model for this improvement will be presented using the data obtained from microstructural analysis of the nitrided and unnitrided films.
TFTR vacuum system
Authors: Abel Bruce D.
Published: July 2002

The Tokamak Fusion Test Reactor (TFTR) will be the first magnetic plasma device in the United States capable of producing energy in any significant quantity by the fusion of deuterium and tritium nuclei. The function of the vacuum pumping system is to provide the high-vacuum environment for plasma initiation, to remove spent plasma constituents at the conclusion of each plasma pulse, and to provide initial high vacuum and regeneration of the neutral beam cryopanels. Radiation produced by the fusion reaction and the requirement to pump tritium have presented significant design problems not ordinarily encountered in the design of ultrahigh vacuum systems. The configuration and piping schematic of the preliminary design vacuum pumping system capable of fulfilling the requirements is discussed. The selection process for the high-vacuum pumps is reviewed and the rationale for the use of turbomolecular pumps, based on projected overall vacuum pumping system reliability, is presented. A computer was used to predict vacuum system performance. Preliminary computer-generated pumpdown curves are presented for plasma pulsing operations and pumpdowns from atmospheric pressure.
Behavior of sorb–ac wafer pumps in plasma machines
Authors: Rosai L. , Ferrario B. , Porta P. della
Published: July 2002

Vacuum pumps used in machines studying plasma physics are exposed to peculiar operating conditions. Especially the auxiliary pumps, such as cryopumps and getter pumps which are used in close proximity to the discharge or in injectors, can be exposed to very severe conditions. These pumps must exhibit very high pumping speeds and capacities, particularly for hydrogen, and must operate over a wide range of pressures. They must also be safe and reliable in use. Finally, their characteristics should not be influenced by energetic particle bombardment, radiation incidence, sputtered material on the sorbing surface, and by the presence of radioactive substances. The behavior of getter pumps based on the use of nonevaporable getter material and on a modular structure, known as sorb–ac wafer pumps, is reviewed and discussed here. The operating conditions and the behavior under radiation, particle bombardment, vacuum breakage accidents, etc. of these pumps meet most of the requirements in nuclear fusion machines and make them particularly suitable for this field of application.
Structural and compositional characterization of sputter-deposited WC+Co films
Authors: Eser E. , Ogilvie R. E. , Taylor K. A.
Published: July 2002

WC+Co films were sputter deposited by both rf and dc techniques on the electrically floating flat beryllium substrates. Film thickness varied from 1.0 to 1.68 μm. Structural and compositional analysis of the coatings were done by x-ray diffraction, SEM, EMA, and AES. Columnar growth and preferential nucleations present in the coatings by dc sputtering were not found in the coating by rf sputtering. X-ray diffraction showed that dc sputter-deposited coatings are beta tungsten carbide. Compositional analysis showed that the films were deficient in both carbon and cobalt and this deficiency was more pronounced in the films deposited by rf sputtering. Oxygen concentrations were found to be lower and argon concentrations higher for films deposited by rf sputtering. Results show the effect of ion bombardment on the substrates during deposition by the negative self-bias obtained by electrically floating the substrates. Carbon deficiency is associated with the low sticking coefficient of carbon due to its low mass.
Friction and wear results from WC+Co coatings by −dc-biased rf sputtering in a helium atmosphere
Authors: Eser E. , Ogilvie R. E. , Taylor K. A.
Published: July 2002

WC+Co films were deposited on flat polished beryllium substrates by rf sputtering with selected values of −dc bias applied to the substrates. Topographical, structural, and compositional analysis of the coatings were done by SEM, x-ray diffraction, and EMA. X-ray diffraction results show the deposits to vary from amorphous to αW2C. Compositional analysis showed variations in carbon and cobalt in relation to the bias level. Friction and wear tests carried out in a helium atmosphere by rotating one specimen in contact with another at constant speed and load for a specified time showed coefficient of friction and wear effects to be related to substrate bias. WC+Co coatings have been shown to be effective wear-resistant surfaces when applied by predetermined deposition parameters.
Quality assurance procedures for MEBES
Authors: Lieberman Barry
Published: July 2002

MEBES is the first commercially available electron-beam-lithography system intended for production use. This paper describes the techniques that are employed to perform final system calibration and to evaluate system performace. These techniques simultaneously provide a quantitative and systematic method for demonstrating the machine’s ability to meet specifications.
Enhanced etching of ion-implanted silicon nitride in buffered hydrofluoric acid
Authors: Parry Peter D. , Bristol Suzanne P.
Published: July 2002

The preferential etching of ion-implanted pyrolytic silicon nitride (Si3N4) and plasma-deposited silicon nitride in buffered hydrofluoric acid has been studied as a function of ion mass, energy, and dose. The dose dependence of etching enhancement produced by light ions (H and He) shows that the relevant concentration parameter is the density of displaced atoms rather than the concentration of the implanted impurity. In addition to the atomic displacement mechanism, a species-dependent contribution is seen. For Si3N4 the enhancement produced by most ions is 7, whereas P gives 15. For plasma-deposited nitride, the average enhancement is 3, with values of 8 observed for P and 1.5 for B. These enhancement values can be reduced by in situ annealing due to localized ion beam heating. This annealing occurs at bulk sample temperatures which are several hundred degrees Centrigrade lower than the temperatures required to produce the same result in a furnace anneal.
Inspection for defects of a mask containing one- to submicrometer patterns using a scanning electron microscope and feature extraction method
Authors: Goto Y. , Furukawa Y. , Inagaki T.
Published: July 2002

The automatic inspection for defect of x-ray patterns using a scanning electron microscope and feature extraction is proposed. A new algorithm in feature extraction method for the automatic inspection is contrived. After confirming the feasibility of the algorithm by computer simulation, this inspection method is applied to the SEM image of an actual x-ray mask containing a few-micrometer patterns and the defect of 0.5 μm in size can be extracted successfully. It is found that this new method is a very suitable one for the automatic inspection for the defect of x-ray masks containing one- to submicrometer patterns.
An automated Faraday balance susceptometer
Authors: Kulick J. D. , Scott J. C.
Published: July 2002

A computer-controlled Faraday balance has been constructed, calibrated, and tested. Magnetic moment and susceptibility measurements can be performed at fields 0–15.5 kG, and at temperatures 2–300 K. Gradient coils in the magnet gap permit separate variation of the field and its inhomogeneity. The system is interfaced to a computer which collects data from the electrobalance and thermometer, and controls the magnitude of the applied field and the sign of the field gradient. An independent programmer controls the temperature in such a way that computer-monitored sweeps of temperature are achieved with optimal thermal equilibration.
Simulation of x-ray resist line edge profiles
Authors: Neureuther A. R.
Published: July 2002

X-ray resist line edge profiles are explored as a function of exposure, mask, and resist properties. The study is based on an exposure-scission and development-etching model of positive resists. Development rate curves for two actual and three hypothetical resists are used. The simulation is implemented by using a string of points to follow the contour of the developer–resist interface as a function of development time. Control of the resist profile suitable for liftoff of 0.4-μm lines is explored in the context of low flux levels for a high throughput production environment. High aspect ratio lines (3:1) and profiles degradation due to mask edge effects for Alkα and CuL exposures are considered.
Projection ion lithography with aperture lenses
Authors: Free Bernard A. , Meadows George A.
Published: July 2002

This paper reports on experiments in projection ion lithography in which multiple demagnified images have been etched directly into a substrate through an aperture lens array, without using a resist or proximity mask. The ion source is an 8-cm-beam-diam, Kaufman-type mercury ion thruster, which accelerates ions through a grid of perforated plates, and then neutralizes the resultant beamlets by injecting electrons at ground potential. The neutralized ion beam is allowed to pass through a suitable mask and thence onto an array of apertures of a few tens of microns in diameter. Ions impinging on the apertures are accelerated through a field produced by imposing a negative potential on a substrate placed just downstream of the aperture array. An image of the mask is etched in the substrate directly below each aperture. The substrate is a polished metal disk which has been sputter coated with a number of alternating layers of chromium and copper, each about 500 Å thick. Etching of these layers quickly produces an easily visible contour map which accurately depicts variations in the etch rate over the substrate surface. It is necessary to generate random motion of the substrate relative to the ion source to prevent projection of a superimposed image of the ion source grid system. To date, mask elements of the order of 2–3 mm in diameter have been used to produce multiple images demagnified by about 20–30× with resolution better than 10 μm. Suitable equipment is now being fabricated to permit exploration of the submicron region.
Matrix lens electron-beam recording systems
Authors: Parks H. G.
Published: July 2002

State-of-the-art achievements of matrix lens recording systems are presented in this paper. Also the primary beam limiting aberrations and physical constraints of matrix lens electron-beam recording systems are discussed. A new concept in matrix lens optics, known as the short focus plus relay with improved performance over conventional matrix lens systems is presented. Analytical projections of the beam current and spot size for this configuration are shown indicating significant performance improvements in matrix lens capabilities. Preliminary experimental data for the short focus plus relay matrix optics is presented.
Kinetic focusing requirements for precision e-beam machining of unfired ceramic material
Authors: Sturans M. A. , Koste W. W.
Published: July 2002

Unfired ceramic and other substances containing organic materials generate relatively large quantities of ionized gases during e-beam thermal machining and, thus, cause beam defocus. The defocus problem is discussed theoretically and demonstrated experimentally. A practical solution for keeping the beam in focus is suggested. It is shown that high-speed machining is possible by the application of a ’’kinetic focus’’ current function to a kinetic-focus lens.
Contact resistance response surface of sintered Al films on (100) silicon
Authors: Hecht Lewis C.
Published: July 2002

Al–Si contact resistance for (100) p-type Si was studied as a function of sintering gas ambient, temperature, and time. Variables were N2 vs forming gas (10%H2, 90%N2); 540°C, 500°C, 450°C; 10, 20, 30, and 40 minutes. Results showed that forming gas yields higher contact resistance values than does N2. Away from the Al–Si eutectic point, time and temperature did not appear to be significant variables. The quantum mechanical electron tunneling model for metal–semiconductor contact resistance developed by Yu in 1970 is briefly described. This model predicts very well the range of contact resistance values measured in this experiment. The effects of forming gas can be understood by the addition of a space charge due to H2 diffusion into the Al film.
Direct-current glow discharge furnace for high-rate carburzing
Authors: Grube William L.
Published: July 2002

A direct-current glow discharge vacuum furnace for high-rate carburizing of full-size automotive components is described. Methods for introducing the required high voltage and for limiting the glow discharge to the workload in an all-metal, cold-wall furnace are discussed. Carburizing rates more than twice that achieved by conventional vacuum carburizing at the same temperature can be realized in this furnace by employing a low-pressure methane glow discharge during the carburizing stage.
Oxygen chemisorption on Bi (0001): LEED/Auger/loss study
Authors: Taylor T. N. , Rogers J. W. , Ellis W. P.
Published: July 2002

The (0001) crystal face of Bi and its reaction with oxygen have been studied using LEED, Auger electron spectroscopy, and electron loss measurements. Loss spectra from the clean surface included two peaks from the 5d levels, a 14-eV bulk plasmon loss, and a 6.5-eV loss which like that from a surface plasmon became more pronounced with decrease in incident electron energy. Room-temperature exposure to 104 L of oxygen was necessary before the onset of appreciable chemisorption and the development of overlayer diffraction features. For the oxidized condition, the 5d loss peaks were seen to shift away from the elastic peak while the 6.5-eV loss was replaced by one at 9.3 eV.
Semidynamical RFS technique for LEED analysis, with an application to GaAs(110)
Authors: Cisneros Gerardo
Published: July 2002

Realistic dynamical calculations using Pendry’s renormalized forward scattering (RFS) scheme are almost impossible to perform at energies E≳100 eV for the structure of GaAs(110) reported by Kahn et al., which includes subsurface atomic displacements, because of the time needed to compute layer reflection and transmission matrices. The technique presented is based on the RFS scheme, using kinematically computed layer matrices, which reduces computation times by almost two orders of magnitude. Curves computed thus are in good agreement with dynamically computed curves over an energy interval where the latter calculation is feasible. The kinematical RFS curves are also compared with experimental data taken at normal and off-normal angles of incidence.
4f core threshold effects in photoemission from Pt
Authors: Williams G. P. , Lapeyre G. J. , Anderson J. , Dietz R. E. , Yafet Y.
Published: July 2002

Marked changes in the Pt 5d photoemission intensity are observed at the 4f photoabsorption threshold (hν∠70 eV), which are attributed to a configuration interaction between 4f→5d and 5d to continuum transitions. The modification of the photoemission intensities at the resonance have been studied in detail by measuring energy distribution curves (EDC’s) and constant initial energy spectra (CIS’s). The data are compared with electron energy loss and photoabsorption spectra in which similar effects have been reported and treated theoretically.
Validity of mass spectrometric measurements at pressures exceeding 10−4 mbar
Authors: Huber W. K. , Rettinghaus G.
Published: July 2002

In modern thin-film processes the working pressures often exceed the high or ultrahigh vacuum range. For sputtering, ion plating, etc., pressures go up to the 10−2 mbar region. The knowledge of impurities and reaction products is of importance. With differentially pumped mass spectrometers the question arises whether all information can be retained. Comparative measurements have been performed with a quadrupole mass spectrometer pumped differentially in two alternative ways: (1) The whole QMS is pumped differentially but with the ion source arranged favorably with respect to the sample gas flow. (2) A special high-pressure ion source is directly exposed to the process environment and only the rod system is pumped differentially. Results are given. Advantages and drawbacks of the two systems will be discussed.
LEED analysis and energy minimization calculations for Si(111) (7×7) surface structures
Authors: Miller D. J. , Haneman D.
Published: July 2002

The low energy electron diffraction patterns from a variety of surface models of the (7×7) structure of Si(111) surfaces have been computed. Kinematic (single scattering) theory was used, together with a 10 phase-shift atomic scattering factor, Debye–Waller factor, and depth correction. Comparison with limited experimental data currently available was made by averaging data over the voltage range 95–140 V, a procedure which is justified by the similarity of kinematic and dynamical analysis in the case of Si. In addition quantitative spot ratio parameters were defined as an aid in evaluating comparison with experiment. The structures tested included the Lander vacancy, Harrison adatom, and Levine–McFarlane–Mark distortion models, together with combinations of these. In addition, developments of these models were tried, as well as a Peierls instability structure and three new models. Several of the models were part specified, and then allowed to relax to a minimum surface energy configuration. This involved atom shifts down to four layers with a maximum shift in general of about 0.5 Å. The results showed that vacancies or adatoms are not required to match LEED data but a surface distortion is necessary. The computed averaged LEED screens outstrip current experimental data but at this stage the best fit appears to be achieved with a hexagon-based distortion model. This has a physical basis in chemical bond rehybridization considerations and is shown to be compatible with a variety of other surface data.
Electronic structure of the Si(111) 7×7 surface studied by angle-resolved photoelectron spectroscopy
Authors: Hansson G. V. , Uhrberg R. I. G. , Flodström S. A.
Published: July 2002

Angle-resolved photoemission measurements have been performed on the Si(111) 7×7 structure by using photons in the energy range 7.8–11.6 eV. The dominant spectral features are due to direct transitions in the bulk. Experimentally determined final state bands are found to be more free-electron-like than in LCAO or APW calculations. Three different surface states or surface resonances are observed at E−EF?−0.2,−0.8, and −2.0 eV. The two uppermost in energy are of Λ1 character.
Abstract: The (110) surface of GaAs
Authors: Chelikowsky James R. , Cohen Marvin L.
Published: July 2002

The electronic structure of GaAs(110) is analyzed by means of a surface relaxation model through low energy electron diffraction studies. (AIP)
Use of the cluster–Bethe-lattice method in surface studies
Authors: Laughlin R. B. , Joannopoulos J. D. , Chadi D. J.
Published: July 2002

A general review of the cluster-Bethe-lattice method is presented which emphasizes its use as a tool in surface studies. The basic elements of the method are summarized, with simple models used to illustrate the most important ideas. The strengths and weaknesses of the method are contrasted, and the types of questions the method can best deal with ar identified. The method is then illustrated with an example. Recent results are presented which show that both bond-angle and structural disorder can produce localized states at the Si–SiO2 interface which have no analog in either bulk silicon or bulk SiO2. Inhomogeneities at the interface, particularly small ’’peninsulas’’ of silicon protruding into the oxide, are found to produce strong interface resonances approximately 2 eV below the valence band maximum. Distortions of the Si–O–Si angle near the interface are found to cause tailing into the gap in the oxide near 10 eV below the silicon valence band edge. Finally, distortions of the tetrahedral angles on a silicon atom at the interface are investigated and found to have effects similar to those observed in bulk elemental silicon.
Dissolution of carbon adlayers into the (110) face of nickel
Authors: Sau Radhesyam , Hudson John B.
Published: July 2002

The rate of carbon dissolution from adsorbed layers through the (110) face of a nickel crystal has been measured for a wide range of initial surface carbon concentrations over the temperature range from 600 to 913 K. Auger electron spectrometry was used to measure the decrease in surface carbon concentration with time at temperature. For graphitic monolayers at T≳873 K, dissolution is controlled by the transport of carbon from adsorbed layer to bulk. For dilute adlayers at T?723 K, dissolution is controlled by the bulk diffusion rate of carbon. At intermediate values of initial carbon concentration and temperature, quantitative treatment of the dissolution rate was not possible.
A possible conflict of J. Vac. Sci. Technol. 15, 1182 (1978) with the second law of thermodynamics
Authors: Edwards D.
Published: July 2002

It is shown that two connected vessels at the same temperature, in equilibrium, may contain gases at different pressures without violationg the second law of thermodynamics.(AIP)
Emission characteristics of gallium and bismuth liquid metal field ion sources
Authors: Swanson L. W. , Schwind G. A. , Bell A. E. , Brady J. E.
Published: July 2002

Emission characteristics such as energy distribution, angular intensity distribution, noise current, and temperature effects have been measured and compared for liquid bismuth and liquid gallium ion sources. The full width half maximum (FWHM) at low currents (IT?1 μA) was ?4.5 eV for gallium at ?300 K and ?9 eV for bismuth at ∠600 K. For both gallium and bismuth the FWHM increased monotonically with current. Gallium beam angular intensity at IT?1 μA was 15 μA/sr increasing to ?65 μA/sr at 30 μA emission current while for bismuth the angular intensity increased from ? 12 μA/sr to ?35 μA/sr as the emission current increased from 1 μA to ∠30 μA. A large increase in beam angular divergence was observed as IT was increased over the range 1–30 μA for bismuth. An unusually low noise current almost entirely accounted for by shot noise was exhibited by both the bismuth and the gallium ion sources. These results point towards a strongly space charge limited emission process.
H2 and rare gas field ion source with high angular current
Authors: Hanson Gary R. , Siegel Benjamin M.
Published: July 2002

We have built and carried out initial tests on a field ion source that has been designed to operate at very low temperatures with a physisorbed surface supply to the ionization region. This mode has been found to give beams of high angular current density and is expected to have low energy spread in the beam. Presently we have measured dI/dΩ?10 to 60/sr with a probable energy spread of ?l eV. The UHV system allows processing of the field emitter under clean, high vacuum conditions. A liquid He cooled finger maintains the tip at controlled temperatures from that of liquid He to room temperature. The tip is mounted on a sapphire block to provide both excellent thermal conduction and electrical insulation to ?30 kV. Differential pumping allows a high supply pressure of H2, He, Ar, etc. in the region of the tip (≳ 10−2 Torr) and a low pressure in the rest of the system. Observation on the characteristics of the field ionization pattern are made under varying conditions of pressure, temperature, field and tip processing, and orientation by using a channel electron multiplier array and phosphor screen (CEMA). An alignable aperture defines the angular divergence.
Ultrahigh vacuum system for ISABELLE full cell
Authors: Skelton R. , Briggs J. , Chou T. S. , Foerster C. , Stattel P.
Published: July 2002

A vacuum system consisting of a 40 m long 8.8-cm-diam stainless steel tube, pumped by seven pumping stations, has been assembled using automatic welding methods. All components have been fired at 950°C in a vacuum furnace at a pressure <1×10−4Torr. Each pumping station contains a Ti-sublimator, a 20 1/s ion pump and a UHV gauge. After assembly, the entire system was baked out at 250°C for 24 h. A pressure <1×10−11Torr was reached after titanium flash. In this paper we will discuss: (a) surface treatment of stainless for 10−11 Torr operation, (b) bake out and conditioning cycle to read 1×10−11 Torr, and (c) leak checking at low pressures.
Glow discharge conditioning of the PDX vacuum vessel
Authors: Dylla H. F. , Cohen S. A. , Rossnagel S. M. , McCracken G. M. , Staib Ph.
Published: July 2002

A glow discharge technique has been developed and applied to the conditioning of the large (38 m3) Poloidal Divertor Experiment (PDX) vacuum vessel. The discharge parameters and working gas (H2) were chosen to maximize C and O removal and minimize metal sputtering. The glow discharge was produced by biasing one or two internal anodes at 400 V to sustain a discharge current of 2–4 A per anode. Purified H2 at a pressure of 3×10−2 Torr was flowed through PDX at ∠10 Torr l/s. The effectiveness of the glow discharge conditioning was monitored by measuring impurity gas (CH4, C2H4, and CO) exhaust rates by mass spectrometry and C and O surface removal rates by in situ AES and XPS. Initial glow discharge operation was accompanied by frequent arcing which subsequently decreased with time. Low Zeff (?2) high-power discharges were obtained in PDX after 120 h of glow discharge treatment, during which more than 100 equivalent monolayers of C and O were removed from the vessel.
Soft x-ray appearance potential spectroscopy study of pure rare-earth metals with a sealed-off analyzer tube
Authors: Hua Z. Y. , Zhuge J. , Fan C. S. , Chen H. X. , Pan X. L. , Huang J. L.
Published: July 2002

A comparative study of the soft x-ray appearance potential spectra of various pure rare-earth metals has been carried out with a specially designed sealed-off analyzer tube. It is shown that for lanthanide elements with even number of 4f-electrons (except Eu) no spectrum is found in a region of accelerating potential from 50 to 1400 V. The most sensitive peaks are M5 (3d5/2) and M4 (3d3/2), which can serve as ’’finger prints’’ to identify the rare-earth metals. The ratio of the M5/M4 peak heights might be classified into three groups, according to their various values. Satellite peaks also exist, although no satisfactory explanation has yet been given. The purity of most samples is checked by a Mattauch–Herzog type mass spectrometer or by the proton-induced x-ray emission (PIXE).
Chemistry of solid–solid interfaces — A review of its characterization, theory, and relevance to materials science
Authors: Seah M. P.
Published: July 2002

The chemistry of solid–solid interfaces in metals is reviewed in relation to its characterization, theory, and relevance to materials science. The current techniques for measuring interface segregation, AES, STEM with x-ray analysis, and mass-resolved field desorption microscopy, are outlined and their advantages discussed. The expression of quantitative measurements from these techniques is unified. The behavior of segregation is discussed for the experimental variables—localization, crystal orientation, chemical system, time, and temperature. The theories to describe segregation in binary and ternary systems are then presented together with the analysis of the kinetics of segregation. The importance of these different aspects arises in a number of segregation sensitive materials properties. These will be described together with remedial procedures that result from the characterizations.
Characterization of AlxGa1−xAs–GaAs layer structures by scanning Auger electron microscopy
Authors: van Oostrom A. , Augustus L. , Nijman W. , Leswin W.
Published: July 2002

Crater-edge and conventional depth profiling have been used to characterize epitaxial films of AlxGa1−xAs grown by LPE on GaAs (100) substrates. In order to reduce damage low energy (?500 eV) argon ions were used. From the high energy Auger transitions values of x were derived with an accuracy Δx=0.01. Minimum chemical interface widths were observed of 2.5 nm, independent of depth below the surface.
Electrochemistry of single-crystal surfaces
Authors: Hubbard Arthur T.
Published: July 2002

Well-defined surfaces functioning as electrodes in solution are yielding electrochemical information from which the role of surface structure can be seen clearly for the first time. Techniques, results, and conclusions of recent work in this new area are reviewed and analyzed. Experimental procedures for transferring the surface between vacuum and solution without contamination have been perfected. Low-index planes and ordered overlayers are surprisingly stable toward electrolytic solutions. Electrode reactions are sensitive to substrate orientation and superlattice structure. Practical polycrystalline electrodes behave as mixtures of low-index planes; accordingly, the import of well-defined surface experimentation extends to nonideal materials.
Advanced undergraduate experiments in vacuum physics and mass spectrometry
Authors: Golecki I. , Rossel J.
Published: July 2002

A comprehensive high-vacuum system has been set up and operated in an advanced undergraduate laboratory for students majoring in physics and microelectronics. The aim of the experiment is to provide the students with both practical experience and basic theoretical understanding of the production and measurement of low pressures. The students measure the pumping speed of a rotary forepump and of an oil diffusion pump, as a function of pressure, using procedures adopted by the AVS. A hot-cathode ionization gauge and a thermocouple gauge are calibrated against a McLeod (absolute) manometer for several gases. The compositions of ambient air, of an isotopic mixture of neon, and of the residual gases in an oil-diffusion-pumped system are determined with the aid of a mass spectrometer. The influence of a liquid-nitrogen-cooled surface is assessed. Helium leak detection is demonstrated, and the response and sensitivity of the mass spectrometer as a leak detector are evaluated.