bluuebunny/crossref_metadata_2025 huggingface dataset:
An overview of pattern data preparation for vector scan electron beam lithography
Authors: Grobman Warren D.
Published: July 2002

An overview is given of a pattern data preparation system which changes computer-aided design (CAD) data to data which drives the pattern generator of a vector scan electron beam system. The software described is basically independent of the particular CAD system or electron beam system, and is joined to these two systems by custom formatting modules. Internally, the pattern data preparation system performs a series of functions on the original design data, with the functions falling into two general classes — those which operate on individual shapes (such as etching), and those which depend on shape–shape interrelationships (e.g. dose correction, overlap removal, etc.). The design data may be described in a compacted ’’nested’’ form, or in an extended ’’unnested’’ form. Shape interrelationship manipulations cannot be simply applied to nested data, which implies that CPU time efficiency may suffer if certain operations are performed. Within this framework we describe the importance of performing manipulations in a particular order, methods for removing overlaps and for shape breakup prior to dose correction, and sorting techniques for optimizing electron beam writing performance. We also discuss methods for renesting data which has previously been unnested, and for dealing with memory arrays. The overall structure of such a software package is shown to permit system independence, and also to permit the path from CAD system to electron beam system to include only those functions which are appropriate to the device technology to which the vector scan system is applied.
X-ray lithography for microfabrication
Authors: Maydan D.
Published: July 2002

Recent advances in x-ray lithography combined with the application of reactive sputter etching techniques for the pattern transfer are reviewed in this paper. The x-ray system, the mask structure, and the x-ray resist are described. Resist processing and pattern transfer are discussed as applied to the fabrication of NMOS devices with 0.7 μm effective channel lengths.
Phase boundary segregation in the multiphase–multicomponent alloy IN 738 studied by AES and SEM
Authors: Kny E. , Stolz W. , Stickler R. , Goretzki H.
Published: July 2002

Ni–base superalloys which are used in thermodynamically metastable conditions develop an undesired decrease in mechanical strength during serivce. In situ fracture experiments of aged (10 00 h/788 °C) and fully heat treated specimens of IN 738 subsequently examined with AES and SEM revealed pronounced segregation of P and S to phase boundaries. In spite of the low levels of these elements in such alloys (?0.003 wt. % in the case of S), a considerable enrichment of S and P was found in their interfacial layers. A weakening effect is expected due to interface segregation of these elements. SEM results show that the fracture morphology is different for thermally aged and fully heat treated specimens. These SEM results confirm the weakening effect of phase boundaries by segregation.
Cathodoluminescence studies of anodic oxides on GaAs
Authors: McKnight S. W. , Palik E. D. , Bhar T. N.
Published: July 2002

We have studied the light emission in the 1.5–6 eV spectral range of anodic–oxide films on GaAs under moderate energy (100–3000 V) electron bombardment. Two major features are observed in the luminescence spectra—a line at 3.78 eV and a broad feature near 3.3 eV. Comparison with cathodoluminescence data of bulk As2O3 and Ga2O3 samples leads to the identification of the 3.78 eV line with local As2O3 groups and the 3.3 eV emission with Ga2O3 groups in the mixed oxide. The nature of the luminescence centers is not known, but since these emissions are well below the bandgap at ∠5 eV, it is believed that the luminescence is related to defect sites. Featureless emission increasing toward the IR is also observed in the anodic oxides. Studies as a function of film thickness and beam voltage demonstrate that the Ga2O3-type luminescence centers are uniformly distributed throughout the film, while the As2O3-type centers are predominantly accumulated near the oxide–semiconductor interface. The behavior at the highest voltages when the electron beam penetrates into the GaAs indicates that carriers created in the GaAs readily migrate across the interface and recombine at centers in the oxide.
Surface states at unrelaxed ZnO(101̄0)
Authors: Lee D. H. , Joannopoulos J. D.
Published: July 2002

The electronic structure of an ideal ZnO(101̄0) surface has been studied using a tight-binding approach, with the surface modeled in a semi-infinite geometry. It is found that the surface states follow the band edge very closely due to the ionic character of the surface. Moreover, the close spacing between Zn 3d and O 2p levels produces a small but not negligible amount of d character in the surface states.
The Ga core exciton at unrelaxed GaAs (110)
Authors: Wang Y. , Joannopoulos J. D.
Published: July 2002

Core excitonic effects at an unrelaxed GaAs (110) surface are studied using a localized orbital approach. A realistic Hamiltonian for the conduction bands is obtained with inclusion of 5s orbitals and third nearest neighbor interactions. The binding energies of core excitons both in the bulk and at the surface are calculated. The results are in good agreement with experimental measurements, with a contact potential of ∠l.0 eV. In addition it is shown that the binding energy has a maximum value and the limiting case can be thought of as an ideal vacancy.
An interpretation of quantitative analysis of Arthur and LePore for AlxGa1–xAs using AES
Authors: Ichimura S. , Aratama M. , Shimizu R.
Published: July 2002

A Monte Carlo simulation approach was applied for an interpretation of quantitative analysis using AES. This approach has described experimental results by Arthur and LePore for AlxGa1–xAs with considerable success. The theoretical calculation has indicated that the shape of the energy distributions of backscattered electrons hardly changes as concentration (x) of AlxGa1–xAs changes from x = 0 to 1 and this leads to the linearity observed by Arthur and LePore.
High-T
c superconducting films
Authors: Gavaler J. R.
Published: July 2002

The present lively interest in superconducting films is largely due to the discovery that thin film growth methods are sometimes capable of forming high critical temperature (Tc) superconducting phases which cannot be prepared by standard bulk methods. In this paper, we review the current state of understanding of how such high-Tc phases are formed as thin films. There is growing evidence that at least two effects are operative in the formation of the various superconductors in question. First, a common factor in most cases is the deliberate or, more often, accidental inclusion of impurities into the forming material. Second, epitaxial growth is involved. The implication of these effects with respect to reproducibility and to the possibility of preparing ultrathin films having enhanced critical current and field properties is discussed in the context of recent data on the Nb–N and the Nb–Ge systems.
Cryopumped beam mass spectrometry
Authors: Visser J.
Published: July 2002

A system is described for the sampling of chemically reactive species from a plasma reactor in a mass spectrometer integrated in a 20 K cryopump. The performance of this system is characterized by high detection sensitivity and low background interference. The application of the sampling method with appearance-potential discrimination measurements of chemically active species is demonstrated.
Pumping efficiencies of three-dimensional cryopumping structures
Authors: Hemmerich J. L. , Deksnis E. B.
Published: July 2002

The necessity of protecting low temperature cryopanels by radiation shields limits the pumping efficiency of area-covering, i.e., two-dimensional arrays of state-of-the-art cryopumps to about 0.2 to 0.25 of the bare cryopanel efficiency. By using the same basic element in a volume filling arrangement of moderate depth, the pumping efficiency can be increased (typically by a factor of about 1.5), in one case even at an overall reduction in cryopanel area. Analytically and numerically (Monte-Carlo) optimized configurations will be given. A less conventional element, i.e. cryopanels protected by louvre blinds and arranged perpendicular to the wall in optimized distances, promises pumping efficiencies in excess of 0.4. For this element, however, a more detailed study of basic geometry and mechanical design seems advisable.
Recent European developments in MBE
Authors: Farrow R. F. C.
Published: July 2002

Recent key European developments in MBE have come from work in two quite distinct areas. In the area of narrow band gap semiconductors, an improved understanding of the surface properties of Hg1−xCdxTe has been achieved using MBE-related techniques. Low temperature heteroepitaxial growth of low angle grain boundary free CdTe films on InSb substrates has been achieved, and heteroepitaxial films of the semiconducting α-phase of the element Sn have been prepared for the first time. In the area of MBE growth of III–V compounds, significant improvements have been made in the electrical quality of GaAs as a direct result of changing the group V beam species from tetramer to dimer. The first GaAs ’’nipi’’ superlattice has been prepared, and the existence of a two-dimensional electron gas at a single GaAs–Ga1−xAlxAs heterojunction confirmed and utilized in a new device structure. These developments are reviewed and future trends discussed.
Thick zone plate fabrication using reactive sputter etching
Authors: Kalk F. , Glocker D.
Published: July 2002

Reactive sputter etching has been used to produce patterns for thick micro-Fresnel zone plates. An integral aluminum mask was formed on 50 μm thick Mylar, and the exposed Mylar was etched in oxygen. Gold was then electroplated into the pattern to form a micro-Fresnel zone plate 40 μm thick.
Cylindrical magnetron co-sputter etching of copper with applications for solar selective absorbing surfaces
Authors: Lake M. R. , Harding G. L.
Published: July 2002

Solar selective absorbing surfaces have been produced on large areas of copper plate seeded by a flux of titanium in a cylindical magnetron co-sputter etching system. Surface oxide on the copper and the introduction of reactive gas during the etching were necessary for production of reproducible textured surfaces. The variation of optical properties and surface morphology as a function of sputter etching conditions has been studied. Optimum selective surfaces have absorptance α∠0.92 and emittance ε∠0.18 at 300 K. Both absorptance and emittance decrease slightly after annealing for thousands of hours at 500 °C in vacuum.
On the use of ’’downward-looking’’ sources in MBE systems
Authors: Collins D. M.
Published: July 2002

A proceedure is described which allows for the preparation and mounting of Si and Be dopant source resulting in the control and reproducibility of the dopant concentration.
Fabrication of thick narrow electrodes on concentrator solar cells
Authors: Blakers A. , Kosel P. B. , Willison M. R. , Green M. A.
Published: July 2002

Narrow electrodes of thickness greater than 15 microns have been fabricated on concentrator solar cells by the PMTP (photoresist-metal-thick photoresist) process. This technique provides grid lines of low series resistance while minimizing the active area of silicon covered by electrodes, both advantages which increase the conversion efficiency of concentrator solar cells. In addition, as this technique is a ’’liftoff’’ technique, it allows the use of composite or alloy metals which normally suffer in the course of chemical etching. Finally, the thick photoresist layer smooths out short range surface roughness and allows this technique to be used equally effectively on polycrystalline, textured or amorphous surfaces.
Changes in the surface composition of Si, TiO2, and SiO2 induced by pulsed ruby-laser irradiation
Authors: Bermudez V. M.
Published: July 2002

The electron-excited Auger spectra of contaminated surfaces of Si, TiO2, and SiO2 are examined as functions of pulsed (∠25 ns) ruby-laser irradiation (λ = 0.694 μ) in the 0.3–2.4 J/cm2 range of energy density. This is the first such study on ’’simple’’ oxides. For Si with a very high initial level of surface carbon and oxygen contamination, the impurity coverage can be diminished but not entirely eliminated. The dependence of C and O coverage on the number of pulses suggests that ’’laser cleaning’’ in this case is limited by diffusion of the adsorbates into the substrate, to a depth much greater than the Auger sampling depth. For semiconducting TiO2, AES after bakeout reveals a moderate coverage of C, together with some Ca, S, Cl, and Al contamination. All of these impurities are eliminated, to within the detection limits of AES, by several pulses at about 1.5 J/cm2 each. The TiM1VV and L2,3V transitions are used to monitor the reduction of the clean surface by the Auger primary beam, leading to Ti+3 defects, and the removal of these species by laser annealing. Laser irradiation of electron-damaged SiO2 (Corning 7740 Pyrex) is found to decrease the intensity of the 91 eV ’’free Si’’ peak, relative to the 78 eV ’’SiO2’’ peak, in the Si L2,3VV spectrum. This is interpreted in terms of absorption by, and subsequent evaporation of, some of the small Si clusters formed by ESD of lattice oxygen.
The effect of magnetic field on the performance of Bayard–Alpert gauges
Authors: Hseuh H. C.
Published: July 2002

The performance of a Bayard–Alpert type ionization gauge under the influence of weak magnetic fields (<60 G) has been studied in detail. The sensitivity of this BA gauge varied with (1) the magnitude of the magnetic field, and (2) the direction of the magnetic field, especially the angle between the direction of the emitting electrons and the direction of the magnetic field. If a BA gauge is required to operate in a magnetic field, the optimum condition could be obtained by carefully choosing the mounting orientation relative to the direction of the magnetic field.
Plasma generation in gas box fueling for tandem mirrors
Authors: Hooper E. B. , Gryczkowski G. E. , Drake R. P.
Published: July 2002

The deposition of plasma in the central cell of a tandem mirror such as TMX has been calculated for gas box fueling, in which injected gas is confined to the thin fan of the quadrupole magnetic field. For TMX parameters the neutral density in the plasma center arises primarily from Franck-Condon atoms generated at the plasma edge. The fueling at the center is quite insensitive to the plasma parameters because the Franck-Condon mean free path is comparable to the plasma thickness.
Mott insulator model of the Si(111)–(2×1) surface
Authors: Redondo Antonio , Goddard William A. , McGill T. C.
Published: July 2002

Theoretical cluster calculations for the Si(111)–(2×1) surface lead to a description in which there is a singly occupied dangling bond on each surface atom. These orbitals are weakly coupled, forming a nondegenerate, nonmetallic two-dimensional Mott insulator, a description involving very strong electron correlation effects. Strong experimental support for this Mott insulator description is provided by (i) the magnitude of Si(2p) core level shifts, (ii) the dispersion of the dangling bond energy bands, and (iii) the absolute ionization potential from the dangling bond levels.
Large grain CdTe thin films on Sb–Bi alloy-coated Ta substrates
Authors: Romeo Nicola , Bube Richard H.
Published: July 2002

Description is given of the preparation and structural properties of thin CdTe films deposited on two Sb–Bi alloys with compositions of 60% and 70% by weight of Sb on Ta substrates, at temperatures just below that of the melting temperature of the alloys, 380° and 430 °C, respectively. The Sb–Bi alloy films grow with an (003) preferential orientation that matches the (111) plane of CdTe, and are expected to provide low-resistance Ohmic contacts to p-type CdTe in solar cell applications. The grain size of the CdTe films was about 2 μm when deposited at 350 °C on the 60% Sb alloy; after vacuum annealing of the deposited film for 10–15 h at 350 °C, the grain size of both the Sb–Bi film and of the CdTe film increased to about 20 μm. With controlled conductivity, CdTe films deposited in this way should make ideal solar cell components.
Deposition rate dependence of the critical optimization temperature for thin film properties: Evidence for the disordered area reevaporation mechanism
Authors: Vincett P. S.
Published: July 2002

A wide variety of inorganic and organic vacuum-deposited materials have previously been shown to exhibit sharply optimized properties when the condensation (substrate) temperatures Ts are held in a very narrow range near 0.33 of the respective normal boiling points. The optimized properties include many electrical, photoelectrical, optical, and structural parameters, and the immediate cause has been shown to be singularities in the crystallite size and orientation in films formed at the critical temperature T0. It has been proposed that the underlying mechanism of this critical optimization effect is a new process involving reevaporation of small well-defined but disordered (amorphous) areas of the film. This mechanism predicts an ∼7.5% change in T0 for each decade change in deposition rate at typical rates. A definitive check of this prediction is in fact experimentally complicated, and none has previously been attempted. We report here a careful study of the deposition rate dependence of T0 for a model material, metal-free phthalocyanine (PC) (chosen because of its lack of stoichiometric complications). The experimental rate dependence of T0 for PC (18±3 °C for a decade change in rate) is found to be in excellent agreement with the theoretical prediction (∼20 °C). This is good evidence for the disordered-area reevaporation model. In addition, we discuss in detail the alternative possibility that only conventional surface diffusion factors are at work, and conclude that such mechanisms are not likely to be the explanation. Based on our confirmation of the rate dependence of T0, we indicate how to calculate T0 for any appropriate material and deposition rate. Finally, measurements on films whose initial layers were deposited at different values of Ts from the bulk suggest that the disorder which is present for Ts<T0 is associated with difficulties in establishing the first fully crystalline layers of the film (probably because of the presence of the disordered areas); they also suggest that the shortcomings of films deposited at Ts>T0 may arise during the later stages of deposition, perhaps because of excessive out-of-plane crystallite growth.
Energy bands of thin films of diamond and zinc blende semiconductors (100)
Authors: Shen Yuyi
Published: July 2002

Using a formulism based on the Dyson’s equation and a tight binding Hamiltonian, we have calculated the energy bands along the Γ–X–M–Γ line in the first Brillouin zone of (100) semiconductors thin films of diamond and zinc blende structure. The calculations are carried out for thin films with a varying number of layers and for various configurations of diamond and zinc blende structure, e.g., elemental, binary, pseudobinary, ternary, and superlattice semiconductor thin films. The influence of the surface on the energy bands is investigated. Also for composite thin films the effect of varying the ratio of the number of the layers of the two components on the energy bands is investigated and found to be considerable. In this paper, we only give a simple example considering s wave interaction and show the method is feasible. In fact, it is transformation of difficulties from physics into computer technology. The method can be naturally extended to the case of semiconductor thin films with s–p hybridization.
The effect of passivation thickness on the electromigration lifetime of Al/Cu thin film conductors
Authors: Lloyd J. R. , Smith P. M.
Published: July 2002

Although it has become common practice to cover thin film conductors with tough passivation layers, the reliability of the underlying conductor has not been well established. Most investigators have observed an increase in lifetime for stripes covered with glass as compared to uncovered stripes, but have disagreed as to the extent and the cause of this effect. A research program was undertaken in which the electromigration lifetime of Al/Cu conductors was studied as a function of passivation thickness. Stripes covered with 1.5 μm of glass lasted longer than those which were not covered. A further increase in lifetime was found for samples with thicker glass, but a change in failure mode was also observed. All uncovered stripes and all stripes covered with thin glass failed by open circuit, whereas those with thick glass failed by short circuit, as well. Electromigration-induced compressive stresses are believed to be responsible for these observations.
Chemical bonding and reactions at Ti/Si and Ti/oxygen/Si interfaces
Authors: Butz R. , Rubloff G. W. , Ho P. S.
Published: July 2002

In an attempt to understand the fundamental chemistry of the refractory metal/Si interface and the influence of other chemical constituents, we have investigated the microscopic chemical bonding and reactions which occur at the Ti/Si and Ti/oxygen/Si interface under atomically clean interface conditions and with controlled, well-characterized oxygen interlayers produced on Si prior to the Ti deposition. Surface spectroscopy techniques (UPS, XPS, AES) were used to identify the interface electronic structure, composition, and chemical reactions. Although bulk silicide contacts (TiSi and TiS2) have not previously been observed to form below ∼500–600 °C, we find that significant atomic mixing across the interface occurs over significant distances (∼100 Å) at temperatures as low as 300 °C. The UPS spectra differentiate clearly between Ti–O and Si–O chemical bonds and reveal the microscopic chemistry in the Ti/oxygen/Si interfacial system. With oxygen already present on the initial Si surface, deposition of Ti at 25 °C reduces the Si, replacing Si–O bonds by Ti–O bonds. However, upon sufficient annealing to promote the Ti–Si reaction, the Ti atom bonding is changed to Ti–Si. As a result, the oxygen is then rebonded to Si, primarily that Si which has segregated to the overlayer surface during Ti–Si reaction. Thus this refractory transition-metal/Si interface displays strong chemical reactions well below normal silicide formation temperatures (∼550 °C)—first, in Ti–Si intermixing at ∼300 °C, and second, in reduction of the Si–O bonds at ∼25 °C.
Summary Abstract: A microprocessor-controlled surface analysis system for fracture-related and other surface studies
Authors: McDonnell L. , Lawless B.
Published: July 2002

A surface analysis system incorporating a cylindrical mirror analyzer, integral electron gun, fracture stage, and specimen interlock is described. A particular feature of this ‘‘in-house’’ designed and developed system is the microprocessor control of the cylindrical mirror analyzer and the vacuum instrumentation.
Alpha particle simulation and diagnostics using 3He++ minority ICRF heating
Authors: Post D. , Hwang D. , Mikkelsen D. , Seidl F.
Published: July 2002

We have investigated the theoretical feasibility of using fast 3He++ ions, produced by ICRF minority heating, to simulate the behavior of fusion-produced 4He++ ions in large fusion experiments. This proposed technique would allow the study of ‘‘alpha particlelike’’ heating in near term experiments, such as TFTR, JET, and JT-60, without the necessity of high levels of neutron production and the subsequent activation. The results of our calculations study show that ICRF minority heating should be able to produce confined fast 3He++ distributions in TFTR-sized experiments with an energy distribution and density similar to those expected for fast alpha particles in fusion reactor experiments, such as INTOR/FED/NET.
Thermal cycling and torque analysis of an ultrahigh vacuum flange
Authors: Fuente A. O.
Published: July 2002

A major design objective of a vacuum assembly in a specialized ultrahigh vacuum exhaust/leak detection processing system was to incorporate replaceable vacuum sealing flange ports. The vacuum processing operation with which the system was to be used required that these ports be capable of repeatable thermal cycling, from ambient to 525±25 °C and be torqued between the range of 17 to 50 ft lb prior to each thermal cycle while guaranteeing a leak-free seal to less than 1×10−12 std cm3/s. This design concept was proven to be feasible through computer analysis and documented experiments. One of the major breakthroughs was the employment of nickel metal gaskets for sealing as opposed to OFHC copper (standard high vacuum gasket material). This nickel gasket was proven to be vastly superior to copper in its sealing reliability with respect to thermal cycling at elevated temperatures. Torque analysis results have shown that these ports could be torqued to as high as 50 ft lb, both at ambient and elevated temperatures, and still be leak free.
A new type of turbomolecular vacuum pump bearing
Authors: Osterstrom Gordon E.
Published: July 2002

It has been found practical to operate a vertical rotor turbomolecular vacuum pump with at least one oil lubricated journal or ‘‘sleeve’’ bearing of ringlike proportions running at film sheer speeds of 87 m/s (194 mile/h). Aside from unlimited life and low noise, the new bearing has heat transfer capabilities which will extend the pump’s useful blowers.
Vacuum systems for microelectronics
Authors: O’Hanlon John F.
Published: July 2002

Sophisticated vacuum systems are required for modern growth, deposition and etching processes, and analytical techniques. These systems have been developed to the point where they are available with optional pumping packages, system designs, and procedures. We discuss the applications of high and ultrahigh vacuum pumping systems and procedures used for device fabrication. Plasma processing in the medium vacuum range is attractive because it is fast, economical, and does not require especially clean vacuum technique. It is now clear that certain device structures must be fabricated under ultraclean plasma conditions. We discuss the current state of ultraclean high flow processing.
Design of a dee vacuum vessel for Doublet III
Authors: Davis Larry G.
Published: July 2002

The Doublet III tokamak is to be modified wherein the original ‘doublet’ plasma containment vacuum vessel will be exchanged with one of a large dee-shaped cross section. The basic dimensions of the dee vessel will allow plasmas of 1.7-m major radius, 0.7-m minor radius, and a vertical elongation of 1.8. Installation of a large dee vessel in Doublet III is made possible by the demountable toroidal field coils and the large, low-ripple volume they include. Ripple at the plasma edge will be less than one percent. The plasma parameters affecting the design of the vessel will be reviewed including plasma current, power, disruption time, allowable error field, impurity control techniques, pulse length, and limiter schemes. A driving requirement for the design of the vessel is to maximize the access to the plasma for auxiliary heating (both neutral beam injection and radio frequency heating), diagnostics, developmental component and material testing, and pumping. The dee vessel is structurally designed along the same lines as the present vessel: an Inconel 625, all-welded, continuous chamber in a corrugated sandwich construction. An overview of the vessel design and its solutions to the design criteria will be presented. An overview will also be presented of the entire modification project which includes replacement of some coils, and addition of support structure, limiters and vessel armor, and power system components.
Ion milling source with slot extraction system
Authors: Rangel/ow I. W. , Radzimski Z. , Czarczyński W.
Published: July 2002

An ion source with a slot extracting system for micromachining and surface treatment applications has been designed and built. It has an ion extracting system which does not change its geometry when heated. The slot extracting electrodes have been made of Mo rods mounted in a way that allows for thermal elongation without distortion. The source was tested using an array of 49 Faraday cages. Measurements of the ion current density distribution have been made for helix- and meander-shaped cathode filaments. The source has been designed for the energy range 500–1000 V and for an ion current density of 2 mA/cm2. The ion beam divergence in the direction perpendicular to the slots is 5° and in the direction parallel to the slots is about 7°.
A performance comparison of vacuum deposition monitors employing atomic absorption (AA) and electron impact emission spectroscopy (EIES)
Authors: Gogol C. A. , Reagan S. H.
Published: July 2002

A review of the fundamental properties of the newer deposition monitoring techniques is combined with an experimental comparison of atomic absorption (AA) and electron impact emission spectroscopy (EIES). The results presented show that EIES has practical advantages when stability and sensitivity are the dominant requirements. However, when operation over wide pressure ranges is necessary the superior selectivity of AA is shown to have advantages.
Influence of composition and substrate bias on structure and inert gas content of sputter-deposited Ni–La alloys
Authors: Knoll R. W. , McClanahan E. D.
Published: July 2002

High concentrations of inert gases can be incorporated into the structure of certain bias-sputtered rare earth/transition metal alloys, and these materials are useful as stable reservoirs of inert gas. Ni–La alloys containing a composition gradient ranging from about 0.3 to 30 at.% La have been deposited at several bias voltages, in a dc triode system, with cylindrical target–substrate geometry, using an asymmetric composite target, and a Kr discharge. The dependence of Kr content and alloy structure on composition (La/Ni atom ratio) and substrate bias has been determined systematically. Deposit structure was examined by x-ray diffraction, and Kr content was measured by energy dispersive x-ray spectroscopy and by vacuum fusion. At constant bias, Kr content initially increases rapidly with La/Ni, then saturates. As La/Ni ratio increases, alloy structure changes from fully crystalline to fully amorphous. Bias has a pronounced effect on preferred orientation and on relative fraction of crystalline phase. The work is discussed in terms of previous studies of sputter-deposited RE/TM alloys and amorphous metals.
Effect of magnetic field and bias potential on the distribution of plasma luminosity during rf sputtering
Authors: Auner G. , Hsieh Y. F. , Padmanabhan K. R.
Published: July 2002

The variation in the distribution and intensity of plasma between the target and substrate and its effect on the film deposition rate and uniformity in a rf sputtering system was photographed by incorporating a mirror arrangement within the chamber. The distribution was studied as a function of magnetic field, substrate bias potential, substrate temperature, and rf power. The thickness of the films and hence, their deposition rate, was determined by Rutherford backscattering technique. On flat substrates, the film deposition rate and uniformity were strongly dependent on the strength of the magnetic field. Substrates with irregular geometry exhibited a dark sheath. The diameter of the dark space was a function of both bias potential and magnetic field strength. The plasma distribution was also found to change with the orientation of the substrates. The application of this study in rf sputter deposition of hard coatings on drills and cutting tools are discussed.
Thin film electrodes for an artificial ear
Authors: White R. L. , Roberts L. A. , Kwon O. , Cotter N.
Published: July 2002

It is possible to generate auditory percepts in profoundly deaf subjects through the direct electrical stimulation of the auditory nerve. To achieve auditory percepts having the complexity and information content of speech, it is necessary to stimulate separately a number of discrete subsets of fibers of the auditory nerve. Thin film electrodes fabricated through photolithographic techniques are attractive as stimulation microelectrode arrays because of the high dimensional resolution and good electrical and mechanical reproducibility of such electrodes. The requirements of survival of such arrays for decades in the biological environment have led us to use materials and techniques not typically handled photolithographically. Rigid electrode arrays have been developed using sapphire substrate tantalum conductors and tantalum pentoxide insulation. Flexible arrays have been developed using a polyimide–titanium–platinum–polyimide sandwich. These electrodes and their fabrication will be described.
The effects of palladium–gold on the chemisorptive activities of thin film tin oxide
Authors: Chang Shih-Chia
Published: July 2002

A thin, discontinuous palladium–gold deposit (≤3.5 nm) was evaporated on top of thin film tin oxide (∼100 nm). The resistance of the resulting device decreased greatly with increasing ambient content of propylene (C3H6) or hydrogen (H2). The device has the capability of detecting 10 ppm of C3H6 or H2 in air. These observed phenomena may be explained by bifunctional catalysis (activation of the adsorbate, enhancement of chemical reaction, and electronic interaction) and the surface sensitive electronic properties of semiconductors. The possibility of applying the bifunctional catalysis concept for sensor fabrication is examined. The advantage of using thin film samples for catalysis studies is discussed.
Annealing of Hg1−xCdxTe: Hg loss rates and annealing of ion implantation damage
Authors: Dimiduk K. C. , Opyd W. G. , Gibbons J. F. , Sigmon T. W. , Magee T. J. , Ormond R. D.
Published: July 2002

An important problem in processing the infrared detector material Hg1−xCdxTe is avoiding undue mercury loss. Here we quantify that loss and apply the information to the annealing of ion implanted Hg1−xCdxTe. We thus extend the work of Takita et al. on Hg loss in HgTe to the ternary Hg1−xCdxTe. The Hg loss is generated with a thermal-pulse annealing system and measured by Rutherford backscattering spectrometry (RBS). The loss rate is studied as a function of temperature, composition, and surface preparation (chemimechanical and contactless polishing). For each set of conditions the data is fit to an Arrhenius equation N⧠ /t=A exp(−ΔE/kT) and the fitting parameters A and ΔE are determined. ΔE ranges from 1.0 to 2.5 eV and A varies from 1023 to 1036 atoms/cm2 s. Channeling RBS was also used to study the effect of thermal pulse annealing on boron implanted material. The rate of change of the minimum yield (χmin) with depth, which can be related to certain types of damage, was consistent with the calculated implant damage profile. A 260 °C 8 s anneal restored the crystal quality to better than the as-received material, as observed by channeling.
Control of the UTI 100C quadrupole mass spectrometer with an inexpensive microcomputer
Authors: Dahlgren David , Arnold John , Hemminger John C.
Published: July 2002

The interfacing of a UTI 100C quadrupole mass spectrometer to an inexpensive microcomputer system (the Commodore 32K Pet) is described. The system is capable of selecting and monitoring up to 13 masses simultaneously (on a time scale of 1 s). An example is given of the utilization of this system in the temperature-programmed decomposition of dimethyltetrazine on a platinum surface.
The interaction of hydrogen with silicon surfaces: A field ion microscope and pulsed-laser atom-probe study
Authors: Kellogg G.L.
Published: July 2002

Field ion microscope and pulsed-laser atom-probe studies of silicon surfaces following various types of heat treatment in ultrahigh vacuum and in hydrogen have been carried out to identify any structural or compositional changes produced by the heating. In particular, the possibility of surface hydride formation due to hydrogen segregation from the bulk at moderate temperatures has been explored. Results from high purity whisker samples show no evidence of surface structural or compositional changes following vacuum heating up to temperatures of 625 K, unless gas phase hydrocarbons are present. At 700 K, thermal faceting, which indicates surface atom mobility, is observed. Results from samples prepared from 5-Ω-cm boules indicate that hydrogen segregation may occur along extended defects. Pulsed-laser heating of Si samples in molecular hydrogen is found to produce an amorphous overlayer on the surface, and the predominant species detected from this surface with the pulsed laser atom probe is SiH+3 . This observation suggests the presence of a silicon-trihydride surface phase.
Epitaxial growth and electronic structure of CdTe films
Authors: Pessa M. , Jylhä O. , Huttunen P. , Herman M. A.
Published: July 2002

Atomic layer epitaxy (ALE) for growing II–VI compound single crystal films has been described. The growth of CdTe films on p-type CdTe(110) and (111)A substrates by ALE is shown to lead to high structural perfection. Surface crystal structure of these films is studied by LEED. The nonpolar (110) surface exhibits (1×1) symmetry while the polar (111)A surface is reconstructed showing (2×2) symmetry. Electronic valence band features are studied by angle-resolved photoemission and preliminary analysis of the photoemission spectra is presented. Most of the features may be accounted for in terms of the bulk electronic structure via direct transitions including primary and secondary cone emission. An intrinsic surface state (surface resonance) likely associated with a Te-derived dangling bond in the (110) film is observed.
Negative resistance switching in near-perfect crystalline silicon film resistors
Authors: Kenyon P. , Dressel H.
Published: July 2002

This paper describes negative resistance switching in n-type silicon film resistors which contain linear arrays of grain boundaries. These linear arrays have been predictably located in the active region by a laser recrystallization procedure. The grain boundaries are made to bisect the resistors. Effects of parameters such as grain boundary number and grain-dopant concentration have been examined. We show that quasisaturated and asymmetrical I–V characteristics are exhibited by our resistors. This is evidence that the voltages across the depletion region and across the grain boundary layer are not equally divided on each side of the junction, and that dopants are nonuniformly incorporated in the grains during laser recrystallization.
Atomic structure of ion implantation damage and process of amorphization in semiconductors
Authors: Narayan J. , Fathy D. , Oen O. S. , Holland O. W.
Published: July 2002

Atomic structure of ion implantation damage and the process of amorphization in silicon have been investigated using high-resolution electron microscopy techniques. The specific damage energy density for crystalline to amorphous transition has been determined to be 6.0×1023 eV/cm3 or 12 eV/atom at 4 K with no annealing. The amorphous regions are produced when the damage energy deposited by the ions exceeds this critical value. Since the damage energy deposited by the ions is a strong function of ion implantation and substrate variables, the formation of amorphous regions and the process of amorphization are strong functions of these variables. The details of atomic structures of amorphous silicon containing microcrystallites and that of amorphous-crystalline interfaces are presented. The calculations of the mean-free path between collisions and the energy deposited per atom are found to be consistent with experimental observations on amorphization of silicon. Some results on the projected ranges of low-energy recoils, which are primarily responsible for the production of amorphous cascades, are presented. The solid-phase crystallization phenomena and the role of microcrystallites during the crystallization process are discussed.
Wetting of metal surfaces with a liquid metal using a plasma interaction technique
Authors: Sudarshan T. S. , Lim M. H. , Park L. , Chang S. H.
Published: July 2002

Materials such as tungsten, molybdenum, stainless steel, etc., which have low solubility in mercury (Hg) are difficult to be wetted or coated with the liquid metal. This paper describes a general technique for wetting and coating such metals with Hg. The method involves plasma etching the substrate and making the liquid metal interact with the plasma before it contacts the substrate surface, by delivering it to the substrate through the glow discharge, to successfully wet the above metals. Elkonite (70% W and 30% Cu) was also wetted successfully by this technique. A model has been presented to qualitatively explain the observed results. The discharge is postulated to create reactive species on the substrate surface and to produce reactive Hg species as Hg travels through the plasma. Further, the surface free energies of the substrate and the liquid metal are altered suitably to favor wetting and surface complexing as described by Young’s equation.
Pulsed series discharges in crossed fields generated in vacuum switches for pressure-measurement application
Authors: Kageyama Katsuhiro
Published: July 2002

Formative processes of the series crossed-field discharges in vacuum switches were investigated, and pulsed discharges were found feasible for switch-pressure measurement, when solid surfaces within switches are clean. The fact that a vacuum switch is a small, sealed device, causes problems in switch-pressure measurement, to which serious conditions for performance are charged. To solve the problems, pulsed discharges were investigated. The discharge in a switch, identified previously as a series discharge consisting of an inverted magnetron and a magnetron, was generated by rectangular high voltage at amplitude Vd. Discharge currents in formative phases were measured and analyzed. Formative processes were revealed to be composed of triggering and growth. At a large Vd value, the discharges are triggered immediately after the stepped voltage application. Instantaneous discharge triggering assures high reliability in pressure measurement. At small Vd values, times required for triggering are delayed and scattered. In the growth phase, discharge currents proceed to increase in a reproducible pattern, and become saturated. Then they begin to decrease, resulting from pressure decreases due to the pumping effect of discharges. A current increase in the growth phase is always quick, and a decrease after saturation is slow. Magnitudes of the saturation currents are distributed concentratedly. This causes good precision in measurement, typically with errors less than 10% of the measured values. The time intervals necessary to establish the pulsed discharges and the pumping effect to change pressures were analyzed. The measurement range was found to cover a low pressure, down to 1×10−4 Pa, with a pressure decrease of less than 20%, when pumping speed is 4.2 l/s, which is the maximum experimental value. Thus, pulsed series crossed-field discharges were found to be feasible for switch-pressure measurements, when switch interior surfaces are clean.
The operation of a capacitance manometer at 300 °C
Authors: Buckman S. J. , Gascoigne J. , Roberts K. B.
Published: July 2002

The performance of a capacitance manometer operated at 300 °C is described. Calibration against a deadweight primary pressure standard indicates that the stability over a period of 3 months is better than 0.25% of the measured pressure over the pressure range 15–1000 Torr (2.04–131.6 kPa).
The use of sliding metal electrical contacts in UHV
Authors: Newstead S. M. , Kubiak R. A. A. , Parker E. H. C.
Published: July 2002

A simple and versatile method of contacting to sliding stainless steel rods is described. Compact linear motions are made possible, in which the supports of a component also act as electrical feeds. Problems associated with insulated flexible connectors are thus eliminated. The contacts have worked reliably in a III–V MBE system environment.
History of the American Vacuum Society and the International Union for Vacuum Science, Technique, and Applications
Authors: Lafferty J. M.
Published: July 2002

On the 30th anniversary of the American Vacuum Society, the Vacuum Technology Division presented a session on the History of Vacuum Science and Technology. The author was asked to present a paper on the history of the AVS and the IUVSTA for this session. Topics selected for discussion include the formation, growth, organizational structure, and strategy of operation of the AVS. Other subjects covered are publications, scholarships, and the author’s own personal experience in setting up two major awards for the Society. For a more comprehensive and detailed history of the AVS, the reader should consult ‘‘The First Twenty Years of the American Vacuum Society’’ [J. Vac. Sci. Technol. 10, 833 (1978)] and ‘‘The American Vacuum Society—1973 to 1983’’ [J. Vac. Sci. Technol. A 1, 1351 (1983)]. Other countries have also organized their own vacuum societies. Many of these, some 22 in number, including the AVS, are members of the IUVSTA, an international confederation of national vacuum organizations. The formation and early history of this organization is described, including its new scientific divisions patterned after the AVS. Various objectives and activities of the Union are discussed.
Leak detection—common problems and their solutions
Authors: Santeler Don
Published: July 2002

The subject of leak detection will be considered from the viewpoint of a number of classical problem areas that are common to many different techniques. These will include such limitations as temperature change, system outgassing, virtual leaks, gas permeation, and long time constants from large volumes as well as from double leaks in series. The problems as well as their solutions will be discussed for a broad range of leak-test methods, including various total and partial pressure gauges. Some specific advantages of air-leak detection with either a residual gas analyzer or a small mass spectrometer mounted on its own pumping system will be illustrated. A clarification of common misconceptions about the nature of leaks and gas flow through leaks will also be included. This will be illustrated with several typical examples including the technique of high pressure helium bombing.
Use of refrigerator-cooled cryopumps in sputtering plants
Authors: Klein H.-H. , Heisig R. , Augustine C. M.
Published: July 2002

The sputtering process is one of the modern techniques for production of thin films as they are used in the technology of semiconductors, in processing of surfaces, etc. This process demands a high vacuum pump of the following qualities: (1) Easy to handle, (2) Stable and repeatable process conditions, (3) High pumping speed for all gases, especially for water vapor, (4) Ability to achieve a high vacuum environment before process begins (5×10−7 mbar), (5) Usable for process pressure up to 2×10−2 mbar, (6) Rapid evacuating of the process chamber from the process pressure down to a pressure 5×10−7 mbar after process is finished. Modern refrigerator-cooled cryopumps meet the requirements 1 to 4 without problems. Therefore the report especially deals with the 5th and 6th topics. Here special modifications are necessary compared to common cryopumps. There are two possibilities to cover the demand of using the pump at high pressures: (1) Using a refrigerator with high cooling capacity, (2) Installing a throttling valve into the cryopump. Both are discussed. Concerning topic six pumpdown plots of well designed cryopumps are shown. The conditions of the process were simulated while both argon and mixture of argon and hydrogen were let into a chamber. During the sputtering process hydrogen is produced by the process itself.