bluuebunny/crossref_metadata_2025 huggingface dataset:
New enhanced performance low-pressure capacitance manometer
Authors: Grudzien C. P. , Lischer D. J.
Published: July 2002

The measurement performance of low-pressure capacitance manometers has traditionally been influenced to varying degrees by many factors including ambient temperature change, shock, vibration, material creep, and rapid pressure excursions. Many improvements and developments have occurred since the original capacitance manometer technology was commercialized over 40 years ago. Previous capacitance manometer designs addressed several of these pressure-independent influences, but in the process, tradeoff performance in other areas. A new enhanced performance design is described here that incorporates several unique approaches to reducing these influences and provides for a practical, robust platform. Experimental data and computer simulation show that measurements using instruments with full-scale ranges of 100 mTorr (∼10 Pa) and below are superior to that of previous state-of-the-art methods. The enhanced performance capacitance manometer design establishes a basis for continual improvement and a path to meet the future requirements of the vacuum community.
Fundamental functions of a new type of leak detector using oxygen-ion conductor
Authors: Tatenuma K. , Noguchi T. , Uchida K. , Saeki H. , Ando A. , Momose T.
Published: July 2002

A new type of leak detector (LeakD) was developed using the principle of selective and sensitive oxygen detection using oxygen-ion-conducting ceramics, e.g., yttria-stabilized zirconia (YSZ). By comparing the experimental results of the LeakD with a quadrupole mass spectrometer (QMS) and other methods, it was clear that (1) at a large leak, the data of LeakD coincided with theoretical values; (2) at a small leak, the P(O2)vac calculated from the electromotive force (emf) of LeakD differed from the P(O2)vac of QMS, especially at higher temperature for YSZ; (3) at a small leak, using tandem two LeaksDs under both sensing surfaces of YSZ evacuated with any different oxygen partial pressures about 100–10−6,P(O2)vac obtained from the emf of LeakD nearly coincided with the theoretical values; and (4) a leak point is found by blowing nitrogen gas on the point. The phenomena of (2) and (3) showed that the oxygen-ion-conducting ceramics may be especially influenced by a total pressure less than 10−3 or 10−4 Torr. The simple and small LeakD has good reproducibility and rapid response, and it is assumed that it has a smaller outgassing rate compared to some gauges with filaments. The LeakD can continuously detect a leak in the routine installation, and also inform others of an accident or emergency. The LeakD is a convenient and highly sensitive leak detector compared to a traditional helium leak detector using a QMS.
Angle-resolved ESCA methods: Distribution and molecular conformation of perfluoropolyether lubricant
Authors: Karplus Mark A. , Pocker Daryl
Published: July 2002

Simple but useful methods for interpreting angle-resolved ESCA data from real-world samples are presented. First is a two-tiered overlayer model allowing thinly covered and thickly covered substrate. It can be productively applied, even in a manual fashion, with common office spreadsheets. Next is a triangle-wave roughness model that can reasonably approximate substrate polishing texture. Finally, a two-slab overlayer model is presented. With the help of canned minimization routines, it can bring out conformation subtleties in overlayer structures and even isolate a deeply buried monatomic layer. The following are presented as examples. Perfluoropolyether (Zdol) lubricant on hard disk carbon overcoat shows coexisting monolayer and multilayer regions consistent with structures identified by surface energy and ellipsometric surface diffusion measurements. Polishing texture of disks is detected but leads to little change in the two-tiered model results. Layering within the lubricant shows significant perfluoropolyether backbone adjacent to the overcoat surface accompanied by a discernible excess of ether oxygen. The latter indicates that the inverted-U conformation sometimes sketched for bonded lubricants is an exaggeration, certainly for the system studied.
Na- and Li-induced Ge(111)3×1 reconstruction: Different electronic configurations revealed by scanning tunneling microscopy images
Authors: Lee Geunseop , Kim Jonggeol , Mai H. , Chizhov Ilya , Willis R. F.
Published: July 2002

We present scanning tunneling microscopy (STM) observation of the 3×1 reconstruction of the Ge(111) surface induced by the adsorption of Na and Li. The STM images of the Na- and Li-induced Ge(111)3×1 surfaces reveal substantial differences not only from each other but also from those of Si(111)3×1 induced by the same metal atoms. We suggest plausible interpretations of these STM images within the structural models proposed for the alkali-metal-induced Si(111)3 ×1 reconstruction having similar atomic structures but different electron bonding configurations.
A typical example of metastability: Metallic glasses
Authors: Duwez Pol
Published: July 2002

The general term metallic glasses is now generally accepted to define a class of amorphous alloys obtained by rapid solidification from the liquid state. This definition corresponds exactly to the definition of a glass in general, except that in the case of well known silicate glasses the liquid does not require a rapid rate of cooling to prevent crystallization, and that is not the case for metallic glasses. The first metallic glass, an alloy of gold and silicon, was synthesized at Caltech in the summer of 1959. During the last 20 years, the interest in metallic glasses has increased steadily. There is still widespread interest in both theoretical and experimental studies of metallic glasses. About 10 years ago the potential importance of metallic glasses as a class of new materials with unusual physical properties was recognized by industry. It will take a long time before production of metallic glasses can be measured in tons, but it is encouraging to see that an increasing number of industrial research centers are involved in studies of metallic glasses.
A first principles LCAO study of ideal and reconstructed diamond(111) 1×1 and 2×1 surfaces
Authors: Vanderbilt David , Louie Steven G.
Published: July 2002

A first principles self-consistent LCAO approach is applied to the study of the C(111) ideal 1×1 and reconstructed 2×1 surfaces. The surface states are calculated for a variety of buckled, π-bonded chain, dimerized π-bonded chain, and π-bonded molecule reconstructions. None of the models studied to date are found to be in good agreement with photoemission experiments; the theoretical occupied dangling bond surface bands are either too deep in the gap, too dispersive, or both. The dimerized π-bonded chain model is in closest qualitative agreement with experiment.
Deep-UV photolithographic applications of copolymer (methacrylonitrile–methacrylic acid)
Authors: Hiraoka H. , Welsh W. L. , Bargon J.
Published: July 2002

Copolymer (methacrylonitrile–methacrylic acid), which has no significant deep UV absorption prior to prebake, starts to have a broad UV absorption with the maximum at 246 nm after prebake at 130 °C in air. Cyclized structures responsible for this absorption undergo photochemical reactions: (1) main chain scissions at deep-UV exposure, initiated by removal of isocyanic acid, providing positive tone images; (2) hydrogen transfer reactions at mid-UV exposures to result in conjugated structures or cross linkages, providing negative tone images. With relatively high sensitivity, 50 mJ/cm2 for positive and 100 mJ/cm2 for negative tone images, polymer patterns with vertical wall profiles are obtained. Postbake of these resist patterns increases dry etch resistance significantly.
Theory of band line-ups
Authors: Harrison Walter A.
Published: July 2002

Natural band line-ups may be defined in terms of tight-binding energy bands, which place the bands for all materials on the same energy scale. These line-ups account quite well for the observed line-ups at semiconductor heterojunctions. However, for metal–semiconductor interfaces they place the metal Fermi energy a few electron volts above the conduction band edge in most cases, leading to Ohmic contacts. Corrections to the natural band line-ups from interface-bond dipoles are then added. They are found to be very small for heterojunctions, but can be of the order of an electron volt for metal–semiconductor interfaces; the latter were calculated replacing the metal by an ‘‘image lattice,’’ which should provide a good description of the interface. An additional shift due to tails of the metallic states in the semiconductor [Metal-induced gaps (MIGs)] are calculated analytically, including the effects of both light and heavy electron and hole bands; the heavy bands being seen to dominate. The resulting formula leads to a maximum shift of 0.4 eV in the case of metal–GaAs. The cell-averaged Green’s function is also calculated analytically for this system. It is seen to be dominated by the light bands and therefore not to represent well the interface dipole. It also does not address the size of the dipole, which we have found to be small. It is concluded that heterojunction band line-ups are consistent with ideal interface geometry, but defects at the interface are required to understand Schottky barriers at metal–semiconductor interfaces, many defects being required. The observed behavior at a metal–gallium arsenide interface is consistent with positive-U defects, such as arsenic antisites with a gallium antisite spectator; that of the metal–silicon interface is consistent with negative-U defects, such as silicon vacancies.
The dependence of RHEED oscillations on MBE growth parameters
Authors: Van Hove J. M. , Pukite P. R. , Cohen P. I.
Published: July 2002

Oscillations in both the intensity and width of reflection high-energy electron diffraction beams that are measured during the MBE growth of GaAs are observed to depend upon most growth parameters. The envelope of the intensity oscillations, for example, depends upon the flux ratios, the substrate temperature, the sample misorientation, the scattering geometry, the sample flatness, and the flux uniformity. To separate these dependencies we have made RHEED measurements on small, exceedingly flat, near singular samples. The angular profiles of the specular beam were measured during the first two periods of oscillations. These data were analyzed in terms of the two-level diffraction calculation of Lent and Cohen. The measured profiles are in excellent agreement with that calculation. For oscillations with a 26-s period, moderate changes in the substrate temperature and As flux can cause significant changes in the pair correlation length on the surface.
Pressure and irradiation angle dependence of maskless ion beam assisted etching of GaAs and Si
Authors: Ochiai Yukinori , Gamo Kenji , Namba Susumu
Published: July 2002

Maskless ion beam assisted etching of GaAs and Si has been investigated. Focused Ga+ ion beam was irradiated on GaAs and Si in chlorine and xenon difluoride gas atmosphere, respectively. It was found that an optimum gas pressure existed to improve the etching rate. The etching rate showed a maximum at a bombarding angle of 60°–70°. The simulation of the etching profile was in reasonable agreement with the observed profiles. It was also found that redeposition effect is absent for ion beam assisted etching.
Measurement of heterojunction band offsets in InP/Ga0.47In0.53As by admittance spectroscopy
Authors: Lang D. V. , Panish M. B. , Capasso F. , Allam J. , Hamm R. A. , Sergent A. M. , Tsang W. T.
Published: July 2002

We discuss the use of admittance spectroscopy to measure the band offsets of semiconductor heterojunctions. By using this method to analyze the dynamic response of p–n junctions containing lattice-matched InP/Ga0.47In0.53As superlattices we can independently determine both the conduction and valence band offsets for this materials system. We find the conduction band offset to be ΔEc=250±10 meV and the valence band offset to be ΔEv=346±10 meV. The sum of these offsets agrees very well with the known band-gap difference between InP and Ga0.47In0.53As. The ratio of the conduction band offset to the valence band offset is thus 42:58.
A model for comparing process latitude in ultraviolet, deep-ultraviolet, and x-ray lithography
Authors: Smith Henry I.
Published: July 2002

It is widely recognized that process latitude is an important figure of merit in microlithography. We derive a general expression for process latitude based on a model for lithography that takes into account linewidth control, contrast of the imaging system, diffraction, resist contrast, nonuniformity of illumination, and shot noise. We define a normalized process latitude parameter (NPL) that enables one to compare quantitatively the various optical projection systems and x-ray lithography in the submicron linewidth domain. NPL is plotted as a function of linewidth for two optical projection systems [λ=436 nm, numerical aperture (NA)=0.42; λ=193 nm, NA=0.4] at perfect focus and at 0.5 μm out of focus. These plots are compared with a plot of NPL for x-ray lithography, from 1- to 0.25-μm linewidth, using a mask-to-sample gap of 20 μm and a laser-plasma source centered at λ=1.24 nm. The comparison verifies what others have observed experimentally: that x-ray lithography offers a significant advantage in process latitude.
Plasma deposition of SiO2 gate insulators for a-Si thin-film transistors
Authors: Dresner J.
Published: July 2002

The principles governing the plasma deposition of SiO2 films for use as gate insulators in a-Si thin-film transistors (TFT’s) are discussed. A deposition arrangement is described which favors the reaction at the substrate over that in the discharge volume. It is shown that the variables leading to large values of the breakdown field Ebk and to greatest stability of the flat band voltage Vfb are the substrate temperature Ts, the gas flow ratio N2O/SiH4, and the ratio of the discharge half-period to the transit time of the ions between the electrodes. a-Si/SiO2 TFT’s operated in the dc mode and in a mode simulating LC display operation show much less shift of the threshold voltage Vth than do a-Si/Si3N4 TFT’s for equivalent gate fields.
Transverse thermal velocity broadening of focused beams from liquid metal ion sources
Authors: Ward J. W. , Kubena R. L. , Utlaut M. W.
Published: July 2002

Experiments have shown that the target current density in focused ion beam columns have long ‘‘tails’’ outside the central submicron region. We show that these tails result from a transverse velocity distribution which has a Holtsmark probability density. Both theory and experiment show that the tails are reduced as the system magnification and source current are reduced.
Simple negative resist for deep ultraviolet, electron beam, and x-ray lithography
Authors: Stewart K. J. , Hatzakis M. , Shaw J. M. , Seeger D. E. , Neumann E.
Published: July 2002

Negative resists using photo-acid initiated cationic polymerization of epoxy resins were reported in the early 1980s with the advent of onium salts. An efficient, stable onium salt, triphenylsulfonium hexafluoroantimonate produces acid upon exposure to radiation, for example, deep ultraviolet (UV) light, electron beam, and x rays. Combining this onium salt with commercial glycidyl ether epoxy resins provides an inexpensive resist capable of submicron imaging in deep UV, electron beam, and x-ray lithography. Lithographic investigations have concentrated on o-cresol epoxy novolac resin–onium salt resist formulations. Resist contrasts are high, >3 in the deep UV, ≥2 with electron beam, and ≥3 for x ray. Submicron resolution is obtained without solvent swelling. Swelling affects resolution below 0.5 μm, although high aspect ratio sub-half-micron images have been obtained. Epoxide equivalent weight and molecular weight distribution are significant resin properties which influence resist formulating and lithography.
Polarized adsorption of H2O on NaCl(100) in air, observed by second harmonic generation
Authors: Tepper P. , Zink J. C. , Schmelz H. , Wassermann B. , Reif J. , Matthias E.
Published: July 2002

We have observed a pronounced m-symmetry in the azimuthal dependence of optical second harmonic generation in reflection from NaCl(100) in air at room temperature, in spite of the fact that the C4v symmetry of this surface should not exhibit any anisotropy. The observed anisotropy builds up and then disappears again with time of exposure to ambient air. The high solubility of NaCl in water, together with the high polarity of the water molecule, suggests that the dipolar surface hyperpolarization, responsible for second harmonic generation, is caused by adsorbed H2O at a certain range of coverage. The m-symmetry then reflects a macroscopic polarization due to a partially parallel orientation of the adsorbed water molecules. In accord with tentative results of molecular dynamics calculations, this indicates polymerization of water on NaCl(100) at room temperature.
Measurement of the valence band offset in novel heterojunction systems: Si/Ge (100) and AlSb/ZnTe (100)
Authors: Yu E. T. , Croke E. T. , Chow D. H. , Collins D. A. , Phillips M. C. , McGill T. C. , McCaldin J. O. , Miles R. H.
Published: July 2002

We have used x-ray photoelectron spectroscopy to measure the valence band offset in situ for strained Si/Ge (100) heterojunctions and for AlSb/ZnTe (100) heterojunctions grown by molecular-beam epitaxy. For the Si/Ge system, Si 2p and Ge 3d core level to valence band edge binding energies and Si 2p to Ge 3d core level energy separations were measured as functions of strain, and strain configurations in all samples were determined using x-ray diffraction. Our measurements yield valence band offset values of 0.83±0.11 eV and 0.22±0.13 eV for Ge on Si (100) and Si on Ge (100), respectively. If we assume that the offset between the weighted averages of the light-hole, heavy-hole, and spin-orbit valence bands in Si and Ge is independent of strain, we obtain a discontinuity in the average valence band edge of 0.49±0.13 eV. For the AlSb/ZnTe (100) heterojunction system, we obtain a value of −0.42±0.07 eV for the valence band offset. Our data also suggest that an intermediate compound, containing Al and Te, is formed at the AlSb/ZnTe (100) interface.
Parametric modeling of focused ion beam induced etching
Authors: Gandhi Anil , Orloff Jon
Published: July 2002

Focused ion beam induced etching with a (Cl2/GaAs) gas/substrate system was performed and the gas flux dependence analyzed. Using 20 keV Ga+ ions, the focused ion beam, with a Gaussian distribution of current density (Iprobe=0.32 nA) and a spot diameter of 0.4 μm, is scanned over a rectangular area to derive an etch. Ion incidence being kept normal to the surface, etched depths are accurately measured as a function of gas flux. Pressures less than 43 mTorr, corresponding to a gas flux of 1.04×1019 molecules/cm2 s are considered, as compared to the peak ion arrival rate of 1.11×1018 ions/cm2 s. A spiked (current) delivery model is presented for the dependence of etch rate on gas flux. The scanned nature of the process is taken into account in this model, so that the ion flux over a differential area arrives with a gaussian spatial distribution in temporal spikes or bursts. The etch mechanism supported by this model, namely, ‘‘chemically enhanced physical sputtering,’’ is discussed in light of the fitted parameters. Finally, a convenient application of the model is elaborated.
Spectroscopy of dichalcogenides and trichalcogenides using scanning tunneling microscopy
Authors: Wang Chen , Slough C. G. , Coleman R. V.
Published: July 2002

The scanning tunneling microscope has been used to measure the charge-density wave (CDW) energy gap in the layer structure compounds 1T-TaSe2, 1T-TaS2, 1T-VSe2, 1T-TiS2, 2H-TaSe2, 2H-TaS2 and 2H-NbSe2. The measured values show a systematic dependence on the strength of the CDW and calculated values of 2Δ/kBTc are compared. CDW gap measurements on the trichalcogenide compounds NbSe3 and TaS3 are also included.
Damage studies of dry etched GaAs recessed gates for field effect transistors
Authors: Salimian S. , Yuen C. , Shih C. , Cooper C. B.
Published: July 2002

Reactive ion etching of recessed gates for metal–semiconductor field effect transistors (MESFETs) and high electron mobility transistors (HEMTs) devices has been studied in SiCl4 and SiCl4/SF6 plasmas. The effects of etch parameters such as dc bias and overetch, on device characteristics were evaluated and compared with wet-etched samples. Results indicate damage-free etching of MESFETs in SiCl4 plasma for dc bias values in the range of −100 to −300 V. The etched features did not exhibit any undercut, however, the etch profiles were generally sloped and more vertical etch profiles were obtained at higher dc bias conditions. The use of thin stop-etch layers of Al0.26Ga0.74As inserted in the active epilayer of GaAs, in conjunction with selective etching of GaAs over AlGaAs in SiCl4/SF6 mixtures resulted in significant improvement in etch uniformity as well as good device performance. The etch profiles became more vertical with increased overetching after etch stop on the AlGaAs layer. However, it was found that the value of drain-source saturation current Idss decreased with increased overetching, as a result of the depletion of the active layer. Consequenty, devices with more than 200% overetch failed to operate in the depletion mode and could only operate in the enhancement mode. The SiCl4/SF6 mixture was also utilized for etching of recessed gates for HEMT devices with an Al0.26Ga0.74As layer of 250 Å. These devices only operated in the enhancement mode and hold transconductance gm values similar to wet-etched samples. The data indicate less damage with etching at lower dc bias conditions. Etching at a dc bias of −200 V with more than 200% overetch resulted a completely damaged device.
Soft x-ray projection lithography using a 1:1 ring field optical system
Authors: MacDowell A. A. , Bjorkholm J. E. , Bokor J. , Eichner L. , Freeman R. R. , Mansfield W. M. , Pastalan J. , Szeto L. H. , Tennant D. M. , Wood O. R. , Jewell T. E. , Waskiewicz W. K. , White D. L. , Windt D. L. , Silfvast W. T. , Zernike F.
Published: July 2002

An iridium-coated Offner 1:1 ring field camera has been used to carry out projection lithography using 42 nm light from an undulator in the vacuum ultra violet storage ring at Brookhaven National Laboratory. Near-diffraction-limited resolution has been obtained showing features as small as 0.2 μm within a 2 mm×0.25 mm image field. Images of both transmission and reflection masks have been obtained. The impact of source coherence on imagery has been investigated. Hydrocarbon contamination problems experienced in this photon energy range have been investigated and possible solutions are suggested.
HgZnTe for very long wavelength infrared applications
Authors: Patten E. A. , Kalisher M. H. , Chapman G. R. , Fulton J. M. , Huang C. Y. , Norton P. R. , Ray M. , Sen S.
Published: July 2002

HgZnTe has been of considerable interest in the last few years as an alternative infrared (IR) detector material to HgCdTe because of HgZnTe’s greater mechanical hardness, higher Hg vacancy formation energies, and other desirable properties which may lead to greater producibility (yield) and reliability (operation life). We are developing very long wavelength IR (VLWIR) HgZnTe detectors (17 μm at ≥65K) for longterm Earth Observing System NASA missions. In recent months we have been able to achieve, nearly routinely, outstanding quality HgZnTe on lattice-matched substrates (Cd0.84Zn0.16Te). By careful screening of substrate quality and refinement of the growth system and growth parameters, we overcame previous melt retention problems observed when using these high Zn% substrates. X-ray rocking curve widths (full width at half-maximum) as narrow as 26 arc-sec (for a 1×8 mm spot) for these epilayers have been achieved which is comparable to that for the best HgCdTe ever reported. In addition, we have, for the first time, fabricated and demonstrated high performance VLWIR (λco>17 μm at 80K) photoconductors made from liquid phase epitaxy HgZnTe which exhibit near background limited performance (peak D* up to 1011 cm(Hz)1/2/W) at high background. From these device results we see a clear correlation between the layer/substrate lattice match and the resulting device performance.
Sputtering damage in the Pt(111) surface by He+ ion bombardment
Authors: Michely Thomas , Comsa George
Published: July 2002

The morphology of an initially almost ideal Pt(111) surface upon bombardment with 1 keV He+ ions at 735 K has been investigated by scanning tunneling microscopy. In addition to vacancy islands previously observed upon Ar+ ion bombardment, the He+ -damaged surface exhibits a large density of hexagonal adatom islands with threefold symmetry and of subatomic height bumps with smooth height profiles already after fluences as low as 5.3×1019 ions/m2. The formation of bumps is ascribed to strain fields resulting from subsurface helium bubbles. The observed adatom islands are pushed out of the surface by such bubbles. With increasing fluence the density of dislocations penetrating the surface is drastically enhanced.
Three-dimensional analysis of a microstructure by submicron secondary ion mass spectrometry
Authors: Satoh H. , Owari M. , Nihei Y.
Published: July 2002

By utilizing the sharpness of a focused ion beam, lateral resolution of SIMS analysis has been improved by one or two orders of magnitude. The authors constructed the submicron SIMS by using a gallium focused ion beam. On the other hand, a focused ion beam is frequently used as a tool for micromachining due to its high current density and sharpness. In situ combination of micromachining and high spatial resolution analysis brings a new field of microbeam analysis on materials. In the development of thin-film multilayer devices or large scale integrated circuits, three-dimensional analysis of local microstructure has a great importance. In order to determine location and composition of a specific subsurface microstructure, a focused ion beam is used as (1) a machining tool to expose a vertical cross section on which the center of the specific microstructure lays, and (2) a primary beam of SIMS element mapping. Through the analysis of a buried fine particle, the submicron SIMS is shown to be a powerful tool for three-dimensional analysis of a microstructure.
Dependence of the quality factor of micromachined silicon beam resonators on pressure and geometry
Authors: Blom F. R. , Bouwstra S. , Elwenspoek M. , Fluitman J. H. J.
Published: July 2002

An experimental study of damping and frequency of vibrating small cantilever beams in their lowest eigenstate is presented. The cantilever beams are fabricated from monocrystalline silicon by means of micromachining methods. Their size is a few millimeters in length, a few 100 μm in width, and a few 10 μm in thickness. Damping and resonance frequency are studied as a function of the ambient pressure p (1–105 Pa) and the geometry of the beam. The purpose of this research was to obtain design rules for sensors employing vibrating beams. The analysis of the experimental results in terms of a semiqualitative model reveals that one can distinguish three mechanisms for the pressure dependence of the damping: viscous, molecular, and intrinsic. For viscous damping a turbulent boundary layer dominates the damping at high pressures (≊105 Pa), while at smaller pressure laminar flow dominates. In the latter region, this leads to a plateau for the quality factor Q and in the former to Q α √p. The pressure pc at which the transition from laminar flow dominated damping to turbulent flow dominated damping occurs depends on the geometry of the beams. pc is independent on the length and decreases with both, the width and the thickness of the beams.
Reactive ion etching of via holes for GaAs high electron mobility transistors and monolithic microwave integrated circuits using Cl2/BCl3/Ar gas mixtures
Authors: Nordheden K. J. , Ferguson D. W. , Smith P. M.
Published: July 2002

A process for through-the-wafer via hole connections to each individual source contact for monolithic microwave and millimeter wave integrated circuits and power high electron mobility transistors has been developed using reactive ion etching in Cl2/BCl3/Ar gas mixtures. Placing vias in this manner eliminates the need for source airbridges, which minimizes source inductance and results in increased gain and efficiency. The GaAs etch rate and resultant etch profiles have been studied as functions of bias voltage, gas mixture, flow rate, via mask dimension, and etch time.
Improving productivity on a single wafer aluminum etcher by the use of total productive maintenance
Authors: Hackenberg John , Flaim Dave
Published: July 2002

In order to maintain an effective and competitive manufacturing environment in the microelectronic industry, continual improvement to the fabrication tools is mandated. One of the myriad of measurement philosophies available is the concept of overall equipment effectiveness (OEE), which is a part of total productive maintenance (TPM). Results of an 18 month study on improving the OEE of single wafer aluminum plasma etchers are presented. At the start of the project, several designed experiments were performed to optimize the plasma etch process. A detailed logging procedure was implemented that accounted for the various equipment operating states as well as the number of wafers processed. The OEE for the initial 6 months of the program was determined to have an average value of 42%. Improvements to the etchers, their operation and maintenance were implemented as a result of the TPM program. During the last 4 months of the study, the average value for OEE was 67%, an increase of 60%.
Wafer scale processing of InGaAsP/InP lasers
Authors: Dzioba Steven , Cook J. P. D. , Herak T. V. , Livermore S. , Young M. , Rousina R. , Jatar S. , Shepherd F. R.
Published: July 2002

Chemically assisted ion beam etching (CAIBE) and electron cyclotron resonance (ECR) plasma deposition have been used to etch and coat 1.3 μm InGaAsP/InP heterostructure lasers in full wafer form. Ar/Cl2 CAIBE, using an ECR dual grid ion source, was used to etch 4 μm deep vertical (90°±0.5°), smooth facets at rates up to 1.3 μm/min. An integrated back facet monitor was simultaneously fabricated in the same heterostructure. High-reflectivity Si/SiO2 optical coatings were deposited on the etched facets by low-temperature (<120 °C) ECR plasma deposition and selectively patterned by liftoff. Full wafer testing of the processed devices showed good uniformity (±3%) with laser threshold currents of 25 mA and a slope efficiency of 0.23 W/A at 25 °C and 0.11 W/A at 85 °C. Back facet monitor efficiency was 0.4 A/W over the whole temperature range.
Atomic force microscopy study of the fractal shape of residual barium cuprate/copper oxide flux on the surface of Y2Ba4Cu7O15 and YBa2Cu4O8 single crystals
Authors: Lang H. P. , Karpinski J. , Kaldis E. , Ramseyer J.-P. , Güntherodt H.-J.
Published: July 2002

Atomic force microscopy has been applied to study the surfaces of Y2Ba4Cu7O15 (247) and YBa2Cu4O8 (124) high-temperature superconductor single crystals at ambient temperature and pressure. In contrast to very thin (<10 μm) crystal platelets, which exhibit by scanning tunneling microscopy clean terraces with steps of the height of one or multiple unit cells, thicker crystals show surfaces partially covered by a contamination layer with a highly curved boundary line originating from BaCuO2/CuO flux used to grow 124 and 247 single crystals under high oxygen pressure. The evaluation of the length of such flux boundaries by the box counting method reveals that they are fractal with a fractal dimension of about 1.4. Close to crystal steps, higher fractal dimensions are observed provided the terrace width is sufficiently large. The fact that the residual flux is always found on the lower terrace level of a crystal step allows discussion of a possible mechanism of flux migration on the crystal surface.
Workpiece charging in electron beam lithography
Authors: Ingino J. , Owen G. , Berglund C. N. , Browning R. , Pease R. F. W.
Published: July 2002

A major contribution to total overlay error can be pattern placement imprecision due to charging of the workpiece in electron beam lithography for mask manufacture. A first-generation, worst-case model is presented which indicates that an electron can experience quite a large placement error for a modest workpiece surface potential (100 nm/V). This model also predicts that the amount of error is proportional to the working distance. A novel method which measures the surface potential, to within 50 mV, is also presented. Results indicate that when exposed with 10 kV electrons the surface potential of 3000 Å PMMA on silicon is 1.5 V while that of 4000 Å SAL-601 on chrome on quartz is 0.5 V. The discharging time for both samples was found to be of the same order as the write time for a typical mask.
Scanning tunneling microscopy observation of the growth evolution of gold films evaporated on highly oriented pyrolitic graphite
Authors: Hammiche A. , Webb R. P. , Wilson I. H.
Published: July 2002

The growth evolution of gold films evaporated on highly oriented pyrolitic graphite has been investigated using scanning tunneling microscopy. This is achieved by monitoring the morphology of sample surfaces which have been covered with increasing amounts of deposit. The smallest clusters observed at an early stage of the growth are a few nanometers in size. A saturation density of these clusters of about 2×1011 cm−2 was statistically estimated. Both random and oriented grains were observed.
Fabrication of controlled slope attenuated phase-shift x-ray masks for 250 nm synchrotron lithography
Authors: Gentili M. , Di Fabrizio E. , Grella L. , Baciocchi M. , Mastrogiacomo L. , Maggiora R. , Xiao J. , Cerrina F.
Published: July 2002

This article reports the manufacturing process of 250 nm resolution x-ray masks featuring gold absorbers optimized for synchrotron radiation lithography in both thickness and absorber slope. X-ray optics modeling predicts that nonvertical absorber flanks may provide better linewidth control by suppressing higher spatial frequencies. To test these conclusions, masks were patterned by electron beam lithography at accelerating voltages of 30 kV with the final goal of developing various slopes and feature sizes. Monte Carlo simulation is used to predict the best exposure conditions. An intelligent usage of the resist thickness and exposure conditions allow us to exploit forward scattering of electrons to provide the required resist profile in a well controlled way. By adjusting exposure dose and development time, the slope profile can be altered from 90° to about 82°. We demonstrate that lines and spaces of 250 nm with controlled and repeatable profile slope of 87° are achievable in 400-nm-thick gold with good exposure latitude. Under such optimized process conditions a dose variation of 10% leads to a 10% linewidth change for 250 nm features. Exposure latitude for all the writing conditions was also determined. Finally, we performed x-ray exposure using a mask including both sloped and nonsloped absorbers using Suss XRS 200/2M aligner at the Centre for X-Ray Lithography of the University of Wisconsin (CXrL). The results confirmed the theoretical model used in image calculations, providing experimental evidence that the exposure latitude is not degraded, but actually improves in case of sloped patterns.
Reactive-ion-beam etching of InP in a chlorine–hydrogen mixture
Authors: Vawter G. Allen , Ashby Carol I. H.
Published: July 2002

We present the first application of Cl2+H2 reactive-ion-beam etching of InP. Specularly smooth etching is achieved using an ion beam of 53%–73% Cl2 in H2 at a 300 eV extraction potential with the substrate held at 250 °C. InP etch morphology and rate are examined as functions of Cl2+H2 mixture, sample temperature, and chamber pressure. Significant deviation from the optimum smooth-etch conditions are seen to result in rough surfaces.
Study of nanoscale magnetic structures fabricated using electron-beam lithography and quantum magnetic disk
Authors: Chou Stephen Y. , Wei Mark , Krauss Peter R. , Fischer Paul B.
Published: July 2002

Two types of nanoscale single-domain magnetic structures were fabricated using e-beam nanolithography and were studied using magnetic force microscopy. The first structure is the isolated and interactive arrays of Ni bars on silicon that are 35 nm thick, 1 μm long, and have widths ranging from 15 to 200 nm and spacings ranging from 200 to 600 nm. The second structure is an array of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a density of 65 Gbits/in2—over two orders of magnitude greater than the state-of-the-art magnetic storage density. It was found that the magnetic properties of these structures can be controlled by engineering their size and spacing. When the bar width is smaller than 150 nm, the bars become single magnetic domain. As the width of the isolated bars decreased from 200 to 55 nm, the magnetic field needed to switch the magnetization of these bars increased monotonically from 100 to 740 Oe which is the highest field reported for Ni. However, further reduction of bar width led the switching field to decrease due to thermal effect. Furthermore, it was found that as the bar spacings become smaller, the interaction between the bars will reduce the switching field. Finally, based on the artificially patterned single-domain magnetic structures, we propose a new paradigm for ultra-high-density magnetic recording media: quantum magnetic disk.
Surface characterization of flexible magnetic disk with scanning probe microscopy
Authors: Masai J. , Shibata-Seki T. , Seki K. , Mori K. , Yamauchi H. , Sasaki K. , Yoshiyama R. , Yamamoto M.
Published: July 2002

Using scanning probe microscopy such as scanning tunneling microscopy (STM), atomic force microscopy (AFM), and magnetic force microscopy (MFM) as well as conventional scanning electron microscopy (SEM), the surface morphology and intentionally recorded magnetic bit pattern on the surface of a flexible magnetic disk have been investigated. Typical images taken with SEM, STM, and AFM of acicular Co–γ-Fe2O3 magnetic particles and protrusions of abrasive aluminum particles appeared on the disk surfaces are shown. Closer examination of the simultaneously measured AFM images and MFM images at the same regions of the flexible disk surfaces suggested that the nonuniform distribution of Co–γ-Fe2O3 magnetic particles and appearance of aluminum abrasive particles on the surface are major causes of the irregularity of magnetic bit patterns in the MFM images. Showing those images, this paper demonstrates that the complementary use of SEM, STM, AFM, and MFM is very effective to examine the above-mentioned surface characteristics in relation to the friction and wear at a magnetic read/write head–disk interface.
Effects of the tip shape on scanning tunneling microscope images: First-principles calculations
Authors: Watanabe Satoshi , Aono Masakazu , Tsukada Masaru
Published: July 2002

Taking the Si(111)√3×√3–Ag surface as an example, it has been investigated how the atomic arrangement of the probe tip affects obtained scanning tunneling microscope (STM) images using first-principles theoretical calculations. Various shapes of the tip were represented by tilting the symmetry axes of four kinds of clusters consisting of several tungsten atoms. Tips having a few equivalent atoms at their apexes produce distinctly different STM images from experiment if their symmetry axes are normal to the sample surface. Even in these cases, however, calculated STM images become similar to the observed ones by tilting the symmetry axes. This fact indicates that only one atom at the tip apex gives essential contribution to the tunneling current. Furthermore, it can be explained why good images can be obtained, in spite of the fact that the shape of experimental STM tips must be quite arbitrary on the atomic scale.
Topography of brittle fracture surfaces of titanium aluminide alloy as revealed by a scanning tunneling microscope
Authors: Wang Z. , Bai C. , Dai C. , Huang G. , Zhang P. , Zhang Y. , Chu W. , Qiao L. , Wang Y.
Published: July 2002

The brittle fracture surfaces of Ti3Al+Nb and Ti3Al were investigated with a scanning tunneling microscope (STM) under ambient conditions using a mechanically cut platinum iridium alloy wire and electrochemically etched tungsten tips. The results show that the fracture surfaces consist of cleavage steps with dimensions of the order of ∼2 nm for Ti3Al+Nb and ∼60 nm for Ti3Al, similar to cleavage surfaces observed by scanning electron microscopy. Some cavities between the microcleavage steps on the scale of a few nanometers were observed for Ti3Al+Nb. The reproducibility of the STM images under ambient conditions depends on the applied bias voltage. The quality of the STM images obtained via tungsten tips is better.
Theoretical study of the band offsets at GaN/AlN interfaces
Authors: Albanesi E. A. , Lambrecht W. R. L. , Segall B.
Published: July 2002

The valence-band offset at the zincblende AlN/GaN (110) interface is calculated self-consistently by means of the linear muffin-tin orbital method using up to 5+5 layer supercells. The value obtained is Ev(GaN)−Ev(AlN)=0.85 eV corresponding to a type I offset. Assuming interface orientation and polytype effects on the valence-band maximum to be reasonably small, a type I offset can also be expected for wurtzite interfaces. By means of separate calculations, we also test the validity of two simplified approaches, the self-consistent dipole approximation (SCD) of Lambrecht, Segall and Andersen and the dielectric midgap energy (DME) model of Cardona and Christensen. We find that the SCD results are in very good agreement and the DME results, in fairly good agreement with the fully self-consistent results. The interface local densities of states show no indication of interface states in the main gap.
Molecular-beam epitaxial growth of high quality InSb for p-i-n photodetectors
Authors: Singh G. , Michel E. , Jelen C. , Slivken S. , Xu J. , Bove P. , Ferguson I. , Razeghi M.
Published: July 2002

We report the growth of high quality InSb p-i-n structures which have been optimized using reflection high energy electron diffraction. Optimized InSb p-i-n structures of 5.8 μm thickness demonstrated x-ray full widths at half-maximums (FWHMs) of 101 and 147 arcsec for GaAs and Si substrates, respectively, and exhibited excellent uniformity and morphology. Prototype InSb p-i-n detectors on Si have been fabricated and have demonstrated photovoltaic response at 6.5 μm up to 200 K. A 4.8 μm InSb layer grown on GaAs at a growth temperature of 395 °C and a III/V incorporation ratio of 1/1.2 had an x-ray rocking curve FWHM of 158 arcsec and a Hall mobility of 92 300 cm2 V−1 s−1 at 77 K.
Atomic force microscopy of Au implanted in sapphire
Authors: Henderson D. O. , Mu R. , Tung Y. S. , George M. A. , Burger A. , Morgan S. H. , White C. W. , Zuhr R. A. , Magruder R. H.
Published: July 2002

Ion implantation of gold into sapphire followed by annealing at 1100 °C leads to the formation of metal colloids. We report on the atomic force microscopy (AFM), infrared reflectance, and optical spectra for Au implanted in sapphire. The presence of the metal colloids is revealed in the optical spectra by the appearance of an absorption at 547.5 nm for the annealed sample, which we attribute to the surface plasmon resonance of Au colloids. The infrared spectra indicate that annealing Au-implanted sapphire at 1100 °C relaxes most of the ion-induced damage in the crystal. Tapping mode AFM has been applied to image the Au colloids embedded in the sapphire matrix. Colloids ranging in size from 10 to 30 nm were observed by AFM measurements. The shape of the colloids appear to be predominantly spherical.
Structural characteristics of a uniquely nanostructured organic thin film
Authors: Debe M. K. , Drube A. R.
Published: July 2002

The red pigment N,N-di(3,5-xylyl)perylene-3,4:9,10 bis(dicarboximide) is easily vacuum deposited and when subsequently vacuum annealed, a 1500 Å film transforms to a random array of crystalline whiskers of extremely high number density (∼50 whiskers per square micron), uniformly oriented with their long axes normal to the substrate. We have previously reported on growth kinetics of the whiskers by surface diffusion to screw dislocations. Here we present a structural characterization of the whiskers using transmission electron microscopy and selected-area electron diffraction. The whiskers’ dimensions, size distributions, specific surface area, and lattice structure are determined. They are lath shaped with mean cross-sectional widths and thicknesses of 525±120 and 270±75 Å, respectively. Surprisingly, the lattice is determined to be body centered cubic with a 14.5(4) Å lattice constant. The growth tips are in the [211] direction, bounded by(1_11) and (011_) side planes. The latter side plane surfaces are decorated with steps lying parallel to the long axis, and spaced ∼44 Å apart. The pigment whiskers can be readily sputter or vapor coated over large areas to provide conformally coated nanostructure-sized features with numerous novel chemical and physical properties.
Diffusion of atoms on Au(111) by the electric field gradient in scanning tunneling microscopy
Authors: Méndez J. , Gómez-Herrero J. , Pascual J. I. , Sáenz J. J. , Soler J. M. , Baró A. M.
Published: July 2002

It has been shown in field ion microscopy experiments that the electric field gradient drives the diffusion of atoms on a surface. The same idea has been proved to work in a scanning tunneling microscopy experiment, as was first demonstrated when Cs atoms were induced to move on GaAs(110) by the electric field, taking advantage of the high Cs static dipole moment. In this work we demonstrate that this effect is more general and can be used even in systems that have a small dipole moment, such as the surface Au adatoms of Au(111). The experiment is performed in ultrahigh vacuum with a clean surface and tip. By applying a voltage increase and maintaining constant the tunneling current we are able to produce protrusions under the tip of several atom-heights and smaller clusters occupying large areas. We study the influence of the time duration of the pulse and the voltage amplitude. Surface modifications are already produced at 0.2 V/Å electric field value. We suggest that the clusters are produced by an increase of the density of free adatoms in the high electric field region.
Study of plastic flow in ultrasmall Au contacts
Authors: Stalder A. , Dürig U.
Published: July 2002

Yielding properties of Au point contacts of nanometer-scale dimensions have been studied using a scanning tunneling microscope supplemented by a force sensor for measuring tip–sample forces. The contacts are made by indenting the tip typically 10 nm into the substrate, whereby an adhesion neck is formed. Three consecutive deformation phases of the neck can be identified during retraction of the tip: (1) buildup of tensile stress, (2) incomplete fracture, and (3) quasicontinuous plastic flow. Finally the neck breaks when a maximum of three to four atoms are left in the contact. In the plastic flow regime, the conductance and thus the contact area shrink exponentially with elongation of the neck. This provides strong evidence that plastic deformation occurs locally within five to six atomic layers. The latter is inferred from the decay constant of the exponential decrease of the cross section. The applied stress during plastic flow is initially of the order of 10 GPa and gradually increases to ≂20 GPa shortly before the neck breaks. From a fit to the data accounting for a surface force contribution, an intrinsic yield strength of the order of 6 GPa is obtained, which is more than one order of magnitude larger than the macroscopic yield strength of Au.