bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of chemical vapor deposited tetraethylorthosilicate oxides: Correlation with deposition parameters, annealing, and hydrogen concentration
Authors: Nguyen Ann Marie , Murarka Shyam P.
Published: July 2002

The deposition of thin silicon dioxide films using plasma enhanced and ozone assisted thermal chemical vapor deposition techniques and tetraethylorthosilicate (TEOS) as precursor in AME Precision 5000 reactor has been carried out. The properties of the oxide, such as etch rate, hydrogen concentration, dielectric constant, and C–V behavior, were investigated as a function of the deposition parameters, such as radio-frequency (rf) power, gas composition, and temperature, and post rapid thermal annealing (RTA). The paper reports these results and discusses the findings. The electrical properties of these oxides, plasma, and ozone, were influenced primarily by water vapor that was absorbed and trapped into the bulk of the film either during or within a short time of deposition. The film quality can be considerably improved by RTA between 800 and 1000 °C.
Development of a chlorofluorocarbon/oxygen reactive ion etching chemistry for fine-line tungsten patterning
Authors: Daubenspeck T. H. , Sukanek P. C.
Published: July 2002

Tungsten patterning by reactive ion etching has been studied in batch and single-wafer reactors using photoresist as the etch mask and a chemistry comprised of CHF3/O2 with CF2Cl2. Tungsten etch rate and patterned profile were found to depend upon energetic ion levels and reactor loading, as well as on the basic reactor control parameters of power, pressure, and gas composition. Process conditions suitable for fine-line anisotropic profile formation through a single layer of resist were demonstrated for the low-pressure batch reactor. At the higher pressure and power density typical of the single-wafer reactor, multistep processing was required to balance the competing reactions of etch and deposition of ‘‘polymer’’ in order to maintain process control.
Characteristics of double-heterostructure GaAs/AlGaAs laser diodes on Si substrates by selective-area molecular-beam epitaxy
Authors: Lee Henry P. , Liu Xiaoming , Wang Shyh
Published: July 2002

We report successful fabrication of GaAs/Al0.26Ga0.74As double-heterostructure (DH) laser diodes grown on patterned Si substrates by molecular-beam epitaxy. The patterned substrate consists of exposed Si stripes with widths ranging from 9 to 70 μm and surrounded by 900-Å thick SiN films on both sides. Oxide-defined contact stripe lasers with stripe widths ranging from 3 to 50 μm were fabricated. Reduction in threshold current densities is observed for selective-area grown lasers due to current confinement effect by the high resistivity polycrystalline GaAs/AlGaAs films surrounding each of the lasers. Built-in index guiding is also observed for the 10 μm-wide stripe laser as evident from its longitudinal mode spectrum and far-field patterns.
Focused ion beam micromachined three-dimensional features by means of a digital scan
Authors: Ximen H. , DeFreez R. K. , Orloff J. , Elliott R. A. , Evans G. A. , Carlson N. W. , Lurie M. , Bour D. P.
Published: July 2002

Focused ion beam micromachining (FIBM) is a promising new technique capable of forming optical quality surfaces in semiconductor laser materials. A beam of 25 keV Ga+ ions focused to a 50–250 nm spot can sputter materials from a wafer surface providing a method for fabricating submicron features, such as diode laser output mirrors and coupled cavity oscillating mirrors. To date, all mirrors fabricated by traditional FIBM have been made up of lines or rectangles (i.e., fabricated by straight line scans). However, straight line scans cannot be satisfactorily used for many kinds of applications. In order to fabricate arbitrary structures such as curves and intersecting lines, a fully digitized, nonlinear, three-dimensional (3D) and variable-speed scan strategy, which can produce desired structures with arbitrarily curved paths in a plane and arbitrary depth profiles, has been developed. This strategy has been implemented using a FIB system with an IBM-compatible computer to fabricate ‘‘V’’, micro-‘‘V’’ and parabolic mirrors in GaAs lasers. A simple computer simulation of FIBM in 3D space, which is based upon a Gaussian current distribution for the ion beam, has been developed to demonstrate the difference between the two scan strategies, i.e., with and without variable-scan speed. The aim of the 3D simulation is software support for the computer controlled FIB micromachining of various 3D structures on semiconductor diode laser devices.
Achromatic quadrupole focusing systems for use with liquid metal ion sources
Authors: Harriott L. R. , Brown W. L. , Barr D. L.
Published: July 2002

We discuss the use of achromatic quadrupole lenses to overcome the limitation due to the energy spread of ions from liquid metal ion sources as they are currently focused with axially symmetric electrostatic lenses. Achromatic quadrupoles require both magnetic and electrostatic focusing elements. Each lens acts to focus in one plane and defocus in the other so that multiplet focusing systems are required to form an image of the source. Lens acceptance angles are limited by the bore of the electrostatic elements which in turn is limited by the necessary magnetic gradients required of the magnetic elements. The coefficients relating image distance to lens excitation of some of the elements of the quadrupole multiplets are found to be much larger than those in an axially symmetric electrostatic system. These factors are discussed in terms of the stability requirements of lens power supplies for a particular achromatic triplet system which is undergoing initial test.
Fabrication and characterization of high-flatness mesa-etched silicon nitride x-ray masks
Authors: Moel A. , Chu W. , Early K. , Ku Y.-C. , Moon E. E. , Tsai F. , Smith Henry I. , Schattenburg M. L. , Fung C. D. , Griffith F. W. , Haas L. E.
Published: July 2002

To realize a technology for x-ray nanolithography (<100 nm features), which is compatible with manufacturing, a number of mask design requirements must be met that are unrelated to patterning, repair, and alignment. These include high-flatness membranes and support structures so that mask-wafer gaps less than 10 μm can be achieved without risk of damage, and a rigid mask frame to avoid problems of distortion during handling. The membrane material should be compatible with semiconductor-processing, possess high strength, be radiation hard, and be transparent to light for alignment purposes. Details of a mask architecture that meets these requirements will be described.
Scanning tunneling microscope lithography: A solution to electron scattering
Authors: Dobisz E. A. , Marrian C. R. K.
Published: July 2002

The scanning tunneling microscope (STM) operated in the field emission mode is shown to have important lithographic applications. The technological potential of the technique is demonstrated by patterning films up to 80 nm thick of SAL-601-ER7, a negative resist from Shipley. With the STM, 22 nm lines of developed resist have been written on Si and 35 nm lines on GaAs. For comparison, exposures were made with a 50 kV, 17 nm 1/e diameter electron beam in identically prepared and processed resist films on a variety of substrates. The 50 kV probe produced minimum linewidths of: 60 nm on a 200 nm Si3N4 membrane; 70 nm on a 200 nm Si3N4 film on a bulk Si substrate; 95 nm on a bulk Si substrate; and 186 nm on a bulk GaAs substrate. The strong substrate dependence indicates that the resolution, at 50 kV, is determined by electron scattering rather than the post exposure processing of the resist. Low voltage lithography with an STM offers a technique which greatly reduces the effects of electron scattering with a consequent improvement in resolution. In addition, the results of the Si3N4 film suggest a novel way to reduce the effects of backscattered electrons in 50 kV lithography.
A review of impurity behavior in bulk and epitaxial Hg1−xCdxTe
Authors: Capper P.
Published: July 2002

Extrinsic doping using elements which produce stability of electrical properties will become increasingly important in future infrared device structures based on Hg1−xCdxTe (MCT). This paper reviews the incorporation and activation of dopants in the most widely used bulk and epitaxial growth techniques. Stoichiometry at the growth temperature is demonstrated to be the critical factor which affects dopant activation. A number of factors, including stoichiometry, can affect the as-grown electrical properties of MCT and the importance of determining the type of conduction in the as-grown state, if successful extrinsic doping is to be accomplished, is stressed. The minimum criterion for confirmation of dopant activity is established as agreement between electrical and chemical data on the same low temperature Hg-annealed sample. At low concentrations of dopants, an additional requirement is to confirm the absence of other potential impurity dopants at equivalent levels. Most elements are active dopants in accordance with their relative position in the periodic table but several important exceptions exist, notably group V elements in Te-rich material. Slow-diffusing dopants are preferred and techniques are described which produce stable doped/undoped heterostructures, using As as the acceptor element in metalorganic vapour phase epitaxy growth. Data on dopant segregation behavior, in growth from liquids, acceptor ionization energies and minority carrier lifetimes are presented and their importance is discussed. Ionization energies can be used to differentiate doped from undoped material, providing the degree of compensation is known. Doping using extrinsic acceptors has been shown to improve minority carrier lifetimes in material grown by certain techniques but is unsuccessful in other types of material. Some recent data on annealing undoped Te-rich liquid phase epitaxial material will be presented which suggests that higher minority carrier lifetimes can be achieved purely by defect control.
Adsorption and desorption of sulfur on a GaAs (001) surface by H2S exposure and heat treatment
Authors: Kawanishi Hidenori , Sugimoto Yoshimasa , Akita Kenzo
Published: July 2002

The adsorption and desorption of sulfur on a GaAs (001) surface was studied using in situ Auger electron spectroscopy and reflection high-energy electron diffraction (RHEED). The H2S -treated surface showed a (2×1) sulfur-terminated structure, with the sulfur considered to be a few monolayers thick. RHEED patterns showed that the (2×1) reconstruction changed into an arsenic-stabilized (2×4) structure when heated to 590 °C under an arsenic flux. A sulfur Auger signal on the H2S -treated surface was found to completely dissapear upon heating. These data show that H2S exposure is appropriate for preparing a sulfur-terminated surface and that high-quality crystal regrowth is possible on the surface after being heat treated.
Scanning tunneling microscopy of microstructures on cleaved Si(111) surface
Authors: Tokumoto H. , Wakiyama S. , Miki K. , Murakami H. , Okayama S. , Kajimura K.
Published: July 2002

Scanning tunneling microscopy (STM) of microstructures resulting from stresses during cleaving has been studied on cleaved Si(111) surfaces. STM images with large scanning area (10×10 μm2) have revealed the existence of large-scale microstructures which are closely related to the ‘‘river pattern’’ seen in optical microscope images. When a fairly flat region in the STM images is magnified, several interesting features are found: triangular-shaped terraces and long but narrow terraces with regular parallel [112̄] oriented steps which is contrary to the previous finding of [1̄1̄2] oriented steps. On the triangular terraces, there exist the dimer rows of the Si(111)-2×1 reconstruction. The atomic rows observed in the STM image on the parallel-stepped terraces can be explained by a 3×1 reconstruction on a Si(221) surface.
Stress-controlled x-ray mask absorber using pulse-current gold plating
Authors: Ogawa Taro , Soga Takashi , Maruyama Yoji , Oizumi Hiroaki , Mochiji Kozo
Published: July 2002

The application of pulse-current gold plating has been studied in the fabrication of x-ray mask patterns to attain uniform thickness and low stress. Pulse-current plating with low average current density (iav) has proven effective in improving uniform plating thickness over a wide range of pattern sizes. This result can be explained through the duplex-diffusion layer model. Stress in the gold plated by low iav becomes compressive. However, this stress can be eliminated by annealing. This annealing effect is attributable to the contraction in volume of plated gold due to the thermal desorption of hydrogen atoms.
Curved grating fabrication techniques for surface-emitting distributed feedback lasers
Authors: King Oliver , Erdogan Turan , Wicks Gary W. , Hall Dennis G. , Anderson Erik H. , Costello Dennis , Rooks Michael J.
Published: July 2002

We report on techniques for the fabrication of curved waveguide diffraction gratings for use in novel semiconductor laser structures. In particular, we consider the development of concentric-circle gratings to be employed in circularly symmetric, surface-emitting semiconductor lasers. The gratings are defined using electron-beam lithography and subsequently etched into the semiconductor surface by chemically assisted ion-beam etching. Issues to be addressed include grating design requirements, pattern representation, and scan method. We provide examples of how these techniques can be implemented and their impact on the resulting laser performance.
Formation and damage of sidewalls after Cl2/CH4 based reactive ion beam of InP
Authors: van Roijen R. , Bulle-Lieuwma C. W. T. , Montie E. A.
Published: July 2002

The cause of anisotropic etching of a reactive ion etching (RIE) process for InP/InGaAsP involving a mixture of Cl2, Ar, CH4, and H2 is investigated, applying Auger photoelectron spectroscopy and transmission electron spectroscopy. The extend of sidewall damage is given. An InP/InGaAsP heterostructure quantum wirelike structure is fabricated and the effect on the photoluminescence intensity and wavelength is reported. Successful device fabrication using RIE is demonstrated.
Measurement of reflection high-energy electron diffraction oscillations during molecular-beam epitaxial growth of GaAs on a rotating substrate
Authors: Turner G. W. , Isles A. J.
Published: July 2002

A technique has been developed for the measurement and analysis of reflection high-energy electron diffraction (RHEED) oscillations occurring during molecular-beam epitaxy on a rotating substrate. Previously, it has been necessary to stop substrate rotation in order to perform RHEED oscillation analysis. This limitation has been overcome by combining a computerized video tracking system with a previously reported technique for frequency-domain analysis.
Secondary ion mass spectrometry depth profiling of boron, antimony, and germanium deltas in silicon and implications for profile deconvolution
Authors: Dowsett M. G. , Barlow R. D. , Fox H. S. , Kubiak R. A. A. , Collins R.
Published: July 2002

This article describes the shape of secondary ion mass spectrometry (SIMS) depth profiles from ultra thin ‘‘δ layers’’ in silicon, and its dependence on the impurity species and the primary beam energy. The impurities studied are boron, antimony, and germanium in epitaxial layers grown by molecular beam epitaxy. The use of the data for the assessment of depth resolution and the quantification or synthesis of SIMS profiles from thicker layers and distributions is discussed. Possible limits to deconvolution are explored.
Profiling of composition and carrier concentration in AlxGa1−xAs by point contact techniques
Authors: Chong T. C. , Hillard R. J. , Heddleson J. M. , Rai-Choudhury P. , Moore W. T. , SpringThorpe A. J.
Published: July 2002

Energy gap and carrier concentration are among the most important material parameters governing the electrical performance of AlGaAs/GaAs heterojunction devices. A novel technique for profiling aluminum mole fraction ratio and carrier concentration is presented which is based on point contact current voltage (PCIV) measurements. The method measures point contact voltages at a preselected current as a function of depth. A composition profile is then created by referring to appropriate calibration samples. The PCIV technique is rapid, inexpensive, and offers high spatial and depth resolution. Additionally, both the aluminum mole fraction ratio and the carrier concentration can be obtained sequentially from the same measurement. The application of this technique to several device structures of current interest is presented.
Measurement of defect profiles in reactive ion etched silicon
Authors: Benton J. L. , Weir B. E. , Eaglesham D. J. , Gottscho R. A. , Michel J. , Kimerling L. C.
Published: July 2002

Reactive ion etching (RIE) is used as a method of pattern transfer and anisotropic etching for contact windows to shallow junctions in IC manufacture. We use photoluminescence (PL), junction current–voltage (I–V), transmission electron microscopy (TEM), and Rutherford backscattering (RBS) to characterize the defects introduced in silicon by the RIE process. A displacement damage region extends approximately 1000 Å with defect concentrations ≥1018 cm−3, depending on the etching parameters. A defect reaction region continues from the displacement damage to depths greater than 1 μm. The extent of the defect diffusion is limited by trapping of interstitial silicon at impurity sites. We use anodic oxidation followed by HF acid etch to remove material in 250 Å steps, and then employ the combination of optical (PL), physical (RBS, TEM), and electrical (I–V) measurements to provide a complete defect profile of the near-surface region.
Micromachining in III–V semiconductors using wet photoelectrochemical etching
Authors: Khare Reena , Hu Evelyn L. , Brown Julia J. , Melendes Melissa A.
Published: July 2002

Wet photoelectrochemical etching has been used to create deeply etched structures in both GaAs and InP. It was observed that the conductive n+ substrates etched quite rapidly, while semi-insulating substrates exhibited enhanced etching only when a metal mask patterned the substrate, providing a low resistance contact for electron removal. It was further found that vertical profiles were achievable at high laser intensities, while a crystallographic taper was achieved at lower intensities. Finally, the limitations to microstructure geometry was explored in terms of the dynamics of the photogenerated carriers.
Ammonia plasma passivation of GaAs in downstream microwave and radio-frequency parallel plate plasma reactors
Authors: Aydil Eray S. , Giapis Konstantinos P. , Gottscho Richard A. , Donnelly Vincent M. , Yoon Euijoon
Published: July 2002

The poor electronic properties of the GaAs surface and GaAs–insulator interfaces, generally resulting from large density of surface/interface states, have limited GaAs device technology. Room-temperature ammonia plasma (dry) passivation of GaAs surfaces, which reduces the surface state density, is investigated as an alternative to wet passivation techniques. Plasma passivation is more compatible with clustered-dry processing which provides better control of the processing environment, and thus, improves interface integrity. Passivation was monitored in real-time and in situ using photoluminescence (PL). In addition, the passivated surfaces are inspected using x-ray photoelectron spectroscopy. Passivation with two different plasma excitation methods, downstream microwave (2.45 GHz) and rf (13.56 MHz) parallel plate, are compared, and effects of operating parameters such as pressure, flow rate, and power are examined. In both methods plasma-generated H atoms reduce the surface state density by removing excess As and As2O3 during the first few seconds of the plasma exposure. This step is followed by formation of Ga2O3 which takes place on a longer time scale (5–10 min). While the final passivation result appears to be similar for both methods, surface damage by ion bombardment competes with passivation in the parallel plate method, reduces the PL yield and adversely affects the long term stability of the passivated surface. Although it is common to heat the sample during passivation, we show that NH3 plasma passivation is possible at room temperature without heating. Low-temperature processing is important since passivation can be done at the end of device processing when it is undesirable to expose the device to elevated temperatures. The absence of ion bombardment damage combined with efficient generation of H atoms in the downstream microwave treatment, make this scheme a preferred dry passivation process, which could be easily and inexpensively clustered with existing GaAs processes.
Large-area electron-beam source
Authors: Livesay W. R.
Published: July 2002

A new large-area electron-beam source which can operate continuously, stably, and indefinitely in a poor vacuum environment is described. This novel electron source produces a near monoenergetic electron beam which can uniformly expose large area substrates (i.e., 200 mm diam wafers and larger flat panel displays). The electron gun incorporates a cold cathode which is impervious to solvents and outgassing from irradiated polymer coatings. Unlike glow discharge electron sources, the accelerating voltage can be controlled independently of the emission current from the electron gun with a small bias voltage to a grid anode. Accelerating voltages of 1–60 keV and higher are possible. The principles of operation and performance characteristics of this new source are described, including its ability to expose insulating samples without requiring a conductive overcoat. This new electron source has enabled a number of new process innovations in photoresist stabilization, interlayer dielectric curing, lift-off processing, and pattern lithography.
Photoluminescence study of Si1−xGex/Si heterostructures grown by molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition
Authors: Terashima Koichi , Tajima Michio , Tatsumi Toru
Published: July 2002

Photoluminescence (PL) of Si1−xGex/Si heterostructures grown by conventional molecular beam epitaxy (MBE), gas-source MBE (GSMBE), and ultrahigh vacuum chemical vapor deposition (UHV-CVD) has been investigated in the wavelength region of 1000–1800 nm. Single and multiple quantum wells (SQW and MQW, respectively) and uncapped Si1−xGex alloy epitaxial (EPI) layers on Si substrates have been studied. In the case of GSMBE and UHV-CVD, sharp band-edge PL of Si1−xGex appears and deep-level PL is very weak. PL lines due to bound excitons can be observed up to about 50 K for SQWs and MQWs but they disappear above 12 K for EPI layers. Broadening of the PL lines with an increase in excitation intensity due to bound multiple exciton complexes has been observed for the EPI layers while it can hardly be observed for SQWs and MQWs. In the case of conventional MBE, intense broad emission bands dominate the PL spectrum below the band gap of Si1−xGex for the SQWs and MQWs. Similar broad emission bands sometimes appear also in the PL spectra of the EPI layers grown by conventional MBE, in which dislocation-related D lines are dominant in most cases. From the dependence on the excitation power density, the annealing effects, and the difference between the growth methods, the broad emission bands are considered to be related to defects in the Si1−xGex layer or the interface which are characteristic of conventional MBE.
Effects of As4 flux on reflection high-energy electron diffraction oscillations during growth of GaAs at low temperatures
Authors: Ibbetson J. P. , Mirin R. P. , Mishra U. K. , Gossard A. C.
Published: July 2002

This article reports on the observation of reflection high-energy electron diffraction oscillations during growth of GaAs by molecular beam epitaxy at temperatures as low as 60 °C. At low temperatures (<300 °C), the amplitude of the oscillations is shown to be sensitive to the As:Ga flux ratio. The largest amplitude oscillations are observed under stoichiometric conditions.
Phosphor selection constraints in application of gated field-emission microcathodes to flat panel displays
Authors: Chakhovskoi Andrei G. , Kesling W. Dawson , Trujillo Johann T. , Hunt Charles E.
Published: July 2002

The major issues and tradeoffs surrounding phosphor selection for field-emission flat panel displays are identified. The two main classes of commercially available phosphors applicable to flat panel displays are contrasted, and the major physical, electrical, chemical and optical factors effecting phosphor selection are discussed. The implications of screen layering designs and cathode materials are described as they relate to phosphor characteristics. Resolution requirements for displays severely limits the maximum anode voltage, which in turn forces specific phosphor choices. Possible solutions to these limitations are explored.
Initial operation of a large-scale plasma source ion implantation experiment
Authors: Wood B. P. , Henins I. , Gribble R. J. , Reass W. A. , Faehl R. J. , Nastasi M. A. , Rej D. J.
Published: July 2002

In plasma source ion implantation (PSII), a workpiece to be implanted is immersed in a weakly ionized plasma and pulsed to a high negative voltage. Plasma ions are accelerated toward the workpiece and implanted in its surface. A large-scale PSII experiment has recently been assembled at Los Alamos, in which stainless steel and aluminum workpieces with surface areas over 4 m2 have been implanted in a 1.5 m diam, 4.6 m length cylindrical vacuum chamber. Initial implants have been performed at 50 kV with 20 μs pulses of 53 A peak current, repeated at 500 Hz, although the pulse modulator will eventually supply 120 kV pulses of 60 A peak current at 2 kHz. A 1000 W, 13.56 MHz capacitively coupled source produces nitrogen plasma densities in the 1015 m−3 range at neutral pressures as low as 0.02 mTorr. A variety of antenna configurations have been tried, with and without axial magnetic fields of up to 60 G. Measurements of sheath expansion, modulator voltage and current, and plasma density fill-in following a pulse are presented. We consider secondary electron emission, x-ray production, workpiece arcing, implant conformality, and workpiece and chamber heating.
Modification of Si field emitter surfaces by chemical conversion to SiC
Authors: Liu J. , Son U. T. , Stepanova A. N. , Christensen K. N. , Wojak G. J. , Givargizov E. I. , Bachmann K. J. , Hren J. J.
Published: July 2002

Silicon field emitters have been modified by coating with a thin SiC film through a chemical conversion process. Silicon carbide was formed on Si emitter surfaces by reacting with ethylene gas at temperatures between 850 and 950 °C using pressures as high as 5×10−3 Torr. The thickness of the coatings ranged from 2 to 500 nm, determined by a combination of reaction time, pressure, and temperature. Stable emission currents above 10 μÅ were measured from individual SiC coated emitters.
Laterally coupled distributed feedback laser fabricated with electron-beam lithography and chemically assisted ion-beam etching
Authors: Tiberio R. C. , Chapman P. F. , Martin R. D. , Forouhar S. , Lang R. J.
Published: July 2002

The fabrication and optical performance of laterally coupled distributed feedback (LCDFB) lasers were investigated. This device differs from a conventional DFB laser in that the grating does not extend inside the laser ridge; rather, gratings adjacent to a single ridge are used to couple to the fringing fields of the active region. This structure allows the entire laser epilayer structure to be grown in a single step, thus eliminating any regrowth steps. A recent design with 1.5 mm cavity length and chemically assisted ion-beam etching-defined ridges and gratings resulted in pulsed single-mode operation up to 36 mW at 937 nm with as-cleaved facets. The light-current characteristic of this device demonstrated a threshold current of 15 mA and a sidemode suppression ratio of greater than 30 dB. The spectral temperature sensitivity was 0.65 Å/ °C for this LCDFB. Fabrication processes and optical characterization are discussed.
Ultra-large-scale integration device scaling and reliability
Authors: Hu Chenming
Published: July 2002

Assuming that the requisite lithography and planarization techniques will be available, this article reviews the goals of metal–oxide semiconductor field effect transistor (MOSFET) scaling and the constraints of low leakage and adequate reliability, highlighting the impact of power-supply voltage and oxide thickness reductions. Plasma charging damage is discussed. The first identifiable scaling limit is the direct tunneling of gate oxide at 3.5 nm, which may hinder scaling beyond 0.09 μm. From the 0.5-μm generation onward, MOSFET current will basically cease to increase with scaling. Gate speed will double every four generations rather than two generations of technology as in the past unless technology innovations can pick up the slack.
Angle-resolved photoemission of diamond (111) and (100) surfaces; negative electron affinity and band structure measurements
Authors: van der Weide J. , Nemanich R. J.
Published: July 2002

Angle-resolved photoemission from both (100) and (111) oriented, natural type IIb diamond was used to study the electronic structure of diamond. A negative electron affinity (NEA) was found on the 2×1 reconstructed diamond (100) surface. Photoemission spectra of NEA surfaces exhibit a distinctive peak due to emission from the conduction band edge. This peak was used as a reference point to correlate spectra of (100) and (111) surfaces with a NEA. A feature at ∼7.5 eV above the conduction band edge appears in the spectra of both the (111) and (100) surfaces. Angle-resolved photoemission measurements were used to determine the energy dispersion of this feature for various off-normal angles. The results for the surfaces were correlated, and compared to a calculated band structure. Based on this comparison we attribute this feature to emission from secondary electrons which are collected in a conduction band level at ∼7.5 eV above the conduction band edge.
Effects of growth temperature on the SiO2/Si(100) interface structure
Authors: Lu Z. H. , Graham M. J. , Tay S. P. , Jiang D. T. , Tan K. H.
Published: July 2002

Synchrotron radiation photoemission spectroscopy (PES) has been used to study thermal SiO2/Si(100) interfaces. Oxides were grown at 700, 800, 900, and 1000 °C and etched back to a thickness ∼0.5–1.5 nm for PES measurements. Comparison of Si 2p core levels with in situ ultrahigh vacuum-grown SiO2 on Si(100) indicated that various Si oxidation states, Six+, are present at the interface. The results show that the amount of both Si2+ and Si3+ increases with increasing oxidation temperature while the amount of Si1+ remains constant. For these furnace grown oxides, structural relaxation to relieve strains rather than kinetic growth considerations governs the structure and suboxide distribution at the SiO2/Si(100) interface.
Scanning tunneling microscopy of the reaction of NH3 with GaAs(110)
Authors: Brown G. , Weimer M.
Published: July 2002

The room temperature chemisorption of gaseous NH3 on p-type GaAs(110) has been studied with scanning tunneling microscopy (STM). Atomic-resolution images confirm that the reaction is nondissociative and occurs between lone-pair electrons of the free molecule and cation dangling bonds at the surface. Because the adsorption complex is uncharged, the microscopic dipole screening produced by a single, tilted ammonia molecule is directly observed. The results agree completely with the predictions of Lewis acid-base chemistry.
Structure and electrical properties of Ag-ultrafine-particle–polymer thin films
Authors: Gao H. J. , Xue Z. Q. , Wu Q. D. , Pang S. J.
Published: July 2002

Toluylene 2,4-dicarbamidonitrite (TDCN) and Ag-ultrafine-particle–TDCN thin films were prepared by using an ionized-cluster-beam (ICB) deposition method. TDCN is a newly synthesized conjugated polymer with novel properties. These thin films were characterized by transmission electron microscopy (TEM). The TEM results indicate that the crystalline structure of the organic thin films can be controlled by the parameters of the ICB and the ultrathin crystalline TDCN film can be achieved by using the ICB deposition method. Results also demonstrated that amounts of Ag ultrafine particles embedded in the organic thin films may play an important role in the functional properties of the composite thin films. The electrical bistability of the Ag-ultrafine-particle–TDCN thin films was also achieved, and the possible conductive mechanism of the films was suggested qualitatively.
Method for fabricating a low stress x-ray mask using annealable amorphous refractory compounds
Authors: Dauksher W. J. , Resnick D. J. , Cummings K. D. , Baker J. , Gregory R. B. , Theodore N. D. , Chan J. A. , Johnson W. A. , Mogab C. J. , Nicolet M.-A. , Reid J. S.
Published: July 2002

X-ray masks have been fabricated by depositing a compressively stressed refractory material on a wafer, annealing to a zero stress state, and then forming the membrane. Amorphous TaSiN and TaSi alloys deposited with a magnetron sputter tool have been extensively characterized in terms of resistivity, composition, defectivity, surface roughness, and crystalline state. Optimization in terms of these parameters has resulted in base line selection of absorber films of the following compositions: Ta61Si17N21 and Ta75Si23. The process is shown to be extendable to an entire class of amorphous annealable refractory materials. Careful studies of deposition and annealing conditions have resulted in a 4× reduction of image placement to the 30 nm maximum vector level. Finally, the importance of stress gradients is experimentally verified.
Fabrication of all-optical quantum well bistable microresonators by reactive ion etching
Authors: Rivera T. , Izraël A. , Azoulay R. , Kuszelewicz R. , Bresse J. F. , Oudar J. L. , Ladan F. R.
Published: July 2002

Arrays of all-optical bistable devices have been fabricated by reactive ion etching (RIE). The vertical Fabry–Pérot structures grown by organometallic vapor-phase epitaxy include GaAs/Ga0.7Al0.3As multiple quantum wells and AlAs/Ga0.9Al0.1As Bragg reflectors and exhibit optical bistability under moderately focused laser excitation (10–30 μm spot diameter). After RIE, the arrays show a reduced bistability threshold of 70 μW on 4 μm diameter and 5.7 μm high microresonators. This suggests that surface recombination does not play a significant role. This and the absence of degradation of the etched AlAs layers for more than 10 months indicate a self-passivation of the vertical surfaces during the etching process. Selective plasma etching reveals the presence of a thin cylindrical film clearly visible with a scanning electron microscope. The composition of this film is analyzed by Auger spectroscopy.
Influence of humidity on friction measurements of supported MoS2 single layers
Authors: Schumacher A. , Kruse N. , Prins R. , Meyer E. , Lüthi R. , Howald L. , Güntherodt H.-J. , Scandella L.
Published: July 2002

We have studied friction of MoS2 single layers on mica and Al2O3 in the range of 5%–90% relative humidity. Friction coefficients have been determined simultaneously for the MoS2 platelets as well as for the support. Only a slight influence on the humidity was found for the friction coefficient of MoS2 and Al2O3. On the other hand, water adsorption on mica caused a strong increase of the friction coefficient above 40% relative humidity. The change of the friction coefficient was so strong that the contrast of the friction images inverted. At very high humidities (above 60%), the friction coefficient of mica reverted to its initial value, probably because water acted as a boundary lubricant.
Resist application effects on chemically amplified resist response
Authors: Dentinger Paul M. , Nelson Carla M. , Rhyner Steven J. , Taylor James W. , Fedynyshyn Theodore H. , Cronin Michael F.
Published: July 2002

Chemically amplified negative resist films of Shipley SAL 605 at 1.0 μm thickness show a statistically optimized sensitivity that is twice that observed with 0.5 μm films when exposed to x rays from an electron storage ring. Because of the large ‘‘depth of focus’’ of proximity x-ray lithography, the differences between thick and thin films are due to resist chemical and physical effects and processing conditions, not to the exposure process. Using identical processing conditions, 1.0-μm-thick films showed 34% larger linewidths than 0.5 μm films for isolated lines from one mask with a target linewidth of 0.215 μm. Gel permeation chromatography results indicated that there was no dependence of resin or crosslinker concentration on thickness of the applied film. The photogenerated acid and residual solvent were quantified prior to postexposure bake, and neither was able to explain the apparent sensitivity dependence on thickness. The work suggests that some of the differences arises in the resist application process because of the ability of the thicker film to retain small molecular weight species which facilitate the linewidth production. This implies that thinner films should show better resolution purely because of chemical and physical factors in the resist film.
Preliminary results from a prototype projection electron-beam stepper-scattering with angular limitation projection electron beam lithography proof-of-concept system
Authors: Harriott L. R. , Berger S. D. , Biddick C. , Blakey M. I. , Bowler S. W. , Brady K. , Camarda R. M. , Connelly W. F. , Crorken A. , Custy J. , Dimarco R. , Farrow R. C. , Felker J. A. , Fetter L. , Freeman R. , Hopkins L. , Huggins H. A. , Knurek C. S. , Kraus J. S. , Liddle J. A. , Mkrtychan M. , Novembre A. E. , Peabody M. L. , Tarascon R. G. , Wade H. H. , Waskiewicz W. K. , Watson G. P. , Werder K. S. , Windt D.
Published: July 2002

We have designed and constructed a proof-of-concept projection electron beam lithography system based on the scattering with angular limitation projection electron beam lithography principle. In this system, a thin membrane mask is used in a 4:1 reduction projection system at 100 keV. Image contrast is formed by scattering in the mask and subsequent aperturing of the scattered electrons in the back focal plane of the projection system. We have employed a step-and-scan architecture which uses continuously moving mask and wafer stages to trace out the full pattern. The electron beam can thus be kept small (1×1 mm in our case) which greatly simplifies the design of the electron optical system. In addition, the membrane areas can be kept small in linear dimension in one direction, minimizing in-plane pattern distortions. Our system will be constructed in two stages. In the first stage, the mask stage is static and the wafer stage operates in step-and-repeat mode. This initial version of the system allows for critical experiments regarding the mask, resist exposure, and electron optics to be performed. Later, a continuously moving stage system will be integrated. In this article, we report on the initial results from the static system. We have printed features as small as 80 nm and measured a 75 μm depth of focus for nominal 0.25 μm features in negative tone P(SI-CMS) resist.
Application of optical filters fabricated by masked ion beam lithography
Authors: Morgan M. D. , Horne W. E. , Sundaram V. , Wolfe J. C. , Pendharkar S. V. , Tiberio R.
Published: July 2002

Masked ion beam lithography (MIBL) was employed to fabricate optical filters as a critical component of an energy conversion system which utilizes semiconductor photovoltaics. This article will describe the operation and novel application of these devices and the MIBL pilot production line being facilitized. The conversion concept, thermophotovoltaics (TPV), when coupled with these MIBL produced bandpass filters, is capable of converting heat to electrical power with >20% conversion efficiency. The EDTEK TPV filter is based on a high density array of slotted antenna elements patterned into a single layer of thin gold film.
Reactive ion etch-induced effects on 0.2 μm T-gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistors
Authors: Cheung R. , Patrick W. , Pfund I. , Hähner G.
Published: July 2002

The effect of CH4/H2 reactive ion etching on In0.52Al0.48As surfaces and In0.52Al0.48As/ In0.53Ga0.47As/InP heterostructure have been studied using Schottky diode, x-ray photoelectron spectroscopy, and room temperature transport experiments. The application of CH4/H2 as a dry etch gas for the gate recess step in the fabrication of 0.2 μm T-gate In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistor has been explored. We show that while the room temperature mobility and the dc and high frequency performance of the dry etched devices are at least comparable to the wet etched ones, their microwave noise behaviours are extremely sensitive to dry etch-induced defects.
Ballistic electron emission microscopy of Au–InAs–GaAs system
Authors: Ke Mao-long , Westwood D. I. , Matthai C. C. , Richardson B. E. , Williams R. H.
Published: July 2002

We report an investigation of barrier formation and electron transport across InAs and GaAs interfaces by ballistic electron emission microscopy. The barrier height was found to decrease with the InAs thickness and the detailed variation correlates with the relaxation of the InAs layer. When the thickness is below one monolayer, three thresholds are observed and they are attributed to electron transmission into the Γ, L, and X valleys of the GaAs, respectively. As the thickness increases to three monolayers or beyond, only two thresholds are observed and the reasons are explained in the context of the band structure of the system.
Microscopic characterization of field emitter array structure and work function by scanning Maxwell-stress microscopy
Authors: Itoh Junji , Nazuka Yutaro , Kanemaru Seigo , Inoue Takahito , Yokoyama Hiroshi , Shimizu Keizo
Published: July 2002

Microscopic images of both the structures and surface potential of field emitter arrays were measured by scanning Maxwell-stress microscopy (SMM) in air. Results of the SMM measurements clearly showed nanometer-scale irregularities in the structures and structure-related surface potential distributions. The surface potential of Si was rather flat even at the emitter tip apex. From these results, the work-function values for various emitter materials such as Si, Cr, Mo, W, etc. have been derived by using an Au film as the reference material; the work function of Au was assumed to be 5.1 eV. Experimental procedures and results are described in detail.
Application of scanning tunneling microscopy nanofabrication process to single electron transistor
Authors: Matsumoto Kazuhiko , Ishii Masami , Segawa Kazuhito
Published: July 2002

The single electron transistor was fabricated by quite a new fabrication process using scanning tunneling microscopy. The single electron transistor operates at room temperature showing a clear Coulomb staircase of 150 mV periods. The tip of the scanning tunneling microscope was used as a cathode, and the surface of the Ti layer was oxidized to form a narrow oxidized Ti line. Using this oxidized Ti line, the island region of the single electron transistor was fabricated. The electrical property of the oxidized Ti line was also examined in detail.
C60 manipulation and cluster formation using a scanning tunneling microscope
Authors: Dunn A. W. , Beton P. H. , Moriarty P.
Published: July 2002

We have used the tip of an ultrahigh vacuum scanning tunneling microscope to induce displacements of C60 molecules on the Si(111)-7×7 surface at room temperature. The manipulation is achieved by using a sweeping procedure we have developed which moves the tip closer to the surface and sweeps it across in a predetermined direction. Feedback control of the tunnel current is maintained throughout and the tip-surface separation is adjusted by changing the sample bias and tunnel current. For a 0.007 monolayer (ML) coverage of C60, a sweeping area of 60 Å×60 Å was used to move individual C60 molecules, while for higher coverages (0.05–0.2 ML) a sweeping area of 216 Å×216 Å was used to move large groups of C60 molecules. We show an example at 0.2 ML coverage where we have removed C60 over an area 110 Å×370 Å resulting in the formation of a line of C60 molecules 20–30 Å in width.
Cross-sectional scanning tunneling spectroscopy of cleaved, silicon-based metal–oxide–semiconductor junctions
Authors: Thibado Paul M. , Mercer T. W. , Fu Shelton , Egami Takeshi , DiNardo N. J. , Bonnell Dawn A.
Published: July 2002

Cross-sectional scanning tunneling spectroscopy experiments were performed under air-ambient conditions on cleaved Si-based metal–oxide–semiconductor (MOS) junctions. With the scanning tunneling microscope tip in the vicinity of the oxide–semiconductor interface, the electric field-induced depletion region was found to pinch-off the tunneling current similar to the effect in a MOS field-effect transistor (MOSFET) where increasing gate bias reduces the channel current. In this study, the experimentally observed dependence of the tip-semiconductor I-V characteristics on the gate bias was interpreted within a transfer-Hamiltonian tunneling model representing the tip-semiconductor junction and including both tip-induced band-bending and gate bias effects.
Optical characteristics of the phosphor screen in field-emission environments
Authors: Kang Sang Won , Jeon Byung Soo , Yoo Jae Soo , Lee Jong Duk
Published: July 2002

The required luminance for information display is near 300 cd/m2 for white. The amount of light emitted from phosphor screen depends upon the anode voltage and electron density from field emitter arrays. Field-emission display to date usually do not use high accelerating voltage but the low voltage with a great number of cold electrons from field emitter arrays for required brightness. In these situations, charge accumulations on the phosphors should be minimized to get long lifetimes. It is found that the introduction of a wide band-gap material to the oxide phosphors is effective for improved efficiency of the phosphor screen and that the formation of a leakage path for accumulated electrons may not only increase the cathodeluminescent intensity but also relax the screen degradation. They are presumably due to the prevention of charge accumulation on the surface of phosphors.
Electromigration behavior of hot-sputtered Al(Cu) versus chemical vapor deposition W vias
Authors: Filippi R. G. , Levine E. N. , Rodbell K. P.
Published: July 2002

The electromigration behavior of hot-sputtered aluminum-copper (Al-Cu) vias is compared to that of chemical vapor deposition (CVD) tungsten (W) vias. Al(Cu) vias were prepared by one of two processes: (1) the via was filled and then defined by chemical mechanical polish (CMP) and (2) the via and top metal line were deposited in the same step (this is referred to as the “Sprint” process). During electromigration testing, the W via chains exhibited more uniform resistance changes with time than the CMP Al(Cu) via chains. This had a direct impact on the shape parameter of the log-normal lifetime distribution, where σ was higher for the CMP Al(Cu) via chains. A closer examination of the failure distributions revealed the need to describe the CMP Al(Cu) via lifetimes by a three-parameter log-normal distribution as opposed to the conventional two-parameter log-normal distribution. Failure analysis of the CMP Al(Cu) samples indicated electromigration failures downstream from the via in the direction of the electron flow. Samples prepared by the Sprint process showed >5× electromigration lifetime improvement as compared to either the CVD W or CMP Al(Cu) via samples.