bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of the (In,Al,Ga)As quaternary alloy system on GaAs at low substrate temperatures by molecular-beam epitaxy
Authors: Towe E. , Sun D. , Bennett B. R.
Published: July 2002

The III–V quaternary alloy system of (In,Al,Ga)As has been successfully grown on (100) GaAs substrates at low substrate temperatures. Visible photoluminescence emission spanning the wavelengths from 630 to 700 nm has been observed from material grown at substrate temperatures ranging from 300 to 500 °C. It is found that the emission intensity is influenced by the substrate temperature. Results are presented for the In0.10Al0.41Ga0.49As quaternary alloy.
Device structure characterization using the comparative capacitance–voltage technique
Authors: Taft Robert C. , Noell Matthew S.
Published: July 2002

Although the C–V profiling technique is usually applied to obtain the doping concentration of lightly doped wells, here we extend it to extract structural information of high-performance double poly bipolar transistors (BJTs) by comparing profiles taken from two adjacent but distinct C–V structures. In particular, the trenching that occurs in unprotected substrate silicon during the gate (base) poly overetch can be measured by the change in p+ source/drain implant to n+ buried layer depletion width for two such diodes, one with and one without trenching. The diffused extrinsic base junction depth of the double-poly BJT can be extracted similarly. Both of these physical dimensions must be accurately measured and tracked, to optimize bipolar device performance. Structural measurements by this comparative C–V technique are nondestructive, simple, and agree with scanning electron microscopy and secondary ion mass spectroscopy within ∼100 Å (5%).
Causes of anomalous solid formation in the exhaust systems of low-pressure chemical vapor deposition and plasma enhanced chemical vapor deposition semiconductor processes
Authors: Abreu Raul A. , Troup Alan P. , Sahm Michael K.
Published: July 2002

The waste gases in low-pressure chemical vapor deposition and plasma enhanced chemical vapor deposition semiconductor processes react strongly with residual air in the exhaust of the vacuum pump to form solid deposits. It is common practice to purge the exhaust line with pure nitrogen to reduce the concentration of ambient air between the pump and the scrubber to an acceptable low level. However, the unexpected high quantities of exhaust deposits found in some systems cannot be explained by air leaks, impurities in the nitrogen, or diffusion. The problem of anomalous exhaust deposit formation was examined experimentally. A 40 mm pipe, up to 5 m in length and initially filled with nitrogen, was connected to an 80 m3/h dry vacuum pump exhausting to air at atmospheric pressure. The composition of the atmosphere in the pipe was analyzed with a mass spectrometer. Under static conditions, the gas density distribution was ultimately limited, as expected, by simple interdiffusion. When the pump was running, however, there was a dramatic enhancement of the oxygen concentration throughout the pipe. The experimental observations were interpreted in terms of Richardson’s annular effect. It is shown that the pressure fluctuations typical of vacuum pumps are responsible for the enhanced counterflow of air. The effect can be reduced by applying nitrogen purge but, even with a moderate 20 ℓ/min flow rate, deposits can form due to air transported back from the scrubber or exhaust duct.
Novel in situ electrochemical technology for formation of oxide- and defect-free Schottky contact to GaAs and related low-dimensional structures
Authors: Hashizume Tamotsu , Schweeger Giorgio , Wu Nan-Jian , Hasegawa Hideki
Published: July 2002

The Pt/GaAs Schottky interfaces with excellent qualities were fabricated by a novel in situ electrochemical etching and plating technology using the electrical and photo pulses. The etched GaAs surface was very smooth, and no oxidized and disordered layer was produced at the interface. This technology also prevents formation of process-induced near-surface defect levels of GaAs. The Pt/GaAs diodes exhibited nearly ideal thermionic emission characteristics with a barrier height larger than 1.0 eV and an ideality factor lower than 1.05. Selective deposition of Schottky barriers to the edge of a two-dimensional electron gas in a GaAs/AlGaAs quantum well structure was truly achieved by this process, which is confirmed by the agreement of the experimental C–V results with theoretical predictions, as well as the results of the electron beam-induced current measurements.
Atomic force microscopy of ammonium perchlorate
Authors: Yoo Minsun , Yoon Seokwon , de Lozanne Alex
Published: July 2002

Ammonium perchlorate (NH4ClO4 or AP) is an insulating energetic material and is hygroscopic; the surface degrades easily by absorbing moisture in ambient conditions. An ultrahigh vacuum (UHV) atomic-force microscope (AFM) has been designed and built to study the (210) surface of AP in a moisture-free environment. Large-scale images from this apparatus show nanocracks and grains; cracks are mainly aligned with the direction that matches the main crystal steps and grains are plastically deformed by raster scans. Molecular scale images are taken on grains with a constant frictional force. Popping signals are observed in the frictional-force mode which are about ten times larger than the topography of the surrounding intrinsic surface structure. These signals are intermittent and increase in intensity and abundance as the same area is scanned repeatedly. It is speculated that these signals are caused by local reactions initiated by the increased pressure from the tip as it turns around at the end of each line scan.
Application of MHz-frequency detection to noncontact scanning force microscopy
Authors: Hug H. J. , Moser A. , Weller D. , Parashikov I. , Tonin A. , Hidber H. R. , Güntherodt H.-J.
Published: July 2002

We discuss and compare the application of static and dynamic operation modes of scanning force microscopy to contact and noncontact imaging. The static modes of force microscopy can image the magnetic stray field of a ferromagnetic sample and separate topographic from magnetic information. Very high measurement speeds, up to one image in 2 s are reached. In comparison measurements in the dynamic modes are slower but have an excellent force gradient sensitivity. We have extended the direct frequency measurement method to frequencies up to 1 MHz achieving a frequency resolution of at least 1/10 Hz. The possibility to measure such high frequencies with good resolution allows us to use very stiff cantilevers and to still achieve an excellent force gradient resolution. Such a stiff cantilever does not jump to the surface, if the sample is approached.
Topographical structure of pBR322 DNA studied by scanning tunneling microscope and atomic force microscope
Authors: Zhang P.-C. , Bai C. , Cheng Y.-J. , Fang Y. , Wang Z.-H. , Huang X.-T.
Published: July 2002

Plasmid pBR322 DNA (0.5 mg/ml) isolated from Eschericha coli HB101 was suspended in Tris-HC1/EDTA (1/0.1 mol/L, pH 8.5), deposited on a highly oriented pyrolytic graphite surface, then imaged with scanning tunneling microscope (STM) in air and under paraffin liquid in constant current mode. The methods for preparing DNA samples used in the STM study are discussed. Dynamic changes of apparent width of supercoiled pBR322 DNA were captured during an STM imaging course. The pBR322 DNA is also visualized with an atomic force microscope (AFM) built by this laboratory after the sample was absorbed on the freshly cleaved mica surface. Characteristically relaxed circular structures of pBR322 DNA have been observed in the AFM experiment.
Atomic force microscopy of plasmid DNA and DNA polymerase
Authors: Li Min-Qian , Hansma H. G. , Hong Guo-Fan , Yao Xiao-Wei , Hansma P. K.
Published: July 2002

An improved sample preparation procedure and optimized atomic force microscope (AFM) imaging conditions that makes it possible to obtain reproducible nanometer resolution AFM images of plasmid DNA with nanograms of the sample is presented. The Bst DNA polymerase I is a special kind of DNA polymerase that can keep its function even at high temperature (∼65 °C), but little is known about its surface structure. The AFM images of the Bst DNA polymerase I show its special surface structure.
Nanostructure fabrication and the science using focused ion beams
Authors: Fujisawa Toshimasa , Bever Thomas , Hirayama Yoshiro , Tarucha Seigo
Published: July 2002

We describe the fabrication of nanostructures and the physics of the devices formed in InGaAs-based modulation doped heterostructures using Ga focused ion beam implantation. The two-dimensional electron gas in this heterostructure has a high electron density, a small effective mass, and a high mobility at high temperature, all of which are advantageous for low-dimensional quantum devices and ballistic devices. Ballistic transport at high temperature, quantized conductance with a large spacing of one-dimensional subbands, and a single electron transistor action with nonperiodic Coulomb oscillations are demonstrated.
An increased effective depth of focus at contact mask for nonvolatile memories using an enhanced planarization scheme
Authors: Cork C. , Bacchetta M.
Published: July 2002

Most of the work currently being published treating improvements in depth of focus (DOF) deals with expensive or complicated techniques such as phase shift masks or lower wavelength illumination. In this article we show that there is another much stronger effect that needs to be overcome before the full benefits of the I-line lithography can be realized. A nonoptimized planarization process can have a large effect on the DOF of certain ‘‘marginal’’ contact sites. By using an enhanced planarization scheme we were able to significantly improve the DOF of these marginal sites yet retain process compatibility with the contact cleaning process and the charge retention requirements of nonvolatile memories. With this, we should be able to extend the minimum geometries printable with our current equipment from 0.7 μm down to about 0.4 μm.
Practical phase-shifting mask technology for 0.3 μm large scale integrations
Authors: Mizuno Fumio , Moriuchi Noboru , Hoga Morihisa , Koizumi Yasuhiro , Suga Osamu , Nakaune Hidehiko , Kamiyama Kazumi , Hasegawa Norio , Murai Fumio , Itoh Fumikazu
Published: July 2002

An i-line phase-shifting mask technology intended for practical use has been developed. The new technology can provide defect-free phase-shifting masks and can produce 0.3 μm large scale integration with large lithographic latitudes. The phase-shifting masks manufactured here apply the following two major techniques. The first technique is to form phase-shifting patterns on the chrome mask. This technique features single-layer shifters using an organic spin on glass (SOG), a simple patterning process of the SOG, and a focused ion beam gas-assisted etching repair process of shifter defects. The second technique is to create half-micron chrome patterns using a high-accuracy e-beam writing system ‘‘EB-MX’’ and high-resolution chemically amplified e-beam resist ‘‘PSR’’.
Effect of photo acid generator concentration on the process latitude of a chemically amplified resist
Authors: Petrillo Karen E. , Pomerene Andrew T. S. , Babich Edward D. , Seeger David E. , Hofer Don , Breyta Gregory , Ito Hiroshi
Published: July 2002

A positive tone chemically amplified photoresist was evaluated for use on a 0.44 NA 248 nm excimer laser stepper. The effects of various formulation changes were examined with respect to exposure latitude, depth of focus, resolution, and bias between isolated and grouped features. Of particular interest was the relationship between the percent of photo acid generator (PAG) in the resist and the process latitude. It was found that several aspects of the process window increased as the PAG content of the resist decreased. An increase in dose was expected and observed with the decrease in PAG concentration. This would reduce excimer stepper throughput by approximately 25%.
Real-time observations of extreme-ultraviolet aerial images by fluorescence microimaging
Authors: La Fontaine Bruno , White Don L. , Wood Obert R. , MacDowell Alastair A. , Tan Zhengquan , Taylor Gary N. , Tennant Don M. , Hulbert Steven L.
Published: July 2002

A new technique, fluorescence microimaging (FMI), using single-crystal phosphors was used to look directly at aerial images produced by an extreme-ultraviolet (EUV) camera operating at a wavelength of 139 Å. The achieved spatial resolution was estimated to be ∼0.2 μm. A comparison of this technique with the usual resist-exposure scanning electron microscopy inspection technique as a means of focusing a 20×EUV Schwarzschild camera was performed. FMI could in principle be improved to view fluorescent images with features as small as 0.07 μm, in real time.
Effects of cation diffusion on the monolayer control of chemical beam etching
Authors: Chiu T. H. , Williams M. D. , Tsang W. T. , Kapre R. M.
Published: July 2002

There is a need to develop an etching technology for the fabrication of nanostructures which provides accurate etch rate control at the atomic level, mask pattern transfer at the nanometer scale, and a clean damage-free surface. In addition, it is highly desirable to integrate the etch with the growth so that in regrowth the problem of contamination is eliminated. Chemical beam etching inside a chemical beam growth system has a great potential of becoming such a dry etching technology. Etching at a subnanometer scale is conveniently monitored by using in situ reflection high energy electron diffraction. Unlike other dry etching methods, the only etching parameter that is critical for etch rate control is the gas flow rate. The etch rate varies linearly with the gas flow rate, which can be adjusted easily by well established mass flow technology. However, a surface roughening mechanism due to inadequate cation diffusion may change the initially two-dimensional (2D) process into a three dimensional (3D) etching. The effectiveness in surface impurity removal by etch cleaning also depends on the etched morphology. Using novel methods that enhance the surface cation diffusion, etching can be maintained in a 2D fashion to obtain a mirrorlike surface.
Electron beam-induced deposition of tungsten
Authors: Bell David A. , Falconer John L. , Lü Zhiming , McConica Carol M.
Published: July 2002

Tungsten films were deposited by decomposing films of frozen tungsten hexafluoride (WF6) with an electron beam and then warming the substrate to remove unreacted WF6. Deposition rates increase with increasing beam intensity.
Compositional variation in sputtered Ti–W films due to re-emission
Authors: Rogers B. R. , Tracy C. J. , Cale T. S.
Published: July 2002

To test for re-emission of titanium and/or tungsten during sputter deposition (PVD) of Ti and Ti–W, films were deposited on wafers with test structures which have large interior areas which are not in line of sight to the source volume. Auger electron spectroscopy (AES), scanning electron microscopy, and transmission electron microscopy results show that very little Ti is re-emitted during Ti PVD, but a significant fraction of incoming Ti is re-emitted during Ti–W PVD. AES spectra along the perimeter of a cross section show that Ti–W films become Ti rich in areas of the test structures without line of sight to the source volume. We also considered Ti–W deposited into trench structures. Physically based, three dimensional deposition process simulations, assuming either diffuse or specular re-emission of Ti, qualitatively explain the experimental results for these trenches. The available information is not sufficient to decide whether the Ti sticking factor is lower on Ti–W films or if Ti is resputtered by incoming W.
Novel fiber growth on Ar+-sputtered InP
Authors: Okuyama F. , Kato J.
Published: July 2002

Fiberlike protrusions with a novel structure were found to grow on monocrystalline InP sputtered with 1–3 keV Ar+ at 100 °C. The fibers, which lengthened toward the incident ion beam, were of amorphous InP, except at the tip area receiving the highest ion-flux density. The tip area, including the growth front, was comprised of In and InP single crystals, the In crystals forming topotaxially in the core of the very tip. The crystallization at the tip of these fibers was no doubt attributable to the impact of Ar+ ions, so it may be termed a case of ‘‘ion-induced crystallization,’’ which is an inverse process of the ion-induced amorphization of crystalline semiconductors.
Nearly ideal characteristics of GaAs metal–insulator–semiconductor diodes by atomic layer passivation
Authors: Wada Yoshinori , Wada Kazumi
Published: July 2002

An atomic layer passivation (ALP) structure for GaAs is studied by fabricating metal–insulator–semiconductor (MIS) diodes. An atomically thin GaP layer is grown on a (100) surface of GaAs to form the ALP structure. MIS diodes are fabricated on the GaP surface by depositing SiO2 as the insulator. Between 1 MHz and 20 Hz, the maximum capacitances are very close to the insulator capacitance without frequency dispersion. The accumulation and inversion conditions are observed in the capacitance–voltage characteristics of the diodes at room and low temperature. The capacitance–voltage characteristics of diodes with and without ALP are compared. The results show that ALP unpins the surface Fermi level which can be displaced nearly throughout the GaAs band gap by the applied gate voltage. Interface trap density is estimated to be about 5×1011 cm−2 eV−1 near the midgap. The influence of the SiO2 plasma deposition process on the interface characteristics is also described, and the mechanism of unpinning is discussed.
High-speed single-layer-resist process and energy-dependent aspect ratios for 0.2-μm electron-beam lithography
Authors: Murai Fumio , Yamamoto Jiro , Yamaguchi Hidenori , Okazaki Shinji , Sato Kazuhiko , Hasegawa Keiko , Hayakawa Hajime
Published: July 2002

For industrial application of an electron beam direct writing a single-layer-resist (SLR) process is more attractive than a multilayer-resist process, because the SLR process is less expensive and provides a precise pattern transfer for 0.2-μm large scale integration circuit fabrication. Three key factors for SLR process are (1) high acceleration voltage for clear latent image, (2) high-contrast resist to attain a high-aspect-ratio pattern, and (3) rapid dissolving resist with little effect on the substrate. With 50-kV acceleration voltage an aspect ratio of resist pattern of about 5 is obtainable using a chemically amplified resist. However, pattern collapse limits the maximum aspect ratio for smaller resist patterns. A positive-tone resist (PSR) and negative-tone resist (RE-4200N) showed excellent characteristics for a SLR process with a 0.2-μm feature size.
Application of proximity synchrotron orbital radiation lithography and deep ultraviolet phase-shifted-mask lithography to sub-quarter-micron complimentary metal oxide semiconductor devices
Authors: Liebmann L. , Ferguson R. , Molless A. , Lamberti A.
Published: July 2002

Sub-quarter-micron gate-level device development and process integration of a complimentary metal oxide semiconductor (CMOS) program are being supported at IBM Microelectronics’ Advanced Semiconductor Technology Center with both synchrotron orbital radiation lithography (proximity x-ray) and phase-edge deep ultraviolet phase-shifted-mask lithography. Data highlighting the feasibility of these two advanced techniques for the lithography support of very aggressive CMOS technologies are presented. Issues of design complexity, design rule impact, and mask engineering are discussed, the exposure process is described, and current process latitude data are presented. Both lithography techniques show feasibility for 200 nm lithography, each with its unique set of challenges and trade-offs.
Studies of TiN nucleation and growth by scanning tunneling microscopy in water
Authors: Song J. P. , Pryds N. H. , Glejbo/l K. , Mo/rch K. A. , Carneiro K.
Published: July 2002

In this article we report on investigations of the nucleation and growth of TiN on tungsten by use of scanning tunneling microscopy (STM) in distilled water. In water tip wear is significantly reduced and the STM images are reproducible by successive scannings. Simultaneous measurements of topography and tunneling barrier signals give new information on material compositions, which is supplementary to the results obtained by transmission electron microscopy and scanning electron microscopy combined with energy dispersive x-ray analysis and Auger electron spectroscopy. The combination of methods give an improved understanding of the nucleation and growth of TiN on W not available by the different methods separately.
Atomic force microscope and scanning tunneling microscope studies of superlattices and density waves in Fe doped NbSe2, TaSe2, TaS2 and in NbSe3 doped with Fe, Co, Cr, and V
Authors: Coleman R. V. , Dai Z. , Gong Y. , Slough C. G. , Xue Q.
Published: July 2002

Results of atomic force microscope (AFM) and scanning tunneling microscope (STM) studies of superlattices and long-range modulations induced by impurities in transition metal chalcogenides are presented. Superlattices formed by Fe intercalation into the van der Waals gaps of 2H–NbSe2, 2H–TaSe2 and 2H–TaS2 show ordered occupation of the octahedral holes and STM spectroscopy shows density-wave energy gaps existing in the antiferromagnetic phases. In NbSe3, interstitial impurities such as Fe, Co, Cr, and V induce long-range modulated structures that can be detected at room temperature with AFM scans. These modulations modify the charge-density wave structure forming at low temperature and STM spectroscopy has been used to measure these changes.
Locally focused electron-beam deposition
Authors: Shaw Jonathan L. , Gray Henry F.
Published: July 2002

We describe a patterned deposition process suitable for producing three-dimensional nanostructures. Deposition occurs when adsorbed precursor molecules are decomposed by electrons or ions. Local electrostatic focusing is used to form a pattern from a broad incoming beam. The local focusing field is produced by a set of apertures suspended above the substrate and held at about 100 V with respect to the substrate. The minimum size of the focal spot so produced is roughly 1/100 the original aperture size, hence, structures with 100-Å features may result from 1-μm apertures. This size is not expected to be limited by scattering effects since the impact energy is low. In contrast to scanned beam deposition methods, this process deposits material at all targeted points simultaneously. The technique may be used to fabricate large arrays of structures such as field emitter tips. We have demonstrated the basic process by depositing 0.5-μm features starting from 25-μm square apertures.
Reactive ion etching-induced damage in InAlAs/InGaAs heterostructure field-effect transistors processed in HBr plasma
Authors: Fay Patrick , Agarwala Sambhu , Scafidi Carl , Adesida Ilesanmi , Caneau Catherine , Bhat Rajaram
Published: July 2002

An investigation of the effects of HBr reactive ion etching (RIE) processing for gate recessing in lattice-matched InAlAs/InGaAs heterostructure field-effect transistors (HFETs) has been conducted. The effect of varying the Schottky barrier layer thickness on device performance and the susceptibility of HFETs to RIE-induced damage are presented for barrier layer thicknesses ranging from 10 to 25 nm. The effect of plasma self-bias voltage during gate recess etching on overall device performance for a given layer structure is also examined for voltages ranging from −100 to −200 V. Device performance is assessed through direct current (dc) characterization of transconductance, threshold voltage, reverse gate leakage current, and gate-drain breakdown voltage, and through microwave characterization of the devices. Devices with barrier layers less than 20 nm thick are found to suffer the most degradation due to RIE-induced damage. For devices with sufficiently thick barrier layers, dc and microwave device parameters compare well with those of corresponding devices fabricated using a selective wet-etch process.
Multiple-level phase gratings fabricated using focused ion-beam milling and electron-beam lithography
Authors: Shank S. M. , Chen F. T. , Skvarla M. , Craighead H. G. , Cook P. , Bussjager R. , Haas F. , Honey D. A.
Published: July 2002

The fabrication of eight-level reflective phase gratings in Si by electron-beam lithography and reactive ion etching, and focused ion-beam milling, has been investigated. Electron-beam lithography and reactive ion etching were used to fabricate gratings with 0.5-μm feature sizes. Alignment of successive levels was held to 50 nm by careful control of proximity effects. Focused ion-beam milling was used to fabricate continuously blazed surface reliefs. The effects of binary and continuously blazed surface reliefs on the first-order diffraction efficiency were determined. Eight-level binary reliefs produced efficiencies of 75% and were limited by phase errors while continuously blazed reliefs produced efficiencies of 90%.
Reduced electron transmission in Au/GaAs diodes damaged by focused ion beam implantation studied by ballistic electron emission microscopy
Authors: McNabb J. W. , Skvarla M. , Craighead H. G.
Published: July 2002

We have used ballistic electron emission microscopy to study the technologically important area of metal contacts to III–V semiconductors. Our samples are Au/GaAs diodes selectively damaged by focused ion beam (FIB) implantation. Implanted regions display reduced interface transmission as the implantation dose is increased above 5×1012 ions/cm2 for Au+ at 30 keV energy. Localized current–voltage measurements indicate that implanted regions have Schottky barrier heights slightly different from those of unimplanted regions. However, these differences are insufficient to account for the attenuated interface transmission. We invoke increased scattering from FIB-induced defects to explain the data. Defect sites in the Au or at the interface may scatter electrons away from the Schottky barrier, or increase inelastic scattering, both of which would lower interface transmission. The effects of several FIB related mechanisms on barrier heights and scattering are explored.
Nanometer characterization of single point diamond-turned mirrors on the micrometer and submicrometer scale
Authors: Yu J. , Hou L. , Ma W. Sh. , Cao J. L. , Yu J. Y. , Yao J. E.
Published: July 2002

Single point diamond turning (SPDT) is one of the nanometer machining methods. We deal with the nanometer characterization of diamond-turned mirrors on the micrometer and submicrometer scale with our three-dimensional roughness measuring system based on scanning tunneling microscopy. We have studied the results of amplitude spectral density functions for these surfaces. Finally, we have calculated the total integrated scattering as a function of incident light wavelength λ and root mean square surface roughness σ and the diffracted angle θd as a function of the λ and the surface spatial wavelength λsp. All these measurement results are the basis for improving the SPDT surface quality.
Scanning tunneling microscopy study of ZnS particles generated from a controlled chemical reaction
Authors: Wang Dawen , Liu Yanqiu , Xu Guangzhi , Bai Chunli
Published: July 2002

ZnS particles prepared by depositing a colloidal ZnS suspension on highly ordered pyrolytic graphite surfaces and Au(110) surfaces were investigated by scanning tunneling microscope (STM). STM directly imaged the particles in real space and measured their dimensions to be 1–5 nm despite the 3.82 eV bulk band gap of ZnS material. The surface atomic topography of a single ZnS particle was also obtained by STM. The periodic arrangement of surface atoms was easily seen, which indicates that ZnS particles are crystallites. Vacancy defects were also found on ZnS dried particle surfaces, which can produce surface states. It was also found that several small crystallites can aggregate to form clusters that lead to different shapes and sizes. The clusters can also aggregate to form lumps. Since ZnS particles and small clusters can easily be moved by the STM tip, it can be seen that no serious reactions exist between ZnS and the substrate surfaces. Some clusters were found to be unstable and can fall apart during tip scanning.
Formation of crystalline islands of C60 on Si(111)
Authors: Chen D. M. , Xu H. , Creager W. N. , Burnett P.
Published: July 2002

The formation of epitaxial crystalline islands of C60 on both the Si(111)7×7 and Si(111)√3×√3-B surfaces is shown to follow an initial growth of a disordered layer and islands. This process is associated with a disordered-to-ordered interface transition at a critical coverage of three monolayers. Such a transition is driven and stabilized by the interlayer molecular couplings owing to the short range van der Waals interactions between the C60 molecules.
Observation of the bottom surface of contact holes by hopping scanning atomic force microscopy with a ZnO whisker tip
Authors: Kado Hiroyuki , Yamamoto Shin-ichi , Yokoyama Kazuo , Tohda Takao , Umetani Yukihiro , Yano Kohsaku
Published: July 2002

In this article, it is demonstrated that atomic force microscopy (AFM) can be useful for observing surface microstructures on the bottom of contact holes used for large scale integrated devices. The AFM employs a zinc–oxide (ZnO) whisker tip with high-aspect ratio and a hopping scanning mode operation. In the hopping scanning mode operation, the probing tip is moved up and down with a period synchronized with the movement in the x direction to avoid collisions against the acute protrusions. Some kinds of bottom surfaces of the contact holes with a diameter of 1 μm and a depth of 1.5 μm have been successfully imaged with nanometer-scale resolution by this AFM technique.
Imaging molecular adsorbates: Resolution effects and determination of adsorption parameters
Authors: Chiang S. , Hallmark V. M. , Meinhardt K.-P. , Hafner K.
Published: July 2002

The scanning tunneling microscope has been used to distinguish a series of related molecules (naphthalene, azulene, and various methylazulenes) on Pt(111) on the basis of their shape. Typical lower resolution images are used to measure the relative sticking coefficients and relative diffusion rates of the molecules. The orientations and binding sites of several of the molecules on the surface are also assigned. Tip dependent higher resolution images can show internal structural details on molecular species which have low diffusion rates.
Scanning tunneling microscope investigation of semiconductor nanometer particles
Authors: Min G. W. , Yang X. M. , Lu Z. H. , Yu W.
Published: July 2002

Two kinds of semiconductor nanometer particles, prepared by Langmuir–Blodgett techniques and the colloid method, were studied on highly oriented pyrolytic graphite using a scanning tunneling microscope operating in air. For PbS nanometer particles, striped structures of about 20–30 nm width were found. Further studies demonstrated that the striped structures are caused by tip–sample interactions and preparation processes. Tip–sample interactions can cause lateral motion and vertical transfer of the nanometer particles which are weakly adsorbed on graphite surface. But the preparation method and the properties of the nanometer materials are the decisive reasons for the ultimate structure formation.
C60 adsorption on the Si(100)2×1 and Cu(111)1×1 surfaces
Authors: Hashizume T. , Sakurai T.
Published: July 2002

The adsorption of C60 molecules on the Si(100)2×1 and Cu(111)1×1 surfaces has been investigated by field ion-scanning tunneling microscopy/spectroscopy. The C60 molecules are stable on the Si(100)2×1 surfaces without rotation at room temperature because of the strong bonding with Si dangling bonds. On the Cu(111)1×1 surface, segregation of individual C60 molecules to the terrace edges and two-dimensional island growth of C60 toward the upper terrace are observed. Bias voltage-dependent scanning tunneling microscopy images of the individual C60 of the monolayer film show unique intramolecular structures, which are interpreted as the local density of the states of C60 interacting with the substrate.
Scanning tunneling microscopy/scanning tunneling spectroscopy study of Ge and Si dimers on Si substrates
Authors: Tomitori Masahiko , Watanabe Kōji , Kobayashi Masato , Nishikawa Osamu
Published: July 2002

The atomic arrangements and the surface electronic states of a small amount of Si or Ge deposited on Si(001) were examined by scanning tunneling microscopy/scanning tunneling spectroscopy. Most of the deposited Si or Ge atoms were arranged as extended overlayer dimer rows, where some atoms occupied sites separated by a few surface lattice constants from the ends of the dimer rows. These sites can capture the deposited atoms migrating along the dimer rows of the substrate, indicating a possible difference of the surface electronic states between these sites and those of the substrate. The tunneling spectra on the sample surfaces showed the dependence on the separation between a tip and the surface.
Atomic force microscopy studies of polysilicon growth during deposition on silicon
Authors: Vatel O. , André E. , Chollet F. , Dumas P. , Salvan F.
Published: July 2002

Atomic force microscopy has been extensively used to investigate polysilicon deposited on silicon for times ranging from 10 s to 45 min. The temperature deposition was 620 °C. Two different regimes have been singled out: one corresponding to isolated grain growth followed by another one which corresponds to coalescence growth. For short times (from 10 s to 1 min) the number of grains remains constant and they grow without any interaction with each other; the grain radii increase following a t1/3 law. When polysilicon grains have grown to a size large enough for them to interact with each other, coalescence takes place and the growth regime is modified; the grain number decreases following a 1/t law. For this second growth regime the surface exhibits a self-similarity type of behavior from which a dynamic scale law can be deduced.
Nanostructuring of porous silicon using scanning tunneling microscopy
Authors: Dumas Ph. , Gu M. , Syrykh C. , Hallimaoui A. , Salvan F. , Gimzewski J. K.
Published: July 2002

Local tip-induced compression of porous silicon layers is shown to be capable of controlled patterning of the surface using scanning tunneling microscopy (STM). STM imaging during and after the nanopatterning procedure is discussed with respect to the mechanism underlying the modification. It is shown that local cathodoluminescence characteristics can be modified by this procedure.
Ag on Si(001)(2×1) formation of a 2×3 superstructure
Authors: Winau D. , Itoh H. , Schmid A. K. , Ichinokawa T.
Published: July 2002

We present scanning tunneling microscope (STM), low-energy electron diffraction, Auger electron spectroscopy, and scanning electron microscope results on the growth of Ag on Si(001)(2×1). At room temperature Ag is adsorbed only at the silicon SB steps at first and preferentially forms dimers during further growth. At higher Ag coverages an inhomogeneous layer which does not cover the surface completely is formed and Ag islands grow with Ag(111)∥Si(001). At a substrate temperature of 770 K Ag forms a homogeneous layer which covers the surface completely. This layer shows a novel (2×3) reconstruction, which shows a strong bias polarity dependence in the STM images. On the top of this (2×3) layer, three-dimensional Ag islands grow with Ag(001)∥Si(001).
Au on the Si(001) surface: Room-temperature growth
Authors: Lin X. F. , Nogami J.
Published: July 2002

The growth of Au on the Si(001) surface is studied using scanning tunneling microscopy (STM). We investigate the initial stages of Au overlayer formation on the Si surface at room temperature. Au grows on the substrate in a layer-by-layer fashion for Au coverage up to 3 monolayers. In the first layer growth, Au forms two-dimensional islands of local 2×2 structure with a density of one Au atom per Si surface atom. On the basis of the STM images, a 2×2 structural model is proposed. Au atoms lie in atop sites, forming Au–Au dimers with orientation perpendicular to the underlying Si dimers. Subsequent layers of Au growth are disordered.
Matteucci effect of an amorphous alloy tip used for high-density magnetic recording with a scanning tunneling microscope
Authors: Tsuji Satoshi , Watanuki Osaaki
Published: July 2002

This paper presents a study of the Matteucci effect of a Co–Fe–Si–B amorphous alloy tip used for magnetic recording with a scanning tunneling microscope (STM). The Matteucci effect is a phenomenon in which a pulse-shaped alternating current (ac) voltage is induced between the ends of a torsionally stressed magnetostrictive wire when the magnetization of the core domain is switched by application of an external ac magnetic field parallel to the wire axis. The influence on the tip-to-medium spacing using the above tip is investigated experimentally. Quantitative results for various coil currents and frequencies are obtained. The observed Matteucci pulse voltage is less than 10% of the bias voltage of the STM, and the Matteucci pulse width is approximately 1 μs. The influence of the Matteucci effect on the feedback system of the STM is also discussed.
Systematic studies on the growth process of superconducting YBa2Cu3O7−δ and Bi2Sr2CuOy thin films by scanning tunneling microscopy
Authors: Zhu Xing , Xiong G. C. , Liu R. , Li Y. J. , Lian G. J. , Gan Z. Z.
Published: July 2002

We have systematically studied the growth mechanism and surface topography of YBa2Cu3O7−δ (YBCO) and Bi2Sr2Ca0Cu1Oy-2201 (BSCCO) epitaxial grown superconducting films by scanning tunneling microscopy. Here we report two growth mechanisms of screw dislocation growth and layered growth; the surface characterization; and surface modification of thin films under a controlled manner. Excimer laser ablation technique was applied to synthesize high-quality epitaxial thin films. YBCO thin films were epitaxially grown with c axis perpendicular to the SrTiO3 (100) substrate surface. If the YBCO films were grown on the substrate which normal is slightly off the ideal [001] orientation, the films show layered growth. Whereas on the flat substrate, the films were nucleated and grown with the screw dislocation manner. By using the effect of field-induced evaporation, we were able to analyze the initial stage of growth. Epitaxial grown BSCCO-2201 films on ZrO2 substrates were synthesized and studied by scanning tunneling microscopy (STM). Layered growth and larger atomic flat areas were observed, which are more stable under STM than YBCO films. No screw dislocations were identified in BSCCO-2201 films. The reasons of the different behaviors of the two kinds of thin films are discussed.
In situ ballistic-carrier spectroscopy on epitaxial CoSi2/Si(111) and Si(100)
Authors: Sirringhaus H. , Lee E. Y. , Kafader U. , von Känel H.
Published: July 2002

In situ ballistic-electron-emission microscopy (BEEM) and spectroscopy (BEES) have been performed at 77 K on CoSi2/Si(100) and Si(111) grown by molecular beam epitaxy (MBE). Scattering at individual interface dislocations and point defects gives rise to a localized increase of the BEEM current on n-Si(111) and a decrease on p-Si(111) in agreement with a kinematic interpretation. On n-Si(100), (110)-oriented grains exhibit a Schottky barrier of 0.58±0.04 V compared to 0.74±0.04 V on (100)-oriented CoSi2. The magnitude of the BEEM current strongly depends on the epitaxial orientation on Si(100) and is comparable for CoSi2(100)/n-Si(100) and CoSi2/n-Si(111).
Optimization of intermetal dielectric deposition module using simulation
Authors: Li Junling , McVittie James P. , Ferziger Joel , Saraswat Krishna C. , Dong Jeffrey
Published: July 2002

A major challenge arising in the interlevel dielectric deposition processes in modern multilevel very large scale integrated technology is the filling of high aspect-ratio spaces without voids between metal lines. Here the main concerns are step coverage and material properties of dielectric films. One approach is the multistep silicon dioxide deposition using plasma enhanced chemical vapor deposition followed by atmospheric pressure CVD from ozone/TEOS. To combine the advantages of different processes and to satisfy the device reliability requirements, one needs to optimize the relative thickness of these sequentially deposited oxide layers. In this work a profile simulator, SPEEDIE, is employed to study this multistep process. For the PECVD process a free molecular-flow model based on the combination of a single sticking-coefficient LPCVD model and an ion-induced-deposition model is used. For the atmospheric pressure CVD (APCVD) process a continuum transport model considering both gas-phase diffusion and surface reaction is used with a geometry-variant reaction rate which depends on the ozone (O3) concentration. The major topography-controlling parameters are calibrated for these sequential processes, and verified through simulation. As an example of application, a prediction of void-forming based on the reliability requirements is generated by the simulator, and can be regarded as a measure of this multistep process. In general an efficient design tool is provided to help optimize the interlevel dielectric deposition processes.
Effects of stimulated adsorption in scanning tunneling microscopy investigation of Si surface in ambient air
Authors: Bukharaev A. A. , Samarsky E. A. , Janduganov V. M. , Berdunov N. V. , Antonov P. G.
Published: July 2002

The experimental research and theoretical analysis of current–voltage characteristics and current–distance dependences have been carried out for Si surfaces in ambient air by means of a scanning tunneling microscope (STM). It has been found that extremely large gap distances and low apparent heights of potential barriers may be caused by mobile (fluid-like) adsorbed layers covering both the Si surface and the STM tip. We have demonstrated that the electron transfer mechanism in such conditions follows the Schottky equations. It has been shown experimentally that similar adsorbed layers can be formed by the STM operating in ambient air at low bias voltages and cause the transition from direct tunneling to Schottky emission in the conductivity process. The quality of surface cleaning has been found to be well represented by STM current–distance dependences.
Low-temperature growth of 850 nm quantum well modulators for monolithic integration to very large scale integrated electronics on GaAs
Authors: Cunningham J. E. , Goossen K. W. , Jan W. Y. , Walker J. A. , Pathak R. N.
Published: July 2002

We report a new, low-temperature process for monolithically integrating 850 nm modulators to pre-existing very large scale integrated GaAs electronics. We find pristine GaAs surfaces form below 400 °C in the presence of energetic protons generated by an electron cyclotron resonance plasma. While 850 nm superlattices grown at 430 °C exhibit nearly perfect lattice structure when examined by x-ray diffraction, nonradiative centers are detected with photoluminescence. Transmission spectroscopy reveals the excitons deteriorate too rapidly under bias voltage to fully utilize the quantum confined Stark effect. Efforts to reduce nonradiative trap generation and improve modulator performance under low-temperature growth appear more feasible when growth is performed under tightly controlled stoichiometric conditions than with arsenic pulsed layer molecular beam epitaxy methods.
Scanning force microscope technique for adhesion distribution measurement
Authors: Sasaki Minoru , Hane Kazuhiro , Okuma Shigeru , Torii Akihiro
Published: July 2002

A scanning force microscope technique is described to study the relation between topography and the local adhesion. The drift has been a main problem in investigating this relation since a long period is required to measure force curves over the scan area. To circumvent this problem, we propose a methodology to detect the topography and the adhesion from force curves simultaneously. Since this information is obtained from the same force curve, the distribution of the tip position corresponds precisely to that of the adhesion. The detailed relation between the tip position and the adhesion is measured on a fine lithographic grating.
ZnMgSSe/ZnSSe/CdZnSe strained quantum well lasers grown on (511)A
Authors: Tao I. W. , Wang Y. , Jurkovic M. , Wang W. I.
Published: July 2002

Although low threshold II–VI blue/green lasers have been demonstrated, the device lifetime for these lasers remains an important issue. It has been observed that the dark line defects, which are caused by stacking faults or point defects, are related to the degradation of the lasers. In order to improve the reliability of the laser, we initiated studies of molecular-beam epitaxial growth and device characteristics of II–VI quantum well lasers grown in the (511)A orientation. The photoluminescence spectra of (511)A epilayers always exhibited stronger and sharper emission peaks than their (100) counterparts, which implied that fewer defects were incorporated in the (511)A epilayers. Room temperature threshold current densities of 1 kA/cm2 have been obtained. The performance of these lasers merits further studies on the use of (511)A as a possible solution to the reliability problem of II–VI lasers.
In situ pyrometric interferometry monitoring and control of III–V layered structures during molecular-beam epitaxy growth
Authors: Liu X. , Ranalli E. , Sato D. L. , Li Y. , Lee H. P.
Published: July 2002

A detailed modeling of pyrometric radiation from AlAs/GaAs layered structures during molecular-beam epitaxy growth is presented. Based on simulations using an approximate form of this model and a novel phase estimator, a closed-loop control system was devised and tested. Experimental results are presented for a quarter-wavelength distributed Bragg reflector grown with and without closed-loop control. Improved accuracy is evident for the layers grown with feedback control.
Molecular-beam epitaxy growth of multiple-wavelength mirrors and applications for a dual-wavelength resonant-cavity photodetector
Authors: Srinivasan A. , Murtaza S. , Anselm K. , Shih Y. C. , Campbell J. C. , Streetman B. G.
Published: July 2002

The growth of Bragg mirror structures by molecular-beam epitaxy (MBE) results in a variety of photonic devices employing microcavities. We have grown multiple-wavelength mirrors in the AlGaAs system which were designed to reflect dual and quadruple wavelengths. The dual-wavelength mirror structure has been applied in the design of a high efficiency resonant cavity photodiode. This dual-wavelength resonant cavity photodiode has external quantum efficiencies greater than 50% with very high selectivity of the two wavelengths.
GaAs and InP selective molecular-beam epitaxy
Authors: Streit Dwight C. , Block Thomas R. , Han An-Chich , Wojtowicz Michael , Umemoto Donald K. , Kobayashi Kevin , Oki Aaron K. , Liu Po-Hsin , Lai Richard , Ng Geok I.
Published: July 2002

We present here the selective molecular-beam epitaxy (MBE) techniques used to achieve high quality material that integrates multiple device technologies on the same GaAs or InP substrate. We have successfully demonstrated selective MBE for both GaAs-based high electron mobility transistor (HEMT)—heterojunction bipolar transistor (HBT) integration and InP-based PIN diode—HEMT integration. New merged processing technologies have been developed to achieve high performance monolithic microwave and optoelectronic HEMT-HBT and PIN-HEMT integrated circuits. In each case the performance potential of discrete devices has been maintained throughout the monolithic integration process.