bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simple Estimating Method for Reduction of Welding Residual Stresses in Thick Welded Joint From Stress-Relief Annealing—Part III: Development of Estimating Equations for Multiaxial Stress State in Thick Welded Joint
Authors: Nakacho Keiji
Published: July 2002

Stress-relief annealing (SR treatment) is often applied to relieve welding residual stresses in the fabrication process of pressure vessels, etc. This study aims at development of an efficient method as simple as hand calculation to estimate reduction of residual stresses of a very thick welded joint by SR treatment. In the first report, an estimating method was developed for relaxation tests, in uniaxial stress state, at changing and constant temperatures because the stress relaxation phenomenon is considerably similar to that observed in the SR treatment of a joint. In the second report, the stresses relaxed by SR treatment in a very thick welded joint were analyzed accurately by the finite element method based on thermal elastic-plastic creep theory. The characteristics of the changes of the welding residual stresses in multiaxial stress state were studied in detail for further development of the estimating method to SR treatment of a very thick welded joint, of which the stress state and boundary condition are very complex. In this report, the estimating equations in multiaxial stress states are developed for the stress relaxation phenomenon in the thick welded joints, based on the foregoing characteristics.
Plasticity Index for Contact Between a Head and a Disk With Crater-Shaped Laser Bumps
Authors: Zhao Q. , Talke F. E.
Published: July 2002

A plasticity index formula for the contact between a flat plane and crater-shaped laser bumps is derived based on contact analysis of a circular cylinder in contact with a flat plane. The plasticity index for “cylinder-on-plane” contacts differs by a scale factor from that for “sphere-on-plane” contacts while the criterion for the deformation mode is the same for both types of contacts. For a wide range of typical head/disk interface conditions, the plasticity index for “cylinder-on-plane” contacts is found to be smaller than that of “sphere-on-plane contacts.” [S0742-4787(00)03501-3]
Plasma-enhanced atomic layer deposition of Ta and Ti for interconnect diffusion barriers
Authors: Rossnagel S. M. , Sherman A. , Turner F.
Published: July 2002

Thin films of inert, refractory materials are used in semiconductor interconnect applications as diffusion barriers, seed, and adhesion layers. A typical example is the use of a thin, conformal Ta or Ti/TiN films on the walls of a dielectric trench or via which reduces or eliminates out-diffusion of the primary conductor, usually Cu, into the dielectric. Atomic layer deposition is a known technique which is intrinsically conformal and is appropriate for this application. Plasma enhancement of the process allows deposition at significantly lower temperatures than conventional chemical vapor deposition, which is a requirement for low-k dielectrics. Tantalum films deposited at 25–400 °C using ALD with a TaCl5 precursor and atomic hydrogen as the reactive species at up to a rate of 1.67 Ang/cycle are amorphous, conformal, and show moderate or controllable levels of impurities; primarily oxygen and a small level of Cl. Similar results have been observed for Ti using TiCl4 as a precursor. The process scales to manufacturing dimensions and applications and will facilitate the extension of interconnect technology beyond (below) 100 nm dimensions.
Microfabrication using a Computer-Controlled Scanning Transmission
Authors: Kim J. J. , Sampson H. G. , Everhart T. E.
Published: July 2002

Fabrication and inspection of two-dimensional lattice structures in thin polymer films have been carried out using a computer-controlled scanning electron microscope (CCSEM). Periods of 0.2 μ are quite regular, finer resolutions show some irregularities possibly due to film instabilities. Using the CCSEM permits great flexibility, and using thin films eliminates the problem of backscattered electrons from the substrate, which severely limits the resolution of periodic structures fabricated on a solid substrate. These structures should be useful in integrated optics, and may be used as x-ray lithography or evaporation masks.
Cantilever probes for spatio-temporal imaging of voltage pulses with an ultrafast scanning probe microscope
Authors: Oesterschulze E. , Heisig S. , Steffens W. M.
Published: July 2002

We report on a novel cantilever probe for the investigation of ultrafast signals. High temporal resolution is achieved by integrating a photoconductive switch within a coplanar waveguide structure onto a low temperature GaAs coated GaAs cantilever. Experimental results and numerical calculations on the detection of picosecond electrical signals based on the optoelectronic technique of photoconductive sampling are presented.
Silicon bonding for ultrahigh vaccuum surface science studies
Authors: Gokhale Shubha , Fink Andreas , Trischberger Peter , Eberle Karl , Widdra Wolf
Published: July 2002

A novel silicon bonding technique and its application for surface science studies in a wide temperature range of 30–1400 K is presented. The silicon single crystal is bonded on a polished tantalum plate via thin silver and tungsten interlayers deposited by evaporation in high vacuum. Upon annealing the silicon sample is bonded with a strong mechanical and good thermal contact. Several problems common to alternative sample mounting techniques are solved by this procedure. Excellent temperature control and small temperature gradients across the surface well below 1 K are demonstrated by thermal desorption data for two different adsorbates: ethane and hydrogen on Si(001)-(2×1).
Growth and characterization of GaInNAs/GaAs multiquantum wells
Authors: Gilet P. , Grenouillet L. , Duvaut P. , Ballet P. , Rolland G. , Vannuffel C. , Million A.
Published: July 2002

Thick GaAsN layers and GaInNA/GaAs multiple quantum wells (MQWs) were successfully grown on semi-insulating GaAs substrates by gas-source molecular beam epitaxy equipped with a nitrogen radio frequency (rf) activated plasma source. High resolution x-ray rocking curves indicate that the nitrogen content in the GaAsN layer is increased from 0.7% to 3% with increasing rf cavity pressure. Room temperature photoluminescence measurements show that the emission wavelength decreases when the nitrogen content is increased. The evolution of the strained band gap with nitrogen composition is in quantitative agreement with calculations as well as with other spectroscopic studies, allowing complete characterization of the alloy for a small nitrogen fraction. Furthermore, the influence of the growth temperature and the V–III ratio on the optical and structural properties of the GaInNAs MQWs has been carefully examined. We found that the material properties are optimal at a growth temperature of 400 °C and a V–III ratio of 3.
Study on temperature calibration of a silicon substrate in a temperature programmed desorption analysis
Authors: Hirashita N. , Jimbo T. , Matsunaga T. , Matsuura M. , Morita M. , Nishiyama I. , Nishizuka M. , Okumura H. , Shimazaki A. , Yabumoto N.
Published: July 2002

In this work we propose a standard practice covering temperature calibration of a Si substrate, ranging from 400 to 1000 °C, for temperature programmed desorption (TPD) analysis. The practice consists of heating silicon calibration materials at a controlled rate in a TPD instrument, measuring characteristic desorption peak temperatures, and quadratic calibration fitting the measured temperatures to standard temperatures. The calibration materials are (1) a CaC2O4⋅H2O pellet on Si, (2) Ar, and (3) H ion implanted into Si wafers. The standard temperatures of the characteristic desorption, associated with decomposition, structural transformation, and lamination of Si, were determined by a special TPD instrument with the highest isothermal space around the specimen in several laboratories, which was confirmed to be accurate for practical application. The precision of this practice was determined in an interlaboratory test in which four to five laboratories participated using two different instrumental models. This proved that the correction practice provided interlaboratory precision of 5.7 °C between 400 and 1000 °C for ramping rates of 10, 30, and 60 °C/min.
Wall-dependent etching characteristics of organic antireflection coating in O2+halogen/hydrogen halide plasma
Authors: Xu Songlin , Lill Thorsten , Podlesnik Dragan
Published: July 2002

Process instability in plasma etching of organic bottom-antireflection coating (BARC) using the plasma of O2 mixed with halogen (Cl2) or hydrogen halide (HBr, HCl) has been studied. From a series of process tests performed on a high density plasma etcher, the process instability has been found to be chamber-wall related as the BARC etch rate and critical-dimension bias shift when chamber coating changes. The process sensitivity to the chamber wall condition depends on the type of halogen-containing additive used and the O2 percentage in the total gas feed. Through plasma diagnostics, the root cause of the process shift has been identified as the variation in the surface recombination rate of reactive free radicals with chamber wall condition. The recombination of O radicals to form O2 is faster on alumina/anodized aluminum than on silicon oxide so that the O radical density becomes lower in the bulk plasma. The enhanced competing surface recombination of O and H radicals when HBr or HCl is used further lowers the O density, leading to a more significant process shift. Approaches to improve the process stability and performance consistency have been discussed.
Measurements with a Modulated Bayard–Alpert Gauge in Aluminosilicate Glass at Pressures below 10−12 Torr
Authors: Hobson J. P.
Published: July 2002

The background conditions achieved in a simple ultrahigh-vacuum system with an envelope of aluminosilicate glass (Corning 1720) have been studied. Pressures were measured by a dynamic method and also with a modulated Bayard–Alpert gauge. Good agreement between the two methods was obtained using a modified analysis for the modulated gauge. A total pressure of 8 × 10−13 Torr (equivalent nitrogen) was measured with the whole system at room temperature, and one of 7 × 10−15 Torr (equivalent nitrogen) was measured with a portion of the system immersed in liquid helium. A discussion is given of variations in the residual modulation factor of the gauge in the presence of extremely low gas pressures.
Electron-projection microfabrication system
Authors: Heritage M. B.
Published: July 2002

An electron-optical analog of a photon-optical projection camera is described. The system is designed to meet the requirements of future memory technology with submicrometer resolution over a chip size of several millimeters. A self-supporting foil mask is illuminated by electrons and magnetically imaged onto a wafer with a 10×reduction in size. This paper describes the electron optics required for a high-resolution large-field performance. Particular emphasis will be placed on the means for reducing the third-order aberrations of the magnetic projection lenses. The limitations imposed by the unavoidable aberrations of the condenser system are also discussed. The performance of the system is illustrated by reference to results obtained by exposing test patterns.
Surface and near-surface atomic structure of GaAs (110)
Authors: Kahn A. , So E. , Mark P. , Duke C. B. , Meyer R. J.
Published: July 2002

Low-energy electron diffraction (LEED) intensity–voltage data for a complete set of first-order diffraction beams of the GaAs (110) surface is averaged at constant momentum transfer and compared with kinematical and dynamical model calculations for several surface atomic geometries. The atomic displacements in the surface and first two subsurface layers are obtained via this analysis. The influence of multiple scattering is examined by computing the single and multiple scattering contributions to the intensity–voltage profiles associated with atomic distortions within the first three lattice layers. This procedure allows the identification of the major features of the structure in the LEED–CMTA (constant momentum transfer average) profiles either with multiple scattering effects or with single scattering resonances derived from the lattice geometry.
Atomic and electronic structure of surfaces studied with synchrotron radiation
Authors: Margaritondo G. , Rowe S. E.
Published: July 2002

Many synchrotron radiation techniques developed in the past decade use the photoemission process to study surfaces and, in particular, adsorbates. Most of these probe the local surface electronic states. Recently, some photo− emission techniques have evolved into probes of the surface atomic structure as well. These structure−sensitive techniques are photon−polarization− dependent photoemission, adsorbate band structure mapping, surface−EXAFS, and photoelectron diffraction. In this article synchrotron experiments in both categories are discussed, and representative results are given which illus− trate their applications to surface structural problems of fundamemtal interest. We discuss in particular the distinctive advantages of these new surface− sensitive structural probes with respect to other more established techniques.
Discharge suppression within piezoelectric gas admission valves
Authors: McEvoy A. J.
Published: July 2002

Modification of a Veeco-type PV-10 piezoelectric gas admissions valve to avoid failure due to initiation of a glow discharge producing a conductive film is described. A grounded screening grid is introduced within the valve body.
Possible oxygen chemisorption configurations on the Si(lll) 2×1 surface
Authors: Su C. Y. , Skeath P. R. , Lindau I. , Spicer W. E.
Published: July 2002

Room temperature adsorption of oxygen on the Si(111) 2×1 surface and the effects of annealing of oxygen-covered surfaces were studied with photoemission techniques. Before annealing, the dominant chemical shifts in Si-2p are ∠0.9 and ∠1.4 eV; after annealing, a dominant shift at ∠2 eV is found. Possible chemisorption configurations are discussed in terms of the new information gained and many possibilities are eliminated. However, a few Si–O bonding configurations remain; more precise calculation of chemical shifts will be necessary to choose between them.
Nitrogen-induced fcc phase in rf sputtered Co–Cr films having the hcp phase and perpendicular magnetic anisotropy
Authors: Coughlin T. M. , Wuori E. R. , Judy J. H.
Published: July 2002

The presence of as little as 2.3×10−5 Pa (1.73×10−7 Torr) of residual nitrogen gas in an rf sputtering chamber has been found to promote the formation of the fcc phase in Co-Cr films under conditions otherwise favorable to the formation of the hcp phase. The fcc phase follows the disorientation of the hcp phase as the nitrogen partial pressure or throughput increases. The occurrence of the fcc phase is directly related to the partial pressure or throughput of nitrogen in the system as shown using controlled leaks of both pure nitrogen and air. The nitrogen may destroy the columnar microstructure and the film perpendicular magnetic anisotropy which is due to the well-oriented hcp phase. This sensitivity to nitrogen in the background gases makes it necessary to achieve a low background pressure in the sputtering chamber if films with perpendicular magnetic anisotropy are to be obtained.
A study of the sputtering of copper–nickel using a combination of techniques
Authors: Thomas Michael P. , Ralph Brian
Published: July 2002

Quantitative atom-probe field-ion microscopy (APFIM), x-ray photoelectron spectroscopy (XPS), and qualitative secondary ion mass spectrometry (SIMS) have been applied in a phenomenological study of the modification in surface composition of copper–nickel targets by low energy ion sputtering. In agreement with the bulk of previously reported studies, XPS and SIMS data suggest the preferential loss of copper. APFIM data have revealed that the immediate surface layers remain unchanged in composition while a nickel-enriched layer is found immediately subsurface. This result is in accord with recent studies using ion scattering spectroscopy.
Low temperature reactive sputter deposition of vanadium oxide
Authors: Hansen S. D. , Aita C. R.
Published: July 2002

In the present study, vanadium oxide films were grown on water-cooled sapphire, silicon, and glass substrates by reactive sputter deposition using a vanadium target and rf-excited argon discharges containing 0%–25% oxygen. Optical emission spectroscopy was used for in situ discharge diagnostics. Films were characterized by x-ray diffraction to determine crystallography and by double-beam spectrophotometry to determine optical absorption behavior in the 200–1200 nm spectral region. The results show that film crystallography evolves from single (110) orientation body-centered cubic vanadium to single (001) orientation orthorhombic vanadium pentoxide to a material in which there is no long range atomic order detectable by x-ray diffraction as the sputtering gas oxygen content is increased. Changes in optical absorption behavior which accompany the decrease in atomic order are presented and discussed.
Biplanar source for high rate, large area, reactive sputtering: SiO2
Authors: Rostworowski J. , Parsons R. R.
Published: July 2002

A new type of sputtering source, called a ‘‘biplanar magnetron,’’ is described which permits well controlled, metallic (or ‘‘high rate’’)-mode deposition of SiO2 for large area industrial applications. Two biplanar magnetrons have been used to fabricate optical multilayer coatings on a 1-m-wide web. Clear films of SiO2 have been deposited with optical thickness uniformity equal to ±2% at a deposition rate of 3.6 Å/kW m/min. With one biplanar source operated at 20 kW, this rate corresponds to a line speed of 7.2 cm/min for a 1000-Å physical thickness of SiO2. The device is equally useful for many other compounds, including AlN, ZnO, Al2O3, ZrO2, and indium tin oxide.
Erosion and deposition in tokamaks
Authors: Staudenmaier G.
Published: July 2002

The flow of metal impurities from the wall and limiter to the plasma, and back towards the wall, is investigated using surface collection probes and subsequent surface analysis in order to understand impuritiy generation and impurity transport. Impurity fluxes and their scrapeoff lengths have been investigated for several years in a large number of tokamaks. The results are summarized and discussed. Erosion exceeding deposition was first observed to occur at limiterlike structures closest to the plasma edge. Recently, a new probe has been developed to measure quantitatively the erosion in ASDEX. Subsequent quantitative surface analysis is performed in situ by electron induced x-ray analysis. Erosion caused either by ions (limiter) or charge exchange neutrals (wall) can be investigated separately. The erosion at the wall is about two orders of magnitude smaller than the erosion at limiterlike structures, which is of the order of one monolayer per discharge. Simultaneous measurements of deposition and erosion have been performed to elucidate net values of deposition and erosion.
An elastic recoil detection analysis investigation of the temperature dependence of the adsorption of ethylene and acetylene on Pt(111)
Authors: Yu R. , Gustafsson T.
Published: July 2002

When a high-energy heavy ion collides with a light adsorbate on a surface, the latter may recoil with substantial energy. The interaction is, at sufficiently high energy, described with classical Rutherford formulas and is therefore well understood. This technique (elastic recoil detection analysis or ERDA) is therefore a quantitative tool for the detection of adsorbed light atoms on well-characterized surfaces in ultrahigh vacuum. We demonstrate its use in a study of the temperature dependence of the adsorption of ethylene (C2H4) and acetylene (C2H2) on Pt(111). The results confirm that C2H4 and C2H2 adsorb intact at 100 K, while at higher temperatures conversion to C2H3 takes place. The saturation coverage for adsorption both at room temperature and below is shown to be Θ≊0.5. The results show the applicability and versatility of ERDA for light atom detection on surfaces.
Metal induced crystallization of amorphous silicon
Authors: Robertson A. E. , Hultman L. G. , Hentzell H. T. G. , Hörnström S.-E. , Shaofang G. , Psaras P. A.
Published: July 2002

The reactions between a thin metal film of Al or Ag and a layer of amorphous Si have been investigated using transmission electron microscopy and Auger electron spectroscopy. The samples were analyzed after deposition and after different heat treatments. Al and Ag were found to reduce the crystallization temperature of amorphous Si. A crystallization temperature of 325 °C was observed for the Al–Si structure and of 525 °C for the Ag–Si structure. A new phase between Al and Si, which has not previously been reported, has been detected at a temperature of 150 °C. Some evidence for a formation of a metastable phase between Ag and Si during the crystallization process has also been found.
Percolative aspects of nonequilibrium adlayer structure
Authors: Evans J. W. , Sanders D. E.
Published: July 2002

For any adsorption process where all binding sites eventually fill, there exists a coverage θc at which a filled cluster (defined by linking neighboring filled sites) first spans the substrate. Such percolation features have been studied extensively for random distributions of filled sites. Here θc =0.59 monolayers for ‘‘p(1×1) ordering’’ on an infinite square lattice. Cooperative island-forming adsorption involves competition between nucleation, growth, and coalescence or linkage of individual islands. Here clusters of linked islands eventually span the substrate. We use correlated percolation theory to provide a quantitative description of corresponding θc behavior, and of the fractal structure of the clusters of linked islands and their perimeters. Modified grain growth models, which correspond to continuum percolation problems, are also useful here. We show how percolation theoretic ideas can be extended to analyze nonpercolating c(2×2) ordering. Even for the essentially random adsorption mechanisms of H2O on Fe(001), and oxygen on Pd(100), such nonequilibrium c(2×2) ordering is significant. We also discuss how island-forming cooperativity here affects the c(2×2) ordering.
Fundamental factors governing improved performance of Al–Si/Ti multilayer metallization for very large scale integration
Authors: Joshi A. , Hu H. S. , Yaney D. L. , Gardner D. , Saraswat K.
Published: July 2002

Fundamental factors governing the previously observed improvements in conductivity, hillock growth resistance, and thermal stability of the Al–Si/Ti multilayer metallization system have been investigated using various bulk characterization methods and surface analytical techniques (Auger electron spectroscopy and x-ray photoelectron spectroscopy). Si partitioning from the Al–Si into Ti layer duirng annealing at 450 °C was found to be associated with the formation of a ternary phase similar to TiAl3, but enriched in silicon. In the Al–Si/Ti–Si multilayer metallization system, Si migrates into the Al–Si layer and Al migrates into the Ti–Si layer during annealing. These results suggest that the TiAl3(–Si) phase is thermodynamically more stable than the TiSi2 and TiAl3 phases and that its formation is not kinetically limited by diffusion of Si and Al in either Al or Ti at 450 °C. Formation of TiAl3(–Si) between Al layers is an important factor contributing to improved conductivity of the Al–Si/Ti layered metallization. Formation of interspersed hard layers of TiAl3 or TiAl3(–Si) phases, as well as precipitation of these phases within the Al or the Al–Si layers, appears to be responsible for the improved hillock growth resistance of these multilayered structures.
Modifications in the interfacial reaction between thin films of Ti and Al due to alloying the Al with Si
Authors: Ben-Tzur M. , Fastow R. , Eizenberg M. , Rosenberg J. , Frenkel M.
Published: July 2002

The interfacial reaction between Al(Si) and Ti thin films has been studied and compared to that for pure Al and Ti. The experimental techniques employed were Rutherford backscattering spectrometry, transmission electron microscopy, and measurements of the sheet resistivity. It has been found that alloying the Al with Si delays the onset temperature for Al3Ti formation (430 °C for 1% Si compared to 300 °C for pure Al), decreases significantly the reaction rate, and causes a nonuniform and nonplanar interaction. The effects of the Si concentration and the annealing environment have also been studied. A model based on processes which impede the transport of Ti atoms to the reaction front can explain the obtained results.
Electron assisted glow discharges for conditioning fusion tokamak devices
Authors: Schaubel K. M. , Jackson G. L.
Published: July 2002

Glow discharge conditioning of tokamaks with graphite plasma-facing surfaces has been used to reduce impurities and obtain density control of the plasma discharge. However, a major operational disadvantage of glow conditioning is the high pressure required to initiate the glow discharge, e.g., ≊70 mTorr for helium in DIII-D, which requires isolating auxiliary components that can not tolerate the high pressure. An electron-gun-assisted glow discharge can lower breakdown pressure, possibly eliminating the necessity of isolating these auxiliary systems during glow discharge conditioning and allowing glow discharge operation at lower pressures. An electron-assisted glow discharge experiment has been carried out in a small vacuum vessel to evaluate whether such a system can be employed in the DIII-D tokamak. With an electron gun to produce an initial source of electrons, the pressure at which a helium glow discharge can be initiated has been decreased by two orders of magnitude. The glow was produced in a 0.40 m3 Inconel test chamber (3.5 m2 surface area) and was pumped with a 330 ℓ/s turbomolecular pump. The electron gun consists of a tungsten filament and grid assembly. An electron current of up to 18 mA with energies up to 1.6 kV has been used. The pressure is measured with a capacitance manometer, the gas composition with a residual gas analyzer and the electron temperature, density, and plasma floating potential with a Langmuir probe. With the addition of an electron current of 10 mA, the initiation pressure was reduced from 165 to 1.6 mTorr. The lowest sustaining pressure dropped from 3.0 mTorr in the absence of electron assist to 1.5 mTorr with 10 mA of electron current.
Topographical features of rotated Auger samples sputtered with inert-gas ions
Authors: Sobue S. , Okuyama F.
Published: July 2002

The effect of sample rotation on the ion-induced surface roughening for multilayer Auger samples is described using preliminary scanning electron microscopy. The surface roughness amplitude of Cu/Ag sandwiches bombarded with 1–3 keV Ar+ and Xe+ ions was found to be dramatically reduced by sample rotation, resulting in a significant improvement in depth resolution, especially for Ar+ -bombarded samples. The sputtered surfaces of rotated samples were characterized by planar crystals developed thereon, forming a striking contrast to the stationary sample surfaces thickly covered with conical microprojections. The mechanism of this two-dimensional crystal growth is discussed briefly, in terms of surface atom mobility enhanced by ion impact.
An investigation of electromagnetic field patterns during microwave plasma diamond thin film deposition
Authors: Zhang J. , Huang B. , Reinhard D. K. , Asmussen J.
Published: July 2002

The electromagnetic field patterns and intensities of a microwave-sustained, diamond thin film deposition discharge were measured in a microwave plasma disk reactor (MPDR). The MPDR is a cylindrical, symmetrical cavity applicator which can be excited in single electromagnetic modes and utilizes internal matching and thus lends itself to experimental electromagnetic field diagnosis. The measured electric field intensities indicate that the plasma-loaded TM011 mode provides optimum discharge excitation. During the thin film deposition conditions of 30–100 Torr and 100–300 sccm with mixtures of H2 /CH4 , the electric field intensities in the applicator are 100–200 V/cm and the tangential component of the electric field is the major electric field exciting the discharge. Measured discharge-loaded cavity quality factors are 70–100 and microwave coupling efficiencies into the discharge are in excess of 98%; i.e., the transfer of microwave energy to the discharge is a very efficient process. Using estimated discharge electron neutral-collision frequencies and electron and ion densities, calculations indicate that discharge electromagnetic skin depths vary from 2–5 cm during thin film deposition. It is believed that maximum discharge size is limited by this electric field depth of penetration.
On the low-pressure mode transition in electron cyclotron heated plasmas
Authors: Dandl R. A. , Guest G. E.
Published: July 2002

The properties of plasmas created and sustained by electron cyclotron heating (ECH) have often been found to undergo an abrupt change as the ambient gas pressure is reduced below a value that is typically around 10−5–10−4 Torr. A model is presented in which ambipolar transport of particles and energy are balanced by electron impact ionization and microwave power absorption, respectively. In the absence of magnetic-mirror confinement of high energy electrons, the equilibria predicted by the model exist only for gas pressures greater than a value determined by the ionization rate constant, the average ion mass, and the axial length (along the steady magnetic field) of the discharge. At the critical pressure, the equilibria bifurcate into high-temperature/low-density and low-temperature/high-density branches. Magnetic-mirror confinement of high-energy electrons can lower the critical pressure and modify the bifurcation somewhat. In all cases the equilibrium electron temperature is governed primarily by gas pressure while the plasma density is proportional to the microwave power density absorbed by the plasma.
III–V surface processing
Authors: Ingrey S.
Published: July 2002

The results of exposing cleaved (110) and polished or metal organic chemical vapor deposition (MOCVD) grown (100) single crystal InP and GaAs surfaces to various treatments are reported. The formation of hydrocarbon covered, hydrogen terminated surfaces is shown to provide short term protection against the contamination typically observed when clean surfaces are exposed to air. This protective layer is readily removed on exposure to ultraviolet/ozone irradiation resulting in a surface covered with a thin stoichiometric native oxide which provides a more permanent surface passivation. The thickness of oxides, prepared using this procedure, can be controlled to make them compatible with most III–V process steps. Thermal desorption of the oxides in appropriate ambients yields stoichiometric surfaces appropriate for epitaxial overgrowth.
Application of high-resolution electron energy-loss spectroscopy to the study of adsorbates on metal oxide surfaces: Methylacetylene and allene on ZnO(0001)
Authors: Petrie W. T. , Vohs J. M.
Published: July 2002

In this study, the surface intermediates formed during the adsorption and reaction of methylacetylene and allene on the (0001)-Zn polar surface of ZnO were examined using high-resolution electron energy-loss spectroscopy (HREELS). HREEL spectra indicated that methylacetylene adsorbed dissociatively at low temperature to form both methylacetylide and propargyl species, whereas allene adsorbed dissociatively to form only propargyl intermediates. HREEL spectra also showed that at temperatures near 600 K both adsorbed methylacetylides and propargyls reacted to form a graphitic overlayer. This investigation is a further demonstration of the applicability of HREELS to study adsorbed hydrocarbons on metal oxide surfaces.
Electron gun for producing a low energy, high current, and uniform flux electron beam
Authors: Lin Jong-Liang , Yates J. T.
Published: July 2002

A low energy electron gun to provide a uniform electron flux at an extended target surface has been designed, built, and tested. The simple and unique configuration of the electron gun combined with its low energy, high current, and uniform electron flux properties make it suitable for electron-stimulated desorption studies on extended surfaces requiring uniform bombardment over centimeter dimensions.
Interchain vacancy migration on GaAs(110)
Authors: Lengel G. , Weimer M. , Gryko J. , Allen R. E.
Published: July 2002

At the (110) surface of a III–V semiconductor, the atoms are arranged in zigzag chains. If a surface vacancy is to move to a nearest-neighbor sublattice site, it must migrate within these chains. The scanning-tunneling-microscopy observations reported here, however, demonstrate that As vacancies on GaAs(110) prefer to move between zigzag chains. This phenomenon can be understood in terms of simple bond-breaking and rebonding arguments, and from barrier heights calculated using constrained molecular dynamics.
Interaction properties of molecules with binary alloy surfaces
Authors: Schneider U. , Busse H. , Linke R. , Castro G. R. , Wandelt K.
Published: July 2002

The adsorption properties of binary alloy surfaces may significantly deviate from those of the pure component metals. The physical origin of this deviation arises in a rather complex way from the distribution of both kinds of metal species and their interaction in the surface. In contrast to most other adsorption work on binary alloy surfaces we demonstrate and discuss here a clear-cut distinction between a pure geometrical ensemble effect and an electronic ligand effect on the adsorption of gas molecules by using an ordered alloy surface, namely Cu3Pt(111). Furthermore, we show the extent to which the chemical heterogeneity of the surface playing a role depends also on the nature of the adsorbate.
Effect of substrate temperature on dry etching of InP, GaAs, and AlGaAs in iodine- and bromine-based plasmas
Authors: Chakrabarti U. K. , Ren F. , Pearton S. J. , Abernathy C. R.
Published: July 2002

Electron cyclotron resonance discharges of HBr/H2/Ar and HI/H2/Ar were used to etch III–V semiconductors at temperatures in the range 50–250 °C. The increase in etch rates is non-Arrhenius for both chemistries, but enhancements of up to a factor of 50 are seen, depending on the material, with rates of ∼1 μm min−1 for InP at 250 °C at 1 mTorr, −200 V dc and 250 W of microwave power. InP surfaces show a smooth-to-rough transition at ∼150 °C in HBr-based discharges, with degraded anisotropy of the etched features. Both GaAs and AlGaAs are more resistant to this surface roughening, but preferential loss of As occurs at elevated temperatures. Similar results were obtained with HI-based discharges, with loss of the group V element above ∼100 °C. The electrical properties of all three materials are affected by the etch treatments, with creation of a highly conducting surface layer on InP and hydrogen passivation of dopants occurring in GaAs and AlGaAs. The latter can be reversed by annealing at ∼400 °C.
Auger electron spectroscopy/x-ray photoelectron spectroscopy study of Ti–B–N thin films
Authors: Baker M. A. , Steiner A. , Haupt J. , Gissler W.
Published: July 2002

Ti–B–N layers have been produced by sputter deposition from a BN target onto which small Ti platelets have been positioned. The Ti–B–N composition has been varied and the films studied by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). Quantified chemical state information from the XPS B 1s and N 1s peaks give a thin film phase composition consistent with that predicted from the bulk phase diagram. A method of film composition quantification by AES is proposed, accounting for the Ti L3M2,3M2,3 and N KL2,3L2,3 peak overlap problem. Ti L3M2,3M4,5 peak shape changes have been examined using factor analysis, showing the presence of phases and phase changes in qualitative agreement with the phase diagram. Correlations of the compositional and mechanical testing data show that films of highest hardness are obtained when a composition of approximately TiBN0.5 is obtained, the phase composition being a combination of TiB2 and TiN.
Outdiffusion of deuterium from GaN, AlN, and InN
Authors: Wilson R. G. , Pearton S. J. , Abernathy C. R. , Zavada J. M.
Published: July 2002

Hydrogen passivation of acceptor dopants during metal-organic chemical vapor deposition of GaN limits the acceptor concentration in as-grown samples, and post-growth annealing at ≥550 °C is necessary to reactivate the dopants. We have quantified the outdiffusion of hydrogen using 2H plasma-treated (250 or 400 °C, 30 min) or 2H+-implanted GaN, AlN, and InN annealed from 300 to 900 °C and used secondary ion mass spectrometry to measure the resultant distribution. In plasma-treated GaN samples, two populations of 2H are found: (i) a high concentration (≳1020 cm−3), near-surface (<0.3 μm) region probably due to the formation of platelet defects, and (ii) a lower concentration (∼1018 cm−3) plateau region extending throughout the film thickness (∼1 μm), most likely due to 2H-point-defect pairing. Deuterium in region (i) begins outdiffusion at 300 °C in GaN, but in region (ii) does not commence until ≳800 °C. In implanted samples the 2H redistribution occurs with the same characteristics as the bulk population in plasma-treated material. The thermal stability of the deuterium profiles in all three nitride materials is much higher than that in GaAs and other compound semiconductors.
Excimer laser assisted growth of Au thin films on mica (001)
Authors: Polanski G. , Rubahn H.-G.
Published: July 2002

Mica single crystal (001) surfaces are irradiated with light from an excimer laser (λ=248 nm) and are analyzed via low-energy electron diffraction. It is shown that the excimer laser treatment makes them well suited for epitaxial growth of Au(111) thin films (thickness 150–600 Å). Further irradiation with the laser at reduced fluences improves the quality of the grown Au films significantly without the need for high-energy ion sputtering.
Growth of (111)B-oriented resonant tunneling devices in a gas source molecular beam epitaxy system
Authors: Cong L. , Albrecht J. D. , Cohen D. , Ruden P. P. , Nathan M. I.
Published: July 2002

We demonstrate that high quality (111)B oriented heterostructures can be grown in a gas source molecular beam epitaxy system if unity III/V flux ratio, proper substrate temperature, and misoriented substrates are used. We also show piezoelectric modifications of current–voltage characteristics of double barrier resonant tunneling devices by applying uniaxial stresses along certain crystal directions. We found that, under uniaxial, compressive stress parallel to the (110) crystal direction for (001) oriented devices and stress parallel to the (111) direction for (111)B oriented devices, the resonant current peak voltages shift to higher values, and under stress parallel to the (11̄0) direction for (001) oriented devices, the peak voltages shift to lower values. We attribute the asymmetric peak shifts to piezoelectric effects induced by uniaxial stress. Our experimental results are in agreement with calculations.
Real-time monitoring of surface processes by p-polarized reflectance
Authors: Dietz N. , Sukidi N. , Harris C. , Bachmann K. J.
Published: July 2002

Understanding surface chemistry under steady-state epitaxial growth involving organo-metallic chemical precursor molecules is essential for optimizing growth processes. Surface-sensitive optical real-time sensor techniques are very well suited for this task as their applications are not limited to a high vacuum environment. In this article we report the combined application of the optical sensor techniques p-polarized reflectance (PR) and laser light scattering for the real-time monitoring of low temperature growth of epitaxial GaP/GaxIn1−xP heterostructures on Si(001) and GaAs(001) substrates by pulsed chemical beam epitaxy. The high surface sensitivity of PR allows to follow growth processes with submonolayer resolution during the sequential precursor exposure of the surface that causes periodic alterations in composition and thickness of a surface reaction layer (SRL), the effect of which is monitored by PR as a periodic fine structure. This fine structure is superimposed on interference oscillations, resulting from back reflection at the substrate-layer interface with increasing layer thickness. In a linear approximation of the complex four-layer stack reflectance amplitude RR4 in the phase factor Φ1, the optical response to the SRL is formulated as an additive term in the three-layer model that describes the underlying film growth process. Analytical expressions for the first derivative of the PR signal are presented and discussed with respect to the time scale of observation that allows the separation of film growth induced changes from SRL effects. The amplitude modulation and the turning points in the fine structure are assessed and compared to experimental results, showing that an average complex dielectric function of an ultrathin SRL can be quantified, independent of surface coverage.
Physical properties of dual ion beam deposited (B0.5−xSix)N0.5 films
Authors: Zhao X.-A. , Ong C. W. , Chan K. F. , Ng Y. M. , Tsang Y. C. , Choy C. L. , Chan P. W.
Published: July 2002

( B 0.5−x Si x ) N 0.5 films (0⩽x⩽0.5) were prepared by dual ion beam deposition. Buffer layers were added to improve the film adhesion. The film structure was characterized by x-ray photoelectron spectroscopy, infrared absorption, and x-ray diffraction. The hardness and elastic modulus were measured by a nanoindenter. The I–V curves of the Ti/(B0.5−xSix)N0.5/buffer/p-Si/Ti diodes were investigated. The films are composites of cubic-boron nitride (c-BN), h-BN, and Si–N. When x=0, the film contains 70–75 vol % c-BN and has a hardness ≈38 GPa, but peels off quickly from the substrate after exposure to air. When x increases to 0.013, a small amount of Si–N phase is formed, which serves to release part of the internal stress without affecting the volume fraction of c-BN or the mechanical strength, and good adhesion is achieved. For higher Si content (0.013<x⩽0.067), the c-BN phase is disrupted with simultaneous replacement by h-BN. Rapid drops in the hardness and elastic modulus follow. When the Si content continues to increase (0.067 to 0.51), the fraction of the h-BN phase decreases progressively with simultaneous replacement by Si–N. Both the hardness and elastic modulus rise and approach those of silicon nitride. I–V curves of Ti/(B0.5−xSix)N0.5/buffer/p-Si/Ti diodes show a strong rectifying effect, which becomes less pronounced when x is larger.
Migration-assisted Si subatomic-layer epitaxy from Si2H6
Authors: Suda Yoshiyuki
Published: July 2002

Submonolayer by submonolayer Si epitaxy (subatomic-layer epitaxy, SALE) from Si2H6 on Si(001) has been successfully realized independent of the adsorption coverage by repeating self-limited Si2H6 adsorption and surface adatom migration induced by surface thermal excitation with Ar+ laser irradiation and self-resistive heating. With the self-limited Si2H6 adsorption and the migration assist, a substrate temperature window and a laser power window with a constant growth rate and an atomically flat surface have been obtained. The fact conversely indicates that the surface temperature control within the limited temperature range is important during the thermal excitation to obtain the atomical surface flattening. On the basis of the results of the reflection high-energy electron diffraction study on a Si2H6/Si(001) system together with the SALE growth experiments, models for the SALE growth mechanisms and the growth modes are proposed.
Magnetically neutral loop discharged plasma sources and system
Authors: Uchida Taijiro
Published: July 2002

The magnetically neutral loop discharged (NLD) plasma was applied first for a processing use with a machine composed of three steady current coils and an alternating induction coil. This demonstrated the NLD plasma is much more useful than the inductive coupling plasma for Si/SiO2 etching processes using Ar, C3F8, C4F8, and H2 gases. A remarkable feature of the NLD plasma method is that a high density plasma with a doughnut-shaped distribution in any size on both radii of the major and minor axes can be generated at any distance apart from wafer. Second, the NLD high density plasma is generated at a rather low gas pressure range of 10−2 Pa with the characteristic that thermalization of the electrons is easier when the stronger alternating induction power is supplied. Sufficiently high etching rates with high selectivity were realized in a uniform manner by control of the characteristics on the NLD plasma. Furthermore, anisotropic etching was also achieved. The NLD is based on an unusual mechanism of power absorption that is effective in low pressure regime. In the NL region, an electron shows so called meandering motion, when an alternating electric field is applied. The meandering motion becomes chaotic, and effective heating occurs. The theory predicts that the effective resistance becomes 10–102 times larger than the classical collisional resistance. Under an appropriately selected set of parameters, the effective collision induced by the chaos is comparable to that in a gas of 0.1 Pa. These estimates are consistent with the experimental data. In conclusion, the NLD system opens a new region of plasma processing because of its versatile capability for being used to advantage in the age of 12 in. φ substrates.
Real-time core-level spectroscopy of initial thermal oxide on Si(100)
Authors: Enta Y. , Miyanishi Y. , Irimachi H. , Niwano M. , Suemitsu M. , Miyamoto N. , Shigemasa E. , Kato H.
Published: July 2002

A Si 2p core-level spectroscopic study has been performed in real time for initial thermal oxide on Si(100) by O2 gas. Time evolutions of the intensities of chemically shifted Si 2p peaks during oxidation have been compared with those of O 2p state, as well as with a simulation from a set of rate equations assuming a simple oxidation model. From the best fits to the data, rate constants relevant to the oxidation of the first and the second silicon layers were successfully derived as a function of the oxidation temperature. In particular, the oxidation of the first layer for temperatures of 540–620 °C was found to occur through direct oxidation of silicon atoms to stoichiometric silicon dioxide, without formation of any suboxides.
Generation of optical absorption bands in CaF2 single crystals by ArF excimer laser irradiation: Effect of yttrium impurity
Authors: Mizuguchi Masafumi , Hosono Hideo , Kawazoe Hiroshi , Ogawa Tohru
Published: July 2002

Generation of optical absorption bands was observed in CaF2 single crystals with different Y impurity concentrations, excimer grade (yttrium impurity; <1 ppm) and UV grade (5 ppm), by irradiation with ArF excimer laser light at room temperature. The transmittance at the wavelength of 193 nm gradually decreased from 100% down to a saturation level of ∼95% for the UV grade specimen during the ArF excimer laser irradiation. This degradation process was found to obey first order kinetics. On the other hand, no significant decrease in transmittance was observed for the excimer grade specimen. “Four-band structure” which was a characteristic of Y-associated F centers (YFCs) and a band peaking at ∼6.6 eV were observed in the spectrum of the irradiated UV grade CaF2. The 6.6 eV band, which substantially controlled transmission loss at the wavelength of 193 nm and was generated via one photon process, was tentatively attributed to YFCs from growth kinetics on the laser irradiation and decay kinetics upon annealing. Neither intrinsic F centers nor H centers were observed by the ArF laser light irradiation at room temperature. These results demonstrated that a trace amount of Y impurity enhanced the formation of F centers perturbed by a nearest Y impurity and that an absorption band of the resulting YFCs controlled the transmission loss at the wavelength of 193 nm.