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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Issue 6 • Date Nov 1987

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Displaying Results 1 - 25 of 35
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Pressure dependence of the growth of polycrystalline silicon by low‐pressure chemical‐vapor deposition

    Page(s): 1547 - 1550
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    The growth of polycrystalline silicon at temperatures below 640 °C by the pyrolysis of silane at very low pressures (≪40 mTorr) was found to be activated with an activation energy depending on the pressure. Two modes of growth were observed: columnar and twinned, below and above 10 mTorr, respectively. The rate of growth for both types is only slightly dependent on the pressure. The columnar growth is associated with an increase of the activation energy, while the change to the twinned structure is associated with a drop in the activation energy to almost zero from where it increases with pressure. The influence of the flow mode is also discussed. View full abstract»

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  • Silicon epitaxy on germanium using a SiH4 low‐pressure chemical‐vapor deposition process

    Page(s): 1551 - 1554
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    This work describes a process of Si epitaxy on a (100)Ge surface using a SiH4–H2 gas low‐pressure chemical‐vapor deposition (LPCVD) system. Germanium epitaxial film formed on (100)Si wafers using GeH4–H2 gas in a LPCVD reactor was used as the experimental substrates. It was found that Si grew epitaxially through a SiH4 thermal decomposition reaction on the clean Ge surface within a growth temperature range of 650 to 730 °C. By contrast, (110)‐oriented polycrystalline Si grew at a higher temperature of 790 °C. It was clarified that the reason for this polycrystalline Si growth at 790 °C was that the Si epitaxy was disturbed by the Si oxide layer which forms immediately on the Ge surface through susceptor‐induced SiO in the LPCVD reactor. View full abstract»

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  • Low‐pressure deposition of high‐quality SiO2 films by pyrolysis of tetraethylorthosilicate

    Page(s): 1555 - 1563
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    The deposition of SiO2 by pyrolysis of tetraethylorthosilicate (TEOS) at pressures below 1 Torr was investigated at temperatures between 650 and 800 °C. We found oxide thickness variations of ≪±5% for suitable process conditions (PD ≤500 mTorr, wafer spacing ≥4.7 mm, TD ≪730 °C, deposition rate 16 nm min-1). Tests with 150‐mm wafers showed that uniformities of ±2% can be achieved if the wafer spacing is increased to 10 mm. Raising the deposition pressure improves the step coverage in deep trenches but degrades the thickness uniformity across the wafer. The investigations of etch rates in different media show strong dependences on the anneal temperature for etchants containing HF but only a slight dependence for plasma etching. The dielectric breakdown strength of the oxides was 8 MV cm-1 and the failure rate after 500‐ms current stress at 1 mA cm-2 lower than 20%. We found values for the interface state density of 1×1010 eV-1 cm-2 and for the oxide charge density in the range 3×1010 cm-2 to 2.5×1011 cm-2, depending on the oxide thickness. The hysteresis of C–V scans was ≪2 mV. No substantial shift of the C–V curve was found after temperature–bias stress. Our I–V investigations showed that the carrier transport is governed by the Poole–Frenkel mechanism. These results as well as secondary ion mass spectroscopy investigations of the layers confirm that Merck TEOS can be used to grow oxide films of sufficient electrical quality for microelectronic applications. View full abstract»

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  • Unique very low temperature plasma‐enhanced chemical‐vapor deposition glass process for hot and cold wall commercial reactors

    Page(s): 1564 - 1568
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    High‐quality glass and phosphosilicate glass films have been deposited as low as 165 °C in hot and cold wall plasma‐enhanced chemical‐vapor deposition (PECVD) commercial reactors. The dependence of hydrogen incorporation, chemical stability in buffered oxide etch, and the inducement of hillock growth in underlying Al films upon the deposition conditions have been investigated. In both hot and cold wall commercial reactors a unique process has been developed at 165 °C to deposit glass films which exhibit properties not unlike PECVD glass deposited at 380 °C. Hillock growth induced in Al films during glass deposition is eliminated at 165 °C. Deposition rate, uniformity, etch rate, refractive index, particle and pinhole density, and film stress are reported. View full abstract»

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  • Characteristics of Nb‐based tunnel junctions fabricated by selective trilayer ion‐beam etching process

    Page(s): 1569 - 1574
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    Characteristics of Nb/Nb oxide/Pb‐alloy junctions fabricated by selective trilayer ion‐beam etching process have been studied with respect to junction quality, reproducibility, uniformity, and thermal stability. The key steps in the process comprise in situ junction trilayer formation involving thermal oxidation, junction area definition by deep ultraviolet photolithography, and highly selective Pb‐alloy layer patterning by ion‐beam etching in an Ar–O2 atmosphere. Especially, the junctions fabricated in this process have exhibited excellent uniformity and reproducibility with PbAuIn and PbIn counterelectrodes. Standard deviations in critical current for 100 series‐connected junctions with 4×4 and 2×2 μm areas are 0.8% and 2.4%, respectively. The junctions with critical currents of about 80% of Bardeen–Cooper–Schrieffer values and without any knee structure in I–V curves are obtained reproducibly over a wide critical current range from 102 to 104 A/cm2. Annealing tests have indicated that these junctions have sufficient thermal stability for integrated circuits. View full abstract»

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  • Properties of a laser‐plasma x‐ray source for x‐ray lithography

    Page(s): 1575 - 1587
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    We have used an advanced, near diffraction limited Nd:YAG laser, operated at 1.06 μm and employing a zig‐zag slab amplifier, to generate x rays from the laser induced plasmas of a number of target materials. The x‐ray conversion efficiencies were studied as a function of target material and laser parameters. We have measured the x‐ray spectra, for x‐ray energies above about 1 keV, and used them to evaluate this source with regard to x‐ray lithography. A number of target material, resist, and mask combinations appear suitable for a lithography system capable of 0.25‐μm minimum feature size. View full abstract»

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  • Ultimate resolution and contrast in ion‐beam lithography

    Page(s): 1588 - 1590
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    Ion‐beam lithography with a stencil mask is capable of very high resolution. We quantify the resolution by calculating the modulation transfer function for protons of energies suitable for patterning resist of useful thickness. View full abstract»

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  • Reactive ion etching of GaAs with high aspect ratios with Cl2–CH4–H2–Ar mixtures

    Page(s): 1591 - 1598
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    A new process for RIE of GaAs employing Cl2–CH4–H2–Ar etching gases is presented. The effect of CH4 and H2 on etch rate, etch profile, and surface morphology is studied. The plasma excited species are monitored in situ by emission spectroscopy and etch depths measured by laser interferometry. Anisotropic profiles and residue‐free surfaces are obtained with Cl2–CH4–H2–Ar and Cl2–CH4–H2–Ar gases. Depending on process parameters, selectivities up to 180 with respect to SiO2 are obtained allowing deep etching. X‐ray photoelectron spectroscopy and Auger electron spectroscopy of different etched surfaces are compared with a chemically etched reference surface. This shows that a Cl2/H2/Ar etch leaves the surfaces, contamination free. View full abstract»

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  • Gallium arsenide and aluminum gallium arsenide reactive ion etching in boron trichloride/argon mixtures

    Page(s): 1599 - 1605
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    GaAs and Al0.3Ga0.7As were reactive ion etched in a mixture of boron trichloride and argon. The effects of the independent variables such as the time, power, pressure, and gas composition on the etch depth as well as the quality of the resulting etched surfaces were analyzed through a multiple linear regression approach. This provided second‐order equations with an excellent ability to describe experimental results. The etching conditions for GaAs and AlGaAs were compared and optimum parameters for equal rate etching of GaAs/Al0.3Ga0.7As layers with straight walls were obtained. These were then sucessfully applied to the high‐resolution structuring of multiple quantum well layers, and structures as small as 40 nm were etched. The addition of oxygen to the etch gas produced a high‐quality etch for GaAs with ≫5:1 rate selectivity over Al0.3Ga0.7As. View full abstract»

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  • Dry etching of via connections for GaAs monolithic microwave integrated circuits fabrication

    Page(s): 1606 - 1610
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    Through‐the‐wafer low‐impedance via connections can improve characteristics of GaAs monolithic microwave integrated circuits (MMICs). A reactive ion etch process has been developed to etch via holes through 100‐μm‐thick substrates using SiCl4/Cl2 mixtures in a single‐wafer, load‐locked reactive ion etcher. The process satisfies the requirements of the via etch with regard to anisotropy, selectivity, profile, and surface morphology. In addition, the single‐wafer system has low‐overhead cycle times and a wide‐process latitude. This process was used to fabricate a MMIC distributed amplifier with significant improvements in gain performance. View full abstract»

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  • Cavernous undercuts appearing in reactive ion etched submicron‐wide deep trenches

    Page(s): 1611 - 1616
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    The mechanism for the cavernous undercuts appearing on submicron‐wide Si trench sidewalls etched in Cl2 plasma is investigated. Etching with the inclined Si substrate implies that the ions scattered from the opposing mask edge plane are responsible for the undercut. Angular and energy distributions of ions scattered from the mask edges are simulated with a Monte Carlo method. The number and energies of the scattered ions are calculated as being high enough to etch sidewalls. Etching profile simulation incorporating the ion scattering effect shows good agreement with experimental results concerning the amount and the location of the undercut. These results apparently show that ion scattering at a sloped mask edge is the dominant origin of the cavernous undercut. View full abstract»

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  • An x‐ray photoelectron spectroscopy study of sulfur hexafluoride etchant residue on silicon and silicon dioxide

    Page(s): 1617 - 1621
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    X‐ray photoelectron spectroscopy has been used to characterize sulfur hexafluoride radio frequency (rf) plasma exposure in a reactive ion configuration. Reactive ion etched silicon is coated with a thin layer of SiFx similar to that observed on CF4 reactive ion etched silicon. A similar thin layer is observed on SiO2. When the surface is inadvertently contaminated (in this instance with nickel), sulfur, not observed on a clean surface, is present. In addition, silicon becomes roughened. Dilution of SF6 in argon gas does not significantly change the surface residue chemistry but does greatly decrease the etch rate of silicon. Increasing the power density from 0.2 to 1.2 W/cm2 increases the etch rate by a factor of ∼20. At the highest power densities, surface contamination is observed in the form of nickel and sulfur residues. Finally, as in the case of CF4 reactive ion etched silicon, the surface is observed to be crystalline at the lower power densities due to lack of ion bombardment damage effects and becomes amorphous as the power density is increased. At an equivalent power density, the self‐bias generated in an SF6 plasma was measured to be significantly less than that in a CF4 plasma. High silicon etch rates are achieved at very low power densities as compared with CF4 reactive ion etching confirming the findings reported in literature references. This study leads to the conclusion that CF4 may be a better etchant system than SF6 for contact cleaning. View full abstract»

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  • Photoemission studies of AlAs–GaAs alloys, heterostructures, and superlattices

    Page(s): 1622 - 1627
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    Inner core levels and valence‐band structures of molecular‐beam epitaxy‐grown AlxGa1-xAs alloys, AlAs/GaAs heterostructures and [(AlAs)2(GaAs)2]n superlattices were investigated by photoemission measurements. The variations in accordance with the structures were observed for the valence bands, while the binding energies of inner core levels of all the structures are constant within ±0.1 eV. The minimum layer thickness of GaAs or AlAs necessary to show its peculiar band structure was found to be 5∼6 monolayers. The valence‐band offset between AlAs and GaAs was estimated to be 0.12±0.33 eV. The spectra for the valence bands of superlattices showed the different features from those of GaAs, AlAs, and AlGaAs alloys. View full abstract»

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  • An electrohydrostatic analysis of equilibrium shape and stability of stressed conducting fluids: Application to liquid metal ion sources

    Page(s): 1628 - 1638
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    An exact mathematical treatment of the problem of an electrically stressed fluid from zero field to the onset of instability gives rise to the nonlinear electrohydrodynamic equations which, in general, are not amenable to analytic solution. To make the problem more tractable, one considers two limiting regimes, the electrohydrostatic (EHS) and the electrohydrodynamic (EHD) limits. In the EHS case, the fields and the velocities are assumed to be small so that quasistatic equilibrium exists and the fluid surface is essentially at rest. In this paper we consider the electrohydrostatic analysis of the equilibrium shape and stability of the electrically stressed fluids. The current work reintroduces the EHS stability criterion due to Zeleny, as well as a new set of equations and numerical procedure for analyzing the stability of an axially symmetric fluid with an arbitrary shaped surface. These are contrasted with a stability criterion, introduced by Taylor, which it is argued, is only an equilibrium condition and not a proper criterion for analyzing the general stability of electrified fluids. The Taylor and Zeleny criteria are applied to fluid sources modeled as simple coordinate surfaces, such as the cone, the cusp, and the hyperboloid. These results lead to a new physical interpretation of the onset of fluid instability in the EHS limit. A set of partial differential equations is derived, whose solution describes the equilibrium shape of a conducting fluid as a function of the applied electric field. Numerical results are presented for the evolution of the equilibrium shapes of several liquid metals as a function of the applied voltage. Values of the critical or breakdown voltage are obtained from these results and found to be in good agreement with experiment. Finally, the EHS analysis indicates that a realistic and accurate treatment of the onset of instability requires fluid flow in a dynamical model. View full abstract»

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  • A process dependent study of Al/Si/Cu very large scale integration metallization. I. Spectroscopic properties

    Page(s): 1639 - 1643
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    Spectroscopic characterization of samples of sputter‐deposited Al/Si/Cu very large scale integration metallization 1.3 μ thick having 1 wt. % Si and 0.0, 0.2, 0.4, and 0.8 wt. % Cu with and without a forming gas (N2/H2) 450 °C anneal for 1 h was performed as a function of deposition temperatures of 100, 163, 263, 363, and 463 °C. Secondary ion mass spectroscopic depth profiles of the metallization samples show a unique redistribution of the Si from the bulk to the metal/oxide interface at deposition temperatures between 263 and 363 °C. These data are correlated with scanning electron microscope micrographs of Si module precipitation on the silicon dioxide substrate surface after removal of the Al by an Al‐specific wet etch. In a subsequent paper, electrical and mechanical characterization results of these same metallization samples will be reported from resistivity and Knoop hardness measurements. View full abstract»

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  • Schottky barrier formation of various metals on n‐GaAs (100) by electrochemical deposition

    Page(s): 1644 - 1649
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    Electrochemistry is used to deposit various metals (Pt, Pd, Ni, Co) on n‐GaAs (100) surfaces to form Schottky barriers. For the first time very good rectifying characteristics, with an ideality factor n=1.04–1.08, are obtained, while the barrier heights match quite well those made under ultrahigh vacuum conditions. It is also shown that the possible disadvantages of this wet technique (oxidation, contamination,...), can be overcome provided that the conditions of deposition are carefully looked after: strong correlations between the electrical characteristics (studied by I–V and C–V measurements) and the interfacial morphology and composition (studied by Rutherford backscattering, nuclear reaction observation, and transmission electron microscopy) are evidenced when the electrodeposition conditions are varied for a given metal. The advantages of the method are also discussed within the framework of our results. View full abstract»

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  • Boron contamination of in situ heated silicon surfaces

    Page(s): 1650 - 1653
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    Interfacial  p doping due to B contamination is routinely detected in Si molecular‐beam epitaxy (MBE) when using standard MBE cleaning schemes. The influence of the wet chemical precleaning as well as of the in situ cleaning is investigated with respect to this effect: whenever chemical precleaning results in a hydrophilic Si surface, interfacial  p‐type doping due to B contamination of 1012 cm-2 is detected, whereas for hydrophobic Si surfaces the B contamination is reduced by a factor of about 50. Concerning the in situ cleaning, a reduction of the preheating temperature TH correlates with a decrease of  p‐type doping for hydrophilic cleaned samples, though the chemical B contamination is independent of TH, i.e., the in situ preheating induces an electrical activation of the B contamination. View full abstract»

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  • Transitions in the reflection high‐energy electron‐diffraction pattern as a substrate temperature probe in molecular‐beam epitaxy

    Page(s): 1654 - 1655
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    In molecular‐beam epitaxy systems, a substrate reference temperature can be established from observations of transitions in the reflection high‐energy electron‐diffraction pattern. For GaAs, we present the temperature for one such transition as a function of arsenic background pressure. View full abstract»

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  • Nucleation and growth of chemically vapor deposited tungsten on various substrate materials: A review

    Page(s): 1661 - 1666
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    W films produced by chemical‐vapor deposition (CVD), typically via reduction of WF6, are being used for numerous applications in very large scale integrated circuit technology. Blanket and selectively deposited films require nucleation and growth on a specific underlayer material—Si, metal, or metal silicide. The compatibility of CVD W with various underlayers is reviewed for the device applications of contact/via fill, diffusion barrier, metal interconnect, and source/drain coating. Nucleation of W directly on single crystal Si can sometimes produce tunnel‐defect structures at the edges or along the entire interface of the deposit. Sputtered Mo and W, and to some extent TiW and TiN, have been shown to be suitable nucleation layers for CVD W, yielding a fluorine‐free interface with low‐electrical contact resistance. A sputtered W/Ti adhesion bilayer is demonstrated for a blanket W deposition+etchback process. CoSi2 appears an appropriate choice where CVD W and salicide technologies are combined. View full abstract»

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  • Self‐aligned titanium silicide device technology by NH3 plasma assisted thermal annealing

    Page(s): 1667 - 1673
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    The self‐aligned titanium silicide device technology has been studied by using NH3 plasma assisted thermal annealing and ion implant through titanium metal or silicide film. Enhanced surface nitridation of titanium by activated species suppresses lateral silicide growth and oxide contamination. NH3 plasma assisted annealing can be used as an effective method to form TiSi2 and activate implanted dopant. P+N junction and P channel metal–oxide–semiconductor field‐effect transistor can be produced by boron implant through Ti metal or its silicide and the NH3 plasma assisted thermal annealing. View full abstract»

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  • Dopant redistribution in silicide–silicon and silicide–polycrystalline silicon bilayered structures

    Page(s): 1674 - 1688
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    Dopants in any layer of the silicide–silicon or silicide–polycrystalline silicon bilayer structures are found to distribute readily throughout the bilayer affecting the electrical and the mechanical properties of the composite. In this paper the phenomenon of dopant redistribution in such structures is reviewed. The factors that influence the redistribution processes are (a) the diffusivity of dopants in the structure; (b) the solid solubility of dopants in the silicide and in the silicon; (c) the segregation coefficient of dopant at the surface and at the interfaces, and (d) the evaporative or the reactive losses of dopant to the heat‐treating environment. Each of these factors is discussed. The available experimental results are reviewed in view of these considerations. It is shown that there are a large number of variables and that the available experimental results only provide a technological base for the use of dopants in the structures studied. To obtain a fundamental understanding of the process that determines the dopant redistribution, more carefully planned experiments will be necessary. View full abstract»

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  • Titanium silicide growth by rapid‐thermal processing of Ti films deposited on lightly doped and heavily doped silicon substrates

    Page(s): 1689 - 1695
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    A series of experiments were conducted to obtain a better understanding of the titanium silicide growth on lightly doped and heavily boron and arsenic implanted single‐crystal (100) p‐type silicon, as well as on lightly doped and heavily phosphorus diffused polycrystalline silicon. Experiments were carried out under argon and nitrogen ambients using a two‐step annealing process with a rapid‐thermal processor (RTP). The growth kinetics in the RTP are compared for different ambients, times, and temperatures of annealing and various initial titanium thicknesses. Data will be presented which show that the type and amount of doping have a significant impact on the growth kinetics. View full abstract»

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  • The importance of the short‐circuit failure mode in aluminum electromigration

    Page(s): 1696 - 1700
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    Electromigration was studied in a number of Al‐based metallizations. For pure Al and Al–Cu alloys, open circuits were the dominant failure mode. In other systems, including layered conductors and homogeneous Al–Ti, Al–Cr, and Al–V alloys, interlevel short‐circuit failure was greatly favored. Short circuits were usually detected prior to a significant increase in the conductor resistance. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology B is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
Gary E. McGuire
International Technology Center