bluuebunny/crossref_metadata_2025 huggingface dataset:
Etching of diamond with argon and oxygen ion beams
Authors: Whetten Timothy J. , Armstead Angela A. , Grzybowski Thomas A. , Ruoff Arthur L.
Published: July 2002

The angular dependences of the sputter yield of (100) single crystal diamond under argon and oxygen ion beams were investigated. For argon ion beams a large increase in the sputter yield was observed as the angle of incidence was increased from the normal, with a maximum occurring at approximately 60° from the normal. The magnitude of the increase and the angle at which the maximum was observed were dependent on the ion energy and species. The shape of the yield versus angle of incidence curve indicated the presence of a highly damaged surface layer. Large deviations from this curve were observed where ion incidence was along channeling directions. Studies with oxygen ion beams showed almost no angular dependence for 500 eV ions while at an energy of 1000 eV the angular dependence was similar to that for argon ions. At normal incidence the yield for 500 eV oxygen ions was seven times larger than that for 500 eV argon ions. For 1000 eV oxygen and argon ions the corresponding ratio is only 2.5. Implications for mechanisms of inert and reactive ion etching are discussed. Application of the data to ion beam shaping of diamond tips for ultrahigh pressure research is discussed.
Preferential sputtering of brass studied by AES and XPS
Authors: Hammer G. E. , Shemenski R. M.
Published: July 2002

Preferential sputtering of brass has been investigated for inert gas ion bombardment having incident ion energies between 500 and 4000 eV. Enrichment of the copper on surfaces sputtered to equilibrium was found for all conditions, and was observed to increase with ion energy and mass. Copper concentrations calculated by using Auger electron spectroscopy (AES) peak-to-peak heights in the E dN/dE mode varied from 8% to 13% above bulk composition. This variation was found to be reversible upon changing the incident ion energy and sputtering away the existing damaged layer. Analysis by x-ray photoelectron spectroscopy (XPS) using 2p and 3p peak areas and escape depths showed the existence of a subsurface region with greater enrichment of copper than that produced on the sputtered surface.
TiB2 and ZrB2 diffusion barriers in GaAs Ohmic contact technology
Authors: Shappirio J. , Finnegan J. , Lux R. , Fox D. , Kwiatkowski J. , Kattelus H. P. , Nicolet M-A.
Published: July 2002

The transition metal diboride compounds, ZrB2 and TiB2, interposed between Ni/Ge/Au Ohmic contact metallization on n-type GaAs wafers and an overlying thick Au contact layer, have been investigated to evaluate their effectiveness in stabilizing the Ohmic contact by limiting the in-diffusion of Au. All of the metal layers were e-beam deposited except the ZrB2 which was rf-diode sputtered. The barrier layer thicknesses were 50 and 100 nm for the TiB2 and the ZrB2, respectively. Postdeposition alloying of the contacts was performed at 400, 425, or 450 °C. Auger electron spectroscopy depth profiling of the resultant Ohmic contacts demonstrates that the barrier layers effectively preclude penetration of Au to the Ohmic contact structure. Specific contact resistivities for such contacts are in the low 10−7 Ω cm2 range; although some degradation of the contact resistivity is observed after long term annealing, the values of resistivities do not exceed 1.5×10−6 Ω cm2 after 92 h at 350 °C.
Noncontact thermal gradient method for fabrication of uniform cryogenic inertial fusion target
Authors: Kim K. , Mok L. , Erlenborn M. J. , Bernat T. P.
Published: July 2002

A new method for fabricating a uniform layer of fuel condensate inside a spherical-shell inertial confinement fusion target is described. In this method, target cooling is done in a vertically imposed temperature gradient whose magnitude is continuously controlled until the thermally induced effects precisely counterbalance the gravity effect. As a consequence, gravity-induced fuel sagging is completely eliminated resulting in the formation of a uniform fuel-condensate layer on the inner surface of the target. Since the present method is immune to the gravity effect, it is uniquely qualified for fabricating targets containing a thick fuel layer— an important capability no other existing method possesses. A brief description of the experimental methods and the preliminary results showing the promise of the new method are presented.
Auger electron spectroscopy and sputter/Auger analyses of thin films of SiCx
Authors: Morgen P. , Seaward K. L. , Barbee T. W.
Published: July 2002

Thin SiCx films, fabricated in a two-source sputtering apparatus, are analyzed with Auger electron spectroscopy in combination with inert gas (Ne) sputtering. The compositional depth profiles and local bonding properties of the films are the object of the analysis. Different aspects of the application of Auger electron spectroscopy and sputtering to SiC are critically evaluated. These include the chemical information available from the structure of the Auger spectral lines from C and Si, and the effects of ion bombardment, i.e., preferential sputtering, radiation induced diffusion and segregation, as well as disorder. The samples all contain cubic (polycrystalline) SiC( β-SiC). The films are found to be homogeneous in the bulk, with a thin layer at the surface strongly enriched in carbon. A film with a high percentage of Si was found to be inhomogeneous, and to have a significant amount of SiO2 formed at the surface during storage and handling in a room ambient. The films with higher surface concentrations of carbon clearly showed less tendency to form oxides. Chemical information relating to the local bonding of Si and C is obtained from the Si(L23VV) and C (KVV) Auger spectra. The Si (KLL) Auger spectrum is also included in the discussion. Here a comparison with pure silicon allows assignment of plasmon loss structures, as well as shifts in peak energies.
Spectroscopic study of atomic beams generated by laser ablation of multicomponent targets
Authors: Koppmann R. , Refaei S. M. , Pospieszczyk A.
Published: July 2002

An experiment is described where Li and Al beams were generated by ablation of thin, multilayer targets using a Q-switched ruby laser with a total energy density up to 30 J cm−2. Measurements using laser induced fluorescence (LIF) and mass spectroscopy were combined to analyze the energy and density distribution and the temporal structure of the beams. The maximum translational energy observed was several eV for Li and several 10 eV for Al with a peak density in the range of 1010 cm−3 for both Li and Al. The targets were analyzed by optical microscopy and secondary ion mass spectroscopy providing information about the size of the spots and the structure of the metal film before and after the ablation experiment.
A decision framework for evaluating vacuum pumping technology
Authors: Arbel Ami , Shapira Yoram
Published: July 2002

An analytic model for the selection of vacuum pumping technology is presented. The model identifies selection issues, which may be classified into two groups according to whether they directly contribute or are detrimental to the pumping system performance. These two groups of issues, entitled benefit and cost, respectively, are analyzed through a decision-making methodology called the analytic hierarchy process (AHP). Application of this methodology to the benefit and cost issues results in a priority structure leading to selection of the best choice from a given set of candidate systems. Results of this evaluation are given for a specific case of a vacuum evaporation system.
Surface science aspects of interfacial electrochemistry
Authors: Kolb D. M.
Published: July 2002

One of the most important tasks in physical electrochemistry today is the determination, on a microscopic level, of the structure and the properties of the solid–electrolyte interface. To obtain such information, two somewhat different approaches are currently employed. The first one deals with in situ spectroscopy, i.e., with spectroscopic techniques which are applicable in the presence of the electrolyte. The second route involves electrode emersion and the study of the surface properties outside the electrochemical cell, e.g., under UHV conditions. In the following, selected examples for the study of electrode surfaces are given, which are believed to be of topical interest to a general surface science audience. Those include surface states at the metal–electrolyte interface, adsorbate-induced surface reconstruction and restructuring, and the study of metal deposits in the submonolayer range.
Ionic and neutral decomposition of gaseous bromochloromethanes
Authors: Driscoll D. C. , Bishop J. A. , Sturm B. J. , Dowben P. A. , Olsen C. G.
Published: July 2002

The ionization potentials for CCl4, CCl3Br, CBr2Cl2, CBr4, CCl3, and CBr3 have been measured using electron impact techniques. These numbers have been combined with previously published thermodynamic values in order to construct thermodynamic cycles for ionic and neutral decomposition of the bromochloromethanes. The n to σ*, n to s, and n to p electronic transition energies have also been determined on the basis of photoabsorption spectra.
Langmuir probe characterization of magnetron operation
Authors: Rossnagel S. M. , Kaufman H. R.
Published: July 2002

Conventional planar magnetrons have been characterized with small (0.01 and 0.02 cm diam) Langmuir probes in the plasma region and also extending into the sheath. The plasma potentials, electron temperatures, and electron densities have been measured at low and intermediate magnetron discharge currents. The low currents reduce the effect of the probe on the discharge by reducing probe heating. The pressure range examined was 1.5–30 mTorr in both Ar and He. With Ar, the plasma potential is relatively constant in the abnormal (bright) glow region of the magnetron, and only begins to drop appreciably in the dark space (<1 mm thick) near the cathode. The electron temperatures showed a continual increase as the cathode sheath was approached. Temperatures were measured in the 1–5 eV range at 5–30 mTorr Ar, and as high as 22 eV at pressures of 1.5 mTorr Ar. The measured electron densities were also pressure dependent and were highly peaked in the bright glow region near the cathode surface. The densities fell rapidly through the sheath. Significant departures from a Maxwellian electron energy distribution were found for the He plasmas, with a higher proportion of electrons in the high energy tail. The densities, however, were significantly lower than with Ar.
Surface modification strategies for (100)3C-SiC
Authors: Bellina J. J. , Ferrante J. , Zeller M. V.
Published: July 2002

Several surface modification techniques were performed in situ in an ultrahigh vacuum as part of a program to develop electrical contacts on the (100) face of cubic SiC. The Auger electron spectroscopy line shapes and peak-to-peak heights of the Si LVV and C KLL transitions indicated changes in surface stoichiometry, bonding, and short range order. Changes in the low energy electron diffraction pattern identified changes in the symmetry of long range ordering on the surface. Heating above 1050 °C depleted the surface of Si with an activation energy of 120 kcal/mol, resulting eventually in a disordered graphitic layer which was several atomic layers thick. Bombardment by Ar ions of energies greater than 1000 eV enhanced the Si to C ratio on the surface and destroyed the LEED pattern. Long range order was recovered by simultaneous heating and ion bombardment. Finally, adsorption of Cr on the Ar ion damaged surface and subsequent desorption left a reconstructed, p(2×1)Si enriched surface. Similar treatments with Al did not produce a surface reconstruction.
A simple and versatile liquid nitrogen cooled cryostat on a differentially pumped rotary feedthrough
Authors: George S. M.
Published: July 2002

We report here a simple and improved design which extends the versatility of a liquid nitrogen cryostat on a differentially pumped rotary feedthroug h. The novel modifications are: 1) the cryostat is isolated from the inne r surface of the rotary feedthrough; 2) additional feedthrough ports are incorporated that are not in contact with the liquid nitrogen cryostat; 3) a liquid nitrogen reservoir is employed that is thermally isolated throug h the use of a vacuum jacket. (AIP)
Field ion microscope observations of the reconstruction of platinum and iridium surfaces
Authors: Kellogg G. L.
Published: July 2002

The thermal reconstruction of various Pt and Ir single-crystal surfaces has been studied in atomic detail with the field ion microscope. Unreconstructed surfaces, which were produced by low-temperature field evaporation, were induced to reconstruct by heating the field-ion samples under field-free conditions. As previously reported for Pt, the (110) surface of Ir was observed to reconstruct from a bulk-terminated structure to a structure consisting of missing rows of atoms. The transition took place at a temperature of 500 K, almost 200 K higher than that found for Pt. The (311), (511), and (211) planes of Pt also reconstructed to missing rows at temperatures above 400 K. Transitions from field-evaporated structures to new structures (identified as reconstructed) were also observed on Pt(100) and Ir(100) at temperatures of 270 and 470 K, respectively, but the field ion images did not exhibit sufficient resolution to identify the atomic structure of the reconstructed surfaces.
Iridium surface reconstruction: A field ion microscopy study
Authors: Müller K. , Witt J. , Schütz O.
Published: July 2002

Reconstruction at the (110), (113), and (100) poles of an Ir tip has been observed. The field ion microscopy images showing ordered rows of atoms were analyzed not only by inspection but also by scanning intensity profiles directly taken from the fluorescent screen. The determination of the atom’s positions complies with a missing row model for the (110) surface and with a buckled quasihexagonal surface model for the (100) plane. These reconstructed surfaces appear as stable phases generated by thermal activation from their metastable bulklike planes.
AlN thin films with controlled crystallographic orientations and their microstructure
Authors: Ohuchi F. S. , Russell P. E.
Published: July 2002

C-axis oriented AlN thin films, or AlN 〈001〉, are normally obtained by various reactive deposition methods. We have found the AlN thin films with orientations other than 〈001〉 can be prepared by controlling rf sputter deposition conditions. Three different orientations, 〈001〉, 〈102〉, and 〈101〉, were independently grown and verified by x-ray diffraction. A factor controlling the growth habit is discussed. A cross-sectional transmission electron microscopy/scanning transmission electron microscopy technique with microdiffraction was used to study microstructure of the film. It is found that the AlN thin film is grown in a columnar structure and individual columnar grains were verified to be single crystalline.
Ultrafine particles
Authors: Hayashi Chikara
Published: July 2002

This presentation is a summarized review of the achievements of the ultrafine particle (UFP) project, which was a 5-yr research and development project inaugurated in 1981 by Research and Development Corporation of Japan, a government sponsored organization. Any creative work with regard to UFP’s having diameters in the range of 10 to 1000 Å, was encouraged for the purpose of obtaining new knowledge and basic technology for the future. Four groups, each composed of four or five research staffs, were budgeted at approximately 1.5 billion yen. A high-resolution (∼2 Å) very high vacuum (≲10−6 Pa) multifunctional transmission electron microscope, designed and manufactured for the project, revealed that an UFP (gold <50 Å) under the microscope changed its crystal structure so spontaneously that it should be considered to be in a quasisolid state. Another observation, which was obtained by tangential injection of an electron beam to a UFP, gave pictures of the first lattice layer, a technology which could be valuable for studying surface phenomena and other practical subjects, such as catalytic reactions. One of the possibly valuable techniques developed in the project is the transfer of UFP’s by flowing gas in a fine tube followed by jet formation to deposit the UFP’s on a solid plate. With sufficient jet speed (≳100 m/s), a tight deposit of Ag, Cu, Fe–Ag, TiN–Ni, Pb–Zn, etc., was obtained at a temperature of ≲600 K, exhibiting good homogeneous mixture under x-ray microanalysis. Several other results are presented.
Onset of alkali adsorption on the vitreous silica surface
Authors: Garofalini Stephen H. , Zirl David M.
Published: July 2002

The molecular dynamics computer simulation technique has been used to study the atomic level structure at the vitreous silica surface and the effect that this surface structure has on the early stages of adsorption of K and Li ions. K ions preferentially adsorb at nonbridging oxygen (NBO), often diffusing over the surface prior to finding such sites. After saturation of these NBO’s, the K ions attack siloxane bonds. The K ions do not diffuse into the silica substrate, even though there are channels available for such diffusion. Li ions initially adsorb at both the NBO as well as the bridging oxygen at strained siloxane bonds. Also the Li ions readily diffuse into the subsurface regions of the glass.
Two-dimensional phase transitions studied by thermal He scattering
Authors: Kern Klaus , Zeppenfeld Peter , David Rudolf , Comsa George
Published: July 2002

The structure of physisorbed rare-gas layers depends on the interplay between the mutual interaction of the rare-gas atoms and the periodic corrugation of the substrate holding potential. A fascinating variety of structural phases and of mutual phase transformations of these layers adsorbed on graphite and on Pt(111) has been observed. This variety is due to the delicate balance between these interactions. This balance is also the cause for radical changes of salient layer features induced by minute amounts of impurities and defects. High-resolution thermal He scattering appears to be particularly appropriate for an exhaustive investigation of the properties of these layers: simple diffraction patterns (no substrate scattering contribution) including sensitivity for shallow periodic buckling as well as high-resolution (<0.4 meV) energy-loss spectra are the main capabilities which allow for a complete analysis of the structure and dynamics of these layers. The extreme sensitivity for surface defects and impurities, and the absence of any disturbance induced by the He beam are further advantages.
A real-time holographic interferometry technique for measuring cryogenic fuel layers in large inertial confinement fusion targets
Authors: Pattinson T. R. , Felmlee W. J.
Published: July 2002

We have recently installed a real-time holographic interferometry system on one of our experimental vacuum chambers. This system, which utilizes an argon laser at 488.0 nm and a Newport Research HC-300 holographic camera, will be used to develop and document liquid layer targets for inertial confinement fusion experiments. An interference image is produced when the image of a liquid layer target is superimposed on the stored holograph of the same target with the fuel held in the gas phase. This real-time interference image is due to the change in the fuel state and is a direct measure of the liquid layer uniformity. Routine use of this imaging system will allow us to develop the techniques needed to produce acceptable liquid layers in targets 1–2 mm in diameter with walls 5–50 μm thick. We will discuss the techniques and configuration used to adopt this system for the vibration noise inherent in an experimental chamber.
Photodesorption from stainless steels
Authors: Mesarwi A. , Ignatiev A.
Published: July 2002

The photodesorption by low-energy photons (hν≤6 eV) from three types of stainless steels is examined. For all these systems both CO and CO2 were observed to photodesorb with high yields: ≊10−3 molecules/photon for CO2 and ≊10−4 molecules/photon for CO at λ=250 nm. The observed threshold energies were found to be the same for all systems at E0 =2.92 eV for CO2 and E0=2.92–3.10 eV for CO.
Tritium pellet injector results
Authors: Fisher P. W. , Bauer M. L. , Baylor L. R. , Combs S. K. , Deleanu L. E. , Fehling D. T. , Foster C. A. , Gouge M. J. , Milora S. L. , Schuresko D. D. , Sparks D. O. , Whitson J. C.
Published: July 2002

Injection of solid tritium pellets is considered to be the most promising way of fueling fusion reactors. The Tritium Proof-of-Principle experiment has demonstrated the feasibility of forming and accelerating tritium pellets. This injector is based on the pneumatic pipe-gun concept, in which pellets are formed in situ in the barrel and accelerated with high-pressure gas. This injector is ideal for tritium service because there are no moving parts inside the gun and because no excess tritium is required in the pellet production process. Removal of 3He from tritium to prevent blocking of the cryopumping action by the noncondensible gas has been demonstrated with a cryogenic separator. Pellet velocities of 1280 m/s have been achieved for 4-mm-diam × 4-mm-long cylindrical tritium pellets with hydrogen propellant at 6.96 MPa (1000 psi).
Simplified eight-shot pneumatic pellet injector for plasma fueling applications on the Princeton Beta Experiment and on the Advanced Toroidal Facility
Authors: Schuresko D. D. , Cole M. J. , Fisher P. W. , Qualls A. L. , Bauer M. L. , Wysor R. B. , Lickliter P. , Webster D. J. , Argo B. E. , Combs S. K. , Milora S. L. , Foster C. A. , Foust C. R. , Fadnek A. , Takahashi H. , Kozub T.
Published: July 2002

Plasma fueling via injection of solid hydrogenic pellets has expanded the operating range for tokamaks and stellarators to higher densities than attainable with gas puffing. Pellet injection has also resulted in improved plasma energy confinement in tokamak discharges for which the pellet or pellets penetrate deep into the plasma core. The eight-shot pneumatic pellet injector described herein has been developed for use on the Princeton Beta Experiment and on the Advanced Toroidal Facility for routine plasma fueling and for confinement optimization studies. The injector is based upon the so-called ‘‘pipe-gun’’ concept, which generates deuterium and hydrogen pellets by direct condensation in the gun barrel tubes, segments of which are cooled below the hydrogen triple-point temperature by contact with a liquid-helium-cooled block. Control of the pellet length is achieved both by regulating the deuterium fill pressure and by establishing temperature gradients along the barrel tubes. This injector features eight independent gun barrel assemblies mounted around the perimeter of a single cold block, each coupled to an ORNL-designed fast propellant valve. Thus, the injector is capable of injecting arbitrarily programmable sequences of up to eight pellets of sizes ranging from 1 to 3 mm at speeds up to 1500 m/s.
Solid deuterium pellet injection with a two-stage pneumatic gun
Authors: Reggiori A. , Riva G. , Daminelli G. , Frattolillo A. , Martinis L. , Scaramuzzi F.
Published: July 2002

Recent results on injection of D2 pellets, using an improved light gas gun, are reported. In order to overcome the limits imposed by the low mechanical strength of solid hydrogen, a double-piston gun has been developed, in which the pressure pulse can be shaped in different ways, allowing reduction of the maximum acceleration of the pellet. Experiments have been performed with plastic and D2 pellets. Velocities above 2500 m/s have been obtained with unbroken D2 pellets.
Interfacial reactions at copper surfaces coated with polymer films
Authors: Burrell M. C. , Codella P. J. , Fontana J. A. , Chera J. J.
Published: July 2002

Polymeric coatings on copper surfaces are known to degrade at a faster rate than identical materials on other metals such as aluminum, particularly during thermal aging. We have studied the interfacial reactions occurring at copper surfaces coated with poly(esterimide) and polyimide wire enamels. Thin coatings (100 Å–1 μm) were heat treated at temperatures from 200 to 240 °C. Interfacial reactions were studied by x-ray photoelectron spectroscopy (XPS), Auger profiling, and reflectance infrared spectroscopy. In addition to copper oxide growth at the interface, thermal oxidative degradation of the polymer leads to thinning of the coating. This reaction is catalyzed by the copper (oxide) surface and material loss occurs primarily at the polymer/copper (oxide) interface. Migration of mobile copper species into the bulk of the coating is observed by its appearance at the surface and by depth profiling. For polyimide films prepared from poly(amide-acid) precursors, an interfacial reaction occurs during initial contact, prior to curing or aging, and infrared and XPS measurements show incomplete curing of the film. The formation of a copper carboxylate is postulated.
Comparison of experimental measurements and model predictions for radio-frequency Ar and SF6 discharges
Authors: Gogolides Evangelos , Nicolai Jean-Philippe , Sawin Herbert H.
Published: July 2002

Using a continuum model based on dc field data, the discharge physics of Ar and SF6 has been simulated for 13.5-MHz excitation. In Ar, the ionization primarily occurs at the bulk–sheath interfaces and is temporally modulated with its maximum corresponding to the cathodic phase of the rf cycle. In SF6, the ionization is distributed throughout the bulk with a maximum occurring at the bulk–sheath interface and a temporal maximum occurring during the anodic phase. The plasma induced emission (PIE), which correlates with the predicted ionization rate, has been experimentally measured as a function of position and time and agrees well with the model predictions. These results explain the phase shift of the PIE between electronegative and electropositive discharges.
High velocity carbon dioxide snow for cleaning vacuum system surfaces
Authors: Layden L. , Wadlow D.
Published: July 2002

We recently investigated the efficiency of high velocity jets of carbon dioxide snow for cleaning small, intricate metal and plastic vacuum system components and found the technique to have significant advantages over solvent cleaning.
Molecular dynamics simulations of low-energy particle bombardment effects during vapor-phase crystal growth: 10 eV Si atoms incident on Si(001)2×1 surfaces
Authors: Kitabatake M. , Fons P. , Greene J. E.
Published: July 2002

Molecular dynamics simulations, utilizing the Tersoff many-body potential, were used to investigate the effects of 10 eV Si atom bombardment of a Si lattice with a (001)2×1 reconstructed surface. The irradiation events were initiated at an array of points in the primitive surface unit cell. Each event was followed to determine kinetic energy redistribution in the lattice as a function of time, ion and lattice atom trajectories, and the nature, number, and depth of residual defects. Surface dimer breaking, epitaxial growth (due to both projectiles and lattice atoms coming to rest at epitaxial positions), and the formation of residual hexagonal and split interstitials composed of projectiles and/or lattice atoms were observed. There were no residual vacancies. Impact points leading to each of the above results clustered in distinctly different regions of the surface unit cell. Implications of this work for ion-assisted film growth are discussed.
Reduction of water aerosol contamination during pumping of a vacuum chamber from atmospheric pressure
Authors: O’Hanlon John F. , Shieh Jhy-Jer
Published: July 2002

The drop in temperature resulting from adiabatic expansion during pumping from atmosphere can cause formation of a dense water aerosol in an ordinary vacuum chamber. The aerosol, consisting of water and impurities, can form rapidly, deposit on a silicon wafer and introduce contamination. In this study a unique thermocouple arrangement has been used to obtain the temperature profile of the gas during the pumping transient. From the temperature profile the maximum degree of saturation was calculated. The distance between adjacent surfaces was decreased until the thermocouple measurements no longer indicated supersaturation. Measurements of water aerosol generation were also made in a chamber in which the wall spacing could be varied. Finally a model for a vacuum load lock has been proposed in which water aerosol will not form adjacent to a silicon wafer. This model proposes that wafer be positioned in the x–y plane, with the pumping port located on the 0,0,z axis. For typical system pumping time constants (V/S=3–6 s), a wafer spacing of ≤0.5 mm will permit normal pumping of the load lock without the added processing time required for nitrogen purging or slow pumping.
SiO2 films by low pressure chemical vapor deposition using diethylsilane: Processing and characterization
Authors: Huo D. T. C. , Yan M. F. , Foo P. D.
Published: July 2002

Diethylsilane was used to prepare SiO2 films on Si wafers by a low pressure chemical vapor deposition technique at low temperatures (≤400 °C). The deposited films have good conformality (83%), a low residual carbon concentration (<1 at. %) and a low residual stress (<109 dyn/cm2 ); which compare favorably with films prepared by other processes. We also correlated the growth rates with the processing parameters to show that the deposition process follows the heterogeneous bimolecular reaction kinetics. Infrared spectroscopy was used to detect the presence of HSi–O3 bending band (880 cm−1 ) in SiO2 films prepared under certain processing conditions. Based on the reaction kinetic model, we optimize the processing conditions to reduce the SiH incorporation and mobile charge carrier concentration in SiO2 films.
Structure and physical properties of polycrystalline hexagonal Ta2N films deposited by reactive sputtering
Authors: Rivaud L. , Barnett S. A. , Greene J. E. , Marciniec E. T.
Published: July 2002

Hexagonal-structure polycrystalline Ta2N films with (213̄1) preferred orientation were deposited by reactive sputter deposition onto glass substrates in mixed Ar/N2 atmospheres. Transmission electron microscopy examination of Ta2N films grown on BaF2(111) using the same deposition conditions showed that the average grain size was ≂10 nm. The room-temperature resistivity and temperature coefficient of resistivity of films grown on glass were 2×10−4 Ω cm and 1.2×10−4 K−1, respectively. The films exhibited relatively low compressive stresses, 1–3×109 dyn cm−2, and film/substrate couples photolithographically patterned into thin-film heater elements withstood 2×107 thermal cycles between <200 and ≂850 °C.
Study of volume and surface processes in low pressure radio frequency plasma reactors by pulsed excitation methods. I. Hydrogen–argon plasma
Authors: Bouchoule André , Ranson Pierre
Published: July 2002

In low pressure reactors, for which the mean free paths of reactive particles are of the order of plasma chamber dimensions, the chemical equilibrium of the gas phase is strongly dependent on surface chemistry. Unfortunately data on elementary surface processes are often not available, particularly for surfaces exposed to plasma conditions. In this work such data are obtained through a time resolved analysis of species concentration in a reactor where a square wave modulated rf power is used for excitation. A very short pulse excitation technique, acting as a time resolved ‘‘in situ chemical probe,’’ has been developed in order to follow the radical concentrations in the afterglow where surface processes are dominant. Results for hydrogen–argon plasmas are reported. The surface reactions of hydrogen atoms with reactor walls and silicon surface are studied. The recombination probability on reactor walls is shown to be very sensitive to plasma conditions. These surface properties evolve on time scales as long as few tens minutes, in connection with bulk diffusion process of atomic Hydrogen. For Silicon surface, the measured recombination probability is very high (near unity) while etching appears as an added small effect. In a companion paper determination of F atom reactivity for surfaces submitted to fluorinated plasmas will be described.
Effect of oxygen on filament activity in diamond chemical vapor deposition
Authors: Sommer M. , Smith F. W.
Published: July 2002

Previous studies that have focused on the interactions of CH4/H2 and C2H2/H2 mixtures with the hot W filaments used for diamond chemical vapor deposition have been extended in order to determine the effect of oxygen on filament activity. The behavior of W filaments has now been studied up to 2300 °C in mixtures of 3% CH4/H2, with 0.5, 1.0, and 1.5% O2, at a pressure of 25 Torr. The effects of the addition of O2 on filament resistance, emissivity, and power consumption, as well as on the partial pressures of the gases (CH4, C2H2, O2, CO, and H2O ) in the reaction chamber, have been determined. The significant improvements in filament activity that are observed are shown to be due to removal of carbon from the filament surface by formation of CO. These results can be understood on the basis of our quasi-equilibrium thermodynamic model for the C–H–O system.
Evidence of Si–OH species at the surface of aged silica
Authors: Paparazzo E. , Fanfoni M. , Severini E. , Priori S.
Published: July 2002

Synchrotron radiation (SR) photoemission and x-ray photoelectron spectroscopy (XPS) are used to reveal the presence of Si–OH species at the surface of aged silica. SR Si 2p spectra, recorded in the photon energy range 130 eV≤hν≤240 eV, show the coexistence of Si–O bonding states and Si–OH bonding states, the latter being marked by a component at 105.2 eV in binding energy. The intensity ratio I[Si–OH]/I[Si–O] varies monotonically from 0.24 to 0.77 with increasing photoelectron kinetic energy from 15 to 135 eV, respectively. On the contrary, no sign of silanol groups is evident in the XPS spectra, although some excess oxygen is measured in the nO/nSi atomic ratios. Combination of SR and XPS results suggest that the silanol groups lie in a region which extends approximately 16 to 21 Å from the surface, whereas the composition of the material is virtually that of silica for depths≥30 Å. Possible sources of uncertainty in the analysis of Si–OH species in silica are discussed.
Chemical and structural analyses of the titanium nitride/alpha (6H)-silicon carbide interface
Authors: Glass R. C. , Spellman L. M. , Tanaka S. , Davis R. F.
Published: July 2002

Ion-assisted reactive evaporation (IARE) using low-energy (100 eV) nitrogen ions was employed to deposit TiN films onto the vicinal Si-terminated (0001) face of α(6H)-SiC single crystals at 350 °C in an ultrahigh vacuum chamber operated at a working pressure of 2×10−4 Torr. The initial exposure of the SiC surface to nitrogen ions for a 2-min period resulted in Si–N bonding. This exposure was also an important step in attaining ohmic contact properties at low temperature, and the formation of a thin (≊5–15 Å) amorphous layer at the interface. The disorder was maintained after the deposition of 5 Å of TiN. The TiN contacts were ohmic after deposition; they showed little change in microstructural or electrical properties after annealing at 450, 550, and 600 °C for 15–30 min. The results of this research indicate that a metal–insulator–semiconductor structure was responsible for obtaining the contact properties.
Low-energy electron diffraction study of a disordered monolayer of H2O on Pt(111) and an ordered thin film of ice grown on Pt(111)
Authors: Starke U. , Heinz K. , Materer N. , Wander A. , Michl M. , Döll R. , Van Hove M. A. , Somorjai G. A.
Published: July 2002

We have used a new low-energy electron diffraction (LEED) detector, that features a low beam current electron gun, to investigate for the first time the LEED intensities arising from a water-surface adsorption system. H2O adsorption structures are very sensitive to electron radiation damage. A disordered monolayer of H2O molecules is formed on Pt(111) at 160 K. Upon further exposure an ordered multilayer film is grown that yields new diffraction spots. The periodicity of the diffraction pattern of the multilayer structure is compatible with the model of a molecular ice crystal. Preliminary intensity versus energy spectra of the ‘‘ice crystal’’ are presented. The film thickness is estimated to be well above 10 Å.
Atmospheric pressure chemical vapor deposition of Si and SiGe at low temperatures
Authors: Sedgwick T. O. , Agnello P. D.
Published: July 2002

Ultraclean atmospheric pressure chemical vapor deposition has been used to grow Si and SiGe epitaxial films at low temperatures, 550–850 °C, in several reactors including a commercial production type tool. The use of a load lock, gas purifiers, and careful gas handling procedures allows epitaxial films to be grown down to 550 °C with undetectable levels of oxygen and carbon at the growth interface. This is achieved in part by the discovery that the atmosphere of hydrogen inhibits Si oxidation at the growth temperature. Doped layers with active concentrations of phosphorous and boron to 1–3×1020 cm−3 have been achieved. Phosphine and arsine enhance the growth rate under certain process conditions which is contrary to all previous reports in the literature. N-type doping with phosphine can be modulated more than two orders of magnitude which indicates that dopant retention on sample or reactor wall surfaces is not a problem. Emitter-base diodes formed in the N-type epitaxial layers exhibited ideal forward and low-leakage reverse characteristics. SiGe/Si heterostructures with Ge content of 14%–44% exhibit abrupt interfaces and smooth surfaces. Selective Si and SiGe layers have been grown on oxide patterned wafers without the appearance of facets.
The low temperature catalyzed chemical vapor deposition and characterization of aluminum nitride thin films
Authors: Dupuie Jeffrey L. , Gulari Erdogan
Published: July 2002

Aluminum nitride thin films have been grown via low pressure chemical vapor deposition at substrate temperatures ranging from 584 to 732 K by the catalytic action of a heated tungsten filament. A tungsten filament heated to 2020 K was used to decompose ammonia, which reacted with trimethylaluminum introduced downstream of the filament to form aluminum nitride films at deposition rates between 50 and 200 nm/min. The resultant films were characterized by Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and Raman spectroscopy. Infrared spectroscopy revealed hydrogen bonded to nitrogen in concentrations ranging from 2% to 8% on an atomic basis. Multiple internal reflection infrared spectra showed the presence of aluminum–oxygen bonds at the surface of the films. Surface-enhanced Raman spectra indicated that the films were a mixture of amorphous and polycrystalline phases. XPS sputter depth profiles revealed that the concentration of oxygen in the films decreased, and the concentration of carbon in the films increased with increased trimethylaluminum flow rates. The oxygen concentration in the aluminum nitride films could be reduced to levels below the limits of detection for XPS, while the carbon concentration could be reduced to 0.8% under the best growth conditions explored.
Reactive sticking of As4 during molecular beam homoepitaxy of GaAs, AlAs, and InAs
Authors: Brennan T. M. , Tsao J. Y. , Hammons B. E.
Published: July 2002

We have measured transient and steady-state reflected As4 and desorbing As2 fluxes during molecular beam homoepitaxy on the (001) surfaces of GaAs, AlAs, and InAs. In the absence of growth, the reflected As4 flux decreases, and the desorbing As2 flux increases, with increasing temperature. In the presence of growth, both fluxes decrease linearly, and then saturate, with increasing group III flux. The saturated reflected As4 flux depends on temperature, and ranges from approximately 1/2 at temperatures commonly associated with high-quality epitaxy, to zero at lower temperatures; the saturated desorbing As2 flux is zero, independent of temperature. The reflected As4 (but not the desorbing As2 ) flux also depends on surface reconstruction, resulting in unexpected transients as surfaces sequence through various reconstructions upon initiation of growth.
Design and characterization of a compact two-target ultrahigh vacuum magnetron sputter deposition system: Application to the growth of epitaxial Ti1−xAlxN alloys and TiN/Ti1−xAlxN superlattices
Authors: Adibi F. , Petrov I. , Greene J. E. , Wahlström U. , Sundgren J.-E.
Published: July 2002

The design, fabrication, and operation of a compact, portable, ultrahigh vacuum, two-target magnetron sputter deposition system, consisting of independently pumped sample-exchange and deposition chambers, is described. The target-to-substrate distance is 12.5 cm and, for alloy or superlattice growth, the substrate is typically placed at 45° to both target surfaces. A novel shutter system composed of a hollow cylinder with a rectangular opening is mounted on a rotary feedthrough driven by a precision direct-current motor to controllably expose the substrate to sputter-ejected flux from one or both targets. Film thickness and composition uniformity are achieved through the use of selectively transmitting shields which are first coated with target material to prevent film contamination. Automatic mass-flow controllers, responding to a differential feedback signal from a capacitance manometer, are used to maintain the pressure constant during deposition. The film growth temperature can be varied from ambient to 1000 °C while adjusting the negative substrate bias from 0 to 500 V. In initial experiments using this system, epitaxial metastable Ti1−xAlxN alloys and TiN/Ti1−x AlxN superlattices were grown on MgO(001) and polycrystalline Ti1−xAlxN alloys were deposited on oxidized Si(001) substrates.
Sequential carbon oxygen bond cleavage in chemisorption of CO2 on Fe(100)
Authors: Nassir M. H. , Dwyer D. J.
Published: July 2002

Adsorption and dissociation of CO2 on Fe(100) was studied using temperature programmed desorption, x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy-loss spectra (HREELS), and low-energy electron diffraction. CO2 adsorbs on Fe(100) at 110 K to form two distinct adsorbed species: a physisorbed, molecular CO2 species and chemisorbed, bent anionic CO−2 species. These two species were characterized by HREELS losses at 2258 cm−1 for the asymmetric mode of the molecular CO2 state and at 1634 and 1232 cm−1 for asymmetric and symmetric modes of anionic CO2− state. Two features in O(1s) XPS spectrum for CO2 were observed at 534.9 and 531.1 eV binding energy and were assigned to the physisorbed and chemisorbed species, respectively. UPS data also indicate that a fraction of the adsorbed CO2 molecules at 110 K are in a bent CO−2 configuration. The molecular CO2 was found to desorb at 162 K where as the anionic form remains on the surface to dissociate. The dissociation upon heating is shown to proceed through two sequential carbon–oxygen bond breaking events. Strongly chemisorbed CO is produced as an intermediate in the dissociation process.
Ellipsometry investigation of nucleation and growth of electron cyclotron resonance plasma deposited silicon films
Authors: Li M. , Hu Y. Z. , Wall J. , Conrad K. , Irene E. A.
Published: July 2002

The nucleation and initial growth of Si films is fundamental to the understanding and control of rapid thermal chemical vapor deposition (RTCVD), and plasma enhanced CVD(PECVD) processes. Herein is reported the nucleation and growth of Si deposited on oxidized silicon wafers by electron cyclotron resonance (ECR) PECVD in the 600–700 °C temperature range, under low pressures, and using both in situ spectroscopic ellipsometry and single wavelength real-time ellipsometry. An island growth and coalescence model is used to interpret the real-time ellipsometry data. Initial nuclei distance and growth parameters are derived. Atomic force microscopy was used to observe the early stage of nucleation. In situ spectroscopic ellipsometry is used to measure the final Si film thicknesses and optical properties. The deposited Si films were characterized by cross-sectional transmission electron microscopy.
Precision parts cleaning using supercritical fluids
Authors: Purtell Robert , Rothman Laura , Eldridge Benjamin , Chess Catherine
Published: July 2002

Supercritical fluid extraction and chromatography measurements were made on pieces of disk drive actuator components in order to understand how to clean and analyse these parts. Extract analyses were made by Fourier transform infrared (FTIR) and flame ionization detector measurements. Hydrocarbons, silicones, and fluorocarbons were seen on various pieces of different samples using FTIR, time-of-flight static secondary-ion mass spectrometry (TOF-SSIMS), and x-ray photoelectron spectroscopy. In addition TOF-SSIMS detected di-isooctyl phthalate. Silicones and di-isooctyl phthalate could be removed by CO2 extraction.
Gas permeation through a high density polyethylene microwave window
Authors: Nguyen-Tuong Viet
Published: July 2002

Due to its low dielectric constant and low loss tangent, high density polyethylene (HDPE) has been selected for use as a high power microwave vacuum window in the Continuous Electron Beam Accelerator Facility cryounit. This window isolates the cryounit waveguide vacuum from the dry air in the external waveguide system. Gas permeation through the window will lead to cryopumping of the gas onto the cold waveguide walls and the cold ceramic window of the superconducting cavity. The gas load from permeation and outgassing of the window have to be minimized, due to the possibility of arcing when high power is applied through the waveguide. The outgassing and permeation of air through the 3.2 mm thick HDPE window were measured using the throughput method. A typical outgassing rate of 5.0×10−10 Torr ℓ/s/cm2 for samples baked out at 70 °C was observed 20 h after pump down and bakeout. The gas load due to permeation through 34 cm2 of the window was 1.6×10−7 Torr  ℓ/s. The gas permeation through the 3.2 mm thick HDPE coated with a 300 nm barrier layer of SiOx was also investigated. No improvement was observed. It was presumably due to the presence of defects in the deposited SiOx layer.
Physical properties of radio-frequency magnetron sputtered Pb(Zr,Ti)O3 thin films: Direct determination of oxygen composition by Rutherford backscattering spectroscopy and nuclear reaction analysis*
Authors: Cattan E. , Agius B. , Achard H. , Cheang Wong J. C. , Ortega C. , Siejka J.
Published: July 2002

Ferroelectric thin films of lead zirconate titanate were deposited on platinum covered Si substrates by rf magnetron sputtering from an oxide target of nominal composition [Pb(Zr0.55, Ti0.45)O3 (PZT)] in argon. The PZT films were deposited at different pressures different powers, and different substrate temperatures ranging from floating temperature to 400 °C. The thicknesses of the sputtered films were in the 15–720 nm range. The kinetics of the sputtering process and the effect of sputtering parameters on film composition have been studied and related to the continuously monitored optical emission of the plasma. The relative and absolute cation and oxygen compositions of the thin films were determined by a new method based on the simultaneous use of Rutherford backscattering spectroscopy and nuclear reaction analysis induced by a deuteron beam. The conditions for the deposition at floating temperature of stoichiometric PZT thin films were established. The effect of postdeposition anneal on the structure and the ferroelectric properties are discussed. The remanent polarization Pr was in the range 5 μC/cm2, the coercitive field Ec was between 15 and 25 kV/cm, and the dielectric constant εr evaluated from capacitance measurements, was around 1200, depending on the process parameters.