bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase segregation of Cu in Al–Cu thin films
Authors: Burkstrand J. M. , Hovland C. T.
Published: July 2002

In the metallization of integrated circuit devices, Cu is often added to Al to prevent the formation of hillocks on the Al films and to inhibit electromigration. In an effort to understand changes in these films which occur during further processing, thin films of an Al–Cu alloy (4 wt.% or 1.7 at.% Cu) sputter deposited on SiO2 were studied by scanning Auger microscopy (SAM). In unheated films, large area depth profiling indicated segregation of the Cu at the SiO2 interface. After heating the film to 500 °C, similar depth profiling showed a uniform distribution of the Cu. However, high spatial resolution (500 Å) SAM observations of the heated films indicated the presence of 1 μm and smaller regions having substantially higher Cu concentrations than the surrounding film. The SAM, combined with argon ion etching, indicated that these regions extend through the depth of the film to the SiO2 substrate. Quantitative AES measured the Cu/Al atomic ratio at about 1/2, suggesting the formation of a theta phase of the Al–Cu alloy. These results imply that a more complicated segregation occurs than is normally measured with large area (>10 μm) Auger spectroscopy.
Sub-PPMA gas analysis in 40 μl volumes by rf mass spectrometry
Authors: Schubert Rudolf , Augis J. A.
Published: July 2002

Miniature electrical or electronic devices are usually sealed within their own atmospheres; typically these volumes are of the order of μl. Residual sealed in moisture, fluxes, cleaning agents, etc., can affect the electrical properties of the devices. A mass spectrometry technique has been developed which allows one to determine the mass spectrum of those atmospheres with sensitivities at the 0.05 to 10 PPMA (part per million atomic) level in 10 μl volumes for certain compounds. This is done by concentrating the sample at LN2T by pumping away normal fill gases, i.e., H2, N2, He, etc. Concentration factors can be as high as 103. Although the technique is applicable to any microvolume, sealed electrical contacts (40 μl volume) are used to demonstrate the method in this paper. It is shown that 0.1 PPMA of a glass surfactant can be readily detected. The mass spectrometry results are well correlated with electrical resistance measurements and Auger electron spectroscopy results.
Enhancement of Ta+ flux by substrate biasing during sputter deposition of tantalum–nitrogen films
Authors: Aita C. R. , Myers T. A.
Published: July 2002

A voltage with a negative bias applied to the substrate during sputter deposition of tantalum in argon/nitrogen atmospheres is known to result in films which are more metallic in nature than films sputtered on grounded substrates. In the present study, we investigate the discharges associated with the reactive rf diode sputter deposition of nitrogen-doped tantalum films onto negatively biased substrates. Glow discharge mass spectrometry was used to determine the flux of Ta+/TaN+ species incident on the growing film. We report the enhancement of the Ta+ flux, relative to TaN+, with the application of a negative substrate bias. The changes in film crystallography that are observed, in particular, stabilization of the hexagonal Ta2N phase, as well as a decrease in electrical resistivity, are discussed in terms of this result.
Solid deuterium centrifuge pellet injector
Authors: Foster C. A.
Published: July 2002

Pellet injectors are needed to fuel long pulse tokamak plasmas and other magnetic confinement devices. For this purpose, an apparatus has been developed that forms 1.3-mm-diam pellets of frozen deuterium at a rate of 40 pellets per second and accelerates them to a speed of 1 km/s. Pellets are formed by extruding a billet of solidified deuterium through a 1.3-mm-diam nozzle at a speed of 5 cm/s. The extruding deuterium is chopped with a razor knife, forming 1.3-mm right circular cylinders of solid deuterium. The pellets are accelerated by synchronously injecting them into a high speed rotating arbor containing a guide track, which carries them from a point near the center of rotation to the periphery. The pellets leave the wheel after 150° of rotation at double the tip speed. The centrifuge is formed in the shape of a centrifugal catenary and is constructed of high strength Kevlar/epoxy composite. This arbor has been spin-tested to a tip speed of 1 km/s.
Measured thermal diffusivity of Hg1−xCdxTe solids and melts
Authors: Holland Lawrence Rozier , Taylor Raymond E.
Published: July 2002

The thermal diffusivity of Hg1−xCdxTe melts is found to rise rapidly with temperature to values characteristic of metals. Solid and melt diffusivities for values of x from 0 to 0.3 and over a temperature range from 150 to 900 °C have been determined by the laser flash method of Parker, Taylor, and Cowan. The diffusivity decreases from a maximum at x=0 in both the solid and the liquid, with the values observed at x=0.3 being about 40% of those for x=0. The solid diffusivity for x=0 is 1.7 mm2/s at 150 °C, decreasing to 0.7 mm2/s at the melting point. The x=0 liquid diffusivity increases from 0.7 mm2/s at the melting point to 3.5 mm2/s at 900 °C.
Density of liquid Hg1−xCdxTe
Authors: Chandra Dipankar , Holland Lawrence Rozier
Published: July 2002

Negative thermal expansion has been established in liquid Hg1−xCdx for x<0.2 employing a pycnometric method. Pure HgTe increases in density from its melting point at 670 °C to a maximum value at ∼750 °C, where normal thermal expansion progressively resumes. The dependence of density on temperature for liquid Hg1−xCdxTe arises almost exclusively from the HgTe portion of the melt, while CdTe acts as a diluent. The temperature corresponding to the maximum density changes slightly with composition, increasing by about 5 °C for x=0.1.
Some aspects of Li behavior in ion implanted HgCdTe
Authors: Bubulac L. O. , Tennant W. E. , Riedel R. A. , Bajaj J. , Edwall D. D.
Published: July 2002

SIMS has been used on both unimplanted and B-ion implanted LPE grown HgCdTe to study the distribution of the Li impurity background. In unimplanted layers Li decorates some types of crystal defects and also reflects the p/n distribution in the layer. In implanted layers Li decorates the implantation-induced damage and also reveals the junction region. Ion-implanted junctions have been evaluated by Hall, differential Hall, EBIC, C–V, and TEM techniques and the results correlated with the features exhibited by the Li distribution. The Li distribution analysis reinforces our previous understanding that implanted junctions are several microns deep, n+/p−, graded in the p region and formed by implant-induced native donors.
An investigation of the far infrared optical properties of Hg1−xCdxTe
Authors: Casselman T. N. , Hansen G. L.
Published: July 2002

This paper details results of a study of the optical absorption spectrum of n- and p-type Hg1−xCdxTe for wavelengths from below the band gap to 40 μm. We identify both intervalence band and multiphonon lattice absorption in the data, and have tentatively identified free electron absorption using Jensen’s theoretical model. The intervalence band absorption data are compared to the predictions of a theoretical model. Tentative phonon frequency assignments are made for some of the more prominent multiphonon peaks.
Surface geometries from channeling and blocking
Authors: Tromp R. M.
Published: July 2002

Medium energy ion beam crystallography, using the effects of channeling and blocking, is a technique sensitive to the geometries of solid surfaces. In this paper, we discuss principles, procedures, possibilities, and problems, illustrated by recent results on the Si (100)–(2×1) and –(1×1)2H and the Si (111)–(7×7) and laser-irradiated–(1×1) surfaces. The prominent role of Monte Carlo computer simulations in the preparation and interpretation of experiments is pointed out.
Reactivity of intermetallic thin films formed by the surface mediated decomposition of main group organometallic compounds
Authors: Dubois L. H. , Nuzzo R. G.
Published: July 2002

We have observed that by the reaction of silane with clean Ni, Rh, Pt, Mo, Ta, W, Cu, and Au surfaces at elevated temperatures, thin alloy and intermetallic compound phases can be prepared. For example, SiH4 reacts with atomically clean nickel surfaces to give a >50 Å surface film of predominantly Ni2Si. Subsequent reaction with oxygen leads to the formation of a thin passivating layer of SiO2; structurally similar materials were also obtained from the direct reaction of silane with oxidized nickel surfaces. Our results from studies on a wide variety of metal surfaces suggest a general procedure for the preparation of passivating, non-native oxide thin films. The scope of this methodology as regards applicable metals and reactive gases, and the physical and chemical properties of several representative materials is discussed.
Neutral beam heating of tokamaks: Past performance and future applications
Authors: Eubank H. P.
Published: July 2002

Neutral beam heating of tokamak plasmas has now a history of about one decade. The evolution of these heating systems from those of the early 1970’s to those of the present has been most impressive in terms of size, power, voltage, etc., but also in terms of performance in the sense of the plasma parameters achieved. Future needs for tokamak heating systems have highlighted certain shortcomings of neutral beam systems as they presently exist, and have been the driver behind an effort which has led to many conceptual improvements which should make neutral beams a serious contender for future tokamak heating requirements. A brief history of the highlights of neutral beam–tokamak systems of the last decade and some projections of future applications will be presented.
Generation of H−, D− ions on composite surfaces with application to surface/plasma ion source systems
Authors: Hiskes J. R. , Karo A. M. , Wimmer E. , Freeman A. J. , Chubb S. R.
Published: July 2002

We review some salient features of the experimental and theoretical data pertaining to hydrogen negative ion generation on minimum work function composite surfaces consisting of Cs/transition metal substrates. Cesium or hydrogen ion bombardment of a cesium-activated negatively biased electrode exposed to a cesium–hydrogen discharge results in the release of hydrogen negative ions. These ions originate through desorption of hydrogen particles by incident cesium ions, desorption by incident hydrogen ions, and by backscattering of incident hydrogen. Each process is characterized by a specific energy and angular distribution. The calculation of ion formation in the crystal selvage region is discussed for different approximations to the surface potential. An ab initio, all-electron, local density functional model for the composite surface electronics is discussed.
Characterization of the TEXTOR plasma edge using deposition probe techniques
Authors: Zuhr R. A.
Published: July 2002

Carbon and single crystal silicon passive deposition probes were used to measure the characteristics of the plasma edge region of the TEXTOR tokamak. Analysis of the probes was done by Rutherford backscattering for impurities and nuclear reaction analysis and elastic recoil detection for hydrogen isotopes. Plasma fluxes and energies in the edge were measured using these techniques. The principal impurities in the plasma edge were determined and their behavior as a function of time and position was measured. Measurements were also made of in situ erosion rates. The results are compared with independent measurements of other plasma parameters to study possible impurity introduction mechanisms.
The interaction of Pd with the InP(110) surface
Authors: Kendelewicz T. , Petro W. G. , Lindau I. , Spicer W. E.
Published: July 2002

Palladium phosphide and phase segregated In are found to be produced by room temperature deposition of Pd on the atomically clean InP(110) face using soft x-ray photoemission spectroscopy. The changes of the surface Fermi level position have been followed by subtracting the chemically shifted components from the In 4d and P 2p spectra. The value of the pinning position of ∼0.82 eV above the valence band maximum has been established. This result is compared with theoretical calculations of the surface defects in InP.
Species-specific densities of states of Ga and As in the chemisorption of H2O on GaAs(110)
Authors: Childs K. D. , Luo W.-A. , Lagally M. G.
Published: July 2002

Auger line shape measurements for Ga and As have been made for the adsorption of H2O on cleaved GaAs(110) to determine the species-specific densities of states at the Ga and As sites. The adsorption kinetics for H2O have been compared to that for O2. It is found that at identical exposure conditions H2O adsorbs two or three orders of magnitude faster than O2. The Auger line shapes at corresponding coverages are similar, indicating that the changes in the local charge distribution around Ga and As caused by H2O adsorption are similar to those caused by O2 adsorption.
Carbon 1s studies of diamond(111): Surface shifts, hydrogenation, and electron escape lengths
Authors: Pate B. B. , Oshima M. , Silberman J. A. , Rossi G. , Lindau I. , Spicer W. E.
Published: July 2002

As probed by photoemission, the valence band emission spectra of diamond(111) undergo reversible changes due to cycles of hydrogen adsorption and desorption. We report here carbon 1s spectra from diamond(111) as a function of hydrogen exposure–annealing cycles and as a function of photon energy. We find an additional shoulder to lower binding energy in the C 1s spectra of the hydrogen-free reconstructed 2×2/2×1 surface and interpret this result as due to a chemical shift (0.95±0.1 eV) of the surface atoms. We analyze the data in terms of models for reconstruction and also derive the inelastic scattering length (escape length) of electrons in diamond over the kinetic energy range 25–1000 eV.
Room temperature glow discharge deposition of silicon oxides from SiH4 and N2O
Authors: Kaganowicz G. , Ban V. S. , Robinson J. W.
Published: July 2002

Room temperature plasma deposition of silicon dioxide from silane and nitrous oxide has been described. Depositions were made using a capacitively coupled magnetically enhanced glow discharge system. Near stoichiometric SiO2 was deposited at N2O/SiH4 flow ratios from 11:1 to 2.3:1. Mass spectroscopic analyses of the plasma during the deposition suggest that the SiO2 forming reaction takes place between oxygen from decomposition of N2O and silane. MS data also show that the decomposition rates of N2O and and SiH4 in the glow discharge differ as a function of power with N2O decomposing at a lower rate. As a result, in a magnetically enhanced glow discharge where there are power density variations throughout the system, there will be corresponding variations in deposition rate and deposit properties.
On the development and use of fast atom beams for the SIMS analysis of polymers and insulators
Authors: Ross M. M. , Colton R. J. , Rose S. L. , Wyatt J. R. , DeCorpo J. J. , Campana J. E.
Published: July 2002

A commercial ion gun has been modified to generate a diffuse neutral beam for molecular secondary ion mass spectrometry (SIMS). The mechanism of the ion neutralization process used is summarized. Applications of fast-atom molecular SIMS on insulating specimens are also described.
SAM determination of oxygen gradients in Zircaloy-4
Authors: Aitchison I. , Davidson R. D.
Published: July 2002

To model deformation of Zircaloy-4 fuel sheath under temperature transients in high temperature steam, it is necessary to measure the oxygen concentration gradient beneath the oxide since the flow stress is sensitive to oxygen concentration. A SAM has been used to compare oxygen/zirconium peak ratios on cross sections of sheath with those from Zircaloy-4/oxygen standards. The data show reasonable reproducibility and should permit better modeling of deformation. Some perturbations in the gradient, predicted by theory, have also been found. Practical analysis problems stemmed from the low oxygen concentrations, the reactivity of the alloy, the long counting times, and the sensitivity of the oxygen peak to electron beam current density.
Deuterium transport kinetics for zirconium and Zircaloys with surface oxides
Authors: Mitchell Dean J.
Published: July 2002

The rate at which deuterium permeates zirconium and Zircaloy membranes is investigated in this study. It is shown that the deuterium transport rate is dominated by the influence of surface oxides for zirconium or Zircaloy membranes held in deuterium atmospheres over the temperature range 250–500 °C. Deuterium absorption rates by Zircaloy-2 and Zircaloy-4 are indistinguishable from zirconium. A description of the deuterium transport kinetics is presented which yields simple analytical solutions for the rates of deuterium absorption by and permeation through metals with low permeability surface oxides.
Order, disorder, and band discontinuities at ZnSe–Ge heterojunctions
Authors: Margaritondo G. , Capasso C. , Patella F. , Perfetti P. , Quaresima C. , Savoia A. , Sette F.
Published: July 2002

ZnSe–Ge is, together with GaAs–Ge, the most prototypical heterojunction interface. And it has the advantage with respect to GaAs–Ge of a large valence-band discontinuity which can be directly measured from synchrotron-radiation soft-x-ray valence-band photoemission spectra without needing to analyze the core-level shifts. We used the ZnSe–Ge interface to test the possibility that the valence-band discontinuity ΔEv is affected by the interface ordering or by annealing processes in general. Our experiments demonstrated that ΔEv is not affected by the above factors. This strongly supports the recent suggestions that ‘‘local’’ contributions to the heterojunction discontinuities have small magnitude on the average.
Surface interaction study of TiC single crystal with energetic hydrogen ions by AES and FDS
Authors: Fukuda S. , Mohri M. , Yamashina T.
Published: July 2002

Changes in atomic composition in the near surface region of single–crystal titanium carbide (TiC) due to hydrogen or deuterium ion irradiation in the keV range were studied with the use of AES (Auger electron spectroscopy) and FDS (flash desorption spectroscopy). Depth profiles obtained with sputter-AES showed that carbon atoms were preferentially depleted due to the hydrogen ion irradiation. The amount of depleted carbon approached the equilibrium value above the hydrogen ion fluence of 2×1017 ions/cm2. Depth profiles of this depletion region were found to be similar to the damage distributions caused by the incident particles. The depleted region recovered completely by annealing at 1000 °C for 30 s. The result of FDS measurements suggests that the hydrogen atoms which were implanted into the near surface region replaced the carbon atoms of the TiC lattice to form titanium hydride.
A Pd–MOS structure as a hydrogen sensor in catalytic reactions
Authors: Petersson L.-G. , Dannetun H. M. , Lundström I.
Published: July 2002

By letting a catalytic reaction involving hydrogen occur on the Pd gate metal of a Pd–MOS structure the amount of hydrogen atoms on the surface can be monitored without any external probes by measuring the dipole induced by the hydrogen atoms that have diffused to the Pd–SiO2 interface. The ability to work over a wide pressure range (10−11 Torr to atm) makes the Pd–MOS structure an interesting device in the study of catalytic reactions. In this article, we will give a short review of some of the many applications of this component. We have combined this technique with other surface sensitive techniques such as UPS, XPS, work function measurements and mass spectrometry and, e.g., studied how the hydrogen adsorption–desorption processes are influenced by alloying the Pd surface with various amounts of Ag, thereby also changing the distribution of d states close to Fermi energy. We have also studied the H2+O→H2O reaction on Pd. It, e.g., turns out that the water reaction rate reaches a maximum when the oxygen coverage approaches zero and that the hydrogen atoms on the surface have a larger lateral mobility.
X-ray photoemission spectra for AlxGa1−xAs
Authors: Ireland P. J. , Kazmerski L. L. , Fisher R. F.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) is used in both a qualitative and quantitative fashion to study the AlxGa1−xAs alloy. Gallium and aluminum atoms are always bonded to the arsenic atom. As the concentration of Al increases, a notable shift in the As-3d level could be expected as Ga and Al both have different electronegativities. Spectra taken on molecular beam epitaxially grown samples do not show this shift in the As-3d core level. The composition of the films have been measured with an electron probe, and these results agree very well with the XPS quantitative data. Standard spectra are presented for films with x=0.16, 0.23, 0.32, 0.46, and 0.65.
Lot-to-lot variations in electromigration performance for thin film microcircuits
Authors: Smith P. M. , Lloyd J. R. , Prokop G. S.
Published: July 2002

The variation in electromigration performance measured by the median time to failure (t50) and the standard deviation (σ) of the failure times for a number of lots was studied. It was found that regardless of the metallization technology, a lot-to-lot variation of between 5× and 10× in both t50 and σ can be expected during normal processing. The implications of this finding for predicting chip reliability with regard to electromigration failures are discussed.
Defect measurements in digital optical disks
Authors: Shrawagi S. , Chen D. , Robinson R. S. , Rossnagel S. M.
Published: July 2002

The optical memory storage requires that the storage media should have a low defect density. To obtain the dependence of deposition process on raw bit error rate (BER), we measured BER on disks coated by e-beam thermal evaporation and by ion-beam sputtering. It was demonstrated that the defects on the tellurium coated disks are largely the result of the defects on the uncoated substrate and no significant improvement in defects can be achieved from the deposition process alone. We have prepared glass disks spin coated with polymer subbing layer in clean, dust free conditions. This layer helps to improve the quality of the surface on which the tellurium film is deposited by covering the microscopic pits and the surface roughness, etc. It was found that ion beam sputter cleaning of the polymer subbing layer coated disks prior to the deposition of tellurium film by ion sputtering, achieves an order of magnitude improvement in BER compared to tellurium film directly on glass. Experiments to observe the effect of environment testing on BER were not carried out during these studies.
Optically enhanced low temperature oxygen chemisorption on GaAs(110)
Authors: Bertness K. A. , Petro W. G. , Silberman J. A. , Friedman D. J. , Spicer W. E.
Published: July 2002

Optically enhanced oxidation of GaAs is promising both for insight into fundamental mechanisms of oxygen chemisorption and for possible application in GaAs direct write. For atomically clean GaAs(110), we have found that sample temperature is a key parameter in determining the increase of oxygen uptake under low-intensity argon ion laser illumination (1 W/cm2 at 2.41 eV) relative to the ‘‘dark’’ uptake. Although cooling to 185 K suppresses the dark oxygen adsorption rate, the oxygen uptake with optical irradiation is the same at both 185 and 400 K. The ratio of laser-assisted to dark uptake for 108 L exposure then approaches the enhancement necessary for spatially selective oxidation, showing an increase from 2.5 at room temperature to well over 10 at 185 K. After ruling out sample heating and direct oxygen gas excitation, we suggest that the light-induced increase in uptake is due to electronic excitations in the GaAs. To explain the enhancement, one also needs to assume a weakly adsorbed precursor state that converts to the chemisorption state when thermally or optically activated; the implications for previously suggested oxidation mechanisms will be discussed.
Ion implantation and ion assisted coating of metals
Authors: Dearnaley G. , Goode P. D. , Minter F. J. , Peacock A. T. , Waddell C. N.
Published: July 2002

The ion implantation of nitrogen into steels and titanium alloys can markedly improve their wear resistance especially under mild abrasive conditions, but it is significantly less successful in overcoming metal–metal adhesive wear under high loads. Certain metallic species such as Ti, Ta, Nb, Y, and Sn give better performance under such conditions when implanted into steels, but most of these additives are effective only in the presence of carbon or nitrogen. Among them, yttrium is particularly successful in reducing wear and friction after implantation at relatively low fluences (1016 ions cm−2), thus avoiding problems due to surface sputtering and limited retention in work pieces of complex geometry. Yttrium and other oversized species (e.g., Sn) may act by forming a complex with interstitial carbon or nitrogen: this nonspherical defect interacts strongly with mobile dislocations and so strengthens the material. Ion implantation provides a nonequilibrium method for introducing significant quantities of large atoms on substitutional sites. Abrasive wear is lessened by the application of hard, chemically inert coatings such as the nitrides or carbonitrides of titanium, boron or hafnium, but conventional CVD or PVD coatings of these compounds are often lacking in adhesion to the substrate. When deposited at relatively low temperatures, moreover, they may have an undesirable columnar structure and a nodular surface topography. To overcome such problems research is now being carried out on thin coatings of Ti, B, or Hf on steel which are bombarded heavily with energetic ions. This can bring about ion beam mixing at the interface, followed by the conversion of at least part of the coating to a nitride or carbonitride. It is advantageous to support such coatings by implanting the metal substrate first. Ion assisted coatings of TiN or BN appear promising from the standpoint of their microhardness, friction, adhesion and oxidation properties and so they may reduce adhesive wear.
Sputtered W–N diffusion barriers
Authors: Kattelus H. P. , Kolawa E. , Affolter K. , Nicolet M-A.
Published: July 2002

The thermal stability of reactively sputtered tungsten–nitrogen alloy thin films is investigated for the application as diffusion barriers in silicon contact metallizations. The composition of W–N barriers is varied over a wide range including pure W. Aluminum, gold, and silver are used as low resistivity overlayers. Metallurgical interactions at temperatures ranging from 500 to 900 °C are studied. Incorporating nitrogen into tungsten advantageously stabilizes all three systems. The overall failure takes place rapidly above critical temperatures that depend on both the metal overlayer and the microstructure of the barrier. In some cases, W–N alloys can effectively prevent interdiffusion at temperatures as high as 800 °C for 30 min.
Calibration of an energy dispersive spectroscopy k factor using Rutherford backscattering
Authors: Barbour J. C. , Sickafus K. , Nastasi M.
Published: July 2002

Energy dispersive spectroscopy (EDS) k factors for three systems (Ni–Si, Ni–Al, and Au–Fe) are determined on a JEOL 200cx electron microscope operated at 200 keV. Rutherford backscattering spectrometry (RBS) was used to give an accurate composition analysis for the EDS standards, and to measure thicknesses used in absorption corrections. The k factors (for compositions in weight percent) were found to be kNiSi=1.28±0.045, kNiAl=0.949±0.033, and kAuFe=3.88±0.272. Uncertainties for the k factors determined in this way are ±3.5% except for samples having only trace quantities in which the accuracy is only ±7%–8%. The uncertainty in the k factors is discussed in terms of the accuracy of the technique to calibrate the standards (RBS), the inherent uncertainty in x-ray detection, and the accuracy of the absorption correction. A sample configuration is described to check the necessity for and the accuracy of absorption corrections by analyzing EDS spectra from a bilayer sample of one x-ray absorbing film (Ni) on a nonabsorbing film (Si). These k factors are compared to results using conventional techniques and to theoretically calculated k factors.
Secondary electron effect on power–voltage relationship in rf sputtering
Authors: Bumble B. , Cuomo J. J.
Published: July 2002

Radio frequency power–voltage characteristics for a number of sputtering target-gas combinations are presented. The log–log plots of these data highlight a strong correlation between the target’s secondary electron emission coefficient and the exponent in the expression P∝Vn. Most metal targets sputtered with argon exhibit less than a square law (i.e., n=2) dependence. These target-gas combinations generally have low secondary electron yields for ions at the energies used. However, the addition of an oxidizing gas or the use of targets in the alkali halide and metal oxide families produces exponents greater than two. The increased number of secondary electrons due to ion bombardment accounts best for this higher degree of ionization in the plasma. There is also an electrode coupling effect due to fast electrons from the target surface which is shown in the anode power–voltage characteristics. We suggest a model of the rf power–voltage relationship which includes the energy dependence of the secondary electron yield.
Electrical characterization of rf glow discharges using an operating impedance bridge
Authors: Mlynko W. E. , Hess D. W.
Published: July 2002

The impedance and its inverse, admittance, of nitrogen rf glow discharge are measured with an operating impedance bridge in two geometrically similar, radial-flow, parallel-plate plasma reactors. Separation of these electrical parameters into their constituents, resistance and capacitive reactance for impedance and conductance and susceptance for admittance, permits an evaluation of the electrical behavior of these discharges. At power levels between 0.06 and 0.4 W/cm2 and electrode spacings between 2.5 and 8.2 cm, the discharge conductance generally increases with rf power and electrode spacing. However, the exact trends depend upon the specific reactor. Based upon these results, an electrical similarity criterion is proposed that may assist transfer of plasma etching and deposition processes from one reactor to another.
Oxidation of Ni60Fe40(100) in the presence of sulfur
Authors: Lad R. J. , Schrott A. G. , Blakely J. M.
Published: July 2002

The effect of adsorbed sulfur on the initial oxidation of a Ni60Fe40(100) alloy surface has been studied at 100 and 500 °C using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Measurements of the oxygen uptake rate have been made as a function of sulfur coverage at each temperature. Within the O2 exposure range studied, the uptake of O2 is observed to be inhibited by an ordered c(2×2) sulfur phase at 0.5 monolayers coverage, independent of temperature. For sulfur coverages below 0.5 monolayers, an Fe-rich surface oxide forms with a composition and morphology dependent on the sample temperature. The experimental observations suggest that at 500 °C, sulfur-free oxide islands grow interspersed between c(2×2)S domains whereas at 100 °C, the adsorbed sulfur layer becomes overgrown by coalesced oxide. The mechanisms of oxide nucleation and growth are related to the existence of different phases of the chemisorbed sulfur + oxygen layer as previously studied.
The advanced toroidal facility
Authors: Sheffield John
Published: July 2002

The Advanced Toroidal Facility (ATF) is a new magnetic plasma confinement device, under construction at Oak Ridge National Laboratory (ORNL), which will lead to improvements in toroidal magnetic fusion reactors. ATF is a type of stellarator known as a torsatron, which theoretically has the capability to operate at ≥8% beta in steady state. The achievement of high beta is made possible by the carefully chosen combination of helical and poloidal magnetic field coils which give direct access to the so-called second stability region. In addition, the device has the flexibility to explore the stability boundaries and to study the properties of a variety of magnetic configurations, including some with a helical magnetic axis. The ATF plasma has a major radius of 2.1 m, an average minor radius of 0.3 m, and a field of 2 T for a 5-s duration or 1-T steady state. ATF replaces the ISX-B tokamak at ORNL and will use the ISX-B auxiliary systems, including 4 MW of neutral injection heating and 0.2 MW of electron cyclotron heating. ATF will start operation in the fall of 1986.
Spectroscopic study of sources and control of impurities in TMX-U
Authors: Yu T. L. , Allen S. L. , Moos H. W.
Published: July 2002

An absolutely calibrated spectrograph has been used to study the impurity characteristics in the Tandem Mirror Experiment-Upgrade (TMX-U). The spectrograph measures the time histories of several impurity emission lines in a single plasma shot. The common intrinsic impurities found in TMX-U are C, N, O, and Ti. It has been shown that a large fraction of oxygen and nitrogen in the plasma is associated with the neutral beams. The plasma wall is the main source of carbon. In general, the concentration of each of the impurities is low (<1%), and the power radiated by them is less than 10 kW, which is a small portion of the total input power to the plasma. The concentrations of the impurities can be reduced substantially by glow discharge cleaning and titanium gettering.
Surface analysis of TFTR limiter tiles
Authors: Dylla H. F. , Ulrickson M. A. , LaMarche P. H. , Owens D. K. , Doyle B. L.
Published: July 2002

The plasma contacting surfaces of the TFTR movable limiter consist of an array of titanium carbide coated graphite tiles. The surface characteristics of the graphite tiles were analyzed prior to installation to establish the initial limiter conditions, and after exposure to 800 Ohmically heated discharges in TFTR to provide data on the limiter conditioning process. Some tile surfaces showed nearly complete removal of the TiC surface as a result of plasma exposure. 3D and 2D elemental mapping of the tile near surface regions show deposition of vacuum vessel metals (primarily Ti and Ni) in the form of oxides.
Type conversion of (Hg,Cd)Te induced by the redistribution of residual acceptor impurities
Authors: Tregilgas J. , Beck J. , Gnade B.
Published: July 2002

Bulk (Hg,Cd)Te grown by the quench-anneal process has been found to contain residual acceptor impurities which are normally depleted from the n-type surface by an internal gettering mechanism during low temperature postannealing in saturated Hg vapor. When the n-type slices are postannealed for much longer periods, the Te saturated core is annihilated, and the gettered residual acceptor impurities can redistribute into the surface region. If upon homogenization the residual acceptor concentration exceeds the residual donor concentration, the material will convert to p type. A new method for applying neutron activation analysis (NAA) to (Hg,Cd)Te has been used to identify this acceptor impurity as Cu at levels below 1 ppm. An extension of the NAA technique has employed quartz encapsulated silicon samples to demonstrate Cu may come from either the quartz or annealing environment.
Surface sputtering rate reduction and its effect on SIMS depth profiling in cesium-ion-bombarded GaAs
Authors: Homma Yoshikazu , Ishii Yoshikazu
Published: July 2002

Distortions in secondary ion mass spectrometry (SIMS) depth profiles due to nonuniform sputtering rates have been studied in GaAs crystals bombarded by a cesium ion beam. It is found that a significant sputtering rate reduction occurs in Cs+-beam-bombarded GaAs in a depth range of about 0.1 μm from the surface. In contrast, sputtering rates are almost constant for O+2- and Ar+-beam bombardment. Auger electron spectroscopy results show that the surface composition is greatly distorted in Cs+-beam-bombarded GaAs crystals. Preferential sputtering may be responsible for the surface sputtering rate reduction. It is shown that the sputtering rate reduction causes a depth scale error in the SIMS depth profile.
Effects of charge neutralization on ion-beam-deposited boron nitride films
Authors: Halverson Ward , Quinto Dennis T.
Published: July 2002

Thin films of ion-beam-deposited boron nitride (i-BN) were formed on various substrates from an ion source operating with borazine (B3N3H6). Without space charge neutralization of the beam, the films were severely damaged, with indications of melting, cracking, and delamination. Surface (‘‘Malter’’) discharges were visible in the deposition chamber; surface charging caused tracking and puncture through the dielectric i-BN film. With charge neutralization, the Malter discharges ceased and the films became smooth, uniform and adherent. The neutralizing electrons prevented the buildup of surface charge on the i-BN film and stopped the damage from surface discharges; the bulk properties of the films apparently were not affected by the neutralization. The films were close to stoichiometric BN with typically 2–7 at. % of C and O impurities. The higher impurity levels were found in those formed without neutralization. X-ray diffraction indicates that the film is quasicrystalline, with a lattice parameter somewhat larger than that of cubic-BN.
Primary Ar+ ion bombardment effect on Ni–Fe film composition formed by ion beam sputtering
Authors: Nagai Yasuhiro , Nishimura Chikara , Toshima Tomoyuki
Published: July 2002

This paper reports results of experimental and analytic investigations concerning the Ni–Fe film composition formed by ion beam sputtering under various forming conditions. From experiments involving the substrate angle and temperature that had dramatic influence on the Ni–Fe film composition, it is found that the primary Ar+ ion bombardment dominates the composition variation. Also, the Ni fraction in Ni–Fe film and its deposition rate decrease as the ion current density increases. As a result of simple analysis, this composition variation is found to be caused by preferential resputtering. Conversely, the Ni fraction increases as the substrate temperature increases without a deposition rate change under primary ion bombardment. This phenomenon cannot be explained only by preferential resputtering. It also includes the formation of an Fe-rich layer on the film surface.
Ceramic microstructures and properties
Authors: Rühle Manfred
Published: July 2002

Ceramic materials are currently being used in many applications, and it is expected that there are many new applications of ceramics in high-technology engineering systems, e.g., in microelectronics. However, many problems have to be overcome to improve the properties of the different ceramic components. For an understanding of the properties, a qualitative and quantitative determination of the microstructure is required since many properties are controlled by the microstructure of the materials. The microstructure can be analyzed, e.g., by the different techniques of TEM, which include conventional TEM, high-resolution TEM, and analytical TEM. Those methods allow a detailed description down to the atomic scale of grain boundaries, interphase interfaces, composition, and grain morphologies. Results of microstructural studies on grain boundaries in ceramics and on interfaces of metal/ceramic bonds will be described and correlated to mechanical and electrical properties. The improvement of toughness and strength by various techniques will be discussed.
Characterization of heterojunction parameters by soft x-ray photoemission spectroscopy
Authors: Margaritondo G.
Published: July 2002

We discuss the use of synchrotron-radiation photoemission to investigate valence and conduction band discontinuities and the interface Fermi level position at heterojunction interfaces.
Remote plasma enhanced CVD deposition of silicon nitride and oxide for gate insulators in (In, Ga)As FET devices
Authors: Richard P. D. , Markunas R. J. , Lucovsky G. , Fountain G. G. , Mansour A. N. , Tsu D. V.
Published: July 2002

We have deposited silicon nitride (Si3N4) and silicon oxide (SiO2) thin films using remote plasma enhanced chemical vapor deposition (RPECVD). We have characterized the chemical composition of the films by infrared absorption (IR), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Rutherford backscattering (RBS), and have studied the electrical properties in metal insulator semiconductor (MIS) device configurations. We have configured the deposition system and adjusted gas flow rates in order to minimize: (a) O contamination in the Si3N4 films; and (b) OH groups in the SiO2 films. This paper describes the deposition apparatus and the process, and presents a phenomenological model for the plasma phase and surface reactions involved. We have combined both types of insulators in a trilayer dielectric that has been used as a gate insulator for (In,Ga)As insulated gate field effect transistors (IGFET’s). We have found that the electrical properties of these devices are superior to devices utilizing single layer SiO2 or Si3N4 gate insulators.
Pulsed excimer and CO2 laser annealing of ion-implanted silicon
Authors: Narayan J. , James R. B. , Holland O. W. , Aziz M. J.
Published: July 2002

We have investigated pulsed excimer and CO2 laser annealing phenomena as a function of laser parameters in boron-implanted silicon, using cross-section transmission electron microscopy. The depth of annealed regions or melting was found to increase linearly with the pulse energy density and inversely with the pulse duration. The threshold for melting and depth of the melted regions as a function of pulse energy density and duration were found to be in good agreement with heat-flow calculations. Pulsed CO2 laser annealing required either high doping or substrate heating to increase free-carrier absorption. The annealing results in both cases were consistent with a first-order phase transformation involving melting.
Charge exchange in gas–surface collisions: Momentum transfer
Authors: Olson John A. , Garrison Barbara J.
Published: July 2002

A description of near-resonant charge exchange in gas–surface collisions that includes momentum transfer is presented. The surface is represented by a cluster of metal atoms. A diatomics in molecules procedure is used to obtain the surface eigenvalues and eigenfunctions. These are combined with those of the gas atom or ion to construct the interaction potentials and electronic coupling terms. These provide the input needed to solve for the nuclear and electronic motions in the common eikonal formalism which leads to a time dependent description of the event. The formalism is applied to a sodium atom scattering from a W(110) surface. The surface consists of five W atoms. The center W atom is allowed to move during the collision. Transition probabilities are presented for various two and three electronic state systems and compared to the case where the position of the center W atom remains fixed.
Fabrication of thin cylindrical targets for x-ray laser experiments
Authors: Kim H. , Noyes S. , Richardson M. C. , Yaakobi B.
Published: July 2002

For a laser-produced plasma to be most useful in current x-ray laser experiments, it should have a cylindrical shape and a uniform plasma density and temperature to provide high x-ray gain along the axis. One approach to producing such a plasma is the uniform compression of hollow cylindrical targets with multiple, line-focused laser beams. These targets are typically ultrathin (<3000 Å) cylindrical shells of materials such as Al. These cylinders have diameters ≂100 μm and lengths ≂2 mm. To fabricate such targets, solid polystyrene cylinders are coated with a metal and/or parylene layer of the appropriate thickness. The coated cylinder is then cut to the desired length and the polystyrene is leached out by immersing the system in a solvent.
Tritium gettering from air with hydrogen uranyl phosphate
Authors: Souers P. C. , Uribe F. S. , Stevens C. G. , Tsugawa R. T.
Published: July 2002

Hydrogen uranyl phosphate (HUP), a solid proton electrolyte, getters tritium gas and water vapor from air by dc electrical action. We have reduced the formation of residual tritiated water to less than 2% and demonstrated that HUP can clean a 5.5 m3 working glove box. Data are presented to illustrate the parameters of the gettering and a model is derived. Two other tritium gettering electrolytes have been discovered.
Effects of impurities on the reaction of Ta and Si multilayers processed by rapid thermal annealing
Authors: Davis G. D. , Natan M.
Published: July 2002

The reaction of Ta/Si/Ta/Si... multilayers under rapid thermal annealing (RTA) conditions has been examined using Auger electron spectroscopy (AES) sputter depth profiles and line shape analysis and cross-sectional transmission electron microscopy (X-TEM). Oxygen and carbon contamination present initially in some of the tantalum layers slows the formation of the disilicide for these layers. C remains immobile and bound to the Ta throughout the sequence of RTA temperatures. O, which is also initially bound to Ta, diffuses to the upper Si/Ta interface and forms a Si suboxide that acts as a barrier layer to the reaction of the two adjacent Si and Ta layers until the highest treatment temperatures (1150 °C). In contrast, the uncontaminated region reacts at 750 °C and a contaminated Ta layer and the underlying Si layer (with no suboxide barrier) react together at 850 °C. These results are in qualitative agreement with predictions of the Ta–Si–O ternary phase diagram, but differ from those obtained from long furnace anneals of Ta/Si bilayers. These differences are tentatively attributed in part to the differences in the kinetics of diffusion and formation of the various phases under different annealing conditions and in part to the amorphous nature of the thin Ta/Si multilayers.
On specimen preparation by radio frequency planar magnetron sputtering
Authors: Ochiai Y. , Aso K. , Hayakawa M. , Matsuda H. , Hayashi K. , Ishikawa W. , Iwasaki Y.
Published: July 2002

Sector type targets were used to fabricate a series of alloys by planar magnetron sputtering with an rf mode. From the binary Co–M system (M: Al, Si, Ti, Cr, Fe, Ni, Cu, Zr, Nb, Mo, Ag, Ta, and W) rf sputtering yield ratios were compared with dc sputtering yields by Laegreid and Wehner. It was found that rf planar magnetron sputtering was well predicted by dc plasma discharge data. The relation of the rf peak-to-peak voltage and Ar ion energy is discussed. Cosputtering of dissimilar elements caused cross contamination on the target surface and it was attributed to the seeding effect. The application to a ternary system Co–Nb–Zr known as an amorphous soft magnetic material was quite successful and suggests sector target to be a convenient way for searching new materials.
X-ray study of orientational epitaxy in rare gas monolayers on graphite
Authors: D’Amico K. L. , Moncton D. E.
Published: July 2002

Rotating anode x-ray studies of Kr and Xe monolayers absorbed on the single crystal graphite(001) surface are described. Orientational epitaxy is observed for the Kr monolayer in agreement with previous electron diffraction studies. The Xe solid also displays a rotated phase at ≊115 K. A comparison of the x-ray and electron diffraction techniques for structural studies of adsorbates on single crystals is made.