bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of TiN in an oxygen plasma asher
Authors: Tompkins Harland G. , Sellers James A.
Published: July 2002

In previous work we have studied the thermal oxidation of titanium nitride. This involved temperatures of 350 °C and greater, and times of hours. In this work, we study the oxidation of titanium nitride in a downstream plasma asher, where the sample temperature is about 200 °C. For comparison to an older technology, we also include samples oxidized in a barrel asher where the sample temperature was about 100 °C. Oxidation times of 16 min and less were studied. Thickness and optical constants were measured using ellipsometry along with Auger electron spectroscopy with argon ion etching for depth profiles. The growth kinetics are shown to be logarithmic. In the down-stream asher, films form in 90 s which would require 40 min at 450 °C if grown thermally. We show that only the thinner films can be etched off in 50:1 HF.
Thermal stability of oxidized La on Pd(100)
Authors: Ahmad M. , Rahman Md. M. , Rao B. U. M. , Graham G. W.
Published: July 2002

We have investigated the thermal stability of oxidized La and Al on Pd(100) by Auger electron spectroscopy measurements carried out under ultrahigh vacuum conditions. The oxidized metal layers with varying coverages of La and Al were examined at increasing temperatures in order to follow the removal of oxygen from the surface. For submonolayer La coverages the oxygen was removed at temperatures in the range of 625–850 K. The temperature at which the oxygen was removed from the oxidized La increased as the coverage was increased. For similar coverages of Al on Pd the oxygen removal occurred at relatively higher temperatures. Oxygen removal from thin layers of Al on Pd(100) was accompanied by depletion of Al from the surface, whereas in the case of La a stable metallic layer remained on the surface.
Tapered aluminum interconnect etch
Authors: Allen Lynn R. , Rickard Rick
Published: July 2002

Tapered etching of the aluminum interconnects can assist in planarization of multilevel interconnects by improving step coverage of chemical vapor deposited oxides in tightly spaced arrays. Previously published results have shown that a tapered aluminum profile is formed by adding small amounts of hydrocarbon gases to Cl2-based etch chemistries [Coburn, Winters, and Chung, J. Appl. Phys. 48, 3532 (1977)]. This process relies on the formation of a relatively thick polymer sidewall to achieve the tapered profile. While this mechanism is effective, it can be hard to remove the polymer after etch. A tapered profile was achieved in a transformer coupled plasma etcher using only additions of N2. The polymer sidewall formed during the etch was easily removed with the remaining photoresist. Measurements of the metal lines after etch and cross sections with the resist intact showed that the top dimension of the line was unchanged by the etch while the base of the line was larger than the base of the photoresist. Even though etch rate results show a loss of photoresist selectivity, cross sections show no loss in linewidth of the top of the resulting metal line compared to starting resist linewidth indicating that the slope is achieved by increased sidewall passivation rather than by a typical resist erosion mechanism so the slope of the line is independent of the slope of the resist prior to etch.
Cryogenic targets and related technologies at ILE Osaka University
Authors: Norimatsu T. , Chen C. M. , Nakajima K. , Takagi M. , Izawa Y. , Yamanaka T. , Nakai S.
Published: July 2002

Described are two approaches to make cryogenic inertial fusion targets that have a uniform solid or liquid fuel layer inside a spherical hollow fuel capsule. One is to utilize low-density, low-atomic-number plastic foam to sustain liquid fuel (foam method) and the other is to initiate a glow discharge in the void of a solid fuel layer to symmetrize the solid layer (plasma layering method). In the foam method, we have successfully made a foam shell with a gas barrier to prevent the fuel from evaporation by means of density-matched emulsion method followed by an interfacial polycondensation method. Foam shells having diameters of 600–1550 μm and wall thicknesses of 10–50 μm were coated with a normal density plastic layer having thickness of 4–10 μm. These foam shells were provided for implosion experiments with the Gekko XII glass laser system. In the plasma layering process, we examined the feasibility of the method by performing experiments using krypton gas and liquid nitrogen. A nonuniform solid krypton layer was redistributed into a uniform one after a 30 min discharge induced by an external 2.45 GHz microwave field. Experimental results on the heat generation in shells indicated that this technique can redistribute 10 K solid fuel into a uniform layer using intermittent discharges.
Residual stress in metal ion implanted titanium nitride films studied by glancing incidence x-ray diffraction
Authors: Perry Anthony J. , Treglio James R. , Valvoda Vaclav , Rafaja David
Published: July 2002

The effect of yttrium and molybdenum ion implantation on the lattice parameters, residual stress, and strain distribution (integral peak breadth) in TiN coatings made by chemical vapor deposition was studied by glancing incidence x-ray diffraction in Seemann–Bohlin focusing geometry. It was found that there were no changes in the former two, but that the peak breadth was increased, and particularly between the {220} and {222} families of planes. It is considered that this may be due to grain size comminution or the development of a dislocation network down to depths of the order of 0.5 μm, which is well below the depth where the implant resides. The data also indicate that the limit of usefulness of the Seemann–Bohlin geometry is at the lower end of the angles of incidence set here, namely, 2°–3°.
X-ray photoelectron spectroscopy analysis of cleaning procedures for synchrotron radiation beamline materials at the Advanced Photon Source
Authors: Li Y. , Ryding D. , Liu C. , Kuzay T. M. , McDowell M. W. , Rosenberg R. A.
Published: July 2002

TZM (a high-temperature molybdenum alloy), machinable tungsten, and 304 stainless steel were cleaned using environmentally safe, commercially available cleaning detergents. The surface cleanliness was evaluated by x-ray photoelectron spectroscopy. It was found that a simple alkaline detergent is very effective at removal of organic and inorganic surface contaminants or foreign particle residue from machining processes. The detergent can be used with ultrasonic agitation at 140 °F to clean the TZM molybdenum, machinable tungsten, and 304 stainless steel. A citric-acid-based detergent was also found to be effective at cleaning metal oxides, such as iron oxide, molybdenum oxide, as well as tungsten oxides, at mild temperatures with ultrasonic agitation, and it can be used to replace strong inorganic acids to improve cleaning safety and minimize waste disposal and other environmental problems. The efficiency of removing the metal oxides depends on both cleaning temperature and time.
Correlation of surface morphology with chemical structures of sulfur-passivated GaAs(100) investigated by scanning tunneling microscopy and x-ray photoelectron spectroscopy
Authors: Ha Jeong Sook , Park Seong-Ju , Kim Sung-Bock , Lee El-Hang
Published: July 2002

The surface morphology and chemical structures of GaAs(100) after etching with sulfuric acid and sulfur passivation with ammonium sulfide [(NH4)2Sx] solution were investigated using a scanning tunneling microscope and x-ray photoelectron spectroscopy (XPS). Depending on the chemical treatments which are routinely used in semiconductor processes, the surface morphology was observed to be quite different. The effects of water rinse, HCl treatment, and sulfur treatment time on the surface morphology were studied. Comparison of the surface morphology with chemical structures obtained by XPS was used to explain the evolution of surface morphology during the chemical treatments. In particular, a very flat surface with a surface undulation of ±6 Å was obtained by sulfur passivation with (NH4)2Sx solution after chemical etching of a n-GaAs(100) wafer. These studies enable a better understanding of a correlation of the chemical structures with the surface morphology of the GaAs(100) surface on a nanometer scale.
Interaction of water with clean and gallium precovered Fe(111) surfaces
Authors: Jiang P. , Zappone M. W. , Bernasek Steven L. , Robertson A.
Published: July 2002

The interaction of water with the clean Fe(111) surface and that surface modified by small coverages of Ga has been investigated. Both thermal energy atom scattering and Auger electron spectroscopy have been used to probe this interaction. Water adsorption occurs via a molecular precursor state on these surfaces, and a passivated overlayer is formed on the clean surface exposed to water at 423 K. Small amounts of Ga precoverage, from the decomposition of triethyl gallium, strongly affect the subsequent water adsorption. Preadsorbed gallium reduces the molecular water sticking coefficient and inhibits water dissociation. This effect is proportional to the Ga precoverage. Electron beam irradiation during Auger measurement also strongly affects the water adsorption on the clean and Ga modified surface, and this effect is discussed.
Computational modeling of reactive gas modulation in radio frequency reactive sputtering
Authors: Sekiguchi Hidetoshi , Murakami Takashi , Kanzawa Atsushi , Imai Takahiro , Honda Takuya
Published: July 2002

Computer simulation of reactive sputtering was carried out to explain the enhancement of the deposition rate of complete oxide film using reactive gas flow modulation. The model dealt with the preparation of TiO2 film with a titanium target and oxygen in rf reactive sputtering. The computed results showed good agreements with the experimental data obtained in our previous work. The effects of the flow modulation were elucidated with the calculated timewise variations for partial oxygen pressure and target coverage. The effects of modulation patterns were also evaluated using the simulation.
In situ composition monitoring of InGaAs/InP using quadrupole mass spectrometry
Authors: Celii F. G. , Kao Y.-C. , Liu H.-Y.
Published: July 2002

The use of in situ quadrupole mass spectrometry (QMS) provides the precision necessary for many molecular beam epitaxy (MBE) applications in which the composition of ternary or quaternary epitaxial layers must be controlled. Here we show that the composition of InxGa1−xAs, nearly lattice-matched to InP, can be determined with an uncertainty of Δx∼0.005 in real time (∼4 s averaging time) using QMS in a flux-monitoring mode. Use of an unapertured mass spectrometer extends the range of reflection mass spectrometry into low substrate temperature growth regimes. We also examined system calibration and drift issues. QMS combines routine data acquisition with simple data analysis, and can be easily retrofit on existing MBE systems.
Low energy electron-induced chemistry of biacetyl on Ag(111)
Authors: Pylant E. D. , Hubbard M. J. , White J. M.
Published: July 2002

The electron-induced chemistry of one monolayer (1 ML) of biacetyl (CH3COCOCH3) on Ag(111) has been studied using temperature programmed desorption (TPD), x-ray photoelectron spectroscopy, and Auger electron spectroscopy. Monolayer biacetyl has a sharp saturable parent peak at 180 K, with a tail toward higher temperatures that is attributed to defect sites. No thermal decomposition occurs, confirming that Ag(111) is inert with respect to the breaking of C—C, C=O, and C—H bonds. Nonthermal excitation pathways by which the surface chemistry of biacetyl may be directed were explored by irradiating 1 ML of biacetyl with 50 eV electrons. During irradiation, CO, CH3, ketene (H2O=C=O), and C2H6 desorb. After irradiation, the parent TPD peak area drops with little change in position or shape. The initial total cross section for electron-induced decomposition of biacetyl is 8.0±0.2×10−17 cm+2. As products accumulate, this drops to 4.0±0.2×10−17 cm+2. The cross section has a threshold around 8 eV and rises smoothly with increasing energy. The ionization of biacetyl is proposed as the initiation step.
Metal-dependent Fermi-level movement in the metal/sulfur-passivated InGaP contact
Authors: Kim Y. K. , Kim Sehun , Seo J. M. , Ahn S. , Kim K. J. , Kang T.-H. , Kim B.
Published: July 2002

A high resolution core level photoemission study on the metal contact formed on S-passivated n-InGaP(100) surface reveals that the species produced by the chemical reaction of the deposited metal atoms with the surface atoms induce the gap states responsible for the Fermi level movement. The initial sulfur passivation of n-InGaP(100) surface efficiently reduced the gap states within the band gap and flattened the band bending by 0.6 eV relative to the sputter-cleaned surface. When the metals such as Al(Au) are deposited on the S/InGaP(100) surface, it was found that the deposited Al(Au) reacted with monosulfides resulting in the Al-sulfide (the remaining defective In-polysulfides) which seem to be the origin of the gap states.
High resolution electron energy loss spectroscopy and photoelectron emission microscopy study of Fomblin Y on molybdenum surfaces
Authors: Montei Eric L. , Kordesch Martin E.
Published: July 2002

High resolution electron energy loss spectroscopy was used to measure the vibrational frequencies of in situ deposited films of Fomblin Y on polycrystalline molybdenum. Molecular Fomblin Y vibrations are identified as follows: 35 meV (chain wag); 68 meV, δ(CF3); 88 meV, δ(OCO); 125 meV, ν(CF3−C−CF2); 157 meV, νs(CF3); and 314 meV, 2νs(CF3). The thermal decomposition and electron stimulated decomposition of Fomblin Y on polycrystalline molybdenum have also been investigated. In both cases initial fragmentation of the lubricant molecule proceeds with the disappearance of the vibrational modes at 32 and 88 meV. The decomposition pathways then proceed differently for the respective degradation processes. Thin films of fluorinated lubricants have also been imaged with photoelectron emission microscopy on a rotating cylindrical polycrystalline molybdenum sample. In situ stylus contact is imaged in situ and in real-time. Areas of lubrication are clearly resolved in the image, as are wear tracks formed by contact with the lubricated and clean areas of the surface.
X-ray absorption and Auger electron spectroscopy studies of the quality of diamond thin films grown by the oxy-acetylene flame method
Authors: Gutiérrez A. , López M. F. , García I. , Vázquez A.
Published: July 2002

Diamond thin films grown by the oxy-acetylene flame method have been investigated by x-ray absorption and Auger electron spectroscopies. The quality of the films, defined as the ratio of diamond to non-diamond carbon, has been determined by using both techniques, giving values as high as 95% for the sample grown with the highest C2H2/O2 molar ratio (0.97). Values obtained by Auger electron spectroscopy are slightly lower due to the smaller probe depth of this technique as compared with x-ray absorption spectroscopy (5 Å in the first case against 50 Å in the latter), and to the higher non-diamond carbon content of the surface, as it is expected from the mechanisms of diamond growth by this method.
Microfabricated high intensity discharge lamps
Authors: Khan Babar A. , Pinker Ronald D. , Cammack David A. , Racz Jacqueline
Published: July 2002

Miniaturization of high intensity discharge lamps can lead to cheaper, more efficient, and novel lighting systems for the lighting industry. We are applying micromachining and techniques used for manufacturing integrated circuits, to develop such miniature lamps. We have fabricated electrodeless and electroded high-pressure mercury discharge lamps in quartz substrates using integrated circuit and micromachining techniques, such as photolithography, etching, and wafer bonding. Patterned quartz wafers were bonded together using fusion wafer bonding. The resulting cavities are strong enough to withstand the high pressures (124 atm) and high temperatures (1000 °C) in these lamps. Lamps containing varying amounts of mercury were fabricated to obtain high-pressure discharges in the range of 10–175 atm. The electrodeless lamps were excited by a microwave source, operating at 2.45 GHz and the electroded lamps with a dc voltage. Lamp efficacies over 40 lumens (lm)/W were obtained for the electrodeless lamps and over 50 lm/W for the electroded lamps. These results demonstrate that high-pressure mercury discharges can be sustained in the lamp cavities formed by micromachining techniques. In addition, these cavities are not only hermetically sealed, but can also withstand the high-pressure and high-temperature environment of high-pressure mercury discharges.
How annealing conditions influence the fluctuation of step edges of step bunching on vicinal GaAs(100) formed by annealing in AsH3 and H2 ambient
Authors: Hata K. , Shigekawa H. , Ueda T. , Akiyama M. , Okano T.
Published: July 2002

We report how annealing conditions influence the degree of fluctuation of step edges of step bunching formed by annealing a vicinal GaAs(001) surface in AsH3 and H2 and ambient. At 700 °C, when the partial pressure is high, B steps are straighter than A steps as reported before, however, as the AsH3 partial pressure is decreased, A steps becomes straighter, finally, than the B steps at a partial pressure of 1×10−2 Torr. This reversal of the type of straight step edges can be explained by considering the (2×4)–c(4×4) phase transition. We will also apply the electron counting model established by Pashley in order to explain the experimental results, and by discussing its usefulness and limitations, finally conclude that we cannot determine the stability of steps only by this model.
Scanning tunneling microscopy study of the initial stages of growth of Cu/Si(111): The formation and thermal evolution of the quasi-“5×5” incommensurate structure
Authors: Simão Renata A. , Achete C. A. , Niehus H.
Published: July 2002

The epitaxial growth and the structure of Cu on Si(111)7×7 was investigated by scanning tunneling microscopy (STM) and Auger electron spectroscopy. The so-called quasi-“5×5” incommensurate structure of Cu/Si(111) was observed by STM with atomic resolution only probing the surface empty states with 2.5 V bias. STM analysis showed the “5×5” structure as made out of rounded shaped clusters with periodicity between 5.4aSi and 5.7aSi, where aSi is the lattice parameter of the Si(111)1×1 surface. The quasi-“5×5” incommensurate structure was observed to grow layer by layer, and silicon atoms must be available for reacting with copper to form the two-dimensional (2D) incommensurate layer. The formation of the incommensurate quasi-“5×5” structure at room temperature was only observed on stepped crystals and is considered to be due to the consumption of silicon from the step edges. On 0° miscut Si(111) crystals, the quasi-“5×5” structure is formed upon thermal annealing, which is necessary to break the Si–Si bonds on the terrace. Films of about 2 ML of Cu/Si(111) heated up to less than 800 K present a very interesting and uncommon arrangement. A first, a complete layer of the incommensurate structure is formed and over it a second layer of 2D crystals with irregular interfaces starts nucleating. Over these 2D crystals, more 2D crystals can grow. All the layers are composed of the same clusters and the periodicity of the arrangement can differ from layer to layer. The organized 2D crystals of the quasi-“5×5” layer grow upon annealing, and point defects and dislocations are formed to relieve stress coming from the incommensurability between the layer and the Si(111) substrate. These defect lead to faults in the tiling of the clusters on the quasi-“5×5” layer. The formation of three-dimensional (3D) crystals made out of Cu3Si was also observed on 1–2 ML Cu/Si(111) films annealed to temperatures above 950 K; their electronic structure is completely different from that of the incommensurate “5×5” structure.
Steady-state catalytic C–C bond formation on reduced TiO2 surfaces
Authors: Lusvardi Victor S. , Pierce Keith G. , Barteau Mark A.
Published: July 2002

Previous temperature programmed desorption (TPD) experiments on reduced TiO2 (001) surfaces have demonstrated that alkynes are converted to the corresponding aromatic products with high selectivity. This reaction also represents the first example of catalytic assembly of carbon–carbon bonds on a metal oxide surface in ultrahigh vacuum. Although the catalytic formation of carbon–carbon bonds on single crystal surfaces is a rarity, many important catalytic processes involve carbon–carbon bond formation, and it is therefore worthwhile to consider how such reactions might be studied directly using the tools of surface science. Steady-state experiments involving the production of trimethylbenzene from methylacetylene at low pressure (10−9–10−5 mbar) conditions have demonstrated multiple turnovers of the catalyst and no significant catalyst deactivation at temperatures between 290 and 500 K. A four-step kinetic model is proposed, which contains three nonactivated steps for alkyne adsorption/reaction to form the aromatic, followed by the final step, aromatic desorption. This model captures the measured temperature and pressure dependence of the reaction rate.
Interaction of carbon monoxide with a platinum0.25–rhodium0.75(111) single crystal surface
Authors: Rutten Frank J. M. , Nieuwenhuys Bernard E. , McCoustra Martin R. S. , Chesters Michael A. , Hollins Peter
Published: July 2002

The adsorption of carbon monoxide on a platinum–rhodium alloy (111) single crystal surface was studied with a combination of reflection absorption infrared spectroscopy, thermal desorption spectroscopy, and work function change measurements. It was found that CO shows a pronounced preference for adsorption on Rh sites both at 100 K and room temperature, up to a coverage at which available next-nearest neighbor Rh sites were filled. Adsorption was found to be predominantly in atop sites and only weak bridge bands were detected at 100 and 300 K.
Negative ion densities in chlorine- and boron trichloride-containing inductively coupled plasmas
Authors: Fleddermann C. B. , Hebner G. A.
Published: July 2002

The chlorine negative ion density and the electron density in chlorine- and boron trichloride-containing inductively coupled plasmas were investigated experimentally. Measurements were performed in a GEC reference cell operated in the inductively coupled mode. The chlorine negative ion density was measured as an excess electron density produced by photodetachment of electrons from the negative ions by 266 nm radiation from a frequency-quadrupled Nd:YAG laser. Both the excess electron density and the steady-state electron density were measured using a microwave interferometer. Various gas mixtures were investigated including pure Cl2, pure BCl3, combinations of the two, and combinations of these gases with N2 and Ar. Cl− densities up to 4×1011 cm−3 were measured depending on the gas mixture. The ratio of electron density to Cl− density was as high as 3 in Cl2 mixtures, and up to 5 in BCl3 mixtures. The plasma was probed at lower photon energy (355 nm) to photodetach electrons from other potential negative ions present in the plasma: to within the sensitivity of the measurement (1.3×108 cm−3), no other negative ions such as BClx− or Cl2− ions were detected. Significant interactions between Cl2 and Ar were observed as determined by changes in the Cl− density. The Cl− density also changed when BCl3 was added to Cl2 discharges. Addition of Ar or N2 to Cl2 plasmas had little effect on Cl− density, but nitrogen addition had very dramatic effects when added to BCl3, causing a factor of 2 increase in the Cl− density.
Structure and composition of oxidized aluminum on NiO(100)
Authors: Imaduddin S. , Lad R. J.
Published: July 2002

Aluminum was deposited on stoichiometric NiO(100) in 5×10−6 Torr O2 at substrate temperatures of 250 and 800 °C, and the resulting film interfaces were studied by photoemission [x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS)] and electron diffraction [reflection high-energy electron diffraction (RHEED)]. At 800 °C, RHEED patterns indicate that the growing overlayer interacts with the NiO(100) substrate forming a NiAl2O4 spinel phase. This observation is further supported by XPS and UPS results where peak shapes and relative peak positions correspond to values reported for thick NiAl2O4 films. During film growth at 250 °C, the underlying NiO RHEED pattern becomes diffuse due to formation of an amorphous overlayer. XPS and UPS results indicate that the amorphous film is Al2O3 and that little interaction with the NiO substrate occurs. Postdeposition annealing of the amorphous Al2O3 film to 800 °C in O2 results in a strong reaction at the interface and film crystallization to the NiAl2O4 spinel phase. These results demonstrate that kinetic factors are significant in determining interactions in this system.
Chlorine chemisorption and reaction on the Si(111) surface and its characterization using second-harmonic generation
Authors: Haraichi Satoshi , Sasaki Fumio
Published: July 2002

The electronic states of the Cl-chemisorbed Si(111) surface and the basic characteristics of laser-induced surface reaction of the Si(111)/Cl system have been studied using second-harmonic generation (SHG). The SHG spectrum from the Cl-chemisorbed Si(111) surface showed resonance peaks involving the chlorine-induced electronic states at 1.6 and 2 eV. The laser-induced surface reaction of the Si(111)/Cl system was strongly affected by the interference between the pump and probe beams.
Damage investigation in AlGaAs and InGaP exposed to high ion density Ar and SF6 plasmas
Authors: Lee J. W. , Lee K. N. , Stradtmann R. R. , Abernathy C. R. , Pearton S. J. , Hobson W. S. , Ren F.
Published: July 2002

Both electrical and optical properties of AlGaAs and InGaP were changed by exposure to high density Ar and SF6 plasmas. Capacitance–voltage measurements, photoluminescence, and sheet resistance measurements were used to characterize the degradation of the materials properties as a function of microwave power, rf power, exposure time, and chamber pressure. The results showed the n-type InGaP suffered more damage than the p-type InGaP in Ar plasmas, while the reverse was true for AlGaAs. Annealing of the damaged semiconductors needed high temperature (for example, ∼750 °C for InGaP), which is not suitable for typical III–V semiconductor processing because the high temperature may cause thermal degradation. Electron cyclotron resonance (ECR) SF6 plasmas produce more surface states than reactive ion etching (RIE) (i.e., rf power only). BothC–V measurements and photoluminescence data showed rf power (>50 W) and pressure (<2 mTorr) played important roles in introducing electrical and optical degradation of both AlGaAs and InGaP under ECR conditions, while there was little change as a function of rf power in the RIE case. The minimal overetching time of SF6 plasmas is necessary to avoid severe damage in the materials during opening the windows for the active semiconductors from photoresist, dielectric, or metal layers.
Improved secondary ion mass spectroscopy detection limits of hydrogen, carbon, and oxygen in silicon by suppression of residual gas ions using energy and ejection angle filtering
Authors: Yamazaki Hideyuki
Published: July 2002

A series of secondary ion mass spectroscopy (SIMS) analyses of hydrogen, carbon, and oxygen in silicon has been conducted using a magnetic-sector-type SIMS instrument. The effect of energy and angular filtering of secondary ions on the detection limits was investigated in detail. A Cs+ primary beam was used and H−, C−, and O− negative secondary ions were detected with various sample offset voltages and energy window positions as well as contrast apertures in the secondary ion optics. It was found that the lower detection limits can be achieved by offsetting the sample voltage, by translating the energy window toward higher energies, or by using a smaller contrast aperture in the secondary ion optics. These results indicate that most of the background ions from the residual gases have lower axial energy and higher lateral energy relative to the optical axis.
Repeatability of Si concentration measurements in Si-doped GaN films
Authors: Chi P. H. , Simons D. S. , Wickenden A. E. , Koleske D. D.
Published: July 2002

In high mass resolution secondary ion mass spectrometry Cs+ depth profile measurements of Si in GaN films, the secondary ion intensity ratio of Si-28 to the matrix Ga-69 signal has been observed to be poorly repeatable from measurement to measurement. In some cases the Ga-69 signals from adjacent areas showed different intensity levels even though the Si-28 intensities were similar. Variation of the Ga-69 matrix signal from run to run creates a large uncertainty in the determination of the Si concentration in a GaN film when a relative sensitivity factor is used. The changes in Ga-69 intensity from repeat measurements have been determined to be affected by the instrument vacuum condition, ion energy distribution, sample charging, and type of sample holder used in the measurement.
Installation of a 14 mm vacuum chamber for an undulator in the 1.3 GeV storage ring at Synchrotron Radiation Research Center
Authors: Hsiung G. Y. , Wang D. J. , Shyy J. G. , Hsu S. N. , Hsiao K. M. , Lin M. C. , Chen J. R.
Published: July 2002

An aluminum alloy vacuum chamber, 4 m in length, for an undulator was installed in the 1.3 GeV electron storage ring of the Synchrotron Radiation Research Center in the spring of 1996. The inner cross section of this vacuum chamber is an elliptical shape, 10 mm in height and 80 mm in width. A beam life time of 7 h at 200 mA beam current was quickly achieved after beam cleaning on the new chamber walls. The impact of this new vacuum chamber, before and after the installation, to the storage ring was compared. The injection rate was reduced. The stronger beam loss during the injection was measured. The effects of a small vertical aperture and the effective pumping to the electron beam lifetime are reported. The planning in upgrading the storage ring vacuum system is also described.
Electron field emission from amorphous carbon-cesium alloys
Authors: Bozeman S. P. , Camphausen S. M. , Cuomo J. J. , Kim S. I. , Ahn Y. O. , Ko Young
Published: July 2002

Hard carbon films can be prepared by the condensation of energetic carbon species at and below room temperature. These hydrogen-free films are primarily tetrahedrally coordinated and contain high fractions of sp3 bonding. Field emission from these and other forms of carbon has been considered previously, but it was generally unstable or based on surface treatments that limit their operating conditions. We report electron emission from amorphous carbon-cesium (a-C:Cs) thin films at applied fields as low as 7 V/μm. This emission characteristic is relatively insensitive to surface treatment; films left under ambient laboratory environment for more than six months show these favorable characteristics with no pretreatment. We describe the fabrication process and emission properties of these films.
Electronic structure and electron emission of lithium-containing amorphous hydrogenated carbon films
Authors: Thiele J.-U. , Kania P. , Oelhafen P.
Published: July 2002

Amorphous hydrogenated carbon films were prepared by ion beam deposition. The degree of sp3 coordination and the density of the films were determined from ultraviolet photoelectron valence band spectra and electron energy loss spectra. The films prepared can be described as highly sp3 coordinated (about 80%) and of relatively high density (about 2.3 g/cm3). An indication of a negative electron affinity is found in the valence band spectra. In an attempt to lower the work function, lithium-containing a-C:H films were deposited by lithium evaporation from dispensers during deposition of the a-C:H films. Photoelectron spectra of these films reveal parallel shifts of the core levels and valence band to higher binding energies with respect to the spectra of pure amorphous hydrogenated carbon. These shifts can be attributed to a shift of the Fermi level due to a charge transfer from the lithium to the carbon matrix. From the onset of the valence band spectra at low kinetic energy and from total photoyield spectra the work function of the samples was determined independently. A reduction of the work function from 3.4 eV in pure a-C:H to 2.45 eV in samples containing 35 at. % lithium is observed.
Dynamical aspect of Cl2 reaction on Si surfaces
Authors: Doshita H. , Ohtani K. , Namiki A.
Published: July 2002

The sticking process of Cl2 on the Si(100) surfaces has been studied by employing a molecular-beam method. Initial sticking probabilities, S0, were measured as a function of the incident energy, Ei, and the surface temperature, Ts. The S0 versus Ei as well as S0 versus Ts curves were analyzed with a kinetic model, which includes both a direct sticking channel and a precursor-mediated sticking channel. The physisorption lifetimes were measured as a function of Ts to evaluate the depth of the physisorption well and the preexponential factor for the detrapping rate. The potential structure and the intermediate transition state relevant to the Cl2 sticking on the Si(100) surface were discussed.
Structural, optical, and electrical properties of doped hydrogenated diamond-like amorphous carbon films deposited using the dc saddle-field glow-discharge technique
Authors: Chan W. C. W. , Gaspari F. , Allen T. , Lim P. K. , Moreno E. , Sagnes E. , Manage D. , Szurmak J. , Zukotynski S.
Published: July 2002

The dc saddle-field glow-discharge technique was employed to deposit undoped, phosphorus-doped and boron-doped hydrogenated diamond-like amorphous carbon films. The undoped films were grown using pure methane, while the doped films were grown using methane diluted with dopant gases (phosphine and diborane) in mole fraction ranging from 0.05 to 1×10−5. Secondary ion mass spectroscopy was used to determine the composition of these films. The results showed that various levels of doping in amorphous carbon films can be achieved predictably by using the appropriate mole fraction of dopant gases. The fractions of tetrahedral and trigonal bonds in the films were obtained using x-ray Auger electron spectroscopy. The optical energy gaps of the films were determined from optical absorption measurements. These data were correlated with the doping levels of the films. The electrical conductivities of the undoped and doped samples were determined at temperatures in the range from 225 to 380 °C. The activation energies were determined, and the corresponding conduction mechanisms were examined.
Morphology of nickel and nickel/gold contacts to gallium nitride
Authors: Venugopalan H. S. , Mohney S. E. , DeLucca J. M. , Luther B. P. , Bulman G. E.
Published: July 2002

Changes in film morphology upon annealing Ni and Ni/Au contacts to GaN were examined using scanning electron microscopy and atomic force microscopy. Atomic force microscopy was performed on the GaN surface that was exposed by etching away the metal film. This technique was demonstrated to be a convenient and effective way to evaluate the morphology of the contact/semiconductor interface, rapidly providing spatial information in three dimensions. Metal island formation and a corresponding deep, nonuniform metal penetration into GaN were observed after annealing Ni/GaN and Au/Ni/GaN contacts above 800 and 700 °C, respectively.
Flow rate rule for high aspect ratio SiO2 hole etching
Authors: Chinzei Yasuhiko , Ogata Makoto , Shindo Haruo , Ichiki Takanori , Horiike Yasuhiro
Published: July 2002

Residence time effects on high aspect ratio SiO2 hole etching with a 90% Ar addition to C4F8 have been studied using a planar type neutral loop discharge. An adopted wide-type antenna instead of the original narrow one enabled us to improve uniformity of ion currents, electron densities, and plasma generation over a wide range of pressure. Thus, the residence time (τ) dependence of radical and ion densities, and etched features were investigated for various pressures (P). It was found that the conditions which achieved high aspect ratio features followed a straight line passing an origin in the τ-P diagram. This demonstrated that the high aspect ratio feature etching was determined unequivocally by the adequate flow rate, because the gradient of the line resulted in the reciprocal of the flow rate. On the other hand, at short τ, a large amount of radicals generated due to suppressed recombination produced the excess polymer deposition, causing the “etch stop.” At longer τ, ions and radical densities decreased due to recombination and thus dominated Ar+ ion sputtered the mask resist, forming the tapered feature.
Platinum etching in Ar/Cl2 plasmas with a photoresist mask
Authors: Shibano Teruo , Nakamura Keisuke , Takenaga Takashi , Ono Kouichi
Published: July 2002

Experimental studies of the etching of platinum have been performed with a photoresist mask in Ar/Cl2 plasmas. The etch rate of platinum decreased with addition of Cl2, showing no enhancement of etching by Cl2 addition. Moreover, the etch rate of platinum was found to be independent of substrate temperature in pure Cl2 plasmas. These results indicated that the platinum etching with chlorine-containing plasmas is proceeded mainly by physical sputtering due to incident ions, not by chemical reactions that produce volatile etch products. Thus, in platinum etching with Ar/Cl2 plasmas, the redeposition of nonvolatile etch products was observed to occur on sidewalls of the photoresist mask and platinum pattern; in this situation the etched profiles of platinum were tapered outwardly, because the redeposited films acted as etching masks for platinum. The thickness of deposited films on sidewalls increased with increasing Cl2 concentration, but they were found to be removed by wet treatment with HCl solutions. It was further demonstrated that by optimizing the Cl2 concentration, platinum could be etched without redeposition residues on sidewalls, although the etched profiles still remained outwardly tapered.
Effects of collimator aspect ratio and deposition temperature on copper sputtered seedlayers
Authors: Cooney E. C. , Strippe D. C. , Korejwa J. W. , Simon A. H. , Uzoh C.
Published: July 2002

We have investigated the effects of collimator aspect ratio and deposition temperature of copper seedlayers to improve conformality in aggressive single and dual damascene structures. Collimation filters of various aspect ratios were used to deposit copper seedlayers which were then filled using electrodeposition. It was found that collimators of 1.0 aspect ratio resulted in the best seedlayer conformality, as evidenced by film structure coverage and quality of plating fill. Further, electrical testing using 68 000 via chains also showed the average via resistance to be lowest and the chain opens yield to be highest with the 1.0 aspect ratio condition. Finally, thermal effects on seedlayer conformality were examined by varying the wafer temperature during deposition. It was observed that deposition temperatures of 100 °C and lower resulted in smoother films as compared to seedlayers deposited at 200, 300, or even 400 °C.
Preferential sputtering effects in thin film processing
Authors: Berg S. , Katardjiev I. V.
Published: July 2002

Predicting the partial sputtering yield (sputtered atoms of one element/incident energetic ion) for different elements during sputtering from multielement targets is not a straightforward task. It is commonly observed that ion bombardment of composite targets exhibits preferential sputtering. Such processes are normally studied by computer simulations since theory gives qualitative results only. This work presents a systematic computational study of the major ballistically induced preferential sputtering effects taking place during ion bombardment of composite materials. It is shown that in a vast number of cases ballistic preferential sputtering is a dominant process particularly at moderate temperatures where thermodynamic effects are suppressed. In particular, sputtering from composite targets, resputtering during ion assisted deposition of composite films, sputtering of thin films onto heavy substrates, ion assisted deposition onto different substrate materials, sputter depth profiling, etc. are technological processes shown to commonly exhibit preferential sputtering. It is further shown that a number of sputtering situations exhibit along with the preferential sputtering the so called sputter yield amplification effect. The latter consists in that the partial sputtering yield of a given species is larger than the sputtering yield of the pure material. As a consequence, the sputtering yield of certain materials can be enhanced substantially by introducing small concentrations (a few percent) of impurity species in the target. The work provides ample examples of various situations of academic and technological interest where preferential sputtering and sputter yield amplification occur. The major ballistic mechanisms leading to preferential sputtering and sputter yield amplification are also briefly discussed.
Unbalanced magnetron sputtered carbon composite coatings
Authors: Zeng X. T.
Published: July 2002

Carbon composite coatings combine high hardness and toughness, good adhesion, low friction coefficient, and low wear rate. These properties make it a good candidate for tribological applications. Previous studies commonly used hydrocarbon gases to produce metal (Ti, W, Cr) doped amorphous carbon coating (M–a:C–H) and sputtered Ti–TiN or TiCN as supporting layers. Relatively high hardness and good adhesion could be obtained by optimizing the composition and structure of the supporting layers and by increasing the doping level. However, the friction coefficient increased with the doping level, which resulted in high wear rates. This article reports on the deposition of carbon composite coatings on high speed steel substrates using simultaneous unbalanced magnetron sputtering of metallic and graphite targets. The coating consists of a graded Cr–Ti–N alloyed interlayer and a Cr-containing carbon composite surface layer. Raman spectroscopy, scanning electron microscopy, nanoindentation, scratch tests and pin-on-disk wear tests against alumina were used to characterize the properties of the coatings. Low friction coefficients (below 0.1 at an air humidity of 40±10 RH%), high hardness (18±3 GPa) and good adhesion (55 N in lower critical load) were found, leading to a low normalized wear rate of about 5×10−8 mm3 N−1 m−1, which is substantially lower than those of the metallic nitride coatings such as TiN and CrN. The superior wear resistance coupled with good adhesion implies that the carbon composite coatings may be ideal for sliding wear applications.
Tribological modification of aluminum by electron-cyclotron resonance plasma source ion implantation
Authors: Popovici D. , Bolduc M. , Terreault B. , Sarkissian A. H. , Stansfield B. L. , Paynter R. W. , Bourgoin D.
Published: July 2002

Pure aluminum was implanted with 30 keV oxygen ions by means of electron-cyclotron resonance plasma based ion implantation. Virgin and treated samples were investigated by Auger electron microscopy and x-ray photoelectron spectroscopy to determine the depth distribution and chemical interactions of oxygen near the surface. The results are consistent with precipitation of oxygen and the formation of particles of Al2O3. Several samples were subsequently annealed at temperatures of up to 550 °C for 30 min. As-implanted and annealed specimens were characterized using an ultralow load nanoindentation test system. The results indicated an increase in aluminum hardness by a factor of 2 to 3; annealed samples were found to have lower hardness values than the as-implanted samples. A decrease of the experimental hardness with depth correlates with the concentration of implanted oxygen. This is consistent with the assumption that the improvement in strength is due to the formation of nanoprecipitates whose density increases with the oxygen implantation.
Long term behavior of an axial-symmetric transmission gauge
Authors: Akimichi H. , Takeuchi K. , Tuzi Y. , Arakawa I.
Published: July 2002

Long term behavioral characteristics of an axial symmetric transmission gauge, such as the outgassing rate and sensitivity factor, were examined over a period of 3500 h. It was found that the outgassing rate and the gain of the continuous-dynode-type electron multiplier, which was used for ion detection, were the main factors which determined the gauge characteristics. The outgassing rate of the multiplier as obtained from the manufacturer was very high but decreased to the acceptable level after about two days of continuous operation in high and ultrahigh vacuum. The sensitivity factor of the newly fabricated gauge was very high but decreased with the decrement of the outgassing rate to the quasi-stationary state at which the factor tended to decrease gradually with operating time. When the gauge was exposed to atmospheric air, the sensitivity factor increased temporarily but decreased within the duration of the typical bakeout process. The increment was assumed to be due to the adsorption of gases on the multiplier surface. The lifetime of the electron multiplier estimated from the decay rate of the sensitivity factor during the acceleration test by hydrogen is about nine years for the operation of the gauge in the 10−10 Pa region. It was also found that the gain of the multiplier was proportional to the soft x-ray background signal. The gradual variation in the sensitivity factor of the gauge caused by that of the gain of the multiplier over the period of operation can be compensated by this relation.
Pressure wave propagation by gas expansion in a high vacuum tube
Authors: Takiya Toshio , Higashino Fumio , Terada Yukihiro , Komura Akio
Published: July 2002

In this article we describe an unsteady tube flow model which accounts for the effect of contracted flow around the entrance orifice of the tube which was developed with the aim of preventing vacuum hazards at scientific experimental facilities. Setting an atmospheric pressure drop between the outside and inside of the vacuum tube makes the model applicable to high vacuum, although the model is based on continuous fluid dynamics. We installed an orifice on the inlet end of the tube in the model, and investigated the orifice aperture effect on the propagation velocity of pressure waves.
Outgassing tests on materials used in the DIII–D magnetic fusion tokamak
Authors: Holtrop K. L. , Hansink M. , Kellman A. G.
Published: July 2002

In order to achieve high performance plasma discharges in the DIII–D magnetic fusion tokamak, impurity levels must be carefully controlled. Since first wall materials can desorb volatile impurities during these discharges, it is important to characterize and control the outgassing of these materials. An outgassing chamber was built to measure the outgassing properties of various materials used in the DIII–D vessel. The results of pump-down tests performed on ATJ graphite, thin Grafoil® gaskets, and MgO coaxial cables will be presented. In addition to outgassing tests, it was desired to study the behavior of the materials at temperatures up to 400 °C, which is the maximum temperature to which the DIII–D vessel is baked. The station was modified to include independent heating control of the sample and a simple load-lock chamber.