bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and hydrogenation of formate on Cu(100) at high pressures
Authors: Chorkendorff I. , Taylor P. A. , Rasmussen P. B.
Published: July 2002

In the commercial methanol catalyst, which consists mainly of copper particles highly dispersed on ZnO, copper is believed to be the active component. In order to address this role, the fundamental steps of the methanol synthesis have been investigated on a well defined Cu(100) single crystal under UHV conditions using x-ray photoelectron spectroscopy, low-energy electron diffraction, high-resolution electron energy-loss spectroscopy, temperature programmed desorption and high pressure facilities. The adsorption and desorption of H2, CO2, and HCOO (formate) were studied and it was proved that formate, which is believed to be an important intermediate in the methanol synthesis, can indeed be formed by exposing the Cu(100) crystal to a 2.3 bar mixture of H2 and CO2. The kinetics of this reaction step were studied in detail as a function of temperature. The activation energy was determined to be 55.6 kJ/mol. Further hydrogenation of the formate was found to be possible under high pressure conditions. The activation energy for this process was found to be 82 kJ/mol.
Semiconductor surface and interface dynamics from tight-binding molecular dynamics simulations
Authors: Schenter Gregory K. , LaFemina John P.
Published: July 2002

Tight-binding molecular dynamics simulations have been performed to compute the bulk, (110) surface, and (110)-p(1×1)-Sb(1 ML) interfacial atomic vibrational spectra for GaAs and InP. The same tight-binding total energy model that successfully described the static surface and interfacial atomic and electronic structure for these systems is utilized in the molecular dynamics simulations. The results for the bulk vibrational energies are in semiquantitative agreement with experimental results, displaying approximately the same level of variance as other model computations. Moreover, these simulations are used to examine the effects of anharmonicity in the system by investigating the temperature dependence of the vibrational spectra. The (110) surface vibrational energies are in quantitative agreement with the scattering data, and a comparison of the results for GaAs(110) and InP(110) supports the existance of a surface vibrational mode that is characteristic of the relaxed (110) surface, and whose energy is similar for each zinc blende (110) surface. Last, the computed vibrational energies for the III–V(110)-p(1×1)-Sb(1 ML) interface are in semiquantitative agreement with Raman scattering data and illustrate the effects of the overlayer binding on the surface vibrational spectrum.
Interaction of water, oxygen, and hydrogen with TiO2(110) surfaces having different defect densities
Authors: Pan J.-M. , Maschhoff B. L. , Diebold U. , Madey T. E.
Published: July 2002

We have studied the stoichiometric (annealed in oxygen), the slightly oxygen-deficient (annealed in vacuum), and the highly defective (sputtered with Ar+) TiO2(110) surfaces and their reactivities to molecular oxygen, molecular water, and 50-eV hydrogen ions using x-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectroscopy (LEIS). The use of isotopically labeled 18O enables us to distinguish adsorbed oxygen from lattice oxygen, and the concentration of surface oxygen vacancies is titrated by 18O2 adsorption. LEIS (1-keV He+) is used to analyze the chemical composition of the outermost surface layer before and after 18O2 and H218O exposure. Water adsorbs on both stoichiometric and slightly O-deficient surfaces [with oxygen vacancies ∼0 and 0.08 monolayer (ML), respectively] at room temperature. There is little or no dependence of saturation water coverage (lower limit of ∼0.07 ML for both surfaces) on the concentration of surface oxygen vacancies. On the highly defective surfaces, the saturation water coverage increases to a lower limit of 0.15 ML and the saturation 18O coverage increases to 0.4 ML. The interaction of hydrogen with the stoichiometric surface creates defect states that can be observed by XPS and by subsequent adsorption of 18O.
Role of particle contamination in the corrosion of electronic materials and devices
Authors: Frankenthal R. P. , Lobnig R. , Siconolfi D. J. , Sinclair J. D.
Published: July 2002

Under many circumstances, particularly in indoor environments, ionic dust particles may contribute significantly to the corrosion of integrated circuits, electronic devices, printed circuit boards, and other electronic assemblies. Yet fundamental studies of the role of particles in corrosion processes are rare. In the first part of this article, several types of contaminants and their sources are discussed. The remainder of the paper is devoted to the effects of ionic particulates on the corrosion of electronic materials and devices. Examples of electrolytic corrosion are given. An overview of two on-going research projects that involve submicron-sized salt particles is then presented. The generation, characterization, and deposition of submicron-sized particles of (NH4)2SO4 are described. Results from studies of the effect of these particles on the atmospheric corrosion of copper are presented. Last, a submicron dust particle exposure chamber for life testing integrated circuits, components, printed wiring boards, and other electronic assemblies is described.
Ultrahigh vacuum metalorganic chemical vapor deposition growth and in situ characterization of epitaxial TiO2 films
Authors: Chen Samuel , Mason M. G. , Gysling H. J. , Paz-Pujalt G. R. , Blanton T. N. , Castro T. , Chen K. M. , Fictorie C. P. , Gladfelter W. L. , Franciosi A. , Cohen P. I. , Evans J. F.
Published: July 2002

In a two-chamber ultrahigh vacuum system, epitaxial TiO2 thin films have been deposited by metalorganic chemical vapor deposition on single crystal oxide substrates over a temperature range of 250–800 °C, using titanium (IV) isopropoxide as the precursor. During the initial stage of epitaxial film deposition, the growing surface quickly planarized and the film’s orientations was determined by the substrate structure. This substrate influence is manifested in the growth of anatase (the low temperature phase of TiO2) on (001) SrTiO3, at high deposition temperatures (800 °C), whereas on either (0001) or (11̄02) Al2O3 sapphire, epitaxial rutile (the high temperature phase) is formed. In situ Auger electron spectroscopy analyses, before and after growth, revealed a film composition identical to that of a bulk TiO2 standard. No carbon contamination was detected in films grown throughout the deposition temperature range. The decomposition mechanism of this precursor that leads to the absence of incorporated carbon in the deposited film is discussed. X-ray diffraction confirmed the film crystallinity and the structural orientation between the film and substrate. Cross-section transmission electron microscopy showed an abrupt interface between the film and substrate. High tilt angle scanning electron microscopy revealed that the surface of the films became increasingly smooth with increasing growth temperatures. Conditioning the substrate surface at high temperatures in an O2 environment improved the structural quality and surface smoothness of the subsequently deposited films.
Synchrotron radiation photoemission analysis of ArF laser deposited tin oxide
Authors: Larciprete R. , Borsella E. , De Padova P. , Mangiantini M. , Perfetti P. , Fanfoni M.
Published: July 2002

The composition of films deposited by dissociating pure tetramethyltin (TMT) or TMT/O2 mixtures at 193 nm, was monitored by ‘‘in situ’’ Auger spectroscopy. The presence of C contamination, which was considerable in films obtained from the pure organometallic, was greatly reduced by the occurrence of oxidation and carbon-free films were achieved when the gas phase concentration of TMT was sufficiently small. The dependence of the O/Sn Auger electron spectroscopy peak-to-peak height ratio on the p(O2)/p(TMT) ratio in the precursor mixture showed a saturation for large concentration of oxygen. The surface properties of the tin oxide films were investigated by synchrotron radiation ultraviolet photoemission spectroscopy (UPS). To this aim samples were transferred to a synchrotron radiation facility, without any exposure to air and kept in dynamical high vacuum. The UPS demonstrated that the films were essentially made of SnO2: in fact the valence band exhibited the typical features of SnO2 and the analysis of the 4dSn core levels demonstrated that all metal atoms were oxidized, since no contribution to the peak shape due to metallic tin was found. A weak emission from the band gap region indicated the presence of oxygen vacancies.
Thermal desorption of CO and H2 from degassed 304 and 347 stainless steel
Authors: Rezaie-Serej S. , Outlaw R. A.
Published: July 2002

Thermal desorption spectroscopy (TDS), along with Auger electron spectroscopy, was used to study the desorption of H2 and CO from baked 304 and 347 stainless-steel samples exposed only to residual gases. Both 347 and 304 samples gave identical TDS spectra. The spectra for CO contained a sharp leading peak centered in the temperature range 410–440 °C and an exponentially increasing part for temperatures higher than 500 °C, with a small peak around 600 °C appearing as a shoulder. The leading peak followed a second-order desorption behavior with an activation energy of 28±2 kcal/mol, suggesting that the rate-limiting step for this peak is most likely a surface reaction that produces the CO molecules in the surface layer. The amount of desorbed CO corresponding to this peak was ∼0.5×1014 molecules/cm2. The exponentially rising part of the CO spectrum appeared to originate from a bulk diffusion process. The TDS spectrum for H2 consisted of a main peak centered also in the temperature range 410–440 °C, with two small peaks appearing as shoulders at ∼500 and 650 °C. The main peak in this case also displayed a second-order behavior with an activation energy of 14±2 kcal/mol. The amount of desorbed H2, ∼1.9×1015 molecules/cm2, appeared to be independent of the concentration of hydrogen in the bulk, indicating that the majority of the desorbed H2 originated from the surface layer.
Permeation of argon, carbon dioxide, helium, nitrogen, and oxygen through Mylar windows
Authors: Mapes M. , Hseuh H. C. , Jiang W. S.
Published: July 2002

In secondary beam lines in the alternating gradient synchrotron (AGS) at Brookhaven National Laboratory, low mass vacuum windows are used to reduce background radiation near particle detectors. These windows are fabricated using Mylar (a registered trademark of Dupont) films and are generally made as thin as possible. Mylar films as thin as 0.002 in. have been used as vacuum windows ranging in size up to 36 in. ×76 in. When using Mylar for low mass window applications, permeation must be considered to achieve system design pressures. The permeation of several different gas species through both Mylar and aluminized Mylar films with thicknesses of 0.002 in. and 0.005 in. has been studied. Testing was performed under high vacuum and a quadrupole mass spectrometer was used to identify and quantify gas species during the study. The permeability of argon, carbon dioxide, helium, nitrogen, and oxygen were determined for Mylar from 20 °C up to 90 °C.
Pressure measurement by laser ionization: Direct counting of generated ions by imaging of their spatial distribution
Authors: Ichimura S. , Sekine S. , Kokubun K. , Shimizu H.
Published: July 2002

The spatial distribution of ions generated by nonresonant multiphoton ionization of Xe and H2 with second harmonics of a picosecond YAG laser was imaged with a new detection system. Ions were observed as bright spots on a microchannel plate (MCP) intensifier, and they appeared on a straight line, reflecting the ion generation along a laser beam path. The size of the ionization region, which has a spindle shape, was estimated from the image. The maximum diameter of the ionization region was ∼60 μm, and the length was 3.6 mm for a Xe gas pressure of 5×10−5 Pa and an incident laser energy of 10 mJ/pulse for our measurement system. The size depended on the incident laser energy, and on the lens assembly used for the focusing of the laser beam. The possibility of relative pressure measurement by counting of the bright spot on the MCP intensifier was also investigated.
Correction of dead time effects in time-of-flight mass spectrometry
Authors: Stephan T. , Zehnpfenning J. , Benninghoven A.
Published: July 2002

This is a report on the feasibility of dead time correction of single-ion-counting data in time-of-flight mass spectrometry. Here signals vary on a time scale similar to the dead time of the detector. The correction of dead time effects based on the Poisson distribution is practicable for single peak integrals. This leads to a sufficient correction for most applications like the measurement of isotope, element, and molecule ratios or ion imaging. Even the exact dead time correction of total mass spectra is possible but requires the precise knowledge of the dead time. This is, in general, not a fixed time interval but has to be described by a probability function.
Deposition of AlN at lower temperatures by atmospheric metalorganic chemical vapor deposition using dimethylethylamine alane and ammonia
Authors: Kidder J. N. , Kuo J. S. , Ludviksson A. , Pearsall T. P. , Rogers J. W. , Grant John M. , Allen Lynn R. , Hsu Sheng Teng
Published: July 2002

We have studied an atomic layer growth process using amine–alane adducts as precursors for depositing aluminum nitride (AlN) thin films at temperatures between 300 and 800 K. The atomic layer deposition process was carried out in a horizontal metalorganic chemical vapor deposition (MOCVD) reactor at atmospheric pressure using H2 as a carrier gas. Dimethylethylamine alane [(CH3)2(C2H5)N:AlH3] and ammonia (NH3) were used as source gases and sequentially flowed into the reactor with a hydrogen flush between each source gas step. Thin films were deposited onto Si(001) and Al2O3(0001) substrates that were heated on a susceptor by radio frequency induction. Analysis by x-ray photoelectron spectroscopy and x-ray diffractometry revealed deposition of AlN at temperatures as low as 613 K. Processing at lower temperature (510 K) resulted in no detectable AlN deposition while processing at higher temperature (783 K) resulted in nitridation of the Si(001) surface to Si3N4 but no detectable AlN deposition on Si(001) or Al2O3(0001).
Substrate bias effects in high-aspect-ratio SiO2 contact etching using an inductively coupled plasma reactor
Authors: Westerheim A. C. , Labun A. H. , Dubash J. H. , Arnold J. C. , Sawin H. H. , Yu-Wang V.
Published: July 2002

High-aspect-ratio sub-half-micron contacts were etched in SiO2 using a high-density C2F6 plasma generated by an inductively coupled, low-pressure reactor. As expected, oxide and resist etch rates increased with increasing bias. The aspect ratio (depth/width) dependence of the etch process was also shown to vary with bias power; at high bias power conditions, reactive ion etching (RIE) lag was observed, where high-aspect-ratio features etch slower than low-aspect-ratio features, and at low bias powers, inverse RIE lag was observed. Increasingly vertical sidewall angles and increasing microtrenching depth were also observed for higher rf bias conditions on contacts, trenches, and steps. Topography modeling shows that the microtrench profiles are consistent with specular ion reflection from sidewalls and the increase in their depths with rf bias is consistent with the energy-dependent etching yields in high-density, fluorocarbon plasma etch chemistries reported by Oehrlein et al. [J. Vac Sci. Technol. A 12, 323, 333 (1994)].
Dynamics of particulates in the afterglow of a radio frequency excited plasma
Authors: Yeon Chung-Kyu , Kim Jung-hun , Whang Ki-Woong
Published: July 2002

The formation of a particulate cloud was examined by the laser light scattering method with the diamondlike carbon film deposited wafer on the cathode in a radio frequency (rf) excited Ar plasma. A laser sheet and a medium speed camera were used to obtain the time-resolved images of the moving particulates in the afterglow. When the rf power is turned off, the direction and the characteristic time of the particulate density decaying are highly dependent on experimental conditions such as electrode temperature and gas flow rate. The particulates move to the cold surface with a constant velocity due to the balanced thermophoretic force and the viscous drag force by background neutral molecules. The drift velocity of the particulates is linearly dependent on the temperature difference between the electrodes, and a simplified model is used to explain the experimental result. The dependence of the afterglow particulate behavior on experimental conditions suggests that proper control of the temperature profile and the gas flow direction in the plasma reactor can reduce particulate contamination on the substrate.
Chemical shifts and optical properties of tin oxide films grown by a reactive ion assisted deposition
Authors: Choi Won-Kook , Jung Hyung-Jin , Koh Seok-Keun
Published: July 2002

Highly oriented nonstoichiometric tin oxide thin films were grown by a reactive ion assisted deposition onto Si(100) and glass substrates at room temperature as a function of relative ion (O)/atom (Sn metal) arrival ratio, and concurrently the deposited ion energy per atom (eV/atom) were changed from 10 to 100 eV/atom. As-deposited tin oxide films show preferred orientation along the SnO2〈101〉 axis and the x-ray diffraction peak intensity appears maximum at an average energy of about 50 eV/atom. From quantitative Auger electron spectroscopy, characteristic transitional Auger peaks of Sn metal MNN transitions were shifted to lower kinetic energies by 4–6±1.0 eV as the Sn4+ component becomes dominant in the deposited tin oxide films and the position of O KL1,2L2,3 transition line was also shifted to lower kinetic energy by 1–2±1.0 eV as the composition of deposited tin oxide films were changed from SnO to SnO2, respectively. On the basis of a tin 3d core level and O 1s spectra analysis by x-ray photoelectron spectroscopy, the sizable chemical shift of different valencies between stannous tin (Sn2+:SnO) and stannic tin (Sn4+:SnO2) was 1.0±0.02 eV and that of O 1s was 0.87±0.02 eV, and those values show larger shifts than previously reported ones. The refractive index n of as-deposited tin oxide films was evaluated from an ellipsometer, and spectrophotometric transmittances were measured in the wavelength range of 200–800 nm. In the luminous range, the refractive index varied from n=2.36 to 2.04 as oxygen contents increased.
Atomic nitrogen production in a high efficiency microwave plasma source
Authors: McCullough R. W. , Geddes J. , Croucher J. A. , Woolsey J. M. , Higgins D. P. , Schlapp M. , Gilbody H. B.
Published: July 2002

A high-resolution spectroscopic study of a high efficiency nitrogen atom beam source, which provides dissociation fractions of up to 0.67 and is suitable for the treatment and doping of materials, has been used to identify and study atomic and molecular emissions from the source plasma. The ratio of the intensity of selected atomic and molecular emission lines has been compared with the N/N2 concentrations in the beam measured using a quadrupole mass spectrometer. Our observations show that spectroscopic measurements can be used to determine the N atom content of the beam. This technique is likely to be valuable in applications where nitrogen beams are used for the growth and treatment of materials where other means of characterization are precluded.
Direct observation of β-TaH phase precipitation in tantalum–hydrogen solid solution
Authors: Chen C. L. , Zhou D. S. , Mitchell T. E. , Ye H. Q.
Published: July 2002

An ordered β-Ta2H tantalum hydride precipitate and a disordered α-Ta–H solid solution matrix have been observed directly by field ion microscopy and analyzed by atom probe analysis. The ordered and disordered field ion images have been explained by the electronic transition rate in the theory of field ionization. On the other hand, we found surprisingly that the field evaporation voltage dramatically decreased to approximately one half of its original evaporation voltage as the evaporation of the precipitate moves toward the phase boundary, which may due to the effects of the interface energy.
Miniature peristaltic vacuum pump for use in portable instruments
Authors: Piltingsrud Harley V.
Published: July 2002

This article describes the development, construction, and performance characteristics of a small, low-mass, low-power-consumption vacuum pump for use at pressures down to 5×10−2 Torr. The pump is based on a peristaltic tubing pump modified to overcome rapid tubing deterioration problems normally encountered when peristaltic pumps are used for vacuum pumping. Typical uses of the pump are for portable scientific and engineering instruments requiring pressure and flow characteristics compatible with the pump. These include the backing of high-vacuum pumps, rough-pumping vacuum systems used with certain ion and cryosorption vacuum pumps, and interstage pumping of membrane separators.
Behavior of Si atoms in a silane electron cyclotron resonance plasma at high dissociations
Authors: Yamamoto Y. , Hori M. , Goto T. , Hiramatsu M.
Published: July 2002

The Si atom density at the 3p2 3P2 level in electron cyclotron resonance SiH4/H2 and SiH4/Ar plasmas was measured as a function of total pressure from 0.6 to 3.3 Pa at a microwave power of 400 W and a SiH4 flow rate of 6 sccm using ultraviolet absorption spectroscopy. Parent SiH4 molecules in SiH4/H2 and SiH4/Ar plasmas were found to be considerably dissociated using infrared diode laser absorption spectroscopy. The Si atom density in the SiH4/H2 plasma was larger than that in the SiH4/Ar plasma, which was quite different from that in the capacitively coupled rf SiH4 plasmas. Behaviors of the Si atom density are discussed on the basis of the rate equation for Si atoms. It was concluded from a comparison of the behavior of the density and generation rate of Si atoms that the diffusion loss was comparable to the reaction loss in the removal process of Si atoms in the case of H2 dilution, while the reaction loss was dominant in the case of Ar dilution.
Aspect ratio dependent etching on metal etch: Modeling and experiment
Authors: Xie Richard Jun , Kava Joseph D. , Siegel Mark
Published: July 2002

In process development for submicron and sub-half-micron metal etch, etching rates have been observed to depend on aspect ratio of microstructures. Three major mechanisms, including neutral transport, ion transport, and inhibitor deposition into high aspect ratio features and on open areas, were modeled to interpret the aspect ratio dependent etching (ARDE) phenomena and to explain the experimental results. It is found that the ARDE is mainly controlled by the ion to neutral flux ratio and ion to inhibitor flux ratio. The increase of ion to neutral flux ratio will exaggerate the normal reactive ion etching (RIE) lag. The decrease of ion to inhibitor flux ratio tends to make a reverse RIE lag. Both model and experiment indicate that the appropriate ion to neutral flux ratio and ion to inhibitor flux ratio are the key in minimizing the ARDE and reducing the microscopic nonuniformity.
Electrical characterization and modeling of a dust forming plasma in a radio frequency discharge
Authors: Boufendi L. , Bouchoule A. , Hbid T.
Published: July 2002

In this article we focus on the time evolution of macroscopic and microscopic properties of a dust forming plasma in a silane–argon low pressure radio frequency (rf) discharge. The time evolution of electron density, ion density, dust particle concentration, and the current density were recorded in a low pressure (0.1 Torr) rf Ar–SiH4 discharge. From these data and optical emission spectroscopy simultaneous measurements, the time evolution of the electron mean energy and the particle mean charge are determined. Together with previous experimental data concerning the nucleation and growth of dust particles, a complete experimental set of microscopic and macroscopic data is available and it is compared to a theoretical model including both particle growth and dusty discharge parameters. A clear representation of this closely coupled time evolution of the particles’ formation and plasma properties is given. It includes the nucleation and coagulation phenomena for particles, and the strong increase of the rf electric field in the plasma volume and the increase of the excitation rates of electrons.
Influence of O+2 energy, flux, and fluence on the formation and growth of sputtering-induced ripple topography on silicon
Authors: Vajo John J. , Doty Robert E. , Cirlin Eun-Hee
Published: July 2002

The formation of ripples on Si(100) by O+2 sputtering at an angle of incidence of 40° and energies from 1 to 9 keV has been studied using secondary ion mass spectrometry and scanning electron microscopy. At 1 keV no ripples are observed. Between 1.5 and 9 keV ripples are observed oriented perpendicular to the ion direction with average wavelengths that increase, from ∼100 to 400 nm, approximately linearly with O+2 energy. Two-dimensional fast Fourier transforms of secondary electron images are used to investigate the frequency distribution of the ripples. For the conditions studied, the distributions of frequencies appear approximately Gaussian. At 1.5 keV, the wavelength and growth rate with sputtered depth are independent of flux for fluxes from 15 to 150 μA/cm2. Accompanying ripple formation are changes in secondary ion yields. The changes occur abruptly at depths that increase, from ∼0.2 to 5.6 μm, with O+2 energy. In contrast, sputtering with Ar+ at 1.5 and 7 keV to depths 5–10 times those that produce ripples with O+2 produce no observable topography. These results are discussed using several existing theories for ripple formation and growth. Ripple growth and the variations in secondary ion yield are modeled by accounting for the change in local angles of incidence as the ripples grow. This model describes well the variation in secondary ion yield assuming an exponential growth rate. Ripple formation is discussed in terms of a balance between roughening (by sputtering-induced surface stress and by the dependence of the sputtering yield on surface curvature) and smoothing (by both diffusion and ion mixing). Variation in ripple wavelength with energy is not simply explained by these theories. Surface smoothing by cascade ion mixing can, however, make the wavelength, as observed, independent of ion flux. Finally, the possibility of formation of ripples by phase separation within the SiOx surface layer is discussed.
Photoreactions of methyl iodide multilayers on the TiO2(110) surface
Authors: Kim Seong Han , Briggman Kimberly A. , Stair Peter C. , Weitz Eric
Published: July 2002

The reactions following 257 nm photolysis of CH3I multilayers on TiO2(110) at 90 K were investigated using quadrupole mass spectrometry. The observed photofragments that desorb from the surface are CH4, C2H6, I2, CH2I2, and C2H5I. The linear dependence of the methane and ethane on laser fluence and the absence of a kinetic isotope effect in the formation of methane are consistant with the reaction mechanism in which the hot methyl photofragments react with parent molecules. The relative ratios of photoproducts are different from those observed in the photolysis of gas, liquid, and solid phases and from those observed for CH3I multilayers on a metallic surface at lower fluence.
Surface segregation of silicon in platinum(111)
Authors: Diebold Ulrike , Zhang Lanping , Anderson John F. , Mrozek Pawel
Published: July 2002

We present a study of an ultrathin surface layer of platinum silicide formed on a Pt(111) crystal as a result of surface segregation of Si and Ca trace impurities. The structure and composition of this surface compound is investigated with low energy He+ ion scattering, (LEIS), x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Si surface segregation onto Pt(111) is thermally activated; annealing at temperatures between 750 and 1100 K results in the formation of a surface silicide. The highest Si coverage that can be reached is 0.4 monolayers; the Ca coverage at saturation is below 0.02 monolayers. The enthalpy of Si segregation is found to be −(105±30) kJ/mole. A well-ordered (√19×√19)R23.41° or |−23 25| structure is observed by LEED and STM; the amount of surface area covered with this structure is proportional to the Si coverage measured with LEIS. At low annealing temperatures up to 800 K, two domains coexist with |−23 25| and |−32 35| orientations, but only the first one is stable at Si saturation coverage. No large relaxations of substrate interatomic distances are detected upon formation of the overlayer.
Preparation of ZnGa2O4:Mn phosphor thin films as emitting layers for electroluminescent devices
Authors: Minami Tadatsugu , Kuroi Yoshihiro , Takata Shinzo
Published: July 2002

ZnGa2O4:Mn thin films as the emitting layer in thin-film electroluminescent (TFEL) devices have been prepared by rf magnetron sputtering and low-pressure chemical vapor deposition (CVD). The as-deposited thin films, regardless of preparation methods, were ZnGa2O4 which crystallized with a spinel structure. A green EL emission was realized in TFEL devices using as-deposited ZnGa2O4:Mn thin films as the emitting layer and a thick BaTiO3 ceramic sheet as the insulating layer. Maximum luminances of 0.7 and 7.6 cd/m2 were obtained in TFEL devices using as-deposited ZnGa2O4:Mn thin films prepared by the sputter and CVD techniques, respectively, when driven by a sinusoidal wave voltage at 1 kHz. In addition, a maximum luminance above 600 cd/m2 was obtained in TFEL devices using ZnGa2O4:Mn thin films postannealed at a temperature of about 1000 °C, regardless of preparation methods. The improvement of EL characteristics by postannealing ZnGa2O4:Mn thin-film emitting layers was mainly attributed to an improvement in the crystallinity of the emitting layers.
Enhanced bioadsorption characteristics of a uniquely nanostructured thin film
Authors: Stahl J. B. , Debe M. K. , Coleman P. L.
Published: July 2002

At the two previous AVS symposia we reported on both the growth mechanism and the structural characteristics of a uniquely nanostructured organic thin film consisting of an extremely dense (∼50/μm2), random array of crystalline whiskers (∼50 nm×2 μm), uniformly oriented with their long axes normal to the substrate. We have found that by simply metal coating the whiskers, the unique physical morphology of the surface provides significantly enhanced protein adsorption characteristics. Using radio-labeling techniques, the adsorption kinetics of Protein A, human IgG and BSA were measured for two buffer solutions and four types of meal whisker coatings. The best metal coating, Pt, adsorbs up to 70 times as much protein as the control substrates. The absolute protein binding levels are ∼10 μg/cm2, with 85%–95% being tightly bound and viable. The speed of binding is also very rapid, reaching ∼50% coverage in 15 min and full coverage in 2 h, without vortexing. The nanostructured films are easily produced in large area formats and the exposed whisker surfaces can be readily functionalized.
Total reflection x-ray fluorescence analysis of planarized semiconductor product wafers
Authors: Lavoie M. A. , Adams E. D. , Miles G. L.
Published: July 2002

The use and effectiveness of total reflection x-ray fluorescence (TXRF) have been widely reported. The application of this technique in semiconductor fabrication has become popular and several instrument vendors now make equipment optimized for this particular purpose. Because sample surfaces must be optically flat in order to achieve the total reflectance condition, the majority of the work in investigating semiconductor processing is performed on monitor wafers. The use of TXRF for in-line process control, therefore, has been limited to silicon or dielectric film substrates, either on the surface or the backside of the wafer. This article details the use of TXRF analysis for monitoring the contamination present on production-wafer surfaces, after planarization techniques have been used. The wafer surfaces at several of these planarization steps meet the criteria for the application of the TXRF technique using the normal operating conditions of the TXRF instrument. This technique can be used as process-monitoring tool to study wafer surfaces for particular contaminants that affect wafer yield. TXRF is being used on IBM’s state-of-the-art DRAM and logic circuits.
Phase development in sputter deposited titanium dioxide
Authors: Wiggins M. D. , Nelson M. C. , Aita C. R.
Published: July 2002

We report the formation of highly oriented rutile titanium dioxide films. Films of a primarily amorphous nature were grown on fused silica by rf reactive sputter deposition using a Ti target and rare gas (Ne or Ar)-O2 discharges. Post-deposition annealing was done at 350–1150 °C in air for 60 minute intervals, followed by an air cool. The phase mixture of the as-deposited films, determined by x-ray diffraction, was of two types: (I) amorphous + rutile + anatase, or (II) amorphous + rutile. All phases were highly oriented with (110) rutile planes and (101) anatase planes parallel to the substrate. Upon annealing, the amorphous component of films containing no anatase transformed entirely to rutile, even at temperatures where it is possible to form anatase, <800 °C, indicating that anatase requires ‘‘seeds’’ to form. The results of this study clearly demonstrate that the crystal structure of the as-deposited film determines the development of the rutile phase with post-deposition annealing.
Effect of N2 partial pressure on the structure of MgO thin films deposited by radio frequency-magnetron sputtering with single-crystal MgO target
Authors: Misaki Yukinori , Mikawa Michio , Ishiguro Takashi , Hamasaki Katsuyoshi
Published: July 2002

We report the effect of N2 partial pressure on the structure of MgO thin films deposited on Si(100) substrates by radio frequency-magnetron sputtering in Ar+N2 mixture. The films were evaluated using x-ray diffractmeter. As increasing N2 partial pressure, the intensity of (200)MgO reflection increased and saturated above partial pressure of 4.4×10−1 Pa, which corresponds to N2 flow rate of 3 sccm. Effect of N2 gas on the structure of MgO thin films were investigated by plasma emission spectroscopy. The increase of the optical emission intensity of NH spectrum results in the increase of intensity of (200)MgO reflection. We found the strong relationship between the emission intensity of NH spectrum and intensity of (200)MgO reflection.
Properties of crystallized Si1−xGex thin films deposited by sputtering
Authors: Jelenkovic Emil V. , Tong K. Y. , Sun Z. , Mak C. L. , Cheung W. Y.
Published: July 2002

Si 1−x Ge x were deposited by a radio frequency magnetron sputtering system and were furnace crystallized at a temperature of 550 °C. The crystallization process was characterized by x-ray diffraction (XRD), Raman spectra, electron spin resonance transmission electron microscopy. The effect of germanium content in the films was studied for samples with germanium from 19% to 53%. Doping of Si1−xGex films by phosphorous was investigated through measurement of sheet resistance and carrier mobility. It was found that sputtered Si1−xGex films can be useful for thin film transistors with low temperature budget. No significant clustering of pure Ge or Si in Si1−xGex films was deduced from the recorded XRD and Raman spectra.
Temperature dependence of the electron induced gas desorption yields on stainless steel, copper, and aluminum
Authors: Gómez-Goñi J. , Mathewson A. G.
Published: July 2002

Electron induced gas desorption yields from stainless steel, copper, and aluminum surfaces have been measured for electrons of 300 eV energy. The main gases desorbed were H2, CH4, H2O, CO, and CO2. The effect of increasing the temperature on the gas desorption yields was measured and the only yields affected were those of H2O and H2, while the others remained essentially constant. The dependence on the dose and the temperature using two identical samples was also measured and the yields were found to be proportional to the dose to the power— α, with α positive. No big differences with temperature were seen. The value of the exponent for H2 is bigger than that expected for a diffusion model. The dependence with coverage and temperature was also analyzed, showing that the cleaning effect is quicker at higher temperatures, especially for H2. A diffusion model for H2 was applied to interpret the experimental results, showing that the model explains the results, if we consider that the H2 concentration across the bulk of the material, decreases exponentially.
Back-surface passivation of polycrystalline CdSe thin-film transistors
Authors: Landheer D. , Masson D. P. , Belkouch S. , Das S. R. , Quance T. , LeBrun L. , Hulse J. E.
Published: July 2002

The electrical characteristics of simple inverted-gate CdSe thin-film transistors (TFTs) were monitored after annealing and back-surface passivation treatments and the results were correlated with chemical analysis of the back interface. A dramatic increase in TFT current was observed after a short vacuum anneal at 320 °C. X-ray photoelectron spectroscopy (XPS) analysis showed that the vacuum anneal removed part of the oxide bonded to Se from the back (top) surface. This was confirmed by temperature-programed desorption data for oxidized CdSe, which showed two distinct selenium oxide species desorbing above 300 °C. XPS analysis showed that evaporated SiO, or SiO2 deposited by microwave plasma-enhanced chemical-vapor deposition, reacted strongly with an oxidized CdSe surface by removing the Se-bound oxygen present after an air anneal. Changes in the width of the Cd 3d5/2 peak suggested that the Cd bound oxygen was also transferred to the SiO during the deposition of the oxide. A reoxidation of the CdSe/SiO interface occurred after annealing in air at 350 °C. In contrast, silicon dioxide deposited by e-beam evaporation did not react as strongly with the native oxide. The interfacial oxide was reduced by annealing in forming gas. A reduced CdSe surface with no Se bonded to oxygen and a narrow Cd 3d5/2 XPS peak was associated with a high density of donors at the interface.
Synthesis, composition, surface roughness and mechanical properties of thin nitrogenated carbon films
Authors: Chan Wai-Chung , Zhou Beizhi , Chung Yip-Wah , Lee C. S. , Lee S. T.
Published: July 2002

In this study, we explored the properties of amorphous nitrogenated carbon films grown in a standard magnetron sputter-deposition system without a magnetic trap. Silicon wafers and hard disk substrates were used. To simplify process control, we operated the graphite target at constant voltage and used 3% nitrogen in argon from a premixed feed. Under these conditions, most nitrogenated carbon films contain about 6–8 a/o of nitrogen. Films with the highest hardness values (28 GPa) and lowest root-mean-square surface roughness (0.2 nm on hard disk substrates) were obtained at low sputtering pressure (5 mTorr) and large substrate pulse bias (−300 V). These observations demonstrate the importance of ion bombardment in controlling film morphology and properties. The harder films appear to have better resistance against scratch damage, as is demonstrated by the nano-scratch tests using a two-dimensional nanoindentor.
Scanning tunneling microscopy study of benzene adsorption on Si(100)-(2×1)
Authors: Self K. W. , Pelzel R. I. , Owen J. H. G. , Yan C. , Widdra W. , Weinberg W. H.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to investigate the adsorption of benzene on nominally flat Si(100)-(2×1) substrates. STM images show that benzene adsorbs on top of the dimer rows bonding to the two Si–Si dimer dangling bonds. Bias-dependent imaging indicates that the highest occupied molecular orbital of adsorbed benzene lies approximately 1.2 eV below the top of the valence band and that the lowest unoccupied molecular orbital is at least 3.5 eV above the highest occupied molecular orbital. At higher coverages, the benzene molecules are adsorbed on every other dimer along the dimer row and on every other dimer across the dimer rows resulting in a local c(4×2) periodicity, in agreement with the saturation coverage of ∼0.25 monolayer.
Determination of the atomic nitrogen flux from a radio frequency plasma nitride source for molecular beam epitaxy systems
Authors: Voulot D. , McCullough R. W. , Thompson W. R. , Burns D. , Geddes J. , Cosimini G. J. , Nelson E. , Chow P. P. , Klaassen J.
Published: July 2002

Direct measurements of both the dissociation fraction and the atom flux have been carried out for the first time to characterize a radio frequency (rf) atomic nitrogen source. The measurements have been made over a range of source pressures and rf powers. Dissociation fractions of up to 0.4 and atomic nitrogen fluxes of up to 0.85×1018 atom s−1 were obtained. In addition these results have been correlated with spectroscopic measurements of the ratios of atomic and molecular optical emissions from the source plasma in order to provide a way of estimating in situ the atomic flux.
Comparison of electron property measurements in an inductively coupled plasma made by Langmuir probe and laser Thomson scattering techniques
Authors: Bowden M. D. , Kogano M. , Suetome Y. , Hori T. , Uchino K. , Muraoka K.
Published: July 2002

Langmuir probes and Thomson scattering are two independent methods of measuring electron properties in glow discharges. In this article, measurements of electron properties of an inductively coupled plasma were made using both methods, and the results obtained with the probe were compared with those obtained using the more reliable laser method. The values of electron temperature and density obtained by both methods were similar over a range of plasma conditions but significant differences in the electron energy distribution function were observed. In addition, clear evidence was obtained that the presence of the probe perturbed the discharge. The advantages and disadvantages of each method are discussed with respect to the suitability of each technique for measuring electron properties in inductively coupled glow discharges.
Study of stress evolution of boron nitride films prepared by ion assisted deposition
Authors: Zeitler Michael , Sienz Stefan , Rauschenbach Bernd
Published: July 2002

The evolution of the stress during N/Ar ion assisted deposition of boron nitride films on Si(001) substrates was measured in situ by a very sensitive capacity technique in dependence on the ion energy, temperature during deposition, and the ion to atom arrival rate. The relative amount of c-BN in the films was determined by Fourier-transform infrared spectrometry and the layered structure of these films was studied by spectroscopic ellipsometry and high resolution cross-section transmission electron microscopy. The stress evolution in dependence on the layer thickness is characterized by a high tensile stress in the initial stage of the film growth, followed by a transition from the tensile to the compressive stress state and the saturation or weak relaxation of the compressive stress. The existence of the c-BN phase corresponds to a compressive stress of about 2 GPa. For a compressive stress ⩾3.5 GPa boron nitride films with a c-BN content ⩾80% were obtained. The influence of the ion energy, the temperature during the deposition, and the ion to atom arrival ratio on the development of the stress is discussed.
Characteristics of inductively coupled Cl2/BCl3 plasmas during GaN etching
Authors: Kim H. S. , Yeom G. Y. , Lee J. W. , Kim T. I.
Published: July 2002

In this study, the characteristics of inductively coupled Cl2/BCl3 plasmas during GaN etching were estimated using plasma mass spectrometry by measuring the relative amounts of positive ions, neutrals, and etch products. The results showed that the enhancement of GaN etch rates for Cl2/BCl3 plasmas could be related to the formation of Cl radicals and reactive ions such as Cl2+ and BCl2+ measured by the mass spectrometry during GaN etching. These Cl radicals are responsible for chemisorption and BClx+ and Cl2+ for chemical and/or physical sputtering. Ion assisted chemical desorption seems to be generally enhanced by the addition of BCl3 to Cl2 and also with the increase of pressure. Also, the abundance of BCl2+ in the Cl2/10%BCl3 plasmas appears to be important in GaN etching compared to pure Cl2 plasma. Ga+, GaCl2+, and N2+ were observed during GaN etching as the etch products and the intensities of these ion etch products were correlated with the trend of the GaN etch rate.
Development and characterization of surface chemistries for microfabricated biosensors
Authors: Metzger Steven W. , Natesan Mohan , Yanavich Carolyn , Schneider James , Lee Gil U
Published: July 2002

The high cost and harsh processing conditions associated with microfabricated biosensors demand a new approach to receptor immobilization. We have grafted biotin labeled, 3400 molecular weight poly(ethylene glycol) (PEG) to silicon surfaces to produce a dense PEG monolayer with functionally active biotin. These surfaces have been activated with antibodies through the strong streptavidin-biotin interaction by simply incubating the surfaces with antibody-streptavidin conjugates. The stability of the biotinylated PEG monolayers produces a sensing element that can be regenerated by removal of the streptavidin conjugate and stored in a dry state for extended periods of time.
Hot-carrier effects on radio frequency noise characteristics of LDD n-type metal–oxide–semiconductor field effect transistors
Authors: Kwan W. S. , Chen C. H. , Deen M. J.
Published: July 2002

Hot-carrier damage is a major issue in the long-term reliability of metal–oxide–semiconductor field effect transistors (MOSFETs). Hot-carrier induced damages have been shown to degrade various MOSFET characteristics—threshold voltage, channel charge mobility, parasitic drain and source resistances, and parasitic drain capacitance. The degradation induces changes in the small-signal s parameters of MOSFETs. Further experimental results indicate that such damages also degrade the radio frequency (rf) noise characteristics of a LLD n-type MOSFET (NMOSFET). The minimum noise figure (NFmin) and the normalized noise resistance (rn)–two key noise parameters—increase due to hot-carrier stress. The optimal reflection coefficient (Γopt) versus frequency curve also changes with increase stressing. The degradation in the rf noise characteristics of the LDD NMOSFET implies a serious issue in designing reliable, low-noise rf circuits with MOSFETs.
Dynamic simulations of pulsed reactive sputtering processes
Authors: Jonsson L. B. , Nyberg T. , Berg S.
Published: July 2002

In the reactive sputtering process numerous parameters interact in a complex and nonlinear way. Thus, if any parameter is changed during operation, it is not an easy matter to predict the response of the other involved parameters. The static behavior of the reactive sputtering process has previously been carefully investigated. However, studies of the time dependent behavior of this process are rare. It is important to study the dynamic behavior to gain a more complete understanding of the process. Furthermore, the increased use of pulsed power sources has set focus on the process dynamics. A model describing the time-dependent behavior of the pulsed reactive sputtering process is proposed in this work. The model suggests that the time to reach process equilibrium may vary substantially depending on the process history. This memory effect has been experimentally verified. Finally, the simulations clearly point out that for high repetition frequencies (>1 kHz) of the pulsed direct current (dc) reactive sputtering process there will be no time-dependent variations of the chemical compositions either at the target surface or at the growing film at the substrates. At these high frequencies the chemistry of the process will act identical as to the continuous dc reactive sputtering process having the average pulsed dc power supplied to the target.