bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel vacuum process for OH addition to polystyrene, polyethylene, and TeflonTM
Authors: Sun J. Q. , Bello I. , Bederka S. , Lau W. M. , Lin Zhangda
Published: July 2002

A special vacuum process has been developed for adding an OH functional group onto polymer surfaces with different reactivities. In this novel technique, polymer surfaces were exposed, in a vacuum chamber, to OH radicals generated by the dissociation of water vapor on hot rhenium wires. We found by x-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy that about half a monolayer equivalent of C–OH groups could be generated on a relatively reactive polymer like polystyrene with a 10 s exposure at a water pressure of 1×10−3 Torr. However, under the same experimental conditions, the oxygen incorporation on more stable polymers was much lower; it was reduced by 90% on polyethylene and to practically zero on Teflon. For surface engineering of these stable polymers, thermionic electrons emitted from the hot filaments were used to facilitate electron impact ionization of some of the water vapor. Positive ions from the ionization region were then extracted and accelerated by an electrostatic field toward the polymer target which was separated from the ionization region by an adjustable distance about twice the gas-phase collision mean-free path. Although ion bombardment of the polymer surface was limited by the insulating property of the polymer, ion–molecule collisions in the gas phase were efficient with such a setup in generating energetic neutrals flying toward the polymer surface for the activation of the polymer. With an accelerating voltage of 50 V and a water pressure of 1×10−3 Torr (the collision mean-free path being about 5 cm), about a 0.2 monolayer equivalent of COH was added to Teflon and polyethylene in 60 s.
The chemistry of simple alkyl species on Pt(111) generated by hyperthermal collisions
Authors: Oakes Darren J. , Newell Helen E. , Rutten Frank J. M. , McCoustra Martin R. S. , Chesters Michael A.
Published: July 2002

The identification of the primary dissociation products of hyperthermal collisions of methane and ethane with a Pt(111) surface at ∼150 K and the study of their subsequent thermal evolution has been afforded by the use of reflection–absorption infrared spectroscopy, temperature programmed desorption, and Auger electron spectroscopy. In both cases, the primary dissociation products have been identified as an adsorbed alkyl moiety (methyl, CH3, and ethyl, C2H5, respectively) and an adsorbed hydrogen atom. The thermal treatment of both alkyl adlayers ultimately results in the formation of the ethylidyne (≡CCH3) moiety at temperatures between 300 and 400 K. At ∼500 K, this species itself thermally decomposes to yield adsorbed carbon atoms and gaseous hydrogen. While this behavior may not be unexpected for the C2 ethyl fragment, the formation of the C2 ethylidyne fragment from the C1 methyl fragment can only be explained through the occurrence of carbon–carbon coupling reactions. Such reactions have only recently been observed on the Pt(111) surface. The C–C coupling reactions associated with the formation of ethylidyne from methyl show considerable dependence upon the surface coverage of the methyl fragment and are accompanied by the evolution of both gaseous hydrogen and methane. The latter results from recombinative desorption of methyl moieties with adsorbed hydrogen atoms.
Minimum profile ultrahigh vacuum gate valve based on linear/rotary motion feedthrough
Authors: Stolow Albert
Published: July 2002

A simple, very low profile (<1 in.) ultrahigh vacuum gate valve for isolation of molecular beam sources is described. The radial gate drive is based upon a linear/rotary motion feedthrough. A novel coupling scheme is described where the linear motion is used to translate the gate while the rotary motion is used to independently raise and lower the gate. A molecular beam skimmer, mounted on the gate, may be accurately and reproducibly located.
Coulomb crystal formation from growing particles in a plasma and the analysis
Authors: Hayashi Y. , Tachibana K.
Published: July 2002

A Coulomb crystal formation process from growing particles in an ethylene plasma was analyzed simultaneously by Mie-scattering ellipsometry and charge-coupled device video images. It was confirmed that the phase transition of Coulomb liquid to Coulomb solid occurred after around 20 min of particle growth. The Coulomb crystal formed a body-centered-cubic (bcc) structure at the first stage, while it changed to a hexagonal pole structure after more than 40 min. Particles are collectively bound by cohesion forming a bcc structure. They are closely packed in lateral layers and aligned in the vertical direction when an attractive force between dipoles, which consists of negative particles and the polarized surrounding positive ions, becomes strong.
Sidewall and surface induced damage comparison between reactive ion etching and inductive plasma etching of InP using a CH4/H2/O2 gas mixture
Authors: Etrillard J. , Héliot F. , Ossart P. , Juhel M. , Patriarche G. , Carcenac P. , Vieu C. , Puech M. , Maquin P.
Published: July 2002

We report the results of a comparative characterization between reactive ion etching and inductive coupled plasma (ICP) etching of InP with a CH4/H2/O2 gas mixture. Particular attention was paid to the surface morphology and to the pattern profiles that were observed by scanning electron microscopy. A comparison with morphology of patterns etched by argon ion milling is also included. Auger electron spectroscopy and secondary ion mass spectrometry were used to obtain the elemental composition in the top 30 nm of the etched surface and to evaluate pollution and stoichiometry. Transmission electron microscopy was used to observe the sidewall damage and to evaluate the effect of sidewall deposit. The respective roles of incident and reflected energetic species and deposits are identified. The effect of anisotropy on sidewall deposits was also observed. Finally, surface damage induced on InP etched substrates was characterized through photoluminescence intensity. The destructive effects of high ion energy etching processes on the samples was observed in terms of stoichiometry modification, surface contamination, and polycrystallization of sidewalls. Some very low energy processes were studied with the ICP equipment. An extremely low damage level could be obtained in such processes while keeping a sufficient etch rate. However, the low ion energy ICP etching processes are isotropic.
X-ray photoelectron spectroscopy characterization of radio frequency reactively sputtered carbon nitride thin films
Authors: Kumar Sunil , Butcher K. S. A. , Tansley T. L.
Published: July 2002

Carbon nitride thin films prepared by radio frequency reactive sputtering of graphite in pure nitrogen plasma have been characterized by x-ray photoelectron spectroscopy (XPS) for probing the chemical bonding in the films. The multiple binding energy values obtained for the C 1s and N 1s photoelectrons in the film suggest that both the C and N atoms exhibit at least three types of chemical states, manifestative of different types of the C–N bonding present in the material. The presence of theoretically predicted β-C3N4 phase in our C–N films has been suggested on the basis of XPS and optical data.
Current capabilities and limitations of in situ particle monitors in silicon processing equipment
Authors: Takahashi Ken M. , Daugherty John E.
Published: July 2002

By enabling real time monitoring and control of particle levels in integrated circuit process equipment, in situ particle monitors (ISPMs) have the potential to reduce dramatically the dominant source of yield-killing defects, i.e., process induced particles. However, there are also significant limitations to their use for on-line monitoring. A survey of the ISPM literature shows that the greatest benefit provided by ISPMs for most applications is their immediate indication of high-particle excursions. In only a few applications described in the literature do the sensor data correlate with wafer surface scans and show enough sensitivity to baseline particle levels to control process maintenance cycles. Scaling arguments show that at gas pressures below about 100 mTorr, gravitational settling and particle inertia typically prevent particles from being carried efficiently to exhaust sensors, in spite of experimental evidence that bouncing significantly aids particle transport. Combined with the low sampling efficiency of most sensors, these limitations make exhaust sensors impractical for many applications including most sputtering and many etching processes, unless chambers are regularly vented to high pressures. The cutoff imposed by particle transport limitations is clearly demarcated in the ISPM literature, which indicates good sensitivity of exhaust sensors to baseline particle levels in high pressure processes such as plasma-enhanced chemical-vapor deposition, sensitivity only to high-particle excursions for processes around 100 mTorr, and insensitivity to particle levels in processes that operate at low pressures, except during gas venting or purging. For many applications, standard sensors are susceptible to false counting due to fouled optics, noise from rf and magnetic fields, and optical emissions. High current ion implanters, with their nearly noise-free chambers, are the only fully proven application of in-chamber sensors. To overcome the particle transport limitations in other critical defect-producing processes that operate at low pressure, in-chamber sensors that are insensitive to the harsh chemistry and high noise levels of process chambers need to be developed.
Effect of preadsorbates on the dissociation dynamics of ethane on Ir(110)
Authors: Hago W. , Kelly D. , Weinberg W. H.
Published: July 2002

We have examined the role of the preadsorbates oxygen and potassium in modifying the dynamics and kinetics of ethane activation on Ir(110). Although the effect of these adsorbates is commonly interpreted within the context of promotion and poisoning, we have followed a quantitative approach in determining the influence of O on the trapping-mediated chemisorption and that of O and K on the direct dissociative chemisorption of this alkane. Using a supersonic molecular beam, the direct dissociative chemisorption of perhydrido- and perdeuteroethane on Ir(110) was investigated using translational beam energies of 12–30 kcal/mole, parametric in oxygen and potassium precoverage from the clean surface to the adsorbate-saturated surface. We have observed that the probability of direct dissociative chemisorption decreases in the presence of dissociatively adsorbed oxygen as well as potassium. The magnitude of the poisoning is considered within a one-dimensional tunneling model and the extent of poisoning of both oxygen and potassium is quantified with a model that yields a range parameter of 8.5 Å for O and 13 Å for K. For trapping-mediated chemisorption using beam energies of 1–5 kcal/mole, preadsorption of 0.06 monolayers O was found to lower the activation energy of perhydrido- and perdeuteroethane activation by 400 and 300 cal/mole, respectively, with no effect on the preexponential factor, while a surface saturated with oxygen lowered these activation energies by 800 and 700 cal/mole, also with no effect on the preexponential factor.
Intermediate states in the adsorption of NO on Ir(111): Substrate temperature effects
Authors: Davis J. E. , Karseboom S. G. , Nolan P. D. , Mullins C. B.
Published: July 2002

Measurements of the initial adsorption probability, S0, of nitric oxide (NO) on Ir(111) as a function of incident kinetic energy, Ei, and surface temperature, Ts, are presented. We observe a decrease in S0 with increasing kinetic energy, Ei, from 0.052 to 1.3 eV. At low kinetic energies, the initial molecular adsorption probability decreases with increasing surface temperature (ranging between 77 and 300 K in this study), while at high kinetic energies, this quantity is independent of surface temperature. We propose a trapping-mediated mechanism for adsorption at low kinetic energies. In this low energy regime, the surface temperature dependence reflects a kinetic competition between desorption from a physically adsorbed state and conversion to a more strongly bound, molecularly chemisorbed state. At high kinetic energies, we propose that adsorption initially occurs directly into the molecular chemisorption well. Indeed, electron energy loss spectroscopy measurements show no evidence for direct dissociation at a low Ts and indicate that the surface temperature must exceed ∼400 K for dissociative chemisorption to occur. The probability of dissociative chemisorption of NO on Ir(111) decreases with increasing temperature (in the range 500–900 K in this study) at all kinetic energies investigated. Here, we propose a model for low kinetic energies that includes both a physisorbed species and a molecularly chemisorbed species as precursors to dissociation. For the high energy regime, the trapping probability into the physically adsorbed state is assumed to be zero, and thus, we model the adsorption occurring directly as a molecularly chemisorbed intermediate with subsequent dissociation at elevated temperatures. The success of the model is demonstrated by the agreement of kinetic parameters determined separately for data employing a high kinetic energy beam and a low energy beam.
Role of surface stoichiometry in the Cl2/GaAs(001) reaction
Authors: Simpson W. C. , Shuh D. K. , Hung W. H. , Håkansson M. C. , Kanski J. , Karlsson U. O. , Yarmoff J. A.
Published: July 2002

The room-temperature reaction of Cl2 with GaAs(001)-4×6, -c(2×8), and -c(4×4) surfaces is studied with synchrotron soft x-ray photoelectron spectroscopy. The chemical composition of the reacted surfaces is found to depend on the stoichiometry of the starting surface. In all cases, the reaction occurs stepwise, with Ga and As monochlorides formed prior to the dichlorides. The Ga-rich surface is initially more reactive than either of the As-rich surfaces and it forms more GaCl than the As-rich surfaces, which instead form more AsCl. The sticking coefficient for chlorine on GaAs(001) decays exponentially with coverage. A contribution from Cl atoms comprising the surface dichlorides is identified in the Cl 2p core-level spectra.
Novel method for growing CdS on CdTe surfaces for passivation of surface states and heterojunction formation
Authors: Nelson Art J. , Levi Dean
Published: July 2002

Large-grain polycrystalline CdTe was subjected to in situ H2S plasma processing for <30 min at 100 and 200 °C. High-resolution x-ray photoemission measurements on the Cd 4d, Te 4d, and S 2p core levels, and the valence band were used to determine the resultant chemical environment of S and the electronic structure at the CdTe surface following plasma processing. Auger electron spectroscopy compositional depth profiling was also used to determine the distribution of S in the near surface region. Furthermore, time-resolved photoluminescence was used to measure carrier lifetimes and, thus, determine the degree of passivation of CdTe surface states. These results provide evidence for a CdS/CdS1−xTex/CdTe heterojunction device structure, as a result of the H2S plasma processing, and a reduction in the surface recombination velocity through passivation of surface states. This is a novel method of fabricating CdS/CdTe heterojunction devices.
Experimental investigation of the matching and impressed electric field of a multipolar electron cyclotron resonance discharge
Authors: Mak P. , Asmussen J.
Published: July 2002

The experimental performance of an end excited, internally tuned, multipolar electron cyclotron resonance plasma source is investigated versus several independent input variables: (1) incident power (185–350 W), (2) discharge pressure (1–7 mTorr), and (3) microwave matching (applicator length, Ls, varies from 65–170 mm). Plasma source performance in argon gas is determined from measurements of (1) absorbed microwave power, (2) the magnitude, and (3) the spatial variation of the impressed electric field, and the output (4) plasma density and (5) electron temperature. The nonlinear experimental relationships between variations in the input variables and performance variables are established. Two well-matched stable discharge operational regions or modes are identified as Ls is varied. Using the measured impressed electric field patterns, these two modes are identified as TM, Φ symmetric, λg, and λg/2 standing wave modes. As Ls, pressure and power vary, considerable hysteresis in absorbed power and density is observed. However, it is shown that this complex input/output discharge behavior can be approximately explained using simple global plasma models. Despite the multiple steady states and hystereses, it is shown that the discharge can be easily maintained in well-matched, high density (ne>3×1011/cm3) stable operating conditions. The impressed electric field varies between 3 and 4.5 kV/m. An equivalent circuit of the plasma loaded cavity applicator is developed and provides important insights for the plasma matching process. The microwave coupling efficiencies are greater than 98% and the ion production costs vary between 300 and 450 eV/ion versus the experimental inputs. The data presented is useful for plasma source optimization and in developing intelligent plasma processing control strategies.
Ion assisted deposition of thin films by substrate tuned radio frequency magnetron sputtering
Authors: Lousa A. , Gimeno S.
Published: July 2002

The substrate tuning technique was applied to a radio frequency magnetron sputtering system to obtain a variable substrate bias without an additional source. The dependence of the substrate bias on the value of the external impedance was studied for different values of chamber pressure, gas composition and rf input power. A qualitative explanation of the results is given, based on a simple model, and the role of the stray capacitance is clearly disclosed. Langmuir probe measurements show that this system allows independent control of the ion flux and the ion energy bombarding the growing film. For an argon flow rate of 2.8 sccm and a radio frequency power of 300 W (intermediate values of the range studied) the ion flux incident on the substrate was 1.3×1020 m−2 s−1. The maximum ion energy available in these conditions can be varied in the range 30–150 eV. As a practical application of the technique, BN thin films were deposited under different ion bombardment conditions. An ion energy threshold of about 80 eV was found, below which only the hexagonal phase was present in the films, while for higher energies both hexagonal and cubic phase were present. A cubic content of about 60% was found for an ion energy of 120 V.
Growth of gallium nitride thin films by liquid-target pulsed laser deposition
Authors: Xiao R. F. , Sun X. W. , Li Z. F. , Cue N. , Kwok H. S. , Liu Q. Z. , Lau S. S.
Published: July 2002

Gallium nitride (GaN) thin films have been grown on several kinds of substrates (fused silica, single crystal silicon, and sapphire) by liquid-target pulsed laser deposition at substrate temperature of 600 °C and in the presence of ammonia (NH3) gas. X-ray diffraction, scanning electron microscopy, tunneling electron microscopy, Rutherford backscattering (RBS), and UV/VIS spectrometry were used to characterize the as-grown GaN films. It is shown that c-axis oriented GaN films can be formed if a thin zinc oxide (ZnO) buffer layer was first grown on the virgin substrate. Without the buffer layer the GaN films were found to be polycrystalline with randomly oriented grains. Once the ZnO buffer layer was used, the GaN films immediately grew in a columnar structure with its c-axis normal to the surface of the film. RBS data have shown that the obtained films are stoichiometric GaN. It was also found that the surface morphology and optical transparency of the GaN films were greatly improved by the ZnO buffer layer.
Electron spectroscopy studies of interface formation between metal electrodes and luminescent organic materials
Authors: Park Y. , Choong V.-E. , Hsieh B. R. , Tang C. W. , Wehrmeister T. , Müllen K. , Gao Y.
Published: July 2002

Using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), we have studied the formation of metal/organic interfaces in organic electroluminescent devices. Oligo(p-phenylenevinylenes) (OPV) and tris-(8-hydroxyquinoline)aluminum (Alq3) were used as the organic materials and Ca was used as the metallic layer. Interfaces are formed differently by depositing organic layer on Ca and Ca on organic substrate. For Ca/OPV, UPS revealed a clear evidence for interface state formation upon Ca deposition. The evolution of XPS core level peak as a function of Ca layer thickness was consistent with the energy level bending picture. The XPS and UPS spectra for OPV/Ca as a function of organic layer thickness also confirmed the energy level bending. The data obtained allowed us to deduce the energy level diagram near the interface. Similar data for Alq3/Ca indicated that no electron injection barrier exists at this interface if the Alq3 optical band gap in the literature was used for estimating the energy position of the lowest unoccupied state.
Influence on selective SiO2/Si etching of carbon atoms produced by CH4 addition to a C4F8 permanent magnet electron cyclotron resonance etching plasma
Authors: Den Shoji , Kuno Tatsushi , Ito Masafumi , Hori Masaru , Goto Toshio , O’Keeffe Patrick , Hayashi Yuzo , Sakamoto Yuichi
Published: July 2002

Changes in the densities of fluorocarbon radicals and fluorine atoms in a size-scalable large-area compact permanent magnet electron cyclotron resonance etching plasma source employing C4F8 gas with CH4 addition have been investigated. Measurements using infrared laser absorption spectroscopy and actinometric optical emission spectroscopy show that, for a pure C4F8 plasma, the dominant species is CF2 radicals with a density of the order of 1013 cm−3, followed by fluorine atoms, CF3 and CF2 radicals which have a density an order of magnitude lower at 1012 cm−3. The densities of the different fluorocarbon radical species were found to display different dependencies on increasing CH4 gas addition. Hollow cathode absorption spectroscopy was used to estimate the carbon atom density for the first time, to the best of our knowledge, in an etching plasma. The carbon atom density in the plasma increases linearly with CH4 gas addition between 20 and 80%. Analysis of actual SiO2/Si etching revealed that the etch selectivity and carbon atom to fluorine atom ratio follows a similar trend indicating a direct correlation between the carbon atom density in the plasma and the etch selectivity.
Monolayer incorporation of nitrogen at Si–SiO2 interfaces: Interface characterization and electrical properties
Authors: Lucovsky Gerald
Published: July 2002

This article presents a low-temperature plasma-assisted approach for the preparation of Si–SiO2 interfaces with monolayer concentrations of bonded nitrogen atoms (N atoms) at that interface. Localization of N atoms at Si–SiO2 interfaces has been established by on-line Auger electron spectroscopy (AES), off-line secondary ion mass spectrometry, and optical second harmonic generation. On-line AES studies have established that excess suboxide bonding in interfacial transition regions occurs during plasma-assisted oxidation using N2O and O2 source gases, and that a postoxidation rapid thermal anneal at 900 °C for 30 s in an inert ambient reduces the concentration of these suboxide bonding groups. Defect generation at plasma nitrided interfaces in field effect transistor devices is reduced compared to similar devices in which Si–SiO2 interfaces are formed by furnace oxidation in O2.
Ultrahigh vacuum sample transfer system with multiple electrical connections and grazing optical access
Authors: Krastev E. T. , Tobin R. G.
Published: July 2002

A novel demountable sample transfer system is described that permits movement of large (1×3 cm) samples into and out of ultrahigh vacuum without venting of the main chamber. The system is optimized for infrared reflectance and electrical resistance measurements, and incorporates several features not available commercially. Six electrical contacts are carried with the sample — four for in situ resistivity measurements and two for a thermocouple. A bayonet-type latching mechanism provides rigid and reproducible sample positioning, and optical access to the sample surface is not obstructed, even at the grazing angles necessary for surface infrared spectroscopy.
Transition behavior from coupled to uncoupled GaAs/InAs double quantum wells
Authors: Tit Nacir
Published: July 2002

The electronic structures of the InAs single and double quantum wells buried in bulk GaAs (001) are presented based on the sp3s* empirical tight-binding model. Both electrons and holes are found to be confined in the c-axis direction around the inserted InAs monomolecular plane with a localization length of the order of 110 Å. The inserted InAs monolayer is, therefore, playing the role of a quantum well for all charge carriers and, as a consequence, the formed heterojunction is of type I. The system, composed of two InAs monolayers buried in GaAs and separated by N monolayers of GaAs, is studied versus the barrier thickness (N). Our results of the variation of band gap energy as a function of barrier thickness (N) are in excellent agreement with the available photoluminescence data when a small valence band offset (of order 80 meV including the spin-orbit effects) is employed. A critical barrier thickness of about 220 Å is suggested to decouple the InAs quantum wells.
Plasma and surface reactions for obtaining low defect density amorphous silicon at high growth rates
Authors: Matsuda Akihisa
Published: July 2002

Gas phase and surface reaction processes in the radio frequency plasma enhanced decomposition of silane for the preparation of hydrogenated amorphous silicon (a-Si:H) are discussed. The conditions necessary for obtaining a low defect density material is discussed in terms of the gas phase reactive species and their surface reactions. The problems that occur when attempting to increase the growth rate are discussed from the viewpoint of plasma chemistry and its effect on surface reactions. Thereby, the conditions necessary for obtaining low defect density material at high growth rates are identified.
The use of a Si-based resist system and Ti electrode for the fabrication of sub-10 nm metal-insulator-metal tunnel junctions
Authors: Wada T. , Haraichi S. , Ishii K. , Hiroshima H. , Komuro M. , Gorwadkar S. M.
Published: July 2002

We have developed a process which is applicable for the fabrication of single electron devices by utilizing a SiO2/c-Si bilayer electron beam resist. The process parameters were optimized especially for the fabrication of metal-insulator-metal tunnel junctions of sub-10 nm sizes. A suspended mask suitable for double angle evaporation was successfully fabricated. Employing the highly corrosion resistance material Ti as an electrode metal and two-step removal process against excess Ti over inorganic resist, we fabricated a structure with sub-10 nm Ti/TiOx/Ti double tunnel junctions and an island, which exhibited tunneling property.
Nanoscale scratch resistance of ultrathin protective overcoats on hard magnetic disks
Authors: Anoikin E. V. , Yang M. M. , Chao J. L. , Elings J. R. , Brown D. W.
Published: July 2002

An atomic force microscope-based nanoscratch testing technique has been applied to evaluate scratch resistance of 100 Å thick protective overcoats on hard magnetic disks. Among the overcoats prepared by dc magnetron sputtering, an amorphous nitrogenated carbon (a-C:N) film showed the best performance in the tests, followed by an amorphous hydrogenated carbon (a-C:H) film and an undoped amorphous carbon (a-C) film. Substrate temperature in the overcoat sputtering process was found to be an important factor affecting the film’s scratch resistance. Overcoats sputtered at lower substrate temperature were more stable against scratching. An ion beam deposition process was found to produce an overcoat with superior scratch-resistant properties as compared to the sputtered carbon overcoats. Nanoscale scratch testing results are correlated with the sp3-bonding character in the overcoats assessed by Raman spectroscopy.
Factors affecting interface-state density and stress of silicon nitride films deposited on Si by electron-cyclotron resonance chemical vapor deposition
Authors: Landheer D. , Rajesh K. , Masson D. , Hulse J. E. , Sproule G. I. , Quance T.
Published: July 2002

The physical and electrical properties of nitrogen-rich silicon nitride films deposited by electron-cyclotron resonance chemical vapor deposition with silane and molecular nitrogen have been investigated for pressures below 0.4 Pa. No Si–Si bonding or oxygen has been observed in the nitride films by Auger spectroscopy, and no SiH or NH2 groups have been observed by Fourier transform infrared spectroscopy, showing that the films have the composition SiNy−z(NH)z. As the pressure was decreased by lowering the nitrogen flow, the stress in the films became more compressive while the amount of N–H bonding in the films increased. The electron temperature determined by Langmuir probe measurements increased at lower pressures as the plasma made a transition from overdense to underdense. Despite the increasing stress, electron temperature and NH concentration, capacitance–voltage (C–V) analysis of metal-nitride-Si〈100〉 diodes showed that the SiN/Si interface improved with decreasing pressure. Using Al gates and 5 Ω cm p-type Si〈100〉 substrates an interface state density of 5×1010 eV−1 cm−2 was determined by the high-low frequency C–V measurement method for 30 nm thick films deposited at a substrate temperature of 300 °C and the lowest pressure of 0.055 Pa. Bulk conduction by the Frenkel–Poole mechanism dominated the current–voltage characteristics for negative gate potentials and breakdown voltages >9 MV/cm were obtained at this pressure. In situ single-wavelength ellipsometry showed that the interface is formed predominantly by nitridation of the Si substrate, and thus its high quality must be attributed to this nitridation rather than the chemical vapor deposition process. The results are discussed in terms of recent models for defects at the SiN/Si interface.
Meeting the process challenges for spin-valve fabrication on an industrial scale
Authors: Schwartz P. V. , Bubber R. , Paranjpe A. P. , Kools J. C. S.
Published: July 2002

We investigated industrial deposition processes for spin-valve giant magneto resistance (GMR) multilayers. We compared rf diode with dc magnetron deposited films, as well as films deposited in a cluster tool equipped with single target process modules and a multitarget module. It is found that the best MR response is obtained by using dc magnetron deposition in a multitarget process module, as this minimizes contamination by background gas atoms and interface mixing due to self-biasing of the substrate. Furthermore, dc magnetron deposition allows accurate control of the deposition time, and thus the thickness of 10–100 Å films. Applying this method to spin-valve deposition results in a controllability of 0.5 Å, a uniformity around 1% (=1σ) over 150 mm wafers and repeatability around 1%. This implies that this process meets the requirements for production of GMR magnetic read heads.
Soft x-ray-stimulated positive ion desorption from amorphous SiO2 surfaces
Authors: Akazawa Housei
Published: July 2002

Photon-stimulated desorption (PSD) of positive ions from thick SiO2 films has been investigated by means of time-of-flight mass spectroscopy. From the untreated surface, H+, H2+, O+, OH+, H2O+, SiHx+ (x=0–3), and SiO+ were detected. Both soft x-ray irradiation and Ar+ ion bombardment reduced the H+ and O+ yields and increased the SiHx+ yield as a result of preferential removal of the oxygen-terminated sites at the outermost surface. The O+ and H+ PSD yields are correlated but the SiHx+ and H+ yields are not, indicating that most of the H+ ions originate from hydroxyl sites. Thermal treatment of the specimen at 800 °C, on the other hand, reduced the intensity of all the ion signals because of the structural change induced by condensation of H2O with the formation of surface siloxane bonds.
Momentum resolved electron stimulated desorption ion angular distribution, a new technique, probing the low frequency motion of adsorbed molecules on single crystal surfaces
Authors: Ahner Joachim , Mocuta Dan , Yates John T.
Published: July 2002

A new technique, momentum resolved electron stimulated desorption ion angular distribution (ESDIAD), provides a method for taking snapshots of the zero-point position and lateral momentum of particles adsorbed on crystalline surfaces. By employing state-of-the-art electronics and computer technology it is possible to record for each desorbing particle the desorption direction together with the flight time. High momentum and directional resolved images are obtained, with time-of-flight resolution in the picosecond range and data acquisition rates up to 100 kHz. This enables us to deconvolute spatial and momentum contributions to the ESDIAD pattern and to map the low frequency motion of the adsorbed particles. These maps reflect the adsorbate interactions with the substrate and with neighboring species on the substrate. For selected examples it is demonstrated that by measuring the three dimensional momentum vector for each desorbing particle it is possible to probe the lowest energy states of adsorbed species, as well as to measure the momentum distribution when the adsorbed species gains thermal energy. Such information can be used as a basis for thinking about anisotropies in lateral motion of particles on surfaces. One major opportunity involves the study of dissimilar chemisorbed species which, when imaged together in momentum and real space, give new insights into the first stages of interaction between the species, leading ultimately to a chemical reaction.
Surface dependent electron and negative ion density in inductively coupled discharges
Authors: Hebner G. A. , Blain M. G. , Hamilton T. W. , Nichols C. A. , Jarecki R. L.
Published: July 2002

Electron and negative ion density have been measured in a modified Applied Materials decoupled plasma source commercial metal etch chamber using gas mixtures of BCl3, Cl2 and Ar. Measurements were performed for four different substrate types to examine the influence of surface material on the bulk plasma properties: aluminum, alumina, photoresist, and 50% patterned aluminum/photoresist. Electron densities in the Cl2/BCl3 mixtures varied from 0.25 to 4×1011 cm−3. Photodetachment measurements of the negative ion density indicate that the negative ion density was smaller than the electron density and that the electron to negative ion density ratio varied between 1 and 6. The presence of photoresist had a dominant influence on the electron and negative ion density compared to alumina and aluminum surfaces. In most cases, the electron density above wafers covered with photoresist was a factor of 2 lower, while the negative ion density was a factor of 2 higher than the aluminum or alumina surfaces.
Glow discharge mass spectrometry study of the deposition of TiO2 thin films by direct current reactive magnetron sputtering of a Ti target
Authors: Vancoppenolle V. , Jouan P.-Y. , Wautelet M. , Dauchot J.-P. , Hecq M.
Published: July 2002

The properties of titanium oxide thin films deposited by direct current magnetron sputtering of a Ti target are strongly dependent on the sputtering conditions. The aim of the present work is to investigate the discharge parameters such as plasma potential, discharge voltage, deposition rate, and ion composition of the discharge as a function of the oxygen partial pressure. The plasma potential, relative to the ground, is determined from the ion energy distribution. Working in the constant current discharge mode, we observe, with increasing oxygen partial pressure, a drop of the plasma potential, an increase of the discharge voltage, a drop of the deposition rate, and an inversion of the Ti+–TiO+ intensities. For a given discharge current and pressure, the drop of the plasma potential and the increase of the discharge voltage occur at the same gas composition while the drop of the deposition rate and the ion intensity inversion happen at an oxygen richer gas composition. Both transitions are linearly correlated and depend on the discharge current. For larger oxygen partial pressure, a third transition appears corresponding to an inversion between TiO+ and TiO2+ intensities. These results lead us to consider three regimes in the reactive sputtering of a Ti target.
Thermally induced improvements on SiNx:H/InP devices
Authors: Redondo E. , Blanco N. , Mártil I. , González-Dı́az G. , Pelaez R. , Dueñas S. , Castán H.
Published: July 2002

The influence of rapid thermal annealing treatments on the interface characteristics of Al/SiNx:H/InP devices was analyzed. The insulator was obtained by an electron cyclotron resonance plasma method at a 200 °C-deposition temperature. The films were deposited in a single deposition run but in two steps: first, we deposited the bottom layer with a film composition of x=1.55 and then the top layer with x=1.43. Total film thickness was 500 Å in one set of samples and 200 Å in the other one. Annealings were conducted in Ar atmosphere for 30 s in a temperature range between 400 and 800 °C. To characterize the electrical behavior of these devices, capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) measurements have been performed on each sample. This last characterization shows the presence of features in the spectra at Ec−0.2 eV, Ec−0.25 eV, Ec−0.38 eV. The last one is due to phosphorus vacancies, VP. Devices with 200-Å-thick insulator present the minimum interface trap densities. According to the DLTS analysis, this minimum (3×1011 cm−2 eV−1) is achieved on the 400 °C-annealed samples. A tentative explanation of these results is given in terms of a possible InP surface passivation due to the fact that nitrogen atoms coming from the insulator can fill phosphorus vacancies, giving rise to a low defective insulator/semiconductor interface. This process is enhanced by rapid thermal annealing treatments at moderate temperatures (400–500 °C).
Ionization enhancement in ionized magnetron sputter deposition
Authors: Joo Junghoon
Published: July 2002

To enhance the ionization level of ionized magnetron sputter deposition, the modulation of sputtering power was examined by using optical emission spectroscopy (OES) and probe analysis of the pulsed plasma as in situ diagnostics when Ag is sputtered in Ar. Probe analysis of internal inductively coupled plasma (ICP) was performed over a range of Ar pressures and rf powers, and harmonic analysis was done using fast Fourier transformation. Medium frequency (55 kHz) sputtering power was pulsed with various on/off duties to recover the 4 or 13.56 MHz excited ICP’s electron temperature which is quenched by heavily sputtered metals of low ionization threshold. The volumetric ion fractions of Ag and Ar, estimated by OES, showed distinct increase at 100/100 ms of on-off duty, which resulted in a change in preferred orientation of deposited Ag films from (111) to (200) by 3.6 times in the ratio of integrated diffraction intensities. Moreover, the measured substrate current did not decrease linearly by the expected rate on the basis of on-off duties.
On the active surface layer in CF3+ etching of Si: Atomistic simulation and a simple mass balance model
Authors: Abrams Cameron F. , Graves David B.
Published: July 2002

Molecular dynamics (MD) simulations of CF3+ ion bombardment of Si predict the formation of a steady-state fluorocarbosilyl mixing layer that actively participates in the etching of the underlying Si. The active nature of this mixing layer has been characterized by computing atomic residence time distributions (RTDs) for adsorbed fluorine and carbon. The average residence time of carbon in the layers is seen to increase dramatically as ion energy increases, while that of fluorine is not sensitive to ion energy. The overall RTDs compare well with those of an ideal stirred tank. A simple “well-mixed” transient mass balance model is presented. The phenomenology of this model is based on interpretations of the MD results. The model correctly predicts the evolution of atomic concentrations in the mixing layer. Both the MD and model results shed new light on how CF3+ ions etch Si.
1,3-dipolar cycloadditions on Si(100)-2×1: Theoretical studies of novel attachment chemistry for organic monolayers
Authors: Barriocanal José A. , Doren D. J.
Published: July 2002

Reactions of the Si(100) surface with a class of organic molecules known as 1,3-dipoles are studied by density functional theory calculations. A prototype reaction with diazomethane is found to occur with no activation barrier. The adsorbed species are strongly bound, but in some cases they are unstable with respect to further reaction. Several examples are given to show how the possibility of further reaction is related to the identity of the molecule. Comparisons to relevant experimental data are drawn and strategies for using this class of reactions to systematically modify Si(100) surfaces are discussed.
An XPS study of the influence of ion sputtering on bonding in thermally grown silicon dioxide
Authors: Hofmann S. , Thomas J. H.
Published: July 2002

Thermally grown SiO2 layers on Si were bombarded with He+, Ar+, and Xe+ ions at energies between 0.5 and 2 keV and subsequently studied by XPS. Chemical shifts of the Si 2p and O 1s peaks were not observed as a result of sputtering. Apparently, the oxide is not reduced by ion bombardment. However, the widths of the Si 2p and O 1s peaks increase with ion dose and ion energy. A steady state peak width was obtained at each energy for ion doses above 2×1017 cm−2. Steady state peak width dependence on ion species and energy is explained by a model based on the mean-projected ion range. Peak broadening can be explained by an increase in disorder that results from changes in the Si–O bond angle distribution within the ion range.
Chemical and structural analysis of the GaAs/AlGaAs heterojunctions by spectroscopic ellipsometry
Authors: Erman M. , Theeten J. B. , Vodjdani N. , Demay Y.
Published: July 2002

The dielectric functions of GaAs epitaxial layers have been measured at various temperatures and doping levels in a growth chamber using a spectroscopic ellipsometer. The 3 eV region is found to be especially sensitive to defects and dopants. The experimental dielectric functions can be described by a collection of seven harmonic oscillators with adjustable peak position, width, and height. Using the same set of oscillators with simple variations of the parameters, the dielectric function of AlxGa1−xAs ternaries of any composition can be obtained. These reference data have been used to investigate the chemical and structural nature of GaAs/Al0.54Ga0.46As and Al0.54Ga0.46As/GaAs heterojunctions fabricated in a MOVPE reactor. Interface regions are determined to be respectively, a 15±9Å thick chemical mixture and a nonexistent (0±5 Å) interface. These results upon the relative quality of the two types of heterojunctions are consistent with electrical measurements.
Radiation effects in TaSix/polysilicon MOS gate structures
Authors: Draper Bruce L. , McKeon Donald C.
Published: July 2002

Silicide deposition methods, contamination of underlying oxide layers, and the use of high temperatures to crystallize the films are discussed in relation to their effects on radiation hardness. Large dose enhancement effects for photon energies ≲300 keV are predicted for MOS devices using TaSix/polysilicon gate electrodes. However, experiments at 15, 100, and 1000 keV show no large differences in threshold voltage shifts among MOS capacitors using Al/poly, TaSix/poly, and W/poly gates. Among devices using various gate materials, differences in the amount of interface state generation and hole trapping within the gate oxide after irradiation are attributed to differences in the amount of mechanical stress in the oxide layers.
XPS/AES investigation of cross contamination in a plasma etcher
Authors: Karulkar Pramod C. , Tran Ngoc C.
Published: July 2002

Although dedication of plasma etching equipment strictly to a single process is becoming a common practice in IC labs, a large number of older plasma systems (especially the barrel type) were designed and are still used for multiple processes such as thin film etching in CF4 based plasma and photoresist striping in pure oxygen plasma. An investigation of a cross contamination effect is reported here. Silicon wafers coated with aluminum and exposed to a simulated oxygen plasma resist strip process were analyzed using Auger electron spectroscopy and x-ray photoelectron spectroscopy. Relatively large amounts of carbon and fluorine were found to be present on the wafer surfaces. Wafers exposed to wet chemical treatments were analyzed for comparison. The C and F contamination is believed to be due to redeposition of a fluorocarbon compound on the wafer surface originating from the chamber walls, etc. ESCA examination of the samples resulted in similar observations but the chemical identification of the contamination could not be made.
A Monte Carlo calculation of the virtual source size for a liquid metal ion source
Authors: Ward J. W.
Published: July 2002

We have developed a computer model to estimate the virtual source size of a liquid metal ion source. The ion trajectories were calculated using a Monte Carlo Computer code which included the effects of discrete Coulomb interactions. The analysis assumed the vacuum field of the sphere-on-orthogonal-cone (SOC) diode and used random numbers to simulate an ion emission process which had a Poisson distribution with full shot noise. Using the Monte Carlo generated trajectory data, we estimated the virtual source size by extrapolating trajectory tangents from reference planes normal to the emitter axis back to a plane containing the paraxial image of the virtual source. Extrapolation of the Monte Carlo computed virtual source size growth near the emitter predicts a virtual source size of 500–1000 Å at the extraction electrode.
Control electronics for a new submicron ion probe system
Authors: Ohnishi T. , Okutani T. , Hata K. , Ohiwa H. , Noda T. , Hosaka S.
Published: July 2002

Optical characteristics of a new submicron ion probe system capable of covering a wide area have been investigated; the system is composed of two cylindrical gap lenses, dual octupole deflectors, and a liquid metal ion source. We qualitatively measured the focusing characteristics of this focused ion beam system equipped with a liquid Ga ion source, through scanning ion microscope image of Cu mesh, and through scanning electron microscope observation of the ion etched crater formed in a gold film deposited on silicon. We obtained the on-axis probe size of about 0.2 μm diam under the condition of an accelerating voltage of 15 kV and acceptance half-angle of 1 mrad, leading to a current density of about 1 A/cm2. We also measured deflection characteristics of the system, and from the scanning ion microscope image we confirmed that the on-axis probe size is almost unchanged even at a point 1 mm away from the axis by correcting astigmatism and field curvature. A microcomputer system has been developed for controlling the dual octupole deflector (including dynamic correction) and the ion dose by monitoring probe or source current.
Arsenic-induced intensity oscillations in reflection high-energy electron diffraction measurements
Authors: Lewis B. F. , Fernandez R. , Madhukar A. , Grunthaner F. J.
Published: July 2002

A technique of arsenic-induced RHEED intensity oscillations has been used to accurately measure arsenic incorporation rates as a function of substrate temperature during the homoepitaxial growths of both GaAs and InAs by molecular beam epitaxy (MBE). Measurements were made at growth temperatures from 350 to 650 °C and at arsenic fluxes of 0.1 to 10.0 monolayer/s. The method measures only the arsenic actually incorporated into the growing film and does not include the arsenic lost in splitting the arsenic tetramers or lost by evaporation from the sample.