bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of hydrogen plasmas with hydrocarbon films, investigated by infrared spectroscopy using an optical cavity substrate
Authors: von Keudell A. , Jacob W.
Published: July 2002

The interaction of hydrogen atoms and ions with hydrocarbon (C:H) films plays an important role for the understanding of the growth and erosion of C:H films by plasma enhanced chemical vapor deposition. Elementary steps of the erosion mechanisms were recently identified in dedicated UHV experiments on ion beam deposited films. Furthermore, the interaction of hydrogen plasmas with C:H films was studied by ellipsometry in the visible spectral range. The interaction of H atoms as well as ions leads to a modified layer with a few nanometer thickness at the plasma facing surface of the film. We applied infrared spectroscopy (IRS) to investigate this modified layer created at the surface of C:H films with a thickness of only 10 nm, deposited on an optical cavity substrate. For the interpretation and quantification of the IRS data, a formalism is presented. It allows the calculation of the imaginary part κ of the refractive index n of the thin film samples from the measured IR spectra and includes multiple coherent reflections in the film itself, multiple incoherent reflections in the substrate, and takes into account the Kramers–Kronig relation between the real and imaginary part of the refractive index.
Interface formation between hydrogen terminated Si(111) and amorphous hydrogenated carbon (a-C:H)
Authors: Schäfer J. , Ristein J. , Miyazaki S. , Ley L.
Published: July 2002

In the last few years heterostructures consisting of a-C:H on top of crystalline silicon have revealed a number of interesting properties for electronic applications, for example, as a photodiode (see Ref. 1) or, very recently, as cold cathode electron emitter (see Ref. 2). For those applications the interface properties of the heterostructure play a key role. In this article the electronic and chemical nature of the interface between plasma deposited a-C:H in the form of diamondlike carbon (DLC) and hydrogen terminated silicon (111) was determined by in situ core level and valence band photoemission spectroscopy. The quantitative analysis of core level shifts and intensities indicate that both, an interface layer of mixed composition and a pure a-C:H layer, grow simultaneously with relative growth rates of 2:1 during the initial stages of the interface formation. The interface layer is first carbon rich and then approaches stoichiometric composition which is reached at an interface thickness of 18 Å. Then a reactive SiC interface is completed and acts as a diffusion barrier which prevents further extension of the interface region when the deposition of a-C:H proceeds. Aside from an acceptor passivation of the Si substrate, due to H atoms from the plasma, no overlayer induced band bending is measured. The valence band offset between Si and DLC is determined as 0.7±0.1 eV with the valence band edge of DLC below that of silicon.
Fabrication of electron-beam microcolumn aligned by scanning tunneling microscope
Authors: Park Jeong-Young , Choi Ho-Jin , Lee Y. , Kang S. , Chun K. , Park S. W. , Kuk Young
Published: July 2002

Performance of a low-energy electron beam was tested in a scanning tunneling microscope (STM) aligned field-emission microcolumn system made by using silicon microfabricated electrostatic lenses. The system consists of a STM aligned field emitter, an extractor, an accelerator, a beam dump, a quadrupole deflector, and an einzel lens. The beam current of 1 nA with a diameter of ∼0.2 μm was observed when a sample was placed less than 2 mm away from the exiting einzel lens.
Thermal and photon-induced desorption of NH3 and ND3 from Ag{111}
Authors: Szulczewski G. J. , White J. M.
Published: July 2002

Thermal desorption of NH3 and ND3 from Ag{111} reveals that adsorption is reversible with three desorption peaks at 145, 120, and 104 K. Irradiation of ammonia with 193 nm photons results in the desorption of molecular ammonia from the surface and in subsequent temperature programmed desorption there is no evidence for photodissociation. Below 3 monolayers (MLs) the cross section for photodesorption is less than 1×10−20 cm+2 for both isotopes, and above 3 ML the desorption yield increased linearly with coverage. Time-of-flight distributions were recorded as a function of coverage (3–50 ML) and characterized by two channels with average translational temperatures of 3150 and 600 K. The average flux-weighted kinetic energy of both channels is independent of laser pulse energy and the yield increases linearly with laser power, suggesting a nonthermal excitation mechanism. For multilayers, we propose a photodesorption model involving the direct excitation of ammonia.
Comparison of direct current and radio frequency argon magnetron discharges by optical emission and absorption spectroscopy
Authors: Dony M. F. , Ricard A. , Wautelet M. , Dauchot J. P. , Hecq M.
Published: July 2002

A magnetron sputtering discharge is studied by optical emission and absorption spectroscopy, following an experimental design procedure. The 33-mm-diam target is made in an aluminium base alloy. The radiation is focused on an optical fiber and is spectrally analyzed in a Jobin–Yvon computer-controlled 1.0 m Czerny–Turner scanning monochromator. The spatial resolution is 2 mm. Emission line intensities from the Ar sputtering gas and the sputtered species are studied as a function of geometrical and physical discharge parameters: excitation mode (rf or dc), target thickness, gas discharge pressure, electric power (rf) or current (dc), and the distance from the target. In emission spectroscopy, two Ar I lines are studied: Ar I 425.9 nm 3p55p(3p1)−3p54s(1s2) and Ar I 451.1 nm 3p55p(3p5)−3p54s(1s2) and also an Ar II line 442.6 nm 3p44p(4D0)−3p44s(4P). The first excited level configuration of Ar (3p54s) contains two metastable (1s5,1s3) and two resonant (1s4,1s2) levels. The Al excited and ground states have also been analyzed: the Al I 3p2P0−4s2S and Al I 3p2P0−4s2S. By use of hollow-cathode lamps, absorption due to aluminum atoms and argon metastable and resonant atom states densities are evaluated, as a function of the same parameters as in emission. The experimental responses (emission and absorption intensities) are fitted by a quadratic equation in which interactions between factors are included. The influences of the main factors are deduced and discussed.
Deposition of titanium carbide films from mixed carbon and titanium plasma streams
Authors: Delplancke-Ogletree Marie-Paule , Monteiro Othon R.
Published: July 2002

Dual source metal plasma immersion ion implantation and deposition was used to deposit TixCy films over a wide range of Ti:C composition. This technique is well adapted for this purpose and allows one to tailor the microstructure and properties of the films. We investigated the variation of the composition, bonding states, and structure as functions of the deposition conditions. Excess carbon and contamination oxygen are incorporated in the TiC lattice interstitially and substitutionally, respectively. The wear mechanism of a stoichiometric TiC film was investigated and compared to that of a diamondlike carbon film. TiC fails by wear and microcrack propagation.
Direct current magnetron sputtered W–AlN cermet solar absorber films
Authors: Zhang Qi-Chu
Published: July 2002

W–AlN cermet selective surfaces have been investigated using a special direct current (dc) magnetron sputtering technology. During the deposition of the W–AlN cermet layer, both Al and W targets were run simultaneously in a gas mixture of argon and nitrogen. The total sputtering gas pressure was 1 Pa and the reactive nitrogen gas partial pressure was chosen at 2.5×10−2 Pa, which is beyond the transition point from metal phase to dielectric phase in the deposited material. The ceramic AlN component was deposited by dc reactive sputtering and the metallic W component by dc sputtering due to the excellent nitriding resistance of metallic tungsten. By substrate movement a multi-sublayer system, consisting of alternating W and AlN sublayers, was deposited. This deposited multi-sublayer system can be considered as a macro-homogeneous W–AlN cermet layer with metal volume fraction determined by controlling the thickness of the sublayers. W–AlN cermet selective surfaces with a double cermet layer film structure were deposited. The typical film structure from surface to bottom substrate is an AlN anti-reflection layer on a double W–AlN cermet layer on an Al metal infrared reflection layer. A solar absorptance of 0.92–0.94 with emittance of 0.03–0.05 at room temperature and 0.08–0.10 at 350°C has been achieved for such W–AlN cermet selective surfaces. The W–AlN cermet has excellent thermal stability in vacuum at high operating temperature.
Electrical characterization of a processing plasma chamber
Authors: Roth Weston C. , Carlile Robert N. , O’Hanlon John F.
Published: July 2002

In this article, we discuss techniques for electrically characterizing a plasma processing tool for the purpose of measuring the plasma impedance at the fundamental frequency. This was accomplished by building a “probe station” containing commercially available current and voltage probes which can be inserted into the radio frequency (rf) coaxial cable through which rf power is supplied to the driven electrode. We have applied our techniques to a specific tool, the Tegal modified MCR-1 etch system. We find that an essential part of the characterization is the measurement of the impedance of the device when the plasma is extinguished, which is in parallel with the plasma impedance. We find that this impedance is an inductance in series with a capacitance, similar to that found for the GEC reference cell; thus, this equivalent circuit may be universal although the element values will be machine dependent. Measurement of plasma impedance at harmonic frequencies is discussed. For the Tegal tool, we find that when the rf power is applied as a step function at t=0, the plasma impedance exhibits a transient for both its resistance and reactance. The transient occurs during the first 4 min after rf power is applied, during which the resistance and reactance decrease by 10%–20%, and then finally achieve a value that thereafter is nearly invariant in time. We have ruled out contamination, temperature effects, and plasma chemistry as the source of the transient. The impedance transient correlates well with a similar transient that we observe in the density of water vapor molecules that are present in the chamber, and we speculate that there may be a correlation between the two. The transient should be of concern to processing engineers who may find processing parameters changing during the process time, which is usually comparable to 4 min.
Reaction of the fluorine atom and molecule with the hydrogen-terminated Si(111) surface
Authors: Morikawa Yasuhiro , Kubota Kazuhiro , Ogawa Hiroki , Ichiki Takanori , Tachibana Akitomo , Fujimura Shuzo , Horiike Yasuhiro
Published: July 2002

To establish the self-limiting reaction process that is necessary to achieve the atomic layer-by-layer etching for the damageless fabrication of nanometer-electronics devices, the initial reaction of fluorine (F) atoms and F2 molecules with hydrogen (H)-terminated Si(111) was studied employing a combined system of Fourier transform infrared (FTIR)-attenuated total reflection (ATR) and x-ray photoelectron spectroscopy (XPS). In the ATR measurement, peaks of 2086 cm−1 (B2) and 2090 cm−1 (B3) newly appeared instead of a decrease in the original Si–H peak at 2083 cm−1 (B1) with initial exposure of XeF2. The sum area of B1, B2, and B3 peaks until ∼2000 L was almost constant. This implies that B2 and B3 peaks also resulted from Si–H bonds. The XPS measurement revealed that the initial exposure of XeF2 generated nonbonded F atoms at first, followed by SiF1 bonds. Based on the good correspondence between ATR and XPS results, first the F atoms penetrate just underneath the Si–H bond, generating the B2 peak. After further exposure the B3 peak appears arising from the bonding of an F atom with a Si–H bond at the five-coordination state. However, further exposure of F atoms caused higher order SiFx (x=1,2,3) products. Hence, an F2 gas that was less reactive than F atoms was investigated. It was found that the exposure of H-terminated Si(111) to 5% F2/He reached a plateau value at 5×105 L, where terminated H atoms completely disappeared. The SiF monolayer corresponded exactly to the formation of an atomic layer of Si(111). This indicates that the self-limiting process for the Si/F system is realized first.
Non-contact probing of high speed microelectronics using electrostatic force sampling
Authors: Bridges G. E. , Noruttun D. , Said R. A. , Thomson D. J. , Lam T. , Qi R.
Published: July 2002

The ability to perform non-invasive high-frequency measurements at the internal points of an integrated circuit is important for the design and failure analysis of advanced microelectronics. As integrated circuit densities and speed increase, obtaining information on their internal operation becomes extremely difficult using conventional probing methods due to parasitic loading and low spatial resolution. We present a non-contact probing technique based on a nonlinear Coulomb force interaction for extracting high-frequency signals at internal points of an integrated circuit. Internal circuit voltages are measured by sensing the local electrostatic force on a small micromachined probe that is held in close proximity to the circuit measurement point. The bandwidth of force measurements made using proximal probes are typically limited by the mechanical frequency response of the probe. In the presented instrument high frequency waveform measurements are enabled by using a pulse sampled heterodyne technique. The probing instrument has a bandwidth of 3 GHz and is capable of internal circuit delay measurements with a resolution of less than 10 ps. Measurement of the internal propagation delays and rise times of a complementary metal-oxide-semiconductor inverter chain are given.
Hybrid ferromagnet–semiconductor devices
Authors: Johnson Mark
Published: July 2002

Novel magnetoelectronic devices for application as nonvolatile memory cells, logic gates, or magnetic field sensors are based on a bilayer structure comprised of a high mobility semiconducting Hall cross and a single, electrically isolated, microstructured ferromagnetic film. Prototypes have been fabricated at the micron and sub-micron size scale. The device state is determined by the bistable magnetic state of the ferromagnetic element, and the two corresponding output states can be symmetrically bipolar or HIGH (order of tens of ohms) and LOW (approximately zero). Fabrication involves two lithographic steps, a mesa etch of the semiconductor and a patterning of the ferromagnetic film. Atomic force microscope and magnetic force microscope images are used to correlate the effects of processing on the micromagnetism of the ferromagnetic component and the device output characteristics. Early prototype device sets have been fabricated using high mobility indium arsenide layers for the Hall element, but the concept is compatible with silicon technology. The device demonstrates inverse scalability: output levels increase as the device dimensions decrease.
The birth of electronics: Thermionic emission and vacuum
Authors: Redhead P. A.
Published: July 2002

The early developments in the field of thermionic electron emission are reviewed with emphasis on the importance of improved vacuum technology in understanding the physical mechanism and in the production of reliable vacuum tubes. The period covered is from the discovery of the Edison effect in 1883 until 1920, when improved vacuum technology had resolved the controversy about the source of electrons in thermionic emission and the fledgling electronics industry had started the large scale production of vacuum tubes for radio receivers.
Characteristics of amorphous and polycrystalline silicon films deposited at 120 °C by electron cyclotron resonance plasma-enhanced chemical vapor deposition
Authors: Bae Sanghoon , Kalkan A. Kaan , Cheng Shangcong , Fonash Stephen J.
Published: July 2002

Amorphous and polycrystalline silicon (poly-Si) films, deposited by an electron cyclotron resonance plasma-enhanced chemical vapor deposition system at 120 °C, have been investigated. All films have been grown with either hydrogen or argon dilution. Using the films with the hydrogen dilution, the effect of rf (13.56 MHz) substrate bias has also been studied. Analysis with x-ray diffraction shows that films grown with Ar dilution and no rf bias do not show any crystallinity while the corresponding films deposited with H2 dilution and no rf bias contain a significant amount of the crystalline phase. With only a 3:1 H2 to silane ratio, highly crystallized films can be grown at 120 °C. In the presence of rf (13.56 MHz) substrate bias, there is a decrease of crystallinity in films. It has been found from cross-sectional transmission electron microscopy that films deposited without rf bias develop a very uniform columnar structure whereas films made with rf bias develop a closely packed, continuous but more amorphous structure. It is found that these changes caused by rf bias affect the photoluminescence intensity.
Postdeposition reduction of noble metal doped ZnO films
Authors: Exarhos Gregory J. , Rose Aimee , Wang Li Qiong , Windisch Charles F.
Published: July 2002

Insulating ZnO (wurtzite phase) films containing 1% to 2% Pt, Au, Pd, Ga, or Al dopants have been deposited onto silica, silicon, and aluminum substrates under oxidizing conditions. Substantial enhancement in film conductivity is promoted by postdeposition reduction in hydrogen above a critical temperature or by room temperature cathodic reduction in an electrochemical cell. Film reduction requires the presence of atomic hydrogen, formed at the film surface either by dissociative adsorption of gaseous H2 or its electrochemical generation from a buffered aqueous solution. As deposited and reduced films have been characterized using x-ray photoemission spectroscopy, Raman spectroscopy, optical transmission measurements, spectroscopic ellipsometry, voltammetry, chronopotentiometry, and four-point conductivity measurements. Results indicate that film deposition parameters and postdeposition reduction alter the oxidation states of both the zinc and the resident dopant cations. The zinc reduction reaction appears to be quasireversible while the reduced noble metal dopants in the films are not prone to reoxidation. These results may have implications for enhancing stability of the optical response and electrical conductivity exhibited by these films.
Adsorption of oxygen on Pd(111): Precursor kinetics and coverage-dependent sticking
Authors: Sjövall Peter , Uvdal Per
Published: July 2002

The adsorption of oxygen on Pd(111) was studied using supersonic molecular beam techniques. The dependences of the initial sticking coefficient (zero coverage) on O2 translational energy (0.083–0.69 eV) and substrate temperature (100–650 K) indicate a precursor dissociation mechanism involving a chemisorbed and a physisorbed precursor state. At low translational energies, ⩽0.13 eV, the chemisorbed (molecular) precursor state is populated either directly or via trapping into the physisorbed precursor state, while the direct molecular chemisorption channel dominates at higher translational energies. No indication of direct dissociation was observed. The oxygen coverage dependence of the sticking coefficient shows that extrinsic precursors assist the sticking at low substrate temperatures. The saturation coverage is independent of O2 translational energy, supporting the proposed precursor dissociation mechanism.
Interface studies of tungsten nitride and titanium nitride composite metal gate electrodes with thin dielectric layers
Authors: Claflin B. , Binger M. , Lucovsky G.
Published: July 2002

Interface formation between reactively sputtered tungsten nitride (WNx) or titanium nitride (TiNx) metallic films and thermally grown silicon dioxide (SiO2) layers is studied by interrupted growth with on-line Auger electron spectroscopy. For both composite metals, growth proceeds directly without a metal precursor layer. The chemical stability of these WNx/SiO2 and TiNx/SiO2 interfaces is investigated by rapid thermal annealing up to 850 °C. The WNx/SiO2 interface is stable up to 650 °C while TiNx/SiO2 is stable below 850 °C. Metal–oxide–semiconductor capacitors have been fabricated with WNx and TiNx gates and 7.5 nm thick thermal oxide gate dielectrics with interface trap densities, Dit<2×1011 cm−2 eV−1. Capacitance–voltage and current–voltage measurements indicate the Fermi level for TiNx lies near midgap in Si, while for WNx it lies closer to the valence band.
Electron velocity distribution functions in a sputtering magnetron discharge for the E×B direction
Authors: Sheridan T. E. , Goeckner M. J. , Goree J.
Published: July 2002

The electron velocity distribution function is measured for the E×B (azimuthal) direction in a cylindrically symmetric, planar, sputtering magnetron discharge as a function of height above the cathode. Near the cathode, the distribution function is approximately a warm Maxwellian (Te≈2 eV) shifted in the E×B direction, indicating a strong azimuthal drift. Farther above the cathode, the distribution function is characterized by a cold (Te≈0.5 eV), Maxwellian bulk with energetic, asymmetric tails.
Simulations of BCl3/Cl2/Ar plasmas with comparisons to diagnostic data
Authors: Meeks Ellen , Ho Pauline , Ting Aili , Buss Richard J.
Published: July 2002

A reaction mechanism is reported that describes BCl3/Cl2/Ar plasmas used in the etching of metal lines in microelectronics fabrication processes. Although many of the fundamental electron-impact cross sections for this system are not well known, a reasonable set of reaction paths and rate coefficients has been derived to describe low-pressure reactors with high plasma density. The reaction mechanism describes 59 possible gas-phase events and 18 plasma-surface interactions. A well-mixed reactor model is used to develop the reaction set and to test it against absolute experimental measurements of electron and Cl− densities, as well as relative measurements of BCl and Cl radicals in an inductively coupled research reactor. The experimental data cover a wide range of operating conditions and gas mixtures. The model provides quantitative agreement with measurements over the whole range of conditions and diagnostics, capturing most of the observed trends. In addition, the model predicts relative ion ratios and Cl/Cl2 density ratios as measured by molecular beam mass spectrometry. Comparisons of results from the zero-dimensional model and a two-dimensional continuum plasma model, using the same reaction mechanisms, further validate the chemistry set and show the strengths and weaknesses of the well-stirred reactor approach. Sensitivity analysis shows the dominant reactions contributing to model predictions of species densities.
Detection of trace nitrogen in bulk argon using proton transfer reactions
Authors: Hunter E. J. , Homyak A. R. , Ketkar S. N.
Published: July 2002

Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is being routinely used to quantify trace impurities in bulk gases used in the manufacture of semiconductor devices. APCI-MS has been successfully applied for the quantification of ppt (ng/Kg) levels of O2, H2O, CO2 and CH4 in Ar, N2 and He and trace N2 in He. However it has not been successfully used to quantify ppt levels of N2 in Ar due to unfavorable rate constant for the charge transfer reaction between Ar+ and N2. We report here the detection of ppt levels of N2 in Ar by adding a few percent of purified H2 into the ionization source of the mass spectrometer. The addition of H2 results in a plasma dominated by protonated ions and the detection of trace N2 is facilitated by favorable proton transfer reactions to produce N2H+. Our experimental results indicate statistical detection limits below 50 ppt.
Chemical alteration of the native oxide layer on LiGaO2(001) by exposure to hyperthermal atomic hydrogen
Authors: Wolan John T. , Hoflund Gar B.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to examine the near-surface region and outermost atomic layer of air-exposed, solvent-cleaned, LiGaO2(001) substrates, respectively, before and after room-temperature exposures to the flux produced by a novel electron stimulated desorption hyperthermal H-atom source. The native oxide layer on the solvent-cleaned LiGaO2(001) substrate is nonhomogeneous and contains primarily LiO, Ga, and small amounts of C. Li is initially present in the near-surface region as Li2O, LiGaO2, and a small amount of LiOH. Several forms of O are present including adsorbed water, LiGaO2, Li, and Ga-oxides, and hydroxyl groups with Ga2O3 as the predominant species. Upon exposure to the hyperthermal H-atom flux, low-temperature removal of oxygen and carbon contaminants occurs, and the near-surface region approaches the stoichiometry of a clean LiGaO2(001) surface except for an increased O concentration. The usually difficult to observe Li 1s photoelectron peak increases in intensity significantly with H-atom exposure. XPS binding energies for LiGaO2(001) have been assigned for Li 1s, O 1s, Ga 3d, and 2p peaks at 56.0, 530.2, 19.4, and 1116.9 eV, respectively. According to the He+ ISS data, the H-atom flux is very effective in removing surface contamination and enriches the outermost atomic layer in O through diffusion of subsurface O to the surface under a chemically induced driving potential. This O enrichment implies that the diffusion of O to the surface is more rapid than removal of surface O by impinging H atoms.
Stable anionic sites on hydrogenated (111) surfaces of cubic boron nitride resulting from hydrogen atom removal under chemical vapor deposition conditions
Authors: Komatsu Shojiro , Okada Katsuyuki , Moriyoshi Yusuke
Published: July 2002

In plasma or hot-filament assisted chemical vapor deposition of cubic boron nitride (cBN), the formation of a surface radical site by hydrogen atom removal from a hydrogenated (111) surface was expected to be followed by the formation of an anionic vacant site (AVS) by capturing an electron, since this yields a closed shell structure of the site atom. This possibility was investigated by ab initio as well as by semiempirical molecular orbital calculations using large cluster models. The stabilization energy of the AVS on cBN(111) with a boron top layer, namely (111) B, was 1.8–2.3 eV; this value is comparable with that of diamond. On the other hand, that of cBN(111) on a nitrogen surface, namely (111) N, amounted to 5.3–5.9 eV. The nucleophilic nature of the AVS with a lone pair of electrons suggests electrophilic reagents for related reactions. This helped us to propose SN2 growth reactions for diamond growth both on diamond and cBN(111) surfaces. The difference in chemical reactivity between (111) N and (111) B could be interpreted in terms of the “hard” and “soft” acid base concept that has been renewed by the frontier orbital theory.
Passivation of CdZnTe surfaces by oxidation in low energy atomic oxygen
Authors: Chen H. , Chattopadhyay K. , Chen K.-T. , Burger A. , George M. A. , Gregory J. C. , Nag P. K. , Weimer J. J. , James R. B.
Published: July 2002

A method of surface passivation of Cd1−xZnxTe (CZT) x-ray and gamma ray detectors has been established by using microwave-assisted atomic oxygen bombardment. Detector performance is significantly enhanced due to the reduction of surface leakage current. CZT samples were exposed to an atomic oxygen environment at the University of Alabama in Huntsville’s Thermal Atomic Oxygen Facility. This system generates neutral atomic oxygen species with kinetic energies of 0.1–0.2 eV. The surface chemical composition and its morphology modification due to atomic oxygen exposure were studied by x-ray photoelectron spectroscopy and atomic force microscopy and the results were correlated with current-voltage measurements and with room temperature spectral responses to Ba133 and Am241 radiation. A reduction of leakage current by about a factor of 2 is reported, together with significant improvement in the gamma-ray line resolution.
Formation of alkylsiloxane self-assembled monolayers on Si3N4
Authors: Sung Myung M. , Kluth G. Jonathan , Maboudian Roya
Published: July 2002

The structure of alkylsiloxane self-assembled monolayers formed on HF-treated Si3N4 has been studied using x-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, and contact angle analysis. It is shown that the monolayers are similar in quality to those formed on oxidized silicon, despite the fact that upon etching in HF, the Si3N4 surface contains only 0.2 ML of oxygen. In contrast, on NH4F-treated Si(100) surfaces with similar quantities of oxygen, high-quality monolayers cannot be formed. We argue that these results point to the importance of a water layer in monolayer formation.
Outgassing in thin wall stainless steel cells
Authors: Nemanič Vincenc , Šetina Janez
Published: July 2002

Outgassing of hydrogen determines the ultimate pressure of a metal ultrahigh vacuum system, but also limits the long-term performance of sealed-off metal devices, where a thermal insulating grade of vacuum is required for a period of several years. Hydrogen concentration in stainless steel is related to equilibrium pressure by means of Sievert’s law, while the outgassing rate qout and equilibrium pressure are not related, particularly in the high vacuum range. Thin wall stainless steel cells (wall thickness 0.15 mm, AISI304 and AISI316) were used to test the relation between thermal treatment and the resulting room temperature outgassing rate qout. They were cleaned and baked in situ at ∼205 °C for ∼16 h. The pressure rise was recorded by a spinning rotor gauge after sealoff. The initial pressure rise slope at a H2 equivalent pressure of ∼10−5 mbar was in the order of qout≅1×10−14 mbar l H2/s cm2. During the measurements, which were performed at least 750, but even in excess of 3000 h, the outgassing rate started to decrease, which may be explained by its approaching equilibrium pressure. From the difference, the recombination rate coefficient KL was determined on the basis of a simple model. It lay in the range of KL (296 K)≅10−25–10−24 molecules H2 cm4/(atoms2 H s). The cells inner surfaces were analyzed by Auger electron spectroscopy. Their composition was rather typical for technical grade stainless steel covered by a native oxide layer. The corresponding KL values, which were not measured previously at room temperature, are matched with extrapolated reported values for an electropolished stainless steel surface. In addition, hydrogen annealing at 1030 °C was applied as a pretreatment of two of the cells without any noticeable effect on the final outgassing rate even if the inner surface was covered by a thick oxide layer. By increasing of the bakeout temperature, it was possible to prepare cells where qout was in the order of ≅1×10−15 mbar l H2/s cm2.
Particle measurements in vacuum tools by in situ particle monitor
Authors: Miyashita Haruzo , Kikuchi Toshio , Kawasaki Yohsuke , Katakura Yoshio , Ohsako Nobuharu
Published: July 2002

In situ particle monitors (ISPMs) have been developed and evaluated by installing them onto a variety of vacuum tools. It has been shown that the ISPM’s enable: (1) detection of sporadic particles in vacuum chambers, (2) specification of particle sources, (3) detection of tool maintenance cycles, and (4) optimization of chamber venting conditions. In the process of evaluating the ISPM’s, it has become clear that particle counts measured by ISPM sensors significantly depend on the location where the sensors are installed. As a result of a comparison between the ISPM particle counts and particle-per-wafer-pass particle counts, it has been found that there is a correlation between the two measurements. However, ISPMs offer a broad range of advantages in respect of the reduction of the cost of ownership and being provided real time measurement, and therefore, it is implied that ISPMs have the potential to replace or supplement monitor wafer measurements.
Hydrogen in compound semiconductors
Authors: McCluskey M. D. , Johnson N. M.
Published: July 2002

Hydrogen can be inadvertently introduced at any of several steps in the fabrication of optoelectronic devices. The most common consequence of hydrogenation is the passivation of dopant impurities, which leads to a decrease in the electrical conductivity of the material. The most successfully applied experimental technique for directly determining the involvement of hydrogen has been infrared-absorption local vibrational mode (LVM) spectroscopy. Examples of LVM spectroscopy of hydrogen-related complexes are given for the compound semiconductors GaP, ZnSe, GaN, GaAs, and AlSb. Recent studies have utilized large hydrostatic pressures to probe the vibrational properties of hydrogen-related complexes.
X-ray photoelectron spectroscopy and atomic force microscopy investigation of stability mechanism of tris-(8-hydroxyquinoline) aluminum-based light-emitting devices
Authors: Le Quoc Toan , Avendano F. M. , Forsythe E. W. , Yan Li , Gao Yongli , Tang C. W.
Published: July 2002

Stability is an essential issue in the application of organic light-emitting devices (OLEDs). We have investigated the indium tin oxide (ITO) surface for operated and unoperated OLEDs using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The device structure consists of ITO/phenyl-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag with NPB thickness varied from 0 to 300 Å. The ITO surface was exposed by removing the organic and metal layers with dichloromethane, an organic solvent in which NPB and Alq3 are highly soluble. Electroluminescence characterization demonstrates that the NPB layer substantially enhanced the stability. XPS analysis shows that for the device made without NPB and after 90 h of operation, there exists an insoluble organic material on the ITO surface. This organic material is not observed on the ITO of unoperated devices. Lateral force AFM also shows a striking difference between the ITO surface of devices with and without NPB after operation. The XPS and AFM results suggest that the organic residue is the degradation product of Alq3 that acts as quenching sites at the ITO/Alq3 interface, which contribute to the early failure of the single-layer devices.
X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry study of the role of Ti and TiN caps on the cobalt/SiO2 interface
Authors: Conard T. , Kondoh E. , De Witte H. , Maex K. , Vandervorst W.
Published: July 2002

Continuous down scaling of device features and increases in operation frequency of integrated circuit (ICs) requires a low electric resistance of interconnects to transistors. Due to its low resistivity and high thermal stability, the integration of CoSi2 into ultralarge scale ICs is becoming the main stream. In this study, a 15 or 20 nm Co film was grown on SiO2 and Ti or TiN top layers were deposited on the Co layer without breaking the vacuum. The samples were annealed in N2 ambient and the specimens were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry in depth profile mode. Significantly different depth profiles were obtained depending on the nature of the cap layer and on the annealing temperature. The multilayer with a top TiN layer presents a profile corresponding to sharp interfaces with only a limited diffusion of Ti inside the Co layer and no differences in chemistry of the interfaces. The Co depth profile has a very symmetrical shape. On the contrary, the presence of a Ti cap layer induces very strong modification of the interface reactions. An important diffusion of the Ti is observed through the Co layer and an accumulation of Ti occurs at the Co/SiO2 interface. At the interface, Ti is observed in an oxidized form and reduces the top of the SiO2 layer. When the annealing temperature is reduced to 650 °C no pile up of Ti is seen at the interface and the silicon profile is similar to the profile obtained with the TiN cap layer.
Reversal behavior in a bimodal magneto-optical medium
Authors: Fry R. A. , Bennett L. H. , Della Torre E.
Published: July 2002

Bimodal magnetic behavior, in which Kerr rotation (θK) and ellipticity (εK) each exhibit major magneto-optic hysteresis loops with two distinct field-dependent steps, was encountered in a (0.3 nm Co/1.2 nm Pt)15 multilayer film with perpendicular magnetization. A model is postulated in which there are two different interacting magnetic entities present in the layered structure of this material, each with a stable perpendicular magnetization state either parallel or antiparallel to the applied field, and which reverse quasi-independently from one another. Due to interactions between the two, the reversals occur at the intrinsic coercivities displaced by an interaction field, Hi, whose sign depends upon the magnetization of the other phase. Using major loop and first-order reversal measurements, the intrinsic coercivities, as well as Hi, were obtained.
Microstructure modification of silver films deposited by ionized magnetron sputter deposition
Authors: Chiu K.-F. , Blamire M. G. , Barber Z. H.
Published: July 2002

Silver films have been deposited under controlled ion bombardment by ionized magnetron sputter deposition (IMSD). The technique uses a built-in rf coil to generate an inductively coupled plasma confined close to the substrate. This enables precise control of both the bombarding ion flux (by rf power) and the energy (by substrate bias). By varying the flux and energy of bombarding ions, the film’s structure and properties can be easily modified. Crystallography, grain size, and film texture have been characterized using the x-ray diffraction method, and film stress was measured by a substrate curvature technique. A focused ion beam was used to section the deposited films and to observe the surface morphology and cross-sectional structure. The electrical resistivity ratio (room to liquid nitrogen temperature: R298 K/R77 K) was used to investigate the influence of the film structure on the conductivity. The persistence of bombardment induced film property variation with thickness was studied in terms of the texture variation in bilayers consisting of IMSD and magnetron sputtering deposited films. It is found that the microstructure of deposited films depends predominantly on the ion bombardment during the initial stages of film growth. Using the IMSD technique, the structure and related properties of silver films have been modified by depositing films under precisely controlled ion bombardment.
Ferroelectric properties of Pb(Zr, Ti)O3 thin films deposited on annealed IrO2 and Ir bottom electrodes
Authors: Lee Hee-Soo , Um Woo-Sik , Hwang Kwang-Taek , Shin Hyun-Gyoo , Kim Young-Bae , Auh Keun-Ho
Published: July 2002

Ferroelectric fatigue and hysteresis of reactively sputtered Pb(Zr, Ti)O3 (PZT) thin films were investigated by annealing IrO2 and Ir bottom electrodes at various temperatures. These electrodes were annealed to change their crystallinity and surface morphology in O2 or N2 atmosphere, respectively. There was no appreciable roughening of the PZT/IrO2 interface respective to that of the PZT/Ir; the rms roughness of IrO2 and Ir annealed at 650 °C was about 3.5 and 10 nm, respectively. The ferroelectric properties of the PZT/IrO2 were found to be overall better than those of the PZT/Ir. The PZT/IrO2 thin films exhibited very small fatigue up to 1011 cycles; the P*r-P∧r value decreased only from 16.6 to 14 μC/cm2 until 1012 polarization reversals. This is due to the excellent diffusion barrier property of IrO2 and the smooth PZT/IrO2 interface. On the other hand, although thin IrO2 layer was formed between PZT and Ir, the PZT/Ir thin films began to undergo fatigue after 109 polarization reversals.
Dynamic mixing deposition/implantation in a plasma immersion configuration
Authors: Tian X. B. , Zhang T. , Zeng Z. M. , Tang B. Y. , Chu P. K.
Published: July 2002

A surface layer consisting of titanium, nitrogen, and oxygen is implanted/deposited onto SS304 stainless steel using dynamic mixing and plasma immersion ion implantation. Titanium is introduced into a nitrogen glow discharge plasma from a metal arc plasma source. Dynamic mixing is achieved via the co-implantation of Ti ions with high charge states as well as nitrogen and oxygen ions in the plasma. The resulting surface layer possesses superior tribological properties and corrosion resistance. The observed improvement in the wear resistance is more than a factor of 10. The enhancement in the surface properties is believed to be due to the synergistic effects of the coexistence and dynamic mixing of titanium, nitrogen, and oxygen at the interface.
Preparation and mechanical properties of composite diamond-like carbon thin films
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Sankar J. , Narayan J.
Published: July 2002

We have investigated mechanical properties of diamond-like carbon (DLC) thin films, particularly the internal compressive stress and ways to alleviate it. Foreign atoms such as copper, titanium, and silicon were incorporated into the DLC films during pulsed laser deposition. The chemical composition of the doped films was determined using Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy (XPS). Optical microscopy of the doped films showed that DLC films containing Cu exhibit much less particulate density as compared to the films containing Ti and Si. Visible Raman spectroscopy was used to characterize the films. The effect of dopants on the Raman spectrum was analyzed in terms of peak shape and position. Optical microscopy of the pure DLC of a certain thickness showed severe buckling. The mechanisms of adhesion associated with DLC coatings were discussed. Qualitative scratch tests on the specimens showed that pure DLC films have relatively poor adhesion due to a large compressive stress, while the doped DLC films exhibit much improved adhesion. Wear tests show improved wear resistance in the doped DLC coatings. Nanoindentation results suggest that pure DLC has an average hardness above 40 GPa and effective Young’s modulus above 200 GPa. The doped DLC films showed slightly decreased hardness and Young’s modulus as compared to pure DLC films. These results can be rationalized by analyzing the internal stress reduction as derived from Raman G-peak shift to lower wavenumbers. A preliminary interpretation of the stress reduction mechanism is discussed.
Adhesion improvement of cubic BN:C film synthesized by a helicon wave plasma chemical vapor deposition process
Authors: Kim Kyoung-Bo , Kim Seon-Hyo
Published: July 2002

The growth and adhesion of cubic boron nitride:carbon (c-BN:C) film were investigated using Fourier transform infrared spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. c-BN:C films were prepared on a Si(111) substrate by a helicon wave plasma chemical vapor deposition process using borazine, methane, and hydrogen beyond the critical substrate bias and temperature of −250 V and 450 °C, respectively. The improved adhesion of c-BN:C film with the addition of CH4 and hydrogen resulted from the simultaneous reduction of residual compressive stress and nonbonded (free) boron reaction with atmospheric water vapor. In addition, postheat treatment at 800 °C could further reduce the residual compressive stress in the c-BN:C film. The repetition technique of the combinative process of carbon and hydrogen addition together with postheat treatment (multistep deposition method) enabled the growth of thick c-BN:C film of ∼1 μm.
X-ray photoemission spectroscopy and scanning tunneling spectroscopy study on the thermal stability of WO3 thin films
Authors: Santucci S. , Cantalini C. , Crivellari M. , Lozzi L. , Ottaviano L. , Passacantando M.
Published: July 2002

In this work the surface electronic and structural properties of about 150 nm thick WO3 films, deposited in high vacuum by thermal evaporation onto Si substrates, have been studied in ultrahigh vacuum (UHV) by means of x-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM)/spectroscopy. After deposition these films have been annealed in atmospheric oven for 24 h at different temperatures (300 and 500 °C) to stabilize the film morphology. XPS measurements to follow W 4f, O 1s peaks and the valence band, have been performed on these samples both as prepared and after a re-annealing in UHV at temperatures ranging from 50 to 350 °C. The UHV re-annealing procedure strongly modifies the W 4f peak of both the as deposited and the 300 °C/24 h treated samples, and produces an increase of metallic states at the Fermi edge. Instead, the 500 °C/24 h sample, after heating in UHV shows substantial stability of the nearly stoichiometric WO3 phase. Using STM in UHV we have investigated the morphology of the samples at room temperature and after the annealing at elevated temperatures up to 350 °C. In particular, we have taken I–V curves on typical grains of the polycrystalline sample. Our findings on the electronic structure of samples close to the Fermi level are in agreement and allow a clearer understanding of the findings from the parallel XPS study.
Magnetized inductively coupled plasma etching of GaN in Cl2/BCl3 plasmas
Authors: Lee Y. H. , Sung Y. J. , Yeom G. Y. , Lee J. W. , Kim T. I.
Published: July 2002

In this study, Cl2/BCl3 magnetized inductively coupled plasmas were used to etch GaN, and the effects of magnetic confinements of inductively coupled plasmas on the GaN etch characteristics were investigated as a function of Cl2/BCl3. Also, the effects of Kr addition to the magnetized Cl2/BCl3 plasmas on the GaN etch rates were investigated. The characteristics of the plasmas were estimated using a Langmuir probe and quadrupole mass spectrometry (QMS). Etched GaN profiles were observed using scanning electron microscopy. The small addition of BCl3 (10%–20%) in Cl2 increased the GaN etch rates for plasmas both with and without magnetic confinements. The application of magnetic confinements to the Cl2/BCl3 inductively coupled plasmas increased the GaN etch rates and changed the Cl2/BCl3 gas composition of the peak GaN etch rate from 10% BCl3 to 20% BCl3. It also increased the etch selectivity over the photoresist, while slightly reducing the selectivity over SiO2. The application of the magnetic field significantly increased positive BCl2+ measured by QMS and total ion saturation current measured by the Langmuir probe. Other species such as Cl, BCl, and Cl+ increased, whereas species such as BCl2 and BCl3 decreased with the application of the magnetic field. Therefore, it appears that the increase of the GaN etch rate in our experiment is related to the increased dissociative ionization of BCl3 by the application of the magnetic field. The addition of 10% Kr in an optimized Cl2/BCl3 condition (80% Cl2/20% BCl3) with the magnets increased the GaN etch rate about 60%. A more anisotropic GaN etch profile was obtained with the application of the magnetic field, and a vertical GaN etch profile was obtained with the addition of 10% Kr in an optimized Cl2/BCl3 condition with the magnets.