bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of sol-gel processing as a method for fabricating spherical-shell silica aerogel inertial confinement fusion targets
Authors: Jang K. Y. , Kim K.
Published: July 2002

A feasibility study has been undertaken of a method for fabricating uniform, hollow silica aerogel spheres of controlled size, thickness, and porosity that may be required for manufacture of cryogenic inertial confinement fusion targets. The method is a combination of a droplet generation method and sol-gel processing. The parameters controlling the properties of the resulting silica aerogel spheres are the detailed chemical makeup of the reactant solution (which consists of tetraethylorthosilicate, ethyl alcohol, and water) and the gelation medium (which consists of either ammonia and nitrogen gas or ammonium hydroxide), and the dimensions and relative positions of the nozzles used for the droplet generation. To monitor the hydrolysis and polymerization reactions infrared spectroscopy and 1H and 29Si nuclear magnetic resonance were used. The characterization of the silica spheres was performed using mercury intrusion porosimetry, optical microscopy, and scanning electron microscopy. Hollow silica aerogel spheres with densities as low as 61 mg/cm3 were obtained from a reactant solution of 134 composition (namely, TEOS:EtOH:H2O=1:3:4) by using a levitation-gelation method. Thermogravimetric analysis and differential thermal analysis were used, along with the measurement of weight loss and linear shrinkage, to study the response of the aerogel spheres under heat treatment.
Micromachined tunneling displacement transducers for physical sensors
Authors: Kenny T. W. , Kaiser W. J. , Podosek J. A. , Rockstad H. K. , Reynolds J. K. , Vote E. C.
Published: July 2002

We have designed and constructed a series of tunneling sensors which take advantage of the extreme position sensitivity of electron tunneling. In these sensors, a tunneling displacement transducer, based on scanning tunneling microscopy principles, is used to detect the signal-induced motion of a sensor element. Through the use of high-resonant frequency mechanical elements for the transducer, sensors may be constructed which offer wide bandwidth, and are robust and easily operated. Silicon micromachining may be used to fabricate the transducer elements, allowing integration of sensor and control electronics. Examples of tunneling accelerometers and infrared detectors will be discussed. In each case, the use of the tunneling transducer allows miniaturization of the sensor as well as enhancement of the sensor performance.
Etching rate characterization of SiO2 and Si using ion energy flux and atomic fluorine density in a CF4/O2/Ar electron cyclotron resonance plasma
Authors: Ding J. , Jenq J.-S. , Kim G.-H. , Maynard H. L. , Hamers J. S. , Hershkowitz N. , Taylor J. W.
Published: July 2002

SiO2 and Si etching in a CF4/O2/Ar plasma has been carried out in an electron cyclotron resonance etcher over a wide range of conditions. The etch rate has been compared with the ion energy flux to the wafer surface, JiEi, and the atomic fluorine density in the gas phase, nF. It is found that the etch rate can be divided into two regimes by a critical value of nF/(JiEi), the ratio of the atomic fluorine density to the ion energy flux. The critical value can be determined from a contour plot of the etch rate as a function of the ion energy flux and the atomic fluorine density. The critical value of nF/(JiEi) for Si is higher than that for SiO2. For nF/(JiEi) higher than the critical value, the SiO2 etch rate linearly increases with the ion energy flux, and the Si etch rate shows a nonlinear increase with the ion energy flux. For nF/(JiEi) lower than the critical value, both SiO2 and Si etch rates linearly increase with the atomic fluorine density.
Amorphous silicon alloys on c-Si: Influence of substrate cleaning and ion bombardment on film adhesion and microstructure
Authors: Yang S.-Y. , Abelson J. R.
Published: July 2002

Substrate cleaning and ion bombardment play important roles in the adhesion, morphology, and structure of hydrogenated amorphous silicon and silicon-carbon alloys grown on c-Si by dc reactive magnetron sputtering. Scanning electron microscopy is used to study the surface morphology and fracture cross section of films. The hydrogen bonding and microstructure are studied by infrared absorption, thermal evolution of hydrogen. The best adhesion is obtained by (i) cleaning the substrate with a combination of cycles of ultraviolet/ozone oxidation and HF etching and by (ii) reducing plasma ion bombardment through electrically floating the c-Si substrate. The reduced ion bombardment has a significant influence on the hydrogen bonding configurations and hydrogen evolution process.
Study of the NF3 plasma cleaning of reactors for amorphous silicon deposition
Authors: Bruno G. , Capezzuto P. , Cicala G. , Manodoro P.
Published: July 2002

NF3 plasmas have been investigated for the cleaning of reactors for amorphous silicon (a-Si:H) deposition from silane. Optical emission spectroscopy, also time resolved, has been used to measure F*, N2*, NF*, and SiF* emitting species in the plasma phase. Measurements of mass spectrometry, etching rate and dc self-bias voltage at the rf powered electrode have also been used for process diagnostics. The a-Si:H etching process by F atoms is shown to occur under loading conditions: the etching rate does not correlate with F atom density. The recombination processes NFx+F→NFx+1(x=2,1) and NF+NF→N2+2F together with the NF3 electron impact dissociation into NFx+F have been found to be significant for the NF3 plasma chemistry as well as the fluorine conversion into SiF4.
Investigation of SiO2 plasma enhanced chemical vapor deposition through tetraethoxysilane using attenuated total reflection Fourier transform infrared spectroscopy
Authors: Deshmukh Shashank C. , Aydil Eray S.
Published: July 2002

In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to study surface processes during plasma enhanced chemical vapor deposition (PECVD) of silicon dioxide through tetraethoxysilane (TEOS) and oxygen. ATR-FTIR studies were conducted on thin (about 50 Å) silicon dioxide films deposited on GaAs. This approach allowed us to obtain the infrared spectrum of TEOS adsorbed on SiO2 in the spectral region 4000–770 cm−1 and to determine the surface species and their relative surface concentrations as a function of deposition conditions in a helical resonator plasma reactor. Studies were conducted where the SiO2 surface was exposed to TEOS and O2 plasma sequentially and/or simultaneously. Surface processes were studied as a function of exposure to TEOS and substrate temperature. In situ ATR-FTIR studies of adsorption of TEOS on the SiO2 surface show that TEOS adsorbs chemically and irreversibly onto the SiO2 surface above 100 °C. SiO2 growth was found to occur even without an oxygen plasma at temperatures as low as 200 °C, albeit very slowly. Below 100 °C TEOS was also found to adsorb physically: The extent of the physically adsorbed state was found to increase with decreasing temperature. Hence, during PECVD of SiO2 below 100 °C, physically adsorbed TEOS can be trapped in the growing oxide giving rise to increased ethoxy and OH species which in turn adversely affect the film integrity and quality.

The ATR-FTIR studies of the surface exposed to TEOS at various temperatures indicate that the chemical adsorption of TEOS onto SiO2 proceeds through a precursor-mediated adsorption mechanism where the precursor is a physically adsorbed TEOS molecule. Exposure of adsorbed TEOS to O atoms (oxygen plasma) removed the ethoxy ligands of the surface ethoxysiloxanes, produced surface SiOH species as reaction product, and resulted in deposition of SiO2. In situ and real time studies of the actual PECVD process revealed that water and SiOH species are formed as intermediate surface reaction products and subsequent reaction and elimination of the silanol species can become the rate limiting step (as far as SiOH incorporation in the film is concerned) if the deposition rate is too high.
Sheath impedance effects in very high frequency plasma experiments
Authors: Schwarzenbach W. , Howling A. A. , Fivaz M. , Brunner S. , Hollenstein Ch.
Published: July 2002

The frequency dependence (13.56–70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge. Reduced sheath impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinant. The capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance. It is argued that the frequency dependence of sheath impedance is responsible for the principal characteristics of very high frequency plasmas. The measurements are summarized by simple physical descriptions and compared with a particle-in-cell simulation.
Electron-induced surface chemistry: Synthesis of NHx fragments on Ag(111)
Authors: Schwaner A. L. , Pylant E. D. , White J. M.
Published: July 2002

Electron-induced decomposition of chemisorbed NH3, dosed on Ag(111), at 115 K has been studied using x-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). There is no thermally activated dissociation during dosing or TPD. The N(1s) XPS peak is at 400.1 eV binding energy (BE) and, in TPD, there is a sharp peak at 130 K with a trailing edge toward higher temperatures. Following low energy (50 eV) electron irradiation the 130 K TPD peak area drops sharply while the XPS N(1s) peak area drops much less. This indicates that, while some N-containing species are ejected during electron irradiation, most of the initial N is retained in some form. After irradiating with 5×1016 e cm−2, the N(1s) BE shifts lower and the peak can be fit with two peaks, one corresponding to residual NH3, and a second to NH2 (398.9–399.1 eV BE). Increasing the fluence to 1×1017 e cm−2, shifts the N(1s) profile to even lower BE; two peaks assigned to NH2 and NH (398.1 eV BE) give an acceptable fit.
High-rate magnetron sputtering
Authors: Musil J. , Rajský A. , Bell A. J. , Matouš J. , Čepera M. , Zeman J.
Published: July 2002

This article reports on the process of high-rate magnetron sputtering of solid materials using an unbalanced magnetron with extremely high target power densities of up to 150 W cm−2. Particular attention is devoted to a comparison of sputtering in the 10−1 Pa range, low pressure sputtering (<10−1 Pa), and self-sputtering. The advantages and drawbacks of the sputtering process at different pressures are critically analyzed. The extinction pressure measured as a function of the magnetron discharge current for the magnetron discharge of Cu, Ag, and Ti targets is given. Deposition rates and selected properties of Ti and Cu films are also reported.
Reactive sputter-deposition and characterization of lead oxide films
Authors: Pauleau Y. , Harry E.
Published: July 2002

Lead and lead oxide containing films have been deposited on various substrates by radio frequency sputtering of a lead target in pure argon and argon–oxygen discharges. The sputter-deposited films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analyses, and the x-ray diffraction technique. The composition, deposition rate, and crystalline structure of films were investigated as functions of the oxygen content (1.5%–50%) in the gas phase and sputtering power (50–200 W). The O/Pb atom number ratio increased rapidly up to one as the oxygen content in the discharge was varied from 1.5% to 6%. The films deposited under these conditions were composed of metallic lead, yellow orthorhombic β-PbO and PbO1.57 phases in variable proportions. Amorphous and noncataloged lead oxide phases were also formed for oxygen contents in the discharge higher than 6%. The effect of the composition of the deposited material on the residual stresses developed in the films was determined and related to the morphology of films examined by scanning electron microscopy. The friction properties of lead and lead oxide containing films deposited on stainless steel disks were determined by alumina ball-on-disk tribological tests conducted in air at a sliding speed of 3 cm s−1 under a load of 2 N. The friction coefficient was investigated as a function of the sliding distance, film thickness, and surface roughness of tribological disks and test temperature.
Postdeposition annealing of radio frequency magnetron sputtered ZnO films
Authors: Puchert M. K. , Timbrell P. Y. , Lamb R. N.
Published: July 2002

Zinc oxide (ZnO) films have been deposited on 1 μm SiO2/Si (100) substrates by rf magnetron sputtering. Using a sputtering gas of pure oxygen, a pressure regime is found in which the ZnO films grow on room temperature substrates with a single (0001) orientation, small grains (crystallite sizes ∼10–15 nm), and high intrinsic biaxial compressive stress (∼6 GPa). The effects of post-deposition annealing these films in air was investigated over a range of temperatures (200–1000 °C) and durations (2–2000 min). Annealing resulted in lower biaxial compressive stresses and increased average crystallite sizes in all films. Additional ZnO grain orientations were detected only after annealing above 500 °C for longer than 90 min, and the results are interpreted in terms of film recrystallization. Consequently, a relatively rapid thermal anneal at 1000 °C for 5 min caused grain recovery without recrystallization, resulting in maximum stress reduction (90%–100% of stress was relieved and average crystallized size tripled) while maintaining the original film orientation. The film surface area—measured by atomic force microscopy—decreased by up to 25% during annealing. X-ray photoelectron spectroscopy results indicate that although the surfaces of as-deposited films have a slight excess of oxygen, annealing as low as 200 °C results in a stoichiometric ZnO surface. High values of electrical resistivity (∼105 Ω cm) measured across the thickness of unannealed oriented films indicate low levels of elemental zinc clusters in the film bulk.
Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3
Authors: Takahashi Kunimasa , Hori Masaru , Goto Toshio
Published: July 2002

Gas phase reactions of CFx (x=1−3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma were investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding O2 to CHF3 using infrared diode laser absorption spectroscopy and actinometry, respectively. By adding a small amount of O2 to CHF3, the CF and CF2 radical densities rapidly decreased, while the CF3 radical density rapidly increased but then decreased with further addition of O2 to CHF3. These reaction mechanisms in the plasma were evaluated on the basis of measurement results of CFx (x=1−3) radical and F atom densities. Under the same conditions as the measurements of radical densities, the etching rates of Si and SiO2 were measured. Furthermore, the etched Si surfaces were also analyzed with x-ray photoelectron spectroscopy. The etching mechanisms for Si and SiO2 in the CHF3/O2 ECR plasma were investigated by connecting these etching characteristics on Si and SiO2 with the behaviors of CFx (x=1−3) radical and F atom densities. The Si etching rate was affected primarily by the concentrations of the CF and CF2 radicals and F atoms in the plasma.
Spatial distributions of electron density and electron temperature in direct current glow discharge
Authors: Tao W. H. , Prelas M. A. , Yasuda H. K.
Published: July 2002

The spatial distributions of electron temperature and density in a dc glow discharge that is created by a pair of planar electrodes were studied using double Langmuir probes. The measurement was carried out on the horizontal center plane across vertically placed circular planar parallel plate electrodes. One electrode with magnetic enhancement (magnetron) was paired with a nonmagnetron in the two possible combinations. The measurements were carried out for the following three modes: (nonmagnetron) cathode/(nonmagnetron) anode (C–A), cathode magnetron/(nonmagnetron) anode (CM–A), and (nonmagnetron) cathode/anode magnetron (C–AM). In the C–A mode, electrons gain energy from the imposed electric field, and the electron temperature (Te) rises very sharply from the cathode to the leading edge of the negative glow where Te reaches the maximum. In this region, the number of electrons (Ne) is relatively small and does not increase much. The accelerated electrons lose energy by ionizing gas atoms, and Te decreases rapidly to the plateau value, which is reached near the midpoint between two electrodes and extends to the anode. In this region, Ne increases sharply. As electrons are pulled towards the anode, a steep increase of Ne was found towards the anode and then Ne drops sharply very near the anode as electrons are captured by the anode. The value of Te increases slightly towards the edge of the cathode and the anode (radial position), and the minimum Te was found at the center. There is a clear trend that Te and Ne are inversely related (Te×Ne=constant). This trend was also found in cases in which a magnetron is used as the cathode (CM–A) or as the anode (C–AM) paired with a planar nonmagnetron electrode. In the (CM–A) mode, the magnetic entrapment of electrons is seen in the sharp increase of Ne near the cathode surface. The characteristic toroidal glow near the magnetron cathode is associated with the Ne peak, and the Te peak is found inside the circular toroidal glow where Ne is small. In the (C–AM) mode, a large Ne peak was found near the anode in the center, and the Te peak was found in the center near the cathode. A funnel shaped glow that expands from the center of the anode is distinctively different from the toroidal glow observed for the cathode magnetron glow discharge.
New broad beam gas ion source for industrial application
Authors: Gavrilov N. V. , Mesyats G. A. , Nikulin S. P. , Radkovskii G. V. , Elkind Alexander , Perry Anthony J. , Treglio James R.
Published: July 2002

A source delivering a broad, high current ion beam compatible with both chemically active and inert gases has been developed which gives reliable, long term, maintenance-free operation. It uses a glow discharge with a cold cathode in a magnetic field where a dense uniform plasma is generated in large volumes at low gas pressures. Optimal selection of the electrode configuration and magnetic field ensures operation at pressures lower than 0.1 Pa in pulse–periodic mode (1–10 A discharge current, 1 ms pulse length, 25–50 Hz frequency), and continuous mode (discharge current up to 2 A). The current density of a 15-cm-diam beam can reach 10 mA cm−2 in the former, and 1 mAcm−2 in the latter. Tests with a 50-cm-diam discharge chamber show the uniformity of the ion emission current to be better than ±10%, confirming that the technology is scaleable, and that beams of up to 2000 cm2 cross-sectional area can be obtained without loss of beam uniformity through appropriate design of the extraction system. The source is completely reactive gas-compatible, generating ion beams from oxygen, nitrogen, argon or ionized CH radicals (e.g., using C3H8). Mass-charge beam analysis shows the beams generated to be of high purity (≳99%). Applications include low energy (1–3 keV) ion beam cleaning of glass, ceramic and metal surfaces prior to the deposition of protective and decorative coatings such as TiN and diamondlike carbon, ion beam assisted deposition, and high energy gas ion implantation using, e.g., pulse–periodic beams of ions with energies up to 50 keV.
Effect of hydrogen addition to fluorocarbon gases (CF4, C4F8) in selective SiO2/Si etching by electron cyclotron resonance plasma
Authors: Doh Hyun-Ho , Kim Jung-Hun , Whang Ki-Woong , Lee Seok-Hyun
Published: July 2002

We investigated the etch rate of SiO2 and Si in an electron cyclotron resonance (ECR) etching system as a function of H2 adding percentage to fluorocarbon gases such as CF4 and C4F8. The selectivity increases considerably in the case of C4F8 plasma as the H2 percentage increases. Actinometric optical emission spectroscopy and appearance mass spectrometry were employed to elucidate the mechanism of selective SiO2/Si etching in ECR plasma and the following are confirmed. First, the relative behavior of CF2 radical density as a function of H2 percentage in a CF4 ECR plasma system is very similar to that in a rf capacitively coupled plasma (RFCCP) system but its increasing rate with the addition of H2 is smaller by an order of magnitude compared to the case of CF4 RFCCP system. Second, the dominant polymer precursors that are responsible for the selective SiO2 to Si etching is CF among CFx (x=1–3) radicals in C4F8+H2 ECR plasma and the decreasing rate of the relative concentration of atomic F is higher in CF4 ECR plasma than in C4F8 ECR plasma as the H2 percentage increases. Therefore, it is suggested that the F abstraction reaction with H in the gas phase process is more responsible for the selective SiO2 etching than the F scavenging reaction in C4F8 ECR plasma when H2 is added.
Etching characteristics of tin oxide thin films in argon–chlorine radio frequency plasmas
Authors: Maguire P. , Molloy J. , Laverty S. J. , McLaughlin J.
Published: July 2002

We have developed an etch process suitable for high resolution transparent conductive oxide patterning with high etch rates, up to 70 nm/min, and applicability to large area flat panel display substrates. It was found that the addition of small amounts of Cl2 significantly enhanced the etch rate compared to addition of pure argon but that beyond 25% Cl2 the rate tended to fall. There is a significant loading effect where the etch rate approximately doubled for exposed tin oxide areas between 80% and 10% of the substrate area. This loading sensitivity was found to increase with increasing power and decreasing Cl2 concentration. It was also observed that local changes in pattern dimensions affected the uniformity of the etch rate. A large photoresist etch rate was observed between one and three times that of the tin oxide and it decreased as the area of photoresist coverage increased. Linewidth loss, up to 4 μm at high powers, was overcome using improved ultraviolet exposure, leading to feature resolution capabilities of <5 μm. Etch rate inhomogeneity was also observed on a local scale, possibly due to redeposition of sputtered photoresist. Overetching, however, ensures rapid clearing of tin oxide islands without damage to the underlying SiO2 buffer layer.
Ashing residues on TiN antireflective coating layers
Authors: Miyaji S. , Kato T. , Yamauchi T.
Published: July 2002

Residues appearing on the surface of the TiN antireflective coating (ARC) layer after a resist ashing process were investigated by transmission electron microscope and field emission Auger electron spectroscopy. These residues tend to appear linearly in the center of Al lines covered with the TiN ARC layer, and are generally called the ‘‘backbone.’’ We found that a triangular product mainly composed of Al atoms appears in the center of the resist surface in the final stage of the ashing process and that a thin layer, about 10 nm thick, including Ti atoms, is formed to cover the triangular product and the resist surface. Due to the small solubility of the thin layer including Ti atoms to the alkaline stripper, the triangular product under the thin layer remains as a backbone residue. We demonstrate that the formation of the backbone depends on the distribution of Al and Ti atoms in the sidewall polymer.
Measurements of tritium retention and removal on the Tokamak Fusion Test Reactor
Authors: Skinner C. H. , Blanchard W. , Kamperschroer J. , LaMarche P. , Mueller D. , Nagy A. , Scott S. , Ascione G. , Amarescu E. , Camp R. , Casey M. , Collins J. , Cropper M. , Gentile C. , Gibson M. , Hosea J. , Kalish M. , Langford J. , Langish S. , Mika R. , Owens D. K. , Pearson G. , Raftopoulos S. , Raucci R. , Stevenson T. , Von Halle A. , Voorhees D. , Walters T. , Winston J.
Published: July 2002

Recent experiments on the Tokamak Fusion Test Reactor have afforded an opportunity to measure the retention of tritium in a graphite limiter that is subject to erosion, codeposition, and high neutron flux. The tritium was injected by both gas puff and neutral beams. The isotopic mix of hydrogenic recycling was measured spectroscopically and the tritium fraction T/(H+D+T) transiently increased to as high as 75%. Some tritium was pumped out during the experimental run and some removed in a subsequent campaign using various clean-up techniques. While the short term retention of tritium was high, various conditioning techniques were successful in removing ≊8000 Ci and restoring the tritium inventory to a level well below the administrative limit.
The spinning rotor gauge: Measurements of viscosity, velocity slip coefficients, and tangential momentum accommodation coefficients
Authors: Tekasakul P. , Bentz J. A. , Tompson R. V. , Loyalka S. K.
Published: July 2002

A set of experimental measurements with a spinning rotor gauge (SRG) with 3.85, 4.00, and 4.50 mm nominal diameter steel spheres in He, Ar, and Kr is reported. The experiments covered the continuum and the slip regimes for all three gases. Theoretical results from a companion paper on the SRG, together with a calibration based on known viscosity for helium, are used to extract values of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient for each of the gases. The measured viscosities are in good agreement with existing literature values.
Different growth modes in GaAs(110) homoepitaxy
Authors: Holmes D. M. , Belk J. G. , Sudijono J. L. , Neave J. H. , Jones T. S. , Joyce B. A.
Published: July 2002

The initial growth stages of GaAs(110) thin films during molecular beam epitaxy were studied by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). For the deposition of 0.5 monolayers (ML) at various conditions of substrate temperature, As/Ga flux ratio and As2/As4 ratio, STM images are correlated with the specific growth regimes identified by in situ RHEED intensity oscillation studies. The surfaces obtained after the deposition of submonolayer coverages of GaAs show a striking growth morphology specific to each growth regime studied.
Formation of the Cs/GaAs(001) interface: Work function, cesium sticking coefficient, and surface optical anisotropy
Authors: Kierren B. , Paget D.
Published: July 2002

We have studied at room temperature (RT) and at near liquid-nitrogen temperature [low temperature (LT)], the adsorption of cesium on clean gallium-rich GaAs(001) prepared by sulfide passivation, and annealing in ultrahigh vacuum. We monitor the optical transitions of gallium surface dimers, using reflectance anisotropy spectroscopy (RAS), and the changes of work function and cesium sticking coefficient. The clear correlations between these three quantities allow us to distinguish three adsorption phases: (i) At LT and up to 0.7 ML coverage, cesium adsorption induces a decrease of the RA signal, which perfectly corresponds with the work function decrease. The RA decrease is, therefore, caused by the surface dipole due to charge transfer from cesium to the solid. (ii) At RT, for a coverage smaller than 0.15 ML, both the RA signal and the work function change are different from their LT behavior, so that a distinct adsorption process occurs. This indicates that cesium diffuses to specific surface sites at which the bonding is different. (iii) At a coverage larger than 0.7 ML, and independently on adsorption temperature, no charge transfer to the solid occurs, since no change of RA spectrum and work function is observed. The cesium sticking coefficient is reduced by a factor of 2. Comparison with results obtained on As-decapped GaAs(001) shows the similarity of the formation of the interface for the two surfaces. However, the results are clearer for the surface prepared by sulfide passivation, which seems to be of higher quality.
Effect of bismuth on the ferroelectric properties of SrBi2Ta2O9 thin films deposited on Pt/SiO2/Si by a modified radio-frequency magnetron sputtering technique
Authors: Yang Cheol-Hoon , Yoon Soon-Gil
Published: July 2002

Bi-layered ferroelectric SrBi2Ta2O9 (SBT) films were successfully deposited on Pt/SiO2/Si substrates using a sintered SrBi2Ta2O9 ceramic target, and Bi and Ta metal targets by a modified rf magnetron sputtering technique. The ferroelectric properties of the films were greatly dependent on the bismuth sputtering power. The SBT films deposited under the conditions of rf power of 100 W, Bi dc power of 25 W, and Ta dc power of 10 W showed a dense and uniform microstructure. A remanent polarization, Pr, of 7.51 μC/cm2 and a coercive field Ec, of 28 kV/cm were obtained for an excitation voltage of 5 V. The SBT films show practically no polarization fatigue after 7×1010 switching cycles. Their retention characteristics look very promising up to 106 sec.
Epitaxial growth of TiN films by N-implantation into evaporated Ti films
Authors: Kasukabe Y. , Saito N. , Suzuki M. , Yamada Y. , Fujino Y. , Nagata S. , Kishimoto M. , Yamaguchi S.
Published: July 2002

Nitrogen ions (N2+) with 62 keV have been implanted into 100-nm-thick Ti films prepared by the evaporation on thermally cleaned NaCl substrates held at room temperature. The epitaxial growth process of resultant TiN films has been studied by transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. It has been revealed that the (110)-oriented TiNy is formed by nitriding the (110)-oriented TiHx in the as-deposited Ti film without change of the orientation of the fcc-Ti sublattice, and that the (001)-oriented TiNy and the “rotated” (110)-oriented TiNy rotated by ∼9° with respect to the (110)-oriented TiNy, respectively, are epitaxially formed by the transformation of (03⋅5)-oriented hcp-Ti to (001)-oriented fcc-Ti and by the transformation of (2̄1⋅0)-oriented hcp-Ti to rotated (110)-oriented fcc-Ti. Then, the inheritance of the square atomic arrangement and parallelogram atomic arrangement of hcp-Ti plays a very prominent role in the epitaxy of the (001)-oriented and the rotated (110)-oriented TiNy, as well as the occupation of N in octahedral sites of the fcc-Ti. The increase in the lattice constants of hcp-Ti, especially, the steeper increase of the lattice constant, c, by the N occupation can be considered as one of the driving forces for the hcp-fcc transformation. The growth mechanism of epitaxial TiNy films is discussed.
Silicon hydride composition of plasma-deposited hydrogenated amorphous and nanocrystalline silicon films and surfaces
Authors: Marra Denise C. , Edelberg Erik A. , Naone Ryan L. , Aydil Eray S.
Published: July 2002

In situ attenuated total reflection Fourier transform infrared spectroscopy was used to study the H bonding on the surfaces of a-Si:H and nc-Si:H during plasma enhanced chemical vapor deposition from SiH4/H2/Ar containing discharges. Well-resolved SiHx (1⩽x⩽3) absorption lines that correspond to the vibrational frequencies commonly associated with surface silicon hydrides were detected. During deposition of a-Si:H films using SiH4 without H2 dilution, the surface coverage was primarily di- and trihydrides, and there are very few dangling bonds on the surface. In contrast, during deposition of nc-Si:H using SiH4 diluted with H2, the amount of di- and trihydrides on the surface is drastically reduced and monohydrides dominate the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film surfaces match well with the resonant frequencies of monohydrides on H terminated Si (111) and Si (100) surfaces. The decrease of higher hydrides on the surface upon H2 dilution is attributed to increased dissociation rate of tri- and dihydrides on the surface through reaction with dangling bonds created by increased rate of H abstraction from the surface. Results presented are consistent with SiH3 being at least one of the precursors of a-Si:H deposition.
Obtaining optical constants of thin GexSbyTez films from measurements of reflection and transmission
Authors: Tsu David V.
Published: July 2002

Phase change rewritable optical recording media contain a chalcogenide layer, e.g., GexSbyTez, that undergoes a transition between the amorphous and crystalline phases (by absorption of laser energy). Differences in their optical constants [n,k] result in reflectivity differences in the multilayer optical devices. We have obtained those constants by reflection and transmission [R,T] intensity measurements (200⩽λ⩽2000 nm) at (near) normal incidence for films <50 nm thick. The film’s [n,k] are obtained at each wavelength by direct numerical inversion of the [R,T] expression describing the measured [air/film/substrate/air] configuration. In our approach, based on a graphical technique combined with two-dimensional Newton–Raphson (N–R) iteration, the existence of [n,k] solutions can always be determined, whereas N–R alone often fails. Inverting the nonlinear [R,T] expressions results in multiple [n,k] (one physical and additional mathematically relevant) solutions at every wave length, which combine to provide a powerful indication of the film’s thickness (with ∼1% accuracy). We are thus able to show that when as-deposited amorphous chalcogenides are annealed, their thickness diminishes from 5% to 10% as they crystallize, where the amount depends on the alloy composition.
Processing and characterization of nanometer sized copper sulfide particles
Authors: Seal S. , Bracho L. , Shukla S. , Morgiel J.
Published: July 2002

Nanomaterials have attracted considerable attention in modern-day technology. In this article, sulfide nanoparticles of industrial interest are formed by the sol-gel process using metal chloride precursors dissolved in a mixture of silica gel and organic cellulose network followed by a chemical reaction with hydrogen sulfide gas. Particles are then heated in a vacuum oven. While scanning and transmission electron microscopy are used to study their morphology and structure in the nanometer scale, x-ray photoelectron spectroscopy is employed to understand the bonding chemistry and the stoichiometry of the sulfide particles as a function of H2S exposure and heat treatment. The results from this study are expected to show promising applications and production of other oxides, sulfides and their compounds using sol-gel synthesis are indicated.
Effect of N2 discharge treatment on AlGaN/GaN high electron mobility transistor ohmic contacts using inductively coupled plasma
Authors: Zhang A. P. , Dang G. T. , Ren F. , Van Hove J. M. , Klaassen J. J. , Chow P. P. , Cao X. A. , Pearton S. J.
Published: July 2002

The contact resistance of Ti/Al/Pt/Au metallization on AlGaN/GaN high electron mobility transistors was measured as a function of plasma exposure conditions prior to metal deposition. Inductively coupled plasma N2 discharges were used to create nitrogen-deficient near-surface regions in the AlGaN/GaN structures. At modest ion fluxes (∼4×1016 cm2 s−1) and low ion energies (125 eV), there was no detectable surface roughening of the AlGaN. Under optimized conditions, the plasma treatment reduces the ohmic contact resistance by a factor of approximately 3.
Atom-probe study of the early stage of silicide formation. II. Ni–Si system
Authors: Nishikawa Osamu , Nomura Eiichi , Wada Minoru , Tsunashima Yoshitaka , Horie Shiro , Shibata Mezame , Yoshimura Toshihiko , Uemori Ryuji
Published: July 2002

Silicon-deposited Ni tips were heated at various temperatures up to 1000 K and structures and compositions of thin Ni silicide layers formed in situ were investigated by the atom probe and the field ion microscope (FIM). Although a mixed layer of Ni and Si was formed even at 80 K, FIM images of an ordered silicide structure were observed after heating the tip above 900 K. It was noticed that the evaporation field of the ordered silicide is significantly higher than those of Ni and Si, possibly due to a strong binding force among the constituting atoms. Since Ni is the major moving species, the Ni concentrations in the thin silicide layers were found to be as high as Ni4Si near the surface and decreased to NiSi at the boundary of the silicide and the substrate Ni. Although the composition of the silicide, which showed the ordered image, changed from Ni5Si2 to NiSi as the mass analysis was proceeded from the surface of the silicide to the substrate Ni, the silicide consistently exhibited the FIM image which was characteristic of a cubic structure. The computer-simulated image of the hypothetical structure for the observed silicide, a modified cubic C1 structure, showed the characteristic features of the observed silicide image.
Surface processes in plasma-assisted etching environments
Authors: Winters Harold F. , Coburn J. W. , Chuang T. J.
Published: July 2002

Plasma-assisted etching involves the interaction of radicals generated by a glow discharge (e.g., fluorine atoms) with solid material (e.g., silicon) to produce volatile products (e.g., SiF4). Moreover, this type of reaction is frequently enhanced by bombardment with ions, electrons, and photons. The purpose of the present paper is to review surface processes which lead from the adsorption of radicals to the evolution of products and to formulate a conceptual framework for the interpretation of experimental data obtained in plasma environments. It will be suggested that etching reactions are quite analogous to similar reactions which lead to oxide formation. In particular, it is suggested that field-assisted mechanisms of the Mott–Cabrera type involving place exchange and motion of cations and/or anions are likely to influence or dominate etching reactions. In addition, it will be shown that surface reconstruction, precursor states, and the surface concentration of adsorbed species are likely to be important factors which influence the kinetics. Furthermore, emphasis will be placed on mechanisms which cause radiation (ions, electrons, photons) to enhance the reaction rate. Ion-enhanced etching could be dominated by physical sputtering, chemical sputtering, surface damage, or a combination of these phenomena. Photon-enhanced etching could be initiated by excitation of gas phase molecules, solid atoms or chemical species adsorbed on the surface. The characteristics of each type of reaction will be discussed with experimental illustrations.
A review of laser–microchemical processing
Authors: Ehrlich D. J. , Tsao J. Y.
Published: July 2002

Microfabrication processes based on focused laser-beam activation of surface chemistry are reviewed with an emphasis on the classification of the diverse chemical processes used. Surface reactions are divided according to their method of activation and the material phase most important in the chemical kinetics. Examples of reaction mechanisms and means of confining reaction dimensions are given. New results demonstrating that linewidths for deposition and etching of Si can be <0.4 μm are described. The ultimate limits to spatial resolution are explored in terms of an effective contrast (γ*) for laser–microchemical processes. Enhanced diffusive transport, characteristic of laser microreactions, and its effect on ultimate reaction rates are also analyzed.
Classical stochastic diffusion theory for thermal desorption from solid surfaces
Authors: Redondo Antonio , Zeiri Yehuda , Goddard William A.
Published: July 2002

As a first step in the microscopic study of dynamic processes on surfaces and at interfaces, we have considered the thermal desorption of adsorbed species on solid surfaces. We review recent developments based on a classical stochastic diffusion formulation. Using this theory, we obtained a simple rate expression, R=(Ω0/2π) f(T)exp(−De/kT), where Ω0 is the surface-adsorbate vibrational frequency and De the dissociation energy. For atoms f(T)=1, whereas for molecules f(T) depends on the parameters for the frustrated rotations at the surface. The effect of coverage on the rate of desorption and the process of desorption into a fluid are also examined. Finally, we discuss the relationship between our theory and the expressions obtained from activated complex (transition-state) theory.
An experimental system for surface reaction studies in microwave plasma etching
Authors: Ninomiya Ken , Suzuki Keizo , Nishimatsu Shigeru , Gotoh Yoshitaka , Okada Osami
Published: July 2002

An experimental system for studying surface reactions in the process of microwave plasma etching has been developed. In the system, a surface etched in the microwave plasma can be analyzed with x-ray photoemission spectroscopy (XPS) without exposure of the surface to room air. In addition, we have developed a procedure for calculating a thickness of a surface layer stoichiometrically different from the substrate material and densities of atoms in the layer. Chemical changes in etched Si and SiO2 surfaces caused by exposing these surfaces to room air are investigated with XPS to show the utility of the system. When the surfaces etched in SF6 microwave plasma are exposed to room air, the chemical states of the surfaces change rapidly. This is mainly due to surface oxidation and adsorption of hydrocarbon compounds to the surfaces. The rapid changes are more clearly shown from increases in surface layer thickness and the number of O and C atoms in the layer. It is clarified that exposure of etched surface to room air causes the serious disturbance, and that accurate information can not be obtained any longer. The present system which eliminates this disturbance allows accurate measurement of surfaces for detailed investigation of the surface reaction in microwave plasma etching.
Promising cathode materials for high brightness electron beams
Authors: Zaima Shigeaki , Adachi Hiroshi , Shibata Yukio
Published: July 2002

Materials for high brightness cathodes are evaluated by defining a figure of merit, which is based on the Richardson–Dushman equation. By calculating the figure of merit of borides, carbides, nitrides, and some refractory metals, it is concluded that carbides of transition metals such as TiC, ZrC, TaC, and HfC are promising for high brightness cathodes.
A measurement of intrinsic SiO2 film stress resulting from low temperature thermal oxidation of Si
Authors: Kobeda E. , Irene E. A.
Published: July 2002

A parallel beam reflection technique has been developed in our laboratory for measuring intrinsic residual stress for Si wafers thermally oxidized at temperatures of 600–1150 °C. A detailed description of this technique is provided, and stress values calculated for thermally grown SiO2 films on Si are consistent with those reported in the literature. Low temperature thermal oxidations resulted in compressive intrinsic SiO2 stresses greater than 4×109 dyn/cm2.
Contribution of the ion-energy distribution to the current-density distribution of a focused-ion beam
Authors: Kawanami Yoshimi , Ishitani Tohru , Umemura Kaoru , Shukuri Shoji
Published: July 2002

A general expression for the current-density distribution of a focused-ion beam (FIB) in the chromatic-aberration region is set up in the form of a definite integral. With the experimentally obtained ion-energy distribution of a liquid-metal ion source, its contribution to the FIB current-density distribution is estimated. Calculated results explain the wide-exponential tail of a FIB.
A practical electron beam direct writing process technology for submicron device fabrication
Authors: Okazaki Shinji , Murai Fumio , Suga Osamu , Shiraishi Hiroshi , Koibuchi Shigeru
Published: July 2002

A phenolic resin based resist and an improved development process is proposed for a practical direct writing technology. High resolution, high sensitivity, and high dry etching durability are required for this type of technology. Phenolic resin based resist has the capability of high dry etching durability, and also shows high resolution because of swell-free development. To obtain higher sensitivity, a dissolution inhibitor and a nonionic surfactant were added to the conventional developer solution. MRS(RD2000N) and NPR(RE5000P) were chosen as phenolic resin based resists. Using an improved developer solution, 0.25 μm resolution and 7–9 μC/cm2 sensitivity were obtained at 30 kV acceleration in MRS and 0.4 μm and 2 μC/cm2 in NPR. This practical direct writing process technology was applied to the fabrication of tungsten gate MOSFETs with 0.12 μm effective channel length and 0.2 μm wide emitter bipolar transistors.
GaAs cleaning with a hydrogen radical beam gun in an ultrahigh-vacuum system
Authors: Sugata S. , Takamori A. , Takado N. , Asakawa K. , Miyauchi E. , Hashimoto H.
Published: July 2002

GaAs surface cleaning prior to molecular-beam epitaxy (MBE) using a new hydrogen radical beam produced by an electron cyclotron resonance plasma in an ultrahigh-vacuum system is investigated. Residual oxygen and carbon on the GaAs surface after cleaning are monitored in situ with Auger electron spectroscopy. Oxygen and carbon, which are hard to remove by conventional thermal cleaning, can be removed by hydrogen radical (H*) beam irradiation at a substrate temperature of <400 °C. It is verified that the plasma-dissociated radicals are much more reactive in the gas phase–solid phase surface chemical interaction than the nondischarged molecules. Ga and As stoichiometry is kept after H* beam cleaning. Good crystallinity is obtained according to reflection high-energy elecron diffraction. By carrier concentration measurement at the interface between the cleaned surface and the in situ MBE-regrown layer, it is found that H* beam cleaning reduces the interface state concentration. This cleaning technique makes clean GaAs surfaces available for MBE pretreatment.
Titanium nitride for antireflection control and hillock suppression on aluminum silicon metallization
Authors: Rocke Michael , Schneegans Manfred
Published: July 2002

High reflectivity of aluminum alloy layers causes degradation to occur in photoresist images through reflective light scattering. Titanium nitride used normally as a diffusion barrier under aluminum silicon contacts, can also be applied as an efficient antireflection layer on top of AlSi. Processing advantages over other antireflective layers (ARL) such as hillock suppression and enhanced electromigration resistance are also discussed. Process flow parameters from ARL deposition to wire attach are reviewed as applied to megabit dynamic random access memory development.
Nanometer sidewall lithography by resist silylation
Authors: Vettiger P. , Buchmann P. , Dätwyler K. , Sasso G. , VanZeghbroeck B. J.
Published: July 2002

A new and simple approach of nanometer-scale sidewall formation has been explored and developed for dry-etching-based pattern transfer techniques. The sidewalls are formed by applying a solvent-based silylation process to the optically exposed and developed resist pattern, followed by an anisotropic oxygen reactive ion etching (RIE) step. The new technique is capable of forming sidewall masks with dimensions ranging from 50 to 500 nm, depending on the silylation conditions. The sidewall masks have been used for successful pattern transfer into SiO2 and Si3N4 by CF4–RIE. This new and simple nanometer sidewall formation technique is easily reproducible and very uniform and, in certain application areas, might be an alternative to more complex and expensive lithography techniques.