bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for structure sensitivity in the high pressure CO+NO reaction over Pd(111) and Pd(100)
Authors: Vesecky Scott M. , Chen Peijun , Xu Xueping , Goodman D. Wayne
Published: July 2002

The chemisorption of coadsorbed CO and NO has been studied over Pd(111) and Pd(100) at 1×10−6 Torr using infrared reflection absorption spectroscopy. At a pressure ratio of PNO/PCO= 1, the ratio of adsorbed NO to adsorbed CO, [NOa]/[COa], increased with temperature over both single crystal surfaces. Furthermore, the [NO]a/[CO]a was significantly higher on Pd(111) than on Pd(100) in the temperature range of 100–550 K, with NO being the predominant surface species above 400 K. The reaction of CO+NO to form CO2, N2O and N2 was followed with infrared spectroscopy by monitoring the evolution of gas phase CO2 and N2O. At temperatures from 525–650 K, partial pressure ratios, PNO/PCO, from 16:1 to 1:16, and total pressures of 2–17 Torr, Pd(111) always showed higher activity than Pd(100) for both CO2 and N2O production. The Pd(100) surface, however, gave a higher branching ratio for N2 versus N2O production than Pd(111). The apparent activation energies of the reaction indicate a positive order in PNO and a negative order in PCO over both single crystal surfaces, with a zero order total pressure dependence between 2 and 20 Torr. The higher N2/N2O branching ratio observed on Pd(100) is likely due to the higher stability and surface coverage of dissociated nitrogen atoms on Pd(100) versus Pd(111), thus promoting the reaction 2 Na→N2g. Both the higher activity and the higher selectivity for N2O versus N2 over Pd(111) are strongly correlated with the higher surface coverage of NOa. In contrast, the lower activity of the Pd(100) surface relative to Pd(111) is likely due to enhanced poisoning of NO adsorption on this surface by dissociated nitrogen or oxygen atoms, or by adsorbed CO.
Real-time monitoring of resonant-tunneling diode growth using spectroscopic ellipsometry
Authors: Celii F. G. , Kao Y.-C. , Katz A. J. , Moise T. S.
Published: July 2002

We report in situ growth monitoring of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant-tunneling diodes (RTDs) using spectroscopic ellipsometry. A phase-modulated spectroscopic ellipsometer was triggered synchronously with 20 rpm substrate rotation of the III–V molecular beam epitaxy system. Postgrowth data analysis yielded layer thicknesses which were compared with the electrical characteristics of the processed RTDs. A sample set of 28 RTDs included designed variations in eight growth variables and provided for a linear model fit to the RTD peak current, peak voltage, and valley current I–V characteristics. The I–V characteristics are sensitive to the thickness of the AlAs, InAs, and InGaAs layers.
A model for transport and agglomeration of particles in reactive ion etching plasma reactors
Authors: Huang Fred Y. , Hwang Helen H. , Kushner Mark J.
Published: July 2002

Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. These observations, and the fact that the forces which govern the transport and trapping of particles are partly determined by their size, place importance on understanding particle growth and agglomeration mechanisms. Since individual particles in plasma etching tools are negatively charged, their agglomeration is problematic since the particles must obtain sufficient kinetic energy to overcome their mutual electrostatic repulsion. In this article, we discuss results from a model for particle agglomeration in RIE plasma tools with which we address the transport of particles and interparticle collisions resulting in agglomeration. These results indicate that the rate and extent of particle agglomeration depend on the particle density, plasma power deposition, and, to a lesser degree, gas flow. The dependence of agglomeration on rf power results from the fact that the kinetic energy of a dust particle is largely determined by its acceleration by ion drag forces. Significant agglomeration may occur in particle traps where the particle density is large.
Synthesis of silicon nitride particles in pulsed radio frequency plasmas
Authors: Buss R. J. , Babu S. V.
Published: July 2002

Silicon nitride (hydrogenated) particles are synthesized using a pulsed 13.56 MHz glow discharge. The plasma is modulated with a square-wave on/off cycle of varying period to study the growth kinetics. In situ laser light scattering and ex situ particle analysis are used to study the nucleation and growth. For SiH4/Ar and SiH4/NH 3 plasmas, an initial very rapid growth phase is followed by slower growth, approaching the rate of thin film deposition on adjacent flat surfaces. The average particle size can be controlled in the 10–100 nm range by adjusting the plasma-on time. The size dispersion of the particles is large and is consistent with a process of continuous nucleation during the plasma-on period. The large polydispersity is also reported for silicon particles from silane and differs from that reported in other laboratories. The silicon nitride particle morphology is compared to that of silicon and silicon carbide particles generated by the same technique. Whereas Si particles appear as rough clusters of smaller subunits, the SiC particles are smooth spheres, and the Si 3N4 particles are smooth but nonspherical. Postplasma oxidation kinetics of the particles are studied with Fourier transform infrared spectra and are consistent with a hydrolysis mechanism proposed in earlier work with continuous plasmas. Heat treatment of the powder in an ammonia atmosphere results in the elimination of hydrogen, rendering the silicon nitride resistant to atmospheric oxidation.
Monte Carlo numerical analysis of target erosion and film growth in a three-dimensional sputtering chamber
Authors: Serikov Vladimir V. , Nanbu Kenichi
Published: July 2002

A combination of two mathematical models for three-dimensional Monte Carlo particle simulation of a low pressure sputtering environment is proposed. One is intended for the simulation of a discharge gas flow, and the other for the sputtered atom transport. The combination is used to characterize target erosion and film growth. The models are refined with recourse to experimental measurements made in a practical sputtering apparatus (SPF-210 AS, ANELVA Ltd.) over the range of operating pressures and flow rates of 0.3–10 Pa and 0.5–5 sccm, respectively. A considerable number of numerical analyses are done to find possible reasons for the measured nonuniformity of target erosion and film growth rate distributions. Simulation results show that under the operating and design conditions treated here the nonuniformity of gas flow field appears to be too weak to explain the experimental data. Film growth rates simulated for measured erosion rates show a good agreement with the experimental data for the various operating pressures above. Important features of the present simulation are the inclination of the angular distribution of sputtered atoms, and taking into consideration reemission of sputtered atoms deposited onto the target. The inclination of angular distribution results from the oblique ion incidence onto the target surface. The existence of highly eroded etch track along the target edge is shown to be correlated with the greater sputtering yield for the oblique ion incidence near the edge. Axial asymmetry of the erosion and growth rate distributions may be due to the asymmetry of the electric field lines at the periphery of the target, which leads to a nonuniform incidence angle along the edge. In contrast to erosion and growth rates, the redeposition rate of sputtered atoms onto the target is found to increase considerably with pressure.
Quantitative two-dimensional dopant profiling of abrupt dopant profiles by cross-sectional scanning capacitance microscopy
Authors: Huang Y. , Williams C. C. , Wendman M. A.
Published: July 2002

The scanning capacitance microscope (SCM) is capable of quantitative two-dimensional carrier and dopant density mapping with nanometer scale spatial resolution. The method can be applied to either the top or the cross-sectional surface of a silicon sample. The quantitative inversion of SCM data to carrier or dopant density is achieved using a quasi-one-dimensional model. Cross-sectional SCM measurements have been performed on samples that have abrupt dopant density steps. The dopant density in these samples systematically varies from 1017 to 1020 cm−3. The cross-sectional measurements provide a means to directly compare the SCM results with vertical secondary ion mass spectroscopy (SIMS) profiles. A spatial resolution of approximately 25 nm is achieved. A first order quantitative agreement between the SCM and the SIMS profiles is found.
Multifunctional multilayer optical coatings
Authors: Martin P. M. , Stewart D. C. , Bennett W. D. , Affinito J. D. , Gross M. E.
Published: July 2002

Multilayer optical coatings which heated and defogged the substrate, provided permeation barriers to water and air, and controlled emittance have been developed. All coatings were deposited by reactive dc and rf magnetron sputtering, and the polymer multilayer process being developed at Pacific Northwest National Laboratory. The three coatings discussed in this article were applied to flexible and rigid substrates with diameters up to 28 cm. Fourteen-layers SiO2/Si3N4/TiO2/Ag coatings were applied to surveillance camera lenses to reject at least two laser wavelengths, defog the lens, and provide a high transmission notch at the operating wavelengths. The coatings were able to heat the substrates at a rate of 16 °C/min at relatively modest power inputs of 2 W/cm2. The second coating had eight Cr/Si3N4 layers, and absorbed strongly at the 1.06 μm laser wavelength and emitted strongly in the 3–5 μm wavelength band. This coating was used in infrared displays. The last coating was a 15-layer polymer Al2O3 permeation barrier to water and air on a flexible polyethylene substrate. The coating was transparent. The permeation rates for oxygen were less than 2.55E-6 cm3/cm2/day, and were less than 1.55E-6 g/cm2/day for water. The permeation test results provided further evidence for a synergistic relationship between polymer and oxide layers to prevent surface and solution diffusion of gases and water.
A simplified collisional model of sputtering in the linear cascade regime
Authors: Mahan John E. , Vantomme André
Published: July 2002

Thin film deposition by sputtering is usually performed with projectile-energy-target combinations placing the sputtering mechanism within the linear cascade regime of collisional sputtering. For the purposes of estimating sputter yield values, as well as conveying an understanding of this most important sputtering mechanism, there is a need for an analytical model whose yield expression has a clear and obvious physical meaning, is easy to evaluate with a modest computer, and yet faithfully represents sputtering in this regime. To meet this need, a deliberately simplified model is developed. The yield expression is a product of three terms: the number of recoiling target atoms at the practical endpoint of the cascade, times the probability that they are sufficiently near the surface to escape, and times the probability that they are traveling in the right direction. It is evaluated by calculating (1) the surface binding energy from thermodynamic data, (2) an average energy of the population of target recoils, from their energy distribution at the practical endpoint of a single collision cascade, and (3) an escape probability from the projected ranges of projectile and recoils, based on nuclear energy loss theory. The simplified collisional model reproduces trends in experimental data for the projectile energy-, projectile mass-, and target-dependences of sputter yield.
Determination of the surface silanol concentration of amorphous silica surfaces using static secondary ion mass spectroscopy
Authors: D’Souza Andrew S. , Pantano Carlo G. , Kallury Krishna M. R.
Published: July 2002

A novel method has been developed to determine the concentration of silanol (Si–OH) groups on planar, amorphous silica glass surfaces. This method involves neutral beam static secondary ion mass spectroscopy (SIMS) analysis as a function of sample temperature. The calibration necessary to achieve absolute quantification of the silanol concentrations with static SIMS was obtained using a combination of Fourier-transform infrared (FTIR) spectroscopy and x-ray photoemission spectroscopy (XPS). High purity, amorphous silica glass samples with varying silanol and molecular water concentrations were prepared ex situ, and in vacuo by fracturing and dosing silica rods with water in the sample preparation chamber of a UHV system. Static SIMS spectra collected as a function of sample temperature show a decreasing SiOH+/Si+ peak area ratio with increasing temperature due to desorption of physisorbed, molecular water. It is shown that the equilibrium SiOH+ signal intensity obtained after the heat treatment is proportional to the silanol concentration of the silica surface. XPS analysis of derivatized samples was used to confirm the results of the static SIMS experiments. In order to achieve absolute quantification of the silanol concentration in OH/nm2, FTIR was used to calibrate the SiOH+/Si+ peak area ratios measured from the static SIMS spectra.
Discharge disruptions in a helicon plasma source
Authors: Shamrai K. P. , Virko V. F. , Blom H.-O. , Pavlenko V. P. , Taranov V. B. , Jonsson L. B. , Hedlund C. , Berg S.
Published: July 2002

We study experimentally and theoretically stable regimes and discharge disruptions in a helicon plasma source. At fixed input power and gas pressure, stable operation of the source is possible below some critical value of magnetic field Bcr. The plasma density increases with the magnetic field and reaches a maximum value nmax at Bcr; after which the discharge disruption occurs. Both Bcr and nmax increase almost linearly with the input power and the rate of increase is increasing with the pressure. Matching of the plasma load to the rf power source improves when approaching the disruption point, and becomes perfect at the critical field. The theory of discharge disruptions assumes the power absorption in a helicon source to arise from the linear conversion of helicon waves into electrostatic waves at the plasma edge. The calculated dependence of the absorbed power on the plasma density turns out to be nonmonotonic with minima at antiresonances of the electrostatic wave excitation. This explains qualitatively principal peculiarities of discharge disruptions. The calculated plasma impedance is in agreement with experimental value within a factor of 2.
Gas-phase-reaction-controlled atomic-layer-epitaxy of silicon
Authors: Hasunuma Eiji , Sugahara Satoshi , Hoshino Shinji , Imai Shigeru , Ikeda Keiji , Matsumura Masakiyo
Published: July 2002

Atomic layer epitaxy of silicon has been studied by alternating exposures of atomic hydrogen and SiH2Cl2. An ideal growth rate of 1 monolayer per cycle has been achieved with a wide temperature window from 550 °C to 610 °C under long SiH2Cl2 residence time and high pressure conditions. These requirements seem to come from the generation of dense SiHCl, the desirable precursor, by gas-phase reaction of SiH2Cl2.
Measurements of the helium propagation at 4.4 K in a 480 m long stainless steel pipe
Authors: Hseuh H. C. , Wallen E.
Published: July 2002

The relativistic heavy ion collider (RHIC), with two concentric rings 3.8 km in circumference, uses superconducting magnets to focus the high energy beams. Each sextant of RHIC will have continuous cryostats up to 480 m in length housing the magnets and the cold beam pipes. For an acceptable lifetime of the stored beam, the pressure in the cold beam pipe will be <10−11 Torr. The characteristics of He pressure front propagation due to He leaks will be of importance for beam lifetimes and for vacuum monitoring due to the high vapor pressure of He at 4.4 K, even with small surface coverage. The travels of the He pressure fronts along a 480 m long, 6.9 cm I.D. stainless steel beam pipe cooled to 4.4 K have recently been measured during the RHIC first sextant test. The experiment was carried out over a 12-day period by bleeding in a calibrated He leak of 3×10−5 Torr l/s (20 °C) while measuring the He pressures along this 480 m cold tube at approximately 30 m intervals. The measured speed of the pressure fronts and the pressure profiles are summarized and compared with the calculated ones.
Operation and oxidation of thermionic dispenser cathodes studied by high resolution photoemission
Authors: Bailey P. , Cowie B. C. C. , Norman D.
Published: July 2002

Thermionic dispenser cathodes are practical devices whose action is dominated by their surface properties. At their operating temperature of 1450 K a near-monolayer barium oxide coating in dynamic equilibrium maintains a low work function. We have used high resolution synchrotron radiation x-ray photoelectron spectroscopy (SRXPS) to help elucidate the mechanism of operation and poisoning (by oxidation) of two types of cathode, one made from a pure tungsten matrix (B type) and the other coated with an osmium/ tungsten alloy (CD type). SRXPS measurements have been made on cathodes both at room temperature and at their operating temperature. Comparison between these confirms that room temperature experiments are representative of operational cathodes, with no significant change in the chemical state of the surface species. For the B type cathode, the core level binding energies are consistent with the presence of a single layer of barium oxide at the surface, while for the CD type, the Ba is shifted to a lower binding energy and the O is shifted to higher binding energy suggesting additional electron transfer to the O. Each of the W 4f peaks for the CD type cathode is split, with the lower binding energy peak being W metal and the higher binding energy peak WO. The W has a lower binding energy than for the B cathode, ascribed to the lower coordination number of W in the W/Os lattice. Valence band spectra of reactivated cathodes showed none of the known contamination features and thereby confirm that the study is representative of operational cathodes. The valence bands of both types of cathodes are dominated by a peak at about 6.0 eV, attributed to O 2p with limited hybridization with the substrate valence orbitals. Poisoning of the cathodes by progressive exposure at room temperature to small amounts of oxygen produced a substantial increase in the work function and dramatic changes in the core level spectra. For the tungsten cathode, oxygen appears to react preferentially with the barium surface component, whereas for the alloy cathode the oxygen reacts almost exclusively with the tungsten atoms, to form WO2 and WO3. We conclude that, although the two types of cathode are superficially similar, in fact they have completely different surface and electronic structure.
Micro-Raman study of reactive pulsed laser ablation deposited silicon carbon alloy films
Authors: Trusso Sebastiano , Vasi Cirino , Barreca Francesco , Neri Fortunato
Published: July 2002

Si 1−x C x : H alloy thin films were deposited by pulsed laser ablation of a crystalline silicon target in a reactive environment. The microstructure of the films was studied by means of scanning electron microscopy (SEM) images and spatially resolved Raman spectroscopy. The films were found to consist of mixed microcrystalline and amorphous phases, with a silicon crystallite size of 5–6 nm. Incorporation of carbon and hydrogen was found to occur mainly in the amorphous phase. Results showed that films growth is given by deposition of atomic and molecular sized material reacting with ionized species. Some inhomogeneities observed in the SEM images were attributed to rapid cooling of liquid droplets ejected from the target.
Transmission characteristics of multilayer structure in the soft x-ray spectral region and its application to the design of quarter-wave plates at 13 and 4.4 nm
Authors: Kim Dong-Eon , Lee Su-Mi , Jeon In-joon
Published: July 2002

The increasing usage of soft x-ray radiations due to the development of synchrotron radiation source and others demands varied optical manipulation in the soft x-ray spectral region. The phase manipulation is important because this leads to the control of the polarization state of a soft x-ray radiation. A new criterion for selecting material pairs for the maximum phase difference between the s and p polarization through a multilayer (ML) structure was proposed and tested theoretically. Transmission characteristics of ideal ML structures in the soft x-ray spectral region have been studied by simulation. The results have been applied to optimize ML structures for quarter-wave plates at 4.4 and 13 nm. It was found that Rh/Si and Co/K MLs are good candidates for quarter-wave plates at 13 and 4.4 nm, respectively.
Epitaxial growth and characterization of Ce1−xZrxO2 thin films
Authors: Gao Y. , Herman G. S. , Thevuthasan S. , Peden C. H. F. , Chambers S. A.
Published: July 2002

Epitaxial films of mixed Ce1−xZrxO2(001) oxides with x⩽0.3 have been grown on SrTiO3(001) by oxygen-plasma-assisted molecular beam epitaxy. The film growth at 600 °C is predominantly nucleation and growth of three-dimensional islands. The films become much smoother after rapid thermal annealing at 700 °C for 30 s in the oxygen plasma. High-energy ion channeling reveals that Zr atoms substitutionally incorporate at cation sites in the CeO2 lattice for all doping levels, leading to Ce1−xZrxO2 solid solutions. Analysis of Zr 3d and Ce 3d core-level binding energies shows that the oxidation state of both Zr and Ce is +4. Lattice distortion induced by incorporation of Zr in the CeO2 lattice becomes prevalent for high doping levels and surface roughen accordingly.
Consistency of calculated and measured electron inelastic mean free paths
Authors: Powell C. J. , Jablonski A.
Published: July 2002

We present an evaluation of the consistency of calculated and measured electron inelastic mean free paths (IMFPs) for seven elemental solids (Al, Si, Ni, Cu, Ge, Ag, and Au). These solids were selected because, for each, there were two or more independent IMFP calculations and two or more IMFP measurements by elastic-peak electron spectroscopy. We found that the calculated IMFPs for each element showed a high degree of consistency and that there was greater scatter among the measured IMFPs. Comparison of the measured IMFPs with the calculated IMFPs showed generally good agreement. The greatest consistency in the comparisons was found for Ni, Cu, Ag, and Au. Recommended values of the IMFPs for these four elements can be obtained from a simple formula (used to fit the calculated IMFPs for each element) for electron energies between 50 and 104 eV.
Real-time optical control of Ga1−xInxP film growth byp-polarized reflectance
Authors: Dietz N. , Woods V. , Ito K. , Lauko I.
Published: July 2002

The engineering of advanced optoelectronic integrated circuits implies the stringent control of thickness and composition. These demands led to the development of surface-sensitive real-time optical sensors that are able to move the control point close to the point where the growth occurs, which in a chemical beam epitaxy process is the surface reaction layer, built up of physisorbed and chemisorbed precursor fragments between the ambient and film interface. In this context, we explored the application of p-polarized reflectance spectroscopy (PRS) for real-time monitoring and control of pulsed chemical beam epitaxy during low-temperature growth of epitaxial Ga1−xInxP heterostructures on Si(001) substrates. A reduced order surface kinetics model has been developed to describe the decomposition and growth kinetics of the involved organometallic precursors and their incorporation in the film deposition. We demonstrate the linkage of the PRS response towards the surface reaction chemistry, composition, film growth rate, and film properties. Mathematical control algorithms are applied that link the PR signals to the growth process control parameters to control the composition and growth rate of epitaxial Ga1−xInxP heterostructures.
Volume/surface effects on electron energy and dissociation reactions in large-volume plasma reactors
Authors: Kinoshita Keizo , Noda Shuichi , Morishita Satoshi , Itabashi Naoshi , Okigawa Mitsuru , Sekine Makoto , Inoue Masami
Published: July 2002

The effect of changing the gap width on the bulk plasmas was examined by the simple model calculation and by the diagnostics for ultrahigh frequency (UHF) (nonmagnetized) and UHF electron cyclotron resonance (ECR) (magnetized) plasma. Higher volume/surface ratio (wider gap width at constant chamber diameter) brought higher electron density and lower electron temperature in the bulk plasma. The uniform discharge model explained the effects of the gap width change on these basic plasma parameters by the particle and energy balance. The latest spectroscopic and spectrometric measurements were applied to Ar/c-C4F8-based oxide etching plasma, and monitored the change of the electron impact reaction rate coefficients (〈σv〉) for argon emission, c-C4F8 dissociation, and fluorine radical generation. The results quantitatively showed that the wider gap width (lower electron temperature) suppressed these electron impact reactions. In addition, UHF and UHF-ECR showed different gap width dependency in these 〈σv〉’s by the effect of magnetic confinement for the UHF-ECR plasma. Higher Ne condition was achieved at the wider gap width without changing the fluorine density. As a result, higher etching rate of the thermal oxide was achieved in the wider gap width.
High resolution x-ray photoelectron spectroscopy and INDO/S–CI study of the core electron shakeup states of pyromellitic dianhydride-4,4′-oxydianiline polyimide
Authors: Nakayama Y. , Persson P. , Lunell S. , Kowalczyk S. P. , Wannberg B. , Gelius U.
Published: July 2002

Pyromellitic dianhydride-4,4′-oxydianiline (PMDA–ODA) polyimide films have been studied using high resolution x-ray photoelectron spectroscopy and model semi-empirical INDO/S–CI calculations. Experimental and theoretical C 1s, N 1s, and O 1s spectra are presented, and found to be in good agreement with each other. Shakeup features of the spectra are identified, and their electronic nature analyzed theoretically. The highly nonstoichiometric ratio between the carbonyl and the ether O 1s main peaks is quantitatively explained by the calculations, where the nonstoichiometry is shown to be the result of stronger carbonyl than ether shakeup. Conformational effects on the shakeup spectra, due to torsion between the PMDA and ODA units, were investigated theoretically and found to be small for PMDA–ODA.
Operating high-density plasma sources in a low-density range: Applications to metal etch processes
Authors: Czuprynski P. , Joubert O. , Vallier L. , Sadeghi N.
Published: July 2002

A new way of operating high-density plasma sources is presented which allows the resist/metal selectivity to be significantly increased during a metal etching process while maintaining the anisotropy of the etching profile. The principle of the technique is to operate a high-density plasma source in a low-density range in which the radio-frequency (rf) source power is lower than the chuck power. When the source is operated under these conditions, the ion density is strongly decreased while the source is still operated at low pressures. Optical emission spectroscopy has been used to compare the dissociation efficiency of the source operated in the low- and high-density modes. The photoresist etch rate was measured using light reflectometry. In some cases, after etching, the resist sample was transferred in vacuo into an x-ray photoelectron spectrometer analysis chamber to measure the chlorine coverage on the resist surface. The ion current density (Ji) was determined using a new type of electrostatic probe. The ion flux was determined from the discharging of a RF-biased capacitance in series with the probe. Finally, a simple model is suggested to explain the impact of the plasma operating conditions (source power and chuck power) on the resist etch rate.
Gradational lead screw vacuum pump development
Authors: Ando Kiyoshi , Akutsu Isao , Ohmi Tadahiro
Published: July 2002

Because the semiconductor industry is moving to a larger wafer size and higher process speed, a vacuum pump will be required to have higher pumping speed in both the viscous and molecular flow ranges. The “gradational lead screw (GLS) pump” unlike these conventional pumps demonstrated the ultimate pressure of 0.0004 Torr and a pumping speed of 8000 L/min over the viscous and molecular flow ranges. The improved performance is attributable to the GLS rotor design. The pump utilizes a small amount of oil. Mass analyzer testing (maximum mass number 120) revealed that there is no evidence of reverse diffusion in the pressure range above 0.002 Torr with a small amount of N2 gas injected. In summary, the GLS pump has high pumping speed because of its large intake volume. Electric power consumption is low as a result of its small exhaust volume. By-product is transferred and ejected from the exhaust port through the operation mechanism. The by-product deposition is minimized if the case temperature is maintained above 150 °C. Although manufacturing this pump requires a high level of skill, the pump structure is rather simple and the maintenance is easy. Hence it will increase the mean time between overhaul and reduce maintenance cost. A detailed report will be prepared on the characteristics of the GLS, the pump structure, and the performance attributes.
Nickel-induced effect on the surface morphology of rapid-quenched Si(111)
Authors: Fukuda T.
Published: July 2002

The morphology and atomic structures of Ni-stabilized “1×1” domains formed on rapid-quenched Si(111) surfaces were studied using atomic force microscopy (AFM) in air and scanning tunneling microscopy (STM) in a vacuum. Quantitative analysis of the surface morphologies by ex situ AFM showed that the widths for inhibiting the 1×1 stabilization near monoatomic steps depended on Ni deposition of between 1.8×10−2 and 9×10−4 monolayers (ML). For Ni depositions of less than 9×10−4 ML, the protrusion of the 1×1 domain decreased. In situ STM study revealed that the 7×7 reconstruction had nucleated in the 1×1 domains.
Stoichiometric indium oxide thin films prepared by pulsed laser deposition in pure inert background gas
Authors: Yamada Yuka , Suzuki Nobuyasu , Makino Toshiharu , Yoshida Takehito
Published: July 2002

We have observed a drastic change in the properties of indium oxide (In2O3) thin films prepared by pulsed laser deposition in a pure helium (He) background gas on unheated glass substrates. At high He pressures above 1.0 Torr, transparent crystalline In2O3 films could be prepared, even though the deposition was carried out without the introduction of oxygen gas and substrate heating. At lower He pressures, blackish opaque films were deposited. These results can be accounted for by the inert background gas effects, which cause spatial confinement of the ablated species in the high-pressure and high-temperature region. Facilitated oxidation in this region would suppress oxygen deficiency in the deposited films.
Plasma enhanced chemical vapor deposition of fluorocarbon thin films via CF3H/H2 chemistries: Power, pressure, and feed stock composition studies
Authors: Senkevich Jay J. , Sherrer David W.
Published: July 2002

Since fluorocarbon thin films exhibit unique properties such as a low coefficient of friction, a low index of refraction, chemical inertness, and hydrophobicity they continue to have industrial interest. The ease by which plasma enhanced chemical vapor deposition fluorocarbon thin films properties can be varied is of interest to the present study. Further, it has been found that these properties, such as index of refraction, hydrophobicity, stress and film hardness can be varied much more easily and substantially with the addition of hydrogen to a CxFy feed stock. The present study is continued work which has investigated the chemical structure and properties of fluorocarbon films as a function or pressure, radio frequency (rf) power density and H2/CF3H feed stock. As a function of rf power density, the index of refraction exhibited a large dependence for the thin films deposited from CF3H with 10 sccm H2. Namely, at 0.0877 W/cm2 the film had an index of 1.420 which dropped to 1.388 at 0.219 W/cm2. The addition of H2 to the CF3H feed stock decreased the intrinsic stress from 430 MPa tensile with no H2 added to 70 MPa tensile with a H2/CF3H ratio of 0.75 (30 sccm H2). Further, the addition of hydrogen qualitatively increased the hardness of the films due to a higher crosslinking density and increased the film thickness uniformity due to the high molecular diffusivity of hydrogen.
Wide range temperature dependence of reflection high-energy electron diffraction rocking curve from a Si(111)7×7 surface
Authors: Fukaya Y. , Nakamura K. , Shigeta Y.
Published: July 2002

In order to determine the Debye parameter for the surface layer of Si crystal, we have measured the rocking curves of reflection high-energy electron diffraction (RHEED) from a Si(111)-7×7 surface at temperatures extending over a wide range, 293–1073 K. From the analysis of the dynamical calculation of RHEED intensity taking account of the thermal diffuse scattering, the adatoms and rest atoms largely shifted upward compared with the atomic positions derived by Brommer et al. using ab initio molecular-dynamics scheme [Phys. Rev. Lett. 68, 1355 (1992)] and the optimum Debye temperature has been estimated at 420 K, which is much lower than that of bulk Si (505–658 K). Since the Debye temperature is considered to be an averaged value in a few surface layers, the difference means that the vibrational amplitude of surface atom is large compared to bulk atom.
Molecular transition and slip flows in the pumping channels of drag pumps
Authors: Heo Joong-Sik , Hwang Young-Kyu
Published: July 2002

Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a helical-type drag pump (HTDP) and disk-type drag pump (DTDP). The flow occuring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier–Stokes equations with slip boundary conditions, and the second one is a stochastic particle approach through the use of the direct-simulation Monte Carlo method. From the present study of a HTDP, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number Kn⩽0.01 (i.e., the slip-flow regime). But the results from the second method only agree with the experimental data for Kn>0.01 (i.e., the molecular-transition regime). From the analysis for a DTDP, we found that an actual pumping passage is strictly limited to a narrow region because of the significant backstreaming of molecules from the outlet.
Si(111) 2×1 surface reconstructions calculated by the density-functional method
Authors: Nielsen O. H. , Martin Richard M. , Chadi D. J. , Kunc K.
Published: July 2002

The π-bonded chain and molecular models for the reconstruction of the Si(111) 2×1 surface are compared with each other and with angle-resolved photoemission data. The calculations are based on the local-density-functional approach, using ab initio pseudopotentials for calculating total energy and forces. The chain model is found to have lower energy than the molecular model. The experimental dispersion also favors the chain model, but the molecular model cannot be ruled out from the present data.
Large area ion beam assisted etching of GaAs with high etch rates and controlled anisotropy
Authors: Lincoln G. A. , Geis M. W. , Pang S. , Efremow N. N.
Published: July 2002

Ion beam assisted etching (IBAE) is a dry etching technique in which the sputter etching component of an argon ion beam and the chemical etching component supplied by a Cl2 gas flux are independently controlled. This technique has been used to obtain anisotropic etching of GaAs with minimal surface damage over areas of a few square millimeters. The results reported here are achieved with an improved IBAE system designed to etch considerably larger areas. The system accurately and uniformly delivers reactive gas flux to the sample giving uniform etching rates over the 2-cm-diam area exposed to the ion beam. When the sample is exposed to high reactive gas fluxes, equivalent to a pressure of 1×10−2 Torr, and 1 to 2 keV Ar+ ions at 1 mA cm−2, etching rates of 5 to 10 μm/min are obtained making etched through-holes in GaAs wafers realizable. Control of the ion beam collimation and the reactive gas flux allow for accurate control of undercutting making submicrometer etched structures in GaAs with aspect ratios>35:1 easily obtainable. In addition, damage studies of the ion beam assisted etched GaAs surfaces shows a low trap density in the range of 1013 cm−3 as determined by deep level transient spectroscopy (DLTS). The improved system uses two gas jets to supply the chemically reactive flux and a liquid N2 cooled shroud to trap the unused reactive gas. The absolute reactive flux impinging on the sample is determined with a capacitance monometer and the ion beam collimation is controlled by varying the ion gun to sample distance.
Molecular beam epitaxy of In0.53Ga0.47As and InP on InP by using cracker cells and gas cells
Authors: Huet D. , Lambert M. , Bonnevie D. , Dufresne D.
Published: July 2002

In0.53Ga0.47As and InP were grown on InP substrate by using dimeric molecules of arsenic and phosphorus. A Riber cracker cell and a laboratory designed gas cell were used. Cracking rate inside the two kinds of cells was studied by a modulation beam mass spectrometry technique (MBMS). Cracking rate up to 95% was obtained for the gas cell. The ratio M2/M4 in the flux reaches 103. The use of As2 species for In0.53Ga0.47As growth allows a saving of arsenic compared with As4 species. A reduction of the incorporation rate of carbon is observed. Photoluminescence efficiency is increased by a factor of 5. PIN photodiodes exibit low dark current down to 25 nA at−10 V in As2 grown InGaAs, 103 less than in As4 grown ternary material, on mesa diameter of 170 μm. We describe growth conditions of InP by using cracker cell and gas cell as phosphorus sources. Gas source seems to be a promising phosphorus source due to its large autonomy and hydrogen pressure which favors PH3 recombination and impurities reduction.
Epitaxial growth from organometallic sources in high vacuum
Authors: Fraas L. M. , McLeod P. S. , Partain L. D. , Cape J. A.
Published: July 2002

Herein we describe a process that combines some of the principal advantages of molecular beam epitaxy and metal-organic chemical vapor deposition (MOCVD) systems. We call this process vacuum chemical epitaxy (VCE). In this process, multiple group III-alkyl molecular beams are directed through a water-cooled gas distribution block onto wafers providing for the growth of uniform films over large areas with high group III-alkyl utilization efficiency. The group V source, on the other hand, is injected at a single point on one side of the deposition zone. The group V molecules are confined and undergo molecular flow across the deposition zone. The utilization efficiency of the group V source material can be enhanced by the use of a thermal cracker at the point of group V gas injection. This high group V gas utilization efficiency, combined with the fact that all of the reactants are contained within a stainless-steel vacuum chamber equipped with an air lock for wafer loading, leads to a safer MOCVD scaleup reactor. In this paper our VCE reactor is described in some detail along with the properties of III–V films grown with this equipment. The fabrication of a GaAsSb solar cell with an active area energy conversion efficiency of 26.7% demonstrates that VCE has the capability of producing high-performance devices.
An Auger electron spectroscopy, x-ray photoelectron spectroscopy, secondary ion mass spectrometry and bulk analysis of pyrolytic boron nitride crucibles after vacuum baking
Authors: Chambers F. A. , Zajac G. W. , Fleisch T. H.
Published: July 2002

The growth of high quality GaAs and AlGaAs using the molecular beam epitaxy (MBE) technique requires that all of the components of the system be kept very clean, especially the source materials (Ga, As, and Al), the crucibles, and the furnaces since they are at high temperatures during the growth of the material. The crucibles, made of pyrolytic boron nitride (PBN), are used after a cleaning procedure that consists of a 1 h heat treatment at 1600 °C in a vacuum of approximately 5×10−9 Torr or better. While this cleaning procedure has been used extensively, there have been no reported studies of the effectiveness of this procedure or its effect on the crucible. We have used mass spectrometry, AES, SIMS, XPS, and a modification of the LECO technique to study both baked and unbaked crucibles. In this paper we demonstrate that the cleaning procedure does remove impurities from the crucible, especially carbon. We also demonstrate that the cleaning procedure does not decompose the surface of the crucible as is commonly believed and that the recently observed dark striations on the interior of some of the crucibles after the bakeout are due to a physical restructuring of the surface and a possible local segregation of boron and not due to surface segregation of impurities such as carbon. We also present the first report of e-beam induced decomposition of boron nitride.
Characterization of titanium nitride films sputter deposited from a high-purity titanium nitride target
Authors: Brat T. , Parikh N. , Tsai N. S. , Sinha A. K. , Poole J. , Wickersham C.
Published: July 2002

Titanium nitride films (100–300 nm) were sputter deposited from a high-purity titanium nitride target (nominal purity 99.99%) in an experimental dc-magnetron system. The gold-colored target, 5 cm in diameter, had a density of 92% of the theoretical value. X-ray diffraction indicated that the target material matched the simulated stoichiometric TiN pattern, while the deposited films showed a shift in the crystallographic plane spacing of the (111) and (200) Bragg reflections. Rutherford backscattering spectrometry (RBS) performed on titanium nitride films which were deposited on amorphous carbon substrates indicated the presence of titanium, nitrogen, and oxygen as principal components of the films. No argon was detected in the films within the sensitivity of the RBS technique. Titanium to nitrogen atomic ratios in the films varied from 0.83 to 1.02 according to the RBS results. The binding energy measured by x-ray photoelectron spectrometry (XPS) indicated that Ti and N were present in compound form. The effect of substrate temperature deposition, dc bias, and nitrogen content in the sputtering gas were correlated to the stoichiometry and resistivity of the films. High rates of deposition (3.8 nm/s) on hot Si(100) substrates produced films with a resistivity as low as 40 μΩ cm. The performance of the TiN films as a diffusion barrier was evaluated in a Al/TiN/TiSi2/Si(100) layered structure.
Theoretical studies of reconstructed GaAs(100) surfaces using first principle calculations
Authors: Qian Guo-Xin , Martin Richard M. , Chadi D. J.
Published: July 2002

Full and one-half monolayer Ga stabilized GaAs(100) surfaces are studied using ab initio self-consistent density-functional calculations implemented with our newly generated soft pseudopotential. Particular attention is focused on the Ga terminated missing row model which is nonpolar. Surface energies and surface atomic relaxations are determined through energy-minimization calculations.
Pinning of the Fermi level close to the valence-band top by chlorine adsorbed on cleaved GaAs(110) surfaces
Authors: Troost D. , Koenders L. , Fan L.-Y. , Mönch W.
Published: July 2002

The adsorption of chlorine on cleaved GaAs(110) surfaces was found to increase their ionization energy by up to 1.4 eV and to pin the Fermi level at 0.1 and 0.2 eV above the valence-band top on samples doped p and n type, respectively. These experimental findings are explained by a charge transfer between adsorbate-induced surface states of the semiconductor and the adatoms, which are charged negatively, since chlorine is much more electronegative than GaAs. The adsorbate-induced surface states are identified as virtual gap states (ViGS) of the complex band structure of GaAs. The chemical trends in Fermi-level pinning observed with Cs, Cu, Ag, and Au adsorbed on GaAs are also described by this ViGS model of adsorbate-induced surface states. At larger exposures to Cl2, the Fermi level assumes a second pinning position at 0.55 above the valence-band top for both types of doping. This change of pinning positions is attributed to the formation of adsorbate-induced defects.
Temperature and flow effects in aluminum etching using bromine-containing plasmas
Authors: Keaton A. Landauer , Hess D. W.
Published: July 2002

The effects of sample temperature and reactant flow rate on aluminum etching in BBr3 and BBr3/Br2 mixtures were investigated in a parallel-plate plasma etcher. Etch samples were bonded to the electrode with conductive epoxy to promote thermal equilibrium. Results indicated that the reaction was gas phase controlled between 30 and 140 °C; above 140 °C, the gas phase limitation may be due to reactant adsorption while a product desorption limitation may exist below 30 °C. Transport limitations were encountered at reactant flow rates below 10 sccm.
Scanning ion microscopy and microsectioning of electron beam recrystallized silicon on insulator devices
Authors: Kirk E. C. G. , McMahon R. A. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

Structures fabricated during the development of a process for making three-dimensionally interconnected integrated circuits using electron beam recrystallization of silicon on insulator have been microsectioned and examined in the scanning ion microscope. This provided detailed information, not accessible by standard analysis techniques, concerning the effects of processing at specific sites in the structures.
Mechanistic studies of oxygen plasma etching
Authors: Hartney M. A. , Greene W. M. , Soane D. S. , Hess D. W.
Published: July 2002

Oxygen dissociation was measured in reactive ion etching (RIE) plasmas using a quadrupole mass spectrometer which sampled the particle flux through a pinhole in the lower electrode of a parallel-plate reactor. The oxygen atom flux increased with increasing power and generally decreased with increasing pressure. Ion currents and bombardment energies also decreased with increasing pressure, while the etch rate of novolac resists increased. In the low-pressure (20–75 mTorr) regime of oxygen RIE plasmas, etch rates of novolac polymers correlated most directly with the supply of oxygen molecules to the surface.
Dynamics of strained-layer epitaxy: Simulation of growth and annealing of GexSi1−x/Si systems
Authors: Kobayashi Akiko , Paik S. M. , Das Sarma S.
Published: July 2002

We simulate the epitaxial growth and annealing of GexSi1−x alloys on a Si(001) substrate using a stochastic Monte Carlo technique. Our simulation indicates that: (i) the overgrowth is defect-free for x≤0.2, whereas defect formation is inevitable for x≥0.5; and (ii) initiation of phase segregation into Si and Ge(001) layers is obtained by means of solely surface diffusion effects during growth and annealing. These result from the kinetically more active nature of Ge atoms as compared to Si atoms, together with an effect arising from the compressive strain in the alloy layers.