bluuebunny/crossref_metadata_2025 huggingface dataset:
Surfactant-mediated control of surface morphology for Co epitaxial film on S-passivated semiconducting substrate
Authors: Nath Krishna G. , Maeda Fumihiko , Suzuki Satoru , Watanabe Yoshio
Published: July 2002

Using atomic force microscopy and scanning electron microscopy, we demonstrate that a Co epitaxial film surface grown on S-passivated GaAs(001) is smoother than one grown on bare GaAs(001) and establish that the surfactant nature of sulfur plays a vital role in the formation of a smooth surface. Synchrotron radiation photoemission spectroscopy results confirm that S passivation greatly reduces the segregation of substrate atoms during film growth on a S-passivated surface. It was also found that methanol rinsing after chemical S passivation provides an even smoother surface.
Making superior corrosion resistant aluminum oxide films using ozone-electrochemical and electron microscopy studies
Authors: Kuznetsova A. , Popova I. , Zhukov V. , Yates J. T. , Zhou G. , Yang J. C. , Chen X.
Published: July 2002

Aluminum surfaces have been subjected to oxidation at 300 K, using a molecular beam of ozone of 97% purity. An enhancement of the kinetics of oxidation is found compared to oxidation by O2. The oxide film produced exhibits enhanced corrosion resistance as measured by several electrochemical methods compared to comparable thickness oxide films made by oxygen exposure. Transmission electron microscopy measurements show that the ozone-grown films exhibit small pore sizes and also increased average density as measured by the behavior of the radial distribution function derived from electron diffraction measurements on films made from ozone and oxygen. These effects may be due to the lower oxygen vacancy defect density in films made from ozone. The special properties of ozone-grown aluminum oxide films are preserved even after the films are removed from vacuum and exposed to the atmosphere.
Micro-crystalline diamond and nano-carbon structures produced using a high argon concentration in hot-filament chemical vapor deposition
Authors: Baranauskas Vitor , Peterlevitz Alfredo C. , Ceragioli Helder J. , Durrant Steven F.
Published: July 2002

Micro-crystalline diamond films and nano-carbon structures in the form of wires have been grown by the introduction of argon at very high concentrations (60%–87.5% vol Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament chemical vapor deposition reactor. The argon, in addition to acting as an inert diluent, also modified the kinetics of the carbon deposition process; its presence apparently minimized the deposition of intergranular hydrogenated species, induced an increase in the number of flaws between the diamond grains, increased the porosity of the films, and formed new carbon structures. Well-faceted diamond films, diamond-like carbon (DLC) balls, spongy-like wires, and multilayer structures were observed at different concentrations of Ar. Raman spectroscopy of the deposited material showed that structures of high quality diamond (60%–65% vol Ar) and carbon structures related to DLC, fullerenes and carbon nanotubes, may be deposited by this process.
Transition from thermally grown gate dielectrics to deposited gate dielectrics for advanced silicon devices: A classification scheme based on bond ionicity
Authors: Lucovsky Gerald
Published: July 2002

This article discusses the bonding chemistry of alternative high-k gate dielectrics that have been considered for advanced complementary metal–oxide–semiconductor devices. The replacement of SiO2 by alternative gate dielectrics requires a transition from a thermally deposited native oxide to a deposited gate dielectric. A classification scheme based on bond ionicity separates alternative gate dielectric materials into three groups that are differentiated by their amorphous morphology and electronic structure and properties. This scheme establishes trends between bond ionicity and (i) the average bonding coordination of the constituent atoms, (ii) the thermal stability against chemical phase separation and/or crystallization, and (iii) the dielectric constant. It also provides a framework for the evaluation of different criteria that have been proposed for optimization of alternative high-k metal and transition metal oxides, and their alloys with SiO2 and Al2O3. Based on technology targets for device and wafer performance and reliability, there is as yet no ideal replacement for SiO2 that increases capacitance while at the same time maintaining low levels of interfacial defects.
Hydrogen-induced surface blistering of sample chuck materials in hydrogen plasma immersion ion implantation
Authors: Chu Paul K. , Zeng Xuchu
Published: July 2002

Hydrogen plasma immersion ion implantation (PIII) coupled with ion cut is an economical way to synthesize silicon-on-insulator wafers. In order to avoid premature surface blistering caused by the coalescence of hydrogen microcavities, the implantation temperature must be low (<300 °C), and sample cooling is usually required due to the high ion flux in hydrogen PIII. In addition, the entire sample chuck including the silicon wafer and all the exposed surfaces are bombarded by ions and sputtered impurities from the sample holder can be reimplanted or deposited onto the silicon wafer. Ideally, the problem can be solved if the sample chuck is made of silicon but engineering a silicon sample chuck with sufficient electrical conductivity and a cooling mechanism is very complicated. In addition, the hydrogen ions implanted into the exposed silicon chuck surface can cause surface blistering and exfoliation similar to the silicon wafer. The silicon particles released into the vacuum chamber will reduce the process yield. One practical approach is to engineer the sample chuck with stainless steel and then coat the surface with a material compatible with silicon. If the blistering resistance of the coating is better and the lifetime of the coating is sufficiently long, periodic cleaning can ensure particle and contamination free operation. In this work, we investigate the blistering behavior of three such materials, single-crystal silicon, polycrystalline/amorphous silicon, and silicon dioxide. Our results show that silicon dioxide is the best candidate, followed by polysilicon. However, the insulating nature of silicon dioxide must be considered. Our theoretical simulation results show that an oxide layer several micrometers thick will not affect the surface potential significantly even at a relatively low bias voltage.
Pressure dependent mode transition in an electron cyclotron resonance plasma discharge
Authors: Aanesland Ane , Fredriksen Åshild
Published: July 2002

Despite the wide range of applications of the electron cyclotron resonance (ECR) plasma sources, the ECR plasma processing control is tricky at certain operation parameters. There are several reports of regimes where abrupt changes and instabilities in plasma parameters occur. In the present work we report extensive probe measurements of plasma potential, electron temperature, ion beam energy, and velocity as well as plasma density over a mode change appearing when the neutral argon gas pressure is changed. The parameters were measured over the entire pressure range from 0.15 to 7 mTorr. We found a large drop in electron temperature and plasma potential when the pressure increased from 0.15 to 0.4 mTorr. At 0.4 mTorr the temperature reached a minimum and the density a local maximum, while at 1 mTorr the density reached a minimum. When increasing the pressure above 1.2 mTorr the temperature decreased and the density increased rapidly. While the plasma appearance at low and high pressure can be explained by a global conservation model, the behavior in the intermediate pressure between 0.4 and 1.2 mTorr needs a deeper investigation. We discuss the possibility that the mode change is connected to the competition between stepwise and direct ionization of neutral argon and excitations to metastable argon atoms.
Effect of time-varying axial magnetic field on photoresist ashing in an inductively coupled plasma
Authors: Park Se-Geun , Song Ho-Young , O Beom-hoan
Published: July 2002

Time-varying axial magnetic field is added to an inductively coupled plasma. Weak axial magnetic field of about 10–15 G can be obtained by a pair of Helmholtz coils attached to the chamber. This scheme has been applied to etch SiO2 and silylated photoresist, where processing pressures are generally below 7 Pa, and ions are major reaction species. In order to extend this concept to other etching conditions, this method is applied to photoresist ashing, where processing pressure is usually higher than 133 Pa, and downstream oxygen radicals are important species. It is found that 60 Hz of the ac current gives the maximum ash rate and that ash rate is increased from 6.1 to 7.0 μm/min, and uniformity is improved from 8% to 4.5% over an 8 in. wafer. When aluminum baffle is placed between plasma source and reaction chambers, the ash uniformity improves further to 2.0% over a 300 mm wafer. The presence of axial magnetic field increases the plasma density and thus ash rate, and better uniformity comes from redistribution of ions and radicals during the off period in a periodic magnetic field.
Valence band alignment and work function of heteroepitaxial nanocrystals on GaAs(001)
Authors: Heun S. , Watanabe Y. , Ressel B. , Schmidt Th. , Prince K. C.
Published: July 2002

The differences in valence band structure and work function between heteroepitaxial nanocrystals and the surrounding substrate were measured with a spectroscopic photoemission and low energy electron microscope which allows laterally resolved photoemission spectroscopy. The nanocrystals were obtained by depositing nominally 2 and 4 monolayers (ML) of InAs on a Se-terminated GaAs(001) surface. The samples showed differences in the valence band edge energy and work function both between nanocrystals and substrate as well as between 2 and 4 ML. We suggest that Se termination of the nanocrystals is the reason for these differences.
Cross section for removing chemisorbed oxygen from an aluminum target by sputtering
Authors: Depla D. , Gryse R. De
Published: July 2002

By chemisorption of oxygen on an aluminum target, an absolute target voltage increase is noticed which can be attributed to the reduction of the secondary electron emission from the target. By following the target voltage behavior during magnetron sputtering of the aluminum target precovered with a chemisorbed oxygen layer, the cross section for removing the chemisorbed layer could be calculated based on a proposed model that relates the measured target voltage to the target coverage.
Height control of InAs/GaAs quantum dots by combining layer-by-layer in situ etching and molecular beam epitaxy
Authors: Yang T. , Ishikawa T. , Kohmoto S. , Nakamura Y. , Nakamura H. , Asakawa K.
Published: July 2002

A technique for controlling the height of InAs quantum dots (QDs) on GaAs surfaces is proposed and investigated. This technique involves combining layer-by-layer in-situ AsBr3 etching and molecular beam epitaxy (MBE). One layer of InAs QDs in Stranski–Krastanow (SK) growth mode is initially deposited on a GaAs surface by MBE. After growth of a thin GaAs layer on the InAs SK QDs, in situ etching of this thin GaAs layer creates an array of nanoholes vertically aligned with the underlying SK QDs on the etched GaAs. The nanoholes offer highly selective nucleation centers for the subsequent growth of InAs QDs. Finally, a second-layer of QDs is grown by providing InAs in limited quantity of about 1 monolayer (ML). Atomic force microscopy surface observations show that the nanoholes are completely filled, and that a planar growth surface is obtained with ∼1 ML. Furthermore, cross-sectional structural observations with a transmission electron microscope and energy dispersive x-ray analysis reveal that vertically overlapping InAs QDs are achieved. These results demonstrate that this technique can be applied to form height-controlled InAs QDs.
Selective etching of Al/AlN structures for metallization of surface acoustic wave devices
Authors: Engelmark F. , Iriarte G. F. , Katardjiev I. V.
Published: July 2002

Metallization is a critical step in the fabrication of high frequency AlN thin film based surface acoustic wave devices. Both state-of-the-art lithography as well as high selectivity and anisotropy during etching of Al with respect to AlN are required for low loss and high performance devices. In this work, the etch rates of reactively sputtered AlN, sputtered Al, thermal SiO2, and Shipley 1813 photoresist as well as the selectivity among Al/AlN, Al/SiO2, and resist/Al have been systematically studied during inductively coupled plasma (ICP) etching. Emphasis is focused on obtaining high Al etch rates, while at the same time keeping the etch rate of AlN and that of the resist sufficiently low. High anisotropy is obtained by passivating the sidewalls by the addition of oxygen. The recipe developed is based on a modified Al etch using a mixture of BCl3, Cl2, O2. The parameters varied were gas composition, and substrate bias. Generally it is found that the Al etch rate exhibits a maximum with the O2 flow, while the AlN etch rate decreases monotonically. Substrate bias is found also to be an important parameter with respect to both etch rate and selectivity. At optimized conditions with respect to process selectivity (500 W ICP power, 83 V bias, 50 sccm BCl3, 25 sccm Cl2, 10 sccm O2, pressure 10 mTorr) the Al etch rate is 1000 nm/min with a selectivity of 1000 toward AlN and 9 toward the resist. The same recipe, slightly modified, has also shown similar Al etch rates when etching Al over SiO2 with a selectivity of up to 200. High anisotropy of the Al etch rate is observed with increasing O2 flow. The former has been determined from cross-sectional scanning electron microscope observations.
Growth of GaInNAs quaternaries using a digital alloy technique
Authors: Hong Y. G. , Egorov A. Yu. , Tu C. W.
Published: July 2002

Strain-compensated Ga0.92In0.08As/GaN0.03As0.97 and strained InAs/GaN0.023As0.977 short-period superlattices (SPSLs) were grown as a digital alloy of GaInNAs by gas-source molecular beam epitaxy. Material quality of GaInNAs was improved through the spatial separation of In and N by SPSL growth mode. The photoluminescence (PL) intensity of the strain-compensated Ga0.92In0.08As/GaN0.03As0.97 digital alloys is 3 times higher than that of random alloys at room temperature, and the improvement is even greater at low temperature, by a factor of about 12. Room-temperature PL intensity of the GaInNAs quantum well grown by the strained InAs/GaN0.023As short-period superlattices (SPSL) growth method is higher by a factor of 5 as compared to the continuous growth mode. The strained InAs/GaN0.023As SPSL growth method allows independent adjustment of the In-to-Ga ratio without group III competition since the In composition can be easily adjusted by controlling the InAs growth time.
Substrate-Temperature Measurement and Control
Authors: Hanson M. M. , Oberg P. E. , Tolman C. H.
Published: July 2002

Knowledge of the glass-substrate temperature and its control is often very important in the vacuum deposition of nickel-iron thin films. Discrepancies in vacuum-component-temperature measurements and control prompted a study on the subject. A theoretical investigation showed that a large-area low-temperature radiation source would be most desirable for glass-substrate heating. Experimentation with various heating techniques resulted in two acceptable methods. A temperature variation of less than two degrees at 250 °C was achieved over a large volume.
ATRI—A Tesla-transformer-type electron-beam accelerator
Authors: Boscolo I. , Brautti G. , Leo M. , Luches A. , Perrone M. R.
Published: July 2002

An electron-beam transformer accelerator is described. Its high voltage terminal rises up to 1.2 MV with an input voltage of 18 kV. The maximum electron-beam current is 16 kA; the pulse length is about 20 nsec. Aluminized Mylar anodes and foilless anodes are used. With foilless anodes the repetition rate is at present 3 pulses/sec. Pulse shape details are given and discussed to understand the behavior of the machine and its output characteristics. An improvement program is also presented.
Low-voltage triode sputtering with a confined plasma: Part V—Application to backsputter definition
Authors: Tisone T. C. , Cruzan P. D.
Published: July 2002

The concept of backsputter or ion-etch pattern definition is considered. This includes a discussion of ion sources and basic problems encountered in this type of definition. Two types of ion bombardmant are considered which include conventional sputtering systems and ion guns. Five major problem areas in backsputter definition are considered: (i) relative removal rates of mask and pattern films; (ii) secondary mask defects; (iii) redeposition effects; (iv) substrate temperature; and (v) radiation damage. The principles of backsputter definition are then developed. This includes a discussion of sputter yield vs angle of incidence, forward ion scattering effects which result in the trenching phenomenon, redeposition effects, and reactive backsputtering. It was concluded from this analysis that an ion-beam approach with substrate tilt and rotation relative to the ion beam is the optimum configuration for backsputter definition. The design of a low-voltage triode backsputtering system (LVBS) is discussed which is capable of generating low- energy (∠200 eV), high-current-density (1–5 mA/cm2), and large-diameter [in excess of 12 in. (30.48 cm)] ion beams. This system eliminates many of the usual problems associated with conventional sputtering systems and is readily adapted to large-scale manufacturing requirements. A characterization of the system is presented which includes measurements of: (i) plasma and beam properties; (ii) substrate temperatures as a function of beam potential and current density; (iii) film removal rates; (iv) application to pattern definition; and (v) application to device processing.
Alternating ion plating—A method of high-rate ion vapor deposition
Authors: Schiller S. , Heisig U. , Goedicke K.
Published: July 2002

Under certain circumstances, alternating ion plating (AIP) results in the same effects as conventional ion plating (IP). These conditions are satisfied if vapor and ions alternately act on each point of the substrate at rates and action times that are mutually adapted within each period. Based on energy situations in the coating process, it is then shown that energetic activation of the condensate can be enhanced by an increase in ion energy only within a limited range. Proper selection of the ionization arrangement, however, allows alternation of the ratio of ion to vapor rates and thus to change energetic activation by some orders of magnitude. An experimental setup for AIP is given. After that, nickel films produced by vapor deposition, pressure plating, and alternating ion plating are investigated with respect to some applicative features; i.e., optical reflectivity, corrosion resistance to H2S vapor, and protective action as per the Hutschenreuter porosity test. With reference to the examined properties, AIP gives the best results. According to the Hutschenreuter test, protective action increases with growing ion rate. The variation of optical reflectivity of the deposits is the same with AIP and the conventional IP technique. Expanded industrial application of IP calls for high depostion and ion rates, low working pressure, and adequate facilities for large-area coating. One way to approach this goal is AIP with an ionization arrangement of the planar magnetron type. The possibilities of this technique are then outlined by way of the following parameter example: deposition rate 200 kÅ/min; energetic activation about 100 times higher than with vapor depostion; alternating frequencies up to some thousand cycles per minute.
Evaluation of impurity and contamination levels on mica surfaces using SSIMS
Authors: Dowsett M.G. , King R.M. , Parker E.H.C.
Published: July 2002

Static secondary-ion mass spectrometry (SSIMS) has been used to analyze surfaces of Brazilian muscovite subjected to various standard cleaning techniques, viz., air cleavage, UHV cleavage, and UHV heating. The purpose of these experiments is to establish the surface composition and contamination state before and after application of the technique. Major contamination species are identified as hydrocarbon compounds, probably of atmospheric origin, either from carbonaceous gases or dust. UHV cleavage is established as the only method of those tried which produces a contamination-free surface. Preliminary results of UHV heat treatment of the surface are given. Results from a simultaneous SSIMS and ion cleaning experiment are used to indicate the form of the surface
Study of planarized sputter-deposited SiO2
Authors: Ting) C. Y. , Vivalda V. J. , Schaefer H. G.
Published: July 2002

A theoretical model is proposed to explain the mechanism of the formation of sputter-deposited ’’planarized glass’’; a phenomenon which describes the topography change during sputter glass deposition on top of a metal strip when sufficient bias is applied to the substrate target, and the sputter-deposited ’’standard glass’’ when little or not bias is applied to the substrate target. By assuming that the deposition rate is independent of the substrate topology, and that the removal rate is a function of the slope angle of the substrate surface, it is able to explain the various experimental phenomena observed for both ’’planarized glass’’ and ’’standard glass’’. A delineation scheme is adopted to support the model by displaying the glass contour step-by-step in formation of both kinds of sputter-deposited glass.
Photolithographic fabrication of lead alloy Josephson junctions
Authors: Havemann R. H. , Hamilton C. A. , Harris Richard E.
Published: July 2002

Techniques for the photolithographic fabrication of thin-film Josephson junctions are presented in detail, including metal liftoff processes, lead alloy composition, and formation of tunneling junction barriers using plasma oxidation in an rf discharge. A comparison with earlier rf plasma oxidation studies on Pb(In) –oxide–Pb junctions shows the tunneling resistance of Pb(In,Au) –oxide–Pb(Au) junctions to be nearly two decades lower for a given oxygen pressure in the rf discharge; this difference was attributed to the use of different alloys and sputtering parameter measurement techniques in the respective studies. Typically, tunneling resistance decreased by only 2% after ten thermal cycles, but decreased at an accelerated rate with subsequent cycling. Room-temperature storage often induced downward resistance changes on the order of 30% per month. Junctions stored at −15°C generally showed little change after a period of three months.
Plasma polymerization of ethylene by magnetron discharge
Authors: Morosoff N. , Newton W. , Yasuda H.
Published: July 2002

The deposition rate of plasma-polymerized ethylene is measured on the electrode and on a substrate placed midway between electrodes in a capacitively coupled system with internal electrodes. Polymerization is carried out under a variety of conditions including low flow rate and pressure, high flow rate and pressure, three frequencies (60 Hz, 10 kHz, 13.56MHz), and with and without a magnetic field at the electrodes. It is found that the low pressure (30–50 mTorr) plasma yields considerably higher conversion of monomer to polymer at the substrate than the high-pressure plasma (500 mtorr). With a low-pressure plasma, the use of magnetic field results in higher deposition rates at a given power input. A plasma polymer which adheres exceptionally well to aluminum is formed only midway between electrodes (not at the electrodes) in the 10-kHz and 13.56-Mhz low-pressure plasma.
Silicon nitride layers on gallium arsenide by low-energy ion beam sputtering
Authors: Bradley L. E. , Sites J. R.
Published: July 2002

Silicon nitride layers are formed on gallium arsenide for encapsulation purposes. The process utilizes a 500-eV neutralized ion beam containing argon for sputtering and nitrogen for reactive deposition, directed at a pure silicon target. It is found that, with proper surface preparation, layers having mechanical stability to above 900 °C can be formed. Photoluminescence shows that no radiative transitions are introduced in the deposition process, but that annealing inevitably leads to diffusion of silicon into the GaAs. Auger studies reveal significant oxygen impurity in the Si3N4, particularly near the interface. Index of refraction was found to be a sensitive, nondestructive test of encapsulant quality.
Recent developments in molecular beam epitaxy (MBE)
Authors: Cho A. Y.
Published: July 2002

Semiconductor material research is motivated by the need for new devices which may improve the performance of a system. In turn, a new material technology may generate new devices and new technology. Molecular beam epitaxy (MBE) is a high-vacuum technique for the growth of epitaxial layers, usually semiconductors, that utilizes thermal beams of source atoms or molecules impinging on a single-crystal substrate. The ultrahigh vacuum nature of the process permits in situ metallization and growth of insulating materials on freshly grown semiconducting surfaces resulting in contamination-free interfaces. In situ Schottky barriers, nonalloyed ohmic contacts, and high-quality MIS structures have been grown with MBE. In addition, shadow masking techniques have been used to produce three-dimensional epitaxial structures on the substrate for possible monolithically integrated optical devices and patterned amorphous coatings have permitted the growth of isolated conducting islands of GaAs within a semi-insulating ’’sea’’. Ultrathin layered structures and superlattice structures have been grown and recently modulated doping of superlattice structures has yielded increased mobility anisotropic semiconductor material. This review is limited to recent developments in MBE of III–V compound and an extensive reference list is also included.
Two-dimensional electron gas at differentially doped GaAs–AlxGa1−xAs heterojunction interface
Authors: Störmer H. L. , Dingle R. , Gossard A. C. , Wiegmann W. , Sturge M. D.
Published: July 2002

We report the first observation of a two-dimensional electron gas bound to a differentially doped semiconductor heterojunction interface. Low temperature Hall mobilities up to 25 000 cm2 V−1 s−1 are observed. Angular-dependent oscillatory magnetoresistance data demonstrate the two dimensionality of the electronic system and the population of two electronic sub-bands. Cyclotron data establish the carrier mass to be 12% bigger than the conduction band edge mass of GaAs and a scattering time that is in good agreement with the scattering time obtained from the Hall mobility.
AES and XPS study of plutonium oxidation
Authors: Larson D. T.
Published: July 2002

The initial oxidation of plutonium metal at 27°C has been studied using AES and XPS. Initially a ’’clean’’ plutonium surface was prepared by prolonged Ar+ bombardment followed by 500°C anneal and Ar+ bombardment cleaning cycles. Changes occurring in the plutonium Auger electron spectra in the energy range of 40–120 eV and the 4f5/2, 4f7/2 (core levels), and valence band XPS peaks were monitored during oxygen exposures of 10 to 1.8×108L. Examination of the 4f7/2 level revealed two oxidation states which are attributed to a suboxide an PuO2. The 4f7/2 binding energies for the two oxidation states and plutonium metal are 426.1, 424.4, and 422.2 eV, respectively. It was observed that oxidation proceeded in two steps. In the first step there was a rapid reaction of oxygen with the formation of a suboxide. In the second stage, the uptake of oxygen leveled off with conversion of the suboxide to PuO2.
Measurements of shock wave flight times in long pipes
Authors: Peatman W. , Weiner E. W.
Published: July 2002

In order to determine the time interval between the catastrophic failure of a vacuum component and the arrival of the resulting shock wave at some critical point in the rest of a long vacuum pipe, e.g. the beam line system at a synchrotron radiation storage ring, experiments were performed with various entrance geometries and pipe diameters. Perhaps the most salient conclusion that can be drawn from these experiments is that a slit, e.g. the exit slit of a monochromator, serves very effectively to slow the shock wave. Thus if accidents can be restricted to the experimental chambers employed on beam line systems behind a monochromator, shock wave flight times of greater than 30 ms can be easily reached in a length of 3 m.
X-ray lithography using a pulsed plasma source
Authors: Pearlman J. S , Riordan J. C.
Published: July 2002

An imploding gas jet plasma has been developed as a soft x-ray source for lithographic applications. The plasma is an efficient source of krypton L radiation, which closely matches the wavelength of tungsten anode electron bombardment sources. Resist exposures have been made to evaluate the suitability of the source and determine the filtering requirements necessary to protect the resist. COP resist required 20 shots for a proper exposure; no reciprocity failure was observed with these pulsed, high-power exposures.
Overtones in vibration spectra of adsorbed species
Authors: Ibach H.
Published: July 2002

The sensitivity of present-day electron spectrometers allows one to detect and to distinguish experimentally overtones, combination bands, and multiple excitations in vibrational losses of adsorbed species. The use of overtone spectra in order to see vibrations which are dipole forbidden as a fundamental is demonstrated. Surface molecules with a low internal binding energy exhibit a large frequency shift of the overtone which may be used to estimate the bond energy.
Photoemission and photon-stimulated ion desorption studies of diamond(111): Hydrogen
Authors: Pate B. B. , Hecht M. H. , Binns C. , Lindau I. , Spicer W. E.
Published: July 2002

The interaction of hydrogen with the diamond (111) surface is examined using our new results in photoemission spectroscopy (PES) and photon-stimulated ion desorption (PSID) yield at photon energies near the carbon K edge. Also discussed in the light of our new results are previous studies using PES and low energy electron diffraction (LEED). PSID verifies that the mechanically polished 1×1 surface is hydrogen terminated and finds that the reconstructed surface is hydrogen free. Atomic hydrogen is found to be reactive with the reconstructed surface, while molecular hydrogen is relatively inert. Exposure of the reconstructed surface to atomic hydrogen results in chemisorption of hydrogen and removal of the intrinsic surface state emission in and near the band gap region.
A practical high capacity, high evaporation, rate-resistance-heated source
Authors: Dobrowolski J. A. , Waldorf A. , Wilkinson R. L.
Published: July 2002

The design and performance is described of a 150-cc-capacity resistance-heated evaporation source capable of sustained evaporation of ’’soft’’ optical coating materials at steady rates of up to 600 Å/s measured on a stationary substrate in a plane 25 cm above the source. Its angular evaporation characteristics do not depart greatly from the cosine distribution. The source has been designed to operate in an industrial environment.
Ion-assisted etching of silicon by molecular chlorine
Authors: Sanders F. H. M. , Kolfschoten A. W. , Dieleman J. , Haring R. A. , Haring A. , de Vries A. E.
Published: July 2002

The reaction of Si with Cl2 alone and under simultaneous exposure to an Ar+ ion beam is investigated as a function of target temperature and Ar+ ion energy using mass spectrometry and time-of-flight studies. The main products of the thermal reaction are SiCl4 at low and SiCl2 at higher temperatures. The main products of combined exposure are atomic Si and Cl and molecular SiCl and SiCl2. The contributions of atoms and molecules are of a comparable order of magnitude. It appears that the main fraction of the products of the combined exposure results from sputtering and not from stimulation of the thermal reaction path by ion bombardment. The results strongly suggest that a modification of the top atomic layers of the Si, from which the products are sputtered, by incorporation of significant quantities of Cl plays a dominant part in the reaction mechanism.
The growth of thin oxides on a-Si and a-Si:H in an O2 plasma
Authors: Collins R. W. , Tuckerman C. J. , Huang C.-Y. , Windischmann H.
Published: July 2002

We have used in situ and spectroscopic ellipsometry measurements to study the growth of thin oxide layers on the surface of both unhydrogenated and hydrogenated amorphous silicon (a-Si and a-Si:H) using an oxygen rf discharge. Spectroscopic ellipsometry data were taken on samples both before and after oxide growth to derive the maximum information about the surface structure of the films. In situ single wavelength ellipsometry measurements taken during plasma oxidation showed that the growth curves were nearly identical for glow discharge a-Si:H and both ion-beam sputtered a-Si and a-Si:H. The initial stages of oxide growth could not be easily fit to a model of uniform or planar growth, probably because of a surface modulation or roughness which exists on the film before growth. Further growth appeared to follow, or at least approach, a layer-by-layer process. The thickness of the surface roughness layer on the a-Si:H before growth matched that observed at the oxide/a-Si:H interface after growth. For oxide thicknesses greater than 10–20 Å, the growth rate is consistent with a diffusion limited model. Under our plasma conditions, the diffusion coefficient of the plasma species through the oxide is 2.1×10−17 cm2/s for all samples.
Surface bonding of the NH3 and NH2 species to Ni(110)
Authors: Alvey M. D. , Klauber C. , Yates J. T.
Published: July 2002

Using electron impact, we have converted NH3(ads) to NH2(ads) on the Ni(110) surface. Below 300 K, NH3 is bound nondissociatively to Ni ridge atoms on Ni(110) by electron donation from lone pair N electrons. Upon electron bombardment, the process NH3(ads)→e−(55 eV)NH2(ads) +H(ads) occurs quantitatively with a cross section of 1.6 Å2. ESDIAD results indicate that the initial NH3 species is oriented normally to the (110) surface with no azimuthal ordering down to 29 K. In contrast, NH2 is azimuthally ordered at 300 K with the plane of the species perpendicular to the rows of Ni atoms on the surface; this bonding orientation is consistent with the molecular orbital structure of NH2. This species is stable to 375 K where it decomposes to N(ads) and H2(g).
Adsorption kinetics of acetylene on Fe(110)
Authors: Miyata Kunio , Hudson John B.
Published: July 2002

The kinetics of acetylene adsorption on clean Fe(110) have been investigated using a combination of molecular beam relaxation spectroscopy (MBRS) and Auger electron spectroscopy (AES) techniques. AES studies indicated significant beam-surface interaction, and were not used for quantitative measurements. An extension of previously developed techniques for the analysis of MBRS data to the case where the mean surface coverage is increasing with time was developed and applied to acetylene scattering data obtained as a function of acetylene adlayer coverage. Results indicate that adsorption takes place through a weakly bound precursor state. Dissociative and nondissociative chemisorption take place simultaneously on the surface, with dissociative adsorption being increasingly favored at higher temperatures.
The bonding of hydrogen on water-dosed Si(111)
Authors: Rosenberg R. A. , Love P. J. , Rehn Victor , Owen Ian , Thornton G.
Published: July 2002

The interaction of water with the clean Si(111) surface was studied with photon-stimulated ion desorption (PSID). Results of these experiments show that water dissociates on this surface to produce Si–H and Si–OH. The Si(L) edge of the Si–H site is shifted to higher energy by 0.5 eV from the bulk. At the O(K) edge, the H+ PSID spectrum is shifted by −2.6 eV from the acid-etched (oxidized) surface. These studies help resolve a current controversy on the water/Si(111) surface.
Design advances and applications of the rotatable cylindrical magnetron
Authors: Wright Michael , Beardow Terry
Published: July 2002

The principles and design of the rotatable cylindrical magnetron are described with respect to recent advances. The basic design for the coating of large flat glass sheets has been extended in order that the rotatable magnetron may be used in a wide range of laboratory and production applications. The use of combinations of rotating target and magnetic assembly to facilitate the sputtering, through angles of up to 360°, of both single and multimaterial targets is outlined. The advantages of the system over the planar magnetron are discussed in the light of these developments together with examples of current and potential applications.
Significant improvement in step coverage using bias sputtered aluminum
Authors: Skelly David W. , Gruenke Lothar A.
Published: July 2002

The degree to which deposited metals cover steps over topography is important to the yield and reliability of devices in very large scale integrations. In evaporated and sputtered films the most difficult steps to cover are those with straight walls. This is especially true with aluminum and its alloys. Via step coverage has been studied as a function of bias sputtering parameters. It was found that 1.3 μm diam, straight-walled vias 1 μm deep, are planarized (100% step coverage) under the same conditions that 60% coverage is achieved in 2.8 μm vias. Unbiased deposition results in only 20% coverage. The effects of target power, bias voltage, and anode voltage on bias current and step coverage were studied. The low power delivered to the substrate under conditions for planarization is not consistent with a mechanism involving backsputtering of aluminum; no significant change in the measured deposition rate was found when bias was introduced. Cross-sectional microscopy suggests a mechanism involving forward scattering of surface atoms at the via edge under bombardment by bias ions.
Porosity in thin Ni/Au metallization layers
Authors: Chao Y.-K. , Kurinec S. K. , Toor I. , Shillingford H. , Holloway P. H.
Published: July 2002

Thin films of Ni covered with Au and supported on oxidized silicon wafers were deposited by thermal evaporation or electron beam evaporation. After heating in oxidizing environments from 250 to 400 °C, porosity was observed in the Au films. The pores were typically 2000 Å in diameter and ∼2 μm apart after heating for 1 h at 400 °C in oxygen. By considering models of grain boundary grooving, it has been shown that a porous, discontinuous thin Au film is thermodynamically stable.
Inverse photoemission studies of the (100) surface of tungsten: Clean and with adsorbed submonolayers of hydrogen
Authors: Krainsky Isay L.
Published: July 2002

The W(100) surface has been studied using k-resolved inverse photoelectron spectroscopy. Several peaks associated with unoccupied states were discovered. The energies of these peaks were mapped along the Γ̄M̄ line of the surface Brillouin zone. Exposure of the tungsten surface to small amounts of residual hydrogen caused the tungsten surface to reconstruct to its c(2×2)–H structure and drastically changed the band structure which has also been mapped. The obtained experimental results confirm the theoretical notion that the energy driving this reconstruction originates from the splitting of a partially occupied surface-state band into occupied bonding and unoccupied antibonding subbands.
Low-energy hydrogen ion bombardment damage in silicon: An i
n s
i
t
u optical investigation
Authors: Collins R. W. , Cavese J. M.
Published: July 2002

I n situ and spectroscopic ellipsometry measurements have been applied to probe damage mechanisms induced by low-energy hydrogen ion bombardment of single-crystal silicon. Ion beam voltages from 20 to 1500 V have been employed, covering the range found to passivate grain boundaries in polycrystalline Si and near-surface defects in dry etched single-crystal Si. The spectroscopic data for room-temperature samples after bombardment provide information needed to model the in situ data, obtained using a fixed photon energy of 3.4 eV at a nominal sample temperature of 200 °C. Models for the in situ ellipsometry data for ion energies <500 V allow determination of the evolution of damaged surface layers as a function of exposure time. Two layers dominate the time evolution of the optical data: (1) a polycrystalline Si (p-Si)-like layer, modeled as an effective medium mixture of c-Si, a-Si, and void, which develops on the scale of 1 min (dose: 6×1017 ions/cm2), and (2) a more slowly evolving transparent layer, interpreted as an oxide. The latter layer, also observed in earlier studies, may be attributed to oxidation caused by vacuum residual oxygen ions in the hydrogen ion beam. The oxidation consumes the top-most p-Si-like region of heaviest damage.
Electron energy-loss studies on radio frequency sputtered a-Ge1−xCx:H films
Authors: Shinar R. , Shinar J. , Wu H.-S. , Shanks H. R.
Published: July 2002

Valence-band and core level electron energy-loss spectroscopy (EELS) were used to study rf sputter deposited hydrogenerated amorphous germanium carbide films (a-Ge1−xCx:H, 0≤x≤1). The optical gap of the films ranged from 0.8–1.0 eV in a-Ge:H to 1.2–2.3 eV in a-C:H. Valence-band EELS of clean sputter etched a-Ge and a-Ge:H films (x=0), as compared to that of Ar+ sputter etched Ge(111) and hydrogen covered single crystals of Ge, respectively, indicated preferential sputtering of hydrogen by Ar ions, in contrast to recent observations on rf sputter deposited a-Si:H, where Ar+ etching did not cause complete depletion of hydrogen from the surface. In a-Ge1−xCx:H alloy films (0<x<1) loss peaks related to carbon and Ge–C bonds were identified. Auger analysis of as prepared a-C and a-C:H films (x=1) indicated relatively clean surfaces. Typically, only 1%–2% oxygen was found on the surfaces. EELS experiments indicated graphitelike surface structures. In addition, the hydrogen bulk content had no influence on the spectra, suggesting that the surfaces of the a-C:H films were hydrogen depleted. The Auger carbon line shape further confirmed this assumption.
Pressure and plasma effects on the properties of magnetron sputtered carbon films
Authors: Rossnagel S. M. , Russak M. A. , Cuomo J. J.
Published: July 2002

Thin, amorphous films of carbon have been deposited by conventional and hollow cathode enhanced magnetron sputtering of a pyrolytic graphite target. Films in the range of 15 to 200 nm were deposited over a pressure range or 50 to 0.1 mTorr on fused silica, sapphire, and Si substrates at 20 °C. Langmuir probe measurements of the local electron temperature, density, and plasma potential were made at several locations in the plasma as well as the substrate location as a function of pressure in both the conventional mode (50–1 mTorr) and the hollow cathode enhanced magnetron mode (1–0.1 mTorr). Several film properties were found to vary markedly over the pressure range investigated. For example, electrical resistivity was reduced from about 1×106 Ω cm at 50-mTorr sputtering pressure to a value of 0.01 Ω cm at 0.1-mTorr pressure. The optical band gap was reduced over the same pressure range from 2.1 to 0.4 eV. The index of refraction increased from n=2 at 50 mTorr to n=2.7 at 0.1 mTorr. The electron temperature of the plasma at the substrate location changed from a value of less than 1 eV at the higher pressure to over 8 eV at the lowest pressure, and the electron density increased 1 to 2 orders of magnitude in the same range. The results suggest that the local energy imparted to the growing film from the plasma environment can dramatically change the properties of the carbon films.
Development of a hydrogen electrothermal accelerator for plasma fueling
Authors: Schuresko D. D. , Milora S. L. , Combs S. K. , Foust C. R. , Argo B. E. , Barber G. C. , Foster C. A. , Ponte N. S.
Published: July 2002

We have developed a prototype high-velocity pneumatic pellet injector that uses hydrogen plasma propellant generated in a high-current arc discharge. A single-barrel pneumatic pellet gun has been fitted with a cylindrical arc chamber interposed between the hydrogen propellant inlet valve and the gun breech. The chamber incorporates a ceramic insert for generating vortex flow in the incoming gas stream, which provides azimuthal arc stabilization. The arc is initiated after the propellant valve opens and the breech pressure starts to rise; a typical discharge lasts 150–300 μs with peak currents up to 2 kA. The gun has been operated with 4-mm-diam, 6- to 11-mm-long deuterium and hydrogen pellets. At 100-bar plenum pressure (hydrogen propellant), the arc characteristics are 〈V〉=350–800 V, 〈I〉=600 A, so that 60–150 J of electrical power is dissipated. Pellet speeds increase by 300 to 600 m/s depending on the projectile mass, which typically represents a 10-J increment in the pellet kinetic energy. Velocities up to 1.7 km/s for deuterium pellets and 2.0 km/s for hydrogen pellets have been achieved. Comparing these data to muzzle velocities calculated from idealized one-dimensional compressible flow gun theory demonstrates that substantial propellant heating, resulting in increased propellant sound speed, has been achieved.
Plasma-surface interactions: The role of charged particle emission
Authors: Hofer Wolfgang O.
Published: July 2002

It is pointed out that several of the main erosion processes in plasma-surface interactions are governed by electron emission from the solids’ surfaces.
A method for performing angle-resolved Auger electron spectroscopy using a cylindrical mirror analyzer
Authors: Hoflund Gar B. , Asbury Douglas A. , Corallo Cheryl F. , Corallo Gregory R.
Published: July 2002

An experimental method is presented for performing angle-resolved Auger electron spectroscopy (ARAES) using a cylindrical mirror analyzer. The significant increase in surface sensitivity attainable with this technique is illustrated by spectra taken from sputtered and annealed Pt3Sn surfaces and the native oxide layer on a Si(111) surface. Comparison of compositions obtained from Pt3Sn surfaces using surface-sensitive Auger electron spectroscopy (AES) and ion scattering spectroscopy (ISS) show that the surface sensitivity of AES can approach that of ISS. Comparison of results taken from the native oxide layer on Si(111) suggests that ARAES may be more highly surface sensitive than angle-resolved x-ray photoelectron spectroscopy.
The influence of substrate temperature on the optical properties of ion-assisted reactively evaporated vanadium oxide thin films
Authors: Case F. C.
Published: July 2002

The properties of vanadium dioxide (VO2) films bombarded with oxygen ions during deposition are examined as a function of substrate temperature. Electrical and optical properties of the as-deposited films are discussed. After annealing to the VO2 form, these films exhibit phase transition temperatures reduced from a nominal 67 °C, the lowest thus far in this series being 38 °C. Rutherford backscattering analysis indicates low-level tungsten contamination of the films, presumably from the ion gun filaments. The contaminant has a role in properties modification but does not provide a complete explanation for our observations.