bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary ion mass spectrometry quantification of elements in TiSi2, TiN, and TiW matrices
Authors: Lux G. E. , Stevie F. A. , Kahora P. M. , Wilson R. G. , Cochran G. W.
Published: July 2002

The titanium based matrices TiSi2, TiN, and TiW are used extensively in current semiconductor fabrication. Quantification of elements in these matrices using secondary ion mass spectrometry (SIMS) is hampered by a lack of available information on the relative secondary ion yields for the elements of interest and by a large number of mass interferences. This study provides the ion yields in the form of relative sensitivity factors (RSFs) for a large number of elements ion implanted into these three matrices and describes methods of analysis to circumvent mass interferences of important elements. The RSFs can be organized into patterns of positive secondary ion RSFs versus ionization potential and negative secondary ion RSFs versus electron affinity, similar to those measured for other matrices. The use of molecular ions can improve detection limits for some elements with mass interferences that are beyond the mass resolution capabilities of many SIMS instruments. Depth resolution in TiW is adversely affected by surface roughening during ion bombardment.
Adsorption of acetylene on the Si(100)-(2×1) surface
Authors: Huang C. , Widdra W. , Wang X. S. , Weinberg W. H.
Published: July 2002

The adsorption of acetylene on the Si(100)-(2×1) surface has been studied by high-resolution electron energy-loss spectroscopy (HREELS) and temperature programmed desorption. An energy loss peak at 1450 cm−1, which can be assigned to a C=C double bond, is observed unambiguously in the HREEL spectra. This observation provides direct evidence for the sp2 di-σ adsorption model. The unusually low frequency for the C=C vibration is most likely due to an interaction between the Si atoms and the rehybridized acetylene π orbital. As the surface temperature is increased, one of the C–H bonds cleaves to form a monohydride (Si–H). Most of the acetylene dissociates over a wide temperature range to produce surface carbon and hydrogen. The carbon atoms remain on the surface to form silicon carbide (SiC), while the hydrogen atoms recombine to form molecular hydrogen, which desorbs from the Si(100) surface.
Beam damage of self-assembled monolayers
Authors: Rieke P. C. , Baer D. R. , Fryxell G. E. , Engelhard M. H. , Porter M. S.
Published: July 2002

X-ray and electron beam damage studies were performed on Br-terminated and methyl-terminated alkylsilane self-assembled monolayers. X-ray beam initiated damage was primarily limited to removal of the labile Br group and did not significantly damage the hydrocarbon chain. Some of the x-ray beam damage could be attributed to low-energy electrons emitted by the non-monochromatic source, but further damage was attributed to secondary electrons produced in the sample by x-ray exposure. Electron beams caused significant damage to the hydrocarbon chains. Maximum damage occurred with a beam energy of 600 eV and a dosage of 6×10−3 C/cm2.
Spatial density of lines exposed in poly(methylmethacrylate) by electron beam lithography
Authors: Huang Xiaokang , Bernstein Gary H. , Bazán Greg , Hill Davide A.
Published: July 2002

In this article we report the experimental investigation of the density of patterns exposed with electron beam lithography (EBL). A linear relationship was found between the minimum width of poly(methylmethacrylate) (PMMA) walls and the given resist thickness (height of the walls). Below the minimum width, PMMA walls become wavy or fail due to the internal stresses caused by PMMA swelling during development. Previous research pertaining to proximity effects at feature sizes and spacing below the 0.25 μm range is limited. We have experimentally investigated proximity effects in very-high-density gratings in the pitch range from 50 to 330 nm. The relationship between electron beam dose and grating pitch, where proximity effects during electron beam lithography play a major role, was achieved. By fitting the experimental results with a triple Gaussian model, the contributions of the different electron distributions in proximity effects were determined. It was found that fast secondary electrons dominate the proximity effects in the range we studied and they limit the density of patterns fabricated by EBL.
Growth and morphology of carbon grains
Authors: Ganguly B. , Garscadden A. , Williams J. , Haaland P.
Published: July 2002

Carbon grains less than 1 μm in diameter have been formed in low pressure rare-gas discharges using graphite electrodes and audio frequency excitation. The grains have been examined in situ with Mie etching scattering to determine growth rates and ex situ using scanning and transmission electron microscopies to quantitatively examine their morphology. These results, as well as perturbation of the plasma impedance by the dust, suggest a dust formation mechanism based on ionization of sputtered carbon and subsequent collection of C+ ions by the Debye sheaths which surround negative particles in the plasma.
Electronic and geometric structure of C60 molecules on Au(001)
Authors: Kim D. K. , Suh Y. D. , Park K. H. , Noh H. P. , Kim S. K. , Oh S. J. , Kuk Young
Published: July 2002

The electronic and geometric structures of C60 molecular layers on the Au(001) surface were studied by scanning tunneling microscopy (STM) and spectroscopy (STS) and ultraviolet photoemission spectroscopy (UPS). Due to the lattice mismatch between the overlayer C60 and the substrate Au(100)-(5×20) surface, a uniaxial stress is applied to the overlayer along the 〈110〉 direction, resulting in several types of oblique lattices. The electron charge density around a C60 molecule appears to be an ellipsoid due to the modified electron charge density by the uniaxial stress. The molecules can be considered to be chemisorbed on the Au substrate by the UPS and STS data. Charge transfer from the substrate to the molecules and intermolecular bonding under stress were observed in STM and STS data.
Highly conductive silicon films via plasma-enhanced chemical vapor deposition at low temperatures
Authors: Mauskar Ashutosh S. , Naseem H. A. , Brown W. D. , Ang S. S.
Published: July 2002

The primary advantage of using plasma-enhanced chemical vapor deposition (PECVD) over conventional chemical vapor deposition is lower substrate temperatures, i.e., 200–300 °C. Using heavy hydrogen dilution, highly conductive poly or single-crystal silicon films were deposited in a conventional parallel plate, ultrahigh vacuum, PECVD reactor at temperatures as low as 200 °C. The source gas used was silane mixed with 1% PH3. The hydrogen concentration was varied between 80% and 98% of the total gas flow. The films were characterized both electrically and optically. The optical properties of the films were evaluated using Fourier-transform infrared spectroscopy. The electrical characterization was done by measuring resistivity and activation energy. P–N diodes were fabricated using these hydrogen-diluted films and I–V characteristics were plotted to obtain the diode quality factor. The current conduction mechanism was determined using I–V curves. The results obtained in this work suggest that PECVD can be successfully employed to deposit highly conductive silicon films at temperatures as low as 200 °C, with preservation of the crystalline structure of the underlying substrate.
High quality, high deposition rate SiO2 films at low temperatures using silicon fluorides and plasma assisted deposition techniques
Authors: Falcony C. , Alonso J. C. , Ortiz A. , Garcia M. , Zironi E. P. , Rickards J.
Published: July 2002

High quality SiO2 films have been deposited by the plasma enhanced chemical vapor deposition technique using SiF4 and N2O. It has been determined that a small amount of hydrogen is needed to reduce the amount of residual fluorine atoms in the oxide improving the structural and electrical properties of the film. Using SiH4 as a source of hydrogen instead of H2 results in a high deposition rate increasing from 7 to more than 500 A/min depending on the total content of SiH4. However, for the high deposition rates studied, hydrogen related impurities start to appear and some degradation of the electrical characteristics of the films are observed.
Studies of hydrogen desorption from cobalt surfaces
Authors: Cabrera A. L.
Published: July 2002

The adsorption of hydrogen at room temperature on cobalt samples was studied with thermal desorption spectroscopy. Desorption from cobalt foil was studied using a mass spectrometic method in an ultra high vacuum system, while desorption from cobalt powder was studied in a microreactor system using a thermal conductivity detector. Two hydrogen desorption peaks are observed in both cases. These states correspond to the β1 and β2 states observed in most transition metals. An activation energy of 4–5 kcal/mol is obtained for the β1 state while an energy of 12–19 kcal/mol for the β2 state. These two states are observed for complete hydrogen coverage on polycrystalline samples, independently of surface orientation. The hydrogen desorption peaks can be fitted with near Gaussian curves which facilitates the analysis of the curves to obtain activation energies. A tentative explanation of the appearance of these two states is offered based on surface atomic morphology.
Preparation of YBa2Cu3O7−x superconducting thin films over large area substrates
Authors: Zhang Hui , Sun Zhijian , Yang Senzu , Ji Zhengming , Wu Peiheng , Zhang Shiyuan , Zhang Hongchai , Hang Yin
Published: July 2002

Using facing targets and off-axis direct-current magnetron sputtering, we have prepared high quality YBa2Cu3O7−x (YBCO) superconducting thin films on ZrO2 (100) with Tc≤90 K (R=0) and Jc as high as 1.6×106 A/cm2 (78 K, zero magnetic field) over an area of 70 mm diameter. Over this large area, the fluctuations of Tc and film thickness are from less than +0.9% to −1.3% and from +6.3% to −10%, respectively. In this article, also discussed are the differences between two sputtering modes used in our experiments, one of which gives larger area of superconducting thin film, higher deposition rate, and better thickness uniformity than the other. It is found that the smoothness and the temperature uniformity of the substrate holder are a of extreme importance for the fabrication of large area superconducting thin films. An electroquartz with little deformation during deposition has turned out to be very successful as the substrate holder in our fabrication.
Improved heteroepitaxial growth of layered NbSe2 on GaAs (111)B
Authors: Yamamoto Hideki , Yoshii Kenji , Saiki Koichiro , Koma Atsushi
Published: July 2002

Growth of layered NbSe2 has been carried out on a GaAs (111)B surface by molecular beam epitaxy (MBE). The optimum growth conditions to obtain high quality films were investigated by use of reflection high energy electron diffraction. Single crystalline films as thick as 100 nm were obtained when suitable surface treatment of the GaAs substrate was made with the interruption of the Nb beam or the use of a cracked Se beam. The factors determining the MBE growth of layered NbSe2 are also discussed.
Growth mode of Ge on GaAs(100)
Authors: Wang X.-S. , Self K. W. , Weinberg W. H.
Published: July 2002

The surface morphology of single- and multilayer Ge films on GaAs(100) has been studied using low-energy electron diffraction and scanning tunneling microscopy (STM). After deposition of 0.5 monolayer, the Ge atoms form dimers with Ga atoms after annealing to 875 K, resulting in a (1×2) ordered surface layer. A Ge multilayer deposited at 700 K shows a mixture of (1×2) and (2×1) phases. When annealed at higher temperatures, the (2×1) structure begins to disappear, and, eventually, only the (1×2) phase remains after annealing at 875 K. STM images of the surface reveal faceted clusters of Ge that are surrounded by relatively smooth areas of (1×2) order. Based on these observations, we suggest that the Ge film grows on GaAs(100) by the Stranski–Krastanov mechanism at high temperatures. Because the lattice strain is negligible, the driving force for this growth mode is a reduction in the total surface energy by minimizing substrate-induced electronic effects. Comparison of Ge growth on GaAs(100), GaAs(110), and Si(100) substrates shows the important role of surface and bulk electronic structure in determining the growth mode. The observed antiphase-domain-free GaAs growth on Ge/GaAs(100) is explained based on our results.
Micromechanics via x-ray assisted processing
Authors: Guckel H. , Skrobis K. J. , Klein J. , Christenson T. R.
Published: July 2002

The application potential of micromechanics is very large and falls into very-large-scale-integration-like markets such as magnetic recording and electromechanical components and application specific markets such as surgery tools and sensors. Many of these markets cannot now be addressed because cost effective fabrication technology is not now available to fabricate the required highly complex devices. Idealized fabrication tools must address three dimensional processing with tolerances in the 100 ppm range and must extend over a large material base. They must do that with some integrated circuit-cofabrication compatibility in a cost effective manner. There is a premium for tools which can handle large structural heights with small critical dimensions. X-ray assisted processing can satisfy some of the requirements of the idealized tool. X-ray assisted processing started with the basic LIGA process in Germany. This process can be extended by merging it with surface micromachining and assembly. The current versions of LIGA and LIGA-like processing are restricted in performance by photoresist strain which is typically found in thick photoresist processes. Photoresist strain can and has been reduced significantly by introducing solvent bonded photoresist application procedures which are followed by precision milling and polishing. This extends allowed photoresist thicknesses to heights in the centimeter range. Exposure via synchrotron generated x-ray fluxes and subsequent developing has produced structures with structural heights to 1 cm. This implies that x-ray assisted processing does not only play a major role in micromechanical fabrication but also in precision engineering. This statement is further supported by results that indicate that multiple x-ray mask processes are feasible and that plastic parts can be fabricated by direct x-ray exposure over large surface areas without injection molding. Test vehicles for x-ray assisted processing at the University of Wisconsin fall into two categories: modular micromechanical building blocks such as gear boxes and novel sensors such as high speed magnetic micromotors.
High frequency potential probe using electrostatic force microscopy
Authors: Said R. A. , Mittal M. , Bridges G. E. , Thomson D. J.
Published: July 2002

This paper presents a technique for performing high frequency measurements with a scanned electrostatic force microscope. The technique is used to non-invasively measure the local voltage waveform on the interconnects of an operating integrated circuit. The signal voltage at a point on the circuit is extracted by nulling the electrostatic force interaction between a small probe and the test point. A heterodyne approach is used where a high frequency sampling signal, modulated at the lower probe resonance, is applied to the probe and the nonlinear force interaction between the probe and circuit mixes the signals. This allows the measurement of signal frequencies which are much greater than the mechanical response of the probing mechanism. Accurate measurements can be performed without complex calibration or probe positioning requirements, and the technique is not sensitive to dc offset effects. The ability to measure passivated circuits is discussed.
Oxidation of liquid gallium surface: Nonequilibrium growth kinetics in 2+1 dimensions
Authors: Wang Y. L. , Doong Y. Y. , Chen T. S. , Haung J. S.
Published: July 2002

The formation process of a thin oxide film on liquid Ga is studied in situ using scanning ion microprobe imaging analysis. Oxide clusters form spontaneously on the liquid surface exposed to oxygen at room temperature. Small clusters diffuse and aggregate to form large clusters, and the process eventually leads to the formation of a thin porous oxide film. The fractal dimension of the oxide clusters is ∼1.4. The total number of clusters in the system decays exponentially with time, while the average cluster size increases exponentially with time. These results are compared with Monte Carlo simulations based on different models of particle–particle and cluster–cluster aggregation.
Surface precipitation process of epitaxially grown graphite (0001) layers on carbon-doped nickel(111) surface
Authors: Fujita Daisuke , Yoshihara Kazuhiro
Published: July 2002

The surface precipitation process of epitaxially grown graphite (0001) layers on the C-doped Ni(111) surface has been investigated by in situ x-ray photoemission spectroscopy measurements. Peak intensity measurements at various temperatures clarified the change of the carbon chemical state from the segregated carbon through the monolayer graphite to the multilayer graphite. The simple thickness estimation in the transition region from the monolayer graphite to the multilayer graphite indicates that once the estimated thickness is calibrated, controlling the thickness of the graphite thin film in the monolayer range by a precise adjustment of the temperature may be possible. Changes of the chemical states of carbon on the Ni(111) surface with temperature were clarified by high-resolution measurements with a monochromated Al Kα source. From the observed chemical shift of the C 1s peaks, a negative charge transfer from the monolayer graphite to the substrate can be postulated. This C–Ni interaction is considered to be the possible cause for the stability of the monolayer graphite over 100 K.
Analysis and removal of impurities and defects in reactive ion etched silicon using a novel depth-profiling technique
Authors: Chang W. H. , Huang L. J. , Lau W. M. , Mitchell I. V. , Abraham T. , King M.
Published: July 2002

The analysis and removal of residual damage induced by reactive ion etching of silicon were studied with a new ultrashallow depth-profiling technique of silicon. In this technique, which is known to give a depth resolution of better than 0.5 nm [Lau et al., Appl. Phys. Lett. 63, 78 (1993)], a few atomic layers of silicon were oxidized by an ultraviolet/ozone exposure at room temperature and subsequently removed by an HF wet etch. In the present study, the compositional changes during depth profiling and the amount of silicon removed per oxidation/etch cycle were estimated by x-ray photoelectron spectroscopy. In addition, Rutherford backscattering spectroscopy was used to confirm the compositional changes and to measure defect depth distributions. Further, surface-charge spectroscopy was applied to determine the minimum oxidation/etching required to completely remove Fermi-level pinning associated with the residual damage. The results showed that these profiling and analysis techniques, when applied in a coherent manner, can provide an accurate picture of the residual damage induced by reactive ion etching. More importantly, the study also showed that the oxidation/etching technique can be applied as a well-controlled process for removing the residual damage.
Characteristics of polyimide films deposited by ionized cluster beam
Authors: Kim K. W. , Hong C. E. , Choi S. C. , Cho S. J. , Whang C. N. , Shim T. E. , Lee D. H.
Published: July 2002

Ionized cluster beam deposition (ICBD) technique has been employed to fabricate high-purity crystalline polyimide (PI) film. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were co-deposited using dual ICB sources to form a polyamic acid film, which was subsequently thermally cured to form a PI film. Fourier transform infrared spectroscopy (FTIR), x-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) studies show that the bulk and surface chemical properties and the crystalline structure are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have a maximum imidization, negligible impurities (∼1% isoimide), and a good crystalline structure probably due to the high surface migration energy, and surface cleaning effect. The weight average molecular weight as determined by quasielastic light scattering was found to be ∼45 000. These characteristics are superior to those of films deposited by other techniques such as solvent cast, vapor deposition, or sputtering techniques.
Epitaxial growth of body-centered-cubic transition metal films and superlattices onto MgO (111), (011), and (001) substrates
Authors: Mattson J. E. , Fullerton Eric E. , Sowers C. H. , Bader S. D.
Published: July 2002

We demonstrate epitaxial growth of the bcc transition metals Nb, Mo, Fe, and Cr via sputtering onto single crystal MgO substrates. The epitaxial growth orientations are (011), (112), and (001) when grown onto MgO (111), (011), and (001), respectively. Further, we demonstrate that, under appropriate growth conditions, superlattices of these materials (e.g., Fe/Cr, Fe/V, and Mo/V) can be grown with the same epitaxial order as the films.
Boron-induced reconstructions of Si(001) investigated by scanning tunneling microscopy
Authors: Wang Yajun , Hamers Robert J.
Published: July 2002

The local geometric and electronic structures of boron-induced reconstructions produced by thermal decomposition of diborane and decaborane on Si(001) have been investigated using scanning tunneling microscopy (STM). STM images show that boron induces several related reconstructions arising from ordered arrangements of simple structural subunits. These boron-induced atomic rearrangements order even at very low boron exposures, leading to a striking spatial segregation of boron on the surface. Similar reconstructions are observed using diborane and decaborane as boron precursors. Annealing at 1000 K for 90 s substantially improves the surface ordering, without significant diffusion of boron from the surface to the bulk.
Fabrication and characterization of a nanosensor for admittance spectroscopy of biomolecules
Authors: Montelius Lars , Tegenfeldt Jonas O. , Ling Torbjörn G. I.
Published: July 2002

We have fabricated nanometer-sized interdigitated electrode patterns using electron beam lithography and liftoff techniques. The aim of the investigation was to find out whether the dimensions (i.e., the electrode separations) of the pattern would affect the admittance signal of the biomolecules in between the electrodes. Since the admittance signal scales with the geometrical factor A/d, where A is the electrode area and d is the separation, we chose to keep A/d constant when changing the electrode separation in order to eliminate this trivial effect on the admittance signal. An interdigitated electrode structure having an interelectrode spacing in the nanometer regime makes it possible to reach high nonstationary as well as stationary electric field strengths while having a low applied voltage level. Hence, electrode reactions will be as small as possible, while a high signal to noise ratio is obtained. We have been able to experimentally study the response of the impedance behavior to high electric fields exhibiting either a positive or a negative shift of the permittivity as a function of the field being a high alternating-current or a direct-current field, respectively.
Reduction of outgassing rate by glow discharge cleaning
Authors: Li Minxu , Dylla H. F.
Published: July 2002

The effectiveness of glow discharge cleaning (GDC) as a means of decreasing the pump-down time of vacuum systems was studied. We measured the outgassing rate of an electropolished stainless steel surface after it was exposed to glow discharges fueled by various gases (He, He/1%–3%H2, He/1%–3%CH4, H2, Ar) following a standard 1 h of venting to ambient air. It is shown that He GDC is most effective in reduction of outgassing rate: a He GDC trial with a dose of 0.8 C/cm2 reduces the outgassing rate and subsequently the pump-down time by a factor of 13. For given glow discharge currents, the outgassing reduction factor is directly proportional to the glow discharge duration. The reduction of post-GDC outgassing is a result of enhanced desorption of H2, CO, and CO2 by He GDC as observed by residual gas analysis during the discharge. The GDC results are consistent with our previously proposed diffusion models for water outgassing from metal surfaces.
Monitoring InP and GaAs etched in Cl2/Ar using optical emission spectroscopy and mass spectrometry
Authors: Thomas S. , Ko K. K. , Pang S. W.
Published: July 2002

Optical emission spectroscopy (OES) and mass spectrometry (MS) have been used to monitor the etching of InP and GaAs in a Cl2/Ar plasma. The plasma was generated by an electron cyclotron resonance source. Emission from atomic In and Ga has been detected with the strongest signal to background measured at 410.2 nm for In and 417.2 nm for Ga. The optical emission signals have been studied for varying etch conditions to determine their effectiveness for real-time control applications. It was found that, by increasing the total gas flow rate, the etch rate remained unchanged but the detected etch product signals decreased due to reduced residue in the plasma system. The residence time of the etch products causes the optical emission signals to be dependent upon previous etch conditions. The In and Ga emission signals have been correlated to the etch rate for various etch conditions. A downstream mass spectrometer was able to detect P and As etch products. The strongest signal for InP etching was 101PCl+2 and the strongest signal for GaAs etching was 145AsCl+2. The ability of the mass spectrometer to detect the group V etch products coupled with the ability of OES to detect the group III elements allows for noninvasive study of a variety of III–V material systems. Smooth, vertical etching of InP via holes at 2.7 μm/min for GaInAs/AlInAs-based power devices has been monitored. Optical emission measurements showed that the surface oxide removal time for the via hole etching can be decreased from 95 s to an immediate removal by increasing the self-induced dc bias (‖Vdc‖) from 50 to 300 V, in agreement with MS results. End point detection for via hole etching of GaInAs/AlInAs power devices to Ti/Au contacts on InP substrate was studied using 145AsCl+2 and 155TiCl+3 signals. The thickness of Ti removed can be limited to 18 nm. The optical emission from Ga and Al (at 396.1 nm) have been used to monitor etching of GaInAs/AlInAs heterojunction bipolar transistors. Less than 10 nm of the GaInAs base material is removed at the end of the emitter etch.
Transmission electron microscopy investigation of biaxial alignment development in YSZ films fabricated using ion beam assisted deposition
Authors: McIntyre Paul C. , Ressler Kevin G. , Sonnenberg Neville , Cima Michael J.
Published: July 2002

Detailed microstructural development of biaxially aligned yttria-stabilized zirconia (YSZ) films fabricated using ion beam assisted deposition is reported for the first time. The YSZ films in this study were deposited by ion beam assisted deposition onto Pyrex substrates. A columnar microstructure was exhibited in all the films studied. There are three populations of columns with (001) azimuthal orientation in the film microstructure. The (001) YSZ columns have a faceted dendritic microstructure, consistent with atom attachment at {101} layer source planes during growth from the vapor. Selected area electron diffraction from cross-sectional specimens indicates that most of the biaxial alignment is achieved within 100 nm of the substrate, with little improvement thereafter. The microstructural development of biaxial alignment is consistent with a previously proposed model involving anisotropic growth and extinction of the YSZ columns during ion beam assisted deposition.
Granular superconductor contacts to two-dimensional electron gases
Authors: Marsh A. M. , Williams D. A.
Published: July 2002

Superconducting contacts are made to a buried two-dimensional electron gas using metal multilayers (Sn:Cr:Au) patterned by electron-beam lithography, and sintered using rapid electron-beam annealing. The contact structure has been analyzed using transmission electron microscopy and high-resolution scanning electron microscopy, and many alloys are found to be present, but the structure is predominantly a honeycomb mixture of AuSn4 and CrAs. The resultant contacts are granular superconductors with relatively high critical temperatures of 5–7.5 K.
Outgassing from aluminum surface layer induced by synchrotron radiation
Authors: Ota N. , Kanazawa K. , Kobayashi M. , Ishimaru H.
Published: July 2002

The photon stimulated gas desorption (PSD) from aluminum is investigated experimentally in relation to the amount of carbon on surface. The photodesorption yield (η) during the first stage of irradiation is reduced three orders of magnitude by removing carbon on the surface using argon ion etching. The amount of desorbed CH4, CO, and CO2 decreases almost linearly as the carbon is removed. The results indicate that desorbed gas comes from the surface layer on the aluminum, at least in the initial stage of irradiation.
Compact electron cyclotron resonance plasma source for molecular beam epitaxy applications
Authors: Rössner U. , Brun-Le Cunff D. , Barski A. , Daudin B.
Published: July 2002

We describe a compact, versatile electron cyclotron resonance (ECR) nitrogen plasma source specially designed to be mounted on a 35 conflat flange. The operation frequency is 2.45 GHz. The magnetic field is produced by permanent magnets. In order to eliminate ions in the plasma stream, a nonaxial geometry of the magnetic field was chosen. Two applications are discussed, namely, the p-type doping of II–VI tellurides and the growth of III–V nitrides. In both cases, use of the ECR plasma source results in high quality material.
Properties of radio frequency–sputtered alumina films on flat and grooved substrates
Authors: Ross C. A.
Published: July 2002

Mechanical and chemical properties of rf-diode sputtered alumina films have been measured as a function of deposition conditions including substrate bias, bias phase, and sputter power. Similar films were deposited over grooved substrates, and the effect of the grooves on film microstructure and intrinsic stress was examined. Films deposited over nonplanar substrates show distinct regions in the vicinity of substrate steps where the material has a different microstructure, composition, stress, and chemical etch rate compared with material far from the steps. The elastic modulus and hardness of the material near the steps were measured by nanoindentation.
Low-temperature growth of aluminum nitride thin films on silicon by reactive radio frequency magnetron sputtering*
Authors: Cheng Chien-Chuan , Chen Ying-Chung , Wang Horng-Jwo , Chen Wen-Rong
Published: July 2002

Low-temperature growth of c-axis oriented aluminum nitride (AlN) thin films on silicon (Si) substrates by reactive rf magnetron sputtering was investigated. The structural and morphological characterizations determined by x-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) were found to be sensitive to the deposition conditions, such as sputtering pressure, rf power, substrate temperature, and N2 concentration. A strong AlN (002) preferred orientation perpendicular to the substrate surface was identified at substrate temperatures as low as 150 °C by XRD and a densely pebble-like surface texture of c-axis oriented AlN thin films was observed by SEM. The cross-sectional SEM photograph of AlN thin film showed a high degree of alignment of the columnar structure with c-axis preferred orientation. The selected-area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure.
Massively parallel simulations of Brownian dynamics particle transport in low pressure parallel-plate reactors
Authors: Choi Seung J. , Rader Daniel J. , Geller Anthony S.
Published: July 2002

An understanding of particle transport is necessary to reduce contamination of semiconductor wafers during low-pressure processing. The trajectories of particles in these reactors are determined by external forces (the most important being neutral fluid drag, thermophoresis, electrostatic, viscous ion drag, and gravitational), by Brownian motion (due to neutral and charged gas molecule collisions), and by particle inertia. Gas velocity and temperature fields are also needed for particle transport calculations, but conventional continuum fluid approximations break down at low pressures when the gas mean free path becomes comparable to chamber dimensions. Thus, in this work we use a massively parallel direct simulation Monte Carlo method to calculate low-pressure internal gas flow fields which show temperature jump and velocity slip at the reactor boundaries. Because particle residence times can be short compared to particle response times in these low-pressure systems (for which continuum diffusion theory fails), we solve the Langevin equation using a numerical Lagrangian particle tracking model which includes a fluctuating Brownian force. Because of the need for large numbers of particle trajectories to ensure statistical accuracy, the particle tracking model is also implemented on a massively parallel computer. The particle transport model is validated by comparison to the Ornstein–Furth theoretical result for the mean square displacement of a cloud of particles. For long times, the particles tend toward a Maxwellian spatial distribution, while at short times, particle spread is controlled by their initial (Maxwellian) velocity distribution. Several simulations using these techniques are presented for particle transport and deposition in a low pressure, parallel-plate reactor geometry. The corresponding particle collection efficiencies on a wafer for different particle sizes, gas temperature gradients, and gas pressures are evaluated.
In situ infrared absorption spectroscopy of dusty plasmas
Authors: Kroesen G. M. W. , den Boer J. H. W. G. , Boufendi L. , Vivet F. , Khouli M. , Bouchoule A. , de Hoog F. J.
Published: July 2002

In situ, time-resolved Fourier transform infrared spectroscopy was used to study particulate formation in rf discharges in mixtures of silane, argon, and nitrogen. The spectra were taken at a maximum rate of 20 Hz. The discharge conditions were chosen such that previous calibrations of the time evolutions of particle size and density could be used. The measurements indicate that the onset of the solid-state vibrational absorptions of the SiH and SiH2 bands only takes place after the nucleation and coagulation phase have finished; it coincides with the previously predicted start of the deposition of amorphous hydrogenated silicon on the particles. The dissociation of the silane feed gas is found to be in the range of 30%, and its time development suggests that also the large-scale dissociation of silane only starts after the coagulation phase. This is in agreement with previously observed trends for the electron temperature. If silicon partilces are grown in the plasma, and the silane flow is stopped, the Si particles stay trapped in the glow. The infrared measurements, however, show that they almost completely oxidize: the SiH/SiH2 vibrations disappear and a strong SiO vibration appears. If nitrogen gas is allowed into the plasma, the SiO vibration is replaced by a SiN vibration.
Dynamic laser light scattering studies of dusty plasmas in the Gaseous Electronics Conference Reference Cell
Authors: Anderson H. M. , Radovanov S. B.
Published: July 2002

Particle generation has been studied during reactive ion etching of oxide wafers in CF4/CHF3 plasmas using the Gaseous Electronics Conference Reference Cell. Under certain discharge process conditions, copious amounts of submicron particles form due to plasma interactions with the oxide substrate. Particles were observed in situ by laser light scattering and dynamic laser light scattering (DLLS). DLLS can be used to determine information about particle size, motion, and growth dynamics. DLSS measurements show process-induced dust particles confined in an electrostatic trap exhibit low-frequency oscillatory motion consistent with charge-density-wave motion. These results are also consistent with the plasma dust particles forming a strongly coupled Coulomb liquid phase.
Production and control of K–C60 plasma for material processing
Authors: Hirata T. , Hatakeyama R. , Mieno T. , Sato N.
Published: July 2002

An ultrafine-particle plasma including large negative fullerene ions is produced by introducing fullerene particles into a low-temperature (≊0.2 eV) potassium plasma column confined by a strong axial magnetic field. The density ratio of the negative fullerene to positive potassium ions is controlled by changing the oven temperature for fullerene sublimation and the plasma density being varied in the range from 0 to 0.97 in the central region of the plasma cross section. Since the electrons are well confined in the central region, the ratio increases radially and is more than 0.9999 in the radial edge region. A thin film consisting of the potassium and fullerene particles is formed on a metal end plate which terminates the plasma column. Depending on the end plate potential and radial position, the film is verified to contain metal-doped fullerenes with the potassium atom in the endohedral cavity, which are formed as a result of the potassium-atom insertion into the stable cage of fullerene particles.
Simple setup combining ferromagnetic resonance and surface magneto-optic Kerr effect for measurements of magnetic properties of ultrathin films in ultrahigh vacuum
Authors: Li M. , Wang G.-C.
Published: July 2002

We describe a setup consisting of a ferromagnetic resonance (FMR) cavity and an ultrahigh vacuum (UHV) chamber. The magnetic sample under UHV can be moved into a quartz tube finger which is an integral part of the UHV chamber. This 2-cm-o.d. finger can be inserted with a small clearance into the entrance hole of a cylindrical microwave cavity. The FMR absorption versus applied magnetic field spectra were measured at various angles θ between the applied magnetic field and the sample plane for Co films deposited in situ on a Si(111) surface. When the finger is withdrawn from the cavity, the hysteresis loop of the magnetic sample can be measured using the surface magneto-optic Kerr effect.
Response characteristics of lead phthalocyanine gas sensor: Effect of operating temperature and postdeposition annealing
Authors: Liu C. J. , Hsieh J. C. , Ju Y. H.
Published: July 2002

Effects of operating temperature and postdeposition annealing, as well as gas concentration and flow rate, on the response characteristics of the lead phthalocyanine sensor are investigated in this work. A simple model based on the gas adsorption/desorption kinetics was developed; it predicts that the reciprocal of the response time is proportional to both NO2 concentration and gas flow rate, but decreases with operating temperature. From the temperature dependence of the reciprocal of response time, the activation energy of the adsorption process, Ea, and that of the desorption process, Ed, can be calculated. It is also found that heat treatment of the lead phthalocyanine film in air at 250 °C for 3 h will reduce the activation energies, and lead to faster sensor response.
Nitrogen-ion irradiation during the deposition of C1−xNx thin films by ion beam sputtering technique
Authors: Kobayashi Satoshi , Miyazaki Keiko , Nozaki Shinji , Morisaki Hiroshi , Fukui Shigeo , Masaki Susumu
Published: July 2002

The morphology of the carbon nitride (C1−xNx) thin films deposited by the reactive ion beam sputter deposition technique has been studied. A pure graphite target has been sputtered using nitrogen ions. Some of the deposited films have been irradiated with the primary nitrogen ion beam during the deposition. The films were prepared at room temperature on the crystalline Si substrates. The IR absorption spectrum of the C1−xNx film irradiated with lower energy (0.6 keV) ions has an absorption band that peaked at 1550 cm−1, which has been attributed to the graphitic sp2-bonded carbon (G band) in the study of Raman spectroscopy, while the nonirradiated film which was deposited with a 0.6 keV beam has shown neither a G band nor a D band corresponding to the disordered sp3-bonded carbon in the IR spectra. On the other hand, the films irradiated with a higher energy (1.0 keV) ion beam have shown a very broad ‘‘D-band’’ IR spectrum in the IR range between 1000 and 1700 cm−1. The x-ray photoelectron spectroscopy spectra indicate that all films contain nearly equal quantities of the C≡N triple and C=N conjugated double bonds, while the IR absorption peaks attributed to the C≡N stretching mode are larger in the ion-irradiated samples than in the nonirradiated ones. These results suggest that sputtering by and/or irradiation of a higher energy ion beam contribute to form terminations of the diamondlike carbon network, which contains pyridinelike structures, in the form of cyano-radicals since the absorption peak due to the C≡N stretching mode is enhanced when cyano-radicals bond with a conjugated system in the neighboring sites.
The chemical composition of diamond plasmas
Authors: Zhu H. , Webb S. F. , Blumenthal Rik
Published: July 2002

A new technique for probing the chemical composition of low pressure environments, including plasmas, is described. The technique is based on the expansion of a high pressure pulse of noble gas into the plasma region. As the expansion takes place, stable and radical gas-phase species are incorporated into the developing shock wave and carried to the mass spectrometer in a matrix of frozen noble gas atoms. This method of plasma sampling has been applied to electron cyclotron resonance microwave plasmas as the chemical nature of the carbon species is varied, within the range of conditions known to deposit diamond films. In each of these experiments, a rapid pseudoequilibrium is observed to exist in the plasma environment, covering a range of carbon species from C2H2 to C2H5 and favoring the formation of acetylene. These results are consistent with the broad spectrum of previously observed phenomena in diamond deposition and provide insight into the empirically observed species independence of diamond growth.
Transmission electron microscopy of the sequence of phase formation in the interfacial solid-phase reactions in Ta/Si systems
Authors: Noya Atsushi , Takeyama Mayumi , Sasaki Katsutaka , Aoyagi Eiji , Hiraga Kenji
Published: July 2002

The interfacial reaction of Ta thin films on (100) Si was investigated by high-resolution transmission electron microscopy. An amorphous layer was observed at the as-deposited Ta/Si interface. A phase of Ta5Si3 was first found to form at the interface between a Ta overlayer and the amorphous layer after annealing at 560 °C for 1 h. Annealing at 630 °C for 1 h led to the formation of another interlayer due to the outdiffusion of Si between the amorphous layer and Si. The phase in this interlayer transformed from a metastable one to TaSi2 due to annealing at 680 °C for 1 h. The first nucleation of Ta5Si3 at the interface between Ta and the amorphous layer implies that the initially formed amorphous layer has a metal-rich composition close to Ta5Si3. The formation of the interlayer between the amorphous layer and Si prior to the nucleation of TaSi2 was considered as a result of a kinetic constraint to favor the nucleation of TaSi2.
Determining the number of chemical steps responsible, for the distribution of molecular species within an electron cyclotron resonance-microwave plasma
Authors: Webb S. F. , Gaddy G. A. , Blumenthal Rik
Published: July 2002

Pulsed supersonic, plasma sampling mass spectrometric measurements of the concentrations of the molecular species present in 2% acetylene in deuterium electron cyclotron resonance-microwave plasmas have been compared to the concentrations observed in analogous plasmas based exclusively on hydrogen. In the hydrogen plasmas, the molecular composition is found to be ∼76% acetylene. In the deuterium plasmas, unlabeled, singly deuterated and doubly deuterated acetylene are all observed with a relative abundance of ∼1:3:5, respectively. A simple statistical analysis of the observed isotopic ratios leads to the conclusion that the distribution of molecular species in the plasma environment is the result of an average of only six reactive collisions.
Compositional characterization of very thin SiO2/Si3N4/SiO2 stacked films by x-ray photoemission spectroscopy and time-of-flight-secondary-ion-mass spectroscopy techniques
Authors: Santucci S. , Lozzi L. , Ottaviano L. , Passacantando M. , Picozzi P. , Moccia G. , Alfonsetti R. , Di Giacomo A. , Fiorani P.
Published: July 2002

The chemical composition of ultrathin oxide–nitride–oxide multilayer films grown onto p-type silicon substrates and subjected to different annealing processes and to various oxidation times of the nitride layer has been studied by means of x-ray photoelectron spectroscopy and time-of-flight–secondary-ion-mass spectroscopy. Our results show that the annealing process strongly influences the bottom SiO2/Si interface allowing the saturation of the dangling bonds present at this interface and decreasing the concentration of free hydrogen. By increasing the oxidation time, a better silicon dioxide layer is formed in the topmost layer of this structure.
Chemical reactions induced by the room temperature interaction of hyperthermal atomic hydrogen with the native oxide layer on GaAs(001) surfaces studied by ion scattering spectroscopy and x-ray photoelectron spectroscopy
Authors: Wolan John T. , Mount Charles K. , Hoflund Gar B.
Published: July 2002

A surface characterization study using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy has been performed on solvent-cleaned, n-type GaAs(001) substrates before and after room temperature exposure to the flux produced by a novel atomic hydrogen source based on electron-stimulated desorption of hyperthermal (∼1 eV) hydrogen atoms. The native oxide layer on the solvent-cleaned GaAs(001) substrate contains C, As2O5 , As2O3 , and Ga2O3 according to the XPS data with Ga2O3 being the predominant species. Before H atom exposure, the C is present as hydrocarbons, carbonates, alcohols, and carbides with hydrocarbons as the predominant chemical state. Upon room temperature exposure to a 1 eV hyperthermal H atom flux, the O in As and Ga oxides is removed, and the amount of C present is reduced through methane formation and desorption. In this process hydrocarbons are not converted to carbides, which are difficult to remove, as in the case of ion sputtering. After reduction the predominant form of O is a subsurface, dissolved O, and the outermost atomic layer is enriched in O by a chemical-induced driving force.
Surface kinetic study of ion-induced chemical vapor deposition of copper for focused ion beam applications
Authors: Chiang T. P. , Sawin H. H. , Thompson C. V.
Published: July 2002

A systematic surface kinetic study of ion-induced chemical vapor deposition (II-CVD) of Cu from Cu(I) hexafluoroacetylacetonate vinyltrimethylsilane was performed using quartz crystal microbalance mass deposition rate measurements, x-ray photoelectron spectroscopy compositional analysis, and laser-induced thermal desorption coverage measurements in a multibeam scattering apparatus. With the above, a phenomenological surface kinetic model describing the adsorption, deposition (both of the desired source metal and of unwanted impurities), byproduct desorption, and sputtering processes involved in II-CVD was formulated. The surface kinetic model predicts the deposition rate, composition, and precursor coverage dependencies in agreement with experimental results.