bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization of electronic charge and distortion of surface geometry by a scanning tunneling microscopy tip: Si(100)
Authors: Huang Z.-H. , Weimer M. , Allen R. E. , Lim H.
Published: July 2002

First-principles calculations have been performed of (a) the electronic structure, (b) the Hellmann–Feynman forces, and (c) the distortion of the surface geometry at a Si(100) surface when a voltage is applied by a model scanning tunneling microscopy (STM) tip. As one expects, a polarization charge forms under the tip at the semiconductor surface. For the voltages and distances typical of STM experiments, and corresponding to electric fields of ∼0.1 V/Å, the electronic structure is only weakly perturbed and the surface atoms are displaced by only a few hundredths of an angstrom. These results rule out tip-induced perturbations of the surface as an explanation for the symmetric dimer images seen in STM experiments on Si(100).
Contamination control in the design and manufacture of gas flow components
Authors: Sullivan John , Schaffer Skip , King Steve , Manos Dennis , Dylla H. F.
Published: July 2002

To assure the cleanliness of gas flow components such as mass flow meters and controllers, there must be an initial concentrated effort on the design for cleanliness. The design effort must include all elements, such as materials, sensor, and control valve technologies. The design must then be implemented by an appropriate manufacturing philosophy, facility, and etiquette. We describe in detail the design considerations, cleaning procedures, and quality assurance measurement tools and methods used in the process. This methodology is compared with alternative techniques, and is shown to produce gas flow components that indeed verify the conceptual ideas. Experimental data show the results of surface analysis (profilometry, x-ray photoelectron spectroscopy, scanning electron microscopy), particulate measurements using both laser particle and condensation nucleus, and moisture analysis (vibrating quartz crystal) instrumentation.
In situ study of poly(methyl methacrylate) adsorption from solution onto chemically modified Si(100) surfaces by internal reflection infrared spectroscopy
Authors: Zazzera L. , Tirrell M. , Evans J. F.
Published: July 2002

A liquid attenuated total reflection cell designed to accommodate in situ cleaning and/or chemical modification of Si(100) surfaces, has been employed to study the adsorption poly(methyl methacrylate) (PMMA) from solution. In situ cleaning of the substrate surface was accomplished by photochemical generation of ozone to produce a clean oxide film, while aqueous HF etching was carried out by introduction of an aqueous HF solution to produce a hydrogen terminated silicon surface (silicon hydride). The in situ cell allowed for observation of infrared bands from the polymer adsorbate, as well as the silicon substrate surface during the course of polymer adsorption. The fraction of PMMA segments with the carbonyl groups hydrogen bonded to the silanol sites on the silicon substrate was 0.25–0.29 on the clean oxide surface and 0.09–0.13 on the hydrogen terminated surface. For the highly contaminated, ‘‘as-received’’ native oxide surface, no hydrogen bonding was detected, although PMMA was found to adsorb. The integrated carbonyl intensities indicate that the relative amount of polymer adsorbed onto the ultraviolet/ozone cleaned and HF etched surfaces was significantly greater than the contaminated surface. The Si–H stretching band decreased during the adsorption on the hydrogen terminated surface, suggesting that some oxidation of the HF etched surface occurred during 12 h in the PMMA-CCl4 medium. Even so, 90% of the Si–H intensity is retained in that experiment.
Ultrathin heteroepitaxial SnO2 films for use in gas sensors
Authors: Poirier G. E. , Cavicchi R. E. , Semancik S.
Published: July 2002

Tin oxide films, 1.5, 4.0, and 8.0 nm thick, were grown on elevated-temperature sapphire (11̄02) and (0001) substrates by reactive sputter deposition. The structural, chemical, and electrical properties were investigated by low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, and four-point conductance measurements. The SnO2 films grown on sapphire (11̄02) were crystalline with the [101] axis parallel to the growth direction. In contrast, for films up to 8.0 nm thickness grown on sapphire (0001), no long-range order was evident in LEED images. The film resistance depended on the growth substrate, film thickness, and thermal history. Gas sensing measurements were carried out on palladium-activated films and showed a response for all the thicknesses studied.
X-ray fluorescence measurements of x-ray absorption near edge structure at the Si, P, and S L edges
Authors: Kasrai Masoud , Yin Zhanfeng , Bancroft G. Michael , Tan Kim H.
Published: July 2002

High-resolution (≤0.2 eV) x-ray absorption near edge structure (XANES) spectra have been recorded at the Si, P, and S 2p edges of several compounds using microchannel plates to detect the ultrasoft x-ray fluorescence after 2p excitation or ionization. The fluorescence yield (FY) XANES of SiO2, Si, InP, FeS2, and Na2S2O3 are of at least as good quality as the XANES recorded using total electron yield (TEY), despite the extremely small fluorescence yield. The FY spectra obtained show two significant advantages over the TEY spectra. First, the FY XANES is much more bulk sensitive; and second the resolution of the FY spectra is usually considerably better.
Dependence of resolution on sample material in rotational Auger depth profiling
Authors: Tanemura M. , Okuyama F.
Published: July 2002

Dependence of optimum sample rotation on sample material in Auger in-depth analysis was investigated for Al, Mo, Ag, and Ta films deposited on Si wafers, using 1 and 3 keV Ar + and Xe+ ions as projectiles. For Ar+ and 3 keV Xe+ bombardment, depth resolution was improved by increasing the rate of rotation up to a critical rate, except for Ta. The resolution improvement resulting from sample rotation was dramatic for the samples whose surface was covered with conical projections under stationary sputtering (Al and Mo), but less dramatic or none for the samples whose surface was granulated (Ag) or fine-grained (Ta) by sputtering. Nevertheless, the critical rate of rotation was almost of the same degree, independently of the sample material and sputtering condition, except for Ta. For 1 keV Xe+ sputtering, there was no necessity for sample rotation, with regard to improving the depth resolution. Since the deviation of the rotation axis from the depth analysis point caused a discernible deterioration in the depth resolution, even if the deviation was of the order of micrometer, we concluded that stationary Xe+ sputtering at 1 keV is the best sputtering in practical depth analyses.
Reduction of photodesorption yield by oxygen discharge cleaning
Authors: Ota N. , Saitoh M. , Kanazawa K. , Momose T. , Ishimaru H.
Published: July 2002

The effect of a surface cleaning using oxygen Penning discharge on the photodesorption by synchrotron radiation was measured for specially extruded 99.99% aluminum chambers. Oxygen plasma produced through a high current Penning discharge removes surface contamination without giving any damage on a surface of a vacuum chamber. This is quite a different point from a usual glow discharge cleaning. The oxygen discharge cleaning reduced the photodesorption yield of all the main components such as H2, CO, and CO2. The total photodesorption yield for a cleaned sample was 1/10 that of an uncleaned sample at an early stage of irradiation (1019 photons m−1). The desorption of CO and CO2 still found for cleaned samples is due to carbon contained in the oxide layer of aluminum. For further reduction of the desorption coefficient, the surface oxide layer must be removed.
Ion kinetic energy distribution of electron stimulated desorption of O+ from TiO2(110)–SO2
Authors: Torquemada M. C. , de Segovia J. L.
Published: July 2002

In this paper we describe an investigation of the ion kinetic energy distribution (IED) with electron stimulated desorption of O+ from SO2 adsorbed on TiO2(110) at 153 K. The IED at the clean surface shows a bimodal structure with two well differentiated peaks, at most probable kinetic energies of 4 and 7.2 eV. The SO2 adsorption produces a dramatic change in the IED. There is a new peak at 2 eV kinetic energy, and the peaks at 4 and 7.2 eV vary in intensity according to the electron incident energy. The O+ ion yield curve shows, in addition to the onset at the Ti 3p core level at 35 eV electron energy, a second threshold at 160 eV corresponding to S 2p core level excitation. Changes in the IED curves following annealing of the SO2 layer at room temperature and 400 K as well as an adsorption model are also presented.
Composition and morphology of a MgF2/Al multilayer thin film reflective coating
Authors: Weimer J. J. , Kim J. , Zukic M. , Torr D. G.
Published: July 2002

Multilayer Al thin films with interleaving and protective MgF2 dielectric layers for use as far and extreme ultraviolet reflectors have been characterized using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The devices were prepared in a conventional high vacuum system. Sputter depth profiles were obtained using XPS in a separate ultrahigh vacuum system. The MgF2 layers may contain Mg vacancies, and F appeared to be segregated to the MgF2/Al boundaries where it may form AlF3. Oxide regions on the Al surfaces are thicker than previously reported from optical measurements and are not pure Al2O3 throughout. The AFM images showed columnar growth of the Al and MgF2 layers. Root-mean-square roughnesses determined across these surfaces were on the order of at least 1–2 nm. A more comprehensive picture of the composition and morphology of each layer in a multilayer device was obtained from this investigation than typically provided from measurements with optical techniques.
Application of high-resolution electron energy loss spectroscopy to the adsorption and the photoreaction of CH2I2 and CD3OD on a MoOx thin film
Authors: He Hong , Nakamura Junji , Takehiro Naoki , Tanaka Ken-ichi
Published: July 2002

The adsorption and the photoreaction of CH2I2 and CD3OD on sublimated molybdenum oxide surfaces have been studied using high-resolution electron energy loss spectroscopy combined with thermal and photoinduced desorption spectroscopy. The energy loss peaks for ν(C–H), ν(C–D), ν(C–O) and δ (CH2) are detected for CH2I2 and CD3OD adsorbed on the MoOx thin film, where the energy losses of the ν(C–H) stretch and ν(C–D) stretch are mainly caused by impact scattering. CD3OH adsorbed on the MoOx thin film surface photodesorbs as CD3OD and CD2O due to illumination by ultraviolet (UV) light. CH2I2 adsorbs on the MoOx thin film without dissociation at room temperature, but undergoes photodissociation upon illumination by UV light via the production of intermediate =CH2(a) species.
Comparative analysis of trimethylmethoxysilane and trimethylchlorosilane bonding on polished copper surfaces
Authors: Mishra S. , Weimer J. J.
Published: July 2002

Bonding of two monofunctional silanes, trimethylmethoxysilane and trimethylchlorosilane, was studied on copper surfaces. Polished and silinated surfaces were analyzed using x-ray photoelectron spectroscopy, glancing angle Fourier transform infrared spectroscopy, and atomic force microscopy. The feasibility of various reactions paths leading to bonding was considered for the two silanes based on the spectroscopic results. The methoxysilane is proposed to form covalent metal siloxane bonds, whereas the chlorosilane removes oxides and hydroxide groups from the surface and forms CuCl. The results imply that chlorosilane forms mainly silanols and siloxane dimers.
Surface chemistry of 1,1-dimethylhydrazine on platinum
Authors: Schwaner A. L. , Kovar M. , Alberas Diann J. , White J. M.
Published: July 2002

The surface chemistry of 1,1-dimethylhydrazine on polycrystalline Pt has been investigated to determine the major reaction pathways followed by this asymmetric molecule. Thermal dissociation plays an important role during and/or after adsorption at 100 K. In this paper we focus on a fixed dose that is sufficient to saturate the dissociation paths and give a measurable amount of parent desorption. Temperature-programmed desorption spectra also evidence the desorption of ammonia (340 K), hydrogen (320 and 430 K), hydrogen cyanide (490 and 610 K), cyanogen (780 K), and nitrogen (855 K). Auger spectra after heating to 1000 K indicate the accumulation of surface carbon. Complementary temperature-programmed static secondary-ion mass spectrometry provides evidence for surface rearrangements during heating. The experimental facts are readily interpreted within the framework of a reaction path model that is initiated by some N—H bond dissociation at low temperatures (<180 K) to form (CH3)2NNH and H. This is followed by N—N bond breaking between 250 and 300 K, forming −NHx (x≤2) and −N(CH3)2. These species are then involved in a series of hydrogenation and dehydrogenation reactions that lead to the observed products. Somewhat surprisingly, we find no evidence for methane desorption, one of the products observed when the isomer, 1,2-dimethylhydrazine is used [J. Somers and M. E. Bridge, Surf. Sci. 159, L439 (1985)].
Surface relaxation of PbTe(100)
Authors: Lazarides A. A. , Duke C. B. , Paton A. , Kahn A.
Published: July 2002

An analysis of surface Pb core-level shifts from rock salt structure PbS(100) suggests large top layer contractions for group IVA element chalcogenides, in contradiction to expectations from other binary cubic semiconductors like MgO. To test this hypothesis, we have performed a structure analysis on PbTe(100) using eight beams of diffracted low-energy electrons from PbTe(100) at 50 K. An intensity analysis, based on relativistic potentials shown to be accurate for fifth row elements, leads to the conclusion that the Pb sublattice in the top layer is contracted by 0.23 Å (7%), whereas the Te species is unrelaxed, and the spacing between the second and third layers is 0.07 Å (2%) larger than that of the bulk. Our analysis gives results analogous to those found for the (100) surfaces of other cubic materials rather than the large uniform top-layer contraction suggested by the analysis of the core-level shifts.
Increasing the selectivity of commercially available tin oxide based gas sensors for monitoring combustible gases in process environments
Authors: Hawk Roger M. , Narayanaswamy Arvind
Published: July 2002

Tin oxide (SnO2) is one of the most popular metal oxide semiconductors used as a gas sensor. Commercial sensors that use tin oxide are inexpensive and readily available. Computer controlled thermal cycling techniques were used with only one sensor to collect a series of conductance surfaces for various compounds versus concentration. These patterns were treated as inputs to a neural network program that was trained to associate particular patterns to a specific compound. When the neural network was successfully trained to recognize pure patterns, the network was presented with a conductance pattern from a combination of compounds to test if the neural network could identify the constituents. This analysis method allowed the qualitative recognition of the different gases in a mixture or in one single gas. The results using a one sensor approach for the neural network identification of methanol, isopropanol, and hexane are presented and discussed. This, to our knowledge, is the first attempt to use data from a single sensor and process it via a neural network program to identify gases found in process environments.
Initial growth of ultrathin Pd films on Cu(001)
Authors: Yao J. , Shen Y. G. , O’Connor D. J. , King B. V.
Published: July 2002

The submonolayer deposition of Pd on Cu(001) at room temperature (<50 °C) has been studied by low energy alkali ion scattering and low-energy electron diffraction (LEED). The Cu(001)c(2×2)–Pd and Cu(001)p(2×2)-p4g–Pd LEED patterns were observed at Pd coverage of 0.5 and 1.0 monolayers, respectively. The results of the azimuthal scans at grazing incidence showed evidence of surface alloying by the substitution of Cu with Pd atoms in the first layer even at very low coverages. This evidence was confirmed by observing Pd–Pd double scattering peak along the [100] azimuthal direction using 2 keV K+ ions. The structure of the Cu(001)c(2×2)–Pd surface alloy has also been probed by measuring the intensity of Li+ ion scattering as a function of the incidence angle along the mixed Cu and Pd rows. The results showed that the Pd atoms were coplanar with the Cu atoms in the topmost layer.
Surface chemistry of 1,1-dimethylhydrazine on GaAs(100)
Authors: Sun Y.-M. , Sloan D. W. , McEllistrem M. , Schwaner A. L. , White J. M.
Published: July 2002

The thermal chemistry of 1,1-dimethylhydrazine (DMH) on GaAs(100) has been studied by x-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS). With the GaAs(100) at 150 K, DMH adsorbs molecularly and forms three-dimensional islands. In subsequent TPD, molecular desorption occurs at 180 K with a high temperature shoulder extending to 400 K. No evidence was found for dissociation during the temperature ramp. However, dissociation does occur during adsorption at 400 K; N(1s) XP spectra and HREEL spectra indicate cleavage of the N–N bond. There are two products in subsequent TPD; dimethylamine and ammonia desorb at 490 and 580 K, respectively. There is no evidence for C–N bond cleavage at dosing temperatures up to 773 K. GaN is formed when DMH is dosed at surface temperatures above 600 K; carbon contamination is below XPS detection limits.
Surface morphology induced by Ga and Sn overlayers on Si (100) and Si (311) surfaces
Authors: Li L. , Wei Y. , Tsong I. S. T.
Published: July 2002

The development of surface reconstructions and facets on Si (100)–(2×1) and Si (311)–(3×2) was followed as a function of Ga and Sn coverages and annealing temperatures. When the Ga coverage on Si (100) exceeded 1 monolayer (ML), rectangular and square depressions shaped like inverted pyramids were formed on the Si (100)–(n×8)Ga surface. The walls of the inverted pyramids were (311) facets. Deposition of Sn on Si (100) at coverages exceeding 2 ML also produced (311) facets, but they formed the faces of long parallel and orthogonal prisms, giving rise to a large scale mazelike structure on the surface. Deposition of Ga on Si (311) produced ordered (211) and (611) facets at coverages above 1 ML. On the other hand, deposition of Sn on Si (311) did not produce any facet. Layer-by-layer growth of (1×1) pseudomorphic Sn was observed on the Si (311) surface up to 6 ML.
Structural surface phase transitions during segregation competition
Authors: Militzer M. , Hofmann S.
Published: July 2002

The kinetics of surface segregation competition, when the segregants form different saturation structures, is investigated for two cases: Sn–Si at the (100) surface in Fe–6.2 at. % Si–0.03 at. % Sn, and S–P at the (110) surface in Cu. In these cases, the weaker segregant (P,Si) first forms a c(2×2) structure before being replaced by the stronger segregant (S,Sn) with a p(1×1) saturation structure. The surface phase transition, c(2×2)→p(1×1), indicates complex site competition mechanisms; these are described with phenomenological models. Furthermore, enrichment by bulk as well as pipe diffusion is taken into account. The changes in the enrichment rates associated with the surface phase transition can be explained within the proposed approach. The S segregation rate is markedly reduced by the phase transition since the contribution from pipe diffusion vanishes when the new surface phase nucleates at the pipes. For Sn, on the other hand, the surface phase transition provides a higher driving force for segregation by removing the retardation effect of Si, allowing the Sn segregation rate to increase. The models are in good agreement with results from Auger electron spectroscopy measurements.
Origins of atmospheric contamination in amorphous silicon prepared by very high frequency (70 MHz) glow discharge
Authors: Kroll U. , Meier J. , Keppner H. , Shah A. , Littlewood S. D. , Kelly I. E. , Giannoulès P.
Published: July 2002

The authors have studied the effect of plasma power, reactor outgassing rates, and of silane purity on the oxygen, carbon, and nitrogen contents of amorphous silicon material prepared by the very high frequency (70 MHz) glow discharge technique. The silane purity could be optionally enhanced by the application of a getter-based silane gas purifier. It was found that oxygen incorporation was enhanced at lower deposition rates, whereas the nitrogen and carbon film contamination were unaffected. The deposition rate dependence of the incorporation is in excellent agreement with a proposed model. Apart from the effects of plasma power on the incorporation probability, the reactor outgassing rate and the purity of the silane gas itself were identified as the main contamination sources for the atmospheric contaminants in the deposited films. At the low outgassing rate, at least around one-half of the oxygen detected in the a-Si:H material originates from the silane gas. Due to the reduced outgassing rate and an enhanced purity of the silane gas used, the authors have deposited a-Si:H-material with the lowest concentrations of atmospheric contaminants reported to date. Furthermore, the present results exclude a contamination of the a-Si:H-material by a post- oxidation after air exposure.
In situ measurements of the recombination at the crystalline silicon/amorphous silicon heterointerface by time resolved microwave conductivity measurements during low temperature annealing and silane plasma exposure
Authors: Neitzert H. C. , Kunst M.
Published: July 2002

The decay of optically generated excess charge carriers at the heterointerface between crystalline silicon and amorphous silicon has been monitored in situ during plasma deposition of the amorphous layer. A dramatic increase in the interface recombination rate is seen instantly when the silane plasma is ignited. In a later stage of amorphous layer deposition, the recombination rate decreases. This interface passivation depends strongly on the substrate temperature and is more efficient at higher temperature and in the presence of silane plasma. The effect is not due to a change in the band bending at the heterointerface.
Coadsorption of alkalis and hydrogen on W(100)
Authors: Hago W. , Estrup P. J.
Published: July 2002

The influence of substrate reconstruction on the interactions between alkalis and hydrogen on W(100) has been investigated by studying the thermal desorption and low-energy electron diffraction behavior of the coadsorbed systems Li+H/W(100), Na+H/W(100), and K+H/W(100). It is found that on a clean surface Li adsorption favors fourfold distortions of the W(100) substrate, whereas Na and K stabilize the zigzag distortions which occur on clean W(100). At low alkali coverages, in a competition between an alkali-stabilized structure and a H-induced dimer structure, the dimer structure is preferred. At high alkali coverages, this preference is maintained for Li, but not for Na and K. We find that coadsorption of alkalis raises the desorption energy of the most strongly bound state of hydrogen by 0.4, 0.1, and 0.02 eV in the case of Li, Na, and K, respectively. Thus, for all three coadsorbed systems, there is evidence of attractive interactions between the alkalis and hydrogen at early coverages of each coadsorbate. The possible structural arrangement of the coadsorbed species as well as possible substrate contribution to these interactions are discussed briefly.
Real-time feedback for sidewall profile control in reactive ion etching
Authors: Rashap B. , Freudenberg J. , Elta M.
Published: July 2002

Reactive ion etching is an important process in the fabrication of microelectronic devices. This article reports on work in progress towards developing a strategy for controlling sidewall profile during this process. In this strategy, a response surface is developed between plasma characteristics and etch rate components. This is then used to determine the plasma properties necessary to achieve a desired sidewall profile. Finally, a real-time feedback controller is used to regulate the plasma to these conditions during an etch. Presented in this article are preliminary experimental results towards implementing such a strategy.
A model-based technique for real-time estimation of absolute fluorine concentration in a CF4/Ar plasma
Authors: Hanish P. D. , Grizzle J. W. , Giles M. D. , Terry F. L.
Published: July 2002

A technique for quantitative interpretation of actinometric data to deduce bulk plasma fluorine concentration in a CF4/Ar plasma has been developed and tested on a commercial reactive ion etcher. This static, in situ measurement is useful for monitoring fluorine in a manufacturing environment and, in particular, for application of real-time feedback control to plasma etching. Based upon a model of CF4 chemistry reaction pathways and products, it improves upon current fluorine estimation techniques by accounting for varying levels of argon dilution resulting from CF4 dissociation. A simple experiment was also developed in order to obtain an estimate of the actinometric scaling factor without an independent measurement of fluorine. Performance of this model-based fluorine estimation technique was compared to that of a standard technique by using time resolved etch rate measurements as an independent indicator of fluorine concentration, while a feedback control scheme decoupled the effects of physical etching by stabilizing the induced dc bias. The model-based estimator significantly reduced perturbations in the etch compared to those seen when using the standard estimator.
Photodesorption from a copper chamber with a broached inner surface
Authors: Kobari T. , Matumoto M. , Hirano N. , Katane M. , Matsuzaki M. , Hori Y. , Kobayashi M. , Nagai M.
Published: July 2002

A new method for surface treatment of copper vacuum chamber has been developed to easily obtain lower photodesorption coefficients due to synchrotron radiation at low cost. An oxygen-free high-conductivity (OFHC) copper test chamber is extruded and degreased, then the inner surface is cut by broaching. The length of the test chamber is 300 mm and the outer diameter is 65 mm. For comparison, three OFHC copper test chambers are manufactured with different surface treatments. These treatments are (1) acid cleaning (pickling in a mixed solution of HNO3 and H2SO4, followed by passivation in a chromic acid with H2SO4), (2) broaching with oil, and (3) oil-free broaching. These test chambers were exposed to synchrotron radiation with 4 keV critical energy from BL21 beamline at the Photon Factory 2.5 GeV storage ring at KEK. The photodesorption coefficients (N2 or CO equivalent) for the chamber treated with oil-free broaching and for the chamber treated with acid cleaning are almost the same. However the decreasing slope of the photodesorption coefficients for oil-free broaching is steeper than for the acid cleaning. These photodesorption coefficients are proportional to D−0.53 and D−0.47, respectively, as a function of beam dose. The surface of the broached chamber is evaluated by measuring the roughness and by Auger electron spectroscopy analysis. The average roughness of the broached chamber is less than 1 μm, and the carbon concentration in the surface of the chamber treated by oil-free broaching is less than that of other two chambers.
Sb ion implantation and annealing of SiGeC heteroepitaxial layers on Si(001)
Authors: Garcia R. , Daley K. E. , Sego S. , Culbertson R. J. , Poker D. B.
Published: July 2002

Si-capped SiGeC films grown on Si(100) substrates by chemical vapor deposition were implanted with several doses of 200 keV Sb ions. One sample was implanted with 1×1016 ions/cm2 of 200 keV Si ions at 77 K in order to completely amorphize the layer. Three sets of samples were rapid thermal annealed for 200 s at both 600 and 800 °C and for 1 min at 960 °C. Samples were studied using Rutherford backscattering spectrometry and ion channeling. The carbon composition was quantified using the 12C(α,α)12C resonance at 4.265 MeV. It was found that the regrowth kinetics were significantly different from those of SiGe alloys. A greater thermal budget is required for regrowth. Furthermore, at the higher temperatures the carbon diffuses out of the layer leaving a carbon depleted region.
Further studies of ion beam-assisted deposition of Si–C films in reactive environments
Authors: He Zhigang , Inoue Shinichiro , Carter George
Published: July 2002

Several different reactive gases were introduced into an ion-beam-assisted deposition system as precursors to achieve low temperature synthesis of Si–C films. The substrate on which the films were grown was bombarded concurrently by an argon ion beam. By using Rutherford backscattering spectroscopy and elastic recoil detection, it was shown that the films produced had a range of C/Si ratios from carbon rich to silicon rich and doped with argon and hydrogen. The coatings with near-stoichiometric composition demonstrated a Knoop hardness higher than that of bulk SiC materials. X-ray photoelectron spectroscopy analysis showed a binding energy shift resulting from ion bombardment.
Sputter deposition of boron nitride using neon–nitrogen discharges
Authors: Heil R. B. , Aita C. R.
Published: July 2002

Boron nitride films were grown by sputtering a hexagonal boron nitride (BN) pressed powder target in Ne/N2 discharges at two levels of substrate bias. Optical emission spectrometry was used to monitor the N2+ ion population in the discharge. Postdeposition, information about B–N bonding in the films was obtained using near ultraviolet-visible spectrophotometry to determine optical absorption edge characteristics, and infrared transmission spectrometry to determine vibrational frequencies of B–N groups. The results are compared to films grown in Ar/N2 discharges at the same excitation conditions. The goal was to examine the effect of an enhanced N2+ ion population (characteristic of Ne/N2 discharges) on B–N bonding. The results show that N2+ enhancement alone, without substrate bias, cannot produce sp3 bonding. Biasing results in sp3-bonded BN with wurtzite short-range order. Without exception, films on grounded substrates have sp2 bonding. A simple model is proposed to relate optical edge disorder in sp2-bonded BN (associated with B–N bond length randomness) to N2+ adsorption at the growth interface.
X-ray photoelectron spectroscopy and scanning tunnel microscope studies of formate species synthesized on Cu(111) surfaces
Authors: Nakamura J. , Kushida Y. , Choi Y. , Uchijima T. , Fujitani T.
Published: July 2002

The synthesis of formate species on Cu(111) surfaces by hydrogenation of CO2 at atmospheric pressure was studied by x-ray photoelectron spectroscopy and scanning tunnel microscope (STM). The initial formation rate of formate was measured to be 2.1×10−4 molecules site−1 s−1 at PH2=PCO2=380 Torr and 333 K. The saturation coverage of formate species was estimated to be ΘHCOO=0.24, where Θ=1 corresponded to the number of Cu surface atoms. No promotional effect of Zn on the formation of formate species over a Cu(111) surface was observed, indicating that the promotional effect of Zn previously observed for methanol synthesis on Cu(111), is not ascribed to promotion in the formate formation, but is ascribed to promotion in a hydrogenation process of formate species. STM images were obtained for individual formate species synthesized on a clean Cu(111) surface by hydrogenation of CO2 at PH2=PCO2=380 Torr and 333 K for 20 min. Formate species arranged in a hexagonal structure with a distance of 6.6±0.2 Å were attributed to a (√7×√7) R19.1° periodicity. A different domain with a c(2×8) structure and the boundary with the (√7×√7) R19.1° domain were observed. It was found that formate species tended to be arranged with their molecular planes parallel to each other.
Role of N2 addition on CF4/O2 remote plasma chemical dry etching of polycrystalline silicon
Authors: Matsuo P. J. , Kastenmeier B. E. E. , Beulens J. J. , Oehrlein G. S.
Published: July 2002

The remote plasma chemical dry etching of polycrystalline silicon was investigated using various CF4/O2/N2 gas compositions. The effects of O2 and N2 addition on the etch rate and surface chemistry were established. Admixing O2 to CF4 increases the gas phase fluorine density and increases the etch rate by roughly sevenfold to a maximum at an O2/CF4 ratio of 0.15. The addition of small amounts of N2 (N2/CF4=0.05) can again double this etch rate maximum. Strong changes in surface chemistry were also seen as a result of N2 addition to CF4/O2. Real-time ellipsometry and atomic force micro-roughness measurements reveal that nitrogen addition at low O2/CF4 ratios leads to the smoothing of surfaces, but to increased oxidation at high O2/CF4 ratios. Based on etch rate data and gas phase species analysis, we propose that NO plays an important role in the overall etching reaction. Variable tube lengths separated the reaction chamber from the discharge. These tubes were lined with either quartz or Teflon liners. In general, etch rates diminished with quartz tube length. At the longer transport tube lengths (e.g., 125 cm), using a Teflon lining material strongly increases the etch rate for pure CF4/O2 discharges as compared to the quartz. For discharges containing N2, the etch rate is more than doubled. This can be explained by the low recombination rate of atomic fluorine on Teflon and the subsequent high density of F atoms that reach the process chamber, even for long transport tube lengths. In situ ellipsometric measurements reveal postplasma surface modifications for certain etching chemistries. Comparisons of these results to x-ray photoemission measurements reveal a dependence of the stability of the postprocessing surface reaction layer on the etching conditions and hence the thickness and composition of the layer, i.e., whether the layer is comprised of volatile (SiFx-like) or involatile (SiOy-like) species. Thicker, more SiOy-like reaction layers create a barrier for the diffusion and subsequent desorption of the volatile products and a postplasma removal of a portion of the reaction layer is observed. Thinner, more SiFx-like layers leave a fluorine deficient surface in the postplasma stage which results in increased tendency to postplasma layer growth. The etching of silicon is not always limited by the arrival rate of atomic fluorine for our processing conditions.
Control of silicon crystal temperature by measurement of resistivity
Authors: Dohnálek Z. , Mezhenny S. , Lyubinetsky I. , Choyke W. J. , Yates J. T.
Published: July 2002

A new technique for the temperature programmed heating suitable for high resistivity (>1 Ω cm) silicon crystal samples was developed and evaluated. This method, which is based on measurement of the silicon resistance during heating, can be used for investigations that require ultrahigh purity of the crystal and its surface during programmed heating and annealing, since thermocouple and other metallic connections to the crystal are avoided. The method was found to be applicable for automated temperature control above ∼600 K. The dependence of sample resistance on temperature can be calibrated using a single temperature measurement by pyrometer.
Carbon based thin film cathodes for field emission displays
Authors: Weber A. , Hoffmann U. , Klages C.-P.
Published: July 2002

Thin films of nitrogen doped and undoped amorphous carbon were investigated for their application as field emission cathode materials. Field emitter films based on amorphous carbon (a-C) were deposited by sputtering of graphite employing an electron cyclotron resonance plasma as argon ion source. The a-C films with a nitrogen content of 0.6 at. % showed the best vacuum electronic properties. Field emission of electrons started at macroscopic electrical fields as low as 3.2 V μm (current density 1×10−5 mA/mm2) and current densities up to 0.6 mA/mm2 were achieved at an electrical field of 5.8 V/μm. To locate the emission sites the excitation of a low voltage phosphor (ZnO:Zn) was monitored by a CCD camera. The film resistivity of the a-C films is in the range of 0.1–1 Ω cm. As revealed by nanoindentation measurements the microhardness is 10–15 GPa indicating a relatively low sp3 content compared to tetrahedral amorphous carbon (ta-C) films.
Soft x-ray photoelectron diffraction study of epitaxial InGaAs/GaAs(001)
Authors: Proietti M. G. , Turchini S. , Garcı́a J. , Arsenio M. C. , Casado C. , Martelli F. , Prosperi T.
Published: July 2002

The structural properties of epitaxial InGaAs grown (001) oriented GaAs have been studied by soft x-ray photoelectron diffraction. Polar and azimuthal scans at the Ga 3d, As 3d and In 4d core levels have been recorded to investigate the effects of strain on the epitaxial layer. The experimental results are compared with single scattering cluster calculations and a good agreement is obtained between theory and experiment showing that the lattice expands in the growth direction as predicted by the elastic theory. The influence of GaAs surface reconstruction (2×4) and (4×2) has also been studied and shows that the reconstruction does not induce significant changes in the photoelectron diffraction spectra.
Hydrocarbon plasma polymerized coatings
Authors: Bénardais A. , Leprince P. , Zielinski F. , Floch H.
Published: July 2002

As parts of targets used in laser–matter interaction experiments, hydrocarbon plasma polymerized coatings of thickness between 100 nm and 30 μm with a smooth surface finish (rms⩽100 nm) are realized. For this work, a mixture of transbutene and hydrogen with the substrate in or out of the discharge is used in a low frequency (2.4 kHz) plasma reactor. The plasma is characterized by emission spectroscopy and mass spectrometry. The best results are obtained in postdischarge conditions: rms=18 nm for 2.6 μm thickness.
Deposition rate dependence of step coverage of sputter deposited aluminum-(1.5%) copper films
Authors: Taylor Donald S. , Jain Manoj K. , Cale Timothy S.
Published: July 2002

Al-(1.5%) Cu films were deposited at selected temperatures and rates into trenches on patterned wafers in order to study the deposition rate dependence of film step coverage. No substrate bias was applied to minimize resputtering of deposited material. Step coverage improves with increasing temperature and decreasing deposition rates. EVOLVE, a physically based low pressure deposition process simulator that incorporates curvature driven surface diffusion of adsorbed species, yields simulated film profiles in good agreement with experimental profiles. The results demonstrate that diffusion is a rate process critical to improving step coverage.
Preparation and operation of hydrogen cleaned GaAs(100) negative electron affinity photocathodes
Authors: Elamrawi K. A. , Elsayed-Ali H. E.
Published: July 2002

We report on the preparation and operating conditions of negative electron affinity GaAs, cesium-oxygen activated photocathodes, cleaned using atomic hydrogen generated by a thermal cracking source. Atomic hydrogen is effective in removing surface contaminants and in producing a smooth reconstructed surface free of oxides and carbon compounds at a relatively low GaAs temperature. A clean (2×4) reconstructed GaAs(100) reflection high-energy electron diffraction (RHEED) pattern is obtained after atomic hydrogen cleaning. From the RHEED patterns, the thickness of the cesium layer that causes maximum photoemission is estimated to be ∼0.5 monolayer. High quantum efficiency photocathodes (∼12%) are produced after activation to negative electron affinity. Atomic hydrogen cleaning is effective not only in the initial cleaning but also in reviving the photocathode after its performance is degraded by operation. The GaAs is kept at 500 °C during the cleaning process, a temperature that preserves the arsenic stabilized surface necessary for negative electron affinity activation. By reducing the accelerating voltage of the photoemitted electrons and the photocurrent intensity, and by keeping a low level of continuous cesiation, the photocathode lifetime can be significantly enhanced.
Sorption properties and temperature-dependent near-surface chemistry of the BaLi4 intermetallic compound
Authors: Caloi R. M. , Manini P. , Vandré S. , Magnano E. , Kovac J. , Narducci E. , Sancrotti M.
Published: July 2002

BaLi 4 alloy has been analyzed using x-ray photoelectron spectroscopy and Ar+ ion depth profiling. A series of gases sorption tests have also been performed. The effects induced by room temperature (RT) gas exposure (air, N2, and O2) and vacuum annealing at low temperature (≈100 °C) have been studied in detail. High sorption capabilities are confirmed compared with previous works. Dosing the BaLi4 with N2 does not lead to appreciable change in the nitrogen surface concentration. However, its apparent concentration increases after repeated Ar+ sputtering, demonstrating the existence of a chemical reaction with the bulk alloy. This is shown to be in good agreement with N2 sorption tests carried out at RT on BaLi4 powder.
Influence of wafer’s back-surface finish on dry-etching characteristics
Authors: Muramatsu S. , Ando K. , Nanbu H. , Miyamoto H. , Kitano T.
Published: July 2002

Process tolerance and controllability requirements have become more severe with device scaling down and increased integration. The finish of a wafer’s back surface is a factor that affects process conditions for dry etching and rapid thermal annealing. The correlation between back-surface roughness and dry-etching characteristics was investigated. The back-surface roughness was changed from 0.34 nm (rms) to 66.7 nm by final back-surface treatment such as mechanical–chemical polishing or chemical etching. Contact-hole etching with CHF3 gas was performed for interlayer chemical vapor deposited oxide on the front surface of wafers. The etching rate for a smooth back surface (0.34 nm) was increased by 1.1 times over that for a rough back surface (66.7 nm). During contact-hole etching, the wafer temperature of the smooth back surface was 10 °C lower than that for a rough back surface. This is due to the difference in electrostatic chucking force (rms=85–125 nm) during contact-hole etching. When the wafer with the smooth back surface was used, the adhesion area between the dry-etching stage and the wafer’s back surface increased. Consequently, the wafer can be sufficiently cooled and the etching rate was increased. These experimental results indicate that the roughness of the back surface should be well controlled when fabricating advanced devices.
Cathodic plasma polymerization and treatment by anode magnetron torch: II. The influence of operating parameters on the argon sputtering rate distribution
Authors: Zhao J. G. , Yasuda H.
Published: July 2002

In this study, the distribution of argon sputtering rate on the cathode surface was used to investigate the anode magnetron torch plasma system, which was developed for large substrate surface treatment. The Ar sputtering rate was estimated using the colorimetric method. The experimental results showed that a uniform sputtering rate could be achieved by adjusting the distance between the two electrodes, because a suitable electrode distance creates a uniform magnetic field near the cathode surface. A small gap distance can increase the Ar sputtering rate in the focused area, but also creates deposition near the vicinity or outside of the edge of the glass tube, which is used to focus the gas flow. The optimum gap distance is equal to the cathodic dark space thickness at the edge of the glass tube; this configuration maintains a high sputtering rate in the focused area, but does not allow deposition to occur near the vicinity or outside of the edge of the glass tube. A higher Ar sputtering rate can be achieved under low system pressure. At low system pressure, a high magnetic-field strength is important for increasing the Ar sputtering rate, as it improves the magnetic confinement of electrons.
Study of the impact of the time-delay effect on the critical dimension of a tungsten silicide/polysilicon gate after reactive ion etching
Authors: Lin Shih-Po , Ou Chen-Hsien , Lee Szetsen , Tien Yu-Chung , Hsu Chin-Fa
Published: July 2002

The addition of HBr has been used with oxygen and chlorine-based chemistries to improve selectivity of polysilicon to gate oxide in gate-stack etching. As a consequence of high selectivity, polymer residues become a major factor in critical-dimension (CD) control. It is believed that the presence of HBr in the plasma is responsible for polymer formation. HBr and its polymer residues may induce surface reactions to form thin oxide layers. Such a phenomenon has been observed if the wafers are not treated with HF vapor immediately after reactive ion etching (RIE) of the gate. The magnitude of the oxide film growth is proportional to the delayed time between RIE and HF vapor treatment. The sidewall thickness of the gate is also affected by the time-delay effect. The growth of the oxide film on the sidewalls can eventually affect the gate CD, and thus the device performance. A simple reaction model for the growth of the oxide film is proposed to explain the correlation between delayed time and CD bias.
Strength of nanoscale copper under shear
Authors: Heino P. , Holloway P. , Ristolainen E.
Published: July 2002

Properties and processing of copper have received much interest among the electronics community mainly because of its low electrical resistance. One of its important application fields is in electrical interconnections. Mechanical properties of such nanoscale copper connections are, however, not well known and understood. In this article we study the effects of shear strain and stress in several nanoscale copper systems consisting of about 200 000 atoms with the effective-medium theory and molecular dynamics method. The role of polycrystalline microstructure on the shear strength is analyzed. It seems that the strength decreases as the grain size decreases, in contrast to macroscopic systems. In single crystals we study dislocation initiation and propagation. The results indicate that both sub- and supersonic dislocations may be present in copper. The minimum stress and strain, at which a dislocation initiated in a single crystal was 1.2 GPa and 4.6%. These values can be much larger than the values for a large scale copper sample, since polycrystalline microstructure was seen to decrease the system strength.