bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon nitride thin films prepared by reactive sputtering: Elemental composition and structural characterization
Authors: Lacerda M. M. , Franceschini D. F. , Freire F. L. , Achete C. A. , Mariotto G.
Published: July 2002

Amorphous carbon nitride thin films (a-CNx) have been deposited onto Si (100) substrates by using a rf diode sputtering system. The films were deposited in reactive nitrogen-argon atmospheres. The partial pressure of nitrogen ranged from 0% to 100% at two different deposition pressures (Pd=2 Pa and Pd=8 Pa). The film composition was determined by ion beam techniques: Rutherford backscattering spectrometry and nuclear reaction analysis. The relative amount of carbon and nitrogen in the films is nearly independent of the nitrogen partial pressure in the reactive plasma. The maximum nitrogen content is 48 at. %. The structural characterization was performed by means of Raman and infrared spectroscopies. Raman spectra revealed the presence of the D and G bands, typical of disordered carbon based materials, and a third band, at about 680 cm−1, also attributed to film disorder. Infrared spectroscopy results showed the D and G Raman bands, IR allowed due to the nitrogen incorporation in the carbon network, the presence of a band at 2220 cm−1 due to C≡N bonds, and a broadband at 3300 cm−1 that can be attributed to the O–H stretching of water molecules absorbed in the films’ voids. A linear correlation between the density and the internal stress of the films was also determined and the maximum values of the film density and the mechanical internal stress were measured for films deposited at 50% of nitrogen partial pressure (Pd=8 Pa).
Morphology-dependent oxidation behavior of reactively sputtered titanium–nitride films
Authors: Hinode Kenji , Homma Yoshio , Horiuchi Mitsuaki , Takahashi Toshikazu
Published: July 2002

The oxidation behavior of titanium–nitride (TiN) films, which were formed at different biasing voltages, was investigated. The four film properties investigated (oxygen concentration, electrical resistivity, density, and stress) changed monotonically with the biasing voltage. Two films with extreme biasing conditions, a dense film and a porous film, were used for a detailed investigation of oxidation behavior. The dense film (density equal to bulk) showed a square-root-of-time growth of the oxide layer, and its oxidation rate had an Arrhenius-type temperature dependence with an activation energy of 2.4 eV. The porous film (density 75% of bulk) showed a time-proportional increase in resistivity initially, then saturation. Film composition profiling using Auger electron spectroscopy showed that the initial stage corresponds to fast oxidation and proceeds along the gaps in the film grains; the saturation stage corresponds to the ordinary oxidation process. The oxidation rates for the ordinary process were the same for both films and corresponded to the intrinsic TiN oxidation rate. The fast oxidation rate along the gaps decreased with the oxidation time, corresponding to the so-called stuffing effect.
Comparative effects of adatom evaporation and ad-dimer diffusion for Si on Si(100)-2×1
Authors: Iguain J. L. , Mártin H. O. , Aldao C. M.
Published: July 2002

The aim of this article is to compare the effects of adatom evaporation and ad-dimer diffusion on the growth of silicon structures on the Si(100)-2×1 surface in the range of 350–500 K. We study the results predicted by two models. Model A includes two types of evaporation (the breaking of ad-dimers and the detachment of single adatoms from islands) but excludes the diffusion of ad-dimers. Model B includes ad-dimer diffusion but no evaporation processes. We found that model A reproduces experimental findings much better than model B for fluxes greater than 6.75×10−5 ML/s and doses lower than 0.1 ML. Indeed, ad-dimer diffusion seems to have no appreciable consequences on the final adatom structures. Also, the main experimental findings can be reproduced if the breaking of ad-dimers is removed from model A and only the detachment of single adatoms is allowed.
Fine structures of valence-band, x-ray-excited Auger electron, and plasmon energy loss spectra of diamondlike carbon films obtained using x-ray photoelectron spectroscopy
Authors: Seo S.-C. , Ingram D. C.
Published: July 2002

The electronic structures of diamond and graphite using x-ray photoelectron spectroscopy (XPS) are compared to that of diamondlike carbon (DLC) films that were deposited using unbalanced magnetron sputtering. High resolution spectra were obtained for the XPS valence-band, x-ray-excited Auger electron (XAES), and photoelectron energy loss. The electronic structures of DLC films are discussed as a function of argon gas pressure and the results are in good agreement with the optical band gap measurement. The XAES spectra from diamond, DLC, and graphite samples show noticeable differences. The XAES N(E) spectra from DLC films contain four carbon KLL transition peaks. The features of the XAES spectra of DLC films are similar to diamond and do not show a graphitelike shoulder. The DLC films deposited at low argon gas pressure show evidence of diamondlike fine structure in the valence-band and photoelectron energy loss spectra, and have wider optical band gaps.
Low temperature fabrication of amorphous silicon thin film transistors by dc reactive magnetron sputtering
Authors: McCormick C. S. , Weber C. E. , Abelson J. R. , Davis G. A. , Weiss R. E. , Aebi V.
Published: July 2002

We deposit hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiNx:H) films using dc reactive magnetron sputtering at 125 and 230 °C substrate temperatures. We characterize the structural properties using infrared absorption, thermal hydrogen evolution, and refractive index measurements, and evaluate the electrical quality using capacitance–voltage and leakage current measurements. Nitride layers deposited at both temperatures have dominant N–H bonding with hydrogen concentration approximately 1022/cm3. Metal-insulator-semiconductor devices have been fabricated on c-Si and show electrical leakage of <5×10−8 A/cm2 at 3 MV/cm field, flat band voltage magnitude <1 V, and hysteresis <2 V. Low temperature a-Si:H films show monohydride dominant bonding. The photo- to dark conductivity ratio is 5×105 for films deposited at 125 °C. Inverted staggered thin film transistors have been fabricated with the optimized layers. Thin film transistors deposited at 230 °C have a field effect mobility of 0.8 cm2/V s, an Ion/Ioff ratio of 5×105, a subthreshold slope of 1.2 V/decade, and a threshold voltage of 4 V; those deposited at 125 °C have a field effect mobility of 0.3 cm2/V s, an Ion/Ioff ratio of 5×105, and a threshold voltage of 3 V.
Roles of ion irradiation for crystalline growth and internal stresses in nickel films onto silicon substrates prepared by the ion beam and vapor deposition method
Authors: Kuratani Naoto , Murakami Yasuo , Imai Osamu , Ebe Akinori , Nishiyama Satoshi , Ogata Kiyoshi
Published: July 2002

The roles of ion irradiation for crystalline growth and internal stresses in Ni films prepared by the ion beam and vapor deposition method were studied. Ni films were prepared on Si〈100〉 wafers by evaporation of Ni metal and simultaneous irradiation with inert gas ions, Ne, Ar, Kr, and Xe. The energies of inert gas ions were changed in the range of 0.5–10.0 keV. Transport ratios of vaporized Ni atoms to inert gas ions to substrates were kept at 15. Ion beam current densities and ion irradiation directions were fixed at 40 μA/cm2 and perpendicular to the substrate surface, respectively. From the x-ray analyses, crystallinities and preferred orientation were changed by ion irradiation conditions. On the other hand, internal stresses were also changed from compressive to tensile depending on ion energies and ion species. It is understood that the variations of crystalline growth and internal stresses in Ni films were caused by the difference of nuclear and electronic energy transfer abilities of irradiating ions.
Properties of Ni/Nb magnetic/superconducting multilayers
Authors: Mattson J. E. , Osgood III R. M. , Potter C. D. , Sowers C. H. , Bader S. D.
Published: July 2002

We examine structural, magnetic, and superconducting properties of magnetic/superconducting Ni/Nb multilayers. The Ni(Nb) films are textured {111}({110}) and have smooth interfaces. The average moment of the Ni atoms in the structure drops by 80% from that of bulk Ni for 19 Å thick Ni layers in proximity to 140 Å thick Nb layers, and goes to zero for smaller Ni thicknesses. The Nb layer is not superconducting for thicknesses <100 Å in the presence of a 19 Å thick ferromagnetic Ni layer. The behavior of the superconducting critical temperature as a function of the superconducting layer thickness was fitted and an interfacial scattering parameter and scattering time for the paramagnetic Ni regime determined.
Role of low-energy secondary electrons in synchrotron radiation-excited chemical vapor deposition of silicon nitride films
Authors: Kyuragi Hakaru
Published: July 2002

The dependence of the deposition rate on the radius of the synchrotron radiation (SR) beam, on the incident angle to the substrate and on substrate configuration to SR beam is investigated in SR-excited chemical vapor deposition of silicon nitride films. Through the experimental results and related analyses, the contribution of gas-phase excitation near the substrate surface to deposition is clarified. In addition, by evaluating the numbers of photoelectrons and secondary electrons emitted from the SR-irradiated substrate, the contribution of low-energy secondary electrons to the excitation of gas-phase and adsorbed molecules is discussed. Finally, a reaction model including the excitation of the core electrons of substrate constituent atoms and the contribution of the interaction between generated low-energy secondary electrons and gas-phase molecules and adsorbates near/at the surface is proposed to explain the material dependence of the film composition observed in the SiH4+NH3 gas system.
Investigations of the surface chemistry of silicon substrates etched in a rf-biased inductively coupled fluorocarbon plasma using Fourier-transform infrared ellipsometry
Authors: Kroesen G. M. W. , Lee Ho-Jun , Moriguchi Hiroshi , Motomura Hideki , Shirafuji Tatsuru , Tachibana Kunihide
Published: July 2002

In situ Fourier-transform infrared (FTIR) ellipsometry has been performed on silicon substrates processed in a rf-biased transformer coupled plasma reactor. Plasmas in CHF3, CF4, C2F6, and C4F8 have been used. The reaction layer, which is present on the surface of the silicon wafer during the plasma process, has been analyzed in detail, addressing both chemical composition and thickness. The absolute reliability (expressed in terms of thickness) of the results is of the order of 0.01 nm, which corresponds to 3% of a monolayer. The instabilities of a silicon surface, which have been observed under specific conditions, can be of the order of tens of percents of a monolayer, which clearly illustrates the advantage of using a real in situ technique like FTIR ellipsometry over quasi in situ techniques like x-ray photoemission spectroscopy and Auger electron spectroscopy. For CHF3 plasmas it has been found that, if the bias increases to moderate levels (30–50 V), the fluorocarbon film deposition rate decreases and the silicon etching reaction rate increases. The reaction layer changes from a thick, predominantly CFx polymerlike film to a thin, carbon dominated layer of plasma and etching products showing vibrational absorptions of SiFx, C–C, and CF2. Increasing the bias voltage in a CHF3 plasma has a similar effect as increasing the F/C ratio of the feed gas.
Characterization of zinc implanted silica: Effects of thermal annealing and picosecond laser radiation
Authors: Chen Jinli , Mu R. , Ueda A. , Wu M. H. , Tung Y.-S. , Gu Z. , Henderson D. O. , White C. W. , Budai J. D. , Zuhr R. A.
Published: July 2002

Zinc ion implanted silica with controlled thermal treatments and pulsed laser radiation has been investigated. Optical spectra of the as-implanted silica at higher doses (>3×1016 ions/cm2) and/or the samples annealed in a reducing atmosphere show both Zn clusters and Zn metal colloid formation. The absorption peak at ∼5.3 eV is attributed to the surface plasmon absorption of Zn metal colloids in silica. The oxidized samples with the ion dose ⩾3×1016 ions/cm2 show an absorption peak in 4.3–4.7 eV region implying ZnO quantum dot formation. It is expected that the average size of the ZnO nanoparticles becomes smaller for lower ion dose. Therefore, a blueshift of the absorption peak with lower ion dose can be attributed to the quantum confinement effects. Pulsed laser radiation at 266 nm with energy density of 30 mJ/cm2 causes a brownish coloration in these optically transparent Zn implanted silica substrates. The color formation is an irreversible process. Therefore, it is believed that new chemical species may have formed through photochemical reactions. The results also show that the coloring process is photon energy dependent.
A study of platinum electrode patterning in a reactive ion etcher
Authors: Chang Li-Hsin , Apen Elizabeth , Kottke Mike , Tracy Clarence
Published: July 2002

This article addresses the problem of Pt electrode etching through the use of a batch load production reactive ion etch (RIE) tool to study etching characteristics and the cleanliness of patterned films with pressure, total gas flow, and percent of Cl2 in Ar as variables, and considers some of the environmental, health, and safety issues. The results show that Pt etching is primarily a sputter etch process in which the Cl2 percentage has little impact on the Pt removal rate, but does significantly affect etch uniformity across the wafer and the surface cleanliness as analyzed with Auger electron spectroscopy. The maximum Pt etch rate achieved was about 5 nm/min with good etch uniformity and surface cleanliness. X-ray photoelectron spectroscopy of the etch by-products shows the presence of PtCl2 and PtCl4 when the Ar–Cl2 etch chemistry was used. These results provide useful information to address material redeposition, wafer cleaning, and etch chamber cleaning safety issues, major concerns in the RIE of Pt.
A fast x-ray photoelectron spectroscopy study of the NO-H2 reaction over Rh(533): Identifying surface species
Authors: Cobden P. D. , Nieuwenhuys B. E. , Esch F. , Baraldi A. , Comelli G. , Lizzit S. , Kiskinova M.
Published: July 2002

The behavior of the NO-H2 reaction over Rh(533) was studied in situ using fast x-ray photoelectron spectroscopy. The high energy resolution achieved by using synchrotron light allowed us to distinguish five surface species by analyzing the line shape and energy positions of the N 1s and O 1s photoelectron spectra. It was established that there are three nitrogen species, labeled NO, N(I) and N(II). The species NO and N(I) are attributed to adsorbed NO and atomic nitrogen, respectively. The nitrogen species N(II) might be attributed to atomic nitrogen adsorbed at step sites or to an NHx species. The short measurement time for the spectra opens the possibility of studying the reaction more dynamically.
Photoexcited Fe2O3 surfaces: Properties and chemisorption
Authors: Toledano D. S. , Dufresne E. R. , Henrich V. E.
Published: July 2002

Transition–metal–oxide particles comprise a small but important fraction of atmospheric aerosols as they are among the few particles in the troposphere having band gaps less than the cutoff of solar radiation (about 4.3 eV), thus allowing photoexcited charge-transfer excitations. We have used single-crystal α-Fe2O3(0001) to study photoinduced charge-transfer processes and chemisorption of SO2, an atmospheric pollutant. Changes in electronic structure as a result of preparation method are presented which complement previous studies. Ultraviolet photoelectron spectroscopy (UPS) was used to study changes in the electronic structure of α-Fe2O3(0001) surfaces due to ultraviolet (UV) irradiation, and to differentiate them from thermal excitations. Intense UV irradiation of the surface by a Hg(Xe) arc lamp results in an increased density-of-states near EF similar to that produced by reduction of the surface; the increase is reversible when the irradiation is terminated. In addition, the upper edge of the valence band is observed to shift upon both UV irradiation and temperature change; however, the band edge shifts to higher binding energy upon UV irradiation, but to lower energy with increased temperature. UPS results show that photoexcited α-Fe2O3(0001) surfaces chemisorb much larger amounts of SO2 than does that surface in the dark; however, adsorbate molecular-orbital peaks were found at similar positions in both cases. X-ray photoelectron spectroscopy (XPS) showed that more SO2 chemisorbed on surfaces at 267 K than at 300 K, and that photoexcitation increased chemisorption at both temperatures, especially at low SO2 exposures. Based upon UPS and XPS results, the adsorbed species is identified as SO3 or SO4.
Second-harmonic generation at the interface between Si(100) and thin SiO2 layers
Authors: Cundiff S. T. , Knox W. H. , Baumann F. H. , Evans-Lutterodt K. W. , Green M. L.
Published: July 2002

In materials that have bulk inversion symmetry, optical second harmonic generation (SHG) is sensitive to regions where the inversion symmetry is broken, i.e., a surface or interface. We measure SHG from the interface between Si(100) and thin layers of SiO2. Measurements on a series vicinal samples (0°–5° off axis) show that one- and threefold symmetries in the SHG signal increase with increasing off-axis angle. Comparison to x-ray scattering measurements of the interface roughness, for a set of on-axis samples, demonstrates the sensitivity of SHG to interface roughness.
Fluoropolymer films produced by sputtering using inductively coupled plasma ion source and their organic vapor sorption characteristics
Authors: Sugimoto Iwao , Hannoe Shinsuke , Katoh Tadashi
Published: July 2002

A method has been developed for preparing fluoropolymer films by sputtering of polychlorotrifluroethylene using an inductively coupled plasma (ICP) ion source. Compared with the conventional sputtering using capacitively coupled plasma, this ICP-sputtering method promotes the defluorination and carbonization reactions that result in the fluorocarbon networks containing oxygen moieties, which are not included in conventionally sputtered film. The organic vapor sorption behavior of these ICP-sputtered fluoropolymer films is principally governed by their dipolar characteristics, and their sorption capacities are markedly higher than those of conventional film, whose sorption behavior is governed by its polarizability.
Crystalline structure of very hard tungsten carbide thin films obtained by reactive pulsed laser deposition
Authors: Mihailescu I. N. , Gyorgy Eniko , Marin G. , Popescu M. , Teodorescu V. S. , Van Landuyt J. , Grivas C. , Hatziapostolou A.
Published: July 2002

Very hard (Hv≅26 GPa), uniform and adherent tungsten carbide thin films were obtained by multipulse excimer laser ablation of tungsten targets in methane at (5×10−2–1) Pa pressure. The films were deposited on substrates placed parallel to the target at a distance of 70 mm. Increases in the gas pressure result in an increase of the carbon content in the deposited films accompanied by a decrease of the mean WC crystallite size in the deposited layers. The microhardness of the films shows a nonlinear evolution with the methane fill pressure with a maximum in excess of 26 GPa at p=1×10−1 Pa.
Study of the surface morphology and gas sensing properties of WO3 thin films deposited by vacuum thermal evaporation
Authors: Santucci S. , Lozzi L. , Passacantando M. , Di Nardo S. , Phani A. R. , Cantalini C. , Pelino M.
Published: July 2002

WO 3 thin films have been obtained by evaporating high-purity WO3 powder at 5×10−4 Pa on SiO2, Si3N4 and annealed at 500 °C for 6, 12, 24, 96, and 200 h. The film morphology, crystalline phase and chemical composition have been characterized through atomic force microscopy, grazing-angle x-ray diffraction, and x-ray photoelectron spectroscopy (XPS) techniques. The as-deposited film is amorphous. After annealing at 500 °C the films are well crystallized with preferential growth along the [200] plane of monoclinic WO3 (JCPDS 43-1035). The mean roughness and the surface area of the films are influenced by the nature of the substrate and the annealing time. The binding energies of the annealed films are close to those of WO3. High-resolution XPS valence-band spectra have shown a well-defined W metallic peak near the Fermi edge, confirming the occurrence of oxygen vacancies on the surface. The electrical response of the films in dry and NO2-rich atmospheres (0.7–7.2 ppm concentration in dry air) has been evaluated by dc current mode.
Fluorination of Si(001)-2×1 surface near step edges: A mechanism for surface defect induced etching
Authors: Srivastava Deepak , Halicioglu Timur , Schoolcraft Tracy A.
Published: July 2002

Fluorination of a dimerized Si(001)-2×1 surface near single-layer high step edges has been studied with molecular statics and dynamics simulations using the Stillinger–Weber potential for Si–Si, Si–F, and F–F interactions. Binding energies for up to three F atoms on Si atoms at the step edges have been investigated for fully relaxed systems. We find that F-bonded Si atoms relax away from the surface with increasing fluorination which lowers the desorption/etching energies of SiFx(x=1,3) species. Room temperature molecular dynamics simulations then show direct etching of SiF3 from Si atoms bonded to step edges. The calculations predict an anisotropy in the step edge induced etching of the Si(001)-2×1 surface. This is in qualitative agreement with an experimental observation on the same surface though using Cl instead of F atoms.
Modeling of silicon deposition process scale-up employing axisymmetric ring nozzle sources. I
Authors: Chen G. , Boyd I. D.
Published: July 2002

The scale-up of a new silicon thin film deposition technique employing supersonic molecular beams is investigated. Small area silicon thin film deposition was proven successful previously. This study aims to investigate the possibility of a larger scale deposition using axisymmetric ring sources through the numerical approach. It is found that the use of axisymmetric ring nozzle sources can significantly increase the deposition area and improve the film uniformity. The simulations show a uniform silicon growth over an area 18 cm in diameter at ∼155 Å/min. The geometrical effects of the ring nozzle sources and the substrate to nozzle distance are studied. The influence of the source flow rate and pumping capacity is also examined.
Three dimensional modeling of silicon deposition process scale-up employing supersonic jets. II
Authors: Chen G. , Boyd I. D. , Engstrom J. R.
Published: July 2002

A new technique to deposit silicon thin film employing supersonic beams is examined. Our previous studies involved both experimental and numerical approaches, in which the thin films were deposited at a high growth rate but over relatively small areas. The current studies are focused on the process scale-up by using multiple supersonic jets. Three dimensional simulations are conducted to investigate the geometrical effects of the molecular beam sources. One source configuration involving four jets is found to successfully deposit uniform silicon films over an area of 18 cm in diameter, with a growth rate higher than 200 Å/min. The molecular beam energy obtained under these conditions is approximately 1.3 eV. A configuration is also designed to increase the deposition area in a laboratory facility for experimental verification.
Ordered binary oxide films of V2O3(0001) on Al2O3
Authors: Guo Q. , Kim D. Y. , Street S. C. , Goodman D. W.
Published: July 2002

Ordered binary oxide films of vanadium oxide have been prepared on an aluminum oxide film supported on Mo(110) under ultrahigh vacuum conditions and characterized by various surface analytical techniques. Auger electron spectroscopy, low energy electron diffraction, high-resolution electron loss spectroscopy, x-ray photoelectron spectroscopy and ion scattering spectroscopy indicate that the vanadia films grow epitaxially on the Al2O3/Mo(110) surface as V2O3(0001). The results of electronic structural measurements show an increase in the energy of the a1g level in the 3d band at low temperatures, which is a possible explanation for the metal-to-insulator transition in V2O3.
Optical and structural characterization of copper-based colloidal particles in SiO2 coatings
Authors: Mendoza-Galván A. , Pérez-Robles J. F. , Espinoza-Beltrán F. J. , Ramı́rez-Bon R. , Vorobiev Y. V. , González-Hernández J. , Martı́nez G.
Published: July 2002

The optical properties and structural characteristics of copper doped SiO2 coatings, prepared using the sol-gel method, were determined from spectroscopy ellipsometry, optical transmission and x-ray diffraction measurements. Coatings with 8 and 25 at. wt % of copper were analyzed. The samples were heat treated in air and under a CO atmosphere at various temperatures. The x-ray data show that samples thermally treated in air have an amorphous structure. In the coatings with 25 wt % of copper and annealed in the reducing atmosphere, there is precipitation of copper particles with nanometer sizes. The effective complex index of refraction of the coatings is deduced from the ellipsometric data using the Forouhi–Bloomer and Maxwell–Garnett expressions for samples with amorphous and composite structures, respectively. The optical transmission measurements indicate that Cu2+ ions are present in oxidized samples. The optical density spectra from reduced samples were analyzed with the Mie theory. There is a good agreement between the results from the different measurements.
Field emission from as-grown and surface modified BN and CN thin films
Authors: Badi N. , Tempez A. , Starikov D. , Bensaoula A. , Ageev V. P. , Karabutov A. , Ugarov M. V. , Frolov V. , Loubnin E. , Waters K. , Shultz A.
Published: July 2002

We have investigated the electron field emission characteristics of BN and CN on highly conductive silicon thin films deposited by End-Hall ion source and electron cyclotron resonance plasma source-assisted physical vapor deposition. The thermal processing and surface laser modification effects on the field emission properties were investigated. Current density-field emission characteristics Iη(E) were tested in a high vacuum environment. Mg-doped BN thin films on silicon exhibited a turn-on field as low as 25 V/μm and a current density higher than 1 A/cm2. The deposition of a thin BN layer on copper lithium (CuLi) metallic substrate yields surfaces with a 75 V/μm onset field and a current density 1000 times higher than that obtained from uncoated surfaces. Under high vacuum laser annealing BN coated CuLi showed no enhancement but more stable emission characteristics. Our results show also that pulsed ultraviolet laser irradiation of CN films in vacuum results in an increase of the field emission current densities and a reduction in threshold field values. The turn-on fields of the irradiated surfaces depend strongly upon the energy density of the laser beam. In addition, the electroconductivity properties of BN and CN surface mapping have been performed using scanning tunneling field emission microscopy. The surface topography mapping and its correlation to the field emission properties were investigated. Preliminary results on surface mapping suggest that the surface relief plays some role in field emission enhancement.
Hollow cathode magnetrons with target gas feed
Authors: Bradley J. W. , Willett D. M. , Gonzalvo Y. Aranda
Published: July 2002

The plasma properties in a magnetron sputtering source can be modified by inducing the hollow cathode effect in a groove machined into the cathode target. Neutral gas is fed directly into the groove supplied from a reservoir behind the target and this is found to significantly increase the discharge current. Langmuir probe measurements made above the sputter trench show a much denser plasma is formed and the proportion of hot electrons in the plasma bulk is increased when gas is fed to the groove rather than to the vacuum chamber. The new design allows low downstream working pressures to be achieved but still maintaining high discharge currents, and gives the ability to run the discharge in one gas while introducing a second (i.e., reactive gas) to the chamber close to the substrate.
Growth of single crystal MgO on TiN/Si heterostructure by pulsed laser deposition
Authors: Sharma A. K. , Kvit A. , Narayan J.
Published: July 2002

High quality epitaxial films of MgO have been grown on a Si (100) surface with TiN as a buffer layer by pulsed laser deposition. The electron diffraction patterns of these films confirmed the single crystal nature of the films with cube-on-cube epitaxy. It is difficult to grow high quality MgO films directly on Si due to large differences in lattice constants and thermal expansion coefficients of the two materials. The high resolution microscopy on our films revealed sharp interfaces between MgO/TiN and TiN/Si with no indication of interfacial reaction. Raman spectrum of MgO films revealed sharp peaks characteristic of MgO and TiN, indicating a good crystallinity. Further, superconducting YBa2Cu3O7−x films were grown on this heterostructure with a sharp transition at 88 K, indicating a high quality of the grown structure. This work opens a way for the growth of a variety of high quality perovskite structures for integration with silicon devices.
Low-energy cathodoluminescence spectroscopy of erbium-doped gallium nitride surfaces
Authors: Levin T. M. , Young A. P. , Schäfer J. , Brillson L. J. , MacKenzie J. D. , Abernathy C. R.
Published: July 2002

We have used cathodoluminescence spectroscopy with variable incident beam energies to study the energy levels and activation of Er impurities in GaN as a function of depth below the free surface. The GaN films were doped in situ during either metalorganic molecular-beam epitaxy (MOMBE) or molecular-beam epitaxy (MBE). Besides the well-known Er3+ luminescence at 0.80 eV, we observe emissions at 1.2, 1.8, 2.2, and 2.3 eV, corresponding to higher energy Er 4f shell transitions. For unannealed MOMBE-grown GaN:Er, these higher energy emissions appear only for excitation depths of hundreds of nanometers. The MOMBE-grown GaN;Er annealed to 500 °C shows a dramatic increase in the 1.8, 2.2, and 2.3 eV peak intensities at shallow probe depths, with its yield increasing with increasing depth. These three features become pronounced at all depths after a 700 °C anneal. MBE-grown GaN:Er grown with lower C and O impurity levels than the MOMBE-grown sample exhibits strong emission at all these energies without annealing. The decreased emission at shallow (tens of nanometer) probe depths suggests a depletion of activation Er in the near-surface region. Enhancement of near-surface Er3+ luminescence with annealing may be due to lattice reordering as well as impurity redistribution.
Amorphous hydrogenated carbon film formation from benzene by electron cyclotron resonance chemical vapor deposition
Authors: Chen Xiao-hua , Ning Zhao Yuan , Hess Dennis W. , Tolbert Laren M.
Published: July 2002

Amorphous hydrogenated carbon thin films have been deposited from benzene vapor in an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor. The effects of gas flow rate, pressure, and microwave power on deposition rates, chemical structure and composition, and on film density were investigated. Plasma enhanced dissociation and ionization reactions were monitored by mass spectrometry and by optical emission spectroscopy. Dissociation products included a variety of unsaturated hydrocarbon species (primarily ethylene) and hydrogen. Deposited films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. Films displayed a condensed, aromatic, hydrocarbon-like structure, albeit without extensive conjugation. Possible reaction sequences leading to the observed film structures have been proposed.
Vacuum gauge self-compensating external environment in the SPring-8 storage ring
Authors: Saeki Hiroshi , Momose Takashi
Published: July 2002

Some Bayard–Alpert gauges mounted on crotch chambers in the SPring-8 storage ring have indicated negative pressures at stored electron beam currents more than 5 mA. Simple measurements have shown that the negative pressure indications of these vacuum gauges are caused by influx of photoelectrons to their collectors. In order to measure the pressure in such a vacuum environment, the authors propose a vacuum gauge which self-compensates for photoelectrons from the external vacuum environment. The gauge has an added correcting electrode which detects the photoelectron current, only from the external environment, and then compensates to show the real pressure from the measured ion current of the gauge collector.
Effect of interface states on the performance of GaAs p+-i far-infrared detectors
Authors: Perera A. G. U. , Shen W. Z. , Ershov M. , Liu H. C. , Buchanan M. , Gunapala S. D. , Bandara S. V. , Liu J. K. , Ye H. H. , Schaff W. J.
Published: July 2002

Interface states have been shown to have an appreciable effect on the performance of p-GaAs multilayer (p+-i-p+-i-…) homojunction interfacial work function internal photoemission (HIWIP) far-infrared detectors. In this article, a comparison of detector performance was made of p-GaAs HIWIP detectors with different interface state densities, with the emphasis on the detector’s dark current, noise, and capacitance characteristics.
Growth characteristics of vacuum coated thick a-Se films for device applications
Authors: Juhasz C. , Gembala V. , Kasap S. O.
Published: July 2002

There has been a resurgence of interest in the growth characteristics of amorphous Se (a-Se) films due to their recently commercialized applications in x-ray imaging as x-ray photoconductors. Electronic quality a-Se films require the substrate temperature during vacuum deposition to be as high as possible but increasing the substrate temperature leads to amorphous films containing crystalline inclusions and eventually to polycrystalline films which have high conductivity and are therefore not useful as photoconductors. We prepared a variety of thick a-Se films on Al substrates by conventional vacuum deposition in which only the substrate temperature Tsb and boat temperature Tbt were varied. Experiments indicated the appearance of crystalline zones (crystallites) in the amorphous Se film as the substrate temperature was increased. We identified an experimental critical Tbt−Tsb boundary between amorphous films with and without crystalline inclusions. A model has been developed for the critical relationship between Tsb and Tbt, i.e., Tbt=f(Tsb) based on two competing rate mechanisms: the rate of deposition (or material condensation on the substrate) and rate of crystal growth in the film assuming heterogeneous nucleation at favorable substrate sites. Over the narrow substrate temperature range, we approximated the Vogel–Tamman–Fulcher behavior of the crystal growth rate by an Arrhenius rate with an apparent activation energy Ecr that accounts for most crystallization studies on a-Se. The condensation rate was assumed to follow an Arrhenius rate with the activation energy determined by the enthalpy of evaporation, Eev. The Tbt=f(Tsb) model was particularly sensitive to the Ecr/Eev ratio. By using the presently accepted values for Eev and Ecr, it was shown that the experimental results could be well fitted to the Tbt=f(Tsb) model. The results have a wider significance than a-Se and can be easily extended to apply to a number of other chalcogenide semiconductor films.
Plasma erosion of a magnesium radio-frequency cathode measured by laser-induced fluorescence
Authors: Brockhaus A. , Georg A. , Wingsch V. , Engemann J.
Published: July 2002

Various diagnostic methods are compared with respect to their abilities in determining the controlled electrode erosion in a radio-frequency (rf) plasma source. The source is cylindrical in shape with a center rf cathode made of magnesium. Due to the unequal electrode area ratio of 1:8 a high self-bias voltage develops. Sputtering from the cathode was studied by means of optical emission spectroscopy, laser-induced fluorescence (LIF), quadrupole mass spectrometry, and deposition experiments. Dependencies of the plasma parameters were measured. The magnesium density decreased exponentially with distance from the target but could be traced down to very low levels around 105 cm−3 in the downstream region by the extremely sensitive LIF method. Laser excitation from the electronic ground state as well as fluorescence detection were performed on the strong 3p 1P1o←3s 1S0 resonance line at 285.2 nm. For absolute calibration Rayleigh scattering from cold nitrogen gas was utilized. Sensitivity issues and detection limits are discussed.
Barrier height and leakage reduction in n-GaAs–platinum group metal Schottky barriers upon exposure to hydrogen
Authors: Aspnes D. E. , Heller A.
Published: July 2002

Current–voltage (I–V), capacitance–voltage (C–V), and photovoltage (PV) data are obtained for Ru, Rh, Pd, Os, Ir, and Pt contacts deposited on chemically cleaned 〈100〉 n-GaAs wafers. By explicitly evaluating the relevant equations using realistic values of all parameters, we show that the currents obtained for small voltages are far too large to be explained by thermionic or recombination effects alone but are indicative of barrier height variations as proposed by Freeouf et al. We used the fact that the thermionic emission component is always present to reconcile the difference between apparent barrier heights determined by I–V and C–V measurements to obtain a consistent set of values for all materials. Upon exposure of the Ru and Ir contacts to atmospheric-pressure hydrogen, the barrier heights are reduced by 160 and 70 mV, respectively, and the ideality factors by 0.3 and 0.3, showing that hydrogen simultaneously lowers the barrier height and makes it more uniform over the contact for these junctions. The introduction of hydrogen into the bulk of these hydrogen-alloying metals has no effect on the transport properties of the Pt, Rh, and Pd junctions despite a reported work function change of nearly 1 eV for Pt, over 0.5 eV for Rh, and a phase change to a metallic hydride for Pd. The change in optical properties with ambient in the Drude region of Ru shows that the bulk Fermi level does not change by more than 40 meV upon hydrogenation, indicating that hydrogen is affecting primarily the interface dipole. The results, in general, conform to the predictions of Spicer’s unified defect model but the dependence of the detailed behavior on specific transition metals and the evidence for lateral barrier height variations show that some corrections are necessary.
Fabrication of apertures, slots, and grooves at the 8–80 nm scale in silicon and metal films
Authors: Muray A. , Isaacson M. , Adesida I. , Whitehead B.
Published: July 2002

Fabrication of apertures, slots, and grooves in silicon, gold–palladium, and lithium fluoride has been demonstrated using a 100 keV electron beam. For the LiF films we have been able to etch<2 nm wide by 50 nm deep grooves on 10 nm centers. Grooves in silicon 8 nm wide by 30 nm deep have been made by reactive ion etching in SF6. Apertures as small as 8 nm in diameter have been produced in AuPd films self-supported over larger holes in 60 nm thick Si windows.
Silicon nitride stencil masks for high resolution ion lithography proximity printing
Authors: Randall J. N. , Flanders D. C. , Economou N. P. , Donnelly J. P. , Bromley E. I.
Published: July 2002

Masked ion beam lithography using silicon nitride stencil masks at a 25 μm mask-to-sample gap has been used to replicate 80 nm lines and spaces in PMMA. An improved reactive ion etching technique for the silicon-rich silicon nitride (SiNx) mask material using CHF3 at a 500 V self-bias potential is reported. A grid support mask is proposed as a means of exposing arbitrary patterns with a stencil mask. The principle of this technique is demonstrated in the special case of a grating.
Effect of ion sputtering on interface chemistry and electrical properties of Au GaAs(100) Schottky contacts
Authors: Wang Y.-X. , Holloway P. H.
Published: July 2002

The effects of sputtering n–type (100)GaAs with 1 to 5 keV argon ions have been studied in ultrahigh vacuum. Auger electron and x-ray photoelectron spectroscopies have been used to characterize the surface before and after sputtering. Gold Schottky contacts were prepared in situ to avoid contamination at the metal/semiconductor interface. The data show that sputtering depletes the surface in As, and the extent of depletion increased as the ion energy was increased. However, angular-resolved photoelectron data showed As was enriched on the outer atom layer by 5 keV but depleted by 1 keV Ar+ sputtering. Current and capacitance versus voltage data showed that sputtering always lowered the Schottky barrier height and generally increased the ideality factor. However, the barrier height after 3 keV sputtering was higher than after 1 keV sputtering. Those effects are explained based on a combined effective work function model and creation of a donorlike surface damage layer. The donor layer was correlated with As depletion by sputtering. Deep level trap formation and annealing of sputtering effects were studied.
Kinetics of Si(100) nitridation first stages by ammonia: Electron- beam-induced thin film growth at room temperature
Authors: Glachant A. , Saidi D.
Published: July 2002

Kinetics of the first stages of Si(100) nitridation by pure ammonia have been investigated for the first time by Auger electron spectroscopy, low energy electron diffraction, and thermal desorption mass spectrometry. Thin nitride film growth is quite slow within the pressure and temperature ranges investigated (10−7–10−5 Torr and room temperature—1030 °C, respectively). At high temperatures (T>800 °C), our results confirm previous studies for Si(100) nitridation by atomic nitrogen; in particular, the kinetics obey a layer-by- layer mode of growth. Moreover, the first reacted layer formation rate is proportional to the ammonia pressure and limited by the dissociation rate of ammonia on the surface. Further growth upon nitridation is limited by diffusion of the reacting species through the reacted layer. The nitride film–silicon interface is quite abrupt. At low temperatures (T≲600 °C), the growth rate is negligible due to a small thermal dissociation rate of ammonia and a lower mobility of the reacting species. Room temperature reaction is enhanced by the electron bombardment giving rise to thin films and growth rates comparable to those obtained at the highest temperatures. This electron-beam-induced nitridation at room temperature is attributed to ammonia dissociation and nitrogen K-shell ionization under electron bombardment.
Doping effects in AlGaAs
Authors: Heiblum M.
Published: July 2002

A summary of the results of a few experiments on a variety of structures based on GaAs–AlGaAs heterojunctions, in which the AlGaAs was Si doped are reported. RHEED and SIMS results are presented for heavily and moderately doped AlGaAs, showing that Si segregated toward the growing front. Photoluminescence spectra of heavily doped AlGaAs has a dominant low energy peak and is absent of the exciton peak. Normal and inverted selectively doped structures were grown at a variety of conditions. Their properties demonstrate that Si segregates toward the growing front, and suggests that this effect could be the main cause of the low mobility in inverted structures.
Anisotropic etching of Al by a directed Cl2 flux
Authors: Efremow N. N. , Geis M. W. , Mountain R. W. , Lincoln G. A. , Randall J. N. , Economou N. P.
Published: July 2002

A new Al etching technique is described that uses an ion beam from a Kaufman ion source and a directed Cl2 flux. The ion beam is used primarily to remove the native oxide to allow the Cl2 to spontaneously react with the Al film forming volatile Al2Cl6. By controlling both the flux equivalent pressure of Cl2 and the ion beam current, this etching technique makes possible the anisotropic etching of Al with etch rates from 100 nm min−1 to nearly 10 μm min−1 with a high degree of selectivity.
Anisotropic etching of silicon using an SF6/Ar microwave multipolar plasma
Authors: Pomot C. , Mahi B. , Petit B. , Arnal Y. , Pelletier J.
Published: July 2002

Etching experiments have been conducted on phosphorus doped Si 〈100〉 samples in low pressure SF6/Ar microwave multipolar plasmas which have been characterized. The influence of SF6 partial pressure on anisotropy has been determined. Strictly anisotropic etching of silicon was obtained under SF6 pressure of about 3×10−4 Torr in an SF6/Ar gas mixture, the total pressure being (3–5)×10−3 Torr. An etching rate of ∼150 nm/min, without any undercutting, has been achieved under low energy ion impact. The anisotropic etching mechanisms involved in the SF6/Ar system are discussed.
On the Fermi level pinning behavior of metal/III–V semiconductor interfaces
Authors: Newman N. , Spicer W. E. , Kendelewicz T. , Lindau I.
Published: July 2002

We present the results of a systematic study designed to investigate the physical mechanisms involved in Fermi level pinning on III–V semiconductor surfaces. This study compares the results of surface sensitive photoemission spectroscopy performed during the initial stages of Schottky barrier formation (sub to several monolayer coverages of metals, as well as nonmetals) to the results of device electrical measurements for thick metal coverages (∼1000 Å). These results give strong support for the basic premises of the unified defect model (UDM), as first proposed in 1979. However, several revisions were found to be important in correcting and/or sharpening several details of the UDM. As proposed in 1979, we find that the same native defect energy levels are created independent of the foreign atoms deposited on the clean GaAs surface. However, the small but finite range in pinning positions in GaAs and InP and the correlation that high (low) barrier heights are formed for high (low) electronegativity metals on n-type substrates indicates that electronic interactions between the foreign atoms and the GaAs can determine the charge state of the defects which are found to pin the Fermi level. The donor at 0.1 eV from the conduction band minimum (CBM) originally associated with a native defect of InP in 1979, was shown to be due to a level in the oxide on the surface of the InP. The reassignment of the energy levels of the native defects in InP to an acceptor level at CBM-0.3 eV and a donor level at CBM-0.5 eV was found to be more consistent with the available experimental data.
Sputtering of SiO2 in a XeF2 and in a Cl2 atmosphere
Authors: Oostra D. J. , Haring A. , de Vries A. E.
Published: July 2002

SiO2 has been bombarded by 3 keV Ar+ ions under simultaneous exposure to a thermal beam of Cl2 or XeF2. Mass spectra and time-of-flight distributions of the sputtered species have been measured. It is observed that during XeF2 exposure the sputtering yield of SiO2 is enhanced with a factor of 2.3. After ionizing the neutral ejected Si species, we have detected SiF+x (x=0–4) and SiOF+y ( y=0–2). The kinetic energy distributions of these particles indicate that the newly formed species have been bound loosely to the lattice and that they are sputtered predominantly by a collision cascade mechanism. The results are explained by assuming that adsorbed F atoms are mixed into subsurface layers in which Si–F bond formation takes place. Hardly any chemical enhancement of the sputtering yield of SiO2 is observed when Cl2 is added. In this case the Si species are detected as SiCl+x and SiOCl+y (x, y=0–2). The chlorine peak (Cl+) is an order of magnitude higher. The kinetic energy distribution of Cl shows that most of the chlorine is in the lattice chemically unbound. From the measurements it is concluded that the heat of formation determines that in the collision cascade Si–F bonds are formed while Si–Cl bonds are not. Differences in the enhancement of the sputtering yield between silicon and SiO2 can also be explained by differences in heat of formation.