bluuebunny/crossref_metadata_2025 huggingface dataset:
Auger sputter profiling and factor analysis of thermally treated Ni–GaAs structures: The influence of oxygen on compounding and diffusion
Authors: Solomon J. S. , Smith S. R.
Published: July 2002

The effects of the presence of surface oxides and oxygen incorporated in deposited Ni films on intermixing and compounding at Ni/GaAs (100) interfaces were investigated with Auger sputter profile analysis. The Ni/GaAs structures were heated in vacuum with a high-intensity incoherent lamp. Chemical changes and compound distributions were extracted from profile data by factor analysis of the Auger peaks. Diffusion coefficients for Ni at different temperatures were obtained from profile concentration gradients. The results showed that the activation energy for Ni diffusion in GaAs was about 0.2 eV higher when oxygen contaminated the Ni/GaAs interface. The presence of interfacial oxygen was also shown to inhibit compound formation, such as Ni2GaAs.
Silicon cold cathodes as possible sources in electron lithography systems
Authors: van Gorkom G. G. P. , Hoeberechts A. M. E.
Published: July 2002

Cesiated silicon cold cathodes are capable of emitting high current densities (in excess of 1000 A/cm2) into a vacuum. The energy spread of the emitted electrons amounts to 1.2 eV. Fortunately, the aperture-limiting diaphragm acts as a kind of energy selector which results in an energy spread of only ∼0.35 eV in the beam after the diaphragm. The intrinsic RC time of 1-μm-diam emitters is only ∼1 ps, which, after reduction of parasitic RC times, means that very fast switching of the emission current is possible, especially because a voltage swing of only ∼1 V is needed. Arrays and matrices of closely spaced emitters can be produced using currently available silicon technology. This means that, in principle at least, writing times in electron lithography systems can be reduced by a very large factor (∼1000), making direct slice writing with 0.1-μm details economically feasible.
Aerospace: Continuing motivator for melting technology
Authors: Domingue J. A. , Schweizer F. A. , Yu K. O.
Published: July 2002

With the inception of aerospace superalloys, power generation played a dominant role for the advancement of specialty alloys melting processes such as vacuum induction melting and vacuum arc remelting (VAR). The powerful motivators of flight reliability, including fracture mechanics design and clean metal requirements, efficiency and performance (temperature and stress capability, homogeneity, and compositional control), and strategic element conservation (scrap reclamation and waste reduction) are spurring the upgrading of methods such as electroslag refining and powder metallurgy for critical part manufacturing. Also, technologies including electron beam melting, molten metal filtration, and casting techniques ranging from fine grain to single crystal are being implemented. Contrasting the exploration into new, or heretofore neglected, melting techniques is the simultaneous advent of microprocessors and other electronic breakthroughs, which promise to improve control capability of established processes such as VAR and to make process modeling affordable. This review addresses the industry-wide emphasis on process, rather than material, development for the near future in aerospace components.
Device for quantitative determination of occluded gases in zinc die casting by vacuum melting
Authors: Robla J. I. , Luis L.
Published: July 2002

In order to determine the occluded gases volume in zinc die castings and to establish its relationship with the degree of porosity in them, after a heating test, it was necessary to use the process of vacuum melting. Hence, a special furnace and melting chamber with an operating system was built. The main elements of the unit are an electric fusion furnace, a steel melting chamber for large samples, a Pirani manometer head for the lowest and a mercury manometer for the highest pressure measurement, systems for vacuum regulation and temperature measurements, and for gas evacuation and graphic registration. For the analysis system calibration, known volumes of gases were injected and the respective calibration graph obtained. Finally, specimens with different amounts of occluded gases were melted by vacuum. This equipment is useful for gas contents between 0.5 and 30 cm3/100 g of sample. It is a simple and useful method for zinc die casting.
Vapor deposited chrome–copper–chrome laminates for electromagnetic interference/radio frequency interference shields
Authors: Miller Walter J.
Published: July 2002

A patented process for shielding electronic enclosures is discussed relative to both process parameters, as well as the finished electrical and physical properties of the composite structures fabricated. The electrical data were obtained by testing standardized composite squares for shielding effectiveness using the shielded box technique of an independent test laboratory. Physical data were obtained by evaluating the same and/or similar composites for standardized adhesion at Underwriters Laboratories Inc. The specific test battery chosen was Underwriter’s standard ‘‘UL746C.’’ In this case sample composites received both thermal cycling as well as thermal/humidity ‘‘aging’’ before performing standardized adhesion testing. All test panels were evaluated versus a standardized ‘‘control’’ panel of a nickel-acrylic coating on ABS. The results indicated that ‘‘thin’’ metallic vapor deposited laminates were as effective as ‘‘thick’’ conductive nickel–acrylic coatings for both coating adhesion and coating shielding effectiveness.
Cryogenic inertial confinement fusion target technology at the Omega facility, University of Rochester
Authors: Musinski D. L. , Ankney J. S. , Decker D. N. , Felmlee W. J. , Frazier R. E. , Groves W. A. , Mruzek M. T.
Published: July 2002

To take full advantage of the capabilities offered by the Omega laser facility, the experimental teams at the University of Rochester need the capability to field cryogenic targets. The cryogenic target delivery system must be able to produce uniform solid or liquid DT layers 2–20 μm within polymer shells which are 300–400 μm in diameter. The facility must be able to maintain its experiment rate of one shot per 1/2 h and each target must be documented within the experimental chamber for postshot analysis. We will discuss the approach and equipment that KMS is using in collaboration with the University of Rochester to provide Omega with the capability to field cryogenic inertial confined fusion (ICF) targets.
Microtarget fabrication in the United Kingdom: An overview
Authors: Sutton D. W.
Published: July 2002

The laser target fabrication groups in the U.K. have continued to develop techniques for the production of laser targets. Special emphasis has been put on targets for x-ray lasers at the U. K. Central Laser Facility (CLF/RAL) and on the use of UV eximer lasers for the noncontact machining of polymer shells and planar foils. Atomic Weapons Research Establishment has concentrated largely on the production of very smooth surfaces and on the development of novel methods for the production of polymer foams. A broad array of characterization techniques are available for inspection and metrology.
Simple approximation to thermal attenuation in low-energy atom–surface scattering
Authors: Manson J. R. , Armand G.
Published: July 2002

We present a set of simple approximations for models of the thermal attenuation of elastic intensities as a function of surface temperature. The results illustrate the complexity of the strongly interacting atom–surface system, yet provide simple closed-form expressions which are no more difficult to apply than a standard Debye–Waller factor. Very good agreement is obtained with existing experimental data. The importance of the various types of multiphonon contributions is assessed and the resummation of bubble diagrams is demonstrated.
Kinetic theory of gas molecules in an extrahigh vacuum
Authors: Da Daoan , Da Xiaodong
Published: July 2002

In general, we apply the pressure equation P=nkT and pumping equation P=Q/S. But, in the extrahigh vacuum environment, when we still use them, some failure occurs. In this article a stochastic model is put forward to solve such problems. The results are different from above. Furthermore, a new method is provided which can measure the accommodation coefficient α and sticking probability β in an extrahigh vacuum chamber. The problem of gas molecular velocity distribution will be discussed in detail in such an environment. There are two ways of solving the problem to be considered.
Contamination effects in glow discharge deposition systems
Authors: Jansen Frank , Kuhman Dan
Published: July 2002

The slow release of reactive gases from the walls and electrodes of practical plasma enhanced chemical vapor deposition (PECVD) systems has been studied. These desorption effects become important when thin films with different compositions are sequentially deposited in single-chamber deposition systems. The pressure rate of rise of a PECVD reactor was measured after exposure of the system to commonly used precursor gases. The nature of the gas, its pressure, the system temperature, and the time duration of the exposure are experimental variables. Contamination effects by dopants at the parts per million level were investigated by their effect on the electrical properties of subsequently deposited films. It is found that ammonia and diborane, both of which are extensively used for device fabrication, are especially difficult to remove from the system. Operational procedures such as long pumpout times, baking, and short exposure times to the gases, preferably at low pressures, can often reduce the extent of the carryover to an acceptable level in a single-chamber system. However, the use of multichamber systems is likely to be the most effective solution to crosscontamination problems in PECVD processes.
Properties of intrinsic and doped a-Si:H deposited by remote plasma enhanced chemical vapor deposition
Authors: Parsons G. N. , Tsu D. V. , Lucovsky G.
Published: July 2002

We have grown films of a-Si:H by remote plasma enhanced chemical vapor deposition (RPECVD) with substrate temperatures Ts between 38 and 400 °C and studied the infrared and optical absorbance (including sub-band-gap absorbance), and other photoelectronic properties. The RPECVD films differ from glow discharge (GD) and sputtered films, most notably in the Ts dependence of the hydrogen bonding environments (SiH, SiH2, etc.) and the photoconductivity. RPECVD films produced with Ts=235 °C are similar to ‘‘device grade’’ GD films. Based on the differences between these films, we construct a model for the RPECVD deposition process that includes SiH3 species as precursors to the growth of high-quality films. We also present experimental evidence of the selectability of precursor formation in the RPECVD process.
Stoichiometric dry etching of mercury cadmium telluride using a secondary afterglow reactor
Authors: Spencer John E. , Dinan J. H. , Boyd P. R. , Wilson H. , Buttrill S. E.
Published: July 2002

A secondary afterglow reactor has been used for the dry etching of mercury cadmium telluride. In this reactor, methane is injected into the flowing afterglow of a microwave discharge in a fluorine source gas. The resulting reaction of F+CH4 produces methyl radicals, which etch mercury cadmium telluride at rates of up to 400 Å/min. Examination of etched surfaces by energy dispersive x-ray analysis and electron beam electroreflectance (EBER) reveals no change of stoichiometry over the unetched surface. EBER analysis further indicates no damage to the crystallinity of the surface. The etched surfaces exhibit crystalline anisotropy. Recent advances in mercury cadmium telluride device fabrication have focused on vacuum processes. The development of a nondamaging, stoichiometric dry etch process provides the potential of processing mercury cadmium telluride focal plane arrays in a continuous vacuum environment.
Studies in differential charging
Authors: Barr Tery L.
Published: July 2002

A detailed examination is presented of the causes, removal, and use of differential charging in x-ray photoelectron spectroscopy [electron spectroscopy for chemical analysis (ESCA)] and related spectroscopies. Particular attention is devoted to the impact of this phenomenon during the dispersion (or conversely crystallite growth) of metals and semiconductors in insulating matrices. A progressive series of models is described to determine their general and specific roles in the charging process. The effects of depth and interaction are considered for the fields involved (e.g., photoionization centers, detection depth, compensation currents, etc.). Thus, in certain cases, the ESCA may be simultaneously employed to analyze macromorphology, as well as surface and near surface chemistry. Practical examples are described from metals catalysis, corrosion and doped thin films.
Magnetic field effect on the R0A product of HgCdTe diodes
Authors: Schacham S. E. , Finkman E.
Published: July 2002

The performance of Hg1−xCdxTe diodes has been thus far investigated assuming it is controlled only by the p side of the junction. Therefore it has been analyzed using a simplistic one-side diffusion model. In order to examine whether this assumption is valid, we placed Hg1−xCdxTe diodes under a magnetic field parallel to the junction plane, and tested its effect on the saturation current. Due to the high mobility ratio, the magnetic field supresses the electron component of the saturation current, while that of the holes is hardly affected. Therefore, it enables a clear separation between the two components. The results prove that the contribution of the n+ region is comparable to that of the other side and should not be disregarded. We analyze the effect of carrier concentration gradient on the R0A product, generating a drift term and affecting the lifetime. The expressions obtained for the saturation current indicate a considerable drift term; however, it still is inversely proportional to the square of the intrinsic carrier concentration.
Internal stress minimization in the fabrication of transmissive multilayer x-ray optics
Authors: Jankowski A. F. , Bionta R. M. , Gabriele P. C.
Published: July 2002

Transmissive multilayer optics have a potential application in the development of high-resolution x-ray microscope and spectrometer systems. Difficulties encountered in the sputter deposition of these multilayer optical structures can be overcome by careful control of the fabrication parameters. The deleterious effects of compressive or tensile intrinsic stresses can be minimized by optimizing both substrate temperature and working gas pressure during the deposition process. This study specifically considers the Al/Ta multilayer combination.
Plasma chemical vapor deposition of thin platinum films
Authors: Feurer E. , Kraus S. , Suhr H.
Published: July 2002

The metal organic plasma-enhanced chemical vapor deposition of platinum films using cyclopentadienyl-trimethyl-platinum as starting material is reported. Three different reactors are compared and the influence of power, substrate temperature, and temperature of the reservoir with the organometallic has been studied. Films with ≊100% Pt and a resistivity of 46 μΩ cm have been deposited.
Determination of H, C, N, and O in indium phosphide by secondary-ion mass spectrometry
Authors: Gauneau M. , Chaplain R. , Rupert A. , Salvi M. , Descouts B.
Published: July 2002

Hydrogen, carbon, nitrogen, and oxygen are electrical active elements in III–V compounds and the knowledge of their concentrations in these materials is of primary importance. The secondary-ion mass spectrometry (SIMS), under cesium bombardment and negative secondary-ion collection, is probably the most powerful technique which has been developed to address this problem because it enables quantitative analyses with good lateral and depth resolutions to be made. Recent investigations using SIMS have shown that the detection limits of gaseous species are limited by the redeposition of vacuum contaminant molecules onto the sample surfaces, or by the ionization of these molecules in the gas phase. As a consequence, these limits critically depend on the experimental conditions, i.e., they are differently dependent on the etching rate: they decrease more steeply when reducing the raster-scanned area for a fixed primary current than when decreasing the primary current for a fixed eroded area. The previous experiments were performed in GaAs, mainly for carbon and oxygen. This paper describes similar investigations for H, C, N, and O in InP. H, C, N, and O were implanted to the same dose (1015 cm−2) at different energies so as to obtain maximum distributions at about 700 nm. The depth profiles of the respective elements were monitored and quantified for three primary beam currents (25, 50, and 100 nA) raster scanned, in turn, over three different areas (75, 50, and 25 μm2). The detection limits were deduced from the background levels without any substraction. The best values were 1–1.5×1016, 1×1016, 5–7×1014, and 5–7×1015 cm−3 for H, C, N, and O, respectively. The low limit measured for nitrogen was obtained by monitoring 31P2N− clusters. Such molecular ions are revealed to exhibit high ionization probabilities and they could be recommended to improve the sensitivity. The technique which consists in rastering moderate primary currents over small areas results in a compromise between low detection limits and sharp depth resolutions, but it will be shown that relatively low detection limits are attainable at low erosion rates by decreasing only the primary current.
Studies of the electrical and interface properties of the metal contacts to CuInSe2 single crystals
Authors: Abou-Elfotouh F. A. , Kazmerski L. L. , Matson R. J. , Dunlavy D. J. , Coutts T. J.
Published: July 2002

The electrical behavior of the metal contacts and ITO and CdS junctions to single crystals of CuInSe2 has been studied using I–V and electron beam induced current measurements, then correlated to the chemical composition and intrinsic defect states in the semiconductor. The results have indicated that the contact resistance, junction characteristics, and crystalline order of surfaces are controlled mainly by the type and relative concentration of the intrinsic defect states dominating the copper-indium-deselenide material; these states are very sensitive to heat treatments and surface preparation procedures. Correlation between the behavior of different samples (polycrystalline thin films or single crystals) should be based upon similarities in the type and relative concentration of the chemical composition.
High-temperature effects on a CoSi2/poly-Si metal oxide semiconductor gate configuration
Authors: Nygren Stefan , Johansson Stefan
Published: July 2002

The thermal stability of CoSi2/poly-Si on SiO2 was investigated. At temperatures above 750 °C silicon recrystallizes within the silicide layer and the structure approaches inversion, i.e., silicon on top of silicide. With higher temperatures, or longer annealing times, overall grain growth continues until each grain (silicide or silicon) is restricted by the free surface and by the gate oxide interface. These phenomena may limit the applicability of CoSi2 as a dopant diffusion source in, e.g., a salicide technology.
Surface roughening of Ge(001) during 200 eV Xe ion bombardment and Ge molecular beam epitaxy
Authors: Chason E. , Tsao J. Y. , Horn K. M. , Picraux S. T. , Atwater H. A.
Published: July 2002

The kinetics of surface roughening of Ge(001) during 200 eV Xe ion bombardment and during Ge molecular beam epitaxy (MBE) are studied by real-time reflection high-energy electron diffraction. In both cases, initially smooth surfaces reach a steady state roughness which depends on temperature and incident ion or adatom flux. The data are analyzed in terms of a phenomenological model in which beam-induced roughening competes with beam-induced smoothening, and in which the defect creation rate and surface diffusivity are fitting parameters. For comparable fluxes, the temperature dependences for the net roughening induced by ions and adatoms are strikingly similar, implying a similarity in the surface diffusivities of vacancies and adatoms. For the case of ion-induced roughening, approximately one surface defect (in units of displaced surface atoms) is created per ion which is consistent with calculations assuming that a large fraction of atomic displacements recombine without producing surface defects at these ion energies.
The chemistry of sulfur passivation of GaAs surfaces
Authors: Shin J. , Geib K. M. , Wilmsen C. W. , Lilliental-Weber Z.
Published: July 2002

Recently, sulfur treatments have been reported which electrically passivate the GaAs and InP surfaces. Since then, a variety of analytical techniques have been applied in an attempt to explain these observations. In particular x-ray photoelectron spectroscopy (XPS) has been used to determine the S–GaAs bonding. These experiments have not fully explained the surface chemistry since a number of different bonding configurations have been reported. This paper reports the results of our XPS and Auger analysis of Na2S⋅9H2O, (NH4)2S, and H2S treated GaAs surfaces. We propose a model which includes a kinetic barrier to S–GaAs chemical bonding. In the absence of an excitation source and/or surface defects, the S only physisorbs on the surface. With an excitation and/or defects the S chemisorbs on the surface and causes shifted core level peaks to appear in the XPS spectra.
Comparison of two primary pressure standards using spinning rotor gauges
Authors: Sharma J. K. N. , Mohan Pardeep , Sharma D. R.
Published: July 2002

In this paper a comparative study of two primary pressure standards viz. static and dynamic gas expander systems is reported. The two systems are compared by using spinning rotor gauges as the transfer standard in the pressure region of 6×10−3 to 2×10−1 Pa. It is observed that if the pressure variation of the conductance of the orifice assembly of the dynamic system is taken into account then the two systems are found to show an agreement of ±0.3% in the overlapping pressure region. A modified mathematical analysis of the equation due to Bureau et al. for molecular conductance of the orifice assembly is also given by taking into account the exit/entrance loss based on the new short-tube transmission probability equation developed by Santeler. The molecular conductance value thus obtained is found to be in close agreement with the corresponding experimental value extrapolated from the conductance versus pressure curve. This modified formula can be used to determine the effective conductance of the orifice assembly irrespective of the position of the orifice inside the tube connecting the two chambers.
Oxidation of Cu in contact with preimidized polyimide
Authors: Chambers S. A. , Loebs V. A. , Chakravorty K. K.
Published: July 2002

We have investigated interface formation and degradation at the junction of preimidized polyimide and Cu by means of scanning Auger and secondary electron microscopies, and x-ray photoelectron spectroscopy. Our approach has been to spin on ultrathin (tens of Å) polyimide overlayers onto Cu substrates, cure the polyimide while in contact with the Cu in an inert atmosphere, and then expose the interface to different environments. We found that only a very small amount of oxidation occurs during the curing process itself. This result is expected on the basis of the preimidization step prior to contact with Cu. The limited amount of oxidation appears to be due to the formation of a Cu–amine complex at the interface. Storage in vacuum leaves the interface abrupt and no further oxidation occurs. However, exposure to room-temperature air or high humidity at 85 °C causes more extensive Cu oxidation to occur. In the case of exposure to high humidity at 85 °C, metal oxidation is accompanied by Cu outdiffusion and polyimide decomposition. The interface degradation process after curing appears to be driven by absorption of water, and the primary degradation reaction product is CuO.
Scanning tunneling microscopy images of metal-coated bacteriophages and uncoated, double-stranded DNA
Authors: Keller Rebecca W. , Dunlap David D. , Bustamante Carlos , Keller David J. , Garcia Ricardo G. , Gray Carla , Maestre Marcos F.
Published: July 2002

One of the primary goals of scanning tunneling microscopy (STM) work in biology is to obtain high-resolution images of biological molecules under conditions that resemble those in vivo. To accomplish this goal two main difficulties need to be overcome. (1) Problems caused by the low conductivity of biological material, and (2) depositing the sample in a controlled and reliable way on a flat, inert conducting substrate. The first problem can be solved by coating the sample with a thin metal layer, at some cost in resolution. This allows the second problem, controllable depositing the sample, to be approached systematically, independent of difficulties caused by low conductivity. Using this approach, two different kinds of viruses have been imaged, bacteriophage T7 and fd. STM images of intact T7 and fd bacteriophages, and lysed T7 phages have been obtained in a straightforward and routine way. To obtain high-resolution images it is necessary to use uncoated samples. The conductivity problems cannot be avoided in this case, but they can be minimized by using thin samples. We have been able to obtain STM images of uncoated DNA molecules with about 10 Å resolution, in a variety of packing arrangements and conformations. One conclusion resulting from these experiments is that the STM tip often makes contact with uncoated molecules and sweeps them aside rather than imaging them. The mechanism of conduction through the DNA, and methods by which the tip contact problem can be overcome are discussed.
Microstructural defect reduction in HgCdTe grown by photoassisted molecular-beam epitaxy
Authors: Harris K. A. , Myers T. H. , Yanka R. W. , Mohnkern L. M. , Green R. W. , Otsuka N.
Published: July 2002

Twinning defects are a severe problem encountered in the growth of HgCdTe by molecular-beam epitaxy on the (100) and (111) orientations. The presence of these defects is a major potential source of noise generation in long-wavelength infrared HgCdTe detectors. Thus, the reduction of microstructural twin defects in the preparation of HgCdTe is of great importance. By tightly controlling the Hg overpressure and substrate temperature during photoassisted molecular-beam epitaxy growth of HgCdTe epilayers, a reduction of these microscopic twin defects has been achieved. In particular, pyramidal hillocks and facets on the (100) orientation of HgCdTe were reduced to 1×104 cm−2. In-plane twin domains were eliminated for (111)B HgCdTe films grown within a stringent parameter space. However, the demanding parameter control resulted in limited yields of twin free material. A new growth approach, compositionally modulated structures, has been developed in an attempt to increase the yield of twin free (111)B HgCdTe films. This approach involves the growth of thin CdTe epilayers spaced periodically throughout the HgCdTe matrix followed by an interdiffusion step. The films were characterized by defect etch, x-ray diffraction, and transmission electron microscopy. Films grown by this technique exhibited an absence of laminar twin defects as well as etch pit density counts comparable to that obtained from excellent liquid phase epitaxy.
Differential conductance imaging under alternate current tunneling bias
Authors: Yagi A. , Tsukada S. , Takahashi Y. , Morita S. , Sugawara Y. , Okada T. , Imai S. , Mikoshiba N.
Published: July 2002

We constructed a scanning tunneling spectroscopy (STS) system which uses ac voltage as a tunneling bias. In this system, for a measurement of a constant current image, time-averaged value of rectified ac tunneling current was maintained to be constant by a feedback circuit, while, for an STS measurement, differential conductance data were obtained using a circuit for analog differentiaion. Therefore, this system enables us on line monitoring of differential conductance images at various voltages as well as a constant current image. As a preliminary result, atomic resolution of a graphite sample in air and tunneling bias voltage dependence of differential conductance images were obtained.
Ion impact etch anisotropy downstream from diffusion plasma sources
Authors: Goeckner M. J. , Goree J. , Sheridan T. E.
Published: July 2002

Plasma processing in chambers located downstream from a source are gaining widespread use because they allow etching and deposition with minimal damage. This minimized damage, however, is achieved by using a low ion impact energy, which can lead to a poorer etch anisotropy. The best anisotropy for a given impact energy requires the lowest possible ion temperature. Laser-induced fluorescence measurements show that room temperature ions can be attained using a multidipole-confined discharge. In comparison, ion temperatures downstream from electron cyclotron resonance sources are much hotter, according to recent reports.
Ordered monolayer structures of boron in Si(111) and Si(100)
Authors: Headrick R. L. , Weir B. E. , Levi A. F. J. , Freer B. , Bevk J. , Feldman L. C.
Published: July 2002

We have prepared metastable, ordered monolayer structures of boron on Si(100) and Si(111) by silicon deposition atop unique surface reconstructions. These superlattice structures suggest possibilities for monolayer doping and ordered alloy structures with new electronic properties. In this paper we summarize our recent results in forming ordered structures and the electrical properties of the preserved layers.
Studies on type-inversion of sulfide-treated p-InP
Authors: Lau W. M. , Jin S. , Wu X.-W. , Ingrey S.
Published: July 2002

The effects of various sulfide treatments on n- and p-InP and the stability of the sulfide-passivated surfaces have been studied by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). When the sulfide treatments were performed at room temperature, a reduction of donor-type surface states was induced as indicated by a decrease of surface band bending on p-InP. However, such surface passivation deteriorated when annealed at 200–300 °C in vacuum, and a strong type inversion with band bending reaching 1.3 eV was observed on p-InP. XPS data from the annealed samples suggest that the presence of polysulfides plays an important role in the cause of the observed strong type inversion. However, SIMS analysis of the type-inverted samples indicated that the sulfur concentration at a depth of 7.5 nm from the surface was less than the SIMS detection limit for sulfur in InP (5×1016 atoms/cm3). In addition, XPS studies of the type-inverted samples showed that reversal of the type inversion occurred when the samples were immersed into water and/or a HF solution. Therefore, the observed type inversion of p-InP is probably caused either by the formation of surface sulfur-containing species, which contribute surface donor states near the conduction-band edge of InP, or by very shallow sulfur doping.
Thin-film deposition in the afterglows of N2 and H2 microwave plasmas
Authors: Meikle Scott , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: July 2002

Deposition of Si and SiNx thin films from addition of SiH4 to the afterglow of N2 and H2 microwave plasmas has been compared. Deposition of Si films requires SiH4 concentrations several orders higher than SiH4 for SiNx deposition. It is concluded that for Si film deposition, luminescence from the H2 plasma induces SiH4 dissociation and reactions between silane species are necessary for Si film formation. The proposed mechanism supports a deposition model based on the SiH2 radical.
Low-temperature (300 °C) stacked oxide–nitride–oxide gate dielectrics with remote plasma-enhanced chemical vapor deposition
Authors: Hattangady S. V. , Fountain G. G. , Alley R. G. , Rudder R. A. , Markunas R. J.
Published: July 2002

Remote plasma-enhanced chemical vapor deposition (RPECVD) has been used to form highly reliable ultrathin, stacked SiO2–Si3N4-SiO2 (O–N–O) structures at low temperatures (300 °C). The key elements of the processing: substrate surface cleaning, oxide deposition, and the nitride deposition are all performed in situ and sequentially at 300 °C in a single-chamber, ultraclean RPECVD reactor. The remote plasma process has produced thin oxide films with excellent interfaces (tox=8 nm, Dit=1–3×1010 cm−2 eV−1) and thin reliable nitride films (tnit=9 nm, charge-to-breakdown=1400 C cm−2). The stacked O–N–O structures exploit the respective advantages of the oxide and the nitride layers. Time-dependent breakdown testing of these structures (tequi=7 nm) utilizing aluminum gate electrodes show total charge-to-breakdown values of up to 180 C cm−2, as against less than 1 C cm−2 typically measured with an oxide film alone. Compared with capacitors based on the SiO2 dielectric alone, the stacked insulator-metal-semiconductor (MIS) capacitors show a lower failure rate of time-zero dielectric breakdown. Limited random sampling for I–V testing of devices with a 7-nm composite structure showed no catastrophic breakdown events for current densities of up to 1 mA cm−2. This contrasts with the observation of nearly 80% of the oxide devices showing catastrophic breakdowns in the Fowler–Nordheim tunneling regime. Note, however, that neither the oxide nor the O–N–O films exhibit low-voltage breakdowns.
Methodology, performance, and application of an imaging x-ray photoelectron spectrometer
Authors: Drummond I. W. , Ogden L. P. , Street F. J. , Surman D. J.
Published: July 2002

The advantages of an x-ray photoelectron spectrometer designed with an integral scanning x-ray photoelectron (XP) imaging system are outlined. Such advantages, as compared with a nonimaging XP spectrometer, include rapid examination of a large area of the specimen allowing the operator to ‘‘zoom in’’ on small details of interest. Up to 20 points of interest on the sample can be unambiguously identified and full spectra obtained from them. High spatial resolution maps can also be produced. The performance of the instrument can be quickly optimized with the aid of the scanning imaging technique which provides various diagnostic features. Analytical data can be obtained in a relatively short time and depth profiling techniques show significant benefits. Details of these benefits and of the self-diagnostic features will be given as will a brief outline of an application of the new instrument.
Temperature-controlled laser-induced polymerization of formaldehyde on Ag(111)
Authors: Fleck L. E. , Ying Z. C. , Dai H. L.
Published: July 2002

The UV-laser-induced polymerization of submonolayer formaldehyde on Ag(111) in UHV was investigated at temperatures between 35 and 85 K using electron energy loss spectroscopy. The yield of polymer decreases sharply as the sample temperature decreases, at approximately the same rate for H2CO as for D2CO. Below ∼60 K, the photochemical initiation step of the polymerization process is still efficient, but the rate-determining, thermally controlled step cannot proceed, resulting in no observable polymer at these low temperatures. The initiator species is stable on the Ag(111) surface at 35 K; polymerization of formaldehyde can be induced long after UV irradiation at 35 K by heating the sample to above 65 K. The overall polymerization yield of formaldehyde on the surface can be controlled by varying the substrate temperature.
Analytical electron microscopy and Raman spectroscopy studies of carbon nitride thin films
Authors: Chen Ming Y. , Li D. , Lin X. , Dravid V. P. , Chung Yip-Wah , Wong Ming-Show , Sproul William D.
Published: July 2002

Deposition of carbon nitride thin films on Si(100) and polycrystalline Zr substrates was performed by dc magnetron sputtering of a graphite target under a pure nitrogen ambient. The resulting carbon nitride films (CNx) are primarily amorphous with a small volume fraction of nanocrystallites. Both energy-dispersive x-ray analysis and electron energy loss spectroscopy measurements showed that the amorphous matrix has uniform nitrogen-to-carbon ratios ∼0.4–0.8 depending on deposition conditions. Carbon and nitrogen K edge structures obtained from electron energy loss spectroscopy studies suggest that the amorphous carbon nitride matrix is primarily sp2 bonded. Apart from the carbon–nitrogen stretching vibration, Raman spectra of CNx films closely resemble those of diamondlike carbon films. Intensity and peak width changes of Raman features in the 1300–1600 cm−1 range due to inorganic carbon (D and G peak) under different deposition conditions are explained in terms of the extent of structural disorder in these films.
Patterning of AlN, InN, and GaN in KOH-based solutions
Authors: Mileham J. R. , Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Shul R. J. , Kilcoyne S. P.
Published: July 2002

Wet chemical etching of single crystal III–V nitrides has proven difficult in the past due to their excellent stability in corrosive liquids. We have found that KOH-based solutions provide reaction-rate limited etching of AlN at rates strongly dependent on the crystalline quality. The activation energy for etching is 15.5 kcal mol−1 for both polycrystalline and single-crystal AlN, but the absolute rates are up to a factor of 103 higher for the polycrystalline material. The etching is selective over GaN and substrate materials such as Al2O3. KOH-based solutions also attack the interfacial region between InN and GaAs causing liftoff of the epitaxial InN layers. We have also studied the wet etching characteristics of GaN, AlN, and InN in all of the common acid solutions employed for conventional semiconductors. The temperature of these solutions was varied from 23 to 85 °C, but no measurable etching was observed under any of these conditions.
Room temperature visible electroluminescence in silicon nanostructures
Authors: Wu Wei , Huang X. F. , Chen K. J. , Xu J. B. , Gao X. , Xu J. , Li W.
Published: July 2002

Nanometer silicon crystallites were fabricated by annealing a-Si:H/a-SiNx:H multiquantum well (MQW) structures with an excimer laser. The films were prepared by rf plasma enhanced chemical vapor deposition. Visible electroluminescence (EL) has been observed at room temperature from the crystallized samples that had Si well layers narrower than 4.0 nm. The EL spectra showed multiple peaks at wavelengths around 600 and 700 nm, and an orange-red colored light emission could be observed by the naked eye. The onset voltage of visible light emission was 7 V. The EL intensity increased dramatically with an increasing laser irradiation value, and the EL peak shifted towards shorter wavelengths with a decrease in the Si well layer thickness. In agreement with the theoretical model, the visible EL phenomenon can be interpreted as the result of carrier injection into the nanosized Si crystallites in the MQWs, and radiation recombination via silicon quantum well states.
Reaction/annealing pathways for forming ultrathin silicon nitride films for composite oxide–nitride gate dielectrics with nitrided crystalline silicon–dielectric interfaces for application in advanced complementary metal–oxide–semiconductor devices
Authors: Lucovsky G.
Published: July 2002

Aggressive scaling of complementary metal–oxide–semiconductor (CMOS) devices requires gate dielectrics with an oxide equivalent thickness, tox,eq∼1 nm or less by the product introduction year 2012. Direct tunneling presents a significant performance limitation in field-effect transistors (FETs) with homogeneous oxide gate dielectrics <1.7 nm. Boron diffusion from p+ poly-Si gate electrodes in p-channel FETs leads to additional electrical problems for oxide thicknesses <3 nm. Interfacial nitridation improves reliability in n-channel FETs; however, by itself, it is not effective in p-type metal–oxide–semiconductor FETs due to boron pileup at the Si–dielectric interface. Proposed solutions include top-oxide surface nitridation and the integration of composite oxide–nitride dielectrics into CMOS devices. This review discusses the integration of hydrogenated silicon nitride films, prepared by remote plasma-enhanced chemical-vapor deposition, into electrical devices with composite oxide–nitride (ON) gate dielectrics. FET devices with ON dielectrics having the same oxide-equivalent thickness, tox-eq and gate dielectric capacitance as devices with homogeneous oxide gate dielectrics display improved performance and reliability. However, reductions in direct tunneling current due to increased physical thickness are below expectations based on tunneling calculations which assume the tunneling mass of electrons in nitride films is approximately the same as in SiO2. The combination of a lower electron tunneling mass and a reduced conduction-band offset energy (i) places important limitations on the extent to which devices with ON gate dielectrics can meet the aggressive scaling needed in advanced CMOS devices, and (ii) raises important questions that have to be addressed when evaluating alternative high-K dielectrics such as Ta2O5, TiO2, and Al2O3. However, tunneling can be reduced by combining monolayer interface nitridation with ON stacks.
Establishing the relationship between process, structure, and properties of TiN films deposited by electron cyclotron resonance assisted reactive sputtering. I. Variations in hardness and roughness as a function of process parameters
Authors: Carney Carl , Durham Delcie
Published: July 2002

Research has been conducted to investigate process control methods to make thinner, yet more cohesive TiN films. An electron cyclotron resonance plasma enhanced reactive sputtering technique was used to deposit TiN films of 1–2 μm thickness on Inconel 718 substrates. A designed experiment was conducted to identify which processing parameters, single or coupled, had significant effects upon the film microstructure and mechanical properties. It was found that Meyer hardness and root mean square (rms) roughness can be changed by varying the deposition conditions of system pressure, substrate temperature, nitrogen flow, and substrate bias. While it was determined that substrate temperature and substrate bias caused a variation in rms roughness, it was found that the interaction of system pressure and substrate temperature had a stronger effect. While system pressure was shown to have a strong effect on hardness, the interaction of system pressure and nitrogen flow caused a greater variation.
A new type of order–disorder transition in metastable (GaAs)1−x Ge2x alloys
Authors: Newman Kathie E. , Dow John D.
Published: July 2002

We propose that the observed V-shaped dependence of the direct gap E0(x) in (GaAs)1−xGe2x alloys is due to an order–disorder phase transition that occurs at the minimum of the ‘‘V.’’ In disordered Ge-rich alloys, the stable phase is one in which either Ga or As atoms can occupy nominal cation and nominal anion sites with approximately equal probability; in ordered GaAs-rich material, Ga (As) atoms preferentially occupy nominal cation (anion) sites. We calculate the order parameter for this transition using a three-component spin Hamiltonian and mean-field theory and evaluate the band structure of the alloys using a modified virtual-crystal approximation, which depends on the order parameter.
Phosphorus out diffusion from double-layered tantalum silicide/polycrystalline silicon structure
Authors: Maa J.-S. , Magee C. W. , O’Neill J. J.
Published: July 2002

In double-layered tantalum silicide/phosphorus-doped silicon films, the resistivity of silicon can increase sharply by high-temperature annealing. The increase depends on grain boundaries in the silicon films, and annealing ambient. It is not affected by the extent of interface reaction or diffusion, or the type of silicide used. A decrease in phosphorus content is due to phosphorus out diffusion from the silicon films, as determined by secondary ion mass spectrometry.
Effects of band bending on real space transfer in GaAs–AlxGa1−xAs layered heterostructures
Authors: Littlejohn M. A. , Kwapien W. M. , Glisson T. H. , Hauser J. R. , Hess K.
Published: July 2002

A program for solving Poisson’s equation in a single-particle Monte Carlo simulation has been used to obtain the transverse electric field distribution in GaAs–AlxGa1−xAs layered heterostructures with an externally applied electric field parallel to the layer interfaces. The effect of transverse electric field on real space transfer in these heterostructures are described. Transverse field amplitudes are equal to or greater than threshold fields for real space transfer, and their effect on real space transfer can be significant. In general, the presence of a transverse field in a real space transfer device reduces the peak velocity and the peak-to-valley ratio. Also, the threshold field can either be increased or decreased by the transverse field. Saturation velocities appear to be higher if a transverse field is present, although this conclusion is somewhat tentative.
Electron transport in planar-doped barrier structures using an ensemble Monte Carlo method
Authors: Littlejohn M. A. , Trew R. J. , Hauser J. R. , Golio J. M.
Published: July 2002

An ensemble Monte Carlo method is used to simulate electron transport through narrow high field regions which occur in planar-doped barrier devices. These structures can achieve average velocities substantially higher than the static drift velocity corresponding to average electric field. Increased velocities in these structures arise primarily from two physical mechanisms. These mechanisms are (1) velocity overshoot and related ensemble hot electron effects, and (2) an ensemble effect due to the collecting nature of the low field/high field boundary, which is not due to hot electrons. Ballistic-like transport can occur through narrow high field spikes. However, ballistic transport is not the major contributor to high ensemble average velocities due to scattering in regions adjacent to the high field spike. Ensemble average velocities at a given point in a device are influenced by the field distribution ahead of this point as well as that behind it.
A field emission e-beam system for nanometer lithography
Authors: Stephani D. , Kratschmer E. , Beneking H.
Published: July 2002

Field emitters offer a particularly high potential in e-beam lithography when writing in the nanometer range. Using a modified VG Microscopes Ltd., model HB 501 STEM, a current of 0.1 nA can be focused into a diameter of 2.5 nm at 100 kV with a final beam aperture of 1.6 mrad. In order to fulfill the demands of microlithography, an objective lens of 15 mm nominal focal length is used. Stage travel in the system is 5 mm in the X and Y directions and the maximum scan field is 250×250 μm2. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The 14 bit digital pattern generator has been electrically isolated by optocouplers from the host computer and is connected via analog differential buffers to the deflection amplifiers. The cold tungsten field emitter exhibits a linear decrease in current of about 20% within 20 min of continuous writing. The decrease in current is corrected during lithography by a feedback to the clock frequency of the digital pattern generator to maintain a constant exposure dose. The high current available enables the use of organic resists as well as low sensitivity inorganic resists such as NaCl or WO3. So far 10 nm resolution has been achieved by in situ vaporization of NaCl.