bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive sputtered titanium carbide/nitride and diamondlike carbon coatings
Authors: Deng Jianguo , Braun Manuel , Wei Ying
Published: July 2002

Nitride and carbide coatings of titanium and diamondlike carbon (DLC) coatings containing a small amount of titanium were deposited onto AISI 420 substrates by unbalanced magnetron sputtering techniques. The structures of the different coatings were analyzed by x-ray diffraction, Rutherford backscattering spectrometry, and infrared spectroscopy. The TiN, TiCxNy, and TiC coatings exhibited strong (111), (111), or (200) and (220) preferential orientations, respectively. The different tribological behaviors of TiN, TiC, TiCxNy, and DLC coatings were investigated and compared. In addition, the microhardness and adhesion of the coatings were also measured. The hardness values for all the coatings increased with the carbon content going from pure TiN to the DLC coating. The experimental results indicated that the DLC-10%Ti coating showed excellent properties, i.e., a high microhardness value (about 40.0 GPa), excellent adhesion (about Lc 11.0 kg), a lower friction coefficient, and an extremely long wear lifetime (about 58 h).
Distribution of species within an ethylene electron cyclotron resonance-microwave plasma
Authors: Webb S. F. , Gaddy G. A. , Blumenthal Rik
Published: July 2002

Electron cyclotron resonance microwave plasmas consisting of 2% ethylene in hydrogen and 2% ethylene in deuterium have been probed using the pulsed supersonic, plasma sampling technique. Comparison of the compositions of these two chemically equivalent plasmas provides the basis for examining the details of species interconversion and overall hydrocarbon chemistry within these plasmas. The ethylene/hydrogen plasma is shown to be composed of 9% ethane radical (C2H5), 38% ethylene (C2H4), 8% ethylene radical (C2H3), and 41% acetylene (C2H2), with the remaining counts attributed to impurities in the plasma. Due to interferences between the daughter ions of the radical species and the parent ions of ethylene and acetylene, the concentrations of radical species, reported above, represent only a lower limit estimate, based only on the parent ion intensity. Analysis of the mass spectrum obtained for the analogous deuterium plasma, based on the results from the hydrogen plasma experiments, reveal the acetylene components of the deuterium plasma to be 14% undeuterated (C2H2), 43% singly deuterated (C2HD), and 43% doubly deuterated (C2D2). The extensive deuteration of the acetylene indicates that the majority of the chemistry in these plasmas is repeated cycles of hydrogen (deuterium) atom addition to acetylene followed by abstractions from the radical species (C2HxD3−x). The absence of any significant intensity due to doubly, triply, or fully deuterated ethylenes indicates that the addition of hydrogen (deuterium) to the radical species C2HxD3−x is a much more rare event than abstraction.
Surface modification of (100) n-GaAs by radio frequency hydrogen plasmas
Authors: Sullivan J. L. , Saied S. O. , Layberry R. , Cardwell M. J.
Published: July 2002

This article describes a study of surface changes of (100) GaAs subjected to rf hydrogen plasma treatment. Hydrogen plasma etching of GaAs leads to the reduction of the As oxide in the native oxide film, leaving a wholly Ga oxide surface film. Further etching of the surface leads to the production of a nonstoichiometric subsurface amorphous GaAs layer which varies from Ga rich at low chamber pressures to As rich as the pressure is increased. This effect is dependent on the ion energy and may be explained in terms of the penetration depth of the hydrogen ions relative to the oxide thickness.
Structural and electrical properties of thin microcrystalline silicon films deposited by an electron cyclotron resonance plasma discharge of 2% SiH4/Ar further diluted in H2
Authors: Jagannathan B. B. , Wallace R. L. , Anderson W. A.
Published: July 2002

Microcrystalline silicon (μc-Si) was deposited in a simple, low cost microwave electron cyclotron resonance plasma system by H2 dilution of 2% SiH4/Ar. The film growth and properties have been examined with substrate temperatures between 300 and 450 °C for pressures of 1–40 mTorr. Raman spectroscopy has been used extensively to study the microstructure of the film, and to determine the crystallized fraction and grain sizes in the film, for growth variations caused by H2 dilution, growth pressure, and temperature. H2 dilution of the plasma is found to increase the grain size and the crystallized fraction of the deposited films. Crystallization could also be initiated in the films deposited using only the Ar diluted SiH4 by increasing the power coupled to the discharge. Increasing the H2 dilution results in compact films with a low hydrogen content, while a decrease is seen to create more voids in the film. The μc-Si films (∼70% crystallized fraction), prepared at 400 °C, with grain sizes between 200 and 300 Å, exhibit a low dark conductivity of 3×10−6 S/cm with conduction activation energies between 0.3 and 0.43 eV. The structural properties of the film, evaluated by Raman spectroscopy and evolved gas analysis, are correlated with the dark/photoconductivity observed in the film. The experimental data suggest etching by atomic hydrogen to be the primary mechanism responsible for the crystallization of the films.
Polycrystalline silicon thin films formed by metal-induced solid phase crystallization of amorphous silicon
Authors: Wang Y. Z. , Awadelkarim O. O.
Published: July 2002

Metal-induced solid phase crystallization (MISPC) was performed on plasma-enhanced chemical vapor deposited a-Si:H films which were deposited at substrate temperatures between 100 and 320 °C on bare or SiNx-coated Corning code 7059 glass substrates. The nickel or palladium layers used in the MISPC were thermally evaporated on the a-Si:H film surfaces to thicknesses of 5, 10, or 15 Å. We then examined the MISPC kinetics and its dependence on the precursor a-Si:H deposition temperature, the substrate coating, and the metal layer thickness. For the metals used in this study, it is found that the crystallization time and the microstructure and size of grains in the MISPC polycrystallization silicon (poly-Si) films are independent of the precursor a-Si:H deposition temperature, the metal layer thickness, and the substrate coating; however they are dependent on the metal type. It is argued that the formation of silicides and the solubility of metal in silicon, during the annealing, play important roles in enhancing crystallization. It is also found out that the diffusion of metal impurities into silicon from the metal layer used in the MISPC is detrimental to the electrical properties of the forming poly-Si and to the characteristics of thin film transistors fabricated in the poly-Si.
Investigation of electron induced damaging of molecular overlayers by imaging static secondary ion mass spectroscopy
Authors: Rading D. , Liebing V. , Becker G. , Fuchs H. , Benninghoven A.
Published: July 2002

We applied time of flight-secondary ion mass spectroscopy (SIMS) imaging under static conditions to investigate the interaction of electrons with a covalently bonded silane self-assembled layer of pentaflourphenyldimethylchlorosilane on Si and a physisorbed Langmuir–Blodgett film of a phospholipide dipalmitoylphosphatidylcholine on Au. Well defined surface areas of the respective layer system were irradiated with electron beams of different energies (0.5–25 keV) and different fluences (up to 3×1014 electrons/cm2). The prebombarded surface areas were analyzed by imaging static SIMS, providing characteristic secondary ion intensities as a function of electron energies and fluences. From these results energy dependent electron induced damage cross sections σe(E) could be determined. We found a strong energy dependence of σe(E), very similar to that well known for electron induced secondary electron yields. For both investigated layers we found very similar damage cross sections σe of about 10−15 cm2 for 1 keV electrons. This is in contrast to the strong influence of the binding energy between the molecular overlayer and the substrate, on ion induced damage cross sections σi. Our results demonstrate the general capabilities of imaging static SIMS to investigate quantitatively damaging effects in molecular overlayers and surfaces.
Surface conductivity induced electron field emission from an indium cluster sitting on a diamond surface
Authors: Küttel Olivier M. , Groening O. , Schlapbach L.
Published: July 2002

Electron field emission has been performed from a 5 μm indium cluster sitting on a nitrogen doped diamond (100) surface (3×3×1 mm3). The motivation to study such a system arose from the fact that electron field emission from N-doped diamond was reported in literature. However, the emission mechanism is not really known and still the subject of an intense discussion in the diamond/amorphous carbon community. We have chosen this setup to conduct a model experiment with well-defined parameters. The emission properties were analyzed by energy resolved field emission (FEED). We found that electron emission takes place at the apex of the indium grain for a hydrogenated diamond surface. However, large energy shifts were observed in the FEED spectra due to a potential drop across the hydrogen saturated surface. An oxygen termination kills the emission. By sputtering the surface the emission reappears with much lower energy shifts in the FEED spectra due to the conductive sp2 layer. We present a model taking into account the ohmic surface resistivity of the diamond surface and discuss the impact on emission properties of nanoclustered films. The results presented in this article show that surface conduction (hydrogen terminated or sputtered surface) can lead to electron field emission with large shifts in the FEED spectra. While the emission stems from a metallic micron sized tip, the electron supply is guaranteed by surface conduction.
Effects of vacuum and inert gas annealing of ultrathin tantalum pentoxide films on Si(100)
Authors: Mao A. Y. , Son K. A. , White J. M. , Kwong D. L. , Roberts D. A. , Vrtis R. N.
Published: July 2002

The effects of vacuum and inert gas annealing of ultrathin (∼20 Å) tantalum pentoxide (Ta2O5) films deposited on Si(100), with and without nitrogen passivation, were examined. Without nitrogen passivation, annealing Ta2O5 to 820 °C for 10 min led to oxidized silicon at both the Si-Ta2O5 and Ta2O5-vacuum interfaces and some tantalum silicide formation at the Si-Ta2O5 interface. Nitridation inhibited these processes.
Characterization of high density CH4/H2/Ar plasmas for compound semiconductor etching
Authors: Eddy C. R. , Leonhardt D. , Douglass S. R. , Shamamian V. A. , Thoms B. D. , Butler J. E.
Published: July 2002

High density plasmas generated using gas mixtures of methane, hydrogen, and argon are characterized using mass spectrometry, optical emission spectroscopy, and three dimensional Langmuir probing. Such plasmas are commonly used to etch compound semiconductors. In this work we examine the chemical and electrical properties of the flux to the region where substrates are placed during processing. The dominant species in the flux are identified as H, H+, CH3, CH3+, Ar, and ArH+. Plasma parameters in the source region include electron temperatures of 4–9 eV, plasma densities of 1–5×1011 cm−3, and plasma potentials of 24–44 V as process conditions are varied. These parameters are considerably reduced in the process region of the plasma to electron temperatures of 2–6 eV, plasma densities of 1×109 to 2.5×1010 cm−3, and plasma potentials of 3–14 V. Mass and optical emission spectral data are correlated to Langmuir probe results and the effects of varying process conditions on plasma properties are presented and discussed.
Field emitter based extractor gauges and residual gas analyzers
Authors: Dong Changkun , Myneni G. Rao
Published: July 2002

Attempts at using the Spindt-type molybdenum field emitter arrays in the extractor gauges and a residual gas analyzer are presented in this article. The sensitivity of the field emitter gauge is as high as 11 Torr−1. The departure from linearity of the pressure versus ion current measurements did not exceed 10% over the pressure range of 10−10–10−6 Torr. Stable sensitivities for nitrogen, helium, and hydrogen were achieved below 10−7 Torr with the field emitter residual gas analyzer. The slightly reduced emission current and sensitivity, after long-term operation, are of concern and need to be addressed. Residual gas spectra indicate that when using field emitters, the electron stimulated desorption ions (O+, F+, and Cl+) are reduced as compared to those made using a hot filament source.
Synchrotron-radiation stimulated desorption of SiO2 thin films on Si(111) surfaces observed by scanning tunneling microscopy
Authors: Miyamae T. , Uchida H. , Munro I. H. , Urisu T.
Published: July 2002

Synchrotron radiation (SR) stimulated desorption of silicon dioxide thin films was studied using scanning tunneling microscopy (STM), low energy electron diffraction (LEED), and Auger electron spectroscopy. Reconstructed Si(111)-7×7 patterns were observed by LEED after 2 h SR irradiation at a surface temperature of 700 °C. The STM images show an atomically flat Si(111)-7×7 surface. STM topographs of SR-irradiated surfaces suggest that the oxide desorption mechanism is completely different from that of thermal desorption of SiO2 film. These results indicate that the atomically flat Si surface can be obtained at low temperatures by using this technique.
Porous polycrystalline silicon conductivity sensor
Authors: Han P. G. , Wong H. , Poon M. C. , Wang N.
Published: July 2002

Porous polycrystalline silicon (PPS) based conductivity sensors were fabricated and characterized in this work. The PPS sensors show excellent sensitivity for detecting ambient pressures, gas species as well as temperature. Results show that the current increases significantly as the pressure decreases and an over two orders of magnitude change has been detected when the pressure was reduced to 10−2 atm. We also find that both ethanol and acetone vapors can significantly change the conduction in the sensors. In acetone vapor, the device even displays diode-like characteristics. Electrical conduction mechanisms of the sensors in vacuum and organic vapors are proposed. The fabrication process can be easily integrated with very large scale integrated technology.
Apparatus for quantitative analysis of residual gases in flat panel vacuum packages
Authors: Chalamala Babu R. , Uebelhoer David , Dean Kenneth A.
Published: July 2002

We describe an apparatus for quantitative determination of residual gases in flat panel display vacuum tubes like field emission displays, vacuum fluorescent displays, and plasma displays. This system is based on the principle of expansion of gases from the test device into a reference volume, where the gases are analyzed using a quadrupole mass spectrometer. The system was calibrated using gas expansion from reference gas cells and vacuum envelopes with known pressures. The effectiveness of the system was demonstrated by measuring the residual gases inside flat vacuum tubes, commercial vacuum fluorescent displays modulus, and field emission displays.
Selective doping of multilayer organic light emitting devices
Authors: Lam J. , Gorjanc T. C. , Tao Y. , D’lorio M.
Published: July 2002

Doping of organic light emitting diodes (OLEDs) has well-established benefits such as tuning emission wavelengths, as well as enhancing device lifetime and quantum efficiency. The use of low percentage doping within the emissive layer is an established tool for the study of energy transfer processes in OLEDs, allowing one to trace electron and hole movement and exciton formation. Delta doping, in which a thin layer of the dopant material alone is incorporated in the device, has the added advantage of a thinner sensing layer and an electroluminescence spectrum distinct from that of the host material. In an ongoing effort to further our understanding of electroluminescent emission processes, we have fabricated multilayer OLEDs which incorporate a narrow (<1 nm) delta-doped DCM region within the emissive layer. The devices studied were deposited on indium tin oxide (ITO) on glass substrates using thermal evaporation, with a structure of ITO, TPD (40 nm)/selectively doped Alq3 (40 nm)/Al (100 nm). The relationship between the doping profile and the emission characteristics will be discussed.
Growth of high-performance GaN modulation-doped field-effect transistors by ammonia-molecular-beam epitaxy
Authors: Tang H. , Webb J. B. , Bardwell J. A. , MacElwee T.
Published: July 2002

The growth of AlGaN/GaN modulation-doped field-effect transistors (MODFETs) by ammonia-molecular-beam epitaxy on sapphire substrates is reported. C-doped GaN (2 μm thick) was used as the insulating buffer layer in the device structures. The MODFET structure was completed by the subsequent growth of 2000 Å of undoped GaN as the channel layer and 130 Å of AlxGa1−xN(0.1⩽x⩽0.3) as the donor barrier layer. Sheet carrier densities of up to 2×1013 cm−2 with mobility of ∼1000 cm2/V s have been achieved even without doping the AlxGa1−xN barrier, indicating a large piezoelectric effect and excellent interface quality. The MODFET layers grown exhibited a unique surface morphology showing very flat plateaus with rms roughness of 0.8 nm on the plateaus and rms roughness of 8 nm over a larger area. A 100-μm-wide device with a 1 μm gate length exhibited a maximum dc current drive of 0.9 A/mm, a peak transconductance of 160 mS/mm, a current gain cutoff frequency of 15.6 GHz, and a maximum oscillation frequency of 49.4 GHz. The high dc and rf performance is attributed to the high two-dimensional electron mobility, high sheet charge density, and insulating property of the C-doped GaN buffer.
Surface orientation dependent surface kinetics and interface roughening in molecular beam epitaxial growth of III–V semiconductors: A Monte Carlo study
Authors: Singh Jasprit , Madhukar Anupam
Published: July 2002

A framework for examining molecular beam epitaxial (MBE) growth of lattice-matched III–V compound semiconductors is presented. It accounts for the basic kinetic parameters such as surface orientation and local environment dependent sticking coefficients, surface migration, and evaporation rates. Monte Carlo computer simulations are employed to examine the influence of these and other features—such as the molecular nature of the group V beam commonly employed—on the nature of the growth mechanism and the resulting interface profile. The [100] growth is found to exhibit a change from the two-dimensional nucleation and (consequently, layer-by-layer) growth mechanism to a three-dimensional nucleation mechanism with increasing growth temperature, thus exhibiting interface roughening. This interface roughening is, however, critically controlled by the surface geometry dependent surface migration kinetics. It is thus fundamentally distinct from the surface roughening transition predicted by Burton, Cabrera, and Frank which is independent of the kinetics and caused by the thermodynamic fluctuations at equilibrium. Recent studies of GaAs/AlGaAs [100] growth revealing the occurrence of interface roughening above a certain temperature, if intrinsic, we propose corresponds to the kinetically controlled surface roughening predicted by the present simulations, rather than to the surface roughening transition of Burton, Cabrera, and Frank as suggested by other investigators. The [110] growth, in the absence of exchange reactions, is found to exhibit the layer-by-layer growth mechanism over the commonly employed growth temperature regime. Consequently, the results predict that occurrence of rough interfaces for the [110] growth of systems such as GaAs/AlGaAs is primarily a consequence of exchange reactions induced during the deposition process. The geometry of the [110] growth front reveals such exchange reactions to be far more facile due to the expected lower activation barriers for exchange as well as for the surface migration processes of relevance. The implications of these results for understanding the [110] growth of GaAs/AlxGa1−xAs system are explored.
Structural studies of Ge–GaAs interfaces
Authors: Chang Chin-An , Kuan Tung-Sheng
Published: July 2002

Interface properties of Ge–GaAs grown by molecular beam epitaxy (MBE) have been studied using reflection high energy electron diffraction (RHEED) and high resolution cross-sectional transmission electron microscopy (XTEM). Growth morphology studies using RHEED revealed a smooth surface for the growth of Ge on (100), (110),and (111)GaAs and for that of GaAs on (110)Ge, but indicated a rough surface on an atomic scale for the growth of GaAs on (100) and (111)Ge. The different surface morphologies observed are attributed to the formation of antiphase domains during the growth of GaAs on (100) and (111)Ge. XTEM study of a (100)Ge–GaAs superlattice showed the presence of antiphase boundaries in the GaAs layers but not in the Ge layers. The interface structures of the Ge–GaAs system are discussed based on these RHEED and XTEM results and other information obtained by channeling, Auger, and x-ray measurements.
Effects of compositional grading on GaAs–Ga1−xAlxAs interface and quantum well electronic structure
Authors: Schulman J. N.
Published: July 2002

The electronic structure of the abrupt GaAs–Ga1−xAlxAs (001) heterojunction is compared with that of the heterojunction in which the transition from GaAs to GaAs–Ga1−xAlxAs occurs over several atomic layers across the interface. The effects of varying the width of the compositionally graded region on interfacial boundary conditions and on quantum well energy levels are studied using the tight-binding method. The compositional grading is modeled in the virtual crystal approximation. Substantial shifts in quantum well energies are found. For example, the ground state energy for a quantum well with 15 central GaAs layers and bounded by AlAs increases by 30% for graded region widths of six alloy layers. The effects of grading on the electronic wave function at the interface are studied by expanding it in terms of bulk states with complex wave vector values. The relative contribution of the bulk states from the neighborhood of the Γ and X points to typical conduction band states are determined. It is found that grading the interface over a small number of layers (two or three) effectively eliminates the X-point state contribution. Thus, the effective mass approximation, which includes Γ-point related bulk states only, is shown to be better justified for slightly graded interfaces.
Schottky barrier formation and the initial metal–atom bonding state: InP(110)–Al vs GaAs(110)–Al
Authors: Zhao Te-Xiu , Daniels R. R. , Katnani A. D. , Margaritondo G. , Zunger Alex
Published: July 2002

We investigated the adatom states for different Al coverages of InP(110) by synchrotron-radiation photoemission, including ultralow coverages below 0.2 monolayer. The adatom states below 0.1 monolayer and above ∼3 monolayer appear similar to the corresponding Al–adatom states on GaAs(110). In particular, the results for both systems appear consistent with the formation of Al clusters at 0.1–2 monolayer coverage, and the Fermi-level pinning occurs when the cluster formation starts. However, the similarity between the two systems is limited at intermediate (0.1–2 monolayer) coverages. At those coverages we observe a new bonded state for Al on InP, which is not observed on GaAs. Our results emphasize, in general, the need to extend the experiments to ultralow coverages when studying the Schottky barrier formation process.
Cyclotron resonance of 2D electrons in GaAs/AlxGa1−xAs heterostructures at low densities
Authors: Englert Th. , Maan J. C. , Uihlein Ch. , Tsui D. C. , Gossard A. C.
Published: July 2002

Cyclotron resonance of the two-dimensional (2D) electron gas in GaAs/AlGaAs heterostructures is studied as a function of the far infrared laser energy at different temperatures. The effective mass, determined from the resonant magnetic field, agrees very well with the values obtained in bulk GaAs. In samples of very low carrier density the linewidth of cyclotron resonance shows pronounced oscillations at He temperatures. A comparison with Shubnikov–de Haas measurements demonstrates that these oscillations are correlated with the filling factor of Landau levels. In samples of slightly higher carrier density ns >3×1011/cm2 the linewidth becomes almost independent of magnetic field.
Oxygen and hydrogen adsorption on GaAs(110)
Authors: Bartels F. , Surkamp L. , Clemens H. J. , Mönch W.
Published: July 2002

The interaction of molecular, ‘‘unexcited’’ oxygen and of atomic hydrogen with clean, cleaved GaAs surfaces was studied by Auger-electron and low-energy electron energy-loss spectroscopy as well as by a Kelvin probe. Up to ≊3×105 L of O2 the coverage slightly increases only up to θ=0.05–0.1, depending on the ‘‘quality’’ of the cleave. This chemisorption, which is attributed to cleavage-induced imperfections, is further correlated with the annihilation of the 20 eV energy-loss, usually characterized as an excitonic Ga(3d) core level-to-dangling bond states transition. The main chemisorption is observed after exposures above 3×105 L and yields θ=0.8 after 1010 L of O2. Two successive stages can be distinguished. The first one saturates at θ=0.4–0.5 after 3×106 L of O2. Larger exposures further increase the coverage and cause two new losses to grow, an O(2p) related one at 7 eV and an As(3d) related one shifted by 2.5 eV to larger binding energies. Illumination of the surface with the light of a Xe-arc lamp dramatically stimulated the oxygen uptake. Under the present experimental conditions, the initial sticking coefficient at RT is increased by a factor of 100, and the coverage reaches θ=1.5 after 1010 L of O2. The chemisorption of hydrogen causes the work function to increase on n-type and to decrease on p-type substrates, by this indicating the formation of depletion layers on both substrates. After exposures of up to 5 L the chemisorption-induced surface states of acceptor- and donor-type, respectively, pin the Fermi level at approximately Evs+0.85 eV and Evs+0.63 eV for n- and p-doped samples, respectively. Above exposures of 3 L the 20 eV energy-loss peak is observed to decay, and it has vanished after 3×104 L of hydrogen. This result clearly demonstrates that hydrogen atoms do not initially bond to the surface Ga atoms. In the exposure range from 50 to 3×104 L the intensity ratio of the surface sensitive As(31 eV) and Ga(55 eV) AES peaks decreases by approximately 20% while the Ga(55 eV) signal itself remains unchanged with respect to the primary peak. This result corresponds to a chemisorption-induced loss of approximately 75% of the As atoms in the topmost layer.
Surface silicon oxynitride films obtained by implanting mixtures of oxygen and nitrogen ions into silicon
Authors: Streb W. , Hezel R.
Published: July 2002

It was demonstrated that very thin silicon oxynitride films with concentrations covering the whole range between SiO2 and Si3N4 can be obtained by simultaneous high dose implantation of low energy oxygen and nitrogen ions into silicon. For ion energies of 5 keV homogeneous films about 5 nm in thickness resulted. These room-temperature-formed silicon oxynitride films were characterized by a combination of Auger electron spectroscopy (AES) and argon ion sputtering. The electron irradiation hardness was studied as a function of film composition.
Photoemission studies of the interaction of hydrogen plasmas with GaAs(001)
Authors: Friedel P. , Larsen P. K. , Gourrier S. , Cabanie J. P. , Gerits W. M.
Published: July 2002

The interaction between hydrogen plasmas and a (001) surface of GaAs grown by molecular beam epitaxy is studied by photoemission using synchrotron radiation and reflection high energy electron diffraction (RHEED). Measurements of the As(3d) and Ga(3d) core levels show that the interaction is complex and bonding to both As and Ga occurs. It is seen from RHEED measurements that plasma exposures lead to an unreconstructed and partly disordered surface. Valence band studies by angle resolved photoemission show a prominent hydrogen induced feature in the heteropolar gap at an energy 7.7 eV below the valence band maximum.
Oxygen redistribution during sintering of Ti/Si structures
Authors: Merchant P. , Amano Jun
Published: July 2002

We have used helium backscattering spectroscopy (RBS) to trace the evolution of oxygen depth profiles after UHV sintering, in 1430 Å titanium films, sputter deposited onto single crystal silicon substrates. The as-deposited films exhibit a roughly exponential oxygen distribution, decreasing from the titanium film surface. After sintering at 350 °C, 30 min the oxygen has moved into the film and after 450 °C, 20 min the oxygen is uniformly distributed in the titanium. At higher temperatures, as silicide formation progresses, the oxygen is snowplowed back toward the surface and is completely driven from the TiSi2 film after sintering at 800 °C, 30 min. The low temperature oxygen redistribution in titanium correlates well with increases in the sheet resistance of the unreacted films, as has been suggested earlier from x-ray diffraction results which revealed an increase in the titanium c axis after sintering at 500 °C [S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51, 342 (1980)]. The sheet resistance reaches a maximum near the onset of silicide formation and continues to decrease as the silicide reaction goes to completion. We do not detect any oxygen at the silicide/silicon interface, within the detection limits of RBS (1.5×1020 oxygen/cm3).
Stoichiometric shifts in cosputtered refractory silicide films during subsequent heat treatment
Authors: Bhandia Aloke S.
Published: July 2002

Stoichiometric shifts in the refractory metal silicides due to subsequent thermal processing have been an important consideration in VLSI processing. Optimal stoichiometry for interconnect application has been controversial. Shift in silicon-to-metal atomic ratio of the metal silicide films, due to heat treatment under inert and oxidizing ambients, have been studied. Existence of a thermodynamical equilibrium stoichiometry has been investigated by studying films on both silicon and silicon dioxide. The silicide films were deposited by planar magnetron cosputtering and Rutherford backscattering was the primary technique used for monitoring the stoichiometry.
Metallic and atomic approximations at the Schottky barrier interfaces
Authors: Spicer W. E. , Pan S. , Mo D. , Newman N. , Mahowald P. , Kendelewicz T. , Eglash S.
Published: July 2002

Stimulated by the work of Zur, McGill, and Smith (ZMS), we have undertaken a broad examination of the ‘‘potential normalization’’ conditions at the metal–semiconductor interface. We have made calculations using a metallic approximation and the model of Bardeen. Strong overall agreement is found with the results of ZMS; however, the details depend on the specific parameters used in the calculations. In particular, parameters were identified which give different pinning positions on n- and p-type semiconductor materials. Experimentally, Cs is found to be in strong disagreement with any ‘‘metallic’’ approximation at the interface; rather, it is shown that the experimental and theoretical understanding of Cs on solids indicates that an atomic model for the last atomic layer of Cs (with some fixed charge due to the induced Cs atomic dipole at the interface) is a more appropriate approximation than the metallic approximation used by ZMS and ourselves. Experimental results for thick noble metals (Au, Cu, and Ag) deposited in situ on clean GaAs(110) formed by cleaving in UHV are reported. These give a pinning position at the donor level as do properly analyzed PES measurements on thin (sub- to full-monolayer) deposits of noble metals on GaAs. An atomic explanation based on the large electron affinity of the noble metals is suggested and this is related to the interfacial chemistry. In contrast, significant differences are found between the thin and thick pinning positions of Al on GaAs in general agreement with the metallic approximations of ZMS and ourselves.
Self-aligned TiSi2 for bipolar applications
Authors: Koh Y. , Chien F. , Vora M.
Published: July 2002

A noble self-aligned process has been developed for bipolar very large-scale integrated (VLSI) applications. The structure considered here is a polysilicon emitter system where diodes and resistors are fabricated within the poly-Si layer and integrated into memory cell units with silicide interconnects. The process was designed to eliminate device degradation related to dopant segregation arising from high temperature cycles. The silicide reaction was studied by conventional furnace anneal in H2 and by rapid thermal anneal (RTA) in Ar and N2. The sintering ambient has a pronounced effect on the silicide growth and film texture. A tremendous improvement in process flexibility and reproducibility can be attained by using N2, which drastically retards the silicide growth. Auger electron spectroscopy (AES) and chemical data suggested that the Ti–N2 interaction is of physical nature. The dependence of TiSi2/poly-Si contact resistance on the poly-Si doping concentration was measured for As and B doses of 1.0×1014–1.5×1016/cm2. Dopant redistribution during RTA and its effect on the contact resistance were investigated. A model is proposed to explain the observed variation of contact resistance with short time anneal cycles.
Refractory metal silicides for self-aligned gate modulation doped n+-(Al,Ga)As/GaAs field-effect transistor integrated circuits
Authors: Cirillo N. C. , Chung H. K. , Vold P. J. , Hibbs-Brenner M. K. , Fraasch A. M.
Published: July 2002

A refractory metal silicide process has been developed for the fabrication of self-aligned gate (Al,Ga)As/GaAs FET’s (MODFET’s). Completely planar, self-aligned gate by ion implantation MODFET’s have been fabricated and have demonstrated typical transconductances of 180–200 mS/mm at room temperature and over 300 mS/mm at 77 K. Self-aligned gate ring oscillator test circuits have demonstrated gate propagation delays as low as 17.6 ps/gate at 2.65 mW/gate at room temperature.
Deep level characterization of AlGaAs and selectively doped N-AlGaAs/GaAs heterojunctions
Authors: Ohno H. , Akatsu Y. , Hashizume T. , Hasegawa H. , Sano N. , Kato H. , Nakayama M.
Published: July 2002

Deep level characterization of Si-doped AlGaAs layers and the interface of selectively doped N-AlGaAs/GaAs heterojunctions grown by MBE is reported. Three electron traps have been detected by DLTS in AlGaAs layers and in N-AlGaAs/GaAs heterostructures. Two of them are the main dominant levels in the bulk of Si-doped AlGaAs, which are identified as the well known DX centers. The remaining one shows a peak in concentration near the AlGaAs side of the heterojunction interface in the N-AlGaAs/GaAs structure and is identified as one of the DX related levels. The effect of these levels on the mobility of electron gas at the N-AlGaAs/GaAs heterojunction is investigated.
Vacancy buckling model for the (111) surface of III–V compound semiconductors
Authors: Tong S. Y. , Xu G. , Hu W. Y. , Puga M. W.
Published: July 2002

Results comparing low-energy electron diffraction show that the (2×2) GaAs (111) and GaP (111) surfaces can both be explained by the vacancy buckling model. In this model, a surface group III atom is missing. This allows dangling bonds on the remaining groups III and V atoms to rehybridize. We also compare the LEED results with those of other spectroscopies and with bond lengths found on GaAs (110).
High pressure thermal oxide/InP interface
Authors: Wilmsen C. W. , Geib K. M. , Gann R. , Costello J. , Hryckowian G. , Zeto R. J.
Published: July 2002

The growth of thermal oxides in high pressure dry oxygen has been investigated and compared with oxides grown at 1 atm. The outer layers of the high and low pressure oxides are almost identical but the interfaces are significantly different. The 1 atm oxide interface contains InPO4, In2O3, and elemental P. The high pressure oxide interfaces contain InPO4, In2O3, and P2O5. This suggests that the high pressure causes O2 to diffuse to the interface where it reacts with the P to form P2O5.
Very thin films of Mn, Ag, and Ag–Mn epitaxially deposited on Ru
Authors: Heinrich B. , Liu C. , Arrott A.S.
Published: July 2002

Mn, Ag, and Ag–Mn alloys have been deposited on 001 Ru in an MBE system for the study of the epitaxy of the first few layers when the lattice constants have large mismatches. A new phase of Mn metal is reported. XPS studies of the splitting of the 3s peak of Mn is essentially the same in various metallic environments. If this splitting reflects the 3d–3s exchange interactions, it appears that Mn metal has 5 μβ per atom on the time scale of XPS measurements.
Light scattering studies of semiconductor heterostructures
Authors: Abstreiter G.
Published: July 2002

Resonant inelastic light scattering experiments have been used extensively for the investigation and characterization of semiconductor heterostructures and superlattices. Allowed phonon Raman scattering acts as a nondestructive tool with high spatial resolution to get information on composition, surface orientation, structure, and strain of thin grown layers. As an example we discuss the growth of Ge on (110)GaAs. Forbidden LO-phonon scattering in polar semiconductors is used to measure barrier heights at surfaces or interfaces. This method has also been applied to study band bending at internal surfaces. Resonant electronic light scattering measures directly the elementary excitations of free carriers which may exist in semiconductor heterostructures and superlattices. The 2D nature of the carriers is demonstrated by the separation of inter- and intrasubband excitations.
High resolution, low-voltage probes from a field emission source close to the target plane
Authors: McCord M. A. , Pease R. F. W.
Published: July 2002

In conventional electron beam systems the minimum value of beam diameter and the maximum value of beam current is set by lens aberrations, beam brightness, and by space charge interaction over many centimeters. The limits are more serious as the beam voltage (V0) is reduced. The scanning tunneling microscope (STM) represents a drastic change in electron beam configuration in that the path length is of the same order as the beam radius. We have modeled a modified STM configuration as a field emitting spherical electrode close to the target plane for values of accelerating potential (V0) in the range 50–1000 V. For a given value of V0 and maximum field E0 there are corresponding optimum values of sphere radius R and sphere-to-plane separation S. It appears that it should be possible to confine a beam of 100 V electrons to a radius of 0.02 μm with a current limited only by practical effects at the target or plane.
Beam current stability from localized emission sites in a field ion source
Authors: Schwoebel P. R. , Hanson G. R.
Published: July 2002

The production of stable ion beam currents using localized, high brightness ion emission from a gas fed, field ion source depends upon the stability of the field emitter surface in the region of the ionization. Research has focused primarily on developing a means of generating a single microstructure on the emitter surface which locally enhances the electrostatic field and thereby serves as an ion beam source. The relative ease of processing and the reliability of such a technique to contour the emitter surface are also factors determining the usefulness of the ion source which is to be used in high resolution microprobe systems. A procedure involving field emission through hydrogen films has been found whereby such a single ion, or electron, emission structure can be formed in situ on 〈110〉 oriented tungsten field emitters. These sites are capable of producing at least 10 to 15 nA beams of H+2 in half angle apertures of 16 mrad. Because the basic physical process involved in the field ionization of H2 is known to yield energy spreads of 1 eV (FWHM), good ion-optical properties are inherently available. This technique is practical in that one may readily and reproducibly localize the emission, but it remains to address the question of whether or not the localized emission structures provide stable beam currents for extended periods of time. Field ion micrographs of these sites indicate that they are protruberances 200 Å in diameter with field enhancement factors of 1.5. The current from these relatively large structures is not affected by surface rearrangement on the atomic scale caused by field induced chemical reactions or molecular contamination. The ability of these sites to provide a stable ion current then depends solely on the structural integrity of the protruberance. As ion bombardment is a factor in microboss growth, the first few surface layers of the field emitter and the microboss itself are radiation damaged tungsten and hence subject to electromechanical detachment. Heating the embossed field emitter to 800–1100 K allows greater ion currents to be drawn from the microboss before detachment occurs. However, these investigations indicate that to provide long term ion current stability a complete anneal (1100 K) of the embossed field emitter, most likely in the presence of an electric field such that the emitter is the anode, thereby holding the microboss in place and simultaneously halting the ion bombardment, is required. The fundamental field ionization mechanism generates ion currents stable to within 0.1% indicating the stability achievable after recrystallization of the surface.
A synchrotron radiation x-ray lithography beam line of novel design
Authors: Cerrina F. , Guckel H. , Wiley J. D. , Taylor J. W.
Published: July 2002

The new synchrotron radiation x-ray lithography facility of the University of Wisconsin is presented and discussed in detail. The facility will make use of the electron storage ring Aladdin, at the Univeristy of Wisconsin Synchrotron Radiation Center. The optical design of the beam line allows large field exposures (5×5 cm2) and a tunable bandpass spectral distribution in the range 300–5000 eV. This is achieved by a suitable combination of mirrors for the low-pass part of the filter and of absorption materials for the high-pass filters. Radiation intensity is such to allow exposures of the order of 10 s for PMMA with the beam line operated at the widest setting. The expected power and spectral distribution uniformity at the wafer is better than 2%.
Excimer laser exposure of Ag2Se/GeSe2: High contrast effects
Authors: Polasko K. J. , Pease R. F. W. , Marinero E. E. , Cagan M. R.
Published: July 2002

The use of an excimer laser for exposing the inorganic resist system Ag2Se/GeSe2 was recently reported (Ref. 1). One of the startling findings of that work was the dramatic (60-fold) decrease in the required dose as the pulse energy was increased; the required dose can be as low as 5 mJ/cm2. One of the questions arising out of that work was whether the high contrast and resolution of this resist system could be maintained under this form of exposure; the work reported in this paper indicates that these desirable quantities are indeed maintained. The value of contrast measured exceeded 10 (i.e., extremely high). By way of demonstrating this high value we exposed, using a KrF excimer laser operating at 249 nm, a film of Ag2Se/GeSe2 in the proximity printing mode with a Cr-on-quartz mask and observed the resulting Fresnel fringes at feature edges. Fringes with a half-period of 0.25 μm and aerial modulation of only 10% were resolved, thus indicating that even under pulsed laser beam exposure this material enjoys very desirable imaging properties both in terms of contrast and resolution. Another aspect which must be considered before the material can be regarded as practical for IC fabrication is that of possible contamination of the workpiece by the resist components—particularly silver. Experiments are currently underway involving both C–V measurements and Rutherford backscattering to determine the extent and the effect of such contaminants; preliminary results suggest that there is no significant contamination.
A water soluble contrast enhancement layer
Authors: Halle L. F.
Published: July 2002

Work on a contrast enhanced photolithographic technique for use in optical microlithography is presented. This method consists of a two layer process. The bottom layer is a conventional positive photoresist. The top layer, or contrast enhancement layer, contains a dye which bleaches at the wavelength of the optical exposure apparatus. This results in a reduction of the contrast threshold of the photolithographic system, leading to an increase in the maximum resolvable spatial frequency. The photobleachable dye used in these experiments is diphenylamine-p-diazonium sulphate. It is put in an aqueous solution of polyvinyl alcohol, which is then spin coated on top of the photoresist. This coating is removed after exposure either by rinsing it off in water before developing the photoresist, or in the developer solution itself. Details of this system as well as experimental results obtained with it are discussed.
Range of boron ions in polymers: A SIMS study
Authors: Tennant D. M. , Dayem A. H. , Howard R. E. , Westerwick E. H.
Published: July 2002

Polymers are often used as ion implantation masks for semiconductor processing, but there is a wide (nearly an order of magnitude) disagreement among calculated values that appear in the literature on the ranges of light ions in these materials. Since shrinking device geometries require reduced mask thicknesses to maintain high resolution, accurate knowledge of ion ranges is important. Secondary ion mass spectroscopy (SIMS) has the sensitivity to determine profiles of implanted ions in many materials, but direct measurements on insulators is difficult because of charging effects. We have developed a technique to measure these profiles using variable polymer thicknesses and subsequent SIMS measurements in the underlying Si substrate. An analysis of the resulting SIMS profiles allow measurement of the projected range and standard deviation of the distribution as a function of energy. The range parameters for boron in two polymers are reported and compared with published calculations as well as with experimental values determined from indirect techniques.
EBS-5: A vector scan electron-beam lithography system for research applications
Authors: Riemenschneider P. , Bui Q. , Grohs A. , Jenzen C. , Landmeier P. , Morgan D. , Cumming D. , Purvis M.
Published: July 2002

EBS-5 is a vector scan electron beam lithography system for research and development which evolved from the EBS-4 system developed by Hughes Research Laboratories in 1977–1980. The EBS-5 system features higher throughput, improved diagnostics, and more user friendly software. The computer architecture of EBS-5 consists of a Micro VAX computer and a distributed microprocessor control system, which achieves continuous writing speeds of 13 MHz. A deflection amplifier has been developed which achieves a rise time of 80 ns. The ratio of noise and drift currents to the signal current is lower than 1×10−5 in both the deflection amplifier and the lens supplies to ensure the reproducible exposure of submicron patterns. Extensive software was developed to support the layout and fracturing of pattern data.