bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and optical properties of GaAsSb quantum wells for 1.3 μm VCSELs
Authors: Cunningham J. E. , Dinu M. , Shah J. , Quochi F. , Kilper D. , Jan W. Y. , Williams M. D. , Mills A. , Henderson W. E.
Published: July 2002

We report compositional dependencies of the 2d–3d growth mode transition for GaAsSb on GaAs. In addition, Sb incorporation, desorption, and segregation versus growth temperature and V/III ratio are measured by secondary-ion-mass spectroscopy. Photoluminescence investigations of Sb compositional dependence of GaAsSb quantum wells and confinement in heterojunctions are reported.
Atomic force microscopy investigation ofa-C:H films prepared by plasma enhanced chemical vapor deposition for inertial confinement fusion experiments
Authors: Dumay B. , Finot E. , Theobald M. , Legaie O. , Baclet P. , Durand J. , Goudonnet J. P.
Published: July 2002

This article deals with the development of a radio frequency plasma enhanced chemical vapor deposition thick film (175 μm thickness) derived from aliphatic chains, trans-2-butene, monomer mixed with hydrogen and various noble gases (helium, argon, and krypton). The main purpose was to engineer an amorphous hydrocarbon film (a-C:H) with low surface roughness of less than 20 nm, designed for use on an “ablator” in a new “MégaJoule” laser facility. Morphology and roughness were characterized by atomic force microscopy. An improvement of 70% is obtained by adding a bias on the substrate.
Coalescence inhibition in nanosized titania films and related effects on chemoresistive properties towards ethanol
Authors: Ferroni M. , Guidi V. , Martinelli G. , Roncarati G. , Comini E. , Sberveglieri G. , Vomiero A. , Della Mea G.
Published: July 2002

Achievement of nanosized thin films of titania was achieved by radio-frequency sputtering of a Ti(97%)–Mo(3%) target. Deposition was performed under inert or reactive atmosphere followed by annealing at temperatures up to 800 °C. The resulting layers became more stoichiometric as annealing temperature increased. The small part of Mo proved useful to prevent exaggerated grain coalescence. Reactive sputtering was more effective than inert deposition to achieve a nanograined layer with lowest size (31 nm). Mo segregated at the surface and partially sublimated as MoO3. The layers became n-doped semiconductors and were tested as chemoresistive gas sensors. Good capability to sense ethanol was determined within a range useful for applications. A model was proposed to explain the response to ethanol.
Investigation of polymethylmethacrylate resist residues using photoelectron microscopy
Authors: Maximov I. , Zakharov A. A. , Holmqvist T. , Montelius L. , Lindau I.
Published: July 2002

Quantitative photoelectron spectromicroscopy has been used to study polymethylmethacrylate (PMMA) resist residues on SiO2 surfaces after electron beam exposure and resist development. It was found that correctly exposed and developed PMMA leaves residues with an average thickness of about 1 nm. Higher exposure doses result in the decrease in film thickness, but with residues of about 0.5 nm. The technique can be applied as a powerful tool for surface and interface quality control in technology of electronic devices.
Modeling of the static and dynamic behavior of hydrogenated amorphous silicon thin-film transistors
Authors: Servati P. , Nathan A.
Published: July 2002

This article reports on physically based models for hydrogenated amorphous silicon (a-Si:H) inverted staggered thin-film transistors (TFT), which accurately predict both the static and dynamic characteristics of the TFT. The model is implemented in VerilogA hardware description language, which comes as a standard feature in most circuit simulation environments. The static model includes both forward and reverse regimes of operation. The model for leakage current takes into account the physical mechanisms responsible for the source of the reverse current, viz., the formation of the conducting channels at the back and front a-Si:H/a-SiNx:H interfaces and their relative dominance at different bias conditions. The dynamic model includes the different charge components associated with the tail states, deep states, interfaces, and traps and their associated time constants. Good agreement between modeling and experimental results is obtained.
Langmuir probe measurements in an inductively coupled plasma: Electron energy distribution functions in polymerizing fluorocarbon gases used for selective etching of SiO2
Authors: Gaboriau Freddy , Peignon Marie-Claude , Cartry Gilles , Rolland Laetitia , Eon David , Cardinaud Christophe , Turban Guy
Published: July 2002

We are interested in the silicon oxide deep etching by inductively coupled fluorocarbon plasmas for integrated optical applications. The understanding and the improvement of this process requires to know at least the electrical characteristics of the plasma (electron and ion densities, electronic temperature,…). Up to now, very few measurements in these plasmas have been published because of problems encountered when using Langmuir probes in depositing environments. In the present article, we report problems we met and solutions we brought, and then present electron energy distribution function (EEDF) measurements in very polymerizing gases such as CHF3 and CHF3/CH4 mixtures. Experiments have been performed over a wide range of experimental conditions, from 3 to 50 mTorr and from 200 to 2000 W inductive power. The shape of the EEDF and the evolution of the plasma electrical characteristics with experimental conditions are discussed. Finally, we point out the presence of a large negative ion fraction when increasing the pressure, particularly in pure CHF3 plasmas.
Ion−beam etching
Authors: Glöersen Per G.
Published: July 2002

In the course of developing techniques for ion−beam etching of solid bulk materials and thin deposited films, we undertook a systematic investigation of etch rates of several materials and the dependence of etch rate on beam parameters and beam angle of incidence. Results of these measurements are presented. Under certain conditions, cones formed on the surface being etched. An explanation for this instability phenomenon is given. In most practical applications of ion−beam etching, suitable masking techniques are necessary. We have developed procedures for photoresist masking for two classes of etching: (a) high−resolution, shallow−depth etching (typical dimension ∠1 μ); (b) low−resolution, very deep etching (typical dimension ∠50 μ). The methods used will be discussed, and in particular we will consider the influence of redeposition of sputtered material and the profile of the photoresist on the final−etched wall shape.
Review of sticking coefficients and sorption capacities of gases on titanium films
Authors: Harra D. J.
Published: July 2002

The pumping speed of a titanium sublimation pump or a sputter-ion pump using titanium cathodes is a function of many variables including the sticking coefficient and sorption capacity of gases on titanium films. Consequently, in vacuum systems employing such pumping mechanisms, the sticking coefficients and sorption capacities play a major role in determining the partial pressures at any given time of various gas species. However, the sticking coefficient data required to determine the partial pressure behavior to be expected is not conveniently available. The literature on this subject has been reviewed and the data for H2, D2, H2O, CO, N2, O2, and CO2 have been summarized. These results are presented and information related to the sorption mechanisms is discussed.
Bilevel high resolution photolithographic technique for use with wafers with stepped and/or reflecting surfaces
Authors: Tai K. L. , Sinclair W. R. , Vadimsky R. G. , Moran J. M. , Rand M. J.
Published: July 2002

We have investigated the feasibility of a two-level scheme to obtain steep profile, thick resist, and high resolution patterns over stepped and/or reflecting surfaces. The two-level scheme provides an alternative to a recently developed three-level approach. The negative photosensitive inorganic resist Ag2Se/GeSe is formed on top of a thick polymer layer, which is not photo-sensitive. High resolution patterns are produced in a 0.3 μm thick, pinhole-free, inorganic resist layer using a commercial projection printer. The pattern is transferred to the polymer layer by oxygen reactive ion etching using the inorganic resist pattern as the mask against etching. Vertical-walled 0.8 μm lines and spaces are obtained in a 2.5-μm-thick polymer. The high absorbance of light by the Se–Ge layer (2.5×105cm−1 at 400 nm) eliminates standing wave effects associated with reflection from the surface.
Resputtering effects in Ba(Pb, Bi)O3 perovskites
Authors: Gilbert L. R. , Messier R. , Krishnaswamy S. V.
Published: July 2002

A resputtering effect in Ba(Pb, Bi)O3 has been found to vary from complete film and partial substrate erosion to slightly altered film surface microstructure and bulk composition. It is strongly dependent on the sputtering conditions; only the films prepared at the higher gas pressures (≳200 mTorr) show no resputtering, apparently due to gas phase interactions. The most striking result, other than the obvious surface erosion, is the Ba deficiency, ranging from 10 to 70 at. %, that is directly related to the degree of resputtering. Similar results have been seen for other alkaline earth perovskites.
Discharge characteristics for magnetron sputtering of Al in Ar and Ar/O2 mixtures
Authors: Maniv S. , Westwood W. D.
Published: July 2002

An Al target has been sputtered in a planar magnetron system using argon and argon–oxygen mixtures at pressures from 0.1 to 2 Pa. The characteristics of both dc and rf discharges have been studied. In the dc case, the current is given by a relation of the form KVn where V is the applied voltage and K and n are pressure-dependent parameters. Values of n up to 9 were obtained at the higher pressures but n decreased at lower pressures. For the rf discharge, the target self-bias voltage, Vsb, at a given power decreased with decreasing pressure and was related to the average rf power by a relationship of the form CVsb/(Vsb−V) where V was approximately 1000 V and C dereased from 900 to 500 W with increasing argon pressure. The deposition rate of Al increased linearly with average dc and rf power and there was good agreement between the values for the same power; the rate was 0.93 μm/min at the maximum power of 2.5 kW. When sufficient oxygen was added, the target surface was oxidized and the deposition rate of Al2O3 was only 5% of the Al rate. This is about half the ration predicted for sputtering yields and can be accounted for by a secondary electron emission coefficient, due to ion bombardment, of between 0.4 and 1.2. This is much higher than the value for Al and accounts for a sharp decrease in Vsb when oxide forms on the target surface. At an average power of 400 W at a pressure of 1 Pa, Vsb is 380 V for the Al case and 190 V for the oxidized target.
Analysis of electrical and optical properties of insulating film–GaAs interfaces using MESFET-type structures
Authors: Ozeki M. , Kodama K. , Takikawa M. , Shibatomi A.
Published: July 2002

The electrical and optical measurements of low-frequency characteristics for the GaAs MESFET structures with long gate width were found to be an effective tool for the studies of interface states between insulating films and GaAs. The surface leakage current through the interface layer plays an important role in the frequency dependence of the transconductance and the gate admittance. An equivalent circuit which quantitatively explains the experimental results is proposed. Using the MESFET structure overcoated with insulating films (SiO2, Si3N4, and AlN), electrical and optical properties of the interface between these insulating films and GaAs were studied and it was found that these films have characteristic activation energies of 0.62, 0.44, and 0.27 eV, respectively.
AES study on the chemical composition of ferroelectric BaTiO3 thin films rf sputter-deposited on silicon
Authors: Dharmadhikari Vineet S. , Grannemann W. W.
Published: July 2002

AES depth profiling data are presented for thin films of BaTiO3 deposited on silicon by rf sputtering. By profiling the sputtered BaTiO3/silicon structures, it was possible to study the chemical composition and the interface characteristics of thin films deposited on silicon at different substrate temperatures. All the films showed that external surface layers were present, up to a few tens of angstroms thick, the chemical composition of which differed from that of the main layer. The main layer had stable composition, whereas the intermediate film–substrate interface consisted of reduced TiO2−x oxides. The thickness of this intermediate layer was a function of substrate temperature. All the films showed an excess of barium at the interface. These results are important in the context of ferroelectric phenomena observed in BaTiO3 thin films.
Surface oxidation of molten soft solder: An Auger study
Authors: de Kluizenaar E. E.
Published: July 2002

The composition of oxide films, formed on stagnant, molten soft solder has been studied. The influence of oxidation time and of solder composition on the oxide films was measured. On clean soft solder SnPb60-40 a complex oxide film was formed, consisting of a thin outer layer of SnO2, a layer of SnO mixed with metallic lead, and a transition layer to the underlying solder metal. The same type of oxide layer was formed on solder with copper or with nickel. On soft solder contaminated with aluminium, zinc, or phosphorus the contaminants were preferentially oxidized, resulting in an aluminium oxide film, a zinc oxide film, and a mixed phosphorus oxide–tin oxide film, respectively.
Minority carrier lifetime in LPE Hg1−x Cdx Te
Authors: Bajaj J. , Shin S. H. , Pasko J. G. , Khoshnevisan M.
Published: July 2002

We report measurements on the minority carrier lifetime in n-type and p-type LPE Hg1−xCdxTe/CdTe with x∼0.2. For n-HgCdTe, we have measured lifetimes of 4–7 μs at 77 K for passivated samples. These values are comparable to the results reported for bulk material. For p-HgCdTe epilayers with thickness ≤20 μm, the measured lifetime is 15–20 ns at 77 K and is suspected to be limited by surface recombination. With excitation through the CdTe substrate, we have attempted to measure the bulk lifetime; preliminary results are reported.
Momentum-resolved bremsstrahlung spectroscopy with a tunable photon detector
Authors: Fauster T. , Himpsel F. J.
Published: July 2002

The first momentum-resolved bremsstrahlung (or inverse photoemission) experiments using a tunable light detector in the energy range from 10 to 40 eV are reported. The experimental setup comprises a Pierce-type electron gun, a Seya monochromator, and a position-sensitive channel plate detector. An energy resolution of 0.3 eV at 20 eV has been achieved and the momentum resolution is 0.1 Å−1. The apparatus has been used to determine the energy band dispersion of unoccupied minority spin 3d states in Co. A ferromagnetic exchange splitting of 0.93±0.1 eV between the unoccupied spin-down and occupied spin-up states (measured with photoemission) is derived. Another application is the measurement of unoccupied adsorbate levels of CO on Ni(111). Detecting the polarization of the photons (using the polarization-dependent reflectivity of the monochromator) enables us to identify the symmetry character of the adsorbate orbitals. For a Si(111)–(7×7) surface, empty surface states are found in the band gap.
Relation between the RF discharge parameters and plasma etch rates, selectivity, and anisotropy
Authors: Zarowin C. B.
Published: July 2002

By extending earlier ideas and introducing new ones in this paper, we relate observable rf discharge parameters to the plasma etch characteristics of rate, selectivity, and anisotropy. The ion energy transport ‘‘ellipsoid’’ generated by the electric field across the plasma sheath is shown to induce anisotropic etch reactions and, under certain circumstances, to ‘‘enhance’’ the intrinsic chemical etch selectivity. The plasma sheath electric field is shown to be determined by observable rf discharge parameters. The rf discharge is reduced to an equivalent circuit, which relates the time averaged plasma body and sheath electric fields to the rf discharge parameters of plasma geometry, current or power and discharge excitation frequency. We find two regimes of excitation frequency, for otherwise identical conditions, generating much larger sheath electric fields below than above the ion plasma frequency (∼1 MHz). Fixing the plasma geometry and etch gas chemical composition is identified as central to obtaining simply behaved and reproducible etch characteristics. At comparable etch anisotropy, the only practical distinction between the etch characteristics of ‘‘high’’ pressure ‘‘plasma etching’’ and ‘‘low’’ pressure ‘‘reactive ion etching,’’ is that the former is capable of significantly higher etch rates and selectivities than the latter.
Explosive welding of Ti–6Al–4V to mild-steel substrates
Authors: Inal O. T. , Szecket A. , Vigueras D. J. , Pak H-r.
Published: July 2002

Ti–6Al–4V sheets were explosively welded to mild steel base plates with an attachment zone that approximates a straight, waveless interface devoid of vorticity and thus the attendant formation of the Fe–Ti intermetallics. The welded interface is seen to be harder than either of the bi-alloys joined and the attachment strength, measured in terms of shear stress required for fracture of the weld zone, is seen to be stronger than the weaker of the materials (mild steel) joined. Stress relief treatments given at 525 °C is seen to induce ductility to the brittle interface without the introduction of recrystallization and/or the formation of Fe–Ti intermetallics at the weld zone. Approximate energy calculations indicate that explosively induced welds that comprise a nearly straight interface make efficient use of the detonation introduced energy, and thus the plastic straining of the alloys adjacent to the weld are minimal as confirmed by the microhardness and tensile test data obtained on the as-welded and stress relieved samples.
Ion beam mixing of Au–Ge and Au–Ge–Ni deposited on GaAs
Authors: Bhattacharya R. S. , Rai A. K. , Ezis A. , Rashid M. H. , Pronko P. P.
Published: July 2002

We have investigated the feasibility of applying ion beam mixing techniques to the fabrication of Ohmic contacts in GaAs. The approach has been to deposit alternating layers of Au, Ge and Au, Ge, Ni with e-beam evaporation on GaAs and then to irradiate these layers with energetic Si+ ions. Mixing has been studied by employing Rutherford backscattering, Auger electron spectroscopy, and cross-sectional transmission electron microscopy (X-TEM). Differing amounts of mixing have been achieved for Au–Ge layers by using 125 keV Si+ at doses in the range of 1×1015 to 1×1016 cm−2. The kinetics of mixing is greatly reduced in the case of Au–Ge–Ni layers. Ni layers in between Au–Ge layers seem to act as inhibitors for ion beam mixing. It has been observed by X-TEM that a band of dislocation loops is produced in GaAs at a depth of about 600 Å from the interface although computer simulation of range and damage indicate shorter penetration distances. Even at an incident ion energy low enough so that no direct penetration across the interface takes place, dislocation loops are found to be present. Contacts in the presence of a damaged region at the interface showed non-Ohmic behavior. However, selected Au–Ge contacts fabricated with low energy and low dose irradiation showed Ohmic behavior with resistivity ∼10−4 Ω cm2 after annealing at 340 °C for 5 min. Ion beam mixed metallizations showed remarkable improvement in surface morphology after annealing compared to conventionally alloyed contacts.
Diffusion of nickel through titanium nitride films
Authors: Nowak W. B. , Keukelaar R. , Wang W. , Nyaiesh A. R.
Published: July 2002

TiN is among the candidates for thin film diffusion barriers on integrated circuit contacts. We have deposited titanium nitride (approximately TiN) and TiN+Sm films onto Ni substrates near room temperature by ion plating. Ti was e-beam evaporated in a chamber containing about 2.8 Pa (21 mTorr) of N2 in the vicinity of the substrate. A plasma was excited between the substrate and a gas source-tube near the substrate by a combination of electrons from the e-beam (or backscattered from the Ti melt) and from an electric field generated by a constant current power supply (usually set at 100 mA) connected with negative polarity to the substrate. Deposition rates were 0.5 μm/min and the film thicknesses were 2 μm. The films are crystalline, slightly burnt gold in color, and are less dense and have an order of magnitude higher electrical resistivity than TiN produced by CVD methods. The addition of at least 12 at. % Sm produced amorphous films. The diffusion of Ni through these films was measured by energy dispersive analysis in a SEM. The amorphous material showed substantially lower diffusivities. Values of D0 and Q, in the equation D=D0 exp (−Q/RT), were determined to be 0.82×10−7 cm2/s and 29 kcal/mol for crystalline TiN, and 0.56 cm2/s and 67.3 kcal/mol for amorphous TiN+12 at. % Sm films. Because of film variation in structure and composition, these values vary. However, there is still a large improvement in the diffusion barrier property of TiN films by using amorphous films containing Sm. Ni diffuses very slowly into amorphous TiN+Sm at temperatures up to 655 °C. One must increase the temperature to 765 °C in order to observe diffusion rates comparable to crystalline TiN at 590 °C.
X-ray photoelectron spectroscopy studies of thin films of TiNx having different annealing histories
Authors: Kaufherr Nurit , Lichtman David
Published: July 2002

TiN thin films prepared by chemical vapor deposition (CVD) and annealed in different atmospheres were studied by means of x-ray photoelectron spectroscopy in conjunction with Ar ion bombardment. The films contained a high level of oxygen, and an intimate mixture of TiN and titanium oxide was postulated, based on the binding energy (BE) values of the Ti 2p core level photoelectrons. This was further supported by the independent effect of Ar ion bombardment on the two components and the constant nitrogen concentration throughout the film bulk. At this stage it seems unjustified to correlate differences in the Ti 2p spectra of the unsputtered samples with their annealing atmosphere histories, mainly because of the high oxygen content in all the films.
The spinning rotor gauge
Authors: Fremerey J. K.
Published: July 2002

The determination of pressure in a high vacuum from the gaseous drag of a freely rotating sphere was already proposed in 1946 by Beams and co-workers. On the basis of novel techniques, this method was developed from its original bulky and delicate experimental state to a practicable, compact instrument for widespread laboratory and industrial use. The present paper gives a detailed description of the gauge head functions, and of the method of evaluation of the rotor deceleration rate. The predictability of the gaseous drag is discussed in view of absolute pressure gauging. The feasibility of extending the measurement range up to atmospheric pressure is demonstrated on the basis of experimental results.
Coevaporation with a rate control system based on a quadrupole mass spectrometer
Authors: Stolt Lars , Hedström Jonas , Sigurd Dag
Published: July 2002

In a deposition system designed for coevaporation, the control of the individual evaporation rates is the crucial point. This paper describes a deposition system where the evaporation rates of three resistively heated elemental sources are controlled by utilizing a quadrupole mass spectrometer. The rate monitoring and control system is characterized for the case of CuInSe2 deposition, where it is shown that a precise control of the properties of the deposited film can be achieved. The results reported are of general interest, and neither restricted to three elements nor to the specific elements used in the case studied.
An historic overview of inertial confinement fusion: What have we learned?
Authors: Glass Alexander J.
Published: July 2002

Although laser fusion has been the subject of research since the early 1960s, it has only been intensively studied for about 14 years. During that time, substantive advances have been made in our understanding of the complex physics of laser-heated plasmas, in the development of sophisticated diagnostic instrumentation, and in the technology of fusion targets and inertial fusion drivers. These advances will be reviewed. Of equal importance are the lessons learned in the economic and political arenas. These lessons may be of greater significance for scientific endeavors in other fields of research. The economic and political issues surrounding inertial fusion research will be discussed. Possible future directions for inertial fusion development will be presented.
M
2,3 electron energy loss studies of Ni(100) at small scattering angles
Authors: Tyliszczak T. , Hitchcock A. P.
Published: July 2002

Reflection electron energy loss spectra of a Ni (100) surface in the region of M2,3 ionization have been recorded at small scattering angles. Extended fine structure in the continuum (EXELFS) is analyzed to yield an estimate of the nearest neighbor distance in the surface region. These results are compared to previous surface M2,3 EXELFS of polycrystalline Ni recorded with lower energy and angle resolution at large scattering angles.  When calculated M2,3 phase shifts are used the derived spacings in both the large and small angle data are about 0.3 Å less than the value for the Ni–Ni spacing in bulk Ni. This indicates that the deviation results from errors in the phase shift rather than nondipole contributions in the large scattering angle data.
Understanding and controlling heterojunction band discontinuities
Authors: Niles D. W. , Colavita E. , Margaritondo G. , Perfetti P. , Quaresima C. , Capozi M.
Published: July 2002

We discuss two recent results on the microscopic nature and control of the band lineup at semiconductor–semiconductor interfaces. First, we identified a correlation between measured heterojunction band discontinuities and Schottky barrier heights of the corresponding semiconductors, as predicted by several theoretical models. Second, we found that ultrathin metal intralayers modify the band lineup of polar interfaces by several tenths of an electron volt. At least in principle, this degree of freedom can be exploited to tailor heterojunction devices.
A new ultrahigh vacuum combination pump
Authors: Audi M. , Dolcino L. , Doni F. , Ferrario B.
Published: July 2002

The number of applications where low ultimate pressure and clean residual environment are required is greatly increasing. Sputter-ion pumps are widely used in such applications, where all species of gases (mainly getterable gases) have to be pumped. Nonevaporable getters, especially the recently developed low-temperature activatable alloy of the Zr–V–Fe type, have gained interest for pumping getterable gases (especially hydrogen) also in ultrahigh vacuum (UHV) environment. An integration of these two pumping means has been studied. A new combined pump results having a simple structure with a suitably shaped getter coated strip incorporated in the body of the ion pump, without changes in geometry or increase of dimensions. The necessary activation and regeneration of the getter are made during bakeout of the ion pump, performed at 300–350 °C for some hours. Performance obtained by this new UHV combination pump are reported and discussed. At low pressures and after regenerative bakeout, this combination pump almost doubles the pumping speed of the ion pump for getterable gases. Very low and clean residual pressures (10−12 mbar region) are reached with a more constant pumping speed.
Transmission electron microscopy studies of brown and golden titanium nitride thin films as diffusion barriers in very large scale integrated circuits
Authors: Kumar N. , McGinn J. T. , Pourrezaei K. , Lee B. , Douglas E. C.
Published: July 2002

The usefulness of reactively sputtered TiN as a diffusion barrier in the AlTiN/Ti/Si metallization scheme in very large scale integration was reported in a previous publication. Two types of TiN thin films were studied in these experiments. Depending on the applied substrate bias voltage, the resulting TiN films can have different properties. Under no-bias conditions, dark brown colored films (called B films) with low density (3.22 g/cm3), high electrical resistivity (∼400 μΩ cm), and 5%–8% O2 are obtained. A+ -75 V dc substrate bias, bright golden colored films (called G films) with high density (∼5.0 g/cm3), low resistivity (∼20 μΩ cm), and negligible O2 are obtained. Even though the B films contain more O2, the G films were found to be better diffusion barriers for silicon. To investigate the effect of film microstructure on the diffusion barriers, cross-sectional and planar transmission electron microscopy samples were used. Both, brown and golden, types of films have columnar grain structure with approximately the same size (∼400–500 Å), contrary to fine-grained structure observed for G films by some other groups. The columns in the G films increase in size with an increase in distance from the TiN/Si interface, while the grain size remains almost constant in the B films. The intergrain structure also differs considerably; the grains in G films are very closely packed while they are very loosely bound in the B films. The intergrain voids in the B films can act as an easy path for silicon diffusion. Also, these films were studied by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and x-ray diffraction to understand the diffusion mechanisms.
Scanning tunneling microscopy of graphite adsorbed metal species and sliding charge-density wave systems
Authors: Lyding J. W. , Hubacek J. S. , Gammie G. , Skala S. , Brockenbrough R. , Shapley J. R. , Keyes M. P.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to study phosphotungstic acid and rhenium carbonyl cluster complexes adsorbed on graphite. For phosphotungstic acid, cluster formation is observed as well as short-range (4-Å period) and long-range (110-Å period) hexagonal ordering. Acetone spun films of [Et4N]3[Re7C(CO)21] on graphite exhibit two distinct nongraphitic periodicities. One of these is rowlike and associated with an adsorbed acetone monolayer (4-Å period), and the other, which is hexagonal (10-Å period), represents an array of individual metal cluster molecules. In a separate effort, STM has been used to study the sliding charge-density wave (CDW) material NbSe3 in its room-temperature non-CDW state in order to obtain structural information which can be correlated with low-temperature, CDW-state studies. The unit-cell features and quasi-one-dimensional chainlike structure are readily observed.
Photoemission investigation of the Cr/Ag(100) and Cr/Au(100) interfaces
Authors: Hanf M. C. , Haderbache L. , Wetzel P. , Pirri C. , Peruchetti J. C. , Bolmont D. , Gewinner G.
Published: July 2002

Valence-band and core level photoemission measurements are reported for ultrathin Cr deposits (1–10 monolayers) on Ag and Au surfaces. In the submonolayer range, the data reveal magnetic Cr 3d virtual bound states located at 1.15- and 0.75-eV binding energy, respectively. On further Cr dosing the evolution of the conspicuous Au 5d and Ag 4d band features shows that strong deviations from simple layer-by-layer growth must occur for both interfaces formed near 300 K. In particular, alloying takes place at the Cr/Au interface and three-dimensional islands are formed on Ag(100) before completion of the first Cr monolayer. Nevertheless the high initial local magnetic moment (≥4 μB) for Cr in (on) Au(100) and Ag(100) are consistent with recent theoretical work for a Cr(100) monolayer on these substrates.
Effects of Kikuchi scattering on reflection high-energy electron diffraction intensities during molecular-beam epitaxy GaAs growth
Authors: Crook G. E. , Eyink K. G. , Campbell A. C. , Hinson D. R. , Streetman B. G.
Published: July 2002

Intensity profiles along the specular streak of the reflection high-energy electron diffraction (RHEED) pattern observed during GaAs growth by molecular-beam epitaxy (MBE) show intensity peaks from diffuse scattering processes as well as the specular intensity peak. Intensity oscillations from the diffuse scattering peaks vary in phase with the intensity oscillation at the specular position, with the phase variation depending on the incident angle of the electron beam. Calculation of major Kikuchi line escape angles near the [110] azimuth shows that the diffuse scattering peaks observed are at Kikuchi angles. At some incident angles, interference between Kikuchi and specular scattering is found to change the phase of the oscillation observed at the specular position, as reported by other workers. Interference from Kikuchi processes should be more easily avoided when observing along an azimuth a few degrees off of the [110] direction than when observing directly along the [110] direction. Oscillation phase versus escape angle measurements along an azimuth 7° off [110] show that the phase versus angle curve is somewhat less erratic than that measured directly along the [110] direction by other workers. We still find, however, that the oscillation phase observed at the specular position is shifted over much of the angular range, complicating the common interpretation in which RHEED oscillation maxima correspond to the smoothest growth surfaces.
Tritium neutral beams for the Tokamak Fusion Test Reactor
Authors: Grisham L. R. , Dylla H. F. , Williams M. D. , Wright K. , Causey R.
Published: July 2002

The Tokamak Fusion Test Reactor (TFTR) has operated for a number of years with deuterium neutral beam injection as its major source of plasma heating. The final phase of TFTR operation, scheduled for 1991, will use a mixture of deuterium and tritium to achieve approximate energy breakeven, where the fusion power output equals the heating power input. In order to maintain a 50–50 mixture in the hot reacting core of the plasma under these conditions, it will be necessary to use two of the four beamlines to produce tritium neutral beams. This paper will discuss our plans for operation with tritium.
X-ray photoelectron spectroscopy and infrared spectroscopy analysis of pyromellitic dianhydride–oxydianiline polyamide-acid and polyamide-ester imidization
Authors: Buchwalter L. P.
Published: July 2002

Pyromellitic dianhydride–oxydianiline amide-acid (PMDA–ODA–acid) and amide-ester (PMDA–ODA–ester) imidization was studied using x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. The data show that the PMDA–ODA–acid bulk and surface have imidized significantly already after 150 °C exposure, while PMDA–ODA–ester shows no imidization until 230 °C exposure. PMDA–ODA–acid reaches maximum bulk and surface imidization after exposure to 200 °C, while the PMDA–ODA–ester requires 300 °C exposure before maximum imidization is reached. The XPS analysis also shows that the PMDA–ODA–acid has two nitrogen 1s species, one at 400 eV due to imide species and another at 399.3 eV possibly due to isoimide species, while the PMDA–ODA–ester shows only a single nitrogen 1s peak at 400.9 eV due to imide species.
Evaluation of elastic emission machined surfaces by scanning tunneling microscopy
Authors: Mori Yuzo , Yamauchi Kazuto , Endo Katsuyoshi , Ide Takashi , Toyota Hiromichi , Nishizawa Keitaro , Hasegawa Minoru
Published: July 2002

Elastic emission machining (EEM) developed by the authors is one of the atomic size machining methods. Roughness of the finished surface is as small as atomic size. It is also found that finished surfaces attain the perfection in the sense of physical properties to the extent of better than or comparable to chemically etched surfaces. EEM can be considered as a machining method utilizing chemical activities of ultrafine powder particle surfaces, instead of an etchant as in the conventional chemical etching. In this paper, the authors have developed a scanning tunneling microscope(STM) in order to evaluate the surfaces finished by EEM with the resolution of atomic size. STM measurements are carried out for the surfaces finished by EEM and by chemical etching. The result shows the existence of the micro pits with the diameter of 1 nm and the depth of 1 nm on the chemically etched surface. In contrast, neither pits nor projections are detected on the surface finished by EEM and an atomically smoothed surface is found to be established. The difference between the micro structure of the surfaces finished by EEM and by chemical etching is evident.
Electron diffusion length and escape probability measurements for p-type GaAs(100) epitaxies
Authors: Vergara G. , Gómez L. J. , Presa J. , Montojo M. T.
Published: July 2002

According to the two-minima electron diffusion model of Spicer, James, and Moll [W. E. Spicer, Quant. Rep. 9, April (1968); L. W. James and Z. L. Moll, Phys. Rev. 183, 740 (1969)] for near threshold photoemission, minority-carrier diffusion length L and escape probability P for a variety of Beryllium doped GaAs(100) epitaxies grown by molecular beam epitaxy, have been obtained. These epitaxies, before being activated with cesium and oxygen by using the two-stages method described by Stocker and Goldstein [B. J. Stocker, Surf. Sci. 47, 501 (1975); B. Goldstein, ibid. 47, 143 (1975)], were passivated in two different ways. (i) Chemically, with a 5:1:1 H2O:H2O2:H2SO4 solution and (ii) by the deposition of a 700–800 Å thick antimony layer. A better performance of the samples using this last type of passivation is shown. In order to evaluate L and P from the electron diffusion model, it is necessary to know the dispersion relation of the absorption coefficient for each sample. They have been obtained from normal-incidence reflectance measurements by means of a Kramers–Krönig analysis. The electronic diffusion length values obtained ranged from 4.5 to 2.1 μm and the escape probabilities between 8.1% and 20.2% for Be concentrations of 1×1018 and 1×1019 cm−3, respectively.
A review of the geometrical fundamentals of reflection high-energy electron diffraction with application to silicon surfaces
Authors: Mahan John E. , Geib Kent M. , Robinson G. Y. , Long Robert G.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) is an experimentally simple technique, and yet a powerful one for examining the structure of a substrate surface and for monitoring the surface crystal structure and the crystallographic orientation of thin films during their growth. However, it can be difficult to learn to interpret the RHEED patterns of new materials, because a practical and adequately detailed introduction to the technique is not generally available. To address this need, we develop the geometrical principles of RHEED; using the kinematic approximation, we show how a particular point of the sample surface’s reciprocal net gives rise to a diffraction maximum at a particular location on the RHEED viewing screen. We explain the origins of ‘‘reciprocal lattice rods,’’ RHEED streaks, and Laue rings. We show how to calculate the streak spacing, and clarify the basic effect on the RHEED pattern of using a nonzero angle of incidence for the incident beam. Crystalline nets, reciprocal nets, and their RHEED patterns are derived for both (001) and (111) silicon surfaces and are compared to experimentally obtained patterns.
Adhesion studies of metals on fluorocarbon polymer films
Authors: Chang Chin-An , Kim Yong-Kil , Schrott A. G.
Published: July 2002

Adhesion of metal films to several fluorocarbon polymer films is studied for Cu, Cr, Ti, Al, and Au. The polymers include polytetrafluoroethylene (PTFE), fluoroethylenepropylene (FEP), and a copolymer containing a perfluoroalkoxy group (PFA), all deposited on Cr/SiO2 substrates by spin coating. Peel strengths of the metal strips on these polymers are compared and are taken as measures of the metal–polymer adhesion. Among the polymers, FEP gives the highest peel strengths to metals, with PTFE the lowest. Among the metals, Ti gives the highest peel strength for each polymer, followed by Cr, with Cu being the lowest. The peel strengths for Ti on FEP, PFA, and PTFE are 85, 75, and 20 g/mm, respectively. Those for Cu to the polymers are around 5 g/mm or less. The strong adhesion for the metals on both FEP and PFA is attributed to the high concentration of carbon sites with three fluorine neighbors, by considering the electronegativities among the various carbon sites in the polymer chains. Among the metals, some correlation with the electronegativity is seen. Ti shows, in addition, penetration into the polymers, contributing to the adhesion with all three polymers and resulting in shifts in binding energy for the C 1s electrons of the CF2 sites. An enhanced adhesion is also seen using a presputtering treatment of the PTFE films prior to the deposition of metal. The increase in peel strength, however, is smaller than that of the bulk PTFE.
Modeling of inhomogeneous film deposition and target erosion in reactive sputtering
Authors: Kadlec S. , Musil J. , Vyskočil J.
Published: July 2002

Presented is a generalized microphysical model for reactive sputtering, taking into account inhomogeneities of both the target erosion and the deposition of films on condensing surfaces of substrates and chamber walls. The integral quantities, as the total metal ejection rate or the reactive gas consumption, can be treated as if the erosion and deposition were homogeneous but over properly determined effective areas. Conversely, the local quantities, as the target coverage by the compound or the film composition, are strongly influenced by the inhomogeneities. Both chamber wall area Aw and the substrate area As influence the system behavior. An increase of As and/or decrease of Aw leads to higher reactive gas content in films. This effect makes it possible to use a simple flow rate control for a high rate deposition of nearly stoichiometric films, as TiN, in the metallic mode of target operation.
Model of energetic electron transport in magnetron discharges
Authors: Sheridan T. E. , Goeckner M. J. , Goree J.
Published: July 2002

A particle model of energetic electron transport in sputtering magnetron discharges is presented. The model assumes time-independent magnetic and electric fields and supposes that scattering by neutral atoms is the dominant transport mechanism. Without scattering, we find that some orbits are confined indefinitely. Using the differential cross sections for elastic, excitation, and ionization collisions in argon, we perform a Monte Carlo simulation of the electrons emitted by ion bombardment of a planar magnetron cathode to predict the spatial distribution of ionization. We find good agreement with experimental measurements of the radial profile of ion flux to the cathode and of the axial profile of optical emission.
Stress in sputtered Mo thin films: The effect of the discharge voltage
Authors: Vink T. J. , van Zon J. B. A. D.
Published: July 2002

The present study reports on internal stress in planar magnetron sputtered Mo films. Characteristic compressive-to-tensile stress transition curves were measured. The transition pressure is observed to shift to higher values when the discharge power to the cathode is increased. Gas density measurements in the plasma region proved that at least part of the observed shift of the stress curves originates from a localized gas heating effect. At low argon pressures the stress in the Mo films appeared to be a function of the discharge voltage, independent of the discharge power. The discharge voltage is directly linked to the energy of the fast neutrals, backscattered from the target in the direction of the growing film. It will be shown that the resultant film stress can be attributed to the level of energetic, neutral bombardment during deposition.
A fully automated hot-wall multiplasma-monochamber reactor for thin film deposition
Authors: Roca i Cabarrocas P. , Chévrier J. B. , Huc J. , Lloret A. , Parey J. Y. , Schmitt J. P. M.
Published: July 2002

We present a study on the development and the evaluation of a fully automated radio-frequency glow discharge system devoted to the deposition of amorphous thin film semiconductors and insulators. The following aspects were carefully addressed in the design of the reactor: (1) cross contamination by dopants and unstable gases, (2) capability of a fully automated operation, (3) precise control of the discharge parameters, particularly the substrate temperature, and (4) high chemical purity. The new reactor, named ARCAM, is a multiplasma-monochamber system consisting of three separated plasma chambers located inside the same isothermal vacuum vessel. Thus, the system benefits from the advantages of multichamber systems but keeps the simplicity and low cost of monochamber systems. The evaluation of the reactor performances showed that the oven-like structure combined with a differential dynamic pumping provides a high chemical purity in the deposition chamber. Moreover, the studies of the effects associated with the plasma recycling of material from the walls and of the thermal decomposition of diborane showed that the multiplasma-monochamber design is efficient for the production of abrupt interfaces in hydrogenated amorphous silicon (a-Si:H) based devices. Also, special attention was paid to the optimization of plasma conditions for the deposition of low density of states a-Si:H. Hence, we also present the results concerning the effects of the geometry, the substrate temperature, the radio frequency power and the silane pressure on the properties of the a-Si:H films. In particular, we found that a low density of states a-Si:H can be deposited at a wide range of substrate temperatures (100 °C≤Ts≤300 °C).
The chemical vapor deposition of SiO2 from tetraethoxysilane: The effect of the surface hydroxyl concentration
Authors: Tedder Laura L. , Crowell John E. , Logan Mark A.
Published: July 2002

The dissociative adsorption of tetraethoxysilane (TEOS) on SiO2 and the subsequent decomposition of the resulting siloxane species has been studied using Fourier transform infrared transmission spectroscopy. The adsorption and decomposition processes have been studied as a function of the initial surface hydroxyl concentration. The results are compared to previous, complementary studies of the surface chemistry of ethanol on SiO2 surfaces and the temperature programmed desorption of TEOS on Si(100).
Reactive alternating current magnetron sputtering of dielectric layers
Authors: Scherer M. , Schmitt J. , Latz R. , Schanz M.
Published: July 2002

Dielectric layers like Al2O3, SiO2, and Si3N4 have been produced by a reactive ac magnetron sputtering process, using a two cathode arrangement. Within a frequency range between 10 and 100 kHz, where the ions still completely follow the ac field, deposition rates comparable to the dc case could be achieved. In contrast to dc sputtering above a certain frequency of some ten kHz no disturbing charges on dielectric parts of the target surface can build up, thus preventing the well-known problem of arcing. Above this frequency the probability of arcing decreases to zero, leading to a stable process. High deposition rates of about 40 Å/s could be realized for the Aland Si-based reactive processes. This was achieved by a control unit combining the discharge voltage and the reactive gas flow in order to stabilize the transition between the metallic and the dielectric sputter mode. In case of dynamic deposition a homogeneous film thickness distribution on a substrate area of 350×450 mm2 of better than ±5% was obtained. An easy scale-up to bigger cathodes is expected due to the simple coupling of the ac power to the cathodes in this frequency range. The investigated dielectric layers are characterized by optical and mechanical measurements.