bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and optical properties of titanium aluminum nitride films (Ti1−xAlxN)
Authors: Schüler Andreas , Thommen Verena , Reimann Peter , Oelhafen Peter , Francz Gilbert , Zehnder Thomas , Düggelin Marcel , Mathys Daniel , Guggenheim Richard
Published: July 2002

Titanium aluminum nitride films (Ti1−xAlxN) have been deposited by reactive magnetron cosputtering. Elemental compositions of these films have been determined by core level photoelectron spectroscopy. Scanning electron microscopy reveals a columnar film growth. This is also reflected by the topography of film surfaces as studied by atomic force microscopy. By x-ray diffraction a crystalline atomic structure is revealed. Single phase samples can be obtained, consisting of the substitutional solid solution (Ti, Al)N. Crystallites show preferential orientation. The optical properties of these films have been investigated by spectrophotometry in the UV-VIS-NIR wavelength range. Depending on the elemental composition, the optical constants vary from metallic to dielectric behavior. For film compositions with x<0.5 typical features are a tunable transmission maximum and reflection minimum in the visible spectral range, a high infrared reflection, and a low infrared absorption. Due to these optical properties, Ti1−xAlxN films are promising candidates for applications such as coatings for solar control windows and optical selective solar absorbers.
Strain relaxation and dislocation filtering in metamorphic high electron mobility transistor structures grown on GaAs substrates
Authors: Lubyshev D. , Liu W. K. , Stewart T. R. , Cornfeld A. B. , Fang X. M. , Xu X. , Specht P. , Kisielowski C. , Naidenkova M. , Goorsky M. S. , Whelan C. S. , Hoke W. E. , Marsh P. F. , Mirecki Millunchick J. , Svensson S. P.
Published: July 2002

Plastic relaxation in metamorphic high electron mobility transistor (MHEMT) structures was investigated by x-ray reciprocal mapping and high-resolution transmission electron microscopy (HRTEM). X-ray data indicates that In(Ga)AlAs M buffers with a linearly graded buffer and an inverse step are completely strain compensated at the buffer-active area interface. HRTEM shows reduction of dislocation density from 109 to 106 cm−2 through the M buffer. Optimized MHEMT structures were found to exhibit low rms roughness of around 2 nm and excellent electrical transport properties. MHEMT devices with 0.15 μm gates were fabricated with a transconductance of 710 mS/mm, maximum current of 500 mA/mm, and gate–drain breakdown of 6.6 V. A maximum ft value of 118 GHz and a maximum rf gain of 18 dB at 10 GHz were measured at a drain current of 200 mA/mm.
Influence of surface condition in Langmuir probe measurements
Authors: Stamate E. , Ohe K.
Published: July 2002

The surrounding sheath focuses the charged particles to distinct parts of the probe surface resulting in nonuniform physical and/or chemical properties. Then, after a time interval dependent of the degree of plasma contamination, this process results in well-defined regions with different work functions that shape the probe characteristic leading to erroneous measurement of plasma temperature and ion density. For Ar/O2 and Ar/SF6 plasmas produced within a multipolar magnetically confined device we investigated bombardment by positive or negative charges and indirect heating to modify the surface of a planar probe.
Electrical Properties of Titanium, Zirconium, and Hafnium Films from 300 °K to 1.3 °K
Authors: Friebertshauser P. E. , McCamont J. W.
Published: July 2002

Electrical properties of titanium, zirconium, and hafnium films prepared by electron beam evaporation have been measured from 300 °K to 1.3 °K as a function of substrate temperature, film thickness, and substrate material (single-crystal sapphire, Corning 7059 glass, and fused quartz). Zirconium films in the thickness range 2000 Å to 12 000 Å have superconductive transition temperatures near 1.3 °K for films deposited at substrate temperatures of 100 °C and below. Expitaxial growth of titanium is observed on single-crystal sapphire substrates in the temperature range 200 °C to 400 °C on at least two orientations of sapphire. Epitaxial titanium films have a resistance ratio (R300 °K/R4.2 °K) of 24 at a thickness of 12 000 Å and of 8 at 400 Å. This is nearly twice those of the corresponding polycrystalline films on Corning 7059 glass or fused quartz. Films of zirconium and hafnium have an enhanced resistance ratio on sapphire substrates only when deposited at a substrate temperature of 400 °C. Their resistivities at 300 °K are about twice the bulk values for films 7000 Å thick or greater. Superconductivity was not observed for either titanium or hafnium films down to 1.3 °K. Only the hexagonal close-packed crystal structure was found for all three film materials.
Formation of Amorphous Films
Authors: Behrndt Klaus H.
Published: July 2002

Numerous materials have been deposited as amorphous films but our understanding of this phase is lacking. Since opinions regarding short-range order diverge, the similarities and differences between the liquid and amorphous phases are discussed first. It is then concluded from experimental data that the atomic arrangement in “ordered agglomerates with spherical close packing” differs from that in small crystallites. A review of experimental results for alloys, for elements with homopolar binding, and for semimetals and metals indicates that the metastable disorder in these groups of materials displays different characteristics. Interpretations for the varying degree of thermal stability, for size-dependent transitions, and for the kinetics of the transformation are given. Based on these considerations, a concept for the formation and crystallization of amorphous films is developed which shows the progressive change of the characteristics among the groups of materials.
Composition and detection of alignment marks for electron-beam lithography
Authors: Wolf E. D. , Coane P. J. , Ozdemir F. S.
Published: July 2002

High energy backscattered electron signals have been measured from 1-, 3-, and 10-μm-wide gold alignment marks on silicon and gallium arsenide substrates as a function of electron-beam energy (5–30 keV) and gold film thicknesses (650–10 000 Å) using an annular silicon-diode detector. Thin films of both silicon dioxide (3500 Å) and polymethyl methacrylate (5200 Å) on gold alignment marks (2600 Å) on silicon reduced the original signal contrast at 30-keV incident-beam energy by only 16% (10% and 6%, respectively) and degraded the original edge acuity by only about a factor of two. Signal contrast maxima for gold on silicon and gold on gallium arsenide were found to be 1.64 and 0.86, respectively, while silicon and silicon dioxide steps (∠4000 Å) produced no more than 0.08 and 0.04 contrast, respectively. The gold on silicon results are presented with the full realization of the general processing incompatibility of gold on silicon devices and circuits at high temperatures. These results are applicable to other high-atomic-number materials which can be optimized for a particular electron-beam lithography process. The advantage of efficient high-energy backscattered electron detection and high-atomic-number alignment marks to produce high-contrast video signals which are not significantly degraded by the addition of low-atomic-number thin films (e.g., SiO2, resists) will become increasingly important when very accurate alignment is required (±0.05 μm).
Silicon nitride single-layer x-ray mask
Authors: Sekimoto Misao , Yoshihara Hideo , Ohkubo Takashi
Published: July 2002

In LP-CVD process, preparation of silicon nitride film with small tensile stress and low refractive index was investigated as a function of deposition temperature and reactant gas ratio (SiH2Cl2/NH3). The small stress film with low refractive index can be prepared easily by high temperature deposition. Applying the film to an x-ray mask membrane, a new silicon nitride single-layer x-ray mask with a large area window (such as 50 mm in diameter) and high transparency to visible light is realized. Using this mask, a submicron resist pattern (0.5 μm line and space) can be replicated easily by Si–K x-ray exposure system.
Plasma assisted physical vapor deposition processes: A review
Authors: Bunshah R. F. , Deshpandey C. V.
Published: July 2002

Increasing use has been made in thin film technology of physical and chemical phenomena occurring in low pressure plasmas which are convenient in situ sources of activated gas and energetic ions to be used as additional process parameters in film growth, structure, and properties. Energetic ions and/or activated species in the vapor phase are now employed in processes for surface treatment (ion nitriding and carburizing), deposition (sputtering, ion plating, activated reactive evaporation, and plasma polymerization) and also for etching (sputtering and plasma etching). In recent years, therefore, considerable efforts have been directed to the analysis of plasma conditions and their correlation with deposited film properties. In this paper, we present a review of plasma-assisted physical vapor deposition processes (PAPVD) used for the deposition of refractory compounds for the two basic PAPVD processes, (i.e., activated reactive evaporation and reactive sputtering). The film growth mechanism and the role of plasmas in these processes will be compared in terms of three steps in deposition processes; synthesis of the deposition species, transport from source to substrate, and film growth.
Density of amorphous germanium films by spectroscopic ellipsometry
Authors: Blanco J. R. , McMarr P. J. , Yehoda J. E. , Vedam K. , Messier R.
Published: July 2002

Over the last 15 years there has been considerable discussion on the maximum density of a-Ge and a-Si. Part of the significance of this research lies in the central role it plays in structural models of these tetrahedrally bonded amorphous semiconductors. Besides the fact that no detailed model of the homogeneous structure exists, the presence of void networks further complicates the issue. In this study we report on the spectroscopic ellipsometric analysis of an extensive series of a-Ge films prepared by rf sputtering. A systematic analysis of the data using n-layer models, the Bruggeman effective medium approximation, and least squares regression analysis were carried out. The thickness dependence of the bulk film density is shown to be consistent with a fractal model of film morphology and the relative values of density for different sputtering pressures related to film bombardment. The highest film density in this study is 5% greater than crystalline density based upon commonly accepted secondary standard reference data.
Pressure effects in planar magnetron sputter deposition
Authors: Helmer J. C. , Wickersham C. E.
Published: July 2002

Argon pressure during magnetron sputtering affects coating uniformity, deposition rate, and target bias under constant current conditions as well as coating microstructure, stress level, and chemical composition. This paper reports the results of an investigation into the effects of argon pressure on coating uniformity, deposition rate, and target bias. The experimental results indicate that both coating thickness uniformity and deposition rate improve with decreasing argon pressure. A diffusion model predicts the variation of deposition rate with argon pressure, in qualitative agreement with experimental data. For pressures greater than 10 mTorr, the deposition rate varies inversely with pressure. The unexpected decrease in uniformity with increasing pressure is explained by comparing a model diffusion ‘‘kernel’’ with the cosine distribution. The width of the diffusion kernel is less than the width of the cosine distribution.
Study of implantation in HgCdTe by electrolyte electroreflectance
Authors: Raccah P. M. , Garland J. W. , Zhang Z. , Yang D. , Bubulac L. O. , Tennant W. E.
Published: July 2002

Electrolyte electroreflectance (EER) and Hall-effect measurements have been performed on liquid phase epitaxy (LPE) layers of Hg1−xCdxTe as grown with x=0.31, implanted with B ions, implanted and annealed, and annealed but not implanted. The use of our generalized theory to fit the EER results allowed us to study in detail as a function of depth the roles of implantation and annealing in Hg migration and in the formation of extended two-dimensional defects, antisites, and inhomogeneous strains. This is the first systematic EER study of the effects of implantation in state-of-the-art LPE materials. In the region affected by implantation our results suggest the diffusion of displaced Hg, in the postimplant annealing process, is associated with Te antisite formation and with compensating inhomogeneous strains. Moreover this Hg migration generates a region located approximately in the middle of the n-type layer, which actually has a wider gap than the bulk. The relaxation of the lattice and the healing of damage promoted by the anneal are accompanied by a Hg redistribution which tends to lessen the disruptive effects of the antisite complexes. This picture of the implantation process is consistent with earlier conclusions.
Plasma enhanced chemical vapor deposition: Differences between direct and remote plasma excitation
Authors: Lucovsky G. , Tsu D. V.
Published: July 2002

Films of silicon oxide, nitride, and oxynitride produced by direct plasma enhanced chemical vapor deposition (DPECVD) and utilizing silane as one of the gas phase reactants generally contain up to ten times more bonded hydrogen than films produced by remote PECVD (RPECVD) and deposited at the same substrate temperature (Ts). We attribute this difference to the way silane is utilized in the deposition process chemistry. In DPECVD, silane is plasma excited along with other reactant gases, resulting in the formation of radicals and molecular fragments, e.g., SiH3 and SiH2, which at low temperatures (200–400 °C) serve as precursors for hydrogen incorporation, and in addition promote significant departures from insulator stoichiometry: SiO2−x, Si3N4−x, etc. In contrast, in the RPECVD process active oxygen and nitrogen species (and generally rare-gas diluents) are extracted from a remote plasma region and reacted with neutral silane to form precursor species with Si–O and Si–N bonding groups. These precursor molecules take part in chemical vapor deposition reactions in which hydrogen from SiH3 groups of the precursors is eliminated from the films through replacement reactions with excess active oxygen and nitrogen species.
Interaction of SO2 with copper and copper oxide surfaces
Authors: Baxter J. P. , Grunze M. , Kong C. W.
Published: July 2002

The adsorption and reaction of SO2 with copper and copper oxide surfaces was studied by in situ x-ray photoelectron spectroscopy between 173 and 473 K and pressures ranging from UHV to 10−1 mbar. It was found that a Cu2SO3 species acts as an intermediate in the formation of CuSO4 at T<300 K, and at T>300 K in the formation of copper sulfide. The presence of gas-phase oxygen was found to accelerate the surface reaction between SO2 and the substrates. In this communication we will focus on the experiments on Cu2O surfaces and discuss our results in the context of the SO2–flue-gas cleanup process on copper oxide.
Measurements of secondary electron emission in reactive sputtering of aluminum and titanium nitride
Authors: Lewis Mark A. , Glocker David A. , Jorne Jacob
Published: July 2002

Measurements have been made of the secondary electron emission coefficients (γ) of several target materials. An ion beam sputtering technique was used with Ar, N2, and mixtures of Ar and N2 in the typical magnetron sputtering energy range of 400 to 700 eV. The accuracy of the technique was determined by measuring γ of two previously characterized materials: Mo and Al. The results are in good agreement with published experimental data. The secondary electron yields of Ti and Al have been measured as a function of N2 content in the ion beam. In both cases, γ was observed to increase with N2 content of the beam. At 700 eV, γ for Ti increased from 0.102 to 0.172 as the sputter gas was varied from pure Ar to pure N2. Similarly, at 700 eV, γ for Al increased from 0.086 to 0.661 as the gas was varied from pure Ar to pure N2. The implications of these data to the interpretation of current–voltage relationships in reactive dc magnetron sputtering will be presented for TiN and AlN. Estimations of the sputter yield for TiN are proposed based on dc magnetron sputtering data and on the secondary electron yield data generated in this study.
Ion energetics in electron cyclotron resonance discharges
Authors: Holber W. M. , Forster J.
Published: July 2002

Measurements have been made of ion energies in an electron cyclotron resonance plasma, under conditions typically employed for semiconductor materials processing. Both ion energies along magnetic field lines and ion energy distributions generated by a radio frequency (rf) sheath are characterized. Ion impact energies are found to vary between 10 and 35 eV under the conditions studied, with corresponding distribution widths from 3 to 8 eV. Ion energy distributions through an rf sheath are found to be highly dependent on bias frequency, with narrower distributions occurring at higher frequencies. Consequences of measured ion energies for processing results are discussed.
Reactive ion etching of plasma enhanced chemical vapor deposition amorphous silicon and silicon nitride: Feeding gas effects
Authors: Kuo Yue
Published: July 2002

Reactive ion etching of PECVD a-Si:H and silicon nitride films was investigated using CF4, C2F6, CHF3, CF3Cl, and CF2Cl2 gases. Under the same power the a-Si:H etch rate decreases in the order of: CF4∼CF3Cl>CF2Cl2>C2F6>CHF3; and the nitride etch rate decreases in the order of: CF4>CF3Cl∼C2F6>CF2Cl2>CHF3. The etch selectivity is controlled by two competitive mechanisms: plasma chemistry and surface reactions. When no surface mass-transfer-limit layer is formed, the plasma phase chemistry dominates the etch rate of the film. For example, the silicon etch rate increases with the chlorine concentration in the plasma phase. When the surface is covered with a thin film, the etch rate is controlled by the ion bombardment energy. For example, the film etch rate in the C2F6 plasma depends on the self-bias voltage only. ESCA and emission spectra results support the above theory.
A diffusion model for indium in Hg1−xCdxTe
Authors: Wong J. , Roedel R. J.
Published: July 2002

A model based on the known defect structure of Hg1−xCdxTe has been developed for explaining indium diffusion in this semiconductor. Based on a charged-vacancy mechanism, the model qualitatively predicts the correct trends for diffused samples which have been electroplated with indium. The diffusion coefficient predicted by the model has a weak mercury partial pressure dependence but a concentration dependence which increases linearly with the indium concentration. This is in agreement with published experimental results. In addition, the model also qualitatively explains why only a small fraction of the indium is ionized without resorting to the current explanation that the unionized portion is tied up as indium telluride (In2Te3).
X-ray photoelectron spectroscopy study of polymer surface reactions in F2 and O2 gases and plasmas
Authors: Tepermeister I. , Sawin H. H.
Published: July 2002

The surface kinetics of polystyrene, polyparaphenylene, and polyvinylmethylketone films in oxygen and fluorine plasmas was studied in a novel reactor which exposes a sample maintained in high vacuum to the species present in a plasma. These polymers were chosen as they contain the same chemical functional groups found in polymers currently used in the semiconductor industry. The reactor configuration enabled the determination of the surface composition using x-ray photoelectron spectrometry as a function of exposure time to the plasma species. The experimental data indicates that the initial reaction probability depends on the functional groups present in the polymer for both atomic oxygen and molecular fluorine attack. Molecular oxygen did not react with any polymers. Polymers containing aromatic functional groups reacted faster with the gas-phase species than polymers containing carbonyl groups. For the reaction of the polymers with an oxygen plasma, production of surface carbonyl and carboxylic acid groups was favored over the formation of surface alcohol species. For the reaction of the polymers with molecular fluorine, formation of surface CF1 species dominated in aromatic containing polymers. The dependence on the functional group was also evident at long reaction times. The effect was most prevalent for the reaction of molecular fluorine with the polymer samples, where the fluorine to carbon ratio for aromatic polymers was more than twice that of a carbonyl containing polymer. Fluorine plasmas were so reactive with all polymers that the effect of the polymer functional group could not be determined. The reaction of the polymers with a fluorine plasma resulted in the formation of surface CF2 species.
Carbon dioxide chemistry on Cu(100)
Authors: Taylor P. A. , Rasmussen P. B. , Chorkendorff I.
Published: July 2002

The binding energy for CO2 adsorbed on Cu(100) has been determined by use of temperature programmed desorption and was found to increase with increasing coverage from 25 to 30 kJ mol−1. The presence of surface oxygen did not significantly increase the CO2 binding energy. High-resolution electron energy-loss spectra results indicate that the molecularly adsorbed CO2 lies flat on both surfaces and resembles gas phase CO2. The dissociative adsorption of CO2 on Cu(100) at a CO2 pressure of 990 mbar and a temperature range of 475–550 K has been investigated by x-ray photoelectron spectroscopy. The dissociative adsorption of CO2 was found to have an activation energy of 93±5 kJ mol−1 and to have a sticking coefficient of 7.5× 10−12 at 500 K. The dissociative adsorption of CO2 and surface oxygen removal by CO reaches equilibrium under our experimental conditions. The heat of reaction was calculated to 70±4 kJ mol−1.
Specific contact resistance of indium ohmic contacts to n-type Hg1−xCdxTe
Authors: Leech Patrick W. , Reeves Geoffrey K.
Published: July 2002

The specific contact resistant ρC of In contacts ton-Hg1−xCdxTe has been measured as a function of the Cd mole fraction and annealing treatment of the Hg1−xCdxTe. Transmission line model measurements were performed on the In/Hg1−xCdxTe junctions with the Hg1−xCdxTe doped n type in the range 3.5×1016 to 1.6×1018 cm−3 (77 K). A linear dependence of In ρC on x was obtained, with values of ρC ranging from 2.0×10−5 Ω cm2 at x=0.30 through to 2.6×10−2 Ω cm2 at x=0.68. Hg annealing of the epitaxial Hg0.38Cd0.62Te layers resulted in a decrease in ρC from 5.9×10−3 Ω cm2 unannealed to 1.2×10−3 Ω cm2 after a 300 °C anneal, corresponding to equivalent changes in the resistivity of the Hg1−xCdxTe. Isothermal annealing of the In/n-Hg1−xCdxTe contacts for x=0.30, 0.40, and 0.62 produced an enhanced indiffusion of In but with only a minor reduction in ρC.
Monte Carlo calculations of the properties of sputtered atoms at a substrate surface in a magnetron discharge
Authors: Turner G. M. , Falconer I. S. , James B. W. , McKenzie D. R.
Published: July 2002

A Monte Carlo calculation of the transport of sputtered atoms in a magnetron discharge has been used to investigate the effect of the mass and binding energy of sputtered atoms, and the pressure of the background filling gas, assumed to be argon, on the sputtered atoms arriving at a substrate surface. The calculation uses a velocity dependent free path for collisions of sputtered atoms with filling gas atoms. The quantities calculated are: the fraction of sputtered atoms arriving at the substrate, the spatial deposition profile and the kinetic energy and impact angle distributions of the sputtered atom flux reaching the substrate. The main conclusion is that, at low filling gas pressures, the energetic component of the sputtered atom flux is a significant factor in the modification of deposited film properties; this is also the case for light atoms sputtered by heavier filling gas atoms at all pressures studied. The small changes in impact angle distribution with filling gas pressure do not seem to be a significant factor in determining film properties.
Electron–sheath interaction in capacitive radio-frequency plasmas
Authors: Vender D. , Boswell R. W.
Published: July 2002

Recent experimental and theoretical work on the interaction of electrons with a moving radio-frequency (rf) sheath has shown that this interaction is an important electron heating mechanism in capacitive rf plasmas. It is usually assumed in the theoretical treatment of rf sheaths that electron inertia can be neglected and the velocity distribution in the sheath vicinity remains close to Maxwellian. This assumption is examined critically and limits to its applicability are derived from a model of the sheath structure. The amplitude of the oscillating sheath voltage Vrf must satisfy eVrf/kBTe ≲ (1/√8π)√mi/me if electron loss is to remain thermal. Two mechanisms enhance electron loss: field reversal at the electrode and distortion of the velocity distribution near the moving sheath edge. The latter is important if the maximum sheath velocity in an rf cycle approaches a critical value υsm = ῡe/2 where ῡe is the thermal velocity. Particle simulations of the electron–sheath interaction are used to study the distortion of the electron velocity distribution in the sheath vicinity and the details of the electron loss to the wall. Plasma oscillations can be excited near the expanding sheath edge when the sheath modulation amplitude is large, and this may have an important influence on the electron velocity distribution in the plasma.
Ion energy distribution functions in a multipole confined argon plasma diffusing from a 13.56-MHz helicon source
Authors: Charles C.
Published: July 2002

Ion energy distribution functions (IEDFs) are measured in a low-pressure multipole confined diffusion plasma produced by a 13.56-MHz helicon source and compared with the nonconfined case. The plasma confinement is efficient below 1-μbar pressure and induces a plasma density increase of a factor of 2 in the diffusion region. Uniform radial profiles over 15 cm diam are obtained at the bottom of the diffusion chamber. The presence of the magnetized wall has a major effect on the IEDFs at 0.5- and 1-μbar pressure conditions at distances over 10 cm from the source exit. The tail of the IEDFs, which corresponds to hot ions coming direct from the source to the bottom of the diffusion chamber, is not affected by the confinement. However, the peak of the IEDFs, which corresponds to the background density, is drastically increased due to the reflection of the ions on the magnetized wall. The ion collisionality, involving resonant charge exchange with neutrals, is enhanced by the confinement: the first reflection on the magnetized wall induces a longer path length in the diffusion area before recombination on the nonmagnetized bottom wall resulting in a better thermalization of the hot ions diverging from the source at very low pressures.
Surface composition of AlN powders studied by x-ray photoelectron spectroscopy and bremsstrahlung-excited Auger electron spectroscopy
Authors: Liao H. M. , Sodhi R. N. S. , Coyle T. W.
Published: July 2002

The surfaces of AlN powders, which are particularly sensitive to moisture and atmospheric oxygen, are characterized by x-ray photoelectron spectroscopy (XPS). The powders used were exposed to ambient air and then heat treated at 100 °C in air, argon, or nitrogen gas. Bremsstrahlung-excited Auger electron spectroscopy was used in combination with XPS to distinguish aluminum hydroxide from aluminum nitride on powder surfaces. The Auger peaks due to aluminum hydroxide and aluminum nitride were successfully resolved. The predominant surface oxygen-containing species was found to be aluminum hydrate with a composition near Al(OH)3, AlOOH, or a mixture of them, depending on the heat treatment employed. Such data are useful in understanding the feedstock surface chemistry involved in the fabrication of AlN ceramics.
Microloading effect in reactive ion etching
Authors: Hedlund C. , Blom H.-O. , Berg S.
Published: July 2002

The etch rate of silicon, during reactive ion etching (RIE), depends on the total exposed area. This is called the loading effect. However, local variations in the pattern density will, in a similar way, cause local variations in the etch rate. This effect is caused by a local depletion of reactive species and is called the microloading effect. Silicon wafers patterned with silicon dioxide have been etched in order to study the microloading effect. The pattern consists of a large exposed area and narrow lines at different distances from the edge of the large area. This arrangement makes it possible to study how the distance from the large area, which depletes the etchants, influences the etch rate. The influence of different processing parameters like, e.g., pressure, gas flow rate, and flow direction on the microloading effect have been investigated. It has been found that the microloading effect is small (<10%) compared to other pattern dependent nonuniformities. It is also shown that the nonuniformities caused by the microloading effect can be decreased by, e.g., decreasing the pressure or increasing the gas flow rate.
Thermal stability of photochemical native oxide films on Hg1−xCdxTe
Authors: Winton G. H. , Warrington N. , Faraone L.
Published: July 2002

Heat treatments were carried out on native oxide films grown on Hg1−xCdxTe by a photochemical process. The thermal stability of such layers was assessed by monitoring changes in depth profiles obtained from x-ray photoelectron spectroscopy in conjunction with argon ion sputtering. After annealing, photochemical oxides grown in N2O showed a large change in the oxide/Hg1−xCdxTe interface width and a movement of the Cd and Te interfaces towards the oxide surface. These results are comparable to previous studies carried out on anodically grown oxides by other workers. For photochemical oxides grown in an O2 ambient at slightly higher temperatures, the oxide/Hg1−xCdxTe interface was observed to be very stable under the same annealing conditions, with no observable change in the oxide/Hg1−xCdxTe interface width and no movement of the individual element interfaces. For both the N2O and O2 grown oxides, there was a significant loss of Hg from the oxide for extended annealing at 250 °C in a vacuum of 10−5 Torr.
Influence of electron diffusion on the cathode sheath of a magnetron discharge
Authors: Lister Graeme
Published: July 2002

This article describes the theory and numerical modeling of the cathode sheath region near the target of a magnetron. Since electrons are assumed to be confined by the magnetic field, a fluid model is appropriate. Collisionless and fluid models for ion motion are considered and the sheath properties are compared for each of the models considered. It is shown that, if electron diffusion in the sheath is classical, the magnetized electrons have a strong effect on the sheath, whereas for the case of Bohm diffusion this effect is negligible.
Theory of the spinning rotor gauge in the slip regime
Authors: Loyalka S. K.
Published: July 2002

The spinning rotor gauge has found increasing use in ultrahigh vacuum measurements, but it also could be attractive in higher pressure regimes provided an accurate theory were available for interpretation of the measurements (that is, the torque or the deceleration rate as a function of the pressure). In this article we numerically solve the Stokes equation with slip boundary conditions for the rotor geometry by using a Green’s function based approach. We verify that the numerical technique provides accurate results, and then we discuss how the rotor gauge can be used for measurements of the viscosity, the velocity slip coefficient, and the tangential momentum accommodation coefficient. A companion article describes experimental measurements and results for several gases.
Atomic layer epitaxy growth of aluminum oxide thin films from a novel Al(CH3)2Cl precursor and H2O
Authors: Kukli Kaupo , Ritala Mikko , Leskelä Markku , Jokinen Janne
Published: July 2002

The deposition of Al2O3 thin films by atomic layer epitaxy was investigated using Al(CH3)2Cl as a new aluminum precursor. All the films grown in the temperature range of 125–500 °C were amorphous as examined by x-ray diffraction analysis. The residual contents of carbon, chlorine, and hydrogen in the film deposited at 200 °C were 0.2, 2.1, and 12 at. %, respectively, and diminished rapidly with increasing growth temperature. The refractive index of the films increased with deposition temperature, stabilizing at the highest value of 1.68 above 300 °C. The permittivity of the films increased from 7.3 to 8.7 with increasing growth temperature from 200 to 500 °C. The leakage current density was lowest in the film deposited at 200 °C and increased markedly at higher deposition temperatures.
Optimization of Bi2Te3 thin films for microintegrated Peltier heat pumps
Authors: Shafai C. , Brett M. J.
Published: July 2002

Bismuth telluride films were deposited by coevaporation at various Te/Bi flux ratios to optimize their resistivity and their Seebeck coefficients for use in a thin film Peltier heat pump. Bismuth telluride films deposited at a flux ratio of Te/Bi=2.3 were found to possess optimal characteristics. Using these coatings, microintegrated Peltier heat pumps were fabricated on micromachined oxide bridges using standard semiconductor patterning and etching techniques. Chrome–gold and bismuth telluride metallizations were used to form the thermoelectric junctions. A maximum heat pumping rate of −30 μW was achieved by the device when operating in the cooling mode. A temperature reduction of 1.5 °C was attained, with an initial thermal response time in the cooling mode of 10 ms/°C.
Preparation and characterization of epitaxial titanium oxide films on Mo(100)
Authors: Oh W. S. , Xu C. , Kim D. Y. , Goodman D. W.
Published: July 2002

Ultrathin (<100 Å) titanium oxide films have been synthesized on the Mo(100) surface and characterized using various surface science techniques. Epitaxial TiO2 films of varying film thickness were prepared by evaporating titanium in an oxygen background (5×10−7 Torr) between 500 and 700 K, followed by annealing to 900–1200 K. The growth, composition, and structure of the TiO2 films have been investigated using ion scattering spectroscopy (ISS), x-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunnel microscopy (STM). A (2√×√)R45° LEED pattern was observed after annealing 4.7, 15, and 90 Å film thicknesses to 900–1200 K in vacuum. LEED and STM results show that the TiO2 films order along the 〈010〉 and 〈001〉 directions of the Mo(100) substrate. XPS data show that unannealed titanium oxide films exhibit only the Ti4+ valence state, whereas annealed titanium oxide films are partially reduced and exhibit the Ti3+ and Ti2+ states, as well. ISS measurements of unannealed titanium oxide films show that TiO2 films wet the Mo(100) surface well.
Growth and characterization of epitaxial films of tungsten-doped vanadium oxides on sapphire (110) by reactive magnetron sputtering
Authors: Jin P. , Tazawa M. , Ikeyama M. , Tanemura S. , Macák K. , Wang X. , Olafsson S. , Helmersson U.
Published: July 2002

Epitaxial films of W-doped vanadium oxides including W–V2O3, W–VO2 and W–V2O5 were deposited on sapphire (110) by reactive magnetron sputtering of a V–W (1.6 at. % W) alloy target in a range of oxygen partial flows. The deposited films were characterized by x-ray diffraction (XRD), Rutherford backscattering spectrometry, atomic force microscopy and resistance-temperature measurement. The W-to-V ratio in the oxide films showed values higher than that in the target, and the ratio increased with increasing oxygen flows. With precise control of the oxygen partial, flow, not only the W–V2O3, W–VO2 and W–V2O5, but also a series of epitaxial films with lattice parameters varying between those of W–V2O3 and W–VO2 were formed. It was found from an XRD pole figure study that the W–VO2 exhibited a triple-domain structure with the three domains correlated by 120° in the in-plane orientation. The W–VO2 epitaxial films clearly showed a semiconductor-to-metal phase transition with a reduced Tc by 23 °C/at. % W, whereas the phase transition of W–V2O3 seemed to be suppressed due, presumably, to the W-doping effect.
Carbon impurity characterization on a linear plasma device using visible emission spectroscopy
Authors: Whyte D. G. , Seraydarian R. P. , Doerner R. P.
Published: July 2002

Visible emission spectroscopy is used to quantify the carbon impurity concentration in the linear plasma divertor simulator of the Plasma Interaction Surface Component Experimental Station (PISCES-B). A technique has been developed to obtain noninvasively the absolute photometric calibration of a visible spectrometer in order to minimize exposure of equipment in the beryllium safety enclosure of PISCES-B. The principal intrinsic source of carbon appears to be chemical sputtering at the vessel walls, with a typical background concentration ∼0.2% with deuterium plasmas. Helium plasmas have a lower carbon contamination ∼0.01%. Methane gas injection is used to increase the carbon contamination in a controlled manner to better simulate tokamak edge plasma conditions. It is found that the spectroscopic method of determining the carbon fraction agrees well with the relative gaseous carbon contamination measured with a residual gas analyzer during plasma operations.
Low-energy xenon ion sputtering of ceramics investigated for stationary plasma thrusters
Authors: Garnier Y. , Viel V. , Roussel J.-F. , Bernard J.
Published: July 2002

The low-energy sputtering of boron nitride, magnesium oxide, boron nitride and aluminum nitride (BNAlN), and boron nitride and silicon oxide (BNSiO2) by xenon ions of bombarding energies 350, 500 eV, and 1 keV was studied experimentally. In order to measure the ion current without being significantly disturbed by slow ions, only planar probes were used during short duration sputtering experiments (of the order of 10 h). Moreover, slow ion current contribution was estimated by numerical simulations and subtracted from each ion current measurement. It was found that the ion-beam incidence effect on sputtering yields was not as important as for theoretical results or experimental results on quasinonrough solid surfaces, for which it is possible to observe a more pronounced angular dependence of the sputtering yield. This phenomenon is due to surface irregularities of ceramic materials and because of surface roughness the macroscopic sputtering yield should actually result from the convolution of the microscopic sputtering yield by the angular distribution of surface facet incidences. The irregular surface structure of ceramics like BNSiO2 or BNAlN seems to be sputtered differently due to a differential erosion from grain to grain and from grain to surrounding matrix. This uneven erosion may be explained by the wide angular distribution of facet incidences of surface microprofiles and the various binding energies in the selvage of material. Finally, the dependence of sputtering yield at normal incidence on ion energy, in the range 0.35–1 keV, is almost a linear one.
Mechanism of columnar microstructure growth in titanium oxide thin films deposited by ion-beam assisted deposition
Authors: Tang Qi , Kikuchi Kazuo , Ogura Shigetaro , Macleod Angus
Published: July 2002

The microstructure of titanium oxide thin films deposited by ion-assisted deposition was studied as a function of various process parameters such as the ratio of oxygen to argon in the ion beam, the ion/evaporant arrival ratio, and the substrate temperature. By changing the ratio of oxygen and argon ions, amorphous-like and different types of columnar microstructure could be induced in the films. The columnar microstructure was investigated by means of transmission and scanning electron microscopes. Crystal structures were investigated by x-ray diffraction and transmission electron microscopy. Growth models of columnar microstructure are proposed and the mechanism of columnar microstructure growth and the resulting optical properties are also discussed.
Hydrogenated silicon nitride thin films deposited between 50 and 250 °C using nitrogen/silane mixtures with helium dilution
Authors: Klein Tonya M. , Anderson Timothy M. , Chowdhury Ashfaqul I. , Parsons Gregory N.
Published: July 2002

Silicon nitride thin films, deposited by plasma enhanced chemical vapor deposition at temperatures between 250 and 50 °C from SiH4, N2 and He, were characterized using transmission infrared spectroscopy, ellipsometry, wet etch rate, and current-voltage analysis. At 250 °C using SiH4/N2/He flow ratios of 1/150/75, films with refractive index=1.80 and H concentrations <20%, distributed equally in Si-H and N-H units were obtained. The concentration of hydrogen and its distribution in N-H and Si-H bonds are sensitive to process temperature, suggesting that thermally driven N incorporation reactions are important during growth. Inert gas dilution allows films to be formed at <100 °C, with bonded hydrogen configurations similar to films deposited at higher temperatures. Current versus voltage traces of as-deposited films show charge trapping, which can be reduced by extended low temperature anneals. These results show that chemical composition can be controlled in low temperature silicon nitride deposition. This processing approach may be useful for encapsulation or for barrier layer formation on low temperature organic electronic devices or flexible transparent plastic substrates.
Effects of chemical etching with sulfuric acid on glass surface
Authors: Jang H. K. , Chung Y. D. , Whangbo S. W. , Lee Y. S. , Lyo I. W. , Whang C. N. , Lee S. J. , Kim G.
Published: July 2002

Glass slides were chemically etched with sulfuric acid using five different methods. We investigated the effects of chemical etching condition on such properties as chemical composition, surface roughness, and thermal stability of the glass. Sodium and carbon atoms on the surface of the glass are effectively eliminated by chemical etching with sulfuric acid. The glass slides were boiled for 30 min in 95% sulfuric acid and were depth profiled at room temperature with x-ray photoelectron spectroscopy (XPS), the Na 1s signal was not detected in the resolution limit of XPS. Surface morphology of the glass was very different depending on the concentration of sulfuric acid. The surface of the glass etched with 50% sulfuric acid was rougher than that of glass etched with 95% sulfuric acid. The sodium concentration of the glass boiled for 30 min in 95% sulfuric acid was nearly zero at the glass surface, and the sodium composition changed very little with annealing temperatures up to 350 °C in a vacuum environment. However the sulfur concentration at the glass surface due to the sulfuric acid increased with increasing temperature.
Study of microinhomogeneities in midwave infrared mercury cadmium telluride grown by metalorganic chemical vapor deposition-interdiffused multilayer process onto GaAs and GaAs/Si substrates
Authors: Irvine S. J. C. , Edwall D. D. , Bubulac L. O. , Gil R. V. , Gertner E. R.
Published: July 2002

The causes for variations in quantum efficiency (QE) for boron-implanted midwave infrared diodes formed in mercury cadmium telluride on CdTe buffered GaAs/Si substrates have been investigated. Smooth layers have QE≳30% with many of the diodes in the 50%–60% range. Layers having a faceted morphology produce diodes with QE<30%. The faceted layers have been shown by infrared absorption measurements and secondary ion mass spectrometry depth profiles to possess microinhomogeneities in composition. Carrying out comparative growths on GaAs substrates have shown that these microinhomogeneities are not due to the growth process or fundamentally due to the interdiffused multilayer process used to grow the alloy layers. A study of the origins of the faceting behavior on GaAs/Si substrates, using in situ laser reflectance, has shown that they form from three-dimensional island growth, nucleating on the substrate and growing outwards to dominate the growth mode after 2 000 Å of buffer growth.
Dramatic work function variations of molecular-beam epitaxially grown GaAs(100) surfaces
Authors: Duszak R. , Palmstro/m C. J. , Florez L. T. , Yang Y.-N. , Weaver J. H.
Published: July 2002

Work function measurements have been performed on molecular-beam epitaxially (MBE) grown GaAs(100) surfaces prepared using As desorption, Ga deposition, and MBE growth. A comparison of As desorption between As-capped MBE grown surfaces with in situ prepared c(4×4) surfaces suggests that the decapping process cannot yield as well ordered c(4×4) surfaces as MBE growth. Remnant excess As is often observed by scanning tunneling microscope measurements on initially decapped samples. In general, the best ordered surfaces were obtained through preparation techniques which were closest to thermodynamic equilibrium. The highest work function was found for the (2×4)/c(2×8)-β surface prepared by annealing with an As4 flux and the lowest for a (1×6) surface formed by Ga deposition. The total variation was ∼0.82 eV. Rapid annealing and large annealing steps lead to surfaces with less order and lower work function differences.
Microhardness of Hg-containing II–VI alloys
Authors: Myles Charles W. , Ekpenuma Sylvester N.
Published: July 2002

The microhardnesses of HgCdTe, HgZnTe, and HgCdZnTe are calculated using a formalism which combines a solid-solution hardening model, an analysis of the composition dependence of the critical stress, and an empirical relation between critical stress and microhardness. Reasonable agreement with available data is obtained for the magnitude of the hardness and its variation with composition in HgCdTe and HgZnTe. In qualitative agreement with previous studies of the lattice strengthening effects of Zn on HgTe and HgCdTe, it is found that the alloys containing Zn have larger hardnesses than HgCdTe for all compositions. Another interesting result is that, for simultaneous variations of the Cd and Zn compositions in HgCdZnTe that leave the band gap fixed in the infrared, the microhardness is between those of HgZnTe and HgCdTe, and it varies almost linearly with Zn composition.
Thermodynamic description of metal Hg(Cd)Te systems
Authors: Helms C. R. , Krishnamurthy Vikram
Published: July 2002

The interactions of Hg(Cd)Te with metals used as potential contacts have been shown to be quite complex, both in terms of electrical as well as metallurgical properties. In an attempt to model such behavior the use of a concept of a metals ‘‘reactivity’’ toward Hg(Cd)Te has been suggested. In this article we investigate the ternary or quaternary phase diagrams of metal Hg(Cd)Te systems and show that a much better understanding of these systems is possible using such diagrams rather than the somewhat ambiguous concept of reactivity. For most metals three basic types of ternary diagrams describe the M–Hg–Te system. In principal, all metals for which there is not a metal–HgTe tie line would be considered reactive. Indeed, the only common metal for which there is a M–HgTe tie line is Au. However, even in this case, Au deposition onto a room temperature free surface may lead to Hg evaporation due to the extra RT ln PHg term in ΔG unless there is a sufficient Hg overpressure. Low deposition temperatures can be used to mitigate this effect, however. The ‘‘reactive’’ systems fall into two categories, one where the elemental Hg/metal telluride couple is stable and one for which the Hg metal compound/metal telluride couple is stable. Al, In, Cd, Ti, and possibly Cu and Ge, fall into the former category whereas Pt, Pd, and possibly Ag, fall into the latter.