bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal chemistry of biacetyl on Si(100)
Authors: Armstrong J. L. , Pylant E. D. , White J. M.
Published: July 2002

X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and high-resolution electron energy loss spectroscopy (HREELS) were used to study the adsorption and decomposition (for temperatures between 160 and 1100 K) of biacetyl (CH3COCOCH3) on Si(100). We conclude from peak positions in the C(1s) and O(1s) XPS spectra that biacetyl initially adsorbs by binding through the carbonyl π-bonds either forming a di-σ bonded form of biacetyl or completely cleaving the carbonyl double bond. In TPD, biacetyl molecularly desorbs at 185 K for the multilayer and between 263 and 285 K for the monolayer indicated in TPD. TPD also indicates ketene, methane, and hydrogen desorption at 330, 823, and 870 K, respectively. On the surface, there is evidence in XPS that all C=O containing fragments completely dissociate or desorb by 700 K. Above 700 K, hydrogen begins transferring to the surface as shown by the appearance of a peak in HREELS at 2103 cm−1 (νSi–H). Surface hydrogen recombines with methyl groups and other surface hydrogen producing methane (823 K) and molecular hydrogen (870 K). SiO desorbs at 1010 K and is reflected in XPS by total loss of the O(1s) signal. Finally, heating to 1100 K results in SiC formation.
Fourier transform infrared diagnostics of gas phase reactions in the metalorganic chemical vapor deposition of aluminum from dimethylethylamine alane
Authors: Yun Jong-Ho , Park Man-Young , Rhee Shi-Woo
Published: July 2002

The gas phase reaction mechanism in the aluminum metalorganic chemical vapor deposition from dimethylethylamine alane (DMEAA) was investigated by Fourier transform infrared spectroscopy. DMEAA in the gas phase was dissociated into dimethylethylamine and alane even at room temperature and the dissociation rate was accelerated at higher gas temperatures. Alane, produced from the dissociation of DMEAA, disappeared rapidly and the intermediates, produced during the degradation of alane, may form Al particles. The dissociation reaction was found to be a first order reaction, and the activation energy was about 9.56 kcal/mol. In H2 carrier gas, the dissociation of DMEAA was slower than that in Ar gas. The deposition rate was decreased when the substrate temperature was above 150 °C because DMEAA decomposed rapidly in the gas phase. From the experimental observations, a gas phase reaction mechanism was proposed and the degradation mechanism of liquid DMEAA was suggested.
Structure and mechanical properties of polycrystalline CrN/TiN superlattices
Authors: Yashar P. , Barnett S. A. , Rechner J. , Sproul W. D.
Published: July 2002

Polycrystalline CrN/TiN superlattice films were deposited on M1 tool steel using unbalanced reactive magnetron sputtering with opposed cathodes. The Cr and Ti targets were sputtered in Ar–N2 mixtures with partial pressure control of the N2. As the N2 partial pressure was increased from 0.1 to 1.1 mTorr, TiNx films went from stoichiometric B1-cubic TiN to slightly overstoichiometric TiN, while CrNx films went from cubic Cr–N solid solutions to hexagonal Cr2N to B1-cubic CrN. Since the N2 partial pressure required to form stoichiometric CrN was ≈10 times that required to form stoichiometric TiN, nitrogen was inlet at the Cr target position to maximize the difference in N2 partial pressures. Two series of CrN/TiN superlattices, with TiN fractions of 0.4 and 0.6, were deposited with periods ranging from 2 to 60 nm. X-ray diffraction showed a very strong (111) texture with first-order satellite peaks around the (111) Bragg peak. Kinematical diffraction simulations of the superlattice x-ray patterns indicated a strong composition modulation and a significant fluctuation in d-spacing that was related to ion bombardment defects. Cross-sectional transmission electron microscope images showed a columnar film structure with well-defined superlattice layers. Nanoindentation of 2-μm-thick CrN/TiN samples showed a maximum hardness of 35 GPa at a period of 2.3 nm, compared to 25 GPa for TiN and 14 GPa for CrN films. The maximum superlattice hardness was thus ≈75% larger than the rule-of-mixtures value. The hardness enhancement mechanisms are discussed.
Wafer-level vacuum packaging for MEMS
Authors: Gooch R. , Schimert T. , McCardel W. , Ritchey B. , Gilmour D. , Koziarz W.
Published: July 2002

Vacuum packaging of high performance infrared (IR) MEMS uncooled detectors and arrays, inertial MEMS accelerometers and gyros, and radio frequency (rf) MEMS resonators is a key issue in the technology development path to low cost, high volume MEMS production. Wafer-level vacuum packaging transfers the packaging operation into the wafer fab. It is a product neutral enabling technology for commercialization of MEMS for home, industry, automotive, and environmental monitoring applications. 4 in. wafer-level vacuum packaging has been demonstrated using IR MEMS bolometers and results will be presented in this article. In addition to the wafer-level packaging results, vacuum package reliability results obtained on component-level ceramic vacuum packages will also be presented.
Stability of transparent conducting oxide films for use at high temperatures
Authors: Minami Tadatsugu , Miyata Toshihiro , Yamamoto Takashi
Published: July 2002

The stability of a number of transparent conducting oxide (TCO) films prepared by magnetron sputtering has been tested in various atmospheres at high temperatures up to 1000 °C: binary compounds such as ZnO, In2O3, and SnO2; ternary compounds such as Zn2In2O5, In4Sn3O12, GaInO3, ZnSnO3, and MgIn2O4; and multicomponent oxides composed of combinations of binary compounds or ternary compounds. With regard to the stability of the electrical properties, In2O3, ITO, SnO2, and SnO2:Sb films were stable in an Ar gas atmosphere at temperatures up to 900 °C. SnO2 and SnO2:Sb films were stable in air at temperatures up to 900 °C, and In2O3 and ITO were stable in air at temperatures up to 800 °C. Although the ZnO:Al film was stable in an Ar gas atmosphere at temperatures up to 600 °C, it was unstable in air at temperatures above 400 °C. The stability improved as the Sn content in Sn containing TCO films was increased, but it lessened as the Zn, Mg, and/or Ga contents were increased. In addition, the chemical stability at high temperatures was mainly determined by the metal elements contained in the TCO film; TCO film rich in Sn were very stable.
Influence of vacuum environment on the aging of phosphors at low electron energies
Authors: Seager C. H. , Tallant D. R. , Shea L. , Zavadil K. R. , Gnade B. , Holloway P. H. , Bang J. S. , Zhang X. M. , Vecht A. , Gibbons C. S. , Trwoga P. , Summers C. , Wagner B. , Penczek J.
Published: July 2002

Screened samples of two different commercial phosphors were aged at 1.5 keV under nominally identical conditions in five different vacuum systems. After aging to doses of ∼5 C/cm2 the changes in cathodoluminescence (CL) spectral output and photoluminescence properties were determined, and x-ray photoemission spectroscopy (XPS) and Auger analyses were performed. We observed that while the CL degradation was similar for all systems at low electron doses, the aging rates diverged at high doses, suggesting an increasing importance of the vacuum environment. Post-aged CL spectra showed distinct redshifts in all cases, and the most heavily degraded samples displayed XPS-determined increases in surface carbon levels. The data suggest an extrinsic CL aging mechanism; a model involving the conversion of surface hydrocarbons to a metallic graphite phase agrees with the data.
Effect of CaO addition on properties of ion-induced secondary electron emission of MgO films
Authors: Cho Jinhui , Park Jong-Wan
Published: July 2002

An excellent correlation exists between the firing voltage and the secondary electron emission coefficient (γ) in MgO films used as protective layers in ac plasma display panels. In order to make a new protective layer with a high secondary electron emission coefficient and with a reduction in the demanding voltage required for discharge, we have studied the effect of CaO addition on the secondary electron emission characteristics of MgO film. Mg1−xCaxO films were prepared by the e-beam evaporation method. As a large number of Ca atoms were substituted for Mg atoms, lattice distortion occurred in MgO films (NaCl crystal structure) in accordance with the increase in the lattice parameter. When the cation ratio in films was 0.088, relaxation of compressive stress seems to be caused by crack formation in the film. The density of pure as grown MgO was 3.214 g/cm3, which was 88% of the bulk MgO’s density. The density of the Mg1−xCaxO films gradually increased by about 14% with CaO addition to MgO. Secondary electron emission yield of pure MgO film was 0.33. Addition of a controlled amount of CaO to MgO resulted in a rapid increase in the secondary electron emission yield. The film with a [Ca/(Mg+Ca)] ratio of 0.134 yielded a secondary electron emission coefficient as high as 0.58.
Synthesis of highly oriented piezoelectric AlN films by reactive sputter deposition
Authors: Engelmark F. , Fucntes G. , Katardjiev I. V. , Harsta A. , Smith U. , Berg S.
Published: July 2002

Nucleation and growth of polycrystalline AlN films on thermal and chemical vapor deposited oxide have been studied during rf reactive sputter deposition. The influence of the growth conditions, namely deposition pressure, rf power, Ar/N2 ratio, and substrate temperature, on film properties has been systematically studied. The properties of interest are crystallinity, degree of orientation, crystallite size, surface roughness, stress, piezoelectric coupling, acoustic velocity, and others. The films have been analyzed with Rutherford backscattering spectroscopy, electron spectroscopy for chemical analysis, x-ray diffraction (XRD), ellipsometry, scanning electron microscopy, atomic force microscopy, stress measurements, etc. It is found that these properties are sensitive functions of all deposition parameters and that there exist optimal deposition conditions under which films of high quality are obtained. The films at optimal conditions were analyzed with the following results: full width half maximum (FWHM) XRD 0.216°, FWHM rocking curve 1.62°, crystallite size 38 nm, optical index 2.15, surface roughness 31 Å, and stress 400 MPa. Further, to study the electroacoustic properties of the films surface acoustic wave filters were fabricated operating at 534 MHz. The thin film structure consists of AlN/SiO2/Si. The electrodes of the interdigital transducers were made of Al. Examination of the frequency response indicated an acoustic velocity of 4900 m/s and a moderate coupling coefficient.
Reactions of maleic anhydride over TiO2 (001) single crystal surfaces
Authors: Wilson J. N. , Titheridge D. J. , Kieu L. , Idriss H.
Published: July 2002

The reactions of maleic anhydride (MA) have been investigated on the “near” stoichiometric and substoichiometric surfaces of TiO2 by temperature programmed desorption (TPD). Moreover, self-consistent field semiempirical PM3 calculations of MA over relaxed and unrelaxed Ti13O45H38 rutile clusters [simulating the rutile TiO2(011) surface] were conducted on two modes of adsorption. The dissociation of one C–O–C bond following adsorption on a Ti5c4+–O2− site results in a more stable adsorbed species (by 0.5 eV) than the nondissociatively adsorbed molecule. Desorption of a wide range of products in several temperature domains was observed during MA-TPD. In addition to the decomposition pathway to carbon monoxide (CO), carbon dioxide (CO2), acetylene (HC≡CH), and ketene (H2C=C=O), the desorption of several coupling products is also seen: vinylacetylene (HC≡CCH=CH2), butene, traces of butadiene ((H2C=CHCH=CH2), and benzene (C6H6). Over the substoichiometric surfaces these coupling products are more accentuated while the decomposition pathway to ketene decreased.
Energy levels of hydrogenic impurities and Wannier excitons in quantum well structures
Authors: Greene Ronald L. , Bajaj K. K.
Published: July 2002

Interest in the study of the behavior of shallow impurity centers and Wannier excitons in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last two years. Several recent calculations of the energy levels of hydrogenic impurity states and Wannier excitons in quantum well structures, such as Ga1−xAlxAs–GaAs–Ga1−xAlxAs, assuming infinite and finite potential barriers at the interfaces, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. It is shown that the behavior of the energy states of these shallow systems in finite height potential wells is both qualitatively and quantitatively different from that in infinite height potential wells especially in thin (<100 Å) wells. Recent experimental data concerning the variations of the binding energies of shallow acceptors and Wannier excitons as a function of the GaAs quantum well size is reviewed. A comparison between these experimental measurements and the results of recent calculations is presented.
Interface properties of n-ZnSe–p-Ge heterojunctions grown by organometallic chemical vapor deposition
Authors: Werthen J. G. , Stutius W. , Ponce F. A.
Published: July 2002

Aluminum-doped, n-type ZnSe layers ranging in thickness from several thousand Ångstroms to several microns were grown epitaxially on differently oriented p-type Ge substrates by a low temperature, low pressure organometallic chemical vapor deposition process. The surface morphology and photoluminescence spectra reveal differences between the ZnSe films grown on (100)Ge substrates and those grown on (111)Ge substrates. Photoluminescence spectra of the former films show strong band gap luminescence, whereas the latter films are characterized by a reduced band gap luminescence intensity and an enhanced intensity in the self-activated region. The lattice structure of the ZnSe–Ge interface has been studied by high resolution transmission electron microscopy, and the electrical characteristics of the corresponding n-ZnSe–p-Ge heterojunctions have been measured. Heterojunctions formed on (100) oriented substrates show good diode behavior with dark saturation currents of 1×10−11 A/cm2. Heterojunctions formed on (111) substrates are characterized by poor diode behavior with dark saturation currents of the order of 4×10−8 A/cm2. The difference in the electrical transport properties is attributed to the distinctly different defect structure at the ZnSe–Ge heterojunction interface.
Some observations on Ge:GaAs(001) and GaAs:Ge(001) interfaces and films
Authors: Neave J. H. , Larsen P. K. , Joyce B. A. , Gowers J. P. , van der Veen J. F.
Published: July 2002

Ge:GaAs(001) and GaAs:Ge(001) interfaces and thin films have been prepared by molecular beam epitaxy (MBE) and studied in situ by reflection electron diffraction (RHEED), angle-resolved photoemission spectroscopy (ARPES), and core level photoemission. The film structures have also been examined by transmission electron microscopy (TEM). Ge films grown on GaAs(001) substrates have a c(2×2) surface symmetry and are free of extended defects and domain structures. ARPES measurements of Ge(001)-c(2×2) surfaces in the photon energy range 20–50 eV show the presence of two surface states and dispersing bulk states. Valence bands along the ΓX symmetry direction are derived on the basis of a free-electronlike final state. The quality of the Ge–GaAs(001) interface however, is determined by the GaAs substrate reconstruction. Ge deposition on an intrinsic (2×4) reconstructed surface produces an abrupt interface, but when a c(4×4) chemisorption phase is used the distribution of arsenic across the interface region is diffuse. TEM examination of GaAs films on Ge(001) substrates has confirmed the presence of a domain structure in which the domains are distinguished by reversal of the polar axis.
The effect of surface oxygen on the intermixing and Schottky barrier at GaAs(110)–Au interfaces
Authors: Lü Z. M. , Petro W. G. , Mahowald P. H. , Oshima M. , Lindau I. , Spicer W. E.
Published: July 2002

The effect of placing controlled amounts of oxygen on the clean, cleaved (110) surface of GaAs before exposure to Au has been investigated with ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). We studied: (a) the shape of the Ga-3d level and changes of Ga (or As) intensity with oxygen and subsequent Au deposition; (b) the position of the Ga-3d core level, with special regard to the surface or interface Fermi level (Efs), as a function of oxygen and Au coverages; and (c) the valence band structure (where both oxygen and Au provide strong characteristic structure). For chemisorbed oxygen coverages of a small fraction up to 1 monolayer (ML) or above the Au:GaAs intermixing and Ef shifts are significantly reduced. For the p-type sample, after much less than 1 ML of oxygen, the maximum rise of Efs is suppressed as Au is added; after 107L exposure Efs remains stationary until approximately 1 ML of Au is deposited; for high oxygen coverage (≥108L), the oxygen appears to effectively retard the Au–GaAs interaction up to 10 ML of Au coverage. The width of the Ga-3d core level increases monotonically with increased oxygen exposure. With 1010L exposure of oxygen, the Au coverage necessary to drop the Ga intensity to 1/e of  its value on the oxidized surface is decreased to 4 ML, instead of 6 ML for the unoxidized surface. Supporting evidence from XPS spectra further demonstrates the intermixing is reduced between Au and GaAs by oxygen. The valence band structure shows the Au is dispersed on the oxidized surface. The results show that, for GaAs surfaces with a few tenths to above 1 ML of oxygen (before Au is deposited and with no annealing), the oxygen–GaAs interaction inhibits Au intermixing with GaAs. It causes a more abrupt interface than the case without oxygen.
Growth, characterization, and properties of metastable and modulated semiconductor structures: Prospects for future studies
Authors: Grunthaner F. J. , Madhukar A.
Published: July 2002

The general field of preparation and study of metastable and modulated semiconductor structures has progressed rapidly in recent years. This short overview offers an assessment of the progress and current understanding in the areas of fabrication, characterization, and utilization of these new material system. The discussion includes the more prominent growth techniques, theoretical and experimental analysis of growth kinetics, and an overview of structural, chemical, electronic, and optical characterization. The probable application of these structures for the technological development of new device structures and concepts is considered. The discussion particularly emphasizes the prospects for future studies in view of the specific current understanding.
Direct engraving on positive resists by synchrotron radiation
Authors: Ichimura S. , Hirata M. , Tanino H. , Atoda N. , Ono M. , Hoh K.
Published: July 2002

Direct engraving of mask patterns in a resist film was tried by exposing with synchrotron radiation. Using a stencil mask made of a Si3N4 substrate, submicron structures could be successfully replicated. Fundamental aspects of resist decomposition by synchrotron radiation were also investigated by mass and electron spectroscopy.
Maskless etching of a nanometer structure by focused ion beams
Authors: Komuro Masanori , Hiroshima Hiroshi , Tanoue Hisao , Kanayama Toshihiko
Published: July 2002

Microfocused heavy ion beams obtained from liquid metal ion sources of gallium, indium, and tin are bombarded onto silicon and gallium arsenide substrates, and the amorphous regions created are selectively dissolved in suitable etchants (ion bombardment enhanced etching). The area exposure doses required to etch to the depth of the calculated projected range of the incident ions are in the region of 5×10−6∼1×10−5 C/cm2 at accelerating voltages of 30∼50 kV,and the dose dependencies of the etched depths show rapid increases in specified dose regions. Widths of etched depths obtained in line delineations depend on a line exposure dose, and the minimum linewidth clearly obtained is 20∼40 nm for all the ion beams. From measurements of the dose dependencies of linewidth, the beam diameters are evaluated for various conditions of the source operation and of a lens acceptance half-angle. The virtual crossover diameters that are independent of the half-angle, are found to be 40∼50 nm for the gallium source and 67 nm for the indium source at the emission current of 4∼12 μA. In the case of the tin ion beam, each line is split into two distinct lines about 100 nm apart at 50 kV. This effect is caused by the separation of singly and doubly charged atomic ions in some stray magnetic field of the order of 50 mG. From variations of the width of grooves produced by the bombardment with the doubly charged ion beam, the crossover diameter for the tin source is estimated to be 56∼67 nm.
Use of antireflective coating in bilayer resist process
Authors: Lin Yi-Ching , Jones Sue , Fuller Gene
Published: July 2002

A new multilayer resist process consisting of a thin antireflective (AR) film between the thick bottom PMMA layer and the top photoresist layer of the conventional bilayer resist process is reported in this paper. Aluminum features of micron and submicron size over topography have been achieved with this novel resist process by using a conventional 10:1 reduction GCA DSW 4800 stepper to expose the top photoresist layer. Excellent linewidth control over steps is demonstrated. Both the standing wave effect in the top resist layer and the interference from the light scattered by the substrate topography are eliminated in this AR coating approach. The mixing of the two resist layers encountered in the original bilayer resist process does not appear in this new process. The plasma etch resistance of this new multilayer resist process is improved by retaining the capping top photoresist layer, which also eliminates the delamination of the AR layer during the PMMA development. This novel resist process provides a low-cost, reliable method for further extending the resolution capability of existing steppers to meet the needs of advanced product designs.
Modulation-doped Al0.48In0.52As/Ga0.47In0.53As photodetector prepared by molecular beam epitaxy
Authors: Chen C. Y. , Pang Y. M. , Cho A. Y. , Alavi K. , Garbinski P. A.
Published: July 2002

We report a single-period modulation-doped Ga0.47In0.53As/Al0.48In0.52As photoconductive detector for long wavelength applications. This detector shows a high equivalent external quantum efficiency. Furthermore, we have also measured the receiver sensitivity of this detector. At 1 Gbits/s, 1.3 μm, and BER=10−9, the receiver sensitivity is −25 dBm. These results suggest that, through further developments, this detector should find applications in monolithic integrated photoreceivers.
Vacuum evaporation system for depositing thick polycrystalline silicon
Authors: Ota Yusuke , Clapper Raymond A.
Published: July 2002

Thick polysilicon (>1 mm) deposition on heated SiO2-coated silicon substrates at high deposition rate (≥4 μm/min) at temperatures to 1100 °C was achieved by vacuum evaporation of silicon using two high power e guns. The deposition system was able to accommodate ten 75 mm diam substrates or eight 100 mm diam substrates. The system was designed as an alternative to the CVD process for depositing polysilicon material for dielectrically isolated integrated circuit substrates. This paper describes the system design and its capabilities.
Low defect density insulating films deposited on room temperature substrates
Authors: Magerlein J. H. , Baker John M. , Proto G. R. , Grebe K. R. , Klepner S. P. , Palmer M. J. , Warnecke A. J.
Published: July 2002

Several types of thin dielectric films which can be deposited on substrates held near room temperature have been tested for use as insulators in integrated circuit structures. The types of insulation studied include single and double layer SiO films, Parylene polymer films, and SiO/Parylene composites. Test structures, which were fabricated with processes used in Josephson integrated circuits, allowed measurement of the number of electrical defects per unit area in the insulation between two Pb–In–Au films as well as the number of defects along edges of the lower metal film. The SiO/Parylene composite films had the lowest defect densities, as low as 0.2 cm−2 over planar metal layers and 0.001 cm−1 at insulated metal edges. Defect densities below those for single SiO films were also obtained by depositing the SiO in two layers through separate but indentical lift-off stencils. The defect densities measured for these insulating films both before and after repeated thermal cycling to 4.2 K are believed to be adequate for proposed Josephson integrated circuits.
Reactive ion etching of GaAs in a chlorine plasma
Authors: Hu E. L. , Howard R. E.
Published: July 2002

Chlorine was used to carry out the reactive ion etching (RIE) of GaAs. At 5 mTorr pressure and 270 V bias, it was found to etch at a rate >1 μ/min, and produced features having vertical sidewalls and a clean substrate surface. The mechanism of chlorine RIE of GaAs was studied by examining etch rates and profiles obtained using gases of different mixtures of chlorine and argon. The results are consonant with proposed mechanisms of GaAs etching by chlorine in both the plasma and reactive ion beam etching regimes.
MBE growth of extremely high-quality GaAs–AlGaAs GRIN-SCH lasers with a superlattice buffer layer
Authors: Fujii T. , Hiyamizu S. , Yamakoshi S. , Ishikawa T.
Published: July 2002

It was found that a thick AlGaAs layer grown on a GaAs–AlGaAs superlattice buffer layer does not affect the optical quality of single quantum well structure successibly grown on the AlGaAs layer; that is, background impurities such as carbon and oxygen, which would come from residual gases, do not accumulate on the AlGaAs surface during molecular beam epitaxy (MBE) growth. Extremely high-quality GaAs–AlGaAs GRIN-SCH lasers were obtained by introducing a superlattice buffer layer. The minimum threshold current density of 175 A/cm2 was achieved for a broad-area Fabry–Perot laser with a cavity length of 450 μm at room temperature. This is the lowest threshold current density of semiconductor lasers with a similar cavity length.
Surface segregation and initial oxidation of titanium silicide films
Authors: Kuiper A. E. T. , van der Ligt G. C. J. , van de Wijgert W. M. , Willemsen M. F. C. , Habraken F. H. P. M.
Published: July 2002

The high-temperature behavior of TiSi2 films, deposited on a polygate structure, was studied by means of Auger electron spectroscopy and low-energy ion scattering. Both techniques reveal that upon heating at temperatures in excess of 600 °C the surface of the silicide film becomes Si-enriched to an extent corresponding to TiSi4. This observation is in qualitative agreement with the theory of surface segregation, which predicts enrichment of the element with the lowest heat of vaporization. However, the effect is found not to be restricted to the topmost atomic layer, but extends to a depth of 30–40 Å. With oxygen, introduced into the vacuum system to a level of 10−6–10−4 Torr, the same amount of enrichment is obtained, now at 500–600 °C. In this temperature range Ti desorbs from the silicide as TiOx. Apart from the outer surface layer the silicide is not oxidized under these circumstances. At higher temperatures, around 800 °C, this reactive adsorption–desorption of oxygen does not result in the formation of a thicker oxide layer but leads to a decomposition of the silicide. The attendant loss of Si and Ti, as measured with Rutherford backscattering, causes a severe roughening of the film surface.
Silicon molecular beam epitaxy
Authors: Shiraki Yasuhiro
Published: July 2002

Many works are now conducted in the worldwide scale on silicon molecular beam epitaxy (Si MBE) including homoepitaxy, doping, heteroepitaxy such as silicon/insulator, silicon/other semiconductor, and silicon/metal (silicide), and poly-Si deposition. As for device applications, work is now moving from conventional discrete devices to integrated circuits and structures unique to Si MBE. In this paper, various aspects of Si MBE are reviewed.
Electron microscopy of epitaxial Si/CaF2/Si structures
Authors: Fathauer R. W. , Lewis N. , Schowalter L. J. , Hall E. L.
Published: July 2002

Epitaxial Si/CaF2/Si(111) structures have been grown by molecular beam epitaxy. Planar and cross-sectional transmission electron microscopy has been used for characterization of these structures. The CaF2 layer is high quality, single crystal material exhibiting type B epitaxy with respect to the Si substrate. On the other hand, the Si overgrowth layer consists of a mixture of crystallites which are aligned either with the Si substrate or with the CaF2. The defect density in the overgrown Si improves with distance from the interface with the CaF2. Variation of the substrate temperature during growth has relatively little effect on the quality of the epitaxial Si.
Repair of x-ray lithography masks using UV-laser photodeposition
Authors: Randall J. N. , Ehrlich D. J. , Tsao J. Y.
Published: July 2002

UV-laser photodeposition of cadmium has been adapted to the repair of clear defects in fully fabricated polymide membrane x-ray lithography masks. The spatial resolution of the process has been explored with carbon x-ray exposures and was found adequate for one-step repair of 1 μm defects. Repair of smaller features should be possible with photodeposition in combination with ion milling with a focused ion beam. A new photodeposition process has been developed for lead, a material with better x-ray opacity than Cd for many practical x-ray wavelengths. Both materials can be deposited with good edge definition and without damage to the fragile x-ray mask membrane.
A focused ion beam system for submicron lithography
Authors: Kurihara Kenji
Published: July 2002

A two-lens optical system for a focused ion beam system has been designed, using a four-electrode accelerating lens as the condenser lens and an Einzel lens as the objective lens. A 1 nA beam current in a 0.055–0.1 μm beam spot is obtained under the following conditions: 20 μA/sr angular current intensity, 10 eV beam energy spread, 30–60 kV acceleration voltage, and 4 mrad object side beam half angle. The chromatic aberration coefficient of the condenser lens is reduced by picking out the dominant design parameters and optimizing them under the design constraints. The four-electrode accelerating lens has an object-side chromatic aberration coefficient Cco=11 mm at the object side focal length fo=25 mm at infinite magnification for 30 kV acceleration voltage. The Einzel lens operating in the acceleration mode has an image-side chromatic aberration coefficient Cci=70 mm at the image-side focal length fi=50 mm. A focused ion beam system is developed using the designed lenses and a Ga ion source. A pattern as fine as 0.15 μm with excellent definition is obtained.
Nanostructure fabrication in metals, insulators, and semiconductors using self-developing metal inorganic resist
Authors: Kratschmer E. , Isaacson M.
Published: July 2002

AlF3 evaporated thin films of 20–80 nm thickness have been used as self-developing positive resists and also as negative resists forming metallic Al structures. The exposure mechanism of AlF3 resist has been investigated, and nanometer scale features have been fabricated in both cases at exposure doses of about 20 C/cm2 and 2 C/cm2 at 100 keV, respectively. Using reactive ion etching, AlF3 resist patterns have been transferred into Si3N4, resulting in feature sizes as small as 20 nm.
Molecular beam epitaxial growth and characterization of Cd1−xZnxTe, Hg1−xCdxTe, Hg1−xMnxTe, and Hg1−xZnxTe on GaAs(100)
Authors: Faurie J. P. , Reno J. , Sivananthan S. , Sou I. K. , Chu X. , Boukerche M. , Wijewarnasuriya P. S.
Published: July 2002

The growth of Cd1−xZnxTe on GaAs (100) is reported here for the first time. In contrast to CdTe, when x is higher than 0.15 only the Cd1−xZnxTe(100)∥GaAs(100) orientation is observed. We also present the growth and characterization of n-type and p-type layers of Hg1−xCdxTe, Hg1−xMnxTe, and Hg1−xZnxTe for the first time, in most of the cases. These layers exhibit high structural and good electrical properties. Several different characterizations carried out on Hg1−xCdxTe layers grown by MBE on GaAs substrates show that this material is at least as good as the best material grown by any other technique and confirm that GaAs is emerging as the candidate for replacement of CdTe as the substrate for growth of Hg1−xCdxTe by MBE. Hg1−xMnxTe and mainly Hg1−xZnxTe, which have electrical characteristics similar to high quality Hg1−xCdxTe, appear as potential candidates for replacement of Hg1−xCdxTe.
Reflection high-energy electron diffraction intensity oscillation study of Ga desorption from molecular beam epitaxially grown AlxGa1−xAs
Authors: Ralston J. , Wicks G. W. , Eastman L. F.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) intensity oscillations are used as an in situ probe to study Ga desorption during molecular beam epitaxial growth of AlxGa1−xAs. A simple thermodynamic model is developed which, in the limit of low As4 : group III beam flux ratios, accurately predicts the measured changes in AlxGa1−xAs growth rate and composition due to Ga desorption at elevated growth temperatures. The desorbing Ga flux is observed to be less in thin epitaxial layers of GaAs growing on top of AlGaAs than in bulk GaAs, giving rise to a growth rate transient at heterointerfaces.
Effect of strain on the elastic properties of superlattices
Authors: Schuller Ivan K. , Grimsditch M.
Published: July 2002

The elastic properties of superlattices are strongly affected by strains in these materials. Elastic anomalies have been found in Nb/Cu, Mo/Ni, V/Ni, and Au/Cr superlattices. The strains measured with x rays explain quantitatively the elastic softening in Mo/Ni. An extension of these arguments explains not only the softening of Nb/Cu but the hardening and softening observed in Au/Cr. The origin of the strains is not known at the present time.
Photoemission study of the reactive Pd/InP(110) interface
Authors: Kendelewicz T. , List R. S. , Bertness K. A. , Williams M. D. , Lindau I. , Spicer W. E.
Published: July 2002

We present a soft x-ray photoemission spectroscopy (SXPS) study of the Pd/InP(110) interface. SXPS has been used to study chemical reactions, overlayer morphology, and Fermi level pinning behavior during the early stages of interface formation. Strong reactions involving Pd and both species of the substrate have been documented and discussed. We took advantage of the tunability of the synchrotron source to study p–d valence band hybridization near to, and far from the Pd 4d cross section Cooper minimum. This was combined with a detailed study of the line shape of the P LVV Auger transition. Because of the strong reactions we had to unfold the core level spectra into their different components to follow the Fermi level pinning. Such an analysis shows that Fermi level pinning is established at the same energy, 0.45 eV below the conduction band minimum, for n and p-type crystals with Pd coverages of about 1 ML. This energy agrees with barrier heights established from the current–voltage characteristics measured on thick diodes grown under identical conditions. On the basis of the data, correlations proposed to describe barrier heights and chemical reactions at metal/InP interfaces are evaluated.
The interaction of Al, Mn, and Ag with clean and oxidized GaAs and InP(110) surfaces
Authors: Williams R. H. , McLean A. B. , Evans D. A. , Herrenden-Harker W. G.
Published: July 2002

Detailed studies are reported of interfaces formed between cleaved surfaces of GaAs and InP, and the metals, Ag, Al, and Mn. Microscopic interactions have been examined by soft x-ray photoemission, with synchrotron radiation, and electrical transport at interfaces have been studied by I–V and C–V methods. Ag is unreactive with clean GaAs and InP, and with oxidized GaAs, but is reactive with oxidized InP. Al and Mn chemically react with air cleaved and vacuum cleaved surfaces. Metals on InP are generally more reactive than on GaAs and Schottky barriers formed are very variable and dependent on intermediate oxide layers. Variable Schottky barriers are also measured for Mn on GaAs. The data are discussed in terms of current models of barrier formation at metal–semiconductor interfaces.
Schottky and Ohmic Au contacts on GaAs: Microscopic and electrical investigation
Authors: Liliental-Weber Zuzanna , Gronsky R. , Washburn J. , Newman N. , Spicer W. E. , Weber E. R.
Published: July 2002

We report here a systematic study which uses electrical device measurements and transmission electron microscopy (TEM) methods to investigate the electrical, morphological, and structural properties of Au/GaAs Schottky diodes. The electrical characteristics of Au diodes formed on atomically clean and air-exposed GaAs(110) surfaces are found to change from rectifying to Ohmic behavior after annealing above the Au–Ga eutectic temperature (360 °C). This change is shown to be due to an Ohmic-like contact at the periphery of the device. TEM studies of these structures indicate that the Ohmic peripheral current pathway can be correlated with the formation of near surface Ga-rich Au crystallites at the diode circumference upon annealing. Further evidence of the correlation of the Ohmic electrical characteristics with the morphology of the periphery comes from data which indicate that the removal of these Au crystallites by mesa etching is also accompanied with the elimination of the Ohmic current. The morphology of the overlayer was found to depend strongly on annealing and surface treatment. TEM indicates that the interface is flat and abrupt for all unannealed diodes, as well as for annealed diodes formed on atomically clean surfaces. For annealed diodes formed on the air-exposed surfaces, the metal–semiconductor interface contains large metallic protrusions extending up to several hundred angstroms into the semiconductor. For comparison to practical structures, the morphology of annealed diodes formed using typical commercial processing technology [i.e., formed on chemically prepared (100) surfaces annealed in forming gas] was also investigated using TEM. The interface for these structures is more complex than interfaces formed on the atomically clean and air-exposed cleaved (110) surfaces. Evidence that Au diffuses through the interfacial native oxide layer and forms islands in intimate contact with the semiconductor was found.
Multiphoton-induced desorption of positive ions from barium fluoride
Authors: Matthias E. , Nielsen H. B. , Reif J. , Rosén A. , Westin E.
Published: July 2002

Subject of this paper is the interaction between laser radiation and surfaces of optically transparent ionic crystals at low-power densities of the order of 106–107 W/cm2. By studying the wavelength and intensity dependencies of electron and ion-emission yields, it is shown that surface states play a decisive role for photon absorption at surfaces of divalent ionic crystals. They resonantly enhance multiphoton processes which leads to a strong-wavelength dependence of both photoemission and ion desorption. Cluster calculations confirm the existence of occupied surface states in the middle of the band gap and of unoccupied states in its upper half as well as above the ionization limit. The dependence on laser intensity reveals both two- and five-photon processes for photoemission, and ten-photon processes for the desorption of positive ions. The latter is interpreted as the creation of two holes, each by five-photon absorption, with subsequent Coulomb repulsion of a positive ion.
Reactive ion etching of GaAs with high aspect ratios with Cl2–CH4–H2–Ar mixtures
Authors: Vodjdani N. , Parrens P.
Published: July 2002

A new process for RIE of GaAs employing Cl2–CH4–H2–Ar etching gases is presented. The effect of CH4 and H2 on etch rate, etch profile, and surface morphology is studied. The plasma excited species are monitored in situ by emission spectroscopy and etch depths measured by laser interferometry. Anisotropic profiles and residue-free surfaces are obtained with Cl2–CH4–H2–Ar and Cl2–CH4–H2–Ar gases. Depending on process parameters, selectivities up to 180 with respect to SiO2 are obtained allowing deep etching. X-ray photoelectron spectroscopy and Auger electron spectroscopy of different etched surfaces are compared with a chemically etched reference surface. This shows that a Cl2/H2/Ar etch leaves the surfaces, contamination free.
Study of n-InxGa1−xAs/n-GaAs heterojunction epilayers
Authors: Jeong J. , Lee J. C. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

Isotype heterostructures of n-InxGa1−xAs on n-GaAs substrates have been grown by molecular-beam epitaxy (MBE) for the composition range x=0–0.15 and thickness about 1 μm. Photoluminescence measurements for the InGaAs have been made at 77 and 4.9 K. X-ray diffraction measurements have provided information on the composition x, and the variation of the band gap at 4.9 K with x is compared with that obtained for liquid phase epitaxy (LPE) InGaAs layers at 300 K. The apparent electron carrier concentrations (in the 1016 cm−3 range) from capacitance–voltage (CV) profiling with a Schottky barrier on the InxGa1−xAs have been examined for the temperature range 77–300 K. Rather than the expected electron depletion dip in the GaAs followed by an accumulation peak in the InGaAs region close to the interface, we find two accumulation peaks that undergo substantial changes in the temperature range 190–160 K. Deep level transient spectroscopy characteristics show five electron traps of which one at Ec−0.13 eV is not typical of GaAs and may be InGaAs or interface related.
Carrier densities in InAs–Ga(Al)Sb(As) quantum wells
Authors: Munekata H. , Esaki L. , Chang L. L.
Published: July 2002

With the aim to study the influence of substitutional species on the band schemes and charge transfers in type-II heterostructures, the InAs–GaSb based quantum well structures have been prepared by molecular-beam epitaxy with a replacement of GaSb by GaSbAs and GaAlSb. Galvanomagnetic measurements show a similar behavior of decreasing hole density with increasing alloy composition in both cases, suggesting a transfer process insensitive to the cation–anion nature of the alloying element. That the high electron mobility also decreases with the composition is primarily governed by the degree of lattice mismatch.
The structure and electrical properties of metal contacts on GaAs
Authors: Liliental-Weber Zuzanna
Published: July 2002

This paper reports a study of the changes in the structural and chemical properties of Au and Al contacts on GaAs at annealing temperatures where significant changes in the Schottky barrier height are found. The annealing of Au contacts above 290 °C caused the Schottky barrier height to decrease. In contrast the Schottky barrier height of Al diodes increases upon annealing. An increase in As/Ga ratio in the GaAs under the as-deposited metal was consistently found in both cases. Upon annealing the As/Ga ratio is found to decrease for Al contacts, while it is found to increase for Au contacts. The orientation relationship of the Au contacts changed upon annealing. This was not observed with the annealed Al. The orientation relationship depended strongly on the surface preparation before the metal deposition and on the annealing environment. It was proposed that the presence of As at the interface can determine the orientation relationship between metals and GaAs.
Attainment of 0.13-μm lines and spaces by excimer-laser projection lithography in ‘‘diamond-like’’ carbon-resist
Authors: Rothschild M. , Ehrlich D. J.
Published: July 2002

Recent results are reported for the use of ‘‘diamond-like’’ hard carbon as a photoresist for excimer-laser projection lithography. Well resolved 0.13 μm lines and spaces have been achieved using 193 nm radiation and reflective optics.
Rapid direct writing of high-aspect ratio trenches in silicon: Process physics
Authors: Treyz G. V. , Beach R. , Osgood R. M.
Published: July 2002

The processes governing direct-write etching of semiconductors with halogen gases are studied by concentrating on a specific materials system: the etching of silicon using the output from an argon-ion laser and chlorine gas to form high-aspect ratio trenches. Specifically, the effects of laser power, laser polarization, laser scan velocity, Cl2-gas pressure, and the addition of buffer gases on the trench formation process have been studied. A simple model has been developed which relates trench depth and these parameters. Model results are presented and compared with experimental data.
Plasma etching of organic materials. II. Polyimide etching and passivation downstream of an O2–CF4–Ar microwave plasma
Authors: Vukanovic V. , Takacs G. A. , Matuszak E. A. , Egitto F. D. , Emmi F. , Horwath R. S.
Published: July 2002

Parameters which influence the etching of polyimide (PI) downstream of an O2–CF4–Ar microwave (MW) plasma were studied. Of particular importance is the influence of the ratio of atomic number densities O/F in the plasma and the gas flow velocity, which caused an almost linear increase in the etch rate within the investigated limits of the experiment. No measurable etching of PI was found downstream of an O2–Ar plasma, although the presence of oxygen atoms in the vicinity of the substrate was verified by the chemiluminescent reaction with NO. Similar to previously reported radio frequency plasma studies, a fluorinated layer at the surface of (PI) was formed by exposure of the substrate downstream of a fluorine-rich O2–CF4–Ar MW plasma. Changing the plasma composition to the optimum etching conditions (an oxygen-rich plasma of about 20% CF4) removed the fluorinated layer after a period of time. Etching then proceeded with an oxygenated layer at the surface. The reported experiments confirmed that the formation of a fluorinated layer, the removal of this layer, and the formation of an oxygenated one was caused only by the interaction of neutrals, without the influence of ion bombardment.
Tungsten chemical vapor deposition characteristics using SiH4 in a single wafer system
Authors: Rosler Richard S. , Mendonca John , Rice M. John
Published: July 2002

Several workers have recently begun using silane as a high-rate, low-temperature alternative to hydrogen for the reduction of WF6 in the chemical vapor deposition of W. The deposition and film characteristics of both selective and blanket W using this new chemistry are explored in a radiantly heated single wafer system using closed-loop temperature control with a thermocouple in direct contact with the backside of the wafer. Selective W deposition rates of up to 1.5 μm/min were measured over the temperature range 250–550 °C with blanket W rates typically 2–5× lower. Resistivity is in the 10–15 μΩ cm range at 300 °C for SiH4/WF6 ratios of 0.2 to 1.0, while above 400 °C the range is 7.5–8.5 μΩ cm. Si content in the W films is quite low at 1016 to 1017 atoms/cm3. Adhesion to silicon is excellent at temperatures of 350 °C and above. Selective W using SiH4 reduction for doped silicon contact fill shows none of the consumption or encroachment problems common to H2 reduction, although selectivity is more sensitive. Contact resistance for p+ and n+ silicon contacts are comparable to aluminum controls and to previously published data. Blanket deposition into narrow geometries gives ≥90% step coverage and without keyholes in the 250–450 °C deposition temperature range. For low-SiH4 flows, deposition at 500 °C causes small keyholes, while at 550 °C even larger keyholes result. At higher SiH4 flows, keyholes are typically not seen from 250 to 550 °C. The SiH4-reduced films are much smoother as indicated by reflectivities that are 2–4×higher than for the H2-reduced films.