bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature independent current blocking due to hot electrons in InAlAs/InGaAs double heterojunction bipolar transistors with composite collectors
Authors: McKinnon W. R. , Driad R. , McAlister S. P. , Renaud A. , Wasilewski Z. R.
Published: July 2002

In InAlAs/InGaAs double heterojunction bipolar transistors (DHBTS) with composite collectors, the reduction in current gain as the collector-base voltage is decreased (current blocking) is almost independent of temperature. This is in contrast to InP/InGaAs devices, where the blocking strongly increases as temperature is reduced. We attribute the temperature independence in InAlAs/InGaAs devices to electrons that are not thermalized as they cross the base. Our results have implications in the design of collectors for InAlAs/InGaAs DHBTs.
Photolithographic deposition of indium oxide from metalorganic films
Authors: Ching Celia L. W. , Hill Ross H.
Published: July 2002

The photochemical deposition of indium oxide films from thin films of indium (III) 2-ethylhexanoate is described. The photolysis of thin films of indium (III) 2-ethylhexanoate results in the fragmentation of the carboxylate ligand and the production of indium along with volatile organic products. When conducted in air, the product of the reaction is indium oxide. Films react depending upon the thickness such that thinner films react more efficiently. This results in a variation in the quantum yield for reaction from near 0.23 for thin films to less than 0.0034 for thicker films. This effect is interpreted as due to partial order within the amorphous precursor film resulting in a lower photosensitivity. Films constructed of indium (III) 2-ethylhexanoate were used to deposit lines of less than 2 micron feature size lithographically using a contact mask.
Excited state density distributions of H, C, C2, and CH by spatially resolved optical emission in a diamond depositing dc-arcjet reactor
Authors: Luque J. , Juchmann W. , Brinkman E. A. , Jeffries J. B.
Published: July 2002

Spatially resolved optical emission spectroscopy is used to investigate excited species in a dc-arcjet diamond depositing reactor. Temperature measurements indicate a cold plasma with electrons, excited states, and gas in nonthermal equilibrium. The H, C, C2, and CH excited state number densities decrease exponentially with the distance from the nozzle and have a pronounced increase in the shock structure above the substrate. The H emission increases throughout the boundary layer to the substrate surface, whereas emission from other species has a maximum in the boundary layer and then decreases again towards the substrate. The reconstructed radial distribution of excited state concentrations are Gaussian, with the C and C2 distributions broader than the H and CH ones. The optical emission is calibrated with either Rayleigh scattering or laser-induced fluorescence to furnish absolute number densities. We find all the excited species to be present in concentrations two or more orders of magnitude smaller than the corresponding ground states measured in the same reactor and conditions. We find that C2(d-a) emission intensity correlates well with laser-induced fluorescence measurements of C2(a) concentration in the arcjet plume. Ground state concentrations of the other species do not vary as their emission intensity except near the substrate, where the variations of CH(A-X), CH(B-X), and C2(d-a) emission intensities are good monitors of the corresponding concentration changes.
Band alignment and barrier height considerations for the quantum-confined Stark effect
Authors: Yip R. Y.-F. , Desjardins P. , Isnard L. , Aı̈t-Ouali A. , Bensaada A. , Marchand H. , Brebner J. L. , Currie J. F. , Masut R. A.
Published: July 2002

Strained-layer multiple quantum wells InAsP/InP and InAsP/InGaP optical modulators based on the quantum-confined Stark effect have been fabricated from layers grown by metalorganic vapor phase epitaxy on InP(001). The device layers have been characterized by complementary high resolution x-ray diffraction, transmission electron microscopy, optical absorption and photoluminescence analyses. The structural properties of the layers were deduced from the above data and an accurate determination of the band alignment of the heterostructures was made by performing multiple transition fits to the optical absorption spectra using the Marzin–Bastard envelope function model for strained-layer superlattices. The electric field-dependent redshift of the fundamental electron-heavy hole transition was measured by a photocurrent method and found to be enhanced for structures with lower valence band barrier heights. This observation leads directly to the conclusion that the overall performance of high speed, low drive voltage optical modulators may be improved by engineering the band alignment of the multiple quantum well stack towards structures with disproportionately large conduction band offsets. An optimization of the band alignment will permit more efficient optical modulation by reducing the drive field required to operate the device, which, in turn, can have direct effects upon the drive voltage, device capacitance, attenuation coefficient, and optical coupling and propagation losses.
Far-infrared transmission study of Bernstein modes in a two-dimensional electron gas with a tunable lateral modulation
Authors: Lefebvre J. , Beerens J. , Feng Y. , Wasilewski Z. , Beauvais J. , Lavallée E.
Published: July 2002

Far-infrared transmission measurements have been performed on a two-dimensional electron gas (2DEG) with a lateral modulation of its concentration induced using an electrostatic gating technique. A strong coupling of the plasmon with the cyclotron resonance harmonics (of index up to n=5), known as Bernstein modes, is observed when the photon energy is close to the plasmon energy of the modulated 2DEG. The behavior of these modes is studied as a function of magnetic field and modulation strength for λ=163 and 229 μm. A classical theory based on the Boltzmann kinetic equation [A. V. Chaplik and D. Heitmann, J. Phys. C 18, 3357 (1985)] gives a good account of the main experimental features.
Photoluminescence quenching of Alq3 by metal deposition: A surface analytical investigation
Authors: Choong V.-E. , Park Y. , Gao Y. , Mason M. G. , Tang C. W.
Published: July 2002

The importance of the interfacial properties in organic light emitting devices (OLED) is well recognized. We will describe our recent efforts to understand interfaces in OLEDs using surface/interface analytical techniques in a well controlled ultrahigh vacuum environment. We observed severe photoluminescence quenching of organic thin films comprising of a model OLED material, namely tris-(8-hydroxyquinoline) aluminum (Alq3), upon deposition of a number of metals. Such quenching may severely affect the electroluminescence device efficiency. We have investigated the interfaces using x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy, and studied the intriguing process of the interface formation at an atomic/molecular level. We will show that microscopic surface and interface properties are intimately related to the device characteristics and performance.
Developments in equipment support technology
Authors: Sullivan J. J. , Gwizdak R. , Gu Y. , Culwell W. , Baker J. M. , Hosch J. W.
Published: July 2002

This article will review the achievements, on-going development activities and needs in “equipment support technology,” i.e., the critical or key components which surround the process chamber and without which an effective process cannot be reliably and repeatably executed. The challenges of the SIA (Semiconductor Industry Association) Roadmap have been the focus for the dramatic developments in many areas, such as the following: delivery of process material vapors into the reactor, control of the exhaust effluent from the reactor, on-process pressure measurement and control sensors and actuators, implementation of a well supported digital sensor bus introduced on 300 mm tool sets, tool and process diagnostics through residual gas analysis, and the incorporation of fault detection schemes and the eventual implementation of model based process control techniques. With the escalating cost of wafers-in-process, and the desire to increase overall equipment effectiveness and reduce cost-of-ownership, it becomes increasingly important to separate, control, diagnose and predict the behavior of critical process variables in real time. In-situ measurement, control, and metrology result in dramatically improved meantime between failures, shorter meantime to repair, and a significantly reduced cost per measurement function.
Film growth of nanostructured C–N/TiNx multilayers reactively sputtered in pure nitrogen
Authors: Jensen Henja , Sobota Jaroslav , Sorensen Gunnar
Published: July 2002

The present communication reports on reactive sputtered nanostructured C–N/TiNx multilayers deposited in pure nitrogen. Carbon and titanium sputtering cathodes are operating concurrently in the side by side configuration. Experimental parameters of relevance for the pseudomorphic growth of the carbon nitride multilayer system, for instance, nitrogen flow and the rotation speed of the substrate holder, varying the bilayer thickness, are discussed. Nanostructured composite coatings, typically 2–3 μm thick, were deposited at a pressure ranging from 0.2 to 1 Pa, and seeding with TiN sputtered in pure nitrogen is reported for the C–N/TiNx system. The acoustic emission scratch test was used, both for measurement of coating adhesion and for tribological characterization. Relevant friction parameters, such as friction coefficient and film transfer, when a WC or a Si3N4 ball is reciprocating on the nanostructured multilayer were studied. Further the dynamic impact method was used for testing the coating system, and tribological studies of pure nitrogen sputtered films are compared with results earlier obtained for C–N/TiNx multilayer coatings, reactively sputtered in nitrogen/argon mixtures.
Interference in far-field radiation of two contra-propagating surface plasmon polaritons in the Kretchmann configuration
Authors: Xiao Mufei , Machorro Roberto , Siqueiros Jesús
Published: July 2002

Work on experimental and theoretical study of interference of two contra-propagating surface plasmon polaritons is reported. In the experiments, the technique of attenuated total reflection in the Kretschmann configuration is used to launch the plasmon polariton on the surface of a thin silver film (∼500 Å in thickness), which covers the flat surface of a semicylindrical prism of optical glass. A mirror is used to send back the reflected light beam to the same area of the film. The reflected beam from the mirror launches another surface plasmon polariton in the direction opposite to the first surface plasmon polariton. Light beam from a He-Ne laser is used in the experiments. Noncoherent light from a monochromator is also used to help alignment. An interference pattern of the two surface plasmon polaritons is observed and is recorded with an optical microscope located in the air side near the film. The above device is also described theoretically with numerical calculations of interference fringe spacing.
Passivation role of fluorine on the anticorrosion of AlCu films after plasma etching
Authors: Baek Kyu-Ha , Kim Chang-Il , Kwon Kwang-Ho , Kim Tae-Hyung , Chang Eui-Goo , Yun Sun Jin , Yoon Yong-Sun , Kim Sang-Gi , Nam Kee-Soo
Published: July 2002

To eliminate corrosion, a subsequent treatment of SF6 plasma after an Al–Cu etching has been carried out. X-ray photoelectron spectroscopy (XPS) studies showed that the F content on the Al–Cu alloy surface caused by the SF6 treatment increased as the chamber pressure increased, and Cl incorporated during the Al–Cu alloy etching was not totally removed by the post-treatment using SF6 gas plasma. However, it was confirmed by scanning electron microscopy (SEM) that corrosion could be eliminated by the SF6 treatment at 300 mTorr. At the same time, the results of angle-resolved XPS showed that elemental Al was distributed under the layer of F-related compounds. These results indicate that SF6 treatment can reduce the corrosion of Al–Cu alloy films by producing a F-containing layer on the etched surface. From the SEM image, the existence of a passivation layer on the Al–Cu alloy film surface by fluorine-related compounds was confirmed. The passivation layer prevents moisture penetration on the SF6-treated surface and suppresses corrosion successfully. The composition of the passivation layer measured by angle-resolved XPS was mostly uniform within a few hundred nm thickness. The passivation film was composed of 32% Al, 43% F, 2% Cl, and 10% O at a SF6 pressure of 300 mTorr. Approximately 2% of Cl was uniformly distributed in the film.
Characterization of low dielectric constant plasma enhanced chemical vapor deposition fluorinated silicon oxide films as intermetal dielectric materials
Authors: Kim K. , Kwon D. H. , Nallapati G. , Lee G. S.
Published: July 2002

The characteristics of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition are discussed. The deposition of these films was carried out in the temperature range of 80–220 °C in a conventional parallel plate plasma reactor with <±3% uniformity across 4 in. wafer by flowing 2 sccm of disilane, 100 sccm of nitrous oxide and 20 sccm of tetrafluoromethane. As the deposition temperature increased from 80 to 220 °C, the deposition rate of the films increased from 16.7 to 18.4 nm/min; meanwhile, the etch rate decreased from 2.69 to 1.48 nm/s. The refractive index was 1.46 regardless of the deposition temperature. The Fourier transform infrared spectra of the films showed a decreasing Si–O stretching wave number with an increasing full width at half maximum as the deposition temperature increased. The high frequency capacitance–voltage measurements of the metal–oxide–semiconductor (MOS) capacitors fabricated using the films showed increasing effective oxide charge density and decreasing dielectric constant with increasing deposition temperature. A deposition temperature of 180 °C resulted in films with the smallest dielectric constant of 3.75. These films showed an average breakdown strength of 9.14 MV/cm with 77.5% of the MOS capacitors having breakdown field strengths ⩾9.5 MV/cm.
Evaluation of trifluoroacetic anhydride as an alternative plasma enhanced chemical vapor deposition chamber clean chemistry
Authors: Pruette L. C. , Karecki S. M. , Reif R. , Langan J. G. , Rogers S. A. , Ciotti R. J. , Felker B. S.
Published: July 2002

One environmental issue currently facing the semiconductor industry is the emission of perfluorinated compounds (PFCs) from a variety of processes including chamber cleaning following plasma enhanced chemical vapor deposition (PECVD) of dielectrics. The emission of PFCs has been targeted for reduction due to the contribution of these species to global warming. An option under investigation is the use of alternative compounds that emit lower amounts of global warming species. The current study presents chamber cleaning times and emissions from the use of one such species, trifluoroacetic anhydride (TFAA), in a widely used commercial PECVD tool, the Novellus Concept One 200. A central composite design-of-experiments was employed to calculate response surfaces for the chamber clean time and PFC emission concentrations as the chamber pressure, TFAA flow rate, and oxygen flow rate were varied. The chamber clean times were measured using optical emission spectroscopy, quadrupole mass spectrometry, as well as Fourier transform infrared (FTIR) spectroscopy, and the PFC emissions were quantified using FTIR spectroscopy. The performance of TFAA is compared to standard Novellus Concept One 200 C2F6 and C3F8 chamber cleaning processes and to processes in which the effect of augmentation of C2F6 with NF3 is studied.
Plasma conditions for as-grown low temperature poly-Si formation on SiO2 substrate by sputtering and plasma enhanced chemical vapor deposition processes
Authors: Takeya M. , Park W. S. , Jong G. S. , Ohmi T.
Published: July 2002

We investigated the deposition condition of the plasma processing for the formation of as-grown poly-Si thin film on the SiO2 substrate with low temperature (300 °C) processing. We intended to compensate the thermal energy loss due to the low temperature processing with the low kinetic energy ion bombardment assist. We adopted both plasma enhanced chemical vapor deposition (PECVD) (SiH4/Ar/H2) and sputtering (Si-target/Ar/H2) processes. Plasma parameters were measured by the advanced Langmuir probe method tuned for 182.5 MHz rf plasma. Crystallinity of the film was estimated mainly by x-ray diffraction. Crystallization occurred by in situ hydrogenation during the deposition. In our experiment, ion bombardment energy was approximately 23 eV. We define the normalized ion (ni) flux number and investigated the correlation between the ni and the film crystallinity. The result is as follows, the crystal size enlarges with the increasing ni up to ∼20 but it diminishes as the ni increases over ∼20. Under the same plasma condition, the PECVD processed Si films have better crystallinity than the sputtering processed ones. The film thickness and crystal size are 1000 and 219 Å, respectively, at the optimum value of the ni in the PECVD process. Atomic hydrogen is thought to be very effective for the crystallization of the film and, as for the ion assist effect, there exists an optimum value of ni for a certain ion bombardment energy.
Vibrational study of CH2 and CH3 radicals on the Cu(111) surface by high resolution electron energy loss spectroscopy
Authors: Chan Y. L. , Chuang Ping , Chuang T. J.
Published: July 2002

Hydrocarbon radicals, methyl and methylene, are generated through hot nozzle sources and dosed onto Cu(111) at 300 K. High resolution electron energy loss spectroscopic measurements show that for the CH2 exposed sample, the radical not only can be chemisorbed on the surface but also can diffuse and react to form complex aromatic species at a monolayer coverage or less. The aromatic species exhibit characteristic vibrational bands at 1436, 1540 and 1613 cm−1. When the adlayer is annealed above 400 K, some species are desorbed while others are decomposed to form methylidyne. For CH3 impinging on Cu(111), some of the trapped radicals dehydrogenate to form CH2. Both H and CH2 are coadsorbed with CH3 on the surface. The results of the two radical-surface systems are compared and discussed.
Surface segregation of low-energy ion-induced defects in Si
Authors: Bedrossian Peter J. , Diaz de la Rubia Tomas
Published: July 2002

Surfaces of Si(100) irradiated at 110 K with 5 keV He ions under ultrahigh vacuum conditions and subsequently annealed isochronally display abrupt healing of the radiation-induced surface roughness at 160 K. Smoothening also occurs at 160 K for Si(100)-2×1 irradiated with 230 eV Ar ions at 110 K, but not for Si(100) following submonolayer Si deposition at 110 K. The data suggest that the smoothening at 160 K following 5 keV He ion irradiation at 110 K results from surface recombination of point defects which are generated on or below the surface by the irradiation and migrate to the surface at 110 K.
Design and pumping characteristics of a compact titanium–vanadium non-evaporable getter pump
Authors: Li Yulin , Hess Daniel , Kersevan Roberto , Mistry Nariman
Published: July 2002

A compact non-evaporable getter (NEG) pump is made by stacking sintered titanium–vanadium blades recently available from SAES Getters as St185. The 50 blades are stacked between copper spacers on a stainless steel tube, and are activated by a removable heater cartridge inserted into the tube. The room temperature pumping speeds for CO and N2 are measured as a function of sorbed gas quantities at various activation temperatures and with different NEG disk spacing, in order to optimize the pump design and operation. The study shows that there is a threshold of activation at a temperature of about 340 °C and optimal pumping speed and pumping capacity can be achieved with activation temperature around 550 °C. Linear pumping speeds of about 2200 l/s m and 1300 l/s m can be achieved for CO and N2, respectively, with activation at temperatures of 500 °C for 1 h. A direct comparison shows a much higher pumping speed for the St185 than that for the St707 (Zr–V–Fe alloy, also by SAES Getters). The low activation temperature of the St185 NEG and the compact design make the NEG pump cartridge particularly attractive for situations with tight space and with components sensitive to high temperature.
Application of calculated physical adsorption isotherms to a radon sensor
Authors: Hobson J. P. , Appleby A. , Kim I. S. , Sigel G. H.
Published: July 2002

Recently a radon sensor using a glass scintillator in a fiber bundle structure was developed at Rutgers University. This instrument employs a flow of atmospheric air carrying the radon gas and its progeny in trace amounts through the bundle at room temperature. A central problem of interpretation is to distinguish whether the radioactive Rn222 atoms whose α decay is detected in the sensor are in the gas phase in the narrow spaces between the fibers or are adsorbed on the surfaces of the fibers. At the 43rd National Symposium of the American Vacuum Society (1996), calculated physical adsorption isotherms of radon were reported over a wide range of pressures, coverages, and temperatures. The latter explicitly included room temperature (300 K). The question arises as to whether this calculated isotherm is applicable to the Rutgers sensor. From radioactive considerations alone, in one experiment, it is estimated that there is either an upper bound of 5.5×10−10 Torr on the partial pressure of Rn or an upper bound of 3.9×10−11 monolayers on the coverage. Application of the theoretical isotherms to this experiment yields a unique value of 4.8×10−10 Torr at a coverage of 5×10−12 monolayers (i.e., 13% of all atoms adsorbed). A careful record of counting rates during temperature variations around room temperature was kept. These variations were between 292 and 308 K, and counting rates varied by 26% being highest when the temperature was lowest. Application of the theoretical isotherms at these two temperatures gave good agreement with the counting rates.
In situ sputter deposition discharge diagnostics for tailoring ceramic film growth
Authors: Aita C. R.
Published: July 2002

Reactive sputter deposition is widely used for growing technologically important ceramic films, including high melting point phases near room temperature, metastable phases, and nanoscale layered structures with controlled interfaces. Film properties are governed by kinetic processes at each electrode and in the gas phase. A knowledge of the reacting species and reaction paths is essential for reproducible growth of desired ceramic phases and structures. Obtaining this knowledge is the first critical step in developing transferrable processes. In this article, we briefly describe reactive sputter deposition of oxides and nitrides from metal and ceramic targets, and identify important chemical features of the process. Production of activated gas species by plasma volume collisions between ground state reactive gas molecules and rare gas atoms in low-lying metastable energy states is discussed. We then review mass and optical spectrometric methods for real-time monitoring of nonelectronic species in the discharge, and using many examples, show how the information obtained from in situ diagnostics gives insight into the chemistry of ceramic film growth.
Plasma-deposited silicon oxide and silicon nitride films on poly(ethylene terephthalate): A multitechnique study of the interphase regions
Authors: da Silva Sobrinho A. S. , Schühler N. , Klemberg-Sapieha J. E. , Wertheimer M. R. , Andrews M. , Gujrathi S. C.
Published: July 2002

The “interphase” region between the deposited layer [e.g., plasma-enhanced chemically vapor deposited (PECVD) SiO2 or SiN] and the poly(ethylene terephthalate) (PET) substrate has been investigated and compared to physical vapor deposited (PVD) (electron beam evaporated) SiO2. Composition profiles determined by time-of-flight elastic recoil detection, electron microprobe analysis, and x-ray photoelectron spectroscopy all show an extended interphase region more than 50 nm in width, while the profile of the PVD SiO2 is narrower. However, since these analytical techniques are invasive and prone to artifacts, we have also examined ultrathin (about 10 and 20 nm) SiO2 and SiN PECVD layers on 50 nm spin-coated PET substrates by nondestructive infrared (IR) techniques. The IR spectra confirm that the thin PECVD deposits also comprise an organosilicon phase with Si–CHx bonds. We explain these observations in terms of a fragmentation/redeposition mechanism: During the earliest stage of PECVD, interaction between the plasma and the polymer surface produces volatile organic species, which intermix with the reagent gas feed, thus giving rise to the observed organosilicon-like deposit with gradually decreasing carbon content.
Effects of wall recombination on the etch rate and plasma composition of an etch reactor
Authors: Font Gabriel I. , Boyd Iain D. , Balakrishnan Jitendra
Published: July 2002

A helicon plasma etch reactor is simulated using direct simulation Monte Carlo and particle-in-cell methods for a chlorine (Cl2) feed gas flow. Computations for the gas discharge are carried out by modeling the ions and neutrals as particles and by imposing the electrons as a background condition conforming to experimental measurements. The neutrals and ions are then allowed to interact with the background electrons and to relax to a steady state. The effects on the reactor flow field and etch rate of chlorine atom recombination into chlorine molecules at the walls is investigated. Results show that recombination at the walls results in the depletion of the amount of chlorine atoms (Cl) in the reactor. The depleted chlorine atom population leads to lower ionization levels and a diminished ion (Cl+) flux to the wafer. Consequently, the etch rate is decreased by as much as 15% when compared to simulations without recombination. The creation of chlorine (Cl2) molecules at the walls through recombination also provides a new source for negative ions (Cl−) which increases the electronegativity of the plasma. In addition, the results of the simulation are compared with ion current and optical emission spectroscopy (OES) measurements. The Cl–Ar ratio (measured by the OES technique) increases less than 20% from the centerline to the wall of the reactor. An inspection of absolute densities, however, reveals that the individual near-wall densities are as much as a factor of 2 greater than the centerline densities. The trace species, Ar, therefore, does not become distributed evenly throughout the reactor.
Influence of sticking coefficients on the behavior of sputtered atoms in an argon glow discharge: Modeling and comparison with experiment
Authors: Bogaerts A. , Naylor J. , Hatcher M. , Jones W. J. , Mason R.
Published: July 2002

Two-dimensional sputtered lithium atom density profiles have been calculated with a model for an argon glow discharge. Since the value of the sticking coefficient of sputtered atoms at the cell walls, which is needed as the boundary condition for calculating the behavior of the sputtered atoms, is not available from the literature, the calculations were performed for a range of sticking coefficient values. It is found that this parameter has a significant effect on the calculation results, and accurate knowledge of its value would therefore be required for an exact description of the behavior of sputtered atoms in a glow discharge. The density profiles calculated have also been compared with experimental results, obtained with concentration-modulated absorption spectrometry at the same discharge conditions and in the same cell geometry, in order to try to make reasonable estimates for the sticking coefficients.
Influences of ion energy on morphology and preferred orientation of chromium thin films prepared by ion beam and vapor deposition
Authors: Kuratani Naoto , Ebe Akinori , Ogata Kiyoshi
Published: July 2002

The influences of ion irradiation on morphologies and preferred orientations of Cr thin films prepared by ion-beam and vapor deposition were studied. Cr films were prepared onto Si 〈100〉 wafers by evaporation of Cr and simultaneous irradiation with Ar ions. The energies of Ar ions were changed in the range of 0.5–20.0 keV, and transport ratios of irradiated Ar ions to vaporized Cr atoms, Ar/Cr, to the substrates were kept at 0.033. Vaporized Cr atoms were deposited onto substrates at an angle of 45° and Ar ions were irradiated normal to the substrates. Si substrates were kept at low temperature during deposition. The experimental results show that the morphologies and the preferred orientations were varied due to the change of ion irradiating energy though other conditions were constant. Every Cr film takes a clear columnar structure. The column widths of Cr films are augmented with increase of ion energy. The columnar growth direction turns toward the deposition direction with increase of ion energy up to 5.0 keV. With further increase of ion energy the direction changes to perpendicular to the substrate, parallel to the direction of the ion irradiation. The preferred orientation to the substrate normal changes from random to 〈100〉 orientation through 〈110〉 and 〈100〉 orientation with increasing of ion energy. The reasons were understood as the mixed effects of nuclear and electronic energy transfers due to the collisions between Cr atoms and irradiated Ar ions.
Analysis of GaAs properties under biaxial tensile stress
Authors: Kim Ki Soo , Yang Gye Mo , Lee Hyung Jae
Published: July 2002

A tetragonally distorted GaAs layer was grown on a Si(100) substrate by metalorganic chemical vapor deposition. From both the splitting and the shift of band-edge exciton lines in photoluminescence, the GaAs epilayer is found to be under biaxial tensile stress, which is quantitatively investigated using optical measurements, namely, Raman and temperature-dependent photoluminescence spectroscopy. The biaxial tensile stresses deduced from the intrinsic excitonic lines vary with temperature. The origin of the stress variation with temperature is discussed in detail. From the photoluminescence intensity ratios between the heavy- and light-hole excitonic transitions, the actual temperature where the conduction to heavy-hole band transition begins to predominate is found to be above 70 K.
Generation of atomically flat MgO(100) surfaces: Influence of ambient gas composition during high temperature anneals
Authors: Perry Scott S. , Kim Hyun I. , Imaduddin Syed , Lee Sang M. , Merrill Philip B.
Published: July 2002

Atomic force microscopy, reflection high energy electron diffraction (RHEED), and x-ray photoelectron spectroscopy (XPS) have been used to follow the regeneration of atomically flat magnesium oxide (100) surfaces from samples initially etched in phosphoric acid. This regeneration process has been carried out by annealing samples at high temperatures in a range of gas compositions. The gas compositions investigated include argon, nitrogen, carbon dioxide, high partial pressures of water in nitrogen, and a range of partial pressures of oxygen. While acid etching produces initially rough surfaces, high temperature anneals (1000 °C) are found to significantly reduce the surface roughness independent of gas composition. In contrast, only annealing cycles in the presence of oxygen (O2) produced atomically flat stoichiometric MgO surfaces exhibiting good crystalline character, evidenced by distinct square-shaped terraces with well-defined step edges, a 1×1 RHEED pattern, and a 1:1 ratio between magnesium and oxygen determined by XPS analysis.
Low-pressure organometallic vapor phase epitaxy of coherent InGaAsP/InP and InGaAsP/InAsP multilayers on InP(001)
Authors: Guillon S. , Yip R. Y.-F. , Desjardins P. , Chicoine M. , Bougrioua Z. , Beaudoin M. , Aı̈t-Ouali A. , Masut R. A.
Published: July 2002

InGaAsP/InP and InGaAsP/InAsP multilayers were grown on InP(001) by low-pressure organometallic vapor phase epitaxy. Large growth rates of ≈0.4–0.6 nm s−1 and an increased element-V overpressure were used to limit the morphological evolution of the strained layers during growth and to compensate for the relatively high temperatures (≈630 °C) necessary for vapor phase epitaxy in a diffusion-limited regime. High-resolution x-ray diffraction and reciprocal lattice mapping analyses indicate fully strained multilayers of high crystalline quality. This structural information, combined with room-temperature photoluminescence (PL) measurements, allows us to determine accurately the thickness and the composition of the layers. Well-resolved excitonic transitions between the heavy- and light-hole valence bands and the conduction band are visible in the low-temperature optical absorption spectra for compressive InGaAsP/InP multilayers. The PL spectra for compressive InGaAsP/InP structures show sharp and intense transitions between the first confined levels in the conduction and the heavy-hole bands. The PL peaks for InGaAsP/InAsP heterostructures are slightly broader than for InGaAsP/InP multilayers due to the more complex (quaternary-ternary) interface but remain sharp and intense.
Surface reaction mechanisms of trifluoroacetylacetone on clean and pre-oxidized Ni(110): An example where etching chemistry does not follow volatility trends
Authors: Nigg H. Lee , Masel R. I.
Published: July 2002

Ni contamination is an increasing problem in the fabrication of thin microelectronic films. In previous work, we examined nickel removal using oxygen and 1,1,1,5,5,5-hexafluoro2,4-pentanedione (Hhfac) or 2,4-pentanedione (Hacac) and oxygen. In both cases, Ni was etched cleanly by the precursors under net oxidizing conditions. Decomposition pathways were prevalent, however, under reducing conditions. In the results reported in this article, we used temperature-programmed desorption to examine the use of another β-diketone, 1,1,1-trifluoro-2,4-pentanedione, and oxygen in the same process. Ni was etched on the oxidized surface by the desorption of Ni(CF3COCHCOCH3)2 between 260 and 430 K. Etching ceased as decomposition products formed. The structures of decomposition products on both surfaces indicates the promotion of β-bond scission by Ni, predominantly at C-CF3, C-CH3 and C-CH/C-CH2. In the hexafluoropentanedione and pentanedione studies, β scission was also the decomposition pathway. However, with trifluoropentanedione, the pathways produced many more species than with either the unfluorinated or the fully fluorinated analog. This observation was unexpected. Another unexpected observation was that some maximum desorption rate temperatures do not follow expectations based on volatility: Instead, Ni(CF3COCHCOCH3)2 desorbed at nearly the same temperature as Ni(CH3COCHCOCH3)2 and much lower than Ni(CF3COCHCOCF3)2. Another trend that does not follow predictions based on volatility is the desorption of the intact precursor from the monolayer on the pre-oxidized surface: Molecular CH3COCH2COCH3 desorbed at a lower temperature than either the CF3COCH2COCF or CH3COCH2COCH3. At present, it is unclear why the results disagree with the volatility trends.
Crystalline SiC thin films deposited at room temperature using pulsed laser ablation of graphite and magnetron sputtering of silicon
Authors: Nainaparampil Josekutty J. , Zabinski Jeffrey S.
Published: July 2002

Crystalline SiC films are typically deposited on substrates at elevated temperatures by sputtering, pulsed laser ablation, thermal chemical vapor deposition (CVD) and CVD plasma assisted. However, high temperature may adversely affect the substrate, especially when metal alloys are used. To maintain substrate properties (temper, dimensional tolerance, etc.), a low deposition temperature is required. In this work, silicon carbide is formed from simultaneous sputtering of silicon and laser ablation of graphite onto suitably biased substrates at room temperature. The advantage of this method lies in the independent selection of plasma characteristics of both magnetron sputtering and laser ablation to achieve the required stoichiometry and species energetics. Desirable film properties such as good adhesion and crystallinity normally requiring elevated substrate temperatures are obtained via the energetic bombardment of the growing film. In this study, films are grown on M50 steel substrates at biasing varied from 0 to −300 V permitting control over crystallinity, chemistry, and stoichiometry. X-ray photoelectron spectroscopy (XPS) analysis shows the existence of silicon carbide bonds and x-ray diffraction analysis demonstrated the growth of crystalline (prominently alpha polytypes (4H–SiC, 6H–SiC) films at room temperature. In addition, XPS is used to find percentage of SiC bonds in the films. The optimum bias −100 V was found to favor crystalline growth in these films. Special emphasis is given to control of film stoichiometry as it relates to mechanical properties.
Different effect of annealing temperature on resistivity for stoichiometric, W rich, and N rich tungsten nitride films
Authors: Lin Jun , Tsukune Atsuhiro , Suzuki Toshiya , Yamada Masao
Published: July 2002

The effect of the annealing temperature on the resistivity for stoichiometric (W2N), W rich (x<0.5), and N rich (x>0.5) tungsten nitride films (WNx) is different. The resistivity of as-deposited W2N is about 230 μΩ cm and it increases slightly and then decreases with increasing the annealing temperature up to 900 °C. However, for the W rich WNx whose initial resistivity before annealing is around 145 μΩ cm, the resistivity monotonically decreases with the annealing temperature increasing from 600 to 900 °C. As to N rich WNx whose initial resistivity is as high as 3000–5000 μΩ cm, though the resistivity must decrease after annealing at 600–750 °C, it irregularly varies at the higher temperature range of 750–900 °C. The different annealing temperature dependence of the resistivity can be explained by considering the nitrogen desorption, conversion of WNx to pure W, and cracking of WNx films.
Hydrogen plasma pretreatment effect on the deposition of aluminum thin films from metalorganic chemical vapor deposition using dimethylethylamine alane
Authors: Jang Tae Woong , Rhee Hwa Sung , Ahn Byung Tae
Published: July 2002

To study the effect of pretreatment of substrates on the deposition behavior of Al thin films, the surfaces of TiN and SiO2 substrates were exposed to hydrogen plasma or Ar plasma before Al deposition. The Al films were deposited by the pyrolysis of dimethylethylamine alane (DMEAA). A uniform Al film was deposited by the hydrogen plasma exposure to a SiO2 substrate, while island grains were grown by the Ar plasma exposure. The pretreatments of a TiN substrate did not affect the deposition rate of the Al film. The concentration of OH radicals at the SiO2 surface was increased by the hydrogen plasma treatment. We suggest a model in which OH radicals enhance the adsorption of DMEAA on a SiO2 surface, resulting in a larger number of nucleation sites.
Facet formation of a GaN-based device using chemically assisted ion beam etching with a photoresist mask
Authors: Lee W. J. , Kim H. S. , Yeom G. Y. , Lee J. W. , Kim T. I.
Published: July 2002

The etch characteristics of GaN were investigated using chemically assisted ion beam etching (CAIBE) for Cl2 as a function of tilt angle. With increasing tilt angle the measured GaN etch rate showed a maximum at 30° similar to the effect of tilt angle on the sputter yield. The etch profiles of GaN etched by tilting the substrate less than 20° showed sidewall trenching. When the tilt angle was more than 30°, an etch tail was observed at the bottom of the etched structure. With the Cl2 CAIBE, the anisotropy of the GaN etch profile was enhanced as the tilt angle was increased, and a vertical etch profile could be obtained at a 50° tilt angle. The sidewall roughness of the etched GaN laser device varied with the Cl2 flow rate and ion beam voltage. A highly anisotropic etch profile with a smooth sidewall could be obtained by optimization of the ion beam voltage/current and Cl2 flow rate. The surface of GaN etched by the Cl2 CAIBE system showed a Ga-deficient surface due to the removal of Ga by the formation of GaClx.
Properties of Y2O3 nanocluster films deposited by Cu-vapor laser at room temperature
Authors: Dinh L. N. , Frischknecht K. D. , Schildbach M. A. , Anklam T. , McLean W.
Published: July 2002

The dependence of stoichiometry, grain size, and surface morphology of yttrium oxide films, deposited by a Cu-vapor laser at room temperature, as a function of oxygen ambient pressure during synthesis were investigated. Auger electron spectroscopy showed that films with a O/Y ratio close to stoichiometry were obtained at oxygen pressures >3×10−1 Torr. X-ray diffraction revealed that pulsed laser deposited yttrium oxide films were composed mainly of nanocrystals, the average grain size of which grew from about 9.3 to 22.1 nm as the oxygen pressure was increased from 1.5×10−2 to 5 Torr. The surface morphology of the films, as determined by secondary electron microscopy, also exhibited increasing roughness as the grain size increased. Films deposited in an oxygen background pressure up to 1.5×10−2 Torr were oxygen deficient but exhibited good adhesion to substrates, while those deposited at higher oxygen background were powdery.
Optoelectronic properties of polycrystalline CdInTe films
Authors: Iribarren A. , Riech I. , Hernández M. P. , Castro-Rodríguez R. , Peña J. L. , Zapata-Torres M.
Published: July 2002

Close-spaced vapor transport combined with free evaporation was used for the growth of polycrystalline CdInTe films on glass substrates. The optoelectronic properties of the films were investigated by absorption at 77 and 300 K, and photoluminescence at 77 K with the indium concentration ranged from 0 to 22 at. %. The band-gap energy was found to vary linearly, and the band-gap temperature coefficient increases as the indium concentration increases. It was found that the ionization energy of indium displaced from the cationic sites of the CdTe lattice corresponds to a donor level at ED>32 meV (ED≃36 meV) below the conduction-band bottom. This level and the acceptor level associated with Cd vacancies stay at the same energy distance of their corresponding bands for all the indium concentrations studied. The relation between Eg and the lattice parameter is also shown.
Excitation states of titanium and nitrogen gas in an electron beam evaporation sustained arc
Authors: Xiao S. Q. , Tsuzuki K. , Sugimura H. , Takai O.
Published: July 2002

The arc discharge studied in this work was sustained by titanium vapor evaporated by an electron beam in nitrogen atmosphere. Optical emission spectroscopy and Langmuir probe diagnostics were carried out to study the excitation of titanium and nitrogen. It was found that with increasing arc current, Ti and nitrogen gas exhibited an opposite tendency of excitation. When arc current increased from 20 to 60 A, Ti was highly excited to Ti+, while the excitation of nitrogen was lowered; this is completely different from that for a conventional cathodic arc, where both Ti and N2 are highly ionized. By Langmuir probe diagnostics, the electron energy distribution followed a two-Maxwellian distribution at an arc current of 60 A; the electron temperatures were 0.98 and 10.1 eV, and the corresponding electron densities were 2.7×1011 and 3.9×109 cm3, respectively. This result provided a theoretical explanation for the difference of excitation between titanium and nitrogen in this arc.
Surface perturbation target for the Rayleigh–Taylor instability in inertial-confinement fusion experiments
Authors: Zhou Bin , Wang Jue , Shen Jun , Deng Zhongsheng , Lai Zhenquan , Chen Lingyan , Zhang Yulong
Published: July 2002

A preparation process of a surface perturbation target was introduced in this article. Through laser interference and a nickel-electroplate process, sinusoidal surface perturbation on the photoresist and nickel plate mold with sinusoidal surface perturbation were obtained. We transferred sinusoidal perturbation on brominated polystyrene foils by a spin-coating process. By removing the brominated polystyrene foils from the nickel-plate mold, the brominated polystyrene sinusoidal surface perturbation target was obtained. The transfer precision of the sinusoidal perturbation was measured by scanning electron microscopy. The measurements showed that the surface perturbation was transferred precisely. The surface roughness on the surface perturbation target was about 15.0 nm, analyzed by an α-step apparatus.
Surface passivation of InGaAs for heterojunction bipolar transistor applications
Authors: Driad R. , McKinnon W. R. , Lu Z. H. , McAlister S. P. , Poole P. J. , Charbonneau S.
Published: July 2002

High-energy resolution x-ray photoelectron spectroscopy and photoluminescence have been used to investigate the properties of InGaAs (100) after different surface treatments using hydrofluoric acid (HF) and ultraviolet (UV)-ozone. The efficiency of these treatments was then evaluated using the leakage currents and the current gain of InGaAs/InP heterojunction bipolar transistors (HBTs). Although the effects on InGaAs material properties differ, they both improved the current gain of large area HBTs. Subsequent dielectric depositions induced a drastic degradation of the device characteristics, demonstrating the noncompatibility of these treatments with plasma-enhanced chemical vapor deposition (PECVD) processes. By appropriately combining the UV-ozone and HF treatments, a successful passivation can be achieved even under PECVD deposition.
Photoluminescence and Hall effect measurements of Te segregation in Te-doped GaSb grown in terrestrial and microgravity conditions
Authors: Labrie D. , O’Brien J. , Redden R. F. , Audet N. , Lent B. , Micklethwaite W. F.
Published: July 2002

Three space-grown and two ground-grown Te doped GaSb samples are studied using Hall effect and photoluminescence (PL) spectroscopy to evaluate the degree of Te segregation in the crystals. A p–n conductivity type transition is observed in the ground-grown samples reflecting Te segregation towards the tail end of the samples while only p type conductivity is measured in the space samples. PL data indicates radial and axial Te segregation in the processed samples. Fluctuations in hole and hence Te concentrations in the space samples are attributed to G-jitters.
The temperature dependence of the dc characteristics of silicon germanium bipolar transistors
Authors: McAlister S. P. , Kovacic S. , Renaud A. , Zhou Z. F.
Published: July 2002

Silicon germanium bipolar transistors provide excellent high frequency performance within the context of silicon, encroaching dramatically on III–V semiconductor’s territory. Applications of the technology, however, will require the performance specifications with regard to the temperature range of operation. Using devices accessible from a BiCMOS technology, adapted to incorporate SiGe, we have measured the temperature dependence of properties such as the dc gain, ideality factors, and VBE at various base current levels, from 100 to 450 K. The ideality factors are close to unity above 250 K but greater than 2.5 at 100 K. We suggest that tunneling at the emitter perimeter can account for the high base ideality factors at low current and low temperature. Our data show a decrease in the gain with increasing current and temperature in normal operating ranges—devices with “box” Ge profiles in the base layer do not have this feature. This is important in preventing thermal runaway in power transistors, and may remove the necessity of emitter ballast resistors and provide higher power-added-efficiency in an amplifier block. We also show that the gain-Early voltage product is roughly linear with 1/T above ambient temperature.