bluuebunny/crossref_metadata_2025 huggingface dataset:
Why cryogenic inertial confinement fusion targets?
Authors: Larsen Jon T.
Published: July 2002

All advanced inertial confinement fusion (ICF) targets will be built with cryogenic thermonuclear fuel configurations. This paper reviews the ICF concept using frozen fuel, with emphasis on the conditions required for efficient energy production, some details of the implosion process, a brief discussion of certain sources of potential inefficiencies, and estimates of target fabrication requirements.
High-rate reactive sputter deposition of aluminum oxide
Authors: Jones Fletcher , Logan Joseph
Published: July 2002

Using a new reactive sputter deposition approach, we are able to consistently deposit stoichiometric Al2O3 films at a rate of 220 nm/min with±6% thickness variations across 82-mm-diam substrates. Thus a 10-μm-thick aluminum film could be deposited in 40 min. Deposition rates as high as 500 nm/min have been demonstrated. However, at these deposition rates, the voltage levels were high and the system was prone to arc during long runs. This paper describes the system and some of the properties of the films deposited at rates of ∼220 nm/min. It is shown that there is a range of experimental parameters over which the properties of films deposited at 220 nm/min show small variations.
Mixed-metal-oxide planar optical waveguides
Authors: Arjavalingam G. , Russak M. A. , Jahnes C. V. , Jackson K. P.
Published: July 2002

Thin films of ZrO2–SiO2 were deposited by reactive magnetron sputtering and reactive ion beam sputter deposition. The films were fabricated into planar optical waveguides by either ion beam milling or using liftoff lithography. The indices of refraction of the mixed-oxide films were found to be approximately a linear function of composition and were varied from 2.15 to 1.67. The films with >12% SiO2 were amorphous and thermally stable to at least 500 °C. Optical loss measurements on films with high ZrO2 content indicated losses of 3 to 4 dB/cm.
Optical and compositional properties of a-Si:H/transparent conductive oxide interfaces
Authors: Rava P. , Perino M. A. , Pirri C. F. , Galloni R. , Carnera A.
Published: July 2002

Films of hydrogenated amorphous silicon were deposited at different temperatures on films of transparent conductive oxides (TCO’s) (tin oxide and indium tin oxide) having different composition, thickness, and resistivity. Microcompositional analysis was performed by secondary ion mass spectroscopy to measure the microdistribution of Si, Sn and In. The optical properties of single a-Si:H films and a-Si:H films deposited on TCO were determined from measurements of transmittance and reflectance. The optical constants, refractive index, absorption coefficient, and optical band gap of single a-Si:H films are different from those of the same films deposited on TCO. The amount of Sn and In in the a-Si:H layer were found to depend on the deposition temperature and on the characteristics of the TCO and to be correlated with the optical properties.
Quantitative secondary ion mass spectrometry depth profiling of TiSi2 films
Authors: Corcoran S. F. , Osburn C. M. , Parikh N. , Linton R. W. , Griffis D. P.
Published: July 2002

This paper reports on an analytical method for the quantitative depth profiling of multilayer samples by secondary ion mass spectrometry (SIMS). This method is applied to SiO2/TiSi2/Si samples containing B and to TiSi2/Si samples containing As. The study involves the dopant redistribution during the self-aligned silicide process, a low-temperature process for 1-μm complementary metal–oxide semiconductor technology. A data processing program was developed which allows the user to input quantitative sensitivity factors and relative sputtering rates for each layer as derived from calibration samples. The processing algorithm converts the dopant (B or As) intensity–time profile to concentration–depth by applying the appropriate sensitivity factor and sputtering rate in each layer. Scaling of sputter rate and sensitivity factor across each interface corrects for transients in sputter ion yields and is accomplished by adjusting values in accordance with the change in the intensity of a matrix specific element. The analytical methodology is discussed for both B and As analyses including the assumptions made during the data acquisition and processing. Correlative sputtered neutral mass spectroscopy and Rutherford backscattering spectroscopy measurements are used to verify SIMS results for B and As, respectively.
A direct current plasma discharge cleaning method to eliminate background signals in secondary ion mass spectrometry
Authors: Hues Steven M. , Colton Richard J. , Wyatt Jeffrey R.
Published: July 2002

A simple technique has been developed to reduce background signals due to contaminants in a time-of-flight secondary ion mass spectrometer. This technique uses an argon dc plasma discharge and allows for rapid (10–15 min), routine cleaning of the interior instrument surfaces and vacuum chamber walls.
Pressure controlled feeding system for vacuum flash evaporation
Authors: Fuenzalida V. , Beltrán N. , Grahmann C. , Pérez M.
Published: July 2002

An automated feeding system for flash evaporation of powder in high vacuum has been developed. It is controlled by the system pressure and gives a nearly constant mean evaporation rate. The device is tested by evaporating ceramic powder (BaTiO3) with a base pressure of 2×10−4 Pa and a peak pressure of 1.4×10−3 Pa.
A solid-state ultrahigh vacuum compatible source of molecular iodine
Authors: Mowbray Andrew , Jones Robert G.
Published: July 2002

The construction and operation of an ultrahigh vacuum compatible source of molecular iodine vapor is described. The iodine is generated by the solid-state electrolysis of AgI doped 5% by weight with CdI2.
Surface electronic structure of semiconductor ( p- and n-Si) electrodes in electrolyte solution
Authors: Tomita E. , Matsuda N. , Itaya K.
Published: July 2002

The topography and the surface electronic structure of p- and n-Si (100) single crystal electrodes have been examined in a sulfuric acid solution by means of scanning tunneling microscopy (STM). It is shown that hydrogen-terminated Si surfaces are resistant to oxidation even in aqueous solutions. The tunneling current-electrode potential (I–E) curve suggests the existence of surface states. STM images of photoelectrochemically oxidized surfaces have been obtained.
Potentiometry for thin-film structures using atomic force microscopy
Authors: Anders M. , Mück M. , Heiden C.
Published: July 2002

The compliance of the tip–sample contact region in a scanning tunneling/atomic force microscope (STM/AFM) is found to increase from ∼1 N/m to more than 200 N/m with decreasing tip-to-surface distance in a distance interval of ∼200 nm. When a tungsten tip and a metal sample are used, this interval includes the distance at which a tunneling current is measurable. An STM/AFM was operated at this tip-to-surface distance in the constant-compliance mode. Since a tunneling contact to the tip is established at conducting sections of the sample, the electrical potential can be measured there. An array of interconnected niobium squares and an array of metal strips alternately connected to two electrodes of different voltage were examined using this method. Both structures were fabricated by electron beam lithography from Nb films on oxidized Si substrates. The topography and the value of the electrical potential were recorded. A potential resolution of the order of 1 mV was achieved.
The decomposition of formic acid on Pd(100)
Authors: Sander D. , Erley W.
Published: July 2002

We have examined the thermal decomposition of formic acid (HCOOH) adsorbed on a Pd(100) surface using thermal desorption spectroscopy (TDS) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS). The first layer of adsorbed HCOOH starts to decompose at 170 K. The main decomposition products are carbon monoxide, carbon dioxide, and hydrogen. Carbon dioxide desorbs upon formation between 170 and 220 K. We have no experimental evidence for a decomposition intermediate containing more than two atoms.
Ordering of metal overlayers on metal substrates studied using atom beam scattering
Authors: Vidali G. , Hutchings C. W. , Dowben P. A. , Karimi M. , Moses C. , Foresti M.
Published: July 2002

We will illustrate how atom beam scattering (ABS) can be used to study the growth and ordering of adsorption of Hg on Cu(001). At low coverage (less than 2% of a monolayer), we obtain that the scattering cross section of He with (adsorbed) Hg is about 50 Å2. We find that mercury forms two stable phases on Cu(001) in the temperature range between 200 and 330 K, a c(2×2) and a high density c(4×4) phase. From ABS diffraction data, we can deduce the corrugation of the surface electron charge density of the mercury layer in the two ordered phases. From the analysis of our data, we obtain a Debye temperature for the Hg overlayer of about 115 K. We will report preliminary calculations on the adsorption energy of Hg on Cu(001) and on the interaction of He with a Hg preplated Cu(001) surface.
Modeling of plasma flow downstream of an electron cyclotron resonance plasma source
Authors: Hussein Makarem A. , Emmert G. A.
Published: July 2002

We have simulated plasma flow along the divergent magnetic field of an electron cyclotron resonance (ECR) microwave plasma source stream. We assume that ions undergo charge exchange and elastic scattering collisions with the neutral gas in the downstream region. A Monte Carlo description for the ion dynamics, coupled with Boltzmann electrons, is used to develop an iterative scheme for solution of the Boltzmann equation and quasineutrality. We have studied the effect of the magnetic field and neutral gas pressure on the plasma and floating potentials, and on the ion energy incident on the sample.
Synchrotron radiation photoionization of sputtered neutrals
Authors: Oshima Masaharu , Maeyama Satoshi , Kawamura Tomoaki , Maruo Tetsuya , Nagai Kazutoshi
Published: July 2002

A photoionization effect of sputtered neutrals by synchrotron radiation (SR) is observed for the first time. Synchrotron radiation from a bending magnet is irradiated 5 mm ‘‘above’’ the Ar ion sputtered area of the sample surfaces, and photoionized ions and secondary ions are detected with a quadrupole mass spectrometer with and without this SR irradiation. A large ratio of photoionized ions to secondary ions is obtained when Au and Pb are sputtered with a low primary Ar ion energy. On the contrary, no detectable photoionization effect is observed from Al, Si, or GaAs. These results are explained qualitatively by the photoionization process where the number of generated ions can be calculated based on the photon flux density, photoionization cross sections, and duration in which sputtered neutrals pass through the SR beam.
Reaction of hydrofluoric acid and water with the GaAs(100) surface
Authors: Gräf D. , Grundner M. , Lüdecke D. , Schulz R.
Published: July 2002

The chemical surface state of polished GaAs (100) wafers after treatments in hydrofluoric acid and in water were investigated by means of x-ray photoelectron spectroscopy (XPS) and high-resolution electron energy-loss spectroscopy (HREELS). After the HF treatment, the wafer surface is As rich and partially covered with fluorine. The fluorine is bonded to Ga atoms as can be deduced out of a chemically shifted component in the XPS spectra. We cannot detect hydride groups using vibrational spectroscopy (HREELS). Fluorine on top of the wafer surface can be removed by a short water rinse. Depending on the storage time of GaAs wafers in HF the As enrichment of the surface increases. We present a model for the surface state after the HF treatment with an As overlayer on top of bulk GaAs. Consistent with our angular dependent XPS measurements, we can give values for the thickness of the As overlayer. Conditions of illumination and concentration of HF influence the reaction rate of HF on the GaAs surface. The reaction with water depends strongly on the illumination and whether the treatment in water is performed in static or dynamic conditions. Rinsing samples in running de-ionized water and dark storage in water results in an oxide removal. Light storage in water in static conditions yields a Ga-rich oxide with the growth rate depending on the illumination. The oxide growth is faster on n-type GaAs than on p-type.
Radiation-enhanced sublimation of graphite in PISCES experiments
Authors: Nygren R. E. , Bohdansky J. , Pospieszczyk A. , Lehmer R. , Ra Y. , Conn R. W. , Doerner R. , Hirooka Y. , Leung W. K. , Schmitz L.
Published: July 2002

Radiation enhanced sublimation (RES) of graphite leads to potentially high erosion rates in advanced fusion devices (Compact Ignition Tokamak, CIT) and (the International Thermonuclear Experimental Reactor ITER) and may be important in the ‘‘carbon blooms’’ observed in Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET). Erosion rates measured by weight loss are reported for POCO graphite exposed to helium plasmas for a temperature range from 900–2000 °C, ion energies of 30–300 eV, ion fluxes of 1–6×1018 cm−2 s−1, densities of 2–10×1012 cm−3, and electron temperatures of 4–10 eV. These are the first data on RES at fusion-relevant particle fluxes. The data show little reduction from a direct linear dependence upon flux. For these conditions, the amount of redeposition and carbon self-sputtering was minimal. Over 1700 °C, there is evidence of electron emission from the sample.
Small-scale high-strength silicon carbide fibers fabricated from thin films produced by plasma-enhanced chemical vapor deposition
Authors: Koskinen J. , Soave R. J. , Johnson H. H.
Published: July 2002

Microfabrication technology has been used to produce free-standing SixC1−xHy fibers of precisely controlled geometry and composition from thin films deposited by PECVD. The films were deposited in a parallel plate reactor from a mixture of SiH4 and CH4. The atomic composition of the films was determined using RBS and forward recoil spectroscopy (FRES). The film composition was varied from x=0.2–0.8 by adjusting the gas flow, the plasma frequency (30 kHz or 13.56 MHz), and plasma power. The films deposited at 300 °C contained from 33 to 50 at. % of hydrogen. The density, internal stress and refractive index of the films were measured. These properties were strongly dependent on gas flow ratio and plasma frequency. The lower frequency plasma yielded denser and higher compressive stress material with higher refractive index. Photolithography and reactive ion etching techniques were used to pattern the films into one centimeter long self-supporting fibers with cross-sectional areas in the gauge section ranging from 1 to 2 μm2. Tensile strength and elastic modulus measurements of these fibers were used to evaluate the films. Fibers with an average tensile strength of up to 2.9 GPa were obtained, suggesting a novel way to produce high strength SiC fibers of controlled geometry and composition.
Study of the SiNx/Si interface by million electron volt ion channeling
Authors: Smith G. A. , Luo Li , Gibson W. M.
Published: July 2002

The structure, stoichiometry, and integrity of 3000-Å silicon nitride films on Si(100) substrates were studied using MeV ion channeling. The silicon nitride film was found to be slightly Si rich with a stoichiometry of Si3 N3.6 . The Si substrate contained a thin region (∼7 ML) of disordered Si atoms located immediately below the silicon nitride film.
Preparation and properties of SiO2–SiOx heterostructures formed by uninterrupted processing by remote plasma enhanced chemical vapor deposition
Authors: Tsu D. V. , Kim S. S. , Theil J. A. , Wang Cheng , Lucovsky G.
Published: July 2002

Heterostructures of SiO2 and SiOx are formed by remote plasma enhanced chemical vapor deposition without switching or interrupting the gases and their flow through the deposition chamber, or the radio-frequency (rf) power. Selectively exciting the process gases, e.g., only oxygen (O2) or both O2 and silane (SiH4) simultaneously, produces SiO2 or SiOx, respectively. Only when the plasma afterglow extends into the chamber, thereby activating silane, do suboxides form. Control of the plasma afterglow is accomplished with the plasma bias assembly, located between the plasma tube and the deposition region, and heterostructures are formed by switching the grid bias between floating and grounded states. We have examined the deposited heterostructures by transmission electron microscopy (TEM) and find the oxide/suboxide transition is abrupt. Electrical properties of the suboxide layers in metal/SiO2/Sio1/SiO2/n-Si structures have been investigated by C–V measurements. Three different structures, having oxide thicknesses of ∼20, 40, and 84 Å deposited onto the c-Si substrate have been investigated; the suboxide layer is 150 Å and the second oxide is fixed at 165 Å. Application of a +5 V gate bias allows electrons to tunnel through the 20 and 40 Å oxides into the suboxide, but the 84 Å oxide prevents any tunnel injection. The electrical characteristics of the metal/SiO2/SiO1/SiO2/n-Si structures are controlled by the tunneling of electrons into, and out of the suboxide layers.
Nonlinear optical coefficients of narrow-gap semiconductors
Authors: Youngdale E. R. , Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Han J. W. , Cook J. W. , Schetzina J. F. , Engelhardt M. A. , Niles E. W. , Höchst H.
Published: July 2002

Nondegenerate four-wave mixing experiments have been performed at CO2 laser wavelengths on HgTe–CdTe superlattices and α-Sn1−xGex films grown by molecular beam epitaxy. In HgTe–CdTe, the magnitude, temperature dependence, and laser-intensity dependences of χ(3) are found to vary systematically with superlattice energy gap. A theoretical model for nonlinear optical coefficients in narrow-gap semiconductors gives excellent agreement with the experimental results when the nonlinearity is assumed to be due to optical modulation of the free carrier temperature. In the first investigation of α-Sn1−xGex as a nonlinear optical material, we find that the measured χ(3)’s are quite large (up to 8×10−5 esu), particularly in heavily strained films with compositions up to x=0.08. The mechanism responsible for the nonlinearity in that system is unclear at present.
Characterization of isothermal vapor phase epitaxial (Hg,Cd)Te
Authors: Lee S. B. , Magel L. K. , Tang M. F. S. , Stevenson D. A. , Tregilgas J. H. , Goodwin M. W. , Strong R. L.
Published: July 2002

We report on the characterization of mercury cadmium telluride (Hg1−xCdxTe) film grown by the isothermal vapor phase epitaxial method (ISOVPE) and on the surface conversion of bulk Hg1−xCdxTe to larger bandgap material. The crystal perfection is evaluated using defect etching, electron beam and electrolyte electroreflectance (EBER and EER), and Rutherford backscattering spectrometry (RBS). Hall measurements are used to measure carrier densities and mobilities. Surface concentrations and concentration profiles are measured for the ISOVPE grown layers by transmission Fourier transform infrared spectroscopy (FTIR) and electron-probe microanalysis (EPMA) to establish quantitative informations about composition control. Metal–insulator-semiconductor (MIS) structures were made and the properties important to device performance such as compositional uniformity, storage time, and carrier concentration are measured. The ISOVPE layers are compared in quality to films grown by other methods and show promise for MIS devices.
The growth of high quality CdTe on GaAs by molecular beam epitaxy
Authors: Reno J. L. , Carr M. J. , Gourley P. L.
Published: July 2002

We have grown CdTe (111) on oriented and misoriented GaAs (100) and have characterized the layers by photoluminescence microscopy (PLM) and transmission electron microscopy (TEM). Photoluminescence microscopy showed a totally different type of defect structure for the oriented substrate than for the misoriented substrates. The CdTe grown on the misoriented substrates exhibited only threading dislocations. The CdTe grown on oriented GaAs showed fewer threading dislocations but exhibited a random structure of loops. The loop structure observed by PLM has been identified by TEM as the boundary between twinned crystallites which extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins. We present for the first time the growth of CdTe on patterned GaAs substrates. By growing on oriented GaAs(100) substrates that had been patterned prior to growth with 12 μm mesas, it is possible to grow material on the mesa top that is twin free and has a low dislocation density.
Tunneling spectroscopy of conductive ceramics
Authors: Oshio Takanori , Tanaka Junzo , Ono Akira , Nagamura Toshihiko , Kamizono Yasuhiko , Sakai Yoshiyuki , Ehara Shaw
Published: July 2002

Conductive ceramics SrTiO3 and ceramic superconductor Bi2Sr2Ca2Cu3O10+δ were studied by the use of a scanning tunneling microscope (STM) in order to clarify the conduction mechanisms related their electronic density of states and energy structures. By measuring voltage dependence of the tunneling currents, I–V curve, the energy band of SrTiO3 was found to be bent at the surface sensitively affected by adsorption. In the superconductor, it was discovered that the additional structures besides the fundamental energy gap are shifted by changing the distance between the point of probe and the sample surface. From this fact, the origin of the additional structures is considered to be related to the structure of the tunneling junction.
GaAs epitaxy and heteroepitaxy: A scanning tunneling microscopy study
Authors: Biegelsen D. K. , Swartz L.-E. , Bringans R. D.
Published: July 2002

In this paper, we will compare and contrast scanning tunneling microscopy images of homoepitaxially grown GaAs(100) and heteroepitaxially grown Si(100):As and Si(100):GaAs. Layers are grown by molecular beam epitaxy and imaged in situ. All samples are deposited under As-stabilized conditions. The GaAs homoepitaxial surface consists of 2×4 cells having predominantly three As-As dimers/cell. The earliest stages of heteroepitaxy are shown, including bare vicinal Si surfaces, the more ordered As-dimer terminated surface, and finally, a vicinal Si substrate with approximately two bilayers of GaAs. The later film shows essentially uniform two-dimensional topographic coverage but chemical inhomogeneity of dimer units.
The epitaxial growth of Ge single-crystal films on a CaF2/sapphire substrate
Authors: Barkai M. , Grünbaum E. , Deutscher G.
Published: July 2002

Ge(100) single-crystal films, up to 30 μm thick, have been obtained by molecular-beam epitaxy (MBE) on a CaF2(100) or BaF2(100) single-crystal film substrate, 2000 Å thick, grown in turn by MBE on a sapphire (11̄02) single-crystal wafer. By dissolving the CaF2 or BaF2 in water, this double epitaxy procedure allowed the recovery and the subsequent reuse of the expensive sapphire substrate. This is of interest for large area devices, such as solar cells. The Ge single-crystal films served as substrates for the growth of GaAs single-crystals by metalorganic chemical vapor deposition (MOCVD). Furthermore, by doping during growth, tandem double energy gap photovoltaic junctions, which may be suitable for high-efficiency solar cells, may be obtained. The growth conditions, orientation relationship, crystalline quality and microstructure of these films was examined by in situ reflection high-energy electron diffraction (RHEED) and by transmission electron diffraction and microscopy and by scanning electron microscopy. The Ge films grew in a parallel orientation to that of the CaF2 or BaF2 substrate and were composed of three-dimensional nuclei. The sharp Kikuchi lines in the RHEED patterns demonstrated their high perfection. The final film of 3–30 μm thickness had a mirror like appearance and was free of cracks due to thermal stresses. The intrinsic p-type carrier concentration was 2.2×1015 cm−3 and the mobility 1300 cm2 V−1 s−1, at room temperature.
Growth and microstructural study of radio frequency magnetron sputtered MgO films on silicon
Authors: Pinto R. , Poothra J. I. , Purandare S. C. , Pai S. P. , D’Souza C. P. , Kumar Dhananjay , Sharon M.
Published: July 2002

Microstructure of magnesium oxide films radio frequency (rf) sputtered on 〈100〉 silicon substrates at various argon: oxygen (9:1) gas pressures in the range 1–6.7 Pa and at various substrate temperatures up to 700 °C have been studied using x-ray diffraction and scanning electron microscopy. The films have shown a tendency for oriented structure with growth orientation perpendicular to the 〈200〉 planes. The tendency for columnar growth has been found to be strong at high argon pressures and has been found to persist to higher substrate temperatures. This observation is consistent with the structure zone model proposed by Movchan and Demchishin [Phys. Met. Mettallogr. 28, 83 (1969)] and later studied by Thornton [J. Vac. Sci. Technol. 11, 666 (1974)]. Annealing of films at 900 °C in oxygen which is needed to reduce oxygen deficiencies and strain generated during growth, and to improve crystallinity by increasing grain size, has been found to cause microcracks in the films depending upon the microstructure and thickness. Films with columnar structure have shown microcracks and the threshold thickness at which microcracks develop has been found to be strongly dependent on the nature of the columnar structure. Dense MgO films deposited at 600 °C at a low pressure of 1 Pa have not shown microcracks upto a thickness of 600 nm. Such films should be potentially applicable as buffer layers for the growth of high quality Y1Ba2Cu3O7−δ films on silicon.
Relation of thickness and some physical properties of NiFe thin films
Authors: Valletta R. M. , Guthmiller G. , Gorman G.
Published: July 2002

The magnetic properties of rf sputtered Ni81Fe19 films were studied as a function of thickness from <100 to ∼1200 Å. In contrast to some recently reported studies, there was no evidence of an oscillatory dependence of resistivity on Δρ as a function of thickness. The magnetoresistance, resistance, coercivity, and anisotropy field varied smoothly with thickness. In contrast, the magnetostriction λs had a minimum of −1.5×10−6 at ∼300 Å. The saturation magnetic moment did not decrease with thickness over the thickness range studied here. The derived magnetoresistance of an ‘‘infinitely’’ thick film was 3.92% compared to the bulk value of ∼4%. The analysis indicates that surface and grain-boundary scattering are the primary cause of lower than bulk values of magnetoresistance in these thin permalloy films.
A study of the secondary-ion yield change on the GaAs surface caused by the O+2 ion-beam-induced rippling
Authors: Karen A. , Okuno K. , Soeda F. , Ishitani A.
Published: July 2002

The oxygen ion-beam-induced ripples observed during depth profiling of the GaAs surface by secondary-ion mass spectrometry has been studied by scanning tunneling microscopy. Under the O+2 primary-ion bombardment with energy of 10.5 kV at an incident angle of 37°, ripples of wavelength of 230 nm with the ridge lines perpendicular to the beam direction are formed, and they are grown to ∼80 nm in amplitude on the sputtered surface. Secondary-ion intensity changes abruptly in accordance with the development of ripples when they reach an amplitude of 30–50 nm. The phenomenon occurs only when the primary beam direction is perpendicular to the ridge orientation. It suggests that the ion yield enhancement is effected by increase of local concentration of oxygen implanted onto the rippled surface. Dependence of the enhancement on sputtered elements also seems to agree with the proposed mechanism.
The effect of substrate temperature and bias on the stress, chemical etch rate, and microstructure of high deposition rate sputtered SiO2 films
Authors: Macchioni C. V.
Published: July 2002

The dependence of the stress, p-etch rate, and microstructure on the substrate temperature and bias voltage were examined for 4-μm thick SiO2 films sputtered at high rates. At a substrate temperature of 111 °C, or less, the stress was a complex function of the bias voltage. High values of the stress and p-etch rate were found when films were sputtered with the substrate grounded. Minimums in the stress and p-etch rates were observed with the application of a substrate bias of −20 V. These correlated well with the transition of the microstructure from one with large fibrous columns separated by regions of open porosity to a dense film with few voids and no distinguishable columns. With more negative values of bias, the stress increased due to incorporation of Ar atoms in the SiO2 and, at voltages more negative than −80 V, to atomic peening of the film by incident Ar ions. At a deposition temperature of 322 °C, the stress was independent of the bias and could be completely accounted for by the difference in thermal expansion coefficients of the substrate and the film. A more dense microstructure was observed for high temperature films even without the application of a bias voltage. The lowest p-etch rates, approximately 3.4 Å/s were obtained at high temperature, and with a bias voltage of −20 V.
Ion beam etching of GaAs and GaAs/AlGaAs heterostructures probed in real time by spectroscopic ellipsometry
Authors: Heyd A. R. , An Ilsin , Collins R. W. , Cong Yue , Vedam K. , Bose S. S. , Miller D. L.
Published: July 2002

A rotating polarizer, multichannel spectroscopic ellipsometer, operating over the spectral range from 1.5 to 4.0 eV, has been employed for process characterization during etching of GaAs and GaAs/AlGaAs heterostructures. The purpose of this study is to assess the capabilities of this relatively new ellipsometric technique for characterizing III–V semiconductor materials, surfaces, and interfaces during preparation and processing. In this work, each pair of ellipsometric spectra, {Ψ(hν),Δ(hν)} is acquired in 3 s with a repetition period of 16 s. Such spectra are analyzed by well-established linear regression techniques to deduce the time evolution of photon energy independent parameters. In the simplest case of sputter etching with Ar ions, the damage layer thickness, composition, and an estimate of surface temperature of the material can be obtained. For the heterostructures, instantaneous etch rates for both GaAs and AlGaAs can be obtained under identical conditions, and the extent of ion-induced intermixing can be determined as the interfaces are crossed. Future advances are expected in this area through assessment and optimization of technologically important reactive ion etching processes.
X-ray absorption fine structure studies of buried Ge–Si interfaces
Authors: Aebi P. , Tyliszczak T. , Hitchcock A. P. , Jackman T. E. , Baribeau J-M.
Published: July 2002

We have used Ge K-edge x-ray absorption fine structure (EXAFS) and a gas ionization detector with sample rotation to study the local environment of nominally pure Ge layers buried in single crystal Si. The samples were grown by molecular-beam epitaxy on Si(100). The dependence on thickness, number of Ge layers and growth temperature is explored. Considerable sensitivity to the quality of the epitaxial growth is observed. For instance the degree of mixing of the Si and Ge layers is a function of the growth temperature. A weak polarization dependence of the Ge K-edge EXAFS is observed. The initial quantitative analysis provides estimates of intermixing in the thinnest layers which are compatible with results of complementary Raman measurements.
Optimized microwave coupling in an electron cyclotron resonance etch tool
Authors: Stevens J. E. , Cecchi J. L. , Huang Y. C. , Jarecki R. L.
Published: July 2002

We have improved the operational characteristics of an electron cyclotron resonance (ECR) plasma etch tool by optimizing the coupling of the 2.45-GHz microwaves to the plasma. Improved coupling is achieved by using a right-hand circularly polarized (r.h.c.p.) mode which is matched to the plasma impedance through a quarter-wave transformer. This design reduces microwave reflected power typically to <5% of the incident power without external tuning and simplifies control of the plasma etch tool operation. The r.h.c.p. mode is azimuthally symmetric when averaged over one microwave cycle and adapts easily to ECR source chambers of larger radii. We present an analytic model, the results of which are in good agreement with our experiments for microwave coupling in ECR etch tools.
Characterization of electron cyclotron resonance hydrogen plasmas
Authors: Outten C. A. , Barbour J. C. , Wampler W. R.
Published: July 2002

Electron cyclotron resonance (ECR) plasmas yield low energy and high ion density plasmas. The characteristics downstream of an ECR hydrogen plasma were investigated as a function of microwave power and magnetic field. A fast-injection Langmuir probe and a carbon resistance probe were used to determine plasma potential (Vp ), electron density (Ne ), electron temperature (Te ), ion energy (Ti), and ion fluence. Langmuir probe results showed that, at 17 cm downstream from the ECR chamber, the plasma characteristics are approximately constant across the center 7 cm of the plasma, for 50 W of absorbed power. These results gave Vp =30±5 eV, Ne =1×108 cm−3, and Te =10–13 eV. In good agreement with the Langmuir probe results, carbon resistance probes have shown that Ti≤50 eV. Also, based on hydrogen chemical sputtering of carbon, the hydrogen (ion and energetic neutrals) fluence rate was determined to be 1×1016 /cm2 s at a pressure of 1×10−4 Torr and for 50 W of absorbed power.
Anisotropy of deposition rate in magnetron sputtering of CeO2
Authors: Kageyama Y. , Taga Y.
Published: July 2002

The sputter depositions of Al2O3, CeO2, Ta2O5, Y2O3, and ZnO were performed in view of elucidating their spatial distribution of deposition rate. Among them, CeO2 and Y2O3 showed a depression of deposition rate in front of the target. Similar results were observed for CeO2 with changing the O2 concentration in the sputtering gas and the sputtering discharge power. This depression of the deposition rate in front of the target is restricted to the cases of 5% to 2% of O2 and of higher discharge power. In these cases, the planar distribution of deposits in front of the target have concave profiles corresponding to the erosion region on the target. Main reason for this depression of deposition rate can be explained in terms of reemission of deposits by energetic particles bombardment from the target. However, another chemical effect of O2 may affect the total amount of the deposits.
Tungsten film deposition by hydrogen atom reaction with WF6
Authors: Lee Wei William , Reeves Robert R. , Halstead Judith
Published: July 2002

The formation of tungsten films using WF6 and molecular hydrogen, H2, usually requires elevated temperatures. Using the reaction of hydrogen atoms with WF6, tungsten atoms can be produced in a gas phase reaction. The atoms then deposit in a near-room temperature process resulting in the formation of tungsten films. The W atoms were measured in situ by atomic absorption spectroscopy during the chemical vapor deposition (CVD) process. The deposited W films were characterized by Auger electron spectroscopy and Rutherford backscattering spectrometry. Surface morphology of the films was studied using scanning electron microscopy. The deposited films were highly adherent to various substrates, including Teflon. The resistivity of the W films was measured and found ≥9 μΩ cm. This method allows deposition of high quality films and has two advantages compared to conventional CVD or plasma-enhanced CVD (PECVD): (1) film growth at low temperatures and (2) deposition in a plasma-free environment.
Characterization of electronic and optical properties of device quality a-Si:H and a-(Si,Ge):H grown by remote plasma electron cyclotron resonance deposition
Authors: Knox R. D. , Dalal V. L. , Popov O. A.
Published: July 2002

The electronic and optical properties of device quality a-Si:H and a-(Si,Ge):H films grown by remote plasma electron cyclotron resonance (ECR) deposition were studied together with the plasma characteristics during growth. 100–350 W microwave plasmas, which were formed by introducing hydrogen and helium into the ECR chamber, were used to decompose silane and germane downstream of the ECR source. Use of hydrogen allows selective etching of the growth surface by reactive ion species. The plasma properties near the deposition surface are characterized using movable plane and cylindrical Langmuir probes and are correlated with the light and dark photoconductivity, optical gap, stability, and silicon–hydrogen bonding distribution of the deposited film in an effort to understand the influence that plasma species have on film quality.
The preparation of microcrystalline silicon (μc-Si) thin films by remote plasma-enhanced chemical vapor deposition
Authors: Wang C. , Williams M. J. , Lucovsky G.
Published: July 2002

We have used remote plasma-enhanced chemical vapor deposition (remote PECVD) to deposit both intrinsic and doped μc-Si thin films at temperatures between 100 and 400 °C. Two different deposition pathways have been studied: (i) plasma excitation of He/H2 mixtures with downstream injection of silane, SiH4, and the dopant gases phosphine, PH3 or diborane, B2H6; and (ii) plasma excitation of He, with downstream injection of SiH4 and H2, as well as the dopant gases. We have observed that the second pathway, (ii) readily promotes nucleation of μc-Si on a number of different substrate materials, including crystalline Si, fused silica, and silicon dioxide, SiO2, deposited by the remote PECVD process. The other pathway, with the H2 coexcited with He, frequency results in the deposition of a thin amorphous silicon transition region between the substrate and the μc-Si film, which then nucleates within the a-Si material, rather than at the substrate itself. The properties of μc-Si films deposited by remote PECVD have been characterized by Raman spectroscopy, transmission electron microscopy (TEM), dark conductivity, and photoconductivity.
Surface adsorption–migration kinetics
Authors: Fong Michael C.
Published: July 2002

A random walk adsorption–migration kinetics model has been developed to describe the time-varying layer-by-layer adsorption buildup on a smooth surface under continuous molecular flux impingement. The basic approach of this stochastic model is to determine the transition probability for each adsorbed layer by detailed balancing of layer-by-layer adsorption, desorption, and migration rates at any given time, whereupon the net surface adsorption quantity as a function of time can be predicted. In essence, this theory constitutes a generalized Brunauer–Emmett–Teller model with adsorption kinetics and interlayer migration considerations. Based on this theory, the transient adsorption–migration problem can be described by a system of Kolmogorov quasilinear differential equations for a Markov process. A numerical scheme has been developed to solve this system of equations, and the solution has been tested with a heavy-molecule DC-704 lubricating oil outgassing-deposition problem. Good theory/data agreement was obtained by using variable heats of desorption and migration, the latter depending on both the incident flux and the deposit quantity.
The interaction of Cl(2P3/2) and Cl(2P1/2) with n-Si(100): Spontaneous etching
Authors: Müller-Markgraf W. , Rossi M. J.
Published: July 2002

The sticking coefficient γ of ground-state Cl (Cl 2P3/2 ) and spin–orbit excited Cl* (Cl 2P1/2 ) on lightly doped n-Si(100) was measured using resonance-enhanced multiphoton ionization of Cl and Cl* at mTorr pressure in a Knudsen cell. For Cl only an upper limit of γ≤5×10−5 could be obtained and for Cl* γ=4.6×10−4 was measured. These γ values are temperature independent in the range of 300–600 K and the sum corresponds to a spontaneous etch rate of 9.4 Å/min for Si(100). SiCl2 was the principal etch product under these spontaneous etch conditions, and no SiCl4 was found over the given temperature range.
Photoluminescence and surface photovoltaic spectra of strained InP on GaAs
Authors: Zhuang Weihua , Chen Chao , Teng Da , Yu Jin , Li Yuzhang
Published: July 2002

A high energy shift of the band–band recombination has been observed in the photoluminescence (PL) spectra of the strained InP epilayer on GaAs by metalorganic chemical vapor deposit. The strain determined by PL peak is in good agreement with calculated thermal strain. The surface photovoltalic spectra gives the information about energy gap, lattice mismatching, and composition of heteroepilayers, diffusion length, surface, and interface recombination velocity of minority carriers of heteroepitaxy layers.
Gravimetric flowmeter calibration
Authors: Kahn J. R. , Wykoff C. A.
Published: July 2002

A flowmeter calibration requires the measurement of the quantity of gas and the time period over which it flows. Gas quantities are typically determined by measuring the temperature and pressure of the gas in a vessel with a known volume. The gravimetric approach uses only a weight measurement to determine the quantity of gas. The use of the gravimetric approach is limited to gases that differ significantly in atomic weight from the surrounding atmosphere, but is convenient and requires only an accurate balance.
The effects of elevated temperature on sputter depth profiles of silver/nickel bilayers
Authors: Simko Steven J. , Cheng Yang-Tse , Militello Maria C.
Published: July 2002

The effect of elevated temperature on the sputtering behavior of silver/nickel bilayers was studied using Auger electron spectroscopy and argon ion sputtering while specimens were held at elevated temperatures (25, 135, 235, 335, and 435 °C). We find that the silver overlayer tranforms from a layer to islands during ion sputtering at temperatures above 100 °C. The transformation to islands is thought to relieve film stresses caused by film-growth and/or lattice mismatch. Surface diffusion of silver is also observed at elevated temperature (>100 °C). This causes the lower surface energy metal (Ag) to cover the higher surface energy metal (Ni) in regions between the islands. These experiments show that properties of the system such as the heat of mixing, and the surface and interface energies need to be considered when the sputter depth profiling technique is used to study thin film structures, particularly when sputtering is performed at elevated temperatures.
Photon- versus electron-induced decomposition of Fe(CO)5 adsorbed on Ag(111): Iron film deposition
Authors: Henderson M. A. , Ramsier R. D. , Yates J. T.
Published: July 2002

The photon- and electron-induced decomposition of monolayer and multilayer Fe(CO)5 on a Ag(111) surface were examined with temperature-programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction. In the absence of photon or electron exposure, Fe(CO)5 thermally desorbs from Ag(111) in monolayer (181 K) and multilayer (168 K) states with minimal decomposition. The small temperature difference between these states (13 K) suggests that the monolayer is physisorbed on Ag(111). Both ultraviolet (UV) photon (3.4 and 4.8 eV) and low-energy electron (3–132 eV) irradiation convert adsorbed Fe(CO)5 into a new species, presumably a Fex(CO)y cluster. The new species thermally decomposes at 330 K with the desorption of CO and the deposition of carbon- and oxygen-free Fe. Also, the new species is much less susceptible to photon- or electron-induced decomposition than is adsorbed Fe(CO)5. In contrast, substantial carbon and oxygen deposition occurs when high-energy electrons (2 keV) bombard adsorbed Fe(CO)5. From a practical viewpoint, low-energy electron-induced decomposition of Fe(CO)5 exhibits higher cross sections than UV photolysis, and is therefore a more effective means of depositing pure iron films on silver.
X-ray photoelectron spectroscopy analysis of ion-beam-induced oxidation of GaAs and AlGaAs
Authors: Alay J. L. , Vandervorst W.
Published: July 2002

The oxidation of GaAs and AlGaAs targets subjected to O2+ bombardment has been analyzed, using in situ x-ray photoelectron spectroscopy, as a function of time until steady state is reached. The oxides formed by the O2+ bombardment have been characterized in terms of composition and binding energy. A strong energy and angular dependence for the oxidation of As relative to Ga is found. Low energies as well as near normal angles of incidence favor the oxidation of As. The difference between Ga and As can be explained in terms of the formation enthalpy for the oxide and the excess supply of oxygen. In an AlGaAs target the Al is very quickly completely oxidized irrespective of the experimental conditions. The steady state composition of the altered layers show in all cases a preferential removal of As.
Enhanced sputtering of one species in the processing of multielement thin films
Authors: Harper J. M. E. , Berg S. , Nender C. , Katardjiev I. V. , Motakef S.
Published: July 2002

We discuss two mechanisms for enhanced selective sputtering which may strongly influence the composition of thin films deposited under energetic particle bombardment. The first mechanism occurs on sloping substrate surfaces which experience a higher fraction of material resputtered than flat surfaces. 500 eV Ar+ ion bombardment during deposition of Al–5 at. % Cu causes an increase in Cu concentration by up to a factor of 2 on sloping surfaces. This effect is modeled with the dynamic Monte Carlo code T-DYN, which simulates film growth under ion bombardment and confirms the selective sputtering of Al. The second mechanism occurs if diffusion of the film constituents is significant, and the film is situated on top of an underlying material containing one of the film components. Enhanced sputtering of one component occurs if that component maintains a high surface concentration by diffusion or segregation. Raising the temperature of TiSi2 on (100) Si to the range in which Si atoms are mobile (500–700 °C) increases the sputtering yield ratio of Si to Ti under 300 eV Ar+ bombardment to a value of 19 from the room temperature value of 2. During high rate sputter deposition, both of these mechanisms of enhanced sputtering of one species may occur, leading to phase separation and extreme concentration gradients on topographically structured surfaces.
Intrinsic mechanism of smooth and rough morphology in etching of InP by Cl2 determined by infrared laser interferometry
Authors: Vernon M. , Hayes T. R. , Donnelly V. M.
Published: July 2002

The effect of Cl2 pressure and substrate temperature (Ts) on the absolute, steady-state etch rates of InP(100) has been measured with ∼1% accuracy from ∼0.02 to 1000 Å/sec by infrared laser interferometry. An unexpected finding was that the etch rate could exceed the calculated evaporation rate of InCl3 by a factor of 50, indicating a weaker binding energy of InCl3 to InP relative to itself. At sufficiently low Ts, the measured slow etch rate is only a factor of ∼3.5 above that predicted from the evaporation rate of InCl3. The transition between the fast and slow etch rates occurs as a first-order phase transition at a substrate temperature, T*s, which depends on the Cl2 pressure. If InP is etched at T*s, the surface roughens while at other Ts the surface remains smooth. The explanation for the surface roughening is that at T*s, InCl3 nucleates to form InCl3 islands. At T*s the etch rate is approximately fifteen times slower where the InP surface is covered by InCl3 compared to the bare InP surface. The large differential etch rates for bare and InCl3 covered InP produces a rough surface morphology. Below T*s, the surface is completely covered by an InCl3 multilayer and etches uniformly although slowly at the nominal InCl3 vaporization rate. This mechanism of surface roughening is intrinsic to the Cl2+InP reaction.