bluuebunny/crossref_metadata_2025 huggingface dataset:
Aluminum alloy ultrahigh vacuum chamber for molecular beam epitaxy
Authors: Suemitsu Maki , Kaneko Tetsuya , Miyamoto Nobuo
Published: July 2002

An aluminum alloy molecular beam epitaxy chamber has been constructed and its vacuum properties tested. Prior to the construction an oil-free lathing technique was developed and was applied to the inner surface of the chamber, which resulted in an extremely low outgassing rate of the order of 10−11 Torr 1/s cm2 before bakeout and less than 1×10−13 Torr 1/s cm2 after a 100 °C, 45-h bakeout. This low outgassing rate of the material enabled the chamber to be pumped down from atmospheric pressure to the order of 10−10 Torr in 23 h of evacuation without bakeout and in only 6 h with bakeout. With this short pumpdown time and its great reduction in bakeout temperature and time together with its reduced weight and the low cost, the aluminum alloy ultrahigh vacuum system provides us with a remarkably convenient tool to access the ultrahigh vacuum region.
The pumping of gases desorbed by pulsed ruby laser irradiation of a Si(111) surface
Authors: Terada K. , Tuzi Y. , Okano T.
Published: July 2002

The pumpdown process of gases desorbed from a Si(111) surface irradiated by a Q-switched ruby laser was observed in an ultrahigh vacuum chamber made of stainless steel. The chamber was pumped through an orifice by a sputter-ion pump and a Ti getter pump. A Si crystal was mounted on a manipulator installed in the chamber and was irradiated without special cleaning. After laser beam irradiation, ion currents of a quadrupole mass spectrometer were measured for m/e=2, 15, 16, 26, and 28. The currents were composed of two peaks irrespective of mass number. One of the peaks corresponded to the direct time-of-flight distribution of molecules desorbed from the Si surface. The second peak showed exponential decay which corresponded to the pumpdown process of gases released from the Si surface and expanded into the chamber. The time constants of the decrements of partial pressures were smaller than the values calculated. The difference can be explained by a small sticking probability and a large mean sojourn time of adsorption on the chamber surfaces.
Thermal desorption measurements for aluminum alloy 6063 and stainless steel 304
Authors: Pang S. J. , Gao Wei , Yang Yixin
Published: July 2002

This presentation describes thermal desorption spectroscopy from two materials: ultrasonically chemically cleaned aluminum alloy 6063 and stainless steel 304. Some new conclusions on vacuum and surface characterization are obtained. (1) On the surface of 304, there exist two types of adsorption states which desorb at 328 and 366 K, originating from air exposure and water rinse separately; the corresponding desorption activation energies E are 22 and 25 kcal/mol. For the unbaked sample, water is the major desorbed species and the quantities which originate from water rinse are two times from air exposure. (2) On the surface 6063, there exists only one type of adsorption state for water, which desorbs at 353 K; E is 24 kcal/mol, regardless of whether it is from air exposure or water rinse. The quantity adsorbed is twice that on the surface of 304 and is not related to exposure time. (3) At 573 K, the bulk structure of 6063, that is the grain size, has been changed due to recrystallization. This process produces an obvious effect on the bulk outgassing rate of CO and CO2.
The effect of beam emittances on x-ray lithography exposure line resolution
Authors: So D. , Lai B. , Wells G. M. , Cerrina F.
Published: July 2002

We have investigated in detail the effect of finite source size and beam divergence on the resolution of the exposure process for the case of an x-ray lithography proximity printing system with a synchrotron radiation source. An analytical expression for the exposure resolution is obtained and a connection between machine parameters and penumbral blur established. The effect of scanning the beam is included and is shown to have a profound effect on the resolution. Between the two cases of field exposure obtained by electron-beam wobbling or by a scanning mirror, we show that the first is preferable. Since such an approach is of difficult implementation in a multistation ring, we have analyzed in detail the effect of the scanning mirror. For this case we conclude that the divergence of the photon beam plays a dominant role in determining the broadening of the exposure. This is true for the vertical scanning direction, while we show that in horizontal the electron-beam divergence plays no role. This conclusion is very important for machine design. The expression for the broadening shows that is possible to keep broadenings well within tolerances of 25 nm (3σ) with machines of relatively large emittance and typical beamlines. Such an excellent definition can be used to advantage in the overall process tolerance budget to relax other parameters, for example, resist contrast. Conversely, if a tolerant process is available, the machine design requirements can be relaxed, leading to a more economical construction. We conclude that x-ray lithography based on storage rings can easily satisfy the strict linewidth control requirement of very large scale integrated processes with a machine of (relatively) modest performances.
The stability and decomposition of gaseous chloroferrocenes
Authors: Barfuss S. , Grade M. , Hirschwald W. , Rosinger W. , Boag N. M. , Driscoll D. C. , Dowben P. A.
Published: July 2002

The ionic and neutral decomposition of gaseous ferrocene, 1, 1′-dichloroferrocene and 1, 1′, 2, 2′-tetrachloroferrocene, has been investigated via photon and electron induced ionization mass spectroscopy. The thermodynamic cycle incorporating the ionic and neutral fragments of ferrocene has been constructed. Elimination reactions in the decomposition of the dichloroferrocene and tetrachloroferrocenes have been identified.
The mechanism and kinetics of the oxidation of Cr(100) single-crystal surfaces studied by reflection high-energy electron diffraction, x-ray emission spectroscopy, and secondary ion mass spectrometry/Auger sputter depth profiling
Authors: Arlow J. S. , Mitchell D. F. , Graham M. J.
Published: July 2002

Reflection high-energy electron diffraction, x-ray emission spectroscopy, and ex situ secondary ion mass spectrometry (SIMS)/Auger analysis by sputter depth profiling have been used to study the oxidation of Cr(100) single-crystal surfaces in the oxygen partial pressure range 10−9–10−7 Torr from room temperature to 700 °C. It was found that at all temperatures and for oxygen partial pressures as high as 10−7 Torr, that the initial sticking probability for oxygen was unity. The rate of oxidation was then found to decrease exponentially to a limiting thickness determined by the sample temperature. Various oxide phases have been observed depending on the temperature and the oxide thickness: two face centered cubic phases with a0’s of 4.2 and 11.8 Å, a tetragonal phase, and finally hexagonal α-Cr2O3. Initial oxidation of the Cr(100) surface results in conversion of bcc Cr to fcc oxide. The fcc and tetragonal structures are thought to arise from the formation of different Cr vacancy superlattices due to oxygen incorporation, which leads eventually to the precipitation of α-Cr2O3. Oxygen 18/16 isotope experiments coupled with ex situ SIMS/Auger analysis have clearly demonstrated that oxygen uptake is accompanied by oxygen movement into the fcc Cr–O lattice for temperatures up to about 500 °C. After the appearance of α-Cr2O3, growth is primarily by cation transport.
Advances in superalloy technology of China
Authors: Fu J. , Gao L.
Published: July 2002

Superalloy technology has an important effect on the composition control, cleanliness, structure, and consequently on the properties of superalloys. The Chinese metallurgists have been thinking highly of superalloy technology, especially the superalloy melting technology. A lot of research work on the electroslag metallurgy (ESR, ESC, and ESM), including engineering and minor element control of superalloys, has been done in China since the early 1960s. Some of the results are presented in this review paper.
Development of polyvinyl alcohol shells overcoated with polystyrene layer for inertial confinement fusion experiments
Authors: Kubo Uichi , Tsubakihara Hiroshi
Published: July 2002

In inertial fusion experiments, the use of polymer shells provides more efficient ablative implosion and significantly reduced radiation preheat compared with the glass shells currently used. We have developed a method of fabricating polyvinyl alcohol (PVA) shells overcoated with a polystyrene (PS) layer. The method utilizes the emulsion technique previously developed by us, and employs three different liquid phases. A 5 wt. % aqueous PVA solution is mixed with a 7 wt. % PS solution in dichloromethane while stirring. The mixture is then poured into a 1 wt. % PS solution in cidhloromethane while stirring. The mixture is then poured into a 1 wt. % aqueous gelatin solution. The resulting emulsion is heated to evaporate the dichloromethane, resulting in solid PS shells encapsulating the PVA solution. The PS shells are subsequently washed and dried in vacuum to drive off the remaining water. As a result, a PVA shell is formed inside an overcoating PS shell which exhibits a good surface quality in the outer diameter and wall thickness regime currently desired by inertial confinement fusion experimenters.
Current–voltage relations in magnetrons
Authors: Rossnagel S. M. , Kaufman H. R.
Published: July 2002

The current–voltage relationship in a magnetron plasma appears to be strongly dependent on the dynamics of the sputtered particle–gas atom interaction. Large fluxes of energetic (several eV) sputtered atoms from the cathode heat the gas in the near cathode region, resulting in a significant reduction in the local gas density as a function of discharge current (and hence particle flux). This reduction in gas density results in a lower rate of ion formation, and hence a more resistive plasma. Thus, the rate of voltage increase with current in a magnetron is related to the magnitude of the gas density rarefaction, which is dependent on the cathode sputter yield, sputtered atom energy, the cross section for sputtered atom–gas collisions, the molecular velocity of the gas, and the gas density. A model has been developed which describes the observed rate of voltage increase in a magnetron as a function of this thermalization process.
Surface composition and distribution of fluorine in plasma-fluorinated polyimide
Authors: Matienzo L. J. , Emmi F. , Egitto F. D. , Van Hart D. C. , Vukanovic V. , Takacs G. A.
Published: July 2002

Surface composition, fluorine distribution, and morphology were determined for polyimide films modified downstream from microwave plasmas containing CF4/O2. Complementary analytical techniques including x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and scanning electron microscopy yielded a more complete understanding of polyimide fluorination and subsequent etching of the modified film. Depth of fluorination increased nonlinearly with treatment time for films exposed downstream from a CF4-rich plasma. Exposure downstream from an O2-rich plasma resulted in a reduction of thickness in both the fluorinated layer and the unmodified polyimide during etching. Finally, a model for fluorination of polyimide and subsequent removal is proposed.
Reactivity of organic molecules on amorphous Si and Ge films
Authors: Piancastelli M. N. , Zanoni R. , Kelly M. K. , McKinley J. T. , Margaritondo G. , Quaresima C. , Capozi M. , Perfetti P.
Published: July 2002

The behavior of amorphous silicon and germanium surfaces exposed to benzene or pyridine was found to be similar to that of their cleaved counterparts. This includes, in particular, the establishment of stable chemisorption bonds at room temperature for C6H6 on Si through a C–H bond breaking mechanism and for C5H5N on both Si and Ge.
Mechanisms of contaminant particle production, migration, and adhesion
Authors: Miller R. J. , Cooper D. W. , Nagaraj H. S. , Owens B. L. , Peters M. H. , Wolfe H. L. , Wu J. J.
Published: July 2002

Three fundamental processes associated with particulate contamination of manufacturing processes are particle generation, migration, and adhesion. A more complete understanding of each of these processes, and their interactions, can aid in efforts to eliminate product contamination and thereby increase product yields. We present results of particle generation studied in the context of mechanical wear. The production of airborne particles from the wear of stainless-steel components is examined. The results indicate that submicron particles dominate the particle population in terms of number of particles generated. The migration and deposition of submicron particles under clean room conditions is described, with reference to a deposition model that includes particle diffusion effects. Experimental results of particle deposition in a clean room are compared to the model. Measurements of the adhesion under vacuum of dry-deposited particles of known size and composition are also presented. These show qualitative agreement with a model having a linear dependence of adhesion on particle diameter. The results are discussed in the context of increased automation in product handling and more stringent product isolation.
Deposition and characterization of ternary nitrides
Authors: Randhawa H. , Johnson P. C. , Cunningham R.
Published: July 2002

Hard coatings of titanium nitride, titanium carbide, and aluminum oxide are the materials most widely used for improved performance and productivity on high-speed steel and cemented carbide tools. However, very little effort has been focused on the deposition of ternary nitrides. This paper presents the deposition and characterization of ternary nitrides of (Ti, Zr) and (Ti, Al) using cathodic arc plasma deposition process. The films were analyzed in terms of surface topography, composition, and mechanical properties. These coatings were also evaluated for wear applications and decorative properties. The results are also compared with TiN and (Ti–6Al–4V)N films obtained by the same process.
Defining the fractal nature of thin-film top surfaces from microdensitometer analysis of electron micrographs of surface replicas
Authors: Varnier F. , Dussert C. , Rasigni G. , Rasigni M. , Llebaria A.
Published: July 2002

In this paper, the very first results are reported about searching for the fractal nature of thin-film top surfaces from the surface relief reconstructed by microdensitometer analysis of an electron micrograph of a shadowed replica of the surface. It is found that such a reconstruction could be very helpful when dealing with the fractal nature of a surface.
American Vacuum Society recommended practices for pumping hazardous gases
Authors: O’Hanlon John F. , Fraser David B.
Published: July 2002

The purpose of this Recommended Practice is to familiarize users with the issues involved with processes using toxic, flammable, or corrosive gases for the deposition or etching of semiconducting, metallic, or insulating films. We examine the general concerns for handling these gases, discuss the nature of several processes, their effluents, reactivity with pump fluids, and how to scrub noxious gases from the exhaust. We describe some specific concerns that relate to materials, components, and facilities layout which result from technical, safety, and regulatory obligations. As an aid in making these concerns clear, we have considered the design of seven different systems that use corrosive, flammable, pyrophoric, or toxic gases. We give examples of a plasma etch system, deposition systems for tungsten silicide, borophosphosilicate glass, amorphous silicon, and silicon nitride, an organometallic deposition system, and finally an ion implantation system. We are keenly aware that design, process, and safety considerations vary throughout the industry. We are not attempting to standardize or claim that the techniques presented here are the only techniques which are acceptable. We are trying to point out some well-known hazards and recommend procedures which, to the best of our knowledge, are reliable, and to urge people to think through the entire process of design, construction, and operation very carefully. The final decision on how a facility is to be designed, constructed, and operated can only be made by the responsible management and facility safety officers.
Experimental and calculated radial pressure gradients in reactive sputter processes
Authors: van Zon J. B. A. D. , Rijpers J. C. N.
Published: July 2002

Partial pressure gradients in reactive dc-magnetron sputtering are investigated. The combination of diffusion of the reactive gas (e.g., O2) in a sputtering gas (e.g., Ar) which is in a dynamic equilibrium and the high pumping speed of the substrate due to gettering of the reactive gas causes large partial pressure variations of the reactive gas along the surface of the substrate. Numerical calculations for an Al/O2 process show quantitative data on the influence of the deposition rate, sputter pressure, target-to-substrate distance, and substrate size. The outcome of the calculations is in good agreement with the measurements. The variations in the partial pressure of the reactive gas can be quite substantial. For example, at an Ar pressure of 8 mTorr, a target-to-substrate distance of 6 cm, and a deposition rate of 20 Å/s, the O2 partial pressure at 20 cm from the substrate center is 2×10−4 Torr (2.6×10−2 Pa) whenever the partial pressure in the center is 4.4×10−5 Torr (5.9×10−3 Pa).
Ultimate pressure of the order of 10−13 Torr in an aluminum alloy vacuum chamber
Authors: Ishimaru Hajime
Published: July 2002

An extremely high vacuum chamber for the calibration of ultrahigh vacuum gauges was fabricated and tested. The chamber has an inner diameter of 250 mm and is 1800 mm long. It has 20 gauge ports and a liquid-nitrogen shroud inside to suppress interference between gauges and to avoid pressure rise due to thermal radiation from the gauges. The vacuum chamber was made of specially extruded aluminum alloy A6063-T6-EX in an oxygen and argon atmosphere. The chamber was assembled using tungsten inert gas welding in an argon atmosphere. After a bakeout at 150 °C for 24 h, a specific outgassing rate of the order of 10−13 Torr l/s cm2 was obtained. The system was evacuated with a turbobacked 300 l/s turbomolecular pump. The extremely high vacuum is maintained by two 300 l/s sputter ion pumps and a titanium sublimation pump with a liquid-nitrogen shroud. These pumps are also made of aluminum alloys. An ultimate pressure of 3×10−13 Torr was measured with a point collector gauge with spherical anode. Residual gas analysis in the 3×10−12 Torr was performed by a newly developed Q-mass filter.
An analysis of the stability of a uniform liquid fuel layer inside a spherical-shell cryogenic inertial confinement fusion target
Authors: Islam Raja M. M. , Kim K. , Bernat T. P.
Published: July 2002

The effects of thickness perturbations on the stability of a uniformly thick liquid layer of a ternary deuterium–tritium mixture inside a spherical-shell cryogenic inertial confinement fusion target are investigated. Initially, the surface tension gradient required at the liquid–vapor interface to keep the liquid fuel layer uniform is calculated directly by balancing the forces acting on the interface. This method is much faster than the trial-and-error method previously employed. Once the value of the surface tension coefficient is known for each cell, the transient, incompressible Navier–Stokes equations, along with the continuity equation, are solved using the volume-of-fluid algorithm for given perturbations. The solution gives the transient behavior of the liquid fuel layer for varying liquid layer thicknesses and different perturbation amplitudes and wavelengths.
Effect of hydrogen on the microstructural, optical, and electronic properties of a-Si:H thin films deposited by direct current magnetron reactive sputtering
Authors: Pinarbasi M. , Maley N. , Kushner M. J. , Myers A. , Abelson J. R. , Thornton J. A.
Published: July 2002

Device quality hydrogenated amorphous silicon (a-Si:H) films have been deposited under a wide range of deposition conditions using dc magnetron reactive sputtering. The total hydrogen content (CH) has been varied from 0 to ∼40 at. % by changing the substrate temperature (Ts) or hydrogen partial pressure (PH2) independent of other deposition parameters. The films that contain CH between 10 and 28 at. % have the highest quality. The optical band gap (Eg) varies linearly with CH for all deposition conditions studied. With increasing CH the dark conductivity at 300 K decreases from ∼1×10−4 to ∼1×10−12 (Ω cm)−1; however, the photoconductivity under AM-1 illumination, for the highest quality films, remains in the 0.8–3.5×10−5 (Ω cm)−1 range. The dark conductivity activation energy (Ea) was measured to determine the Fermi-level (Ef) position with respect to the conduction band (Ec) and a linear correlation between Eg and Ea is found for high-quality films. The films having low hydrogen content (10<CH<17 at. %) are slightly n-type and become intrinsic as CH is increased. The subgap density of states diminishes with the increase in Ec−Ef (taken to be Ea ) as the films become intrinsic. In short, the microstructural, optical, and electronic properties of these films vary monotonically with the total hydrogen content. Therefore we propose that CH is the appropriate structural parameter to correlate changes in the properties of a-Si:H.
Wall collisions, angular flux, and pumping requirements in molecular flow through tubes and microchannel arrays
Authors: Murphy Daniel M.
Published: July 2002

Microchannel arrays can be used to produce intense molecular beams with free molecular flow. Arrays can attain much higher intensities than a single orifice small enough to be in free molecular flow. Pumping requirements are greatly reduced compared to supersonic jets producing similar beam intensities. Theoretical descriptions of the angular flux and wall collisions in single tubes and microchannel arrays are developed. These results are extended to the situation of a finite mean free path and the consideration of wall collisions which occur before transmission through a tube. Despite the large average number of wall collisions experienced by molecules passing through a long tube, molecules along the axis of the beam experience zero or few wall collisions. The near absence of wall collisions on the beam axis allows reactive species to be sampled with microchannel arrays. Tubes with a length to radius ratio of up to ∼40 are useful for reactive species. Most wall collisions for molecules transmitted along the beam axis through microchannel arrays are collisions in which a molecule enters the array, collides with the wall, goes back to the source region, and then is transmitted through the array. The nearly effusive beam allows the selection of species based on their thermal velocities. A long single tube used as a skimmer will provide a greater pressure drop than an orifice.
Power spectra of surface roughness of light emitting tunnel junctions measured by scanning tunneling microscopy
Authors: Takeuchi K. , Uehara Y. , Ushioda S. , Mikoshiba N. , Morita S.
Published: July 2002

Using a scanning tunneling microscope (STM), we have measured the microscopic surface roughness of light emitting tunnel junctions (LETJ) which consist of thin films of Al, Al oxide, and Au. The power spectrum of roughness obtained from the STM data was used to calculate the light emission spectrum, using a theory that takes into account the effect of surface roughness in first order perturbation. The calculated spectrum due to the term first order in roughness fits the measured emission spectrum very well, but when the term due to an unperturbed smooth surface is included, the fit becomes unsatisfactory. We conclude that the theory predicts a wrong ratio between the contribution from surface roughness and the contribution from a smooth surface.
Process effects on radio frequency diode reactively sputtered ZrO2 films
Authors: Yang M. M. , Reith T. M. , Lin C. J.
Published: July 2002

The ZrO2 thin film is deposited by means of a reactive radio frequency diode sputtering from an elemental zirconium target in an argon–oxygen mixture gas. The influence of the deposition process parameters on the microinstructure, composition, film stress, and refractive index is investigated. It is noted that the process parameters, in particular substrate bias, have a profound effect on the structure and properties. The possible mechanism, in terms of bombardment of energetic particles and adatom mobility on the film surface, is discussed.
Studies of the interface between the epoxy molding compound and the copper leadframe by x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary electron microscopy
Authors: Pan F. M. , Horng S. R. , Yang T. D. , Tang V.
Published: July 2002

The interface between the epoxy molding compound and the copper leadframe of an integrated circuit device has been studied by x-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary electron microscopy (SEM). The surface of the copper frame is composed of CuO, Cu2 O, or Cu(OH)2 depending on the heat treatment for the frame before the molding process. The XPS results show that cuprous oxide is the primary copper oxide at the interface between the leadframe and the epoxy polymeric encapsulant after the molding process. Copper was found to migrate into the epoxy resin side. According to AES and SEM, silica fillers in the molding compound abrade the copper oxide layer on the copper frame during the molding process, and the injected hot epoxy fluid can interact directly with the freshly exposed metallic copper surface. The accelerator of the molding compound segregates to the abraded area at the interface. The rugged interfacial structure close to the molding compound injection gate is probably the primary factor causing the microgap problem at the interface.
Sensitivity variation of Bayard–Alpert gauges with and without closed grids from 10−4 to 1 Pa
Authors: Peacock R. N. , Peacock N. T.
Published: July 2002

Since the accurate range of the spinning rotor gauge (SRG) does not extend below 10−4 Pa, constant sensitivity of high vacuum gauges for at least one decade above this value is important for their calibration when using an SRG. Two pairs of nude Bayard–Alpert (BA) gauges were compared with an SRG over the range 10−4–1 Pa. One pair was made from two identical, commercial, nude ultrahigh vacuum (UHV) BA gauges by removing the grid caps from one gauge. At 1.0 mA emission, the sensitivity of the gauge with closed grid started to decrease at 10−3 Pa, falling from 0.18/Pa to 0.047/Pa at 1.6 Pa. With open grid, the sensitivity was constant at 0.096/Pa to 10−3 Pa, increased slightly, and then fell to 0.047/Pa at 1.6 Pa. A pair of nude gauges was built with grids 16 mm in diameter by 26 mm long, identical except that one had a closed grid and the other did not. The sensitivity of the gauge with closed grid was nearly constant at 0.069/Pa to 1.3×10−2 Pa, decreasing to 0.033/Pa at 1.6 Pa, and with open grid was constant at 0.049/Pa to 4×10−1 Pa, falling to 0.033/Pa at 1.6 Pa. At an emission current of 0.10 mA, constant sensitivity extended to higher pressures for all gauges.
The influence of the magnetic field strength upon the characteristic curve of a cold cathode ionization gauge
Authors: Peacock N. T. , Peacock R. N.
Published: July 2002

Cold cathode discharge gauges use crossed electric and magnetic fields to trap electrons and thus obtain a long ionizing path. For many inverted magnetron type gauges, the magnet is cylindrical, located concentrically about the discharge cell, and the peak field is about 1000 G. The slope of the gauge current versus pressure characteristic curve on a log–log plot for gauges reported in the literature usually falls in the range of 1.0 to 1.2 for pressures above 10−9 Torr, and may be steeper at lower pressures. Using an inverted magnetron gauge, gauge characteristic curves have been obtained for fields from 770 to 2330 G. Both the slope and low pressure gauge currents were found to be dependent upon the field. The slope decreases with increasing field, becoming unity by 2240 G for pressures greater than 10−8 Torr, but remains steeper than unity at lower pressures.
Reactive ion etching of silicon using bromine containing plasmas
Authors: Bestwick Tim D. , Oehrlein Gottlieb S.
Published: July 2002

The characteristics of Si and SiO2 etching in HBr reactive ion etching plasmas have been studied by measuring etch rates, optical emission, scanning electron microscopy (SEM) cross-sectional analysis, and x-ray photoelectron spectroscopy (XPS). Etch rate measurements indicate that SiO2 is etched very slowly compared with Si, so that the Si/SiO2 etch selectivity may be as high as 400. Optical emission spectroscopy has been used to examine the gas phase species in the plasma, and emission from excited atomic bromine has been identified. The composition and thickness of reaction layers on silicon surfaces resulting from exposure to HBr plasmas has been obtained by XPS. It is found that the reaction layer on silicon due to HBr reactive ion etching is typically very thin, of the order of 1 monolayer thick. XPS has also been used to investigate the reaction layers on the sidewalls of etched trenches, and a thin oxidized layer has been detected for oxide-masked Si trench etching.
Analysis of growth inhomogeneities in CdTe films by scanning electron microscopy and photoluminescence studies
Authors: Landa-Garcia J. , Cardenas M. , Contreras Puente G. , Mendoza-Alvarez J. G. , Sanchez-Sinencio F. , Zelaya O.
Published: July 2002

Cadmium telluride films have been grown by a modified close-spaced vapor transport technique under different argon pressures (Pg) to get variable grain size and crystalline film properties. These films have been studied in terms of the variations of their structural and optical properties. Using SEM and microanalysis measurements it has been found that films grown at low pressures (∼1.5 mTorr) have a constant grain size; whereas, for films grown at high Pg’s (∼50 Torr), inhomogeneities in grain size and a large density of defects are observed. Photoluminescence spectra taken at different regions in the different films are in good agreement with the presence of Cd vacancies and defects due to the growth process. The presence of an intense exciton-related luminescence peak indicates good crystalline quality grains.
Electronic-structure theory of the dimers adatoms and stacking fault model on Si(111) reconstructed surface—comparison with scanning tunneling spectroscopy
Authors: Fujita Mari , Nagayoshi Hideo , Yoshimori Akio
Published: July 2002

The electronic structure of the Si(111) 5×5 dimers adatoms and stacking (DAS) model has been calculated in the slab geometry, using the local density approximation (LDA) and norm-conserving pseudopotential method. Surface states due to three kinds of dangling bonds are obtained, i.e., of the adatoms, the first layer atoms, and in the corner holes. The local densities of states have been calculated on these dangling bond sites. Since those of 5×5 are expected to be different from those of 7×7, a qualitative comparison of these results with the measured scanning tunneling spectroscopy (STS) of 7×7 has been made. In general, qualitative features agree well with the observed ones.
Surface diffractometry and lattice imaging of scanning tunneling microscopy images
Authors: Demuth J. E. , Koehler U. , Hamers R. J.
Published: July 2002

The ability to directly image surfaces with atomic resolution has many advantages in understanding surface structures. However, a wide variety of present experimental probes, including He-atom diffraction, low-energy electron diffraction, reflectron high-energy electron diffraction, as well as x-ray diffraction, measure reciprocal surface features. Contact with such measurements is also possible with the scanning tunneling microscope (STM) by examining the two-dimensional Fourier transform of the topographic image. Such optical transforms provide, in many cases, detailed reciprocal space information not possible or obvious from the real space image and can be particularly valuable. Several recent cases are discussed and an example on Si(100) is given to illustrate this capability.
Discharge cleaning on Tokamak Fusion Test Reactor after boronization
Authors: Mueller D. , LaMarche P. H. , Bell M. G. , Blanchard W. , Bush C. E. , Gentile C. , Hawryluk R. J. , Hill K. W. , Janos A. C. , Jobes F. C. , Owens D. K. , Pearson G. , Schivell J. , Ulrickson M. A. , Vannoy C. , Wong K. L. , Dylla H. F.
Published: July 2002

At the beginning of the 1990 Tokamak Fusion Test Reactor (TFTR) experimental run, after replacement of POCO-AXF-5Q graphite tiles on the midplane of the bumper limiter by carbon fiber composite (CFC) tiles and prior to any pulse discharge cleaning (PDC), boronization was performed. Boronization is the deposition of a layer of boron and carbon on the vacuum vessel inner surface by a glow discharge in a diborane, methane, and helium mixture. The amount of discharge cleaning required after boronization was substantially reduced compared to that which was needed after previous openings when boronization was not done. Previously, after a major shutdown, about 105 low current (∼20 kA) Taylor discharge cleaning (TDC) pulses were required before high current (∼400 kA) aggressive pulse discharge cleaning (PDC) pulses could be performed successfully. Aggressive PDC is used to heat the limiters from the vessel bakeout temperature of 150 to 250 °C for a period of several hours. Heating the limiters is important to increase the rate at which water is removed from the carbon limiter tiles. After boronization, the number of required TDC pulses was reduced to <5000. The number of aggressive PDC pulses required was approximately unchanged.
Use of oil-free mechanical pumps with leak detectors
Authors: Hablanian M.
Published: July 2002

With the growing demand for contamination-free leak detectors, the replacement of the oil-sealed mechanical pumps has become an important issue. Despite their higher total ultimate pressure (0.010 Torr), the oil-free pumps retain the pumping speed for helium at pressures less than 1×10−7 Torr. This is sufficient in most applications using a turbomolecular pump as the high vacuum pump. Experimental results obtained with a Contra-Flow leak detector with both mechanical pumps replaced by oil-free pumps are presented. System stability and helium background levels permit leak rate measurements near 2×10−10 atm cc/s.
Characterization of radio frequency unbalanced magnetrons
Authors: Window B. , Harding G. L.
Published: July 2002

Magnetron sputtering sources are often used with radiofrequency excitation instead of dc excitation to sputter deposit insulating materials; such excitation alters the ion bombarding properties of the magnetron, generally increasing the flux of ions arriving at the substrate position. This study looks at the dc ion flux and self-bias voltage generated at the substrate for balanced and unbalanced magnetron designs (using copper targets) with either dc or rf excitation at comparable powers. The dc bias on the cathode (applied in the case of dc excitation and generated in the case of rf excitation) is also measured. These quantities are studied as functions of inert gas pressure and magnet design. The magnitude of the rf plasma potential is estimated using the lattice strains produced in deposited chromium films to quantify the degree of ion assistance to be +20 to +50 V.
Influence of adsorbed and implanted sulfur on the corrosion of iron in calcium nitrate at 60 °C
Authors: Baer D. R. , Windisch C. F. , Soran T. F. , Jones R. H. , Engelhard M. H.
Published: July 2002

The influence of S on the anodic corrosion of Fe in a 55 wt % Ca(NO3)2 solution at 60 °C has been examined using both electrochemical and surface analysis methods. Pure Fe, S-implanted Fe, and Fe with S adsorbed on the surface have been studied. The presence of S, in sufficient amounts, was found to accelerate the corrosion of Fe at 750 mV. For S layers adsorbed on the Fe surface this threshold amount was approximately 1 monolayer. The effect of S was to thicken the oxide layer that formed on the metal and the S remained within the film in a nonoxidized form. These results are consistent with an observed rapid stress corrosion crack growth in the nitrate solution for Fe with S at grain boundaries.
In situ real-time ellipsometry for film thickness measurement and control
Authors: Henck Steven A.
Published: July 2002

A rotating compensator type polarizer-compensator-sample-analyzer ellipsometer is used in situ to provide real-time thickness measurements and control of process end point during the etching of polysilicon. The ellipsometer can measure the thickness of the polysilicon layer every 0.15 s. The measured thickness was used to determine end point to obtain a desired film thickness. The polysilicon films etched using in-process ellipsometer control had a thickness accuracy and reproducibility of 4 Å. In comparison, timed etching of polysilicon films in the same reactor had a thickness reproducibility of only 150 Å.
Construction and commissioning of the alternating-gradient synchrotron booster ultrahigh vacuum system
Authors: Hseuh H. C. , Mapes M. , Shen B. , Sikora R.
Published: July 2002

The recently completed alternating-gradient synchrotron booster is a synchrotron for the acceleration of both protons and heavy ions. To minimize the beam loss due to charge exchange of the partially stripped, low β(=v/c), very heavy ions with the residual gas molecules, ultrahigh vacuum of 10−11 Torr is required for the 200 m booster ring. An average pressure of mid 10−11 Torr has been achieved and maintained after initial in situ bakes and commissioning. In this article we describe: (1) design and layout of the vacuum systems; (2) material selection and vacuum processing; (3) personal computers/programmable logic controllers based bakeout system; (4) operation of vacuum instrumentation over long cable length; (5) results of bakeout and evaluation; and (6) experience gained during construction and commissioning.
Measurement and modeling of ion energy distribution functions in a low pressure argon plasma diffusing from a 13.56 MHz helicon source
Authors: Charles C. , Boswell R. W. , Porteous R. K.
Published: July 2002

Helicon sources coupled to diffusion chambers provide a new method for better controlling plasma processing. It is, however, important to understand the effect of diffusion on the plasma evolving from the source to the wafer situated in the chamber. The diffusion of a 300 W argon plasma from a 13.56 MHz (6 cm diam, 20 cm long) cylindrical magnetic field free source into a 30 cm diam, 20 cm long chamber has been experimentally and theoretically investigated. A mobile electrostatic energy analyzer was used to measure the electron temperature, plasma potential, plasma density, and ion energy distribution functions (EDFs) along the common axis of the source and chamber. An analytical model based on experimental results has been developed. Although there is a potential difference of around 40 V between the source and the substrate table, charge exchange collisions associated with the plasma expansion reduce the average energy of the ions impinging on a grounded probe at the bottom of the chamber to about 3 eV. At 1 μbar the number of collisions is too low to cool all of the ions accelerated in the field and a tail remains in the ion distribution function. Although not measured, hot neutrals should also be generated as a consequence of charge exchange collisions and will impinge on the substrate.
Infrared study of the coadsorption of PF3 and CO on the Pt(111) surface
Authors: Fan Jingfu , Trenary Michael
Published: July 2002

We have used temperature programmed desorption (TPD) and Fourier transform infrared reflection absorption spectroscopy to characterize the coadsorption of CO and PF3 on the Pt(111) surface. From TPD studies we find that although PF3 can displace preadsorbed CO, CO does not displace preadsorbed PF3. This is consistent with the lower desorption temperature for CO. When PF3 is adsorbed alone on Pt(111), the P–F stretch region shows two distinct components separated by 5–13 cm−1. In previous work we have attributed these two components to molecules within and outside of two-dimensional islands of PF3. Here we report changes in the P–F stretch band shape upon CO coadsorption that indicate that the CO molecules can induce the formation of PF3 islands. The CO causes formation of islands at lower PF3 coverages than observed for PF3 adsorbed alone. The CO can also increase the size of the PF3 islands already present prior to CO adsorption.
Plasma ion-assisted deposition: A promising technique for optical coatings
Authors: Pongratz S. , Zöller A.
Published: July 2002

Thermal evaporation is commonly used for the production of optical coatings. The well-known thermal evaporation is the most frequently used process for the production of optical coatings. The low packing density of thermally evaporated films implies optical constants and mechanical properties which are inferior to those of the bulk materials. In this paper a range of ion based coating technologies, such as ion-assisted deposition (IAD), ion plating (IP), arc discharge evaporation, and plasma IAD are described. For the investigations of the plasma-IAD process, we used a newly developed advanced plasma source (APS) with special features. The properties of dielectric layers deposited with plasma IAD will be presented in comparison to conventional thermally evaporated films. In particular, the results of scratch resistant layers in combination with antireflection coatings on organic substrates will be shown.
Appearance mass spectrometry of neutral radicals in radio frequency plasmas
Authors: Sugai H. , Toyoda H.
Published: July 2002

High-sensitivity space-resolved measurements of the number density of neutral free radicals in reactive plasmas have been accomplished by appearance mass spectrometry. This technique is based on several electron volts difference among the appearance potentials for electron-impact ionization. First, some difficulties accompanied with the appearance mass spectrometry are considered, especially on the influence of excited parent molecules and radical sticking. Second, spatial distributions of neutral radical CH3 and CH2 in a parallel plate rf discharge of methane at a pressure of 0.01–0.3 Torr have been measured. The results are well described by a one-dimensional numerical modeling whose input parameters are provided by comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficients. Third, the density distributions of CF3 and CF2 radicals in a fluorocarbon etching plasma at a CF4 pressure of 0.01–0.2 Torr have been measured. Finally, several applications of the appearance mass spectrometry to investigations of radical collision processes in gas phase and on solid surfaces are reported, e.g., cross section measurements for electron-impact dissociation of methane into CH3 and CH2 radicals.
Corrosion inhibitor surface chemistry studied by core and valence band photoemission
Authors: Sherwood P. M. A.
Published: July 2002

The surface chemistry of the action of corrosion inhibitors may involve the formation of a surface complex which acts as a barrier to penetration of the oxide film by undesirable corrosion agents. In some cases, the chemistry may involve the reaction of the inhibitor with the oxide layer. This reaction may help to thin the oxide layer, or may form another stable film. Such subtle changes in surface chemistry in a complex amorphous or polycrystalline film can be monitored by valence band photoemission interpreted by Xα cluster molecular orbital calculations. Valuable depth information can be provided by angle resolved photoemission in the valence band. Examples of such behavior are provided for a range of inhibitors and include cases where the inhibitor reacts with the oxide layer. The formation of FeO is reported in some cases, and the valence band spectrum of this compound is interpreted by an Xα calculation.
Bi thin film growth structures prepared at 30 K on GaAs(110) and InP(110)
Authors: Patrin J. C. , Li Y. Z. , Chander M. , Weaver J. H.
Published: July 2002

Orientationally ordered epitaxial thin films of Bi have been grown on GaAs(110) and InP(110) at deposition temperatures of 30 K. These semimetal films grow in triple layers with pseudocubic {110} planes parallel to the substrate. Growth at 30 K produced metastable flat films whereas deposition at 300 K produced more three-dimensional films. This demonstrates that the growth mode can be selected by changing the growth temperature. The pseudocubic [100] directions of the Bi overlayers on GaAs(110) and InP(110) were rotated by ±10° and ±7° from the substrate [11̄0] directions. The surface of these metastable overlayers contains superstructures which are modeled as a Moiré effect between the overlayer and substrate lattice.
Oxygen discharge cleaning method for aluminum storage ring vacuum chambers
Authors: Saitoh Masao , Kanazawa Ken-ichi , Momose Takashi , Ishimaru Hajime , Ota Nobuhiko , Uramoto Jōshin
Published: July 2002

A discharge cleaning method using a dc plasma gun was developed to reduce photon-induced gas desorption by synchrotron radiation in electron storage rings. Hydrocarbon contaminations adsorbed on the inside surface of a long aluminum vacuum chamber (2.5 m) were removed by an oxygen plasma produced by an arc discharge. The plasma density and electron temperature were about 109 cm−3 and 1 eV, respectively, near the inside wall of the vacuum chamber at a discharge current of 5 A. The discharge cleaning was applied for 1 h to an aluminum vacuum chamber manufactured by the EX-extrusion process. The results were as follows: (1) measurements with a quadrupole mass spectrometer determined that 6×1019 CO molecules coming from the hydrocarbon contaminations were removed by the discharge cleaning, (2) in situ Auger electron spectroscopy showed that carbon on the surface of an aluminum sample piece was removed within 1 h of discharge cleaning and (3) the photodesorption yield of the chamber with the discharge cleaning was one order of magnitude smaller than that without cleaning.
Characterization of silicon dioxide films deposited at low pressure and temperature in a helicon diffusion reactor
Authors: Charles C. , Giroult-Matlakowski G. , Boswell R. W. , Goullet A. , Turban G. , Cardinaud C.
Published: July 2002

Silicon dioxide films have been deposited at low pressure (a few millitorr) and low substrate temperature (<200 °C) by oxygen/silane helicon diffusion radio frequency plasmas. High deposition rates (20–80 nm/min) are achieved at 800 W rf source power. The effect of the oxygen/silane flow rate ratio (R) on the film properties has been investigated: characterization of the deposited films has been carried out by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy, Rutherford backscattering, x-ray photoelectron spectroscopy (XPS), and chemical etch rate measurements (P etch) and the results have been compared to thermally grown oxide. The deposition kinetics has a great effect on the internal film structure: for films presenting a good stoichiometry ([O]/[Si]≥1.95 for R≥3), a decrease in the deposition rate is accompanied by a decrease of the refractive index, P-etch rate and XPS line width and by an increase of the Si–O stretching peak frequency toward the thermal oxide respective values. A sufficient oxygen/silane flow rate ratio (R=10) leads to stoichiometric films which exhibit good optical properties. Small differences in the P-etch rate, XPS linewidth, and infrared stretching peak frequency are still observed between our stoichiometric plasma deposited film and a thermally grown oxide film.