bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the interface composition on the corrosion behavior of unbalanced magnetron grown niobium coatings on steel
Authors: Schönjahn C. , Paritong H. , Münz W.-D , Twesten R. D. , Petrov I.
Published: July 2002

Niobium is well known as a chemically extremely stable material. However, the corrosion performance of 0.3 to 1.3 μm thick, unbalanced magnetron (UBM) grown niobium coatings on stainless steel substrates depends not only on the deposition parameters, but also significantly on the in vacuo etching pretreatment of the substrates prior to coating. Corrosion tests, transmission electron microscopy, and scanning transmission electron microscopy analyses have shown, that a dense fine grained, partially implanted, 5–10 nm thick niobium interface layer formed during the metal ion etching pretreatment is paramount to protect stainless steel substrates thoroughly against corrosion in chlorine containing aqueous electrolytes, whereas the pretreatment with Ar and Cr ions leads to comparably inferior corrosion results. Moreover the energy of the impinging Nb ions used during the etching process plays an important role. For 0.3 μm thick Nb coatings, maximum pitting potentials (+1000 mV) and minimum corrosion currents (<3×10−6 A cm−2) were found for bias voltages between −600 and −1000 V. In summary, the results suggest that the UBM deposited Nb coatings are not completely dense and that the major justification for niobium as corrosion barrier depends on the existence of the thin interface layer generated by high-energy ion bombardment during the etching step. The UBM deposited coating (US=75 V) acts therefore as itself a chemically stable mechanical spacer protecting the thin interface layer against mechanical damage.
Comparison of the effective oxide thickness determined by ellipsometry with the result by medium energy ion scattering spectroscopy and high-resolution transmission electron microscopy
Authors: Cho Hyun Mo , Lee Yun Woo , Lee In Won , Moon Dae Won , Lee Hwack Joo , Kim Byoung Yoon , Kim Hyun Jong , Kim Sang Youl , Cho Yong Jai
Published: July 2002

Ellipsometric results may be inaccurate for the measured thickness of ultrathin oxide films on silicon because of the apparent refractive index changes with thickness. We have assessed this problem by comparing results on oxide thickness measured by ellipsometry with results of measurements by two independent techniques, such as medium energy ion scattering spectroscopy and high-resolution transmission electron microscopy, which should not be subject to error. The results show that appropriate ellipsometric models can provide thickness information consistent with two independent techniques, which improves the reliability of ellipsometric analysis in the nm range.
Influence of annealing temperature on simultaneous vapor deposited calcium phosphate thin films
Authors: Hamdi M. , Ektessabi A. M.
Published: July 2002

The effect of annealing temperature on the characteristics of thin film calcium phosphate coatings fabricated by a novel simultaneous vapor deposition method was investigated. Heat treating the as-deposited films was necessary to change the amorphous coating into a crystalline coating. The films were annealed for 3 h at 400, 700, 1000, and 1200 °C in air. After annealing, the structure and the chemical composition of these films were characterized with incident light microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. A scratch test was conducted to measure the strength of the adhesion of the coatings to the substrate. The results showed that after annealing at a temperature higher than 700 °C, crystalline hydroxyapatite appeared to coexist with tricalcium phosphate and tetracalcium phosphate phases. A Ca/P ratio close to that of stoichiometric hydroxyapatite was obtained with certain process parameters. The adhesion of the coatings was highly affected by the annealing temperature. From the results, it can be suggested that 1000–1200 °C is the best annealing temperature range for calcium phosphate coatings produced by the simultaneous vapor deposition method.
Effect of substrate temperature and ion bombardment on the formation of cubic boron nitride films: A two-step deposition approach
Authors: Ye J. , Oechsner H. , Westermeyr S.
Published: July 2002

The influence of substrate temperature and ion bombardment on the formation of cubic boron nitride (c-BN) films has been examined with bias-assisted magnetron sputtering of h-BN for argon and nitrogen as the working gases. It is shown through a two-step deposition approach that higher substrate temperatures are required only to establish an appropriate h-BN base layer which is mandatory as a nucleation base for c-BN. For nitrogen as the working gas the energy of the bombarding ions can also be reduced after c-BN-nucleation. Hence, the conditions for the formation of c-BN films are more restrictive for the initial growth stage than for the later c-BN growth once the nucleation into c-BN has been established. Corresponding results for argon and nitrogen display characteristic differences which lead to the conclusion that the establishment of full BN surface stoichiometry is a key condition for c-BN growth.
Co,Ni-base alloy thin films deposited by reactive radio frequency magnetron sputtering
Authors: Scardi P. , Dong Y. H. , Tosi C.
Published: July 2002

Structural properties and mechanical behavior of Co,Ni-base alloy thin films deposited by reactive rf magnetron sputtering on a tool steel were compared with those of TiN or TiN/Ti two-layer coatings produced by the same technology. Reactive sputtering of the Co,Ni-base alloy in Ar+N2 atmosphere results in the production of amorphous (or nanocrystalline) thin films with interesting properties: (a) high hardness (2000 HV), (b) low friction coefficient (0.06), and (c) absence of acoustic emission and no delamination after scratch test up to a load of 60 N. The strong adhesion to the steel substrate is directly connected with the plastic behavior of these thin films, which is a rather unusual feature for hard, low-friction nitride coatings.
GaAs
(111)B(√19×√19)R23.4°
surface reconstruction
Authors: Farrell H. H. , Lu Jun , Schultz B. D. , Denison A. B. , Palmstrøm C. J.
Published: July 2002

The structure of the GaAs(111)B(√19×√19)R23.4° surface reconstruction has been determined using x-ray photoelectron spectroscopy and scanning tunneling microscopy. This structure is characterized by the sixfold As crown first found by Biegelsen and co-workers. In addition, we find that both As and Ga atoms occur in antisite positions in the top bilayer, and possibly in underlying layers as well. These antisite atoms are proposed to enhance the island formation involved in the epitaxial growth self-assembling nanostructures, and to interfere with the layer-by-layer growth that characterizes homo-and heteroepitaxy on most GaAs surfaces. Unlike several earlier structures proposed for this reconstruction, we propose that all of the As (Ga) dangling orbitals are filled (empty), consistent with the electron counting rule.
Influence of elastic-electron scattering on measurements of silicon dioxide film thicknesses by x-ray photoelectron spectroscopy
Authors: Powell C. J. , Jablonski A.
Published: July 2002

We investigate the systematic error due to neglect of elastic scattering of photoelectrons in measurements of the thicknesses of thin films of SiO2 on Si by x-ray photoelectron spectroscopy (XPS). Calculations were made of substrate Si 2p photoelectron currents excited by Mg and Al Kα x rays for different SiO2 thicknesses, different angles of photoelectron emission, and three representative XPS configurations using an algorithm based on the transport approximation. We calculated practical effective attenuation lengths (EALs) from changes of the computed Si 2p photoelectron currents. These EALs were less than the corresponding inelastic mean free paths by between 6.5% and 9.4%, with the difference depending on the x-ray source, the specific range of SiO2 film thicknesses under consideration, the XPS configuration, and the range of photoelectron emission angles. Useful average values of the EAL were found for emission angles between 0° and about 60° (with respect to the surface normal) and for silicon dioxide thicknesses such that the substrate signal was attenuated to not more than 1% and 10% of its original value. Our calculated EALs are in satisfactory agreement with measured EALs. For larger emission angles, the calculated EALs change rapidly with SiO2 thickness, and specific values should be found for the conditions of interest.
Highly uniform and high optical quality In0.22Ga0.78As/GaAs quantum wires grown on (221)A GaAs substrate by molecular beam epitaxy
Authors: Nitta T. , Ohno Y. , Shimomura S. , Hiyamizu S.
Published: July 2002

We have grown self-organized InGaAs/GaAs quantum wire (QWR) structures on several kinds of (nnl)A and (nnl)B GaAs substrates by molecular beam epitaxy to optimize the substrate orientation. We observed the most uniform and highest-density corrugation with straight step edges running in the [11̄0] direction on the surface of a 3.0-nm-thick InGaAs layer on the (221)A GaAs substrate among the (nnl)A GaAs substrate. The lateral period of the corrugation was 36 nm and the height was 1.8 nm. On the other hand, GaAs surfaces were almost flat. Hence, a nominally 3.0-nm-thick (221)A InGaAs quantum well sandwiched by GaAs layers is a high density and uniform QWR structure due to the lateral thickness modulation. Photoluminescence (PL) from the (221)A InGaAs/GaAs QWRs structure as 12 K was strongly polarized along the wire direction and its polarization degree P[≡(I∥−I⊥)/(I∥+I⊥)] was 0.20. The PL linewidth was as small as 5.8 meV.
Gas-phase studies in inductively coupled fluorocarbon plasmas
Authors: Schaepkens M. , Martini I. , Sanjuan E. A. , Li X. , Oehrlein G. S. , Perry W. L. , Anderson H. M.
Published: July 2002

Quantitative results from infrared laser absorption spectroscopy (IRLAS) of CF and CF2 radicals and COF2 products in inductively coupled plasmas fed with C2F6, CHF3 and C4F8 are presented and compared with results simultaneously obtained by mass spectrometry and optical emission spectroscopy. These plasma gas-phase analysis results are discussed and compared to fluorocarbon deposition and etching rates resulting from plasma–surface interactions at the substrate. It is found that COF2 species are being formed (1) during O2 plasma cleaning of a fluorocarbon contaminated reactor and (2) during SiO2 etching in fluorocarbon plasmas, which in this work occurred at the quartz coupling window as a result of capacitive coupling between the induction coil and the plasma. IRLAS results on CF and CF2 densities are compared to fluorocarbon deposition and etching rates and it is found that low CF and/ or CF2 density does not necessarily translate into a low fluorocarbon deposition rate. A relatively high deposition rate can be achieved at conditions with a high ion current density and low CF and CF2 densities.
Technique for 25 nm x-ray nanolithography
Authors: Toyota Eijiro , Hori Toshitada , Khan Mumit , Cerrina Franco
Published: July 2002

The image-forming limit of x-ray lithography is said to be ∼70 nm using existing devices and technologies. This article presents methods to extend the limit to 25 nm or even below. Preparatory to the study, a light source was designed to improve x-ray beam toward shorter wavelength. In addition, a simulation code has been developed to evaluate the methods. The first method is to use a mask with a larger period and pattern than deigned images. The mask forms the designed images with an enlarged period. Two-dimensional, 25 nm width images can be formed using a 100 nm period pattern mask at 8 μm gap. The second method is to use a mask with interference slits. Since the image pattern is sharply focused, ⩽25 nm images can be formed at 8–12 μm gaps. Multiple exposures are applied to both methods in order to fill in the clearances of the images. Simulation results are shown in both methods for typical patterns.
Inductively coupled plasma etching of GaN and its effect on electrical characteristics
Authors: Rong B. , van der Drift E. , Reeves R. J. , Sloof W. G. , Cheung R.
Published: July 2002

Dry etch behavior in the inductively coupled plasma processing of GaN using SF6/N2 plasma has been found to be highly ion induced with an ion energy threshold of about 100 eV. Temperature dependence of the etch rate indicates a small kinetic component. Maximum etch rate of 67 nm/min and good anisotropy have been demonstrated. The most efficient etch regime is observed for an ICP source power between 500–1000 W where the etch mechanism is ion limited. In contrast to reactive ion etching induced damage behavior, almost ideal diodes are obtained at the higher dc bias condition (300 V). X-ray photoelectron spectroscopy and atomic force microscopy studies indicate that smooth surface with minimal surface contamination, coupled with the incorporation of N on the substrate surface help to produce ideal diodes on surfaces etched at 300 V. Sidewall depletion is found to be in the range of 65 nm at the given SF6/N2 plasma process conditions.
Quantitative determination of dopant dose in shallow implants using the low energy x-ray emission spectroscopy technique
Authors: Staub P.-F. , Hombourger C. , Schuhmacher M.
Published: July 2002

A technique using low energy x-ray emission spectroscopy (LEXES) is used to determine the dose of shallow implanted dopants. This technique is nondestructive and dopant selective. This technique can provide absolute dose values. CAMECA has developed specific instrumentation called the shallow probe which adapts the LEXES technique to the requirements of the semiconductor industry in terms of sensitivity and reproducibility of dose measurements. This work reports the performance of the shallow probe applied to a wide variety of boron, phosphorus, and arsenic implants into silicon wafers. Measured doses are compared to both ultralow energy secondary ion mass spectrometry and implanter tool values.
Modeling SiC etching in C2F6/O2 inductively coupled plasma using neural networks
Authors: Kim Byungwhan , Kong Sung-Min , Lee Byung-Taek
Published: July 2002

Silicon carbide (SiC) has been etched in a C2F6/O2 inductively coupled plasma and modeled using neural networks. A 25 full factorial experiment was used to characterize the relationships between input process factors and etch response. The factors that were varied include source power, bias power, pressure, O2 fraction, and gap between the chuck holder and coil antenna. Neural networks were trained on the resultant 32 experiments and then tested on 18 additional experiments to evaluate prediction accuracy. Due to little variations in etch anisotropy, etch rate was only modeled and its root-mean-squared prediction error was 23.9 nm/min. Etch rate was found to be a strong function of source power. Increasing etch rate with pressure may partly be attributed to increased ion density and ion energy. Placing the chuck holder closer to the source antenna coil increased the etch rate. At higher bias powers, increasing the O2 fraction resulted in a crossover. This crossover seems to be weakened significantly with a decrease in bias power. Although etch anisotropy did not vary consistently with source power, it improved consistently with bias power. Microtrenches were noticed for variations in each of the five factors. With increasing pressure, the anisotropy was slightly degraded while being insensitive to a variation in the gap.
Solid particle production in fluorocarbon plasmas II: Gas phase reactions for polymerization
Authors: Takahashi Kazuo , Tachibana Kunihide
Published: July 2002

Solid particles were observed in fluorocarbon (C4F8) plasmas applied to semiconductor plasma processing. In order to elucidate gas-phase reactions for particle formation, Fourier transform infrared (FTIR) spectroscopy was employed. The method showed that stable molecules (CF4, C2F6, and C2F4) were produced in the plasmas. Several absorption peaks found in a spectrum from a surface polymer were observed in the gas phase. The peaks were regarded to be from plasma-polymerized molecules in the plasmas. In particular, the absorption signals from species of –CF=CF– and –CF=CF2, which were produced from C2F4 molecules, were extinguished with the particle formation. Furthermore, densities of fluorocarbon radicals CFx (x=1,2,3) were measured in CHF3 and C2F6 plasmas as well as in C4F8 plasmas with infrared laser absorption spectroscopy. The pressure dependence of the densities drastically changed with the presence of the particles. This was induced by sticking of the radicals onto gas-phase polymers including the particles. As the results obtained in the infrared spectroscopic methods, it was found that not these radicals but the C2F4 molecule as a reactive product played an important role in the formation of the particles.
Sulfur passivation of InP (100) by means of low energy sulfur ions
Authors: Zhao Q. , Kwok R. W. M.
Published: July 2002

Sulfur ions with well-controlled kinetic energy were used to introduce additional energy for passivating the InP (100) surface. 50 eV S+ bombardment resulted in the formation of a single In–S species on InP surface and assisted the InP (100) surface to form an ordered (1×1) structure. Further annealing removed the damage introduced during the ion bombardment and resulted in a sharp (1×1) low-energy electron diffraction (LEED) pattern. The treatment was extended to repair Ar+ damaged InP (100) surface. When InP (100) samples were damaged by 200 eV Ar+ bombardment followed by 50 eV S+ treatment and annealing, we could obtain an InP surface with (1×1) LEED pattern and with low surface states.
High coercivity thin film for high-density magneto-optical super-resolution near-field recording
Authors: Kim Jooho , Shima Takayuki , Atoda Nobufumi , Tominaga Junji
Published: July 2002

Magnetic and optical properties of magneto-optical TbFeCo thin films were investigated by a helicon-wave sputtering with a 200 mm distance between a substrate and target. According to deposition conditions such as power and pressure, the coercivity (Hc) of the films became very high in comparison with those produced by conventional sputtering distances of 40–80 mm. It was found that the terbium (Tb) composition steeply increases with increased sputtering pressure. Decreasing the power from 150 to 50 W, Tb composition further increased. A linear relationship was also discovered between the magnetic properties (Hc) and optical properties (extinction coefficient, k). It is thought that high coercivity is co-related with the change of magnetic moment configuration of elements (Tb, Fe, and Co), anisotropy constant, and layer properties (the density and impurities) of the films. By controlling the sputtering pressure and power, we could obtain a magneto-optical TbFeCo thin film having a coercivity of 2.55 T and low extinction coefficient of 1.8.
Stress changes in chemical vapor deposition tungsten silicide (polycide) film measured by x-ray diffraction
Authors: Pelleg Joshua , Elish E.
Published: July 2002

Stresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) were evaluated at each stage of the fabrication. The individual layers of the Si/SiO2/poly-Si/WSi2/poly-Si multilayered structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were either heat treated at 1193 K for 30 min or capped with a 25 nm thermal oxide and the strain in the WSi2 film was also analyzed by x-ray diffraction. The change in strain of the WSi2 layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The stress is affected by the layers of the multilayered film. An as deposited poly-Si layer on top of WSi2 reduces its stress, since it introduces a compressive component. The stress in WSi2 is further reduced upon annealing. Poly-Si also maintains a Si supply at the poly-Si/SiO2 interface thus eliminating Si out-diffusion during heat treatment in an oxygen containing ambient. Capping the system by a thin oxide layer modifies the stress pattern of the WSi2 which becomes compressive.
Structural and transport characterization of AlSb/InAs quantum-well structures grown by molecular-beam epitaxy with two growth interruptions
Authors: Sigmund J. , Saglam M. , Hartnagel H. L. , Zverev V. N. , Raichev O. E. , Debray P. , Miehe G. , Fuess H.
Published: July 2002

We have investigated the electron transport properties and the atomic morphology of AlSb/InAs/AlSb quantum wells (QW) grown by molecular-beam epitaxy. Different shutter sequences were used in producing an InSb-like interface. The highest mobility was obtained for a QW width of 15 nm and an InSb-like interface grown by two growth interruptions, one before and one after the deposition of one indium monolayer. For this shutter sequence, several samples with an InAs channel width from 6 to 25 nm were grown and characterized using high-resolution transmission electron microscopy, classical, and quantum Hall measurements. For a channel width less than 15 nm, the interface roughness becomes dominant, leading to a sharp decrease in the electron mobility. The electron effective mass determined by the temperature dependence of the Shubnikov–de Haas oscillazion amplitude is 0.0374m0. Transmission electron microscopy images show an atomically abrupt interface and disordered regions directly above the AlSb/InAs interface which can be as large as 2.4 nm.
Uniformity in large area ZnO:Al films prepared by reactive midfrequency magnetron sputtering
Authors: Hong R. J. , Jiang X. , Sittinger V. , Szyszka B. , Höing T. , Bräuer G. , Heide G. , Frischat G. H.
Published: July 2002

Al-doped zinc oxide (ZnO:Al) films were deposited on glass substrates using a reactive midfrequency magnetron sputtering process. The optical transmission and reflection as well as the electrical resistivity of the films prepared on an area of 1000×600 mm2 were determined at different locations. Films with a uniform distribution of resistivity between 2.9×10−4 and 3.6×10−4 Ω cm and transmittance up to 88% in the visible spectral range were obtained. The ellipsometric spectra of the films were also analyzed using the Drude–Lorentz model. The calculated thicknesses of the films agreed well with those measured by a step profilometer. Secondary neutral mass spectrometry depth profiling showed uniform contents of Zn and O elements, while a slight periodic variation of the Al content was observed at different depths inside the film. A transition zone of 35–55 nm in width between the films and glass substrates due to the interdiffusion was also observed.
Specular ion current measurements as a quantitative, real-time probe of GaAs(001) epitaxial growth
Authors: Ruthe K. C. , DeLuca P. M. , Barnett S. A.
Published: July 2002

Specular ion current measurements, where an ion beam impinges at a glancing angle to the surface and the specularly reflected beam is measured, were used to monitor GaAs molecular beam epitaxy on GaAs(001) surfaces. Scattered ion current oscillations were observed during growth with periods corresponding to monolayer growth times. Kinetic rate equation modeling of growth showed periodic variations in the density of two-dimensional islands; the oscillations arose due to nonspecular ion scattering from step edges. The ion current recovered after growth, and the data were fit well by assuming simple power-law coarsening of two-dimensional islands. The fits provided information on coarsening processes, and the average island size and density at the end of growth. Island statistics vs growth time were obtained by fitting recoveries for growths stopped at various stages. Islands were initially detected at 0.1–0.2 ML, with an initial size of 46 nm2 and density of 4×1011 cm−2. The island size remained relatively constant while the density increased rapidly as the coverage increased to ≈0.4 ML. As the coverage increased above this value, the island density leveled off and then decreased as the size increased, indicating island coalescence.
Effects of the polymer residues on via contact resistance after reactive ion etching
Authors: Ko Hyoung-Soo , Nah Jae-Woong , Paik Kyung W. , Park Y.
Published: July 2002

The effects of CF4 addition to O2 reactive ion etching (RIE) of a polyetherimide (Ultem®) surface and resultant via contact resistance were investigated using scanning electron microscopy (SEM), x-ray electron spectroscopy (XPS), and cross bridge Kelvin resistor (CBKR). In pure O2 RIE, the SEM micrograph showed that the originally smooth Ultem surface became rough and the rough features coarsened with increasing RIE time, resulting in residual particles on the metal pads. However, in the case of O2+CF4 RIE, the Ultem surface remained smooth throughout the etching process, and residue free metal pads were obtained. The XPS experiments identified that the origin of the Ultem surface roughening was organo-Si compound, which is easily converted to silicon oxide during O2 RIE. In contrast, the atomic fluorine in O2+CF4 RIE process etched out the silicon and the silicon oxide, resulting in smooth film surface and residue free metal pads. The metal to metal via contact resistance was measured by CBKR, and the pattern fabricated by O2+CF4 RIE showed lower contact resistance than those by O2 RIE. These results are discussed in the criterion of contact area and contact conformality differences.
Etching of polysilicon in inductively coupled Cl2 and HBr discharges. III. Photoresist mask faceting, sidewall deposition, and microtrenching
Authors: Mahorowala Arpan P. , Sawin Herbert H.
Published: July 2002

The etching artifacts observed during the high density Cl2 plasma etching of photoresist-masked polysilicon [A. P. Mahorowala and H. H. Sawin, J. Vac. Sci. Technol. B 20, 1055 (2002)] were analyzed using a 212-dimensional Monte Carlo profile evolution simulator [A. P. Mahorowala and H. H. Sawin, J. Vac. Sci. Technol. B 20, 1064 (2002)]. A set of profile evolution simulations for the Cl etching of photoresist-masked polysilicon features, including plasma deposition of two representative etching byproducts (C and SiCl2) were performed. The extent of deposition and the formation of facets, straight sidewalls, and microtrenches were strongly affected by the competing etching and deposition. The simulations suggested that the top facet angle was controlled by the surface composition at the top of the photoresist lines and the angular dependence for etching of the deposited material; the facet being less steep when there was more deposition of Si-based byproducts. The lower facet angle and the polysilicon sidewall profile were governed by the feature aspect ratio, the sticking probabilities, and fluxes of the depositing material and the depositing material etching angular dependence. Feature bottom microtrenching was strongly linked to sidewall curvature, i.e., bowing. Microtrenching was found to begin when the sidewalls bowed sufficiently. Scattering of the ions from the curved sidewalls exhibited a focusing effect on the directional ions concentrating them at a point near the sidewall, thereby causing the microtrenching.
Cryosorption Pumping of Hydrogen and Helium at 20 °K
Authors: Stern S. A. , Mullhaupt J. T. , Hemstreet R. A. , DiPaolo F. S.
Published: July 2002

The feasibility of pumping hydrogen and helium gas in large vacuum chambers by adsorption at low temperatures has been investigated. The adsorptive capacity of seven selected adsorbents for hydrogen and helium was determined under equilibrium conditions at temperatures between 20 ° and 40 °K and at pressures from 3×10−8 to 1×10−3 Tort. The adsorptive capacity for hydrogen on coconut charcoal and on several types of molecular sieves at 20 °K was found to be very large. Above 30 °K, adsorptive capacities were found to be too low to be of practical interest. Cryosorption pumping under constant hydrogen gas leak was demonstrated for three of the adsorbents studied: molecular sieves 5A and 13X, and coconut charcoal. However, only the adsorbent surface directly exposed to the gas flow was found to be effective. The capacity and pumping efficiency of this surface were strongly dependent on its temperature. As a result, the adsorbent must be well shielded from radiation, and good thermal contact between the adsorbent bed and the refrigerant must be assured. It is concluded that cryosorption is a promising technique for pumping hydrogen in large space simulation chambers, but cryosorption pumping of helium at 20 °K does not appear practical.
Nucleation and Initial-Growth Behavior of Thin-Film Deposits
Authors: Lewis B. , Campbell D. S.
Published: July 2002

This paper gives a theoretical and experimental treatment of the subject. It is shown that the capture of single atoms can be related to catchment areas associated with stable and critical nuclei. It is then shown that for the materials and conditions used in evaporation work the size of the smallest stable cluster is normally a pair.

Two equations describing the initial stages of growth are then derived dependent on whether the lifetime of single atoms is determined by reevaporation or by capture. For the reevaporation case, it is predicted that nucleation proceeds exponentially to a saturation density Ns of islands, and that Ns increases with temperature T and is independent of incidence rate R. For the capture case, condensation is initially complete and Ns increases with R and decreases with T. Experimental results with gold on vacuum cleaved rocksalt show reasonable agreement with the predicted behavior. Modified growth conditions are also examined experimentally, and the results are interpreted in terms of the parameters of the theoretical expressions. Growth using gold ejected from a sputtered single crystal suggests an increased effective condensate temperature. Normal evaporation with simultaneous electron bombardment of the substrate gives results which can be ascribed to lower mobility of migrating atoms.
Influence of the Temperature History of Condensed Argon on its Hydrogen Adsorptivity at Low Temperatures
Authors: Hengevoss J.
Published: July 2002

Adsorption of hydrogen on to multimolecular layers of condensed argon at the temperature of 9 °K was investigated. Before adsorbing hydrogen the condensed argon has been temperature cycled in different ways. It was found, that the adsorption capacity of the solid argon was 20 times higher when first condensed at 6 °K and subsequently heated to 9 °K than if it had first been condensed at 20 °K and subsequently cooled to 9 °K. Furthermore a loss in adsorption capacity was established, if solid argon condensed at 9 °K has been tempered at higher temperatures during only a few seconds. This result implies that structure and density of the solid argon depends on the temperature at which it has been built up. Presumably the argon molecules condensing at low temperatures only form loose packed layers because their surface mobility is very small in this case.
Ultimate Pressure Limitations
Authors: Bills D. G.
Published: July 2002

Present limitations on attaining low pressures are examined in detail. Evidence for the existence of pumping mechanisms at very low pressures is reviewed and it is shown that the present difficulties in achieving pressures much below 10−12 Torr in room temperature systems appear to be due to inadequate or improper processing of the system materials. Curves showing the partial pressure as a function of time and temperature for volume, surface, dissolved, and permeating gases in a typical system are given. It is concluded on the basis of present evidence that pressures in the 10−16 Torr range should be routinely possible provided the entire system is designed and operated to minimize permeation and is carefully processed to remove dissolved gases.
Hydrogen Pumping Speed of Sputter-Ion Pumps
Authors: Singleton J. H.
Published: July 2002

The pumping speed of a sputter-ion pump for hydrogen may vary over a wide range. At procures below 10−8 Torr the speed decreases rapidly and cannot be explained as a simple decrease in the discharge current. In the pressure range between 10−8 and 10−6 Torr the pumping speed for pure hydrogen is of the same order as that for nitrogen. However, if a second gas having a higher sputtering yield for titanium is also present in sufficient concentration, increases of at least a factor of two are observed in the pumping speed for hydrogen. Finally, at hydrogen pressures above 10−6 Torr the long-term pumping of pure hydrogen can produce a marked increase in speed. The extent of this increase is reduced by the presence of active gases such as nitrogen, indicating that change of the rate of diffusion of hydrogen into the titanium at room temperature is the principal factor involved.
Low-voltage triode sputtering with a confined plasma. Part II: Plasma characteristics and energy transport
Authors: Tisone T. C. , Cruzan P. D.
Published: July 2002

The plasma characteristics of a triode low-voltage sputtering (LVS) system have been measured. The current–voltage relationships in the confined plasma discharge, of the target and of the substrate table, have been investigated as a function of pressure for Ar and Xe, with and without an axial magnetic field. The power dissipation and steady-state temperature at the target and substrate table were also measured as a function of operating conditions. From these measurements the plasma potential and target current densities could be deduced. The application of these results to sputter deposition is considered.
Thermal input to substrate during deposition by hollow−cathode discharge
Authors: Komiya Souji , Tsuruoka Kazuyuki
Published: July 2002

Ag and Cr have been evaporated by a low−voltage, high−current electron beam from a HCD gun and deposited on a negatively biased substrate. The flux of Ag ions which strike the substrate was detected separately from Ag atoms, gas atoms, and ions of argon, as reported elsewhere. In the present study, calorimetric measurement of heat dissipated at the negatively biased receiving plane (substrate) shows that the major contribution to heat input comes from energetic neutrals rather than from metal ions; the contribution is, for example, 48% and 23%, respectively, of the total heat dissipated. The bias voltage, argon pressure, electron−beam voltage, beam current, and Ag deposition rate are −200 V, 0.75 mTorr, 45 V, 55 A, and 0.8 μ/min, respectively. Thick films of Cr deposited on steel sheets are evaluated as functions of substrate temperature and negative−bias voltage.
Poiseuille flow and thermal creep flow in long, rectangular channels in the molecular and transition flow regimes
Authors: Loyalka S. K. , Storvick T. S. , Park H. S.
Published: July 2002

The theoretical Poiseuille flow and the thermal creep flow for rarefied gases in a long, rectangular channel are computed using the BGK model of the Boltzmann equation and diffuse scattering from the walls. These results are compared with available experimental data for Poiseulle flow. The present work provides a way to compute flow in a rectangular channel that is estimated to be accurate to ±5% for common gases.
Thin-film polyimide gasket seals for ultrahigh vacuum
Authors: Edwards T. J. , Budge J. R. , Hauptli W.
Published: July 2002

This article describes flange seals made using very thin films of polyimide compressed between a knife edge and mating groove. Leak-tight seals are effected with small compressive forces, allowing the use of lightweight flanges. Polyimide sheet is inexpensive, and these seals provide an attractive economic alternative to conventional ultrahigh- vacuum seals.
Thickness dependence of structural and electrical properties of Cds films for solar cells
Authors: Amith A.
Published: July 2002

Polycrystalline films of CdS were evaporated on zinc-plated foils of copper so that different thicknesses were obtained in the same evaporation. The different thicknesses were compared with respect to their surface morphologies, acid etching, grain sizes, grain structure, and orientation as well as crystallographic orientation. Concomitant measurements of the electrical properties as functions of thickness were taken. These included average resistance through the thickness, current–voltage characteristics of diodes prepared by evaporating gold dots on the surfaces, and measurements of capacitance as functions of reverse bias on the same diodes. It was established that grain size, the preferential grain orientation and conelike growth towards the source, the preferential c-axis orientation towards the source and the surface roughness, all increased as the film thickness increased. Furthermore, it was found that the concentration of free carriers increased with film thickness, the quality of the diode behavior improved considerably in the same manner, and the existence of voltage-dependent shunting paths diminished as the film thickness increased. An explanation is proposed which relates the observed electrical behavior as a function of thickness to the structural parameters.
Surface diffusion of carbon on (111) platinum
Authors: Martin Michael T. , Hudson John B.
Published: July 2002

An Auger electron spectrometric technique has been employed to measure the diffusivity of carbon atoms on an otherwise clean Pt(111) surface. The technique used was essentially a classical mass transport method, in which the rate the migration of carbon atoms out of a circular surface region initially containing a monolayer of adsorbed carbon was measured by Auger electron spectrometry. The diffusivity D can be characterized by an Arrhenius equation D=D0exp(—ΔH*/RT) in which D0=0.2 cm2/s and ΔH*=31±4 kcal/mol. Additional data are presented to demonstrate the self-consistency of the experimental method used.
Improved integrated circuit failure analysis using SEM video processing
Authors: Gonzales A. J. , Powell M. W.
Published: July 2002

Video processing of voltage contrast information from the scanning electron microscope is used to reduce unnecessary information in order to enhance voltage contrast effects and pattern recognition. A video comparator is employed to sample the video information of any two portions of the device operating cycle. The comparator output is the algebraic difference of the two samplings thereby producing an image of areas that have changed between samplings. Unchanged areas appear gray, whereas bright and dark areas indicate shifts towards a more negative or positive potential. By suppressing static areas, small detail and logical patterns are easily distinguished even at low magnification. Synchronization of the comparator samplings to the device operation cycle isolates specific IC logic functions. The comparator which operates at video frequencies is extended to give a time resolution of one nanosecond by the addition of SEM stroboscopic techniques.
Variable spot shaping for electron-beam lithography
Authors: Pfeiffer H. C.
Published: July 2002

Spot size and shape can be changed rapidly, without loss of resolution and current density, by use of the probe-forming electron-beam system described here. The variable-shaped spot (VSS) method is an extension of the fixed-shaped-beam concept. It further increases the exposure rate, projecting up to 100 or more image points in parallel, and provides more flexible pattern generation. The beam spot at the target is tailored to fit each pattern segment while it steps from one segment to the next. Spots are shaped by projecting two square apertures simultaneously, and by laterally shifting the image of the first aperture electrostatically with respect to the second. The compound image is subsequently demagnified and projected onto the target. The feasibility of this VSS method has been demonstrated experimentally.
Bakable aluminium vacuum chamber and bellows with an aluminum flange and metal seal for ultrahigh vacuum
Authors: Ishimaru Hajime
Published: July 2002

A bakable (200°C) aluminium alloy vacuum chamber and bellows (6063-T6) with an aluminium alloy (2219-T87) flange and metal seal (Helicoflex-HN: aluminium O-ring) has been constructed. Such components may be used in the assemblies of the vacuum chambers in proton synchrotrons and electron storage rings.
Vacuum compatibility of machinable glass ceramics
Authors: Altemose V. O. , Kacyon A. R.
Published: July 2002

The thermal outgassing and helium permeation characteristics of Code 9658 machinable glass–ceramic are discussed. Up to 600° C, it is shown that this material can be treated like glass vacuum system components. The quantities of outgassing constituents under vacuum conditions are given and the need for vacuum baking freshly machined material is demonstrated. Although the material can be used up to 1000° C, between 600° and 1000° C some fluorine evolution from the material takes place and could present a corrosion problem to some systems. Helium permeability of this material is an order of magnitude lower than for Code 7740 glass.
Investigation of the mechanism for Schottky barrier formation by group III metals on GaAs(110)
Authors: Skeath Perry , Lindau I. , Chye P. W. , Su C. Y. , Spicer W. E.
Published: July 2002

New evidence for a defect mechanism which is responsible for pinning states within the band gap on the (110) surfaces of the III–V compounds is presented. Investigations of column III metals on both n- and p-type GaAs revealed a systematic difference in surface Fermi energy stabilization in the gap with p-type samples pinning 0.25 eV below n-type samples. Several current models and theories of Schottky barriers are discussed in terms of both the results given in this paper and previously reported data.
Cylindrical magnetron sputtering system for coating solar selective surfaces onto batches of tubes
Authors: Harding G. L. , Window B. , McKenzie D. R. , Collins A. R. , Horwitz C.M.
Published: July 2002

Construction and operation of a cylindrical magnetron sputtering system for coating glass tubes with solar selective surfaces is described. A metal carbide on copper selective surface produced in the coater is discussed in terms of uniformity of coating thickness, electrical and optical properties. Short pumpdown times and high deposition rates make this a medium volume productive system.
Practical selection of elastomer materials for vacuum seals
Authors: Peacock R. N.
Published: July 2002

Proper selection of polymer seal materials must consider restraints imposed by the application and the properties of available materials. Data and concepts presented enable the working vacuum technician to make an educated selection considering chemical and mechanical properties, outgassing, permeation, and nuclear radiation damage. Early reports on the new perfluoroelastomer Kalrez have shown problems with compression set and adhesion, but these difficulties may have resulted from improper groove design.
Review of the ISX-B experimental program
Authors: Saltmarsh M. J.
Published: July 2002

The ISX-B tokamak is a modestly sized device that is designed to explore questions closely related to the design of future tokamak devices, such as the Engineering Test Facility (ETF). The major program emphasis is on high-β plasma operation using neutral beams to heat plasmas with noncircular cross sections. In addition, substantial efforts are under way or planned in the areas of plasma-wall interactions, coated limiter studies, electron–cyclotron heating, ripple injection, impurity flow reversal, pellet injection, and the application of a bundle divertor. The current status and future plans for these programs are reviewed.
X-ray photoelectron spectroscopy (XPS) studies of oxygen and carbon bonding to tokamak walls
Authors: Staib Ph. , Dylla H. F. , Rossnagel S. M.
Published: July 2002

The binding energies of surface atoms of stainless steel samples exposed to hydrogen plasma discharges in PDX are measured using x-ray photoelectron spectroscopy. After glow discharge conditioning the O1s line is completely shifted to a higher binding energy which is an indication of the formation of hydroxides. The Fe2p lines show a partial reduction of iron. After high power discharges, the oxygen concentration increases and the binding energy of the deposited O atoms corresponds to a metallic oxide. The deposited limiter material Ti is also completely oxidized. For both kinds of discharges the binding energies of Cr2p and C1s remain essentially unmodified.
HF vapor phase etching (HF/VPE): Production viability for semiconductor manufacturing and reaction model
Authors: Weston D. F. , Mattox R. J.
Published: July 2002

A nonplasma silicon dioxide etch process using anhydrous hydrogen fluoride at reduced pressures has been investigated. This technique involves the interaction of HF vapor with negative photoresist which catalizes subsequent etching beneath the photoresist. Etching in nonphotoresist coated areas can be eliminated by a short in situ plasma pretreatment followed by HF etching at 190 °C, 10 Torr, and 500 sccm in a commercial etch system. Experimental details as well as a proposed reaction mechanism will be presented.
X-ray diffraction spectra of cadmium and magnesium thin films
Authors: Halder N. C. , Pita M.
Published: July 2002

The structure and properties of Cd and Mg thin films have been investigated by analysis of the x-ray diffraction spectra (XDS). Cd and Mg thin films in the thickness range of 15 000∠28 000 Å and 23 000 ∠93 000 Å, respectively, were prepared at pressure of about 10−6 Torr and temperature of 45°C. A Fourier analysis of the measured XDS shows quite a contrasting behavior for these two films with regard to particle size, mean strain, and fault probabilities. It has been shown in this paper that some of the previous studies by others were in error and the results inaccurate. These difficulties have been resolved and corrections made to the existing errors.
Method to control specimen charging for SIMS and AES of insulators
Authors: Nelson Art , Green A. K.
Published: July 2002

A method for controlling specimen charging in SIMS and AES of insulators, utilizing an extension of the metal diaphragm technique, is reported. (AIP)
A switching circuit for a dc electron-bombardment sample heater for UHV applications
Authors: Hoflund G. B. , Gilbert R. E.
Published: July 2002

A description is given of a digital-mechanical apparatus for periodic sample heating. A TTL counting circuit drives a solid-state relay which drives a fast mechanical relay which does the load switching.(AIP)
The chemical reactivity and lithographic sensitivity of obliquely deposited germanium selenide films used as low energy ion beam resists
Authors: Venkatesan T.
Published: July 2002

Silver sensitized obliquely deposited germanium selenide films exposed to 25 keV N+ ion beam exposure exhibit an increasing sensitivity with increasing deposition angle with respect to the substrate surface normal. Films deposited at 75° are 20 times more sensitive than the films deposited normally (0°). The film density was found to decrease with increasing deposition angle with a reduction as high as 25% for the films deposited at 75°. The obliquely deposited films are chemically very reactive both in terms of silver adsorption in a sensitizer and their dissolution rate in a developer. Rutherford back scattering spectra of the adsorbed Ag indicate penetration of Ag through more than half the thickness of the film deposited at 60° and 75° indicative of deep voids in these films, a consequence of the oblique deposition. The 45° film shows a photodoping efficiency 3 times that of a 0° film. This enhanced silver doping efficiency may be primarily responsible for the increased sensitivity of the oblique films. Using a bilevel scheme involving a GeSe2 film deposited at 45° on a poly (vinyl formal) PVF layer submicron patterns were written on the GeSe2 film with a 20 keV vector scanned, In+ ion beam focussed to a spot size of 2500 Å. The developed patterns on the GeSe2 were successfully transferred to the underlying PVF by an oxygen reactive ion etch, producing 0.3 μm wide polymer patterns.