bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical mask metrology for next generation lithography
Authors: Vollrath Wolfgang , Schlüter Gerhard , Scheuring Gerd
Published: July 2002

This article addresses the state-of-the-art in optical mask CD metrology based on the most recent deep ultraviolet (DUV) microscope optics operating at 248 nm. It further points out the future potential and limitations of optical CD metrology in general and shows that DUV mask metrology has all of the capabilities to meet the ITRS needs, while avoiding the difficulties associated with scanning electron microscopy based metrology tools, including substrate charging and contamination.
Ultrahigh vacuum scanning probe investigations of metal induced void formation in SiO2/Si(111)
Authors: Håkanson U. , Ohlsson B. J. , Montelius L. , Samuelson L.
Published: July 2002

Using scanning electron microscopy guidance, atomically resolved scanning tunneling microscopy investigations inside openings formed during the decomposition of a thick SiO2 film on a Si(111) surface have been performed. We report, for the first time, the presence of Ni atoms inside self-formed openings. The SiO2 decomposition as a function of annealing temperature and time was studied. By comparing self-formed and lithographically designed openings in the SiO2 layer we have shown that Ni contamination of the SiO2/Si(111) has a profound effect on the formation of self-induced lateral oxide openings.
Electron field emission from hydrogen-free amorphous carbon-coated ZnO tip array
Authors: Mao D. S. , Wang X. , Li W. , Liu X. H. , Li Q. , Xu J. F.
Published: July 2002

Enhanced electron field emission from hydrogen-free amorphous carbon (a-C) films deposited on ZnO-tip-array-coated Si substrates was studied. Both the ZnO tip array and the a-C films were deposited by filtered arc deposition. Compared with the a-C film deposited on Si substrates, the a-C film on ZnO had a lower threshold field (4.5 V/μm), higher field emission current density (0.215 mA/cm2 at 14.3 V/μm) and higher emission site density (>2×103/cm2 at 20 V/μm). The introduction of the ZnO tip array provides high local geometric electric-field enhancement for the a-C film. On the other hand, the amount of excess Zn in the ZnO film provides better conductivity. The result is that the electrons can be easily penetrated into the a-C films, which enhances the field emission properties.
An Absolute High Resolution Calibrator for Vacuum Gauges
Authors: Smetana F. O. , Carley C. T.
Published: July 2002

Since there is at present no standard means of calibrating vacuum gauges at pressures below 1 Torr, one often finds that such gauges frequently differ in their indications by 30% or more. In many areas of research it is necessary to measure pressures accurately to within 2%. Thus, to achieve this goal, it is necessary to devise a means to calibrate the measuring gauges. This calibrator permits one to calibrate a vacuum gauge over the pressure range of 10−4 Torr to atmospheric or above increments as small as 10−4 Tort or as large as 3.5 Torr. Virtually any value in between is possible. Three volumes are interconnected by a pair of solenoid valves. Volume 1, with the gauge to be calibrated connected to it, is evacuated to some very low pressure, say 10−6 Torr, and sealed off. Volume 3 is sealed off at some readily measurable pressure. Then volume 2 is filled from volume 3 and emptied into volume 1. This process is termed a step. If the three volumes are measured, then the pressure in V1 can be calculated at the end of every step and compared with the gauge indications. The general equations describing the pressure rise in V1 as a function of step number are obtained. The effect of an initial pressure, not zero, and a finite leak and/or desorption rate are also considered. A description of the actual apparatus is also included.
Measurement of Pressure for the Determination of the Speed of High-Vacuum Pumps
Authors: Buhl R.
Published: July 2002

The results of the determination of the pumping speed employing conventional methods deviate from the product ACef based on concepts of the kinetic theory of gases, where ACe=Aυav/4 is the conductance of an orifice, if the capture probability f is not small. This deviation may be attributed to the technique of pressure measurement. In order to obtain proportionality between capture probability and speed with a unique constant of proportionality in the whole range 0≤f≤1 it is recommended that the pumping speed be defined using the pressure in a large vessel at a place where the isotropic state is maintained to a high degree. This speed is named intrinsic speed and it may be measured using Knudsen's large chamber fitted with a proper gas inlet system. The measurement of very large pumps according to this definition however may be carried out by applying a conversion for the incidence density in the pump mouth to an isotropic pressure. The considerations presented in this paper are intended as a contribution to an international standardization of the speed measurement of high-vacuum pumps. They are based on molecular flow in the test dome.
Implications of High Vacuum on the Characteristics of the Lunar Surface
Authors: Glaser Peter E.
Published: July 2002

The pressure on the lunar surface, which may be no higher than 10−13 terrestrial atmospheres, has already been shown to have an important effect on the behavior of postulated lunar surface materials. The observational evidence on the nature of the lunar atmosphere is summarized and the implications of the low pressure on lunar surface structural and physical properties are discussed. Lunar environmental effects including micrometeoroid impact and solar radiation are shown to be contributing to the surface characteristics. The effects of low pressures on the vesiculation of lava are used to illustrate structural features which may be present on the lunar surface. Consolidation phenomena, which are expected to produce adhesion of particles on the lunar surface, and the rôles of chemical bonds and van der Waals and electrostatic forces are discussed. The effects of the high vacuum on heat-transfer phenomena on the surface are examined and the required characteristics of postulated materials, ranging from a lightweight interconnected structure to a vesicular low-density foam, are listed. The restraints imposed on lunar exploration by the absence of the atmosphere and the expected contamination caused by lunar probes and future lunar-landing vehicles are considered.
Isolation of Ultrahigh Vacuum Systems from Oil Diffusion Pumps
Authors: Gretz R. D.
Published: July 2002

Surface diffusion and adsorption-desorption are the means by which oil is passed through traps in the molecular flow region. Surface diffusion can be excluded by using zeolite (or any equivalent molecular sieve material) on surface paths in the trap. Elimination of the adsorption-desorption mechanism, however, requires somewhat more careful trap design. It is shown that a long isolation time (the length of time that a system will remain at the base pressure after processing for achievement of ultrahigh vacua, which is the usual criterion for evaluation of isolation methods) is a necessary but not a sufficient condition that must be met to insure complete isolation of a system from an oil diffusion pump. It is shown, using field-electron emission microscopy (FEM), that under certain conditions “oil” can be transferred into the vacuum system during bakeout and also under subsequent quiescent conditions. The use of a trap design that is an optical baffle (all internal trap surfaces see only a molecular sieve material, either zeolite or Fiberfrax) precludes “oil” transfer during bakeout, but does not exclude transfer under quiescent conditions. Addition of a Ti getter in-line between the molecular sieve trap and the high-vacuum chamber precludes “oil” transfer under all operating conditions.
Mass Spectrometric Investigation of the Ion Desorption in UHV Gauges
Authors: Huber W. K. , Rettinghaus G.
Published: July 2002

Electron-induced ion desorption from platinum, platinum-iridium, and molybdenum is studied by means of a quadrupole mass spectrometer, in order to determine its influence on the measurement of pressure by ionization gauges. Adsorbed species studied were H, H2O, CO, and O2. Ion yields, which were obtained under various conditions, are given. Interaction between coadsorbed species caused changes in the electronic desorption probabilities from the values observed for the separately adsorbed species. Suggestions are given for proper operation of ionization gauges in order to minimize ion desorption.
Crystallographic Orientation of Zinc Oxide Films Deposited by Triode Sputtering
Authors: Foster N. F.
Published: July 2002

Zinc oxide films for thin film piezoelectric transducer applications have been deposited by triode sputtering onto gold film surfaces. Films sputtered under relatively hydrocarbon-free conditions showed the “normal” orientation with the c axis perpendicular to the substrate surface. The addition of hydrocarbon vapors to the sputtering gas at the beginning of the deposition resulted in films at least partly oriented with the c-axis parallel to the substrate surface, and the simultaneous application of a reverse bias to the substrate holder produced films essentially completely oriented with this parallel orientation. Under oblique deposition conditions the average c axis direction in the film plane was directed towards the target, yielding good piezoelectric shear mode transducers with a uniform polarization. It is suggested that the hydrocarbon vapors polymerize in the discharge, covering the substrate with an organic film on which zinc oxide grows with the parallel orientation, and that alignment of the c-axis in the oblique deposition arises from preferential growth of crystallites oriented with their c axis towards the target.
Substrate Bombardment During RF Sputtering
Authors: Brodie I. , Lamont L. T. , Myers D. O.
Published: July 2002

It is shown, that for the conditions relevant to the “peak” type of rf sputtering arrangement, and in fact most rf sputtering devices, that ions are essentially unaware of the existence of the rf fields and respond only to the dc fields generated. This enables the sputtering parameters to be viewed in a simple, physical way and calculations based on this approach are shown to be fairly exact. A deduction from the theory is that the majority of the secondary electrons released by ion bombardment of the target plates strike the substrate table with considerable energy. A special gridded probe in the substrate table enabled the simple theory to be verified quantitatively and also verified the existence of the high-energy electrons. By controlling substrate bombardment during sputtering with another grid arrangement, the effects of this high-energy electron bombardment on film adherence and appearance was demonstrated.
High Capacity Sputtering Apparatus
Authors: Muly E. C. , Aronson A. J.
Published: July 2002

The design, construction, and evaluation of a compact, economical four-element sputtering system to be used for handling quantities of substrates and multiple target materials is described. This system operates without the aid of a magnetic field. Details are also given of an accurate large area uniformity measuring technique employing interferometry which does not require the use of optical flats.
Vacuum System for High-Radiation Environment at the RPI Linac Laboratory
Authors: Haken J. , Lewis J. F. , Krasse R. J.
Published: July 2002

Vacuum system components on the RPI Linear Accelerator must operate in radiation fields averaging 5×105 rad/sec. Experience gained since the start of operations eight years ago indicates the special problems of constructing, maintaining, and modifying systems for high-radiation environments.
Outgassing of Multifoil Insulation Materials in Sealed Vacuum Systems
Authors: Reid R. L. , DeWitt W. D. , Gibbon N. C.
Published: July 2002

Multifoil vacuum insulation systems provide maximum thermal protection with a minimum of insulation. In order to obtain the maximum thermal performance in such systems, a good vacuum level must be maintained with the insulation system. In order to determine the amount of getter required to maintain the vacuum environment, the rate of offgassing of the insulation materials must be known. This paper presents the results of offgassing rate measurements on typical multifoil insulation materials in the temperature range of 100 ° to 1800 °F. Rates were determined for aluminum foil, tantalum foil, nickel foil, copper foil, glass-fiber paper, aluminum-opacified glass-fiber paper, quartz paper, copper-opacified quartz paper, and quartz cloth. These materials were subjected to periods of vacuum pumping at temperatures 100 °F in excess of the offgassing measurement temperatures. The composition of the offgas was also measured. The 100 °F over-temperature bakeout was generally effective in suppressing the offgassing rates to acceptably low levels. Because of the bakeout period, some materials became adsorbers when the temperature was reduced. All rates are presented as a function of the time of pumping at the over-temperature so that the length of the bakeout period can be determined for a given desired offgassing rate.
Continuous Observation of Initial Growth and Coalescence of Bismuth Deposits by In Situ Electron Microscopy
Authors: Inuzuka Tadao , Ueda Ryuzo
Published: July 2002

The vacuum deposition of bismuth on a thin substrate of molybdenum disulfide was carried out inside an electron microscope. Time sequences of the formation process of a thin film were recorded using a ciné camera. Initial growth of deposits was studied as a function of substrate temperature. It is found that the linear dimension of particles increases nearly proportionally to the square root of deposition time in the range of substrate temperatures observed. At the temperature of about 150 °C, particles having a dimension less than 150 Å, are liquid, and transformation from liquid to crystalline particles, as they grow larger, is also observed. The coalescence process of particles was recorded on ciné films at relatively higher speeds. It is found that coalesced particles have, in general, a small projected area compared to the sum of areas of initial two particles. The mechanism of this process is discussed in connection with the theory of sintering as proposed by Pashley et al. [Phil. Mag. 10, 127 (1964)].
Motion of Liquid Films on Metal Surfaces in High Vacuum
Authors: Levine L. P. , Landowski James
Published: July 2002

Observations have been made on the motion of thin films of oil on polycrystalline tungsten surfaces at pressures of the order of 10−6−10−8 Torr. Measurements were made by utilizing the difference in secondary electron coefficient between a clean and an oil-covered surface. The apparatus is discussed. Propagation velocities of films of Octoil-S and Dow Corning 702 are presented for surface temperatures between 230 and 310 K. The implications of this motion are discussed.
Response of a Heated Thermocouple Vacuum Gauge in Air and Parylene Systems
Authors: Spivack M. A. , Anderson D. B. , Carpenter L. L.
Published: July 2002

The pressure of a condensible gas such as di-p-xylylene (parylene dimer) or p-xylylene (parylene monomer) may be determined by using a heated thermocouple gauge to retard absorption or polymerization on the gauge elements. An equation has been derived which relates the voltage response of a compensated thermocouple gauge to the true pressure of the system at gauge operating temperatures in the range 25 °–300 °C. Correlation of data and theory have been found using air as a standard reference. Semi-empirical curves fitted to the data for parylene diradical (monomer) shows that the specific heat calculated from the derived equation agrees with theoretical expectations. The specific heats calculated from parylene dimer curves show these values to pass through a maximum at 400 °–450 °C. This corresponds to an inflection point in the gauge response curve and also to the conversion temperature of parylene dimer to parylene monomer.
S-Type Current–Voltage Characteristics in Some Film Systems and their Interpretation
Authors: Zhdan A. G. , Sandomyrskii V. B. , Elinson M. I. , Tchugunova M. E.
Published: July 2002

Advances in investigations of switching phenomena in glassy semiconductors give a possibility of a new interpretation of results on the study of anomalous field emission (AFE) that we observed earlier in thin (<1 μ layers of an amorphous quartz doped with carbon. The main AFE characteristics are quite similar to switching characteristics in glasses, namely, AFE current-voltage characteristics are of the S-type and these characteristics have a high velocity of transition from a high ohmic state to low ohmic state. The AFE phenomenon is quite reproducible. On the emission pictures of AFE in the Muller microscope we observed a distinct narrow current channel which is typical of S-type characteristics. The current densities of AFE were ≃104 A/cm2, and the emission was stable in relatively low vacuum (≃10−7 Torr). The velocity spectrum of electrons in the AFE process is considerably wider than in the normal field emission process. Thus the AFE method is quite an effective tool for investigations of physical mechanisms of switching in similar systems. We have also investigated switching phenomena in CdS single crystal films on Ge. In this system we also observed S-type characteristics having parameters which were dependent on the Ge volume properties and on the conditions of CdS deposition. The theory of switching mechanism for the systems containing a high trap concentration is developed. This theory is based on the idea of space charged limited currents and on the effect of disappearance of local level during screening by free carriers. The theory describes qualitatively many features of switching phenomena in glassy semiconductors.
A Novel Sweep Method for Monopole Mass Spectrometers
Authors: Herzog Richard F.
Published: July 2002

The regular mass range of the monopole mass spectrometer can be extended to very high mass numbers if at the end of the regular mass range, the maximum ac rod voltage is kept constant and the dc rod voltage is reduced. During this extended mass range the mass is inversely proportional go this dc voltage. If the ion energy is kept constant the sensitivity stays essentially constant over the whole mass range and the resolution is inversely proportional to the mass. If the ion energy is reduced in proportion to the dc voltage the resolution stays constant, but the sensitivity is reduced. This method of mass scan permits with excellent sensitivity the detection of vacuum system contaminants of very high molecular weight. The total scanning time necessary to cover this wide mass range is much shorter than the time required for a regular scan over the same mass range.
Effect of excessive-trapping operation of sequential mass spectrometers shown for collision cross-section data of BCl3
Authors: Hafidh Z. A. , Hartnagel H. L.
Published: July 2002

The transients of ion trapping were studied in sequential mass spectrometers. The optimization criteria of the trap are very complex and are dependent on such parameters as the mass of the trapped ions. A new calibration scheme was developed for the measurement of the collision cross section of unknown gases and was applied to BCl3, which is commonly used for boron-ion implantation into silicon.
Electron-beam projection systems with compensated chromatic field aberrations
Authors: Koops H. , Bernhard W.
Published: July 2002

Microminiaturization for the production of modern large-scale integrated circuits requires electron-optical devices capable of recording more than 10 000 resolved lines per frame at a resolution of 0.1 μm. Magnetic demagnifying electron-projection systems with compensated chromatic field aberrations are capable of recording up to 10 000 lines per frame. In our system, the optimum aperture for a maximal number of lines per frame depends only on the coefficients of field curvature, isotropic and anisotropic astigmatism, and on the electron wavelength. A theoretical expression for the maximal number of lines per frame indicates that the number of lines can be increased by using a small demagnification factor and by increasing the dimensions of the electron-projection system.
LAMPF experimental-area beam current monitors
Authors: Tallerico Paul J.
Published: July 2002

This paper summarizes the design and operational performance of a wide- range current monitor system used to measure charged-particle currents in the experimental areas of the Clinton P. Anderson Meson Physics Facility (LAMPF), a proton accelerator. The major features of the system are high sensitivity, wide dynamic range, and the ability to withstand high levels of radiation. The current pulses detected are from 50 μs to 1 ms in duration at repetition rates of from 1 to 120 Hz. The pulse amplitude varies from 1 μA to 17 mA of protons or H− ions. Both real-time and integrated outputs are available, and the minimum detectable currents are 1 μA at the video output and 50 nA at the integrated output. The basic system is comprised of toroids, preamplifiers, signal conditioners, voltage-to-frequency converters, and digital accumulators. The entire system is spread out over 1 km of beam pipe. Provision is made for calibration and for sending the outputs to remote users. The system is normally controlled by a small digital computer, which allows the system to be quite flexible in operation. The design features of the toroids and the associated electronics are discussed in detail, with emphasis on the steps taken to reduce noise and make the toroids temperature and radiation resistant.
Comparative study of the zirconiated and built-up W thermal-field cathode
Authors: Swanson L. W.
Published: July 2002

Angular distribution, total energy distribution, and noise measurements have been carried out on both a zirconium coated and built-up W(100) field cathode operating at high temperature (1400–1800 K). The effect of residual gas on the emission characteristics and emitter life was also measured. The results show that high brightness (∠1010 A cm−2 sr−1) operation with <10% noise levels and <1.5-eV energy spread in a 0.079-msr- beam solid angle can be achieved. Emitter longevity in excess of 1000 h in 10 nTorr (1.3 - 10−7 Pa)gas pressure has been observed.
Two-component model of pyrocarbon and its effect on material parameter analysis
Authors: Luhleich H. , Seeberger D. , Koizlik K. , Nickel N.
Published: July 2002

The results of static cold-wall pyrolysis and deposition experiments suggest a ’’two-component model’’ for pyrocarbon deposition, particularly in fluidized beds. By means of this model it is possible to explain the formation of different structures of pyrocarbon. These structures can be correlated with resultant properties after neutron irradiation.
Refractory metal carbide coatings for LMFBR applications—A systems approach
Authors: Wolfla Thomas A. , Johnson Roger N.
Published: July 2002

Selection of existing coatings or the design of new coatings for wear resistance in sodium-cooled nuclear reactors, particularly applications for core components, requires consideration of numerous unique criteria associated with this class of reactors. Wear resistance, low friction characteristics, and long-term, high-temperature chemical compatibility with the coolant and with the substrate are among the major concerns. Thermal transients in this high-temperature environment necessitate coatings with adequate thermal shock resistance. High neutron fluences require materials that are stable under irradiation and which do not transmute to undesirable elements. The selection, testing, and improvement of high-density, tightly bonded plasma and detonation- gun coatings designed to meet all of these criteria are described. The process descriptions include a review of the important developments in substrate surface preparation which are required to ensure strong bonding and to minimize interface contamination. Coating finishing techniques which were developed to optimize friction behavior are also described. The need for low-friction behavior has been an important requirement in the design of the coatings. Chromium-carbide coatings with a Ni–Cr binder applied with a detonation gun have been shown to possess acceptable friction, wear, and corrosion properties. Further enhancement of these properties was made through modification of the metallic binder particle size and the cabide–binder ratio. The use of Inconel 718, Mo, and Tribaboy 700 binders were evaluated in an effort to improve the friction and self-welding characteristics as well as to improve the corrosion resistance in liquid Na.
Wear properties of cast vs plasma-sprayed Laves intermetallic alloys
Authors: Ferriss D. P. , Cameron C. B.
Published: July 2002

Cast and plasma-sprayed surfaces of the same composition were prepared containing a substantial amount of a Laves intermetallic phase. Other compositions, all containing metal carbides, were prepared by plasma spraying, detonation-gun deposition, casting, and powder metallurgy. The Alpha LFW-1 wear test was used to compare wear properties of these surfaces in both room air and a nonlubricating liquid. No significant difference in wear and surface damage was evident between the cast and plasma-sprayed intermetallic wear surfaces. The performance of surfaces containing the intermetallic phase were equivalent to, or in most cases superior to, those whose hardness was due to metal carbides.
Physical properties of the electrical barriers in varistors
Authors: Morris William G.
Published: July 2002

The nonlinear relationship between current and voltage in the zinc oxide varistor arises from electrical barriers at the grain boundaries in the polycrystalline ceramic. At very low fields, thermionic emission accounts for the majority of the current, with Schottky emission becoming more important as the field increases and assists in lowering the barrier. Tunneling through the barrier dominates in the presence of high fields, giving the highly nonlinear behavior. The bismuth (oxide) which segregates at the grain boundries occurs in two forms: an adsorbed layer present on the interfaces between grains, and a discrete phase which is continuous along grain edges. The latter is in the form of triangular prisms which exhibit a dihedral angle of about 60° as they approach a ZnO–ZnO interface, and thus this phase does not completely wet the ZnO grains. The adsorbed layer can account for the electrical barrier. Its chemical thickness is less than 50 Å as determined by Auger electron analysis. A depletion layer is also present in a manner analogous to a Schottky barrier, giving an electrical thickness of 200 to 400 Å. The capacitance, and its dependence on voltage, is in agreement with this model.
Effect of annealing and agglomeration on the electrical properties of copper films
Authors: Mohan S. , Jayarama Reddy P.
Published: July 2002

The electrical resistivity ρf, temperature coefficient of resistance αf, and Hall coefficient RH have been measured on annealed copper films (160–1490 Å) evaporated at a pressure of ∠10−6 Torr on to glass, mica, and NaCl substrates, held at room temperature. The results are discussed in relation to Fuchs–Sondheimer theory. When the films are heated above their annealing temperatures, they are found to be agglomerated as revealed by the electron micrographs. The temperature at which agglomeration starts is found to be thickness-dependent. On agglomeration, the electrical resistivity increases, Hall coefficient and Hall mobility decrease, and the temperature coefficient of resistance remains unaltered.
Simple titanium and nickel sublimation pump (TNSP)
Authors: Haque C. A.
Published: July 2002

One filament of a commercially available titanium sublimation pump (TSP) was replaced with a nickel filament on a tungsten support. This titanium and nickel sublimation pump (TNSP), besides having the attributes of a TSP, effectively minimizes the hydrogen contamination problem present in stainless steel ultrahigh vacuum chambers, with nickel acting as a getter for hydrogen.
Compact vapor deposition system
Authors: Musket R. G. , Pendley M. H.
Published: July 2002

The design, construction, and operation of a compact vapor deposition system is described.(AIP)
Electrical resistivity of vaccum-deposited molybdenum films
Authors: Oikawa Hideo , Tsuchiya Takaakira
Published: July 2002

The electrical resistivity ρ of Mo films evaporated by an electron-beam gun onto SiO2/Si substrates has been studied in relation to the film structure and purity. The resistivity was profoundly influenced by the substrate temperature during deposition Ts but was almost independent of film thickness d if d exceeded 1000 Å. When the films were heat treated at above 700°C, ρ decreased as the grain size increased. These results can be explained if one assumes that the resistivity is due to grain-boundary scattering. The reflection coeficient of the electrons at grain boundaries R depends on Ts, but shows no change with heat treatments at temperatures up to about 1000°C(R =0.41/0.21 for Ts=300/600°C). It is shown that R is proportional to oxygen content in the grain boundaries.
Solar energy conversion using semiconducting photoanodes
Authors: Gerrard W. A. , Rouse L. M.
Published: July 2002

In recent years, interest in the use of photoelectrochemical devices for solar energy conversion has grown dramatically. The major advantage over more conventional solar cells (e.g., the silicon p–n junction) is the ease with which the device can be constructed, since the interface between the semiconductor and electrolyte is not subject to such problems as lattice mismatch. Prior to 1969 it was thought that semiconductors invariably degraded when illuminated in an aqueous environment. Such corrosion problems have been overcome by using more rugged semiconductors and adding stabilizing redox ions (e.g.,S2−/S2−2) to the electrolyte. The understanding of semiconductor–electrolyte interfaces has been greatly enhanced by the ability to study stable systems. It is now clear that the conversion efficiency of such devices is a function of the quality of the Schottky barrier at the interface, the band gap and electron affinity of the semiconductor, and the redox level in the electrolyte that it acts upon. Another advantage over the silicon solar-cell is the ability to store solar energy by the direct production of chemicals (e.g., H2). At present the best conversion efficiencies that have been observed have been of the order of 7%–9% (AM 2 sunlight). While this is poor compared to that which can be obtained with silicon solar-cells, cheap thin-film semiconductor techniques could make such devices extremely competitive in terms of economics.
Design of electron-beam scanning systems using the moving objective lens
Authors: Ohiwa H.
Published: July 2002

Some considerations and results of designing air-core scanning systems comprising round lenses and saddle-type deflection coils are presented. If the deflection coils are cosine distributed, the third-order deflection aberrations are similar to those of a round magnetic lens. This round-lens-type deflection aberrations can be eliminated or reduced by using the Moving Objective Lens (MOL) and predeflection. As is seen from the first-order Taylor-series expansion, a round lens whose potential is φ (x,y,z) can be moved in the x direction by superposing the deflection field ∂φ/∂x. Such a MOL is placed before the image plane and a predeflection coil placed at the object position deflects the beam into the center of the moved lens. Then, a particular aberration such as coma or astigmatism can be eliminated by properly arranging this predeflection. In particular, if coma is eliminated by the predeflection, astigmatism and field curvature are at the stationary point with respect to the predeflection, which is of importance from the design tolerance point of view. A practical scanning system which may be used in microfabrication has been designed. The deflection coils used are half-inch vidicon printed coils which are of best geometrical precision available. A found system produces at the corner of 5×5 mm deflection field with 0.005 rad semiaperture and 1 in 104 beam-voltage ripple, a total aberration disk of 0.35 μm, of which field curvature is 0.30 μm and chromatic aberrations are 0.10 μm.
Averaging of electron-beam aberrations
Authors: Mauer John L.
Published: July 2002

The design of the imaging and deflection components in an electron probe is directly related to the resolution required in the target plane. The resolution has an especially strong effect on the design when the probe is to be scanned over a large area. The theoretical models of such systems commonly calculate the properties of single trajectories through the column, and from these properties the worst-case aberrations are inferred. But such calculations, though more convenient than direct measurement, are often misleading. In most applications, the average properties of an electron beam have more physical meaning than the relatively few electrons with worst-case trajectories. The calculation of single electron trajectories can be applied to the actual electron-optical system by modeling the actual illumination of the electron beam and averaging over this illumination to get certain specific properties of the beam. The illumination is described by probability distributions over the beam parameters; these distributions are related to the electron source through the optical transfer functions of the column. Intervening apertures also affect the boundary conditions of the distributions. This method can be applied o a shaped electron probe. The dislocation and blurring of the shaped spot can be calculated from the single electron trajectories in the final imaging and deflection system by taking into account the correlation of the various aberrations. Changes in beam energy or lens excitation cause beam dislocation and blurring different from what has usually been reported.
Two-phase high-density charge coupled devices fabricated by electron-beam lithography
Authors: Chatterjee P. K. , Fu H. S. , Tasch A. F. , Holloway T. C. , Blocker T. G.
Published: July 2002

One hundred and twenty-eight-bit, two-phase, high-density CCD linear shift registers with double-level polysilicon overlapping gate electrodes have been fabricated using electron-beam lithography for all levels of pattern delineation. The polysilicon gate electrodes are 0.15 mil long and the channel widths on two shift registers are 0.25 and 0.06 mil. The critical registration accuracy is ±1500 Å. These represent cell sizes of 0.1 mil2 corresponding to packing densities of 10–20 million bits/in. Charge transfer efficiency with VΦ=10 V and without fat zero is at least 0.9997 for 0.05 mil2 shift register. The low, uniform leakage current (1.5–4 nA/cm2) observed in CCD’s fabricated by electron-beam lithography compares favorably with those fabricated using optical lithography and larger geometry sizes. This indicates that no significant electron beam induced residual damage is present in these CCD structures.
Alignment of x-ray lithography masks using a new interferometric technique—Experimental results
Authors: Austin Stewart , Smith Henry I. , Flanders D. C.
Published: July 2002

A new interferometric alignment technique has been developed that is compatible with both photolithography and x-ray lithography, and should be capable of a superposition precision of the order of 100 . The operational features of the technique and experimental results are described. With gratings of 10-μm spatial period a superposition precision ?1000 Å has been demonstrated, and with gratings of 1.2-μm spatial period a superposition precision of about 200 Å has been achieved.
Optical manipulation of resist profile in conformable printing
Authors: Lin B. J.
Published: July 2002

Differences between the developed photoresist profile and the optical image in the resist is a function of exposure and development conditions. Because of absorption of light in the photoresist and lateral etching by the developer, an overcut profile in the developed image of positive resists is inevitable, even if the distribution of the exposing light is perfectly verical. Intentional overexposure followed with quick development, or the use of highly reflective substrates only minimizes the overcut. This paper describes an approach using a rotating plane wave making a predetermined angle with the optical axis to expose a mask–wafer assembly. This type of illumination produces an undercut optical image which compensates for the absorption and lateral etching effects. It also reduces the coherence in the illumination to give better images. The angle of inclination as well as the exposure–development parameters can be adjusted to manipulate the angle of cutting. Analytical intensity distribution based on geometric optics is given to provide an insight to the dependence of the cutting angle to the beam angle and the exposure–development parameters. PMMA in the deep-uv wavelength region and AZ1350J in the near-uv region are used to demonstrate the variation of the cutting angle and the liftoff process.
Sheet resistance variation on color-banded silicon following high dose implantations at high dose rates
Authors: Beanland D. G. , Chivers D. J.
Published: July 2002

With some scanning systems color bands are produced on silicon wafers after high dose implantation. The color bands arise from the amorphous zones within the silicon and the thickness of these zones is determined by the temperature attained by the wafer during implantation. The sheet resistance of ’’color-banded’’ silicon wafers has been measured following a series of isochronal anneals and found to vary considerably across a wafer, in a manner correlated with the color bands. The sheet resistance variation persists through a series of isochronal anneals to 1100°C, although it is reduced in magnitude. The implications for high dose implantation of silicon wafers are briefly discussed.
Method for the cross-sectional examination of molecular semiconductor/metal film junctions using transmission electron microscopy
Authors: Katz William , Evans C. A. , Eaton David R. , Faulkner Larry R.
Published: July 2002

Junctions between thin films of metals and molecular semiconductors are of current interest for their uses in electrochemistry and in photovoltaic devices. Characteristics such as interdiffusion, interfacial structure, and pinhole formation are important for various applications. A method has been developed for microstructural characterization of these junctions by the examination of thin cross sections using transmission electron microscopy (TEM). This method incorporates preparation techniques that are commonly used for both inorganic and biological samples. The thin-film system is vapor deposited onto an epoxy medium, then a second epoxy layer is added, so that one obtains a ’’sandwich’’ arrangement, in which the thin-film system is wholly contained within the rigid epoxy casting. A typical system is zinc phthalocyanine (ZnPc) placed between two gold or silver layers. The whole sandwich casting is then cross sectioned by ultramicrotomy. Results concerning the interfacial morphology, obtained by TEM examination of the thin sections, seem to indicate a sharp interface with no bulk diffusion of one material into the other. However, both the metal and the ZnPc seem to exhibit significant surface mobility during deposition when the substrate is held at room temperature. Pinholes formed in the ZnPc were filled with the metal and formed shorts between the two metal layers. This phenomenon is explained and interpreted.
Tight-binding calculation for the AlAs–GaAs (100) interface
Authors: Schulman J. N. , McGill T. C.
Published: July 2002

We report the results of a study of the electronic properties of the AlAs–GaAs interface using the tight-binding method. The tight-binding matrix for the superlattice system is used in the limit in which the thickness of the repeated superlattice slab becomes large. This system is studied in detail with special emphasis placed on the determination of interface states. No interface states with energies within the GaAs forbidden gap are found. The densities of states per layer are calculated and compared with bulk densities of states. They resemble the bulk densities of states except for layers adjacent to the interface.
Synchrotron radiation photoemission studies of the adsorption of oxygen on magnesium and aluminium
Authors: Norman D. , Woodruff D. P.
Published: July 2002

The sorption of oxygen on polycrystalline films of Mg and Al has been studied by photoemission using synchrotron radiation in the photon energy range 70–150 eV. The 2p levels, situated 50.0 eV (Mg) and 72.8 eV (Al) below the Fermi level in the clean metals, shift to higher binding energy by 1.3 (Mg) and 2.6 eV (Al) on heavy oxidation. There is some evidence of a smaller shift, corresponding to a chemisorbed state, coexistent with the oxide peak. For oxygen on magnesium, an interatomic Auger transition, as previously reported from electron-stimulated Auger electron measurements, was observed for a wide range of exposures. An O 2p valence-band resonance is seen 6.1 (Mg) and 7.1 eV (Al) below the Fermi level, with accompanying shoulders 2.6 eV deeper in both systems. Oxidation also produces a marked increase in the total 2p emission from the metallic species, which we attribute to a longer electron mean free path in the oxide than in the metal. The ratio of the mean free path in oxide and metal is typically a factor of 2 for both Mg and Al, and this ratio is energy dependent.
An x-ray diffraction profile analysis in hexagonal cadmium films vacuum-evaporated from normal and oblique vapor incidence
Authors: Sen Suchitra , Sen Gupta S. P.
Published: July 2002

Microstructural investigations on hexagonal cadmium films, considering a number of H − K=3N (namely, 00.2, 10.0, 11.0, 00.4, N1.2, and 20.0) and H − K = 3N±1 (namely, 10.1, 10.2, 10.3, 20.1, 10.4, 20.2 and 20.3) x-ray diffraction profiles recorded in a counter diffractometer, were done by detailed Fourier analysis of lineshape and also integral breadth measurements. The films, in the thickness range of ∠200–3300 Å, were vapor deposited for both normal and oblique (∠46° to the substrate normal) vapor incidences. For both the source positions Fourier lineshape analysis of the fault-unaffected (H − K=3N) reflections indicate that the effects from the average domain size and rms strain are relatively large in the thin range ≲600 Å, and these decrease at higher thickness ∠3300 Å. The size and strain values along [00.2] are found to be close to the average ones depicting the near isotropy in these parameters. As regards the effective domain size values evaluated for fault-affected (H − K=3N±1) reflections, it has been observed that the size values for L0 odd reflections are more than those of L0 even for films ≲1000 Å thick for both the source positions, and this implies the possibility of the presence of stacking faults. For both the source positions, there is a tendency for the growth-stacking fault to be present in appreciable concentration (probability β ∠60.0×10−3 in the thin range only, <1000 Å with total absence of intrinsic stacking fault (probability α). The dislocation density ρav is found to be ∠1011 cm/cm3 for both the cases of normal and oblique incidences. The integral breadth studies also yield similar observations on the microstructural parameters. The preferential orientation of these cadmium films is along [00.2], and the effect decreases with increasing thickness for oblique incidence case but increases for normally deposited films. The recovery effect as studied by analysing two films ∠680 and ∠930 Å, deposited normally on substrates preheated to about 383 K, is shown by considerable gains in size and strain parameters with a reduced probability of growth faulting.
Tritium permeation and wall loading in the TFTR vacuum vessel
Authors: Cecchi Joseph L.
Published: July 2002

The problems of tritium permeation through and loading of the TFTR vacuum vessel wall structural components are considered for various TFTR operating scenarios and outgassing modes. A general analytical solution to the time-dependent diffusion equation which takes into account the boundary conditions arising from the tritium filling gas as well as the source function associated with implanted energetic charge exchange tritium is presented. Expressions are derived for two quantities of interest: (1) the total amount of tritium leaving the outer surface of a particular vessel component as a function of time, and (2) the amount retained as a function of time. These quantities are evaluated for specific TFTR cases. The results are that permeation through the vessel is important only for the bellows during discharge cleaning if the wall temperature rises above ∠150 °C. At 250 °C, after 72 hours of discharge cleaning ∠200 Ci would be lost. The wall loading is most severe in the stainless-steel plate sections during normal pulsed operation where ∠600 Ci would be retained after 1000 shots if the walls were at 20 °C. Maintaining the temperature of the walls above 100 °C greatly lessens the problem. The 600 Ci in the wall would be reduced to ∠10 Ci if the wall were heated to 250 °C for about 60 h.
Plasma chemistry
Authors: Libby W. F.
Published: July 2002

Many natural situations involve ionized matter. In the high atmosphere, the ionizing ultraviolet makes the ionsphere and further out in space, the solar wind consisting of ionized matter ejected from the sun dominates. On earth, x rays and atomic radiation ionize matter intensely. But less dramatically, many ordinary compounds such as sodium chloride consist of ions, as do their aqueous solutions. So our very substance involves the chemistry of ions which I called ’’Plasma Chemistry.’’ I will attempt, in a broad and general way, to outline the principles of the chemistry of plasmas, whether they be in the gas, liquid, or solid state. To remind, an ion consists of an atom or molecule from which one or more electrons have been added to unbalance neutral charge.
Pressure measurement system for beam experiments in the range 0.5–10−2 Pa
Authors: Elforda) M. T. , Hegerbergb) R.
Published: July 2002

A system for measurements of gas pressure in the range 0.5–10−2 Pa is described. A known pressure is produced by static gas expansion and compared with the pressure in a scattering cell using a capacitance manometer as the null detector. The pressure in the scattering cell is controlled by a separate dynamic expansion system. Sources of error are discussed and the absolute error is estimated to be 0.4% at 0.5 Pa, 0.5% at 0.1 Pa, and 2.3% at 10−2 Pa.
AES detection of TiD2 decomposition
Authors: Malinowski M. E.
Published: July 2002

An experimental study of titanium deuteride decomposition utilizing Auger electron spectroscopy is described. (AIP)
Calibration of a spinning rotor gas friction gauge against a fundamental vacuum pressure standard
Authors: Comsa George , Fremerey J. K. , Lindenau B. , Messer G. , Röhl P.
Published: July 2002

The paper reports the direct calibration of a spinning rotor gas friction gauge (RG) against the multiple expansion vacuum pressure standard of the Physikalisch-Technische Bundesanstalt (PTB), Berlin, with HE, Ne, Ar, Kr, Xe, CH4, N2, and, via a membrane micromanometer, with H2, O2, CO, and CO2. It was found that in the pressure range 10−5–10−2 mbar (10−7–10−4 Pa) the macroscopic coefficient of tangential momentum transfer between gas molecules and the rotor surface, σ, is close to unity. The long term reproducibility of the new RG at p≳10−5 mbar as observed over two years with long intermediate periods of air exposure was within the limits of the total uncertainty of 1% for the comparison with the PTB standard. The RG thus seems recommendable for use as a reliable transfer standard, all the more since the only constituent of the new instrument that must be transferred is a small (typically 4.5-mm-diam) steel ball.