bluuebunny/crossref_metadata_2025 huggingface dataset:
The Initiation of Electrical Breakdown in Vacuum—A Review
Authors: Davies D. Kenneth
Published: July 2002

Recent investigations are reviewed of prebreakdown conduction phenomena in vacuum both for steady and for step-function applied voltages. The results of these investigations have led to the formulation of models to explain the initiation of the vacuum discharge by ionization of a vapor medium, the vapor being composed of atoms of one or both of the electrodes. A detailed examination of the events leading to breakdown has allowed a more critical evaluation of the merits and deficiencies of the various breakdown models.
E-Beam Writing Techniques for Semiconductor Device Fabrication
Authors: Varnell G. L. , Spicer D. F. , Rodger A. C.
Published: July 2002

Electron-beam writing instruments for microcircuit fabrication are currently limited by total cycle time, field coverage, automatic registration, and reliability. A fully computer-controlled electron-beam pattern generator will be described which has been developed to advance the economic feasibility of electron beam writing. The instrument incorporates a fully automated mechanical stage and pattern registration system, computer designed deflection coils and a dynamic focusing system for correction of deflection introduced aberrations. Field coverage at the short working distance is variable, up to 0.120×0.120 in. with 60 000×60 000 addressable points in the field. Resolution over the field is 3500 lines at 8 mrad. Pattern distortion is within 1.0 μ over a 0.1 in. square field. The mechanical stage employs stepping motors driving lead screws to provide 3×3 in. movement in 250 μ in.steps. Additional travel of 7 in. is available in one axis for loading the wafer. The automatic pattern registration system employs four silicon etched “L” shaped fiducial marks located in the corners of each field. The electron beam is used to measure the position of the fiducial marks before each field exposure and position the pattern correctly on the wafer. Pattern position, size, rotation, and orthogonality are all typically set up by the automatic registration system in 300 msec. A vernier test pattern has been used to test the alignment system and shows registration better than ± 0.2 μ.
Direct observations of the growth of sputtered silver and gold films on (111) silicon substrates
Authors: Maa J. S. , Lee J. I. , Hutchinson Thos. E.
Published: July 2002

The growth of ion-beam-sputtered silver and gold films on (111) silicon substrates has been studied using the in situ electron microscope technique. The thin silicon substrates are obtained by jet chemical etching followed by ion-micromilling techniques. The substrate temperatures during growth vary from 300 to 600 °C. A two-layer phenomenon occurs in the growth of silver films. Both layers grow with a (111) orientation parallel to the substrate. Liquidlike coalescence which is observed in the second layer, however, is prohibited in the growth of first-layer islands. Gold films deposited under the same conditions result in the formation of discrete liquid islands even at substrate temperatures as low as 300 °C. Occurrence of solid polycrystalline gold films is first observed at 260 °C by lowering the substrate temperature after deposition. Deposition at lower temperatures results in the formation of polycrystalline and amorphous structures. Both cases can be attributed to the interface interaction between the overgrowth and the single-crystal silicon substrates.
rf-sputtered amorphous Si/crystalline Si junctions
Authors: Mei L. , Greene J. E.
Published: July 2002

The electrical characteristics of metal/amorphous Si/crystalline Si (M/a Si/c Si) structures have been investigated and found to depend strongly on whether the M/aSi contact is Ohmic or blocking. Evaporated 1000-Å-thick Cu and Sb films were found to form Ohmic contacts to aSi after proper annealing. With these contacts, aSi/p-Si junctions exhibited good rectification characteristics with breakdown voltages as high as 60 V. Good rectification was not observed on n-type substrates. Reversible threshold switching was found to occur with junctions formed on both n- and p-type substrates when the M/aSi contact was non-Ohmic. The scanning electron microscope was used to observe the structure of filaments in the a Si films subsequent to the forming process.
Properties of molybdenum films prepared by decomposition of the carbonyl
Authors: DeRosa A. I. , Dove D. B. , Loehman R. E.
Published: July 2002

Results of research directed toward preparation of refractory metal electrodes for amorphous chalcogenide semiconductors are presented. Mo(CO)6 vapor in Ar carrier gas was pyrolytically decomposed at temperatures below 250 °C to form a low-resistance metallic coating on selected substrates. X-ray and electron diffraction experiments indicated these films are amorphous. Heat treatment for 15 min at 865 °C promoted crystallization of the deposits; x-ray analysis then showed the presence of Mo and Mo2C in a 2:1 ratio. Masking techniques to produce particular electrode configurations were only partially successful; however, a photolithographic method produced electrodes completely satisfactory for electrical-properties measurements.
Some applications of Auger electron spectroscopy to metallurgical problems
Authors: Haas T. W. , Pocker D. J.
Published: July 2002

The requirements for applying Auger electron spectroscopy (AES) are relatively simple: (i) a vacuum environment to maintain a stable, surface condition during the measurement interval and to avoid electron-gas collisions; (ii) excitation sources to induce Auger transitions in surface atoms; (iii) an electron spectrometer; and (iv) specimens sufficiently small to fit into the vacuum system and of such geometry that the spot of interest can be properly located with respect to the spectrometer. The applications of AES discussed herein are depth profiling of the chemical composition in the near-surface region, investigation of chemical environment of elements in surface regions, determination of changes in the chemistry of surface atoms, quantitative surface analysis, investigation of grain-boundary segregation and its effect on embrittlement and subsequent fracture. Auger spectra are shown for a fractured Ti-6Al-4V specimen, a René-alloy-specimen surface, an alumina particle imbedded in a René alloy, and an embrittled tungsten material.
Atom movements occurring at solid metal-semiconductor interfaces
Authors: McCaldin J. O.
Published: July 2002

Solid metal-semiconductor interfaces often undergo chemical reaction at rather low temperatures, in some cases not much above room temperature. After some general discussion of these reactions, more detailed consideration is given to simple noncompound-forming systems, and, in particular, to the Si-Al, Ge-Al, and Si-Au systems. Diffusive transport of Si or Ge in these solid metallizations is very rapid, though the converse process, diffusion of metal in solid Si or Ge, is usually so slow as to be negligible. The interface reaction itself is less well understood but is becoming controllable in intrinsically favorable cases like Ge-Al and in other cases by more sophisticated means.
Comparison of infrared frequency selective surfaces fabricated by direct-write electron-beam and bilayer nanoimprint lithographies
Authors: Puscasu Irina , Boreman G. , Tiberio R. C. , Spencer D. , Krchnavek R. R.
Published: July 2002

We report on the fabrication of crossed-dipole resonant filters by direct-write electron-beam and nanoimprint lithographies. Such structures have been used as spectrally selective components at visible, microwave, and infrared wavelengths. Imprinting is accomplished in a modified commercial hot press at 155 °C. The replica is then etched in oxygen plasma and developed in chlorobenzene to selectively dissolve the poly(methylmethacrylate and methacrylic acid) and poly(methylmethacrylate) bilayer resist. This step enhances undercut and improves lift-off metalization. Infrared fourier transform spectroscopy was performed to characterize the transmission response of the frequency selective surfaces (FSSs) fabricated. The resonant behavior for the direct-write FSS was found to be 5.3 μm and for the nanoimprinted FSS to be 6 μm. The shift towards longer wavelengths is consistent with the dimensions obtained for the FSSs elements in both cases.
Heat dissipation in thin-film vacuum sensor
Authors: Berlicki T. M.
Published: July 2002

An analysis was performed of the design of a thermal vacuum sensor. The sensor was made by the thin-film technique and consisted of a heating resistor and a thermopile, including six thermoelements. The surface of the heater has been covered with a reflective Al layer that significantly reduced the heat dissipated by radiation. In that way an increase in sensitivity and extending of the measurement range have been achieved. The effect of surface emissivity and sensor dimensions on its characteristics has been studied.
GaN grown on two-step cleaned C-terminated 6H–SiC by molecular-beam epitaxy
Authors: Guan Z. P. , Cai A. L. , Porter H. , Cabalu J. , Chen J. , Huang S. , Giedd R. E.
Published: July 2002

A contaminant-free C-terminated 6H–SiC (0001) surface has been successfully prepared by a two-step method, which combines H2:He (1:1) plasma and heating at 940 °C for 100 min. On this surface, a high-quality GaN (0001) thin film is obtained by radio-frequency nitrogen-plasma- assisted molecular-beam epitaxy. Near-band-edge emissions have been observed from some of these epilayers, depending primarily on the substrate surface conditions. Auger electron spectroscopy measurements show that temperatures of 940–1245 °C are necessary to thermally desorb the oxide and carbide from 6H–SiC substrates. At 1040 °C for the C-face SiC and 1150 °C for the Si-face SiC, crystalline damage was reported in the form of graphite formation on the surface. This graphite was observed through x-ray photoelectron spectroscopy. Structural analysis by x-ray diffraction and photoluminescence indicates very good in-plane alignment of the GaN epilayers as the substrates are cleaned using H2:He (1:1) plasma at 940 °C for 100 min.
Quantitative analysis of the bit size dependence on the pulse width and pulse voltage in ferroelectric memory devices using atomic force microscopy
Authors: Woo Jungwon , Hong Seungbum , Setter Nava , Shin Hyunjung , Jeon Jong-Up , Pak Y. Eugene , No Kwangsoo
Published: July 2002

The Bit formation using atomic force microscopy (AFM) was studied on 270-nm-thick 〈111〉 preferentially oriented Pb(Zr0.4Ti0.6)O3 (PZT) films prepared by the sol-gel process. To minimize the cantilever-sample capacitive force interaction, the experiment was carried out at or near the sample edge. Bit formation was investigated by calculating the electric field in AFM-tip/PZT film/bottom electrode configuration. It was found both experimentally and theoretically that the bit size is linearly dependent on the pulse voltage and the logarithmic value of the pulse width. The linear dependence of the bit size on the logarithmic value of pulse width was explained from the relationship between the switching time and electric field. It was found that the minimum bit size of a fully penetrating domain equals the film thickness.
Broad ion beam milling of focused ion beam prepared transmission electron microscopy cross sections for high resolution electron microscopy
Authors: Langford R. M. , Petford-Long A. K.
Published: July 2002

A technique is presented which enables both sides of a transmission electron microscopy cross section specimen prepared using a focused ion beam system to be milled using a broad ion beam source. The cross section specimen is prepared using the “lift-out” technique and is placed onto a copper mesh grid with 10 μm sized holes. The upper face of the cross section specimen is first milled in a broad ion beam source, after which a micromanipulator and needle is used to turn it over so that the other side can be milled. The use of a broad ion beam source enables lower incident beam energies and angles of incidence to be used than is currently possible in a commercial focused ion beam system. The technique can be used to decrease the thickness of the damage layer at the sidewalls of a focused ion beam prepared cross section specimen and to reduce its thickness in a controlled way.
Optical and structural properties of sol-gel SiO2 layers containing cobalt
Authors: Ramos-Mendoza A. , Tototzintle-Huitle H. , Mendoza-Galván A. , González-Hernández J. , Chao B. S.
Published: July 2002

SiO 2 coatings containing cobalt were prepared using the sol-gel method and the Si to Co nominal atomic ratio in the coatings was varied from 1.3 to 7.1. The structure and optical properties of the coatings, heat-treated in air at 300 and 500 °C, were characterized using optical, x-ray diffraction, and Auger depth profile measurements. The optical transmission data in the UV-visible range, in samples with low cobalt concentrations, show only the absorption bands associated with the tetragonal Co2+, regardless of the heat treatment temperature. Coatings with a larger amount of Co treated at 300 °C show absorption bands associated with both tetragonal and octahedral Co2+. When these coatings are heat treated at 500 °C, most of the cobalt migrates to the free surface of the coatings, where it is oxidized by the atmospheric oxygen and forms a top layer of Co3O4. The thickness of the cobalt oxide layer depends on the heat treatment temperature and on the Co concentration. To describe the absorption bands of both tetragonal and octahedral Co, the Lorentz oscillator model was used to represent the complex effective dielectric function of the SiO2 cobalt doped layers. The frequency dependence of the optical constants, in the UV-visible range for the top cobalt oxide layer, was obtained with a Jellison–Modine model.
Review of synthesis of low-work function Cu–Li alloy coatings and characterization of the field emission properties for application to field emission devices
Authors: Auciello O. , Tucek J. C. , Krauss A. R. , Gruen D. M. , Moldovan N. , Mancini D. C.
Published: July 2002

Alkali metals have extremely low-work functions and are therefore expected to result in significant enhancement of the electron emission if they are used as coatings on Mo or Si microtip field emission arrays (FEAs). However, the alkali metals are physically and chemically unstable in layers exceeding a few nanometers in thickness. Maximum enhancement of electron emission occurs for alkali metal layers 0.5–1 monolayer thick, but it is extremely difficult to fabricate and maintain such a thin alkali metal coating. We review here our work of the last three years focused on developing Cu–Li alloy coatings for application to field emitter Spindt-type tip arrays and fabrication of edge emitters with low-voltage high electron emission characteristics for field emission devices. The Cu–Li alloy coatings provide a chemically and thermally stable, self-replenishing, segregated lithium monolayer on the surface of the host Cu layer, resulting in a substantial reduction of the work function of the alloy, compared to that of a thick Li layer or a pure Cu surface. We present results that show a 13-fold reduction in the threshold voltage for electron emission, compared with uncoated Si FEAs. The Cu–Li alloy coatings yielded tip and edge emitters with threshold voltages of 2–10 V/μm, depending of the coating thickness and Li concentration in the alloy. New results are presented that show that we can now coat gated Si tip arrays with Cu–Li alloy films, which results in very low emission voltage.
Photoenhanced wet etching of gallium nitride in KOH-based solutions
Authors: Škriniarová J. , Bochem P. , Fox A. , Kordoš P.
Published: July 2002

Photoelectrochemical etching (PEC) of n+-GaN in KOH and AZ400K photoresist developer is presented. We compare the two solutions used for PEC etching without an external bias. The influence of etchant concentration and of the intensity of ultraviolet illumination was studied with emphasis on the resulting etched surface quality. The quality of the shallow etched surface and its roughness are presented. The AZ400K etchant was applied to shallow etching of n+-GaN with threading dislocation densities in the range of 109–1010 cm−2. Moreover, the first analysis of photocurrent monitoring during the electrochemical etching of GaN epitaxial layers in KOH is presented. We found that photocurrent very sensitively reflected the changes in the quality of the etched surface.
Photoelectrochemical undercut etching for fabrication of GaN microelectromechanical systems
Authors: Stonas A. R. , MacDonald N. C. , Turner K. L. , DenBaars S. P. , Hu E. L.
Published: July 2002

The authors have developed a wet, band-gap-selective, photoelectrochemical etching process capable of producing cantilever microelectromechanical systems from InGaN/GaN heterostructures. Fabricated cantilevers were successfully actuated, and resonance spectra were measured. The as-grown strain gradient in the GaN film was found to relax upon removal, resulting in upward curvature of the cantilevers. This curvature was shown to be reversible with the integration of strained InGaN layers on the top surface of the cantilever. All photoelectrochemical wet etching was conducted using a benchtop lamp-and-filter arrangement, employing GaN and InGaN films as filters.
Fabrication of T gate structures by nanoimprint lithography
Authors: Macintyre D. S. , Chen Y. , Lim D. , Thoms S.
Published: July 2002

Nanoimprint lithography is capable of patterning substrates with high definition patterns at relatively high patterning speeds. In this article we describe the fabrication of high resolution “T” gate resist profiles by imprint lithography. The fabrication of high resolution stamping tools and the imprinting process itself are critical to the success or failure of this technique and they are described in the article. Two different techniques were used to fabricate stamping tools. The first involved pattern definition by high resolution electron beam lithography followed by electroforming. The second involved pattern definition by electron beam lithography followed by a two stage silicon etching process. Imprinted T gate resist profiles with footwidths less than 100 nm in length were obtained on gallium arsenide substrates for the purpose of producing metallized gates for a self-aligned gate process.
Control of field emission current of individual sites by a local resistor
Authors: Cui J. B. , Robertson J.
Published: July 2002

Effects of a resistive sheet on the field emission characteristics of carbon films have been studied systematically by monitoring both the emission I–V curves and the emission image. We demonstrate that the emission current of individual sites with different field enhancement factors β can be controlled by the resistive sheet and hence that the homogeneity of the emission sites can be significantly improved. This implies that the use of a local resistor to limit the emission could be one possibility to homogenize emission sites in display device fabrication.
Silicon nanowires with sub 10 nm lateral dimensions: From atomic force microscope lithography based fabrication to electrical measurements
Authors: Legrand B. , Deresmes D. , Stiévenard D.
Published: July 2002

The ability of the atomic force microscope (AFM) to realize lithography patterns on silicon surfaces is widely known and leads to the formation of silicon nanostructures after an etching step. In this article, we aim at improving the fabrication process to yield silicon nanowires with minimum lateral dimensions for the realization of Coulomb blockade based devices. First, we focus on the AFM lithography step: using pulsed voltages for the anodic oxidation of the silicon surface instead of the commonly employed continuous polarization, we obtain an improvement of both AFM lithography resolution and tip reliability. Second, after the wet etching step, we present a technique of oxidation/deoxidation cycles, which allows a controlled thinning of the silicon wires. Combining these two techniques, we obtain silicon nanowires the widths of which are lower than 10 nm. Finally, as the wires are made on a silicon on insulator substrate, it opens the way to electrical characterization and we present some realizations and results.
Materials and Processes for Passive Thin-Film Components
Authors: Glang Reinhard
Published: July 2002

Vacuum evaporation and sputtering processes of materials in use or under investigation for passive thin-film components in integrated circuits are reviewed. Molybdenum, silver, gold, and the platinum metals have been considered to replace aluminum contacts and interconnections. However, silicide formation at low temperatures and lack of the required contact properties limit their usefulness. Dielectric materials amenable to controlled deposition are silicon monoxide and dioxide. Both oxides have low dielectric constants and are more suitable for insulation layers than for capacitors. To produce stress-free, nonhygroscopic SiO films, control of deposition conditions is most important. The integration of SiO2 films depends on the availability of a process yielding good properties at low deposition temperatures. Radio frequency sputtering seems to meet these requirements. Nichrome and Cr-SiO cermet are possibilities for integrated thin-film resistors. Their fabrication techniques and the resulting properties are reviewed. Tighter process control than presently possible is needed for integration into monolithic circuits.
Free Molecular Conductance of a Cylindrical Tube with Wall Sorption
Authors: Smith Craig G. , Lewin Gerhard
Published: July 2002

A Monte Carlo method was used to calculate the probability that a molecule passes through a cylindrical tube with wall sorption. This probability is presented as a function of the ratio of length to radius and the sticking coefficient s of the wall. For s=0, the results confirm those of Clausing for the conductance of a tube of finite length. For s≠0, wall pumping can greatly reduce the flow of gas, even for very small values of s. The backscattering, total flux retained by the wall, and its distribution along the tube also are presented. Finally, the collimation of the emerging beam is investigated.
Epitaxial Thin Films of ZnO on CdS and Sapphire
Authors: Rozgonyi G. A. , Polito W. J.
Published: July 2002

The technique for obtaining polycrystalline thin films of ZnO by sputtering of the compound has been perfected so that epitaxial films can be obtained on sapphire and CdS. Dependence of the crystalline perfection of the films on substrate temperature, deposition rate, and substrate polish has been studied in detail. Substrate temperatures from 100 ° to 500 °C and deposition rates from 1 to 100 Å/min were studied. Film structure was evaluated by x-ray diffraction and reflection electron diffraction. Electrical and optical measurements were made to determine the resistivity, Hall mobility, optical absorption edge, and refractive index of films. It was found that these properties of the films were very similar to bulk crystal data except for the Hall mobility which was lower by almost two orders of magnitude. The poor mobility is attributed to scattering by defects introduced during the high-energy sputtering process.
Vacuum Deposition by High-Energy Laser with Emphasis on Barium Titanate Films
Authors: Schwarz Helmut , Tourtellotte H. A.
Published: July 2002

A laser beam capable of energy outputs up to 500 Joule was directed through a glass window into a vacuum system onto fine grain powder of Cr, W, Ti, C, Sb2S3, ZnS, SrTiO3, and BaTiO3. A neodymium-doped glass laser of 1.06-μ wavelength was mostly used without Q spoiling. Sometimes the beam was focused. Films up to 2000 Å were achieved on glass with one laser burst only, which corresponds to deposition rates of up to 106 Å/sec. The substrate was positioned between the vapor source and laser so that the laser beam passed through it, and therefore, also served as a shield. Electron micrographs were taken. From electron transmission diffraction patterns it appeared as if BaTiO3 had not been decomposed. In order to evaluate electrical properties of the films, platinum-rhodium films were sputtered or “laser-deposited” onto glass slides to serve as base electrode. Then a barium titanate film was evaporated with a laser. On top of this, an array of thin aluminum dots were evaporated through a mask, so that it was possible to investigate different areas of the films. Values of up to 2.5 μF/cm2 at 1 kHz and relative dielectric constants of up to 1000 were measured. Dissipation factors were in a range from 1%–10%. The capacitance at 1 kHz was constant within 0.1% between 50 ° and 105 °C as well as above 160 °C. A sharp peak of the temperature dependence curve could be observed at about 125 °C where the capacitance increased by 30%. For most films the onset of breakdown was observed at a field strength of around 5×105 Vcm−1. Both the capacitance and dissipation factor decrease almost linearly when increasing the frequency from 60 Hz to 500 kHz with the capacitance reaching 90% of its 60-Hz value.
Electroluminescence, Bistable Switching, and Dielectric Breakdown of Nb2O5 Diodes
Authors: Hickmott T. W.
Published: July 2002

Nb–Nb 2 O 5 –metal diodes, after voltage breakdown, exhibit current-controlled negative resistance and switching between two stable conduction states. Before breakdown, Nb–Nb2O5–Au diodes are electroluminescent with hole injection occurring at the Nb2O5–Au interface. After breakdown, electroluminescence is closely related to switching. The energy of emitted radiation has maxima at 1.3 and 1.6 eV. Electroluminescence is both polarity- and voltage-dependent, indicating that hole injection, not heating, produces electroluminescence. Increased electroluminescence accompanies diode switching. Microscopic observation shows that bistable switching and dielectric breakdown of Nb–Nb2O5–Au diodes occur at small conducting regions in the oxide. Destructive dielectric breakdown in Nb–Nb2O5–Cu diodes differs from that in Nb–Nb2O5–Au diodes.
Control system design and alignment methods for electron lithography
Authors: Alles D. S. , Ashley F. R. , Johnson A. M. , Townsend R. L.
Published: July 2002

The electron-beam exposure system (EBES) was designed to economically expose integrated circuit masks on a production basis and to directly pattern semiconductor substrates for special applications where a limited number of devices are required. The machine was designed to assure absolute pattern accuracy over the entire substrate so that masks made by EBES will be interchangable with those made by our optical mask shop or those made by later electron-beam pattern generators. This has been achieved by a combination of control system design and by automated periodic system alignment. The control system design utilizes a laser interferometer to determine precise table position and a feedback system that continuously corrects the writing-beam location for errors in table location. This combination, coupled with a small-angle electron-beam deflection system using an ultrastable sawtooth-scan generator to achieve repeatable beam positioning over a small writing area, allows exposure rates of 107 addresses per second with submicron absolute accuracies over a 10×10-cm area. A series of automated measurements have been implemented in order to maintain this accuracy for extended periods. Every five minutes beam-positioning errors resulting from external magnetic fields, temperature variations, and amplifier drifts are measured by using the electron column as a scanning electron microscope to locate a registration mark permanently affixed to the table. Several times a day, the deflection system is automatically adjusted under computer control to assure that the electron-beam deflection axes agree precisely with the interferometer-controlled table motion in both magnitude and direction. Periodically, a set of special test patterns are written by EBES and then, using EBES as a computer-controlled coordinate measuring machine, these patterns are measured and analyzed to provide an accurate assessment of the machine’s true writing performance. This alerts the mask shop to potential problems and allows service personnel to make the necessary corrections before the final product is materially affected.
Application of moiré techniques in scanning-electron-beam lithography and microscopy
Authors: Smith Henry I. , Chinn S. R. , DeGraff P. D.
Published: July 2002

When a grating is viewed by scanning electron microscopy, a moiré pattern is observed. Applications of the moiré phenomenon in scanning-electron-beam lithography and microscopy are discussed, including adjustment of the spatial period and angle of a scan raster, analysis of distortion in a scan raster, analysis of stray-field beam deflection and measurement errors, and registration of a scan field relative to coded patterns on a substrate.
Recent developments in electron-resist evaluation techniques
Authors: Hatzakis M.
Published: July 2002

A simple procedure for evaluating the performance of any positive electron resist is presented. SEM examination of the developed resist edge profile after electron-beam exposure and development gives simultaneous information on resist sensitivity and resolution for a given resist thickness. This method gives a unique exposure charge-density point for optimum resolution for a given resist system independent of developer strength.
Spurious effects caused by the continuous radiation and ejected electrons in x-ray lithography
Authors: Maldonado J. R. , Coquin G. A. , Maydan D. , Somekh S.
Published: July 2002

X-ray lithography replication using characteristic and continuous x radiation is studied and compared with exposure results obtained using only characteristic radiation. Several spurious effects that affect the mask contrast and system resolution are discussed.
Photoluminescence measurement of ion-etched GaAs surface
Authors: Namba S. , Kawabe M. , Kanzaki N. , Masuda K.
Published: July 2002

The effects of ion etching and annealing of GaAs were studied by observing photoluminescence, reflectance, and electron diffraction patterns. The (100) surfaces of GaAs were rf sputter etched. The intensity of the edge emission decreased to about 1/15 of the initial value in the case of a Si-doped sample when excited by a He–Cd laser (3250 Å) at 10 K. The depth of the damaged layer is deduced to exceed the bombarding ion range. Annealing increased the edge emission intensity up to the temperature of 450 °C, above which edge emission decreased due to thermal dissociation. On the other hand, electron diffraction patterns and reflection spectra showed continuous recovering of lattice ordering above the annealing temperature of 450 °C.
Radiation damage in copper single crystals
Authors: Sood D. K. , Dearnaley G.
Published: July 2002

Mo, Au, and Cu ions of 150−350−keV energy have been implanted, off axis, in <110≳ Cu single crystals at a dose of 1016 ions/cm2. The radiation damage and its annealing are studied by backscattering and channeling of a 3.5 MeV alpha−particle beam. There is no significant surface disorder. The radiation damage, however, has been found to extend to rather large depths, up to 16 times the projected range of the implanted ions. Annealing of the disorder caused by 150−keV Mo ions has been studied up to 900°C. The disorder anneals gradually at rather high temperatures accompanied by a marked decrease in the disorder depth. This suggests depletion of the disorder from within the crystal towards the surface. The disorder has also been studied as a function of substrate temperature, during implantation, from −130° to 350°C. The results are interpreted in terms of the existing radiation damage theory and arguments based upon consideration of surface stress.
Comparison of Auger spectra of Mg, Al, and Si excited by low−energy electron and low−energy argon−ion bombardment
Authors: Grant J. T. , Hooker M. P. , Springer R. W. , Haas T. W.
Published: July 2002

Auger spectra of Mg, Al, and Si excited by low−energy electron and argon−ion bombardment have been measured and compared. The Auger spectra obtained under ion bombardment are interpreted as a combination of Auger production in excited sputtered species and bulk atoms. Under argon−ion bombardment at these low energies, L2,3 level ionization occurs in the target through an electron promotion mechanism. No L1 level ionization occurs (to first order), and the cross section for double L2,3 level ionization is also small at these ion energies, so no Auger transitions originating from such states result.
Preparation and properties of hard-material layers for metal machining and jewelry
Authors: Schintlmeister W. , Pacher O.
Published: July 2002

Cemented carbide parts coated with several-micron-thick layers of hard material are now used in large quantities in machining, particularly for turning and milling. Applications for jewelry purposes are assuming increasing importance. Following a brief survey of wear mechanisms in machining, the wear behavior of homogeneous coatings of TiC, TiN, and Al2O3 is discussed. Some conclusions concerning the wear-reducing effect of these coatings are derived. It is found that a complex interrelationship of several factors, such as diffusion barriers, reduction of friction, thermal conductivity, and others, play an important part. Effects of hardness and chemical behavior of hard-material coatings, especially of TiC and TiN layers on the wear decrease, are mentioned. The wear behavior of composite coatings consisting of TiC and Ti-carbonitrides of varying composition is then considered. By incorporation of these hard materials into multiple, inhomogeneous layers, significant improvements over homogeneous single-layer coatings are achieved. In addition to great hardness, the application of hard material layers for jewelry demands corrosion resistance, an attractive color, and good polishing characteristics. Examples for the corrosion resistance of TiC and TiN and the colors of Ti-carbonitrides are presented. The polishing characteristics of hard-material layers greatly depend on surface roughness. It is shown how roughness and surface structure of TiN layers produced by the CVD method vary in dependence of the deposition temperature but at equal deposition rate. Some important requirements for coatings applied to tools and jewelry articles and possible methods for their production are mentioned.
Outlooks for GaAs terrestrial photovoltaics
Authors: Woodall J. M. , Hovel H. J.
Published: July 2002

GaAs photovoltaic device structure are examined as an attractive alternate to Si devices for large scale terrestrial power generation. The role of other III-V and II-VI compounds, particularly CdS, is also discussed. (AIP)
Contrast mechanisms in electron beam images of interface structures
Authors: Bottoms W. R. , Guterman Daniel , Roitman Peter
Published: July 2002

A technique for imaging internal structures in MIS devices has been developed. The device is scanned by an electron beam in a scanning electron microscope and the induced current is used to modulate a CRT display. Direct−current bias on the sample and incident beam energy determine which structure (metal−insulator interface, semiconductor−insulator interface, or insulator bulk) is observed. Secondary electron images, C−V measurements, and bias temperature stress data are used to facilitate image interpretation. A variety of structures have been observed at both interfaces on MOS capacitors with lateral resolution on the order of 1000 Å. Experimental results support a model with field variations across the oxide film providing the dominant contribution to image contrast.
Correlation between the composition profile and electrical conductivity of the thermal and anodic oxides of InSb
Authors: Wilmsen C. W.
Published: July 2002

The differences between the electrical conductivity of thermal and anodic oxides of InSb have been reported previously. In this paper these differences are correlated with the chemical compositional profiles of the two oxides. The anodic oxide is shown to be an indium oxide containing a large concentration of Sb, while the thermal oxide contains a relatively low concentration of Sb, but has an Sb-rich layer between the indium oxide and the InSb. By postformation annealing of the anodic oxide or application of a large electric field to the thermal oxide, the oxide compositions are changed. These changes are accompanied by a corresponding change in the electrical conductivity of the oxide. From these data and the changes in the Auger line shape for In, it appears that Sb–In bonding in the oxide is related to the change of conductivity.
Schottky barriers on compound semiconductors: The role of the anion
Authors: McCaldin J. O. , McGill T. C. , Mead C. A.
Published: July 2002

The Schottky barrier for holes on common III–V and II–VI semiconductors contacted by Au is shown to depend only on the anion. Compilation of the experimental data shows that compound semiconductors with the same anion but different cations possess very similar values for the the Au Schottky barrier for holes. Further, the data show that the Pauling electronegativity of the anion provides a useful ordering parameter for the height of the Schottky barrier. This correlation is compared with analogous barrier data on rocksalt and layer structures as well as earlier results for the semiconductor–vacuum interface.
Auger depth profiling of interfaces in MOS and MNOS structures
Authors: Johannessen J. S. , Spicer W. E. , Strausser Y. E.
Published: July 2002

Auger electron spectroscopy in conjunction with simultaneous Argon-ion sputtering have been used in a study of the chemical depth profiles of the near-interface regions in MOS and MNOS device structures. Our experimental results show that all of these interfaces are nonabrupt and phase separated. The Al–SiO2 interface has inclusions of Si and A12O3; the SiO2–Si interface appears to be a mixed phase of Si and SiO2 over several nanometers and the nitride–oxide interface is an oxynitride. The width of these interfaces varies from 35 to several hundred angstrom, depending on the deposition technique and on the deposition conditions. The inherent limitations in the depth resolution of Auger/sputter profiling are discussed in some detail. We also describe the precautions we have taken to minimize electron and ion beam induced distortion of the Auger spectra and the depth profiles.
Cyclotron resonance characterization of ion-implanted carriers in semiconductors
Authors: Kaplan R. , Wagner R. J.
Published: July 2002

Cyclotron resonance absorption of GaAs substrates implanted with S+ ions has been investigated. Values of the implanted carrier mobility and concentration, deduced from the resonance width and strength or from comparison with model calculations, compared well with the values determined by transport measurements. The cyclotron resonance measurements require no contacts, are unaffected by the presence of a passivation layer, and do not alter the sample in any way. The technique is also applicable to carriers in semiconductor films.
Effect of surface treatment on surface recombination velocity and diode leakage current in GaP
Authors: Stringfellow G. B.
Published: July 2002

The 2kT leakage current in planar LED’s fabricated by diffusion in GaP has been studied by measuring the current versus voltage characteristics for diodes of various sizes. The surface leakage current is found to be the dominant 2kT current for all practical sized diodes (d<0.1 cm). Its magnitude is found to depend on surface treatment. For mesa diodes, the surface leakage current is approximately 40% lower than for Si3N4-passivated planar diodes. Formation of a native oxide by treatment in H2O2 is found to have no effect. By plasma etching the LED’s, the surface leakage current can be reduced by ≳10X. This is found to be due to F adsorbed on the surface after etching in the CF4 plasma. From the slope of J versus perimeter-to-area ratio, the surface recombination velocity can be determined. Values of 1.7×105 cm/s for planar devices with Si3N4 passivation are typical. This is reduced to 1×105 cm/s in mesa diodes and ∠5×103 cm/s for plasma etched diodes. These values of surface recombination velocity were confirmed by SEM measurements of electron beam induced current versus distance from the p–n junction at values of accelerating voltage between 10 and 30 kV.
Thermally assisted tunnelling in certain GaAs heterostructures
Authors: Owen S. J. T. , Tansley T. L.
Published: July 2002

Theoretical calculations of thermally assisted tunnelling currents enable the ideality factor η to be computed for metal/semiconductor diodes and semiconductor heterojunctions. The calculation is based on a generalization of Bethe’s original formulation of themionic emission theory with the inclusion of a tunnelling factor. Forward current-–voltage isotherms for GaAs-based structures are computed and the values of η are compared with other calculations. The forward current characteristics of Au–nGaAs Schottky barrier diodes and n (Ga,In)As–p+GaAs heterojunctions have been measured and careful comparison is made between these and other closely related structures. The temperature variation of η for highly doped (Nd1017–1018/cm3) junctions shows quantitative variations attributable to thermally assisted tunnelling effects. Applications of this theory in investigations of practical diodes are given.
Photoemission studies of the surface states and oxidation of group IV semiconductors
Authors: Garner C. M. , Lindau I. , Miller J. N. , Pianetta P. , Spicer W. E.
Published: July 2002

Photoemission utilizing synchrotron radiation has been used to study the electronic structure of surfaes and/or interfaces in the photon energy range up to 400 eV. The Si (111) surface exhibits well-established filled surface states which disappear after about 103 langmuirs of O2. At this exposure, only a broad shoulder has appeared on the high-binding-energy side of the Si 2p levels. This shoulder continues to grow in magnitude until much higher exposures, about 108 langmuirs of O2, when a 2.6-eV shifted peak begins to grow, indicating a higher state of oxidation of the Si. After exposure to activated oxygen, to stimulate the oxidation process, the chemical shift of the Si 2p level is found to be 3.7 eV, which is the same as observed in bulk SiO2. Similar results were obtained for the oxidation of the Ge(111) surface.
Si(111) 7×7 surface structure
Authors: Levine J. D. , Mark P. , McFarlane S. H.
Published: July 2002

A comparison between a kinematic analysis of the fractional-order LEED-pattern symmetries of the Si(111) 7×7 structure and experimental data is presented. The surface model comprises a rippling of the first two double layers so as to produce interference in the coherent scattering from this distortion. The ripple deformation is small. It is treated as a perturbation in the analysis. Thus, the surface is nearly ideally terminated; there are no vacancies or adatoms in the model. Triagonal symmetry reversals are observed in the LEED patterns at about 20-V intervals and are also computed theoretically.
Effect of a glassy membrane on the Schottky barrier between silicon and metallic silicides
Authors: Bené R. W. , Walser R. M.
Published: July 2002

We present a model for Schottky barriers on silicon based upon the formation of a glassy membrane layer between the last metal layer and silicon. We postulate that this membrane has the properties of a semiconducting glass with quasiparticle states in the gap, characterized by a negative correlation energy. These states effectively pin the Fermi level with respect to the silicon bands at a level depending on the silicon-metal molecular bonding in the membrane layer. This model thus gives a physical picture for Fermi-level pinning which agrees semiquantitatively with Schottky barrier measurements.
Effect of heat treatment after deposition on internal stress in molybdenum films on SiO2/Si substrates
Authors: Oikawa Hideo , Nakajima Yuji
Published: July 2002

The stress in Mo films evaporated by an electron-beam gun onto SiO2/Si substrates has been studied as a function of temperature of heat treatment after deposition. The structure of the films was observed by x-ray diffraction line breadth and scanning electron microscope. Both tensile stress σHT and columnar grain size 〈D〉 increased linearly with temperature in the range of 600°–1000°C (σHT=0.6/2.0×109 dyn/cm2, 〈D〉=120/1300 Å at 600°/1000°C) and σHT nearly stopped increasing above 1000°C. Such σHT and 〈D〉 behavior can be explained semiquantitatively by the Nakajima–Kinosita model wherein the internal stress can be built up by the volume contraction due to the increase in grain size. It was found that the electrical resistivity of the films was also dominated by the columnar grain boundary.
ESCA study of the passive layer on Sn-Ni alloy
Authors: Thomas J. H. , Sharma S. P.
Published: July 2002

Electron spectroscopy for chemical analysis (ESCA) has been used to study the chemical composition of the passive film which forms on electroplated Sn–Ni alloy. Analysis of the electron binding energy of the tin, nickel, and oxygen lines at various points within the passive film and a depth profile using the structure of (integrated intensities) the Sn 3d5/2 line at 486.5 eV and the O 1s line at 530 eV shows that the passive layer consists of a hydrated surface layer (Sn+4, OH−, O−2, and Ni+2) followed by a SnO2-rich region. The film may also contain some NiO. In the immediate surface region of the passive film, a mixture of stannic oxide, stannic hydroxide, nickel hydroxide, and carbon is observed. The passive film has an overall thickness of ∠30 Å as measured using a quartz crystal oscillator as a mass (thickness) monitor during argon ion sputtering.
Interdiffusion and Schottky-barrier-height variations in Au–W(Ti)/n-GaAs contacts
Authors: Day H. M. , Christou A. , Macpherson A. C.
Published: July 2002

Au–W(Ti)/n-GaAs diodes were constructed for the purpose of examining the thermal stability of the metal–GaAs interface and the integrity of the W(Ti) diffusion barrier. The evaluation procedure consisted of using measurements of the Schottky barrier height and other electrical parameters as a function of annealing temperatures. Barrier heights, Vb(Io), determined by measurement of the zero voltage current intercept, Io, were found to increase with annealing temperatures up to 600°C. Values determined by the measurement of forward current activation energies were in agreement with Vb(Io) up to 500°C. Above 500°C, however, this method was not applicable, due to the onset of excess forward current at low voltages. This current was accompanied by evidence of gold interdiffusion, compensation, and high electric field strength in the depletion layer. Direct identification of the excess current source, however, was not accomplished.
Surface photovoltage experiments on SrTiO3 electrodes
Authors: Mavroides J. G. , Kolesar D. F.
Published: July 2002

Electronic surface states play a significant role in charge transfer between the electrolyte and the n-type SrTiO2 semiconducting electrodes used in the photoelectrolysis of water. To clarify the role of these states, we have measured the wavelength response of the photovoltage developed between the SrTiO3 surface and a vibrating Au reference electrode, both in vacuum and in a water vapor ambient. When the SrTiO3 is exposed to sub-band-gap radiation, the amplitude and sign of the photovoltage vary with photon energy. Significant changes in the spectrum result from the introduction of water vapor. The energy-dependent structure is interpreted in terms of photon-induced electronic transitions between the states near the surface and conduction or valence band states.
Mass spectrometric solutions to manufacturing problems in the semiconductor industry
Authors: Lin Kuo-chin , Burden James D.
Published: July 2002

A mass spectrometric method for routine analysis of electronic specialty gases has been established. Methodology for accurate determination of hermetically sealed-in contaminants of electron devices is described. Leak checking, process monitoring, and process development in sputtering, plasma etching, and CVD are cited.