bluuebunny/crossref_metadata_2025 huggingface dataset:
The Growth of Au on PbS, PbSe, PbTe, and SnTe Thin Film Substrates
Authors: Green A. K. , Dancy J. , Bauer E.
Published: July 2002

The formation of thin Au films by vacuum evaporation on lead and tin chalcogenides is investigated. Single crystal chalcogenide substrates are prepared by vacuum evaporation onto KCl. The films are studied by RHEED prior to removal from the KCl substrate and by TEM and TED after removing the composite Au–chalcogenide film from the KCl. A remarkable variety of orientations and particle shapes is observed. The saturation particle density varies over a very wide range as a function of substrate material and temperature. Results are discussed and compared with the growth of Au on alkali halides.
Light-Emitting Diodes and Semiconductor Materials for Displays
Authors: Nuese C. J. , Kressel H. , Ladany I.
Published: July 2002

A review is presented of the operation and characteristics of electroluminescent p-n junctions which are specifically designed for incoherent emission in the visible region of the optical spectrum. Recombination mechanisms in direct- and indirect-bandgap semiconductors, optical losses and reliability, efficiency and brightness considerations, and material synthesis are treated in sufficient depth to understand their role in the over-all performance of visible-light-emitting diodes (LEDs). The paper is concluded with a summary of the state of the art for each of the various types of LEDs presently under development or commercially available.
rf bias evaporation (ion plating) of nonmetal thin films
Authors: Davy J. Gordon , Hanak J. J.
Published: July 2002

The technique of ion plating, which is widely used for the deposition of metallic films, has been successfully applied to the deposition of II–VI compounds by using high-voltage rf instead of dc biasing of the substrate. As a hybrid of evaporation and bias sputtering, this technique retains the advantages while avoiding most of the disadvantages of each. The deposited films have the uniformity and adherence of bias-sputtered films but are deposited as rapidly as evaporated films. The inherent potential of this method for ion implantation has been explored in doping ZnSe up to 1% with P and Li. The resistivity of freshly prepared ZnSe: Li films was of the order of 105–106 Ω cm; however, it increased rapidly upon exposure to light or moisture and made type determination unfeasible.
Sputter deposition of Cd1−x Znx S photoconductive films
Authors: Fraser D. B. , Cook H. D.
Published: July 2002

An rf-sputtering technique has been developed for the deposition of Cd1−x Znx S photoconductive films to be used in light valve display devices. Targets of CdS containing 19, 29, 49, and 70 mole% ZnS have been used. Thermally sensitive and stress-sensitive substrates necessitated that deposition conditions be adjusted for each of the targets. To help maintain film stoichiometry, an Ar+1% H2S sputtering gas was used at a throughput of about 0.3 Torr liter/sec. In order to minimize contamination of the deposited film and to reduce film buildup in the chamber, a glass ring concentric with the target was used to confine the discharge. With a given target, it was possible to alter the Cd/Zn ratio in the film by altering the sputtering conditions and thus controlling the spectral sensitivity over a limited range. Films were routinely deposited with maximum photoconductivity occurring within a range of 1.0–2.0 nm about 435 nm. Dark resistivity and photoconductive gain as well as stress level in the coated substrate were found to be highly reproducible.
Drilled alternating-layer structure for three-dimensional photonic crystals with a full band gap
Authors: Kuramochi Eiichi , Notomi Masaya , Tamamura Toshiaki , Kawashima Takayuki , Kawakami Shojiro , Takahashi Jun-ichi , Takahashi Chiharu
Published: July 2002

A new three-dimensional photonic crystal structure is designed to simplify fabrication. A calculation of the band structure predicts that this photonic crystal has a complete photonic band gap in all directions. The entire three-dimensional periodic structure, except for the vertically drilled holes, is formed by automatic shaping during bias sputtering deposition. The fabrication technologies used to construct this photonic crystal are electron beam lithography, bias sputtering, and fluoride-gas electron cyclotron resonance etching. Our preliminary fabrication reveals that each technology can be controlled well enough to lead to the creation of a photonic band gap material for an optical communication wavelength.
Transient analysis of carrier gas saturation in liquid source vapor generators
Authors: Mayer Bruce , Collins Craig C. , Walton Mike
Published: July 2002

Bubbler-based chemical vapor generators find wide application in the fabrication of electronic devices. Bubblers generate a carrier-gas+chemical-vapor mixture to supply the device-processing chamber with reactive chemicals. The “dry” carrier gas bubbles through the liquid source chemical, becoming “humidified” with the chemical vapor in the process. This physical-theory-based analysis provides an estimate of the degree of humidification, or saturation, that the dry carrier gas achieves during bubbling. The “single-bubble regime” analysis considers the time period from when the bubble pulls free of the sparger tube, to when the bubble breaks the liquid surface. During this time period liquid evaporates at the bubble edge, and the vapor then diffuses toward the bubble center. The degree of saturation depends upon the: vapor diffusivity (Dv), carrier-gas distribution holes size (Dh), liquid surface tension (σ), liquid density (ρl), and liquid viscosity (ν). Analysis of a bubbler with 0.51 mm N2 carrier-gas distribution hole shows that: the bubbles are ≈2 mm in diameter, the bubbles reach a terminal velocity of ≈0.24 m/s, with Reynolds numbers in the range of 290–1403. Under these conditions the bubbles reach >99% saturation after about 45 ms of liquid exposure, while vertically traversing 4–10 mm of the liquid. Sensitivity ratios of the 99% saturation liquid height to a small change in the controlling variables are approximately: 1.5:1 for vapor diffusivity; [0.93–1.1]:1 for sparger tube hole size, liquid surface tension, and liquid density; and 0.1:1 for viscosity. Similar sensitivity ratios for the 99% saturation liquid-residence time are: 1:1 for vapor diffusivity; 0.67:1 for sparger tube hole size, liquid surface tension, and liquid density; and 0.0:1 for viscosity.
Chemical stability of Sin+ species in SiOx (x<2) thin films
Authors: Barranco A. , Mejı́as J. A. , Espinós J. P. , Caballero A. , González-Elipe A. R. , Yubero F.
Published: July 2002

SiO x thin films have been prepared by evaporation of silicon monoxide powder in an ultrahigh vacuum chamber. The films are characterized by x-ray photoelectron spectroscopy (XPS), synchrotron photoemission, and x-ray absorption spectroscopy at the Si K edge. XPS shows that the films prepared by evaporation in ultrahigh vacuum have a SiO1.3 stoichiometry and are formed by Si3+(∼77%) and Si+(∼23%) species. Based on extended x-ray absorption fine structure analysis, the structure of these films has been described as formed by tetrahedra of the type Si–(Si, O3) and Si–(Si3, O), in agreement with the Si 2p photoelectron spectra. No significant amount of Si2+ species [i.e., Si–(Si2, O2)] tetrahedra) or elemental silicon were detected in these films. When SiOx thin films are prepared by evaporation of silicon monoxide in O2 atmosphere, the oxygen content in the film increases with the partial pressure of this gas. Under these conditions, Si4+ species are formed in detriment of the Si+ and Si3+ oxidation states. The relative concentration of the different oxidation states of silicon is discussed in connection with previous models existing in literature on the distribution of Sin+ states in SiOx thin films. An explanation based on molecular orbital calculations is proposed to justify the absence of Si2+ species in the film structure and the disproportionation reaction Si3+, (Si+)→Si4+, Si0 observed when the SiOx thin films are excited by exposure to the white light of the synchrotron radiation.
Extreme ultraviolet mask defect simulation: Low-profile defects
Authors: Pistor Tom , Deng Yunfei , Neureuther Andrew
Published: July 2002

An assessment is made of the tendency of low-profile EUV multilayer mirror defects to print as a function of their height, width, and proximity to features. The study is based on rigorous electromagnetic simulation with TEMPEST and aerial image calculation with SPLAT. A special numerical technique involving the averaging of material properties at multilayer mirror surfaces is used to reduce error introduced by the FDTD gridding. Aerial images are calculated for Gaussian shaped mirror profiles of heights ranging from 1 to 5 nm and for several widths. The dip in clear field intensity for an isolated defect was found to be a strong linear function of defect height from 1 to 5 nm. For a given defect height a worse-case width was observed. As width increased beyond the worst-case width, defects become less printable because they become very flat and begin to approximate perfect mirror surfaces. Aerial images were calculated for mirrors with defects in proximity to mask features. A 1 nm high, 56 nm wide defect caused a significant change in a line's width depending on where the defect was in relation to the line. In the worst case, when the defect was centered 22 nm from the line edge a 12% line width change was observed.
Study on the chain structure of starch molecules by atomic force microscopy
Authors: Liu Zhongdong , Chen Shenfu , Ouyang Zhenqian , Guo Yunchang , Hu Jun , Li Minqian
Published: July 2002

Starch molecules were stretched and aligned by a special method on a mica surface and imaged with atomic force microscopy (AFM). The AFM images have shown the “chain” structure of the starch molecules. The results also show that there exist complicated structures in the molecules of natural starch and that the glucose units may form thicker “chains.” The length of the chains may reach 1–2 μm.
Low-k materials etching in magnetic neutral loop discharge plasma
Authors: Morikawa Y. , Yasunami S. , Chen W. , Hayashi T. , Uchida T.
Published: July 2002

Low-k materials etching for FLARE™ and a porous silica were carried out in a magnetic neutral loop discharge plasma at low pressure, below 1 Pa. Fluorinated carbon molecules were used as etching gases for porous silica. The etch rate of the porous silica was approximately two times higher than that of thermal SiO2. This result means that consumption of perfluoro compound (PFC) gases is suppressed below at approximately half volumes. And organic low-k materials etching where ammonia gas or a gas mixture of nitrogen and hydrogen were used instead of PFC gas is an environmentally friendly process. After investigating an influence of a N2/H2 mixture ratio in the organic materials etch process, a good experimental condition to get a low microloading profile was found at a N2 ratio of 70%–80%. Under this condition N2+ and N2H+ ions were dominant, and the signal intensity of the N2H+ ion showed a maximum value in the mass spectrum. This may mean N2+ and N2H+ ions play an important role for a low microloading etching. The nitrogen may be adsorbed on the surface and a thin passivation film may be created on the sidewall surface.
Study of the emission characteristics of a rf plasma source for atomic oxygen: Measurements of atom, ion, and electron fluxes
Authors: Kearns D. M. , Gillen D. R. , Voulot D. , McCullough R. W. , Thompson W. R. , Cosimini G. J. , Nelson E. , Chow P. P. , Klaassen J.
Published: July 2002

A 13.56 MHz rf plasma atom source with an alumina discharge tube was characterized for use with oxygen. For a rf input power of 500 W the maximum degree of dissociation was found to be 70% at an indicated source pressure of 0.20 Torr, and a dissociation of approximately 40% was obtained at an indicated source pressure of 0.60 Torr. Corresponding atom fluxes of 6.4×1019 atoms cm−2 s−1 and 1.66×1020 atoms cm−2 s−1, respectively were calculated at the source exit from the measured degree of dissociation and gas throughput. The energy distributions of the charged particle emissions from the source were also measured. It was found that the source produced positive ions with an average energy of 278 eV and electrons with an average energy of 8 eV. The ion and electron spatial distributions were also measured. The electron and positive ion currents were measured as a function of source pressure. Plasma emission spectra in the range 500–1000 nm were monitored at two different source pressures corresponding to maximum and minimum dissociation. No molecular lines could be observed making it impossible to correlate the optical measurements with the dissociation measurements.
Oxide etch behavior in a high-density, low-pressure, inductively coupled C2F6 plasma: Etch rates, selectivity to photoresist, plasma parameters, and CFx radical densities
Authors: Perry W. Lee , Waters Karla , Barela Marcos , Anderson Harold M.
Published: July 2002

Silicon dioxide and photoresist substrates were etched in a gaseous electronics conference inductively coupled plasma reference cell using C2F6 feed gas. The power/pressure/bias parameter space of the study generated a plasma which has plasma and ion current densities, plasma potential, ion energy, and etch rate characteristics typical of commercial high density plasma (HDP) etch tools. Absolute number density trends of CF and CF2 were measured using wavelength-modulated infrared spectroscopy in situ with etch rate experiments. For nonreactive surfaces such as Si and photoresist, typical CF and CF2 number densities varied around 4.9×1012 and 4.8×1013 cm−3, respectively. Over an SiO2 surface, these values decreased and evidence of the reaction of CFx radicals with an oxide surface to form COF2 was observed. Source and bias powers were mapped into ion current densities and ion energies, and correlations were made with etch rate, which was in the 0–150 A/s range. Selectivity ranged from 1 to 6. Typical plasma density was 8×1011 cm−3, typical ion current density was 30 mA/cm2, and typical ion energy was 50–160 eV. Both ion current density (source power) and ion energy (bias power) primarily controlled etch rate and selectivity. Transition from net etch to net deposition of fluorocarbon occurred near 30 W bias power. Increasing substrate temperature decreased the polymer growth rate, and increased the etch rate. This data is expected to be important for developing computer simulation plasma models of the HDP oxide etch process.
Chemical detection based on adsorption-induced and photoinduced stresses in microelectromechanical systems devices
Authors: Datskos P. G. , Rajic S. , Sepaniak M. J. , Lavrik N. , Tipple C. A. , Senesac L. R. , Datskou I.
Published: July 2002

The recent advent of microelectromechanical systems (MEMS) devices opened up possibilities for chemical detection. Microcantilevers respond to chemical stimuli by undergoing changes in their bending and resonance frequency when molecules adsorb on their surfaces. In our present studies, we extended this concept and studied changes in both the adsorption-induced stress and photoinduced stress as molecules adsorb on the surface of microcantilevers. We found that microcantilevers that have adsorbed molecules will undergo photoinduced bending that depends on the number of adsorbed molecules on the surface. Furthermore, when microcantilevers undergo photoinduced bending, molecules will adsorb on their surface differently. Depending on the photon wavelength used and microcantilever material, the microcantilever can be made to bend by expanding or contracting the irradiated surface. By coating the surface of the microcantilever with a thin chemical layer, chemical specificity for the target chemicals can be achieved. Chemical selectivity can also be altered by selecting appropriate photon wavelengths due to the introduction of surface states in semiconductor MEMS. In fact, choosing a handful of different photon wavelengths, tunable chemical selectivity can be achieved due to differentiated photoinduced response without the need for multiple chemical coatings. We present and discuss our results on MEMS interactions with two isomers of dimethylnaphthalene, tetrachloroethylene, trichloroethylene, diisopropyl methyl phosphonate, and trinitrotoluene.
Theoretical study of Cr diffusion in Co–Cr alloy thin film recording media
Authors: Jin Ding , Wang Jian Ping , Gong Hao
Published: July 2002

In order to continuously improve magnetic property of the recording media, the diffusion control has been strongly suggested as one of the possibilities. However, it lacks quantitative descriptions of the diffusion process to guide the diffusion control design. Therefore, a simplified analytical diffusion model of the Cr diffusion based on general diffusion theory was proposed and discussed in this article. In this model, the underlayer Cr first fills the grain boundaries and then diffuses into the adjacent grains, where the initial Cr concentration at the grain boundary was calculated by Fisher’s method. A reasonable match between the theoretical and experimental results on saturation magnetization is obtained in both conventional CoCrPt media films and CoCrPt–SiO2 granular media films by analyzing the postannealing experiments. Some possible methods in diffusion control were also discussed.
Vertical ordering in multilayers of self-assembled Ge/Si(001) quantum dots
Authors: Le Thanh Vinh , Yam V. , Nguyen Lam H. , Zheng Y. , Boucaud P. , Débarre D. , Bouchier D.
Published: July 2002

The effect of vertical ordering in multilayers of self-assembled Ge/Si(001) quantum dots was investigated by a combination of structural and optical characterizations via in situ reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. We show that the vertical ordering observed in quantum-dot multilayers is characterized not only by the alignment of islands along the growth direction but also by a reduction of the critical thickness. The better the vertical ordering, the more pronounced the reduction of the critical thickness is observed. Such an evolution of the critical thickness could be explained by elastic strain fields induced by buried islands and propagate through the spacer layers. An important result issued from this work is the realization of multilayers in which dots have equal size in all layers. Furthermore, experiments performed on the transformation of the island shape suggest that preferential nucleation induced by surface roughness may be the main mechanism responsible for the vertical ordering in quantum-dot multilayers.
Deposition of Ga2O3−x ultrathin films on GaAs by e-beam evaporation
Authors: Oldham N. C. , Hill C. J. , Garland C. M. , McGill T. C.
Published: July 2002

Gallium oxide films 20 Å in thickness were deposited onto GaAs substrates in ultra high vacuum (UHV) via e-beam evaporation from a monolithic high-purity source. The substrates were prepared by molecular-beam epitaxy and transferred to the oxide film deposition site in a wholly UHV environment. The Ga2O3−x films were probed by x-ray photoelectron spectroscopy (XPS). Chemical states were identified and stoichiometry was estimated. Metallic layers were deposited by e-beam evaporation in UHV after XPS analysis as caps and for future work. Film morphology and structure were probed by cross-sectional high-resolution transmission electron microscopy. The films were found to have x⩽0.3 and a metal/oxide interface roughness <1 Å.
Kinetics of the heteroepitaxial growth of Ge on Si(001)
Authors: Yam V. , Thanh Vinh Le , Boucaud P. , Débarre D. , Bouchier D.
Published: July 2002

The kinetics of the growth mode transition from two-dimensional to islanding growth during Ge/Si(001) heteroepitaxy have been investigated by a combination of in situ reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence spectroscopy. It is found that the two-dimensional wetting layers undergo a morphological instability well before reaching the critical thickness. The layer instability appears to be strain driven and gives rise locally to the formation of intermediate clusters between the wetting layers and macroscopic islands. We provide evidence that such intermediate clusters are metastable both in view of structural and optical properties.
Growth and Structure of Electrodeposited Thin Metal Films
Authors: Lawless Kenneth R.
Published: July 2002

The growth and structure of thin electrodeposits of several metals on single-crystal substrates have been studied by means of electron diffraction and electron microscopy. Deposits of copper on nickel, nickel on copper, and gold on copper show a highly perfect orientation at all thicknesses up to 1000 Å. All deposits studied were continuous for thicknesses greater than 50 Å. Gold deposits of 15 Å were discontinuous on the (111) face. Few growth twins were found, but double positioning structures occurred in both nickel and gold films. Evidence for the enhanced nucleation of copper deposits on substrate twins was found.
Insulation of High Voltage Across Solid Insulators in Vacuum
Authors: Shannon John P. , Philp Sanborn F. , Trump John G.
Published: July 2002

Surface conductivity and flashover in vacuum were studied using constant potentials up to 350 kV. Since discharges along the solid-vacuum interface appear to originate at or near the junction of the cathode electrode and the solid dielectric, methods of reducing the electric field at this critical region were explored. The more favorable approaches showed higher initial flashover values and could be conditioned to support more than 200 kV across borosilicate glass insulators in an interelectrode gap of 25 mm. The importance of intimate contact at the cathode-to-glass junction was confirmed.
Vapor Deposited Gold Thin Films as Lubricants in Vacuum (10−11 mm Hg)
Authors: Spalvins T. , Buckley D. H.
Published: July 2002

Gold thin films of 1800 Å to be used as lubricants were vapor deposited on Ni, Ni-Cr, and Ni-Re substrates. Strong bonding (adhesion) and durability between the film and substrate were found to be essential when thin films are used as a lubricant. Factors that were investigated included the selection of the film and substrate material. Strong durability of the thin film is directly related to the type and structure of the interfacial region. Two methods of substrate preparation prior to vapor deposition were investigated: (1) mechanically polished surface and (2) electron bombarded surface. Gold was vapor deposited on the mechanically polished surface at room temperature and on the thermally etched surface at an elevated temperature approximately (800 °F). Strength and durability of the films were investigated in sliding friction experiments with a hemispherical niobium rider sliding on the films at a velocity of 5 ft/min. Results obtained in these friction experiments indicated that the film endurance life was considerably better on the thermally etched surface. This increased film durability with the thermally etched surface is believed to be owing to the formation of a diffusion type interface between the film and the substrate. Because of the disregistry at grain boundaries, a higher rate of diffusion and preferential trapping in and around the grain boundaries occurs, with these regions acting as lubricant reservoirs during the friction experiments.
An investigation of the electrical properties of zinc oxide thin films influenced by oxygen adsorption
Authors: Yen James C.
Published: July 2002

The resistance of a ZnO thin film deposited by rf sputtering exhibits a change of 2 1/2−5 orders of magnitude as the ambient gas is cycled from nitrogen to oxygen. Hall measurements imply that the sputtered films are n−type semiconductor and that the resistance increase caused by oxygen adsorption is related to the decrease of carrier density of the sample. Sample resistivity is found to change with thickness; in oxygen, it decreases as thickness increases, but in a vacuum, it increases as thickness increases. The response time for resistance changes vs environmental changes depends highly on the sample temperature; it is slow at room temperature, but a rapid response can be seen at temperatures higher then 365°C.
Target and substrate interactions in bias sputter deposition
Authors: Kominiak G. J.
Published: July 2002

During bias sputter deposition, the accumulation rate is found to vary significantly with impressed substrate bias. In the case of rf bias sputter deposition, the rate may increase or decrease depending on the biasing method. Measurements of the harmonic content of the radiation from a rf sputtering discharge have been made as a function of impressed substrate bias, both dc and rf, and for self bias obtained by tuning of the substrate circuit. These measurements indicate that for rf sputter deposition with dc bias, the target and substrates are non-interacting. For rf self-bias operation, the two circuits interact strongly, modifying the discharge characteristics to allow the dissipation of greater amounts of useful power.
Influence of Ar sputtering pressure on the adhesion of TiC films to steel substrates
Authors: Mukherjee Jahar L. , Wu L. C. , Greene J. E. , Cook H. E.
Published: July 2002

The adhesion of sputtered TiC films to steel substrates has been found to increase as the Ar deposition pressure is decreased. The films were deposited by rf sputtering with a large initial dc bias on the substrates. The pressures investigated were 35, 25, and 15 mTorr and the films ranged in thickness from 0.3 to 3.2 μm. A modified scratch test was used to measure adhesion. The increase in film adhesion is suggested to result from increased mixing within the film/substrate interfacial region. Auger spectroscopy was used to obtain elemental concentration vs sample depth profiles through the interface.
Contact potential differences for III–V compound surfaces
Authors: van Laar J. , Huijser A.
Published: July 2002

Contact potential difference (CPD) measurements are reported for GaAs, GaP, and InAs UHV-cleaved single crystals, and for GaAs epitaxially grown layers of (110) orientation. For the GaAs and InAs single crystals the CPD between n- and p-type samples of the same material was practically equal to the band gap. This means that the intergap surface state density must be <1012/cm2. For epitaxially grown GaAs layers the CPD appeared to be independent of the volume dope, i.e., the Fermi level is stabilized due to surface states in the forbidden zone. For GaP single crystals the energy bands appear to be flat up to the surface in p-type material, but for an n-type sample a band bending of 0.45 eV occurs.
Covalent bonding of metal atoms at the Schottky-barrier interface of GaAs, Ge, and Si
Authors: Rowe J. E.
Published: July 2002

Electron energy loss and photoemission spectroscopies have been used to identify new interface electronic states due to the chemisorption of In on GaAs, Ge, and Si(111) surfaces. The chemical bonding at the metal–semiconductor interface appears to be intermediate between that of the bulk semiconductor and the free-electron behavior of the bulk metal.
Rate controlling and composition analysis of alloy deposition processes by electron impact emission spectroscopy (EIES)
Authors: Lu C. , Lightner M. J. , Gogol C. A.
Published: July 2002

The technique of electron-impact emission spectroscopy (EIES) has been used to monitor and control the alloy deposition process. The multicomponent evaporant flux is allowed to pass through a sensor where it is excited by electron bombardement. Narrow-band optical filters are employed to select the specific emission line or lines from each component. At a specific electron-excitation energy, the emission intensity of the characteristic spectral lines from any constitutent is proportional to the number density of that constituent in the vapor flux. Experimental results on an aluminum–copper alloy system indicate that this technique has sufficient sensitivity and selectivity for most alloy deposition processes. EIES also offers several advantages over other existing monitoring techniques.
Surface and interface states on GaAs(110): Effects of atomic and electronic rearrangements
Authors: Spicer W. E. , Pianetta P. , Lindau I. , Chye P. W.
Published: July 2002

Research during the last year has led to a better understanding of the electronic and atomic structure of the (110) surfaces of III–V semiconductors. In this paper we will briefly review these new developments as well as point out areas where agreement has been found between various experimental results presented in the literature. It is now generally agreed that there are no intrinsic surface states in the band gap on GaAs and the smaller band-gap materials (e.g., GaSb, InAs, and GaSb) and that Schottky barrier pinning must be due to states produced when the metal adlayer is applied. Particular attention is focused in this paper on the large surface rearrangement which takes place on the (110) GaAs surface and effects of the strain which may be produced in joining this rearranged surface layer to the rest of GaAs crystal. It is pointed out that this may lead to variations in the surface rearrangement which can produce variations in the valence electronic structure at the surface. Such variations are shown in experimental energy distribution curves obtained by the photoemission technique which samples principally the last two molecular layers. It is further shown that surprisingly small amounts of chemisorbed oxygen can produce first-order effects in the valence-band electronic structure. On all GaAs (110) surfaces studied, a phaselike transformation was observed with a few hundredths of a monolayer coverage of chemisorbed oxygen. Near this coverage, the Ga 3d exciton structure disappears and the oxygen uptake increases significantly. On certain samples, first-order changes in the valence-band electronic structure were observed at a coverage of a hundredth of a monolayer or lower. These transformations are discussed in terms of the electronic and atomic configurations at the surface. Experimental data showing As and Ga 3d chemical shifts for oxidation as well as chemisorption are also presented and used to point out difficulties to be expected in passivating practical surfaces. In particular, the effect of mixed As and Ga oxides, the desirability of bonding passivating layers to the GaAs through As bonds, and the effect of strain-induced interface states are discussed.
Electron-beam microzone refining of narrow band-gap semiconducting alloy layers
Authors: Wieder H. H.
Published: July 2002

Electron-beam-induced crystallization, growth, and purification by zone refining from the liquid phase of 1-μm-thick, narrow band-gap semiconducting alloys, eutectics, and semimetal layers require a high-vacuum noncontaminating environment. Experiments are proposed for investigating the process control parameters as a function of the energy density of electron beams, the solid–liquid interface geometry, thermal gradients, and propagation rates.
Stencil technique for the preparation of thin-film Josephson devices
Authors: Dunkleberger L. N.
Published: July 2002

We describe a photoresist stencil technique that has proven to be quite reliable in the preparation of thin-film Josephson logic and memory devices. The method employs multiple layers of resist with the top layer providing patterning and the bottom layer spacing the top layer from the substrate and providing an undercut under the top layer. This method has consistently produced uniform undercuts over ∠1 in. (∠2.54 cm) sample dimensions and has been used to produce micron-sized patterns.
Studies on arrays of Josephson tunnel junction interferometers
Authors: Broom Ronald F. , Mohr Theodor O.
Published: July 2002

Josephson-junction interferometers have previously been proposed as memory devices in which information is stored as a single flux quantum, (SFQ). To investigate the feasibility of making large arrays of SFQ cells suitable for the memory of a cryogenic computer, arrays containing 80 interferometers have been made and measured. The prime objective was to determine the distribution of the dc Josephson current i1 within the arays and to compare it with the design value required for successful operation of all cells in high density arrays. The results show that a substantial fraction of the arrays has standard deviations in i1 less than the maximum allowable, thus demonstrating for the first time that such a memory can be made with present technology. The fabrication, measurement technique and a detailed analysis of the current distributions on the arrays are presented.
Method of optimizing registration signals for electron-beam microfabrication
Authors: Stickel W.
Published: July 2002

This paper discusses a way by which registration signals for pattern overlay in a given process environment can be optimized by emphasizing signal transitions and by exploiting an enhancement effect: The slope of signal transitions increases significantly when the separation of adjacent mark edges (mark width) is such that the corresponding complementary signals interfere. The signal-to-noise ratio can be improved even further because more edges can be confined within a given scan window than with conventional configurations with no signal overlap. Experimental results indicate an overall improvement factor of at least 4. The observed enhancement effect is understood on the basis of a simple qualitative model.
Imaging conditions for electron-beam micromachining
Authors: Fontijn Leendert A.
Published: July 2002

In electron-beam micromachining the highest attainable power density in the substrate material is required for material removal. The application of the Zr/W(100) thermal field emitter combines the advantages of a low electron energy for a minimum electron penetration range in the substrate and a high current density in the final spot. The range of final electron spot sizes considered is from 10 to 100 nm. The spot size on-axis, as well as off-axis when scanning the beam, is mainly limited by chromatic aberration. A considerable improvement of the power density, up to about 108 W/cm2 at 3 kV, is obtained by using a high beam current collection efficiency and a symmetrical imaging system of unit magnification. Therefore, a power density of more than 1013 W/cm3 for most of the substrate materials results, allowing operation times of less than 1 μs per image element. A proposed illumination system for electron-beam micromaching with a working distance of 4 mm is outlined. The intention is to replace the electron optics of a SEM by the proposed illumination system for micromaching purposes.
Field-assisted minority carrier electron transport across a p-InGaAs/p-InP heterojunction
Authors: Gregory P. E. , Escher J. S. , Hyder S. B. , Houng Y. M. , Antypas G. A.
Published: July 2002

A field-assisted photocathode has been made which has a reflection yield quantum efficiency of ∠1% out to a wavelength of 1.6 μ. The cathode is a heterojuncation InP/InGaAs/InP structure fabricated by a hybrid VPE/LPE process. Photoelectrons generated for wavelengths ?1 μm must cross a p-InP/p-InGaAs heterojunction, under bias. To achieve high transfer across the p–p heterojunction, the heterojunction must be carefully lattice matched, the InP emitter must be ?1 μm thick and have p-type doping in the low 1015 cm−3 range, the InGaAs layer must have doping in the low 1016 cm−3 range, and the heterojunction composition grading distance must be ?1000 Å. These criteria are all met by the VPE/LPE grown heterojunction. Heterojunction transfer efficiencies approaching 100% for bias voltages 3–5 V have been measured.
Effects of ultrathin oxides in conducting MIS structures on GaAs
Authors: Childs R. B. , Ruths J. M. , Sullivan T. E. , Fonash S. J.
Published: July 2002

Barrier formation in Schottky barrier-type devices (metal–semiconductor and metal–thin-film insulator–semiconductor structures) is examined as a function of purposeful oxidation of the semiconductor surface and semiconductor surface etch. Metallizations used are thin-film (125–200 Å) Au, Ag, Pd, and Al. Acid and basic etches were employed. Evolution of the barrier with purposeful oxidation is measured by reverse C–V barrier height deteminations, dark I–V barrier height, photoresponse barrier height, and photovoltaic open circuit voltage. For the metals examined on n-type GaAs, the oxidation procedure used resulted in the MIS structures having higher barrier heights than the corresponding baseline MS devices. This cannot be explained simply in terms of the increased, geometrical separation of the metal and semiconductors with oxidation. It does not seem to be explained in terms of the oxidation satisfying bonds at the GaAs interface. Rather, trapping and perhaps chemical interactions are involved in the barrier formation. The evolution of the barrier with purposeful oxidation is similar for Au and Pd. For these devices (with ideality factors ? unity) the change in reverse C–V barrier height with oxidation equals the change in photovoltaic open circuit voltage. These devices were generally stable. Silver and aluminum devices exhibited strong charge trapping in the interfacial region.
Metastable alloy formation
Authors: Poate J. M.
Published: July 2002

Implantation into metals at room and lower temperatures can result in the formation of metastable phases. For low concentrations, ≲1 at. %, substitutional and interstitial solutions have been observed for implantation into Be, Fe, Ni, and Cu. At higher concentrations, ≳10 at. %, both metastable solid solutions and amorphous alloys have been formed in Fe, Ni, and Cu.
Effects of deposition parameters on optical loss for rf-sputtered Ta2O5 and Si3N4 waveguides
Authors: Paulson W. M. , Hickernell F. S. , Davis R. L.
Published: July 2002

Thin-film optical waveguides of tantalum oxide and silicon nitride were prepared by rf diode sputtering. The optical loss α was found to be a sensitive function of the following deposition parameters: reactive gas composition, total gas pressure, gas flow rate, substrate temperature, substrate bias, and postdeposition annealing. Increasing the percentage oxygen in argon from 5% to 30% raised the loss from 2 to 45 dB/cm and changed the film structure from amorphous to crystalline. Optical losses below 1 dB/cm were produced in amorphous Ta2O5 films at 0.5 Pa, 10% O2 in Ar, low gas flow, and low substrate temperatures. The log α was a linear function of the percentage of reactive gas for both Ta2O5 and Si3N4. Optical losses of 15 dB/cm in amorphous Si3N4 films were obtained at 1.5 Pa with 10% N2 in Ar, independent of substrate temperature and gas flow.
TEM study of the two-step annealing of arsenic-implanted 〈100〉 silicon
Authors: Alessandrini E. I. , Chu W. K. , Poponiak M. R.
Published: July 2002

Transmission electron microscopy (TEM) measurements were made to evaluate the distribution of defects remaining in arsenic-implanted silicon after annealing. Samples implanted with arsenic ions—1×1016 ions/cm2 at 40 keV—were individually annealed in either one or two steps. Five samples were subjected to a one-hour preanneal—one each at 500°, 525°, 550°, 575°, and 600°C—in nitrogen ambient. In this temperature range epitaxial recrystallization of implantation damage can be expected. All the samples, whether preannealed or not, were then annealed for one hour at 1000°C in N2, to reduce defects and to diffuse and activate the arsenic. The amount of disorder (dislocations) depended on the annealing cycle. Dislocations were minimized by preannealing for one hour at 550°C and then annealing for one hour at 1000°C. The TEM method proved much more sensitive to fine detail than channeling measurements.
Unintentional dopants incorporated in GaAs layers grown by molecular beam epitaxy
Authors: Covington D. W. , Meeks E. L.
Published: July 2002

Motivated by the stringent material requirements that low noise FET’s place upon underlying buffer layers, the electrical properties of unintentionally doped layers of GaAs grown by MBE have been investigated. A relatively shallow acceptor (0.027 eV) with a room temperature concentration of 2×1014 cm−3 is generally characteristic of undoped material presently grown by a number of laboratories involved in MBE. During experimental investigations, undesirable system configurations leading to higher background doping levels were identified. These configurations include BeO/Ta film substrate heaters (n?6×1016 cm−3), fused quartz/Ta film substrate heaters (n?2×1015 cm−3) and hot stainless steel fixtures illuminated by the Ga oven (p?1016 cm−3).
Inversion layers on InP
Authors: Meiners L. G. , Lile D. L. , Collins D. A.
Published: July 2002

Capacitance versus voltage and surface transport measurements have been made on both p- and n-type single-crystal samples of InP. The results indicate that in all cases the Fermi level at the surface resides near the conduction band edge. In consequence, although it does not appear to be possible to invert the n-type specimens, a strong electron inversion may be achieved on p-type material making this semiconductor potentially suitable for enhancement mode FET applications.
Electronic structure in GaAs/Ge through angle-resolved photoemission
Authors: Denley D. , Mills K. A. , Perfetti P. , Shirley D. A.
Published: July 2002

We present preliminary results of experiments detailing the changes in the valence band electronic structure of GaAs upon the submonolayer evaporative deposition of Ge. Measurements for electron wavevectors along the ?? and ??′ directions in the surface Brillouin zone show a loss of photocurrent from states in the valence band edge and the growth of sharp features. These features are found (1) near but within the calculated valence band edge (∠1.4 eV, ?? direction; ∠1.2 eV, ??′) (2) midband (∠3.2 eV, ??; ∠4.2 eV, ??′), (3) in and near the projected gap (∠4.1 eV, ??; ∠ 2.5 eV, ??′), and (4) in the ionic gap (∠7.1 eV). In addition, a new deeply bound (13 eV) GaAs surface state is observed.
Experimental and theoretical study of cross-sectional profiles of resist patterns in electron-beam lithography
Authors: Murata K. , Nomura E. , Nagami K. , Kato T. , Nakata H.
Published: July 2002

Experimental and theoretical study was carried out on cross sectional profiles of resist patterns for line and area exposures. Experimental work was performed using an electron beam exposure system, where a PMMA film of 6000 Å thickness was used as an electron resist and the incident electron energy was 20 keV. The electron-beam probe size was measured from a line spectrum of the secondary electron signal when the probe was scanned over a fine gold wire. The diameter of the probe was 5500 Å. The developer was a 1:1 solution of MIBK and IPA. The time evolution of the cross sectional profile was obtained from the SEM observation at various development times. Theoretical evaluation of the time evolution was conducted by a combination of Monte Carlo calculation of electron scattering and a well-known equation for the solubility rate. Monte Carlo calculation was performed with a new model based on the Spencer and Fano theory for electron energy loss. For assumed parameters in the solubility rate equation a reasonable agreement between experiment and theory was obtained in the results of the time evolution of the cross sectional profiles. Also a difference between the Monte Carlo results through use of new and old models is discussed for a typical case of an exposure pattern.
Direct device fabrication by selected area e-beam annealing
Authors: McMahon R. A. , Ahmed H.
Published: July 2002

A flexible scanning electron-beam system for annealing ion-implanted semiconductors or partially processed devices, direct device fabrication, or other high flux thermal processing is described. A maximum beam current of 3 mA in a 40 μm spot is available at accelerating voltages of up to 30 kV. Microprocessor controlled scanning over a 10 mm square field is available in this system. Resistor structures and diode arrays fabricated by e-beam annealing of ion-implanted layers show an edge resolution of 40 μm between unannealed and annealed regions. The diodes have characteristics close to those predicted for ideal structures and may be fabricated in arrays to make integrated devices such as vidicon targets.
Modeling of beam voltage effects in electron-beam annealing
Authors: Neukermans A. , Saperstein W.
Published: July 2002

Beam penetration effects can be important if accurate estimates are to be made of the temperature rise in electron beam annealing of silicon. This is because the electron penetration is typically much larger than the thickness of the layer to be annealed. Depth deposition curves and radial energy spread functions are calculated in silicon for beam energies of 5, 10, 15, 20, and 30 keV. Using the image method, the results are applied to calculate temperature profiles for planar beams of infinite extent and for finite beams with Gaussian cross section.
Reactive sputter etching and reactive ion milling—selectivity, dimensional control, and reduction of MOS–interface degradation
Authors: Meusemann B.
Published: July 2002

Recent results on the application of reactive etching techniques in semiconductor device technology are reported. The two systems used are a rf diode system and a dc ion milling system both fed with Ar and various Freon-type gases. The two processes are compared with regard to selectivity, dimensional control and edge profiles. Further results show that, if CF4 and CHF3 instead of Ar are applied in the etching processes, the redeposition of sputtered materials as well as the degradation of the MOS–interface properties can be largely reduced. From our experiments we conclude that neither reactive sputter etching nor dc reactive ion milling can be favored, their potentials however exceed tunnel reactor plasma etching as well as Ar sputter etching and Ar ion milling.
Channeled ion implantation through metallic films
Authors: Hikosaka Kohki , Ishiwara Hiroshi , Furukawa Seijiro
Published: July 2002

Channeled ion implantation through metallic films is studied in such metal-silicides as Pd2Si, NiSi2, and PtSi grown on single crystalline Si. The annealing conditions of crystal growth and the characteristics of radiation damage in those silicides are obtained by using the backscattering and channeling techniques. Electrical measurements have denonstrated that the amount of impurity ions (P+ and B+) introduced by the channeled ion implantation into a Si substrate in the Pd2Si–Si system is, at least, several times greater than that by a random implantation at the same energy, in case when the film thickness is more than 1.5 times thicker than the average projected range in the random implantation.
X-ray lithography by synchrotron radiation of the SOR-RING storage ring
Authors: Aritome H. , Matsui S. , Moriwaki K. , Namba S.
Published: July 2002

The results of x-ray lithography using the synchrotron radiation of the storage ring, SOR-ring, at an electron energy of 0.3 GEV are studied. AIP