bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary of in situ epitaxial nucleation and growth measurements
Authors: Poppa Helmut , Moorhead R. Dale , Heinemann Klaus
Published: July 2002

Semiconducting single-crystal thin films of PbSe and chemically prethinned samples of bulk Si were found to be suitable substrate materials for in situ TEM studies of autoepitaxial and heteroepitaxial film nucleation and growth processes. In situ surface cleaning by either evaporation or sputtering was used in conjunction with a UHV background environment to ensure reliable results. The epitaxial systems which have been studied most extensively are Au and Ag on (100)-oriented PbSe. Detailed results obtained include (a) identification of structure (polymorphism), crystalline perfection, and stoichiometry of the initial and the autoepitaxially thickened PbSe substrates; (b) quantitative nucleation and growth kinetic measurements at low supersaturation of Ag on PbSe—a system characterized by weak interaction energies and high surface mobilities; (c) observations of epitaxial orientations and the development of epitaxy during the deposition process; and (d) demonstration of strong substrate/overgrowth reactions involving alloying and interdiffusion.
Occupational safety and health: the new federal-state partnership
Authors: Levine Louis L.
Published: July 2002

The Occupational Safety and Health Act of 1970 (OSHA) deals with the work environment of the American wage earner. It affects some sixty million work places, requiring employers to provide their employees with safe working environments and conditions. OSHA placed the federal government into the safety and health business on a full-scale basis. It required the U. S. Labor Department to establish occupational safety and health standards to cover almost every working condition. The Act allows states to maintain their own occupational safety and health programs, providing the programs are at least as effective as the federal program. The legislation required federal approval for state plans. It is anticipated that in perhaps as many as half of the fifty states occupational safety and health will shape up as largely a state responsibility and program.
OSHA standards for the product manufacturer
Authors: Proctor John A.
Published: July 2002

The two years experience gained since promulgation of OSHA standards is having a profound effect on the development of future standards. The conversion of voluntary national consensus standards to mandatory Federal standards applicable to millions of places of employment has presented problems which were not considered by standards writers in the past. The new occupational safety and health standards will require broader representation from affected employers and employees, and guidelines for progressive application to insure practical and feasible compliance scheduling, rather than reliance on piecemeal enforcement. OSHA standards now are a mix of performance standards and specification standards. Half our critics want more performance type and the other half want more specification type. I prefer to continue with a mix, but in each instance where a performance standard is cited, I believe at least one example of a specification standard meeting the level of performance required should be spelled out. I believe performance standards can open up the field for American ingenuity to solve problems and meet goals.
Evaluation of a liquid-helium cryopumping system operating with an electron beam gun
Authors: Mongodin G. , Piacentini V. R. , Sajnacki W.
Published: July 2002

A recently developed 14-kW 240 ° electron beam gun was installed in an 18-in. glass belljar pumped by a liquid-helium cryopumping system made by Air Liquide, a French supplier of cryogenic pumps. The cryogenic pump has a speed of 6000 liter/sec for air. Pumping of hydrogen and helium is accomplished by bleeding in a small amount of argon which freezes on the helium reservoir and has a gettering effect on these gases. Experiments were conducted to determine the operating characteristics of this type of system when evaporating various materials such as aluminum, copper, and tantalum. Data taken during the evaporation runs consisted of major gases evolved, time for belljar pressure to recover to 10−7 Torr range, pressure during evaporation, effectiveness of argon sublimator in reducing pressure, and pumpdown curves. It was found that using a liquid-helium cryopumping system in conjunction with an electron beam gun gives exceptional results. It would be particularly advantageous in the fabrication of MOS devices where extreme cleanliness is required.
Study of chemical vapor deposition diamond film evolution from a nanodiamond precursor by C13 isotopic labeling and ion implantation
Authors: Gouzman I. , Richter V. , Rotter S. , Hoffman A.
Published: July 2002

High nucleation densities and short incubation times of polycrystalline diamond films can be promoted by the dc-glow discharge–surface interaction process as in situ surface pretreatment method. As a result of the pretreatment, a carbon nanophase film whose properties are strongly affected by the dc-glow discharge deposition parameters is formed. At optimal conditions this nanophase has a predominant diamond character which promotes diamond growth in the subsequent chemical vapor deposition (CVD) process. In this work, the evolution of the diamond film during a standard hot filament (HF) CVD process, following the dc-glow discharge pretreatment, was studied by nonreactive ion implantation of the precursor film and C13 isotopic labeling during different deposition stages in addition to spectroscopic and high resolution scanning electron microscopic (HR-SEM) techniques. Our results indicate that only part of the diamond growth centers formed by the dc-glow discharge process are placed on the surface but rather they are distributed homogeneously within the precursor film. Using 13CH4- isotopic labeling it was shown that the nanodiamond films formed by the dc-glow discharge process are stable under standard HF CVD conditions. Only a fraction of the nanodiamond particles deposited by the dc-glow discharge processes serve as nucleation centers for the growth of diamond. A complex interlayer composed of a nanodiamond composite is formed between the silicon substrate and the microcrystalline diamond film.
Fabrication of three-dimensional photonic structures with submicrometer resolution by x-ray lithography
Authors: Cuisin C. , Chelnokov A. , Lourtioz J.-M. , Decanini D. , Chen Y.
Published: July 2002

We report on the fabrication of diamond-like photonic structures in PMMA resist and their use as porous templates for transferring three-dimensional patterns to metals or dielectrics. Following the original “three drilling holes” approach first proposed by Yablonovitch, we used three consecutive exposures of PMMA resist to an x-ray beam through a triangular lattice of holes. A submicronic patterning was thus obtained in thick PMMA layers (>6 μm). Optical characterizations of 1.3 μm period templates showed a well-defined photonic gap in the midinfrared. The pattern transfers from the PMMA templates to a metal (copper) and a high refractive index dielectric (titania) were achieved by the electrodeposition and sol–gel filling techniques, respectively. Three-dimensional metallic structures of 1.3 μm lattice constant were obtained with extreme regularity over a thickness of ∼6 μm, thereby providing a way to build submicrometer photonic band gap materials for optical wavelengths.
Quantitative analysis of the molding of nanostructures
Authors: Schift H. , David C. , Gobrecht J. , D’ Amore A. , Simoneta D. , Kaiser W. , Gabriel M.
Published: July 2002

Mass fabrication processes such as injection molding and hot embossing are highly suitable for the replication of micro- and nanostructures. They require thermoplastic polymers with good molding properties at moderate process temperatures. We show a quantitative approach to the analysis of the molding properties of polymers in the nanorange in which the parameters are most important for achieving good replication fidelity. With this information we were able to fabricate high precision calibration chips for scanning probe microscopes.
Fabrication of smooth diamond films on SiO2 by the addition of nitrogen to the gas feed in hot-filament chemical vapor deposition
Authors: Baranauskas Vitor , Peterlevitz Alfredo C. , Jingguo Zhao , Durrant Steven F.
Published: July 2002

Diamond films of small roughness have been deposited onto thermally oxidized Si substrates by a process of anisotropic crystalline growth induced by nitrogen in a hot-filament chemical vapor deposition reactor. Ethanol (C2H5OH), diluted in hydrogen and nitrogen, was used as the source of carbon. At high concentrations, nitrogen tends to suppress the diamond growth in the 〈100〉 direction, which allows the growth of square mesoscopic-like crystals (“plates”) of large area in the directions parallel to the surface of the substrate. These plates stack upon each other, forming a thick diamond coating of uniform thickness. Analysis of the films made by micro-Raman spectroscopy and atomic force microscopy revealed that it is possible to obtain diamond coatings of high quality with a roughness comparable to that of the SiO2 at the diamond/SiO2 interface, and of nanometric roughness on the surface of the plates. A model to explain the morphology of the plates based on the microscopic mechanisms that involve the possible passivation of the (100) plane and an increase of vacancies by nitrogen is also discussed.
Interface formation and electrical properties of a TiNx/SiO2/Si structure for application in gate electrodes
Authors: Kim K. S. , Jang Y. C. , Kim K. J. , Lee N.-E. , Youn S. P. , Roh K. J. , Roh Y. H.
Published: July 2002

In this work, we investigate the interface formation and electrical properties between TiNx and SiO2 for application of a gate electrode as a function of annealing temperature, TA. Auger electron spectroscopy (AES) and four-point probe measurement were performed to measure the chemical composition and sheet resistance, Rs, respectively, of TiNx/SiO2 films. Also, interface formation of TiNx/SiO2 films as a function of annealing temperature was investigated by x-ray photoemission spectroscopy (XPS) depth profiling. X-ray diffraction spectra showed an increase in the crystallinity of TiNx above TA=600 °C. AES and XPS data show that thermal annealing of the sample with TiNx deposited at an Ar/N2 gas flow ratio of 6/1 (QAr/QN2=6/1) above 600 °C increases the oxidation reaction of TiNx layers, resulting in the formation of TiO2 phases. The Rs values increased at elevated annealing temperatures above 600 °C for TiNx deposited with QAr/QN2=6/1, but the Rs values of TiNx deposited at an Ar/N2 gas flow ratio of 6:3 continuously decreased up to TA=800 °C.
Critical behavior of epitaxial Si1−xGex/Si(001) islands
Authors: Budiman R. Arief , Ruda Harry E. , Perović D. D. , Bahierathan B.
Published: July 2002

Island size distributions of three-dimensional Si1−xGex/Si(001) islands of varying Ge fractions (x=0.4–0.7) and thicknesses grown by ultrahigh vacuum chemical vapor deposition are studied. Size distributions for percolating islands obey the dynamic scaling hypothesis due to a random percolation process, only in the small island limit. Island morphologies strongly suggest the presence of Smoluchowski ripening, in which islands collide and ripen. Random percolation and Smoluchowski ripening are thus combined to analyze the size distributions. To understand the critical behavior of the islands, as exhibited by their size distributions, a mean-field theory for coherently strained island formation is formulated, by incorporating surface energy and strain relaxation. The resulting phase diagram shows that island formation in Si1−xGex/Si(001) occurs near the critical region. Order parameter fluctuations can be estimated by calculating the curvature energy for such a system, showing that the strain fluctuations are relevant to properly describe island formation in the Si1−xGex/Si(001) system.
Plasma etching of lead germanate (PGO) ferroelectric thin film
Authors: Ying Hong , Li Tingkai , Maa Jer-shen , Zhang Fengyan , Teng Hsu Sheng , Gao Yufei , Engelhard Mark
Published: July 2002

The lead germanate (PGO) thin film has been proposed for FeRAM devices, especially for one transistor ferroelectric memory cell application. To realize such applications, it is important not only to form the PGO thin film, but also to etch/pattern such thin film. In this work, plasma etching of PGO thin films was investigated by using chlorine or fluorine gas chemistries in an electron cyclotron resonance plasma reactor. Etch rates were studied as a function of etching conditions. The results indicated that a chemical effect, rather than a pure physical sputtering, was the dominant factor during the plasma etching of PGO material. It was also found that under the same etching conditions, a Cl2/Ar chemistry was more effective in PGO etching than a CF4/Ar chemistry. Under the etching conditions studied, there was no obvious plasma etching damage to the composition of the PGO thin films. However, the surface oxygen and chlorine concentration increased after the etching, indicating there might be some etch-induced surface residue. Such residue was thermally unstable, and can be greatly reduced by a postetch anneal in O2.
Investigation of polycrystalline silicon grain structure with single wafer chemical vapor deposition technique
Authors: Bu H. , Hu C. , Bevan M. , Wang S. , Sanchez E. , Luo L.
Published: July 2002

It is known that the grain structure in the polysilicon gate electrode can directly affect dopant activation and gate electrode depletion (GED). It is highly desirable to control the grain size and orientation during polysilicon processing for improved integrated circuit device yield and reliability. This article demonstrates the capability of growing polysilicon films with specific grain structures using a single wafer chemical vapor deposition (CVD) reactor with nitrogen carrier gas. The deposition temperature is varied from 650 to 690 °C. The effect of hydrogen addition during deposition is examined. Films deposited at various process conditions are characterized by transmission electron microscopy and x-ray diffraction techniques. The results show that the polysilicon grain size and orientation are sensitive to the hydrogen concentration. With a carefully selected deposition temperature and hydrogen concentration combination, the single wafer CVD technique is able to engineer the polysilicon grain size and orientations. A desired polysilicon grain structure can be tailored for specific device needs. The effect of the polysilicon grain structure on electrical parameters such as effective oxide thickness and GED will be discussed.
Surface characterization of IM7/5260 composites by x-ray photoelectron spectroscopy
Authors: Ohno Satomi , Lee Moon-Hwan , Lin Kuen Y. , Ohuchi Fumio S.
Published: July 2002

Surfaces of high-performance carbon fiber/bismeleimide (BMI) composites (IM7/5260) have been characterized by x-ray photoelectron spectroscopy. An experimental technique to separately examine the chemical natures of the carbon fibers and BMI resin in the composite form was developed. This technique uses a flood gun to establish differential charging conditions on the BMI resin. The binding energies from the BMI resin were shifted by an amount of voltage applied to the flood gun, whereas those from the carbon fibers were uniquely determined due to their electrically conducting nature. By adding external bias voltage to the sample, the binding energies for conducting fibers were further shifted from those of the BMI resin, thereby separating the IM7 phase completely from the BMI phase in the binding energy scale, allowing independent measurement of the chemical changes associated with those peaks. Using this technique, the effects of thermal aging and surface plasma treatment on the IM7/5260 composite were studied.
Photoluminescence properties of self-assembled InAs quantum dots grown on InP substrates by solid source molecular beam epitaxy
Authors: Zhuang Q. D. , Yoon S. F. , Zheng H. Q.
Published: July 2002

Self-organized InAs quantum dots (QDs) with different depositions grown on an InP (100) substrate were prepared by solid source molecular beam epitaxy at different temperatures. Photoluminescence (PL) measurements are used to investigate optical properties of the QDs. It is observed that the PL emissions of QDs with 10 Å InAs deposition exhibit multiple peaks. Besides emission from the QDs at lower energy, two or three additional peaks are observed. This behavior is attributed to wetting layers with various thicknesses caused by an As/P exchange reaction, and this reaction is enhanced by an increase of the growth temperature. The features of PL emission change dramatically for the samples with increased InAs deposition. The PL emission from the QDs decomposes into two Gaussian peaks, which are associated with emission from QDs with two different size distributions. Atomic force microscopy examination shows the bimodal size distribution branch. This observation of the QD size distribution is simply explained by the surface mass transfer.
ZnO epilayers on GaN templates: Polarity control and valence-band offset
Authors: Hong Soon-Ku , Hanada Takashi , Makino Hisao , Ko Hang-Ju , Chen Yefan , Yao Takafumi , Tanaka Akinori , Sasaki Hiroyuki , Sato Shigeru , Imai Daisuke , Araki Kiyaoki , Shinohara Makoto
Published: July 2002

We report on the growth of polarity-controlled ZnO epilayers by plasma-assisted molecular-beam epitaxy and the measurement of valence-band offset at the ZnO/GaN heterointerface. The polarity of ZnO epilayers is determined by coaxial-impact-collision ion-scattering spectroscopy. The band offset is determined by ultraviolet and x-ray photoelectron spectroscopy. The high-resolution transmission electron microscopy study reveals the formation of an interface layer between the ZnO and GaN epilayers in O-plasma preexposed samples, while no interface layer is formed in Zn preexposed samples. Zn preexposure prior to ZnO growth results in Zn-polar ZnO epilayers (Zn face), while O-plasma preexposure leads to the growth of O-polar ZnO epilayers (O face). The interface layer is identified to be single-crystalline, monoclinic Ga2O3. The estimated valence band offset at the ZnO/GaN(0001) heterojunction with Zn preexposure is 0.8 eV with a type-II band alignment.
Characteristics of carbon nanowires synthesized by local arc-discharging technique
Authors: Kwo Jon-Lian , Yokoyama Meiso , Lin I-Nan
Published: July 2002

Nanosized carbon nanowires were synthesized using “arc discharge” of diamond-like carbon (DLC) films in a parallel plate setup, under 10−5 Torr environment. Thus obtained carbon nanowires can be turned-on at a significantly lower field and emit markedly a larger current than the DLC films. Raman spectroscopy and scanning electron microscopy micrographs reveal that the DLC structure has been converted into nanodiamonds and graphite, presumably carbon nanowires. The mechanism for the formation of carbon nanowires is probably the vaporization of DLC clusters and condensation of carbon species on the acting DLC sites.
Distribution of nitrogen atoms in dilute GaAsN and InGaAsN alloys studied by scanning tunneling microscopy
Authors: McKay H. A. , Feenstra R. M. , Schmidtling T. , Pohl U. W. , Geisz J. F.
Published: July 2002

Nitrogen atoms in the cleaved (11̄0) surfaces of dilute GaAsN and InGaAsN alloys have been studied using cross-sectional scanning tunneling microscopy. The distribution of nitrogen atoms in GaAs0.983N0.017 and In0.04Ga0.96As0.99N0.01 alloys is found to be in agreement with random statistics, with the exception of a small enhancement in the number of [001]-oriented nearest-neighbor pairs. The effects of annealing on In0.04Ga0.96As0.99N0.01 alloys has been studied by scanning tunneling spectroscopy. Spectra display a reduced band gap compared to GaAs but little difference is seen between as-grown versus annealed InGaAsN samples. In addition, voltage dependent imaging has been used to investigate second-plane nitrogen atoms.
Damage in etching of (Ba, Sr)TiO3 thin films using inductively coupled plasma
Authors: Choi Sung-Ki , Kim Dong-Pyo , Kim Chang-Il , Chang Eui-Goo
Published: July 2002

High dielectric (Ba, Sr)TiO3 thin films were etched in an inductively coupled plasma as a function of the Cl2/Ar gas mixing ratio. Under Cl2 (20)/Ar (80), the maximum etch rate of the BST film was 400 Å/min and the selectivities of BST to Pt and PR obtained were 0.4 and 0.2, respectively. Etching by-products remained on the surface of BST and resulted in varying the stochiometry. Therefore, we investigated the surface of the etched BST using x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and x-ray diffraction (XRD). From the results of XPS analysis, we found that metal (Ba or Sr) chloride compounds remained on the surface of the etched BST for high boiling points. The morphology of the etched surface was evaluated with AFM. The surface roughness decreased as the Cl2 increased in the Cl2/Ar plasma. From the results of XRD analysis, the crystallinity of etched BST films under Ar only and under Cl2 (20)/Ar (80) was similar to that of as-deposited BST. However, the (100) diffraction peak abruptly decreased at the Cl2 only plasma. It was assumed that metal (Ba or Sr) chloride compounds remained on the etched BST surface and changed the stoichiometry, resulting in crystallinity of the BST film during the etch process.
Electrochemical characterization and surface analysis of bulk amorphous alloys in aqueous solutions at different pH
Authors: Schennach R. , Grady T. , Naugle D. G. , McWhinney H. , Hays C. C. , Johnson W. L. , Cocke D. L.
Published: July 2002

Bulk amorphous alloys are a new class of materials with a variety of characteristics that make them useful for applications in aqueous environments. While some bulk amorphous metals show increased corrosion resistance, there is still a lack of fundamental electrochemical studies of these materials. Two different compositions of BeCuNiTiZr bulk amorphous alloys have been studied at pH 5, 7, and 10 using cyclic voltammetry (CV), x-ray photoelectron spectroscopy (XPS), depth profiling methods, and optical microscopy. While XPS is used to determine the composition of the resulting oxide films, the CV curves and optical micrographs are compared to pinpoint differences in the corrosion resistance of the amorphous multicomponent alloys. The effect of the amorphicity, multicomponent structure and the presence of elements with widely varying interfacial reactivities on the oxidation process and on the corrosion resistance of the alloys, are discussed with the desire to provide some electrochemical background for the expected wide spread use of bulk amorphous alloys.
Plasma and X-UV source characteristics for Al targets heated by 40 ns Nd-laser pulses
Authors: Whitlock Robert R. , Greig J. R. , Nagel David J. , Topscher Stephen J.
Published: July 2002

The total laser energy (3–32 J), temporal history (40 ns full width at half maximum) and focal energy distribution (3×1013 W/cm2 peak, 1.5×1013 W/cm2 average) for λ=1.06 μm Nd:glass laser interactions with planar Al targets were measured. Laser-produced plasma emissions within the 1–3 keV x-ray range were recorded, with limited measurements in the 10–1000 eV range. Primary emphasis was given to obtaining the dependence of kilovolt x-ray emission on irradiance (varied by altering the energy on target or the lens-target spacing). A maximum efficiency for the conversion of incident laser energy to radiation above 1.5 keV was 0.25% into 2π sr. Integrated x-ray energy radiated over this range of photon energy was found to increase as the 3.2 power of laser energy at best focus. X-ray emission decreased when a prepulse preceded the main pulse by a controlled amount exceeding 0.2 μs but <5 μs, with a minimum emission at 0.5 μs separation. Plasma temperatures were estimated from x-ray line ratios and continuum slopes: a value near 230 eV was obtained from free-bound continuum slope for 3×1013 W/cm2 peak irradiance. Temperatures decreased at lower irradiances, as inferred from x-ray line ratios.
GaAs-substrate-based long-wave active materials with type-II band alignments
Authors: Johnson S. R. , Chaparro S. , Wang J. , Samal N. , Cao Y. , Chen Z. B. , Navarro C. , Xu J. , Yu S. Q. , Smith David J. , Guo C.-Z. , Dowd P. , Braun W. , Zhang Y.-H.
Published: July 2002

The optimized growth conditions and evidence for type-II alignment in GaAsSb/InGaAs heterostructures are reported. The asymmetric GaAsSb/InGaAs bilayer quantum well grown on GaAs shows promising results for device applications around the wavelength of 1.3 μm. Uncompensated type-II GaAs/GaAsSb/GaAs quantum-well systems and strain-compensated GaAsP/GaAs/GaAsSb/GaAs/GaAsP quantum-well systems are compared for 1.3 μm applications. Inhomogeneous photoluminescence-linewidth broadening due to lateral composition and thickness variation is reduced from 74 to 40 meV when GaAsP strain-compensation layers are added to GaAsSb-based trilayer quantum-well systems.
Rapid thermal chemical vapor deposition of zirconium oxide for metal-oxide-semiconductor field effect transistor application
Authors: Chang Jane P. , Lin You-Sheng , Chu Karen
Published: July 2002

ZrO 2 is investigated in this work to replace SiO2 as the gate dielectric material in metal-oxide-semiconductor devices for its high dielectric constant, good thermal stability on silicon, and large band gap. ZrO2 films were deposited on p-Si(100) wafers by a rapid thermal chemical vapor deposition process using a zirconium (IV) t-butoxide Zr(OC4H9)4 precursor and oxygen. At temperatures between 300 and 400 °C, the reaction was thermally activated with an activation energy of 29 kcal/mol, consistent with a β-hydride elimination mechanism leading to ZrO2 deposition. In this regime at substrate temperatures below 350 °C, one atomic layer of ZrO2 can be deposited after each alternating exposure to the precursor and oxygen, ideal for achieving conformal coverage of ZrO2 over high aspect ratio features. Stoichiometric, uniform, and amorphous ZrO2 was obtained, and highly conformal step coverage of the deposited ZrO2 was observed on 300 nm features with an aspect ratio of 4. The dielectric constant of ZrO2 achieved in this work ranged from 15 to 18 depending upon process conditions and small C–V hysteresis and low interfacial state density were observed, ideal for metal-oxide-semiconductor field effect transistor application.
Characterization of damage in InP dry etched using nitrogen containing chemistries
Authors: Carlström C. F. , Anand S.
Published: July 2002

Etching of InP by different ion beam etching processes using chemistries containing nitrogen, such as nitrogen milling, N(CH3)3 and Ar/N(CH3)3 based reactive ion beam etching (RIBE), and N2/CH4/H2 based chemically assisted ion beam etching (CAIBE), is investigated. The residual surface damage is characterized using I–V characteristics of Au/InP metal–semiconductor (MS) contacts and photoluminescence (PL) yield measurements from near surface quantum wells and bulk InP. The contacts formed on as-etched surfaces, irrespective of the etch process, show ohmic behavior. On the other hand, although the PL yield is reduced for the different processes, the measured intensities show variations which are attributed to passivation of defects by hydrogen. Secondary ion mass spectroscopy (SIMS) was used to check (qualitatively) the presence of nitrogen in the etched and annealed InP samples. SIMS data show the presence of nitrogen in the near surface region of the etched samples, but nitrogen levels drop to background levels upon annealing at typical regrowth conditions (650 °C under phosphine flow). Interestingly, the annealing step results not only in a significant recovery of the PL yield, but also in a recovery of Schottky characteristics of the Au contacts formed on the annealed surfaces. These observations show that the etch-induced damage is significantly reduced by annealing and suggests recovery of the near-surface stoichiometry and possibly reduction of nitrogen-related defects.
Direct patterning of nanometer-scale silicide structures by focused ion-beam implantation through a thin barrier layer
Authors: Mitan M. M. , Pivin D. P. , Alford T. L. , Mayer J. W.
Published: July 2002

Recently several new approaches have been proposed to manufacture silicide structures using mask-less techniques. We have developed a new technique for direct patterning and formation of cobalt silicide structures using focused ion-beam (FIB) implantation. Utilizing the effects of ion-beam mixing and properties of thin barrier oxides, silicide lines with dimensions down to 170 nm were produced on (100) silicon substrates using the FIB. The process involves the ion implantation of 200 keV As++ through a cobalt thin film. A thin (∼2 nm) oxide (SiOx) at the Si/Co interface acts as a selective reaction barrier. Ion-beam mixing was instrumental in fracturing of the oxide layer, thereby allowing the silicidation reaction to proceed across the boundary during subsequent rapid thermal anneal treatments. Diffusion controlled reactions advanced rapidly in the implanted areas, while it is inhibited elsewhere. A threshold dose of 3×1015 cm−2 was required for process initiation. Four-terminal resistance test structures were formed for electrical measurements. Reported resistivity was in the range of 12 to 23±1 μΩ cm.
Distortion correction in adaptive membrane masks
Authors: Zhuang X. , Feldman M.
Published: July 2002

Image placement accuracy is a limiting factor for all of the next generation lithographies (NGLs). Previous work has shown that thermally induced displacements can improve image placement in membrane masks, compensating errors on the mask as well as errors already printed on the wafer. Consequently, such “adaptive” masks may find applications even in NGLs that do not presently use membrane masks. We have modeled the thermal distributions needed to compensate arbitrary mask distortions both for full-field and scanned exposures. For full field, the membrane is divided into an array of individual heating zones. We find that a 6×6 array is adequate to minimize many slowly varying distortions, and that even better results are obtained with a 12×12 array. The computation for the 6×6 array takes a few seconds on a personal computer. For a scanned exposure, e.g., an x-ray beam on a storage ring, only the line being exposed must be corrected at any given time. This minimizes the heat load on the mask, as well as permitting a simple Fourier analysis. Detailed procedures for both methods of correction are presented.
First lithographic results from the extreme ultraviolet Engineering Test Stand
Authors: Chapman H. N. , Ray-Chaudhuri A. K. , Tichenor D. A. , Replogle W. C. , Stulen R. H. , Kubiak G. D. , Rockett P. D. , Klebanoff L. E. , O’Connell D. , Leung A. H. , Jefferson K. L. , Wronosky J. B. , Taylor J. S. , Hale L. C. , Blaedel K. , Spiller E. A. , Sommargren G. E. , Folta J. A. , Sweeney D. W. , Gullikson E. M. , Naulleau P. , Goldberg K. A. , Bokor J. , Attwood D. T. , Mickan U. , Hanzen R. , Panning E. , Yan P.-Y. , Gwyn C. W. , Lee S. H.
Published: July 2002

The extreme ultraviolet (EUV) Engineering Test Stand (ETS) is a step-and-scan lithography tool that operates at a wavelength of 13.4 nm. It has been developed to demonstrate full-field EUV imaging and acquire system learning for equipment manufacturers to develop commercial tools. The initial integration of the tool is being carried out using a developmental set of projection optics, while a second, higher-quality, projection optics is being assembled and characterized in a parallel effort. We present here the first lithographic results from the ETS, which include both static and scanned resist images of 100 nm dense and isolated features throughout the ring field of the projection optics. Accurate lithographic models have been developed and compared with the experimental results.
Prediction of placement error of extreme ultraviolet lithography mask by simulation model with equivalent layout pattern
Authors: Chiba Akira , Hoshino Eiichi , Takahashi Masashi , Yamanashi Hiromasa , Hoko Hiromasa , Lee Byoung Taek , Yoneda Takashi , Ito Masaaki , Ogawa Taro , Okazaki Shinji
Published: July 2002

An equivalent modeling technique for estimating the deformation of extreme ultraviolet lithography (EUVL) masks caused by a complex pattern layout has been developed. An equivalent layout pattern (ELP) model provides a means of investigating ways of improving pattern placement accuracy. The simulation model is based on the finite difference method. In order to investigate the possibility of making EUVL masks with a high pattern placement accuracy, the ELP model was used to simulate how pattern density and substrate thickness affect placement error. The results obtained agree well with those for an exact model, with the relative error being at most 4%. They suggest that, when the stresses of the multilayer and absorber films cannot be reduced, it may be useful to increase the substrate thickness to improve the pattern placement accuracy. In addition, when the exposure field covers two chips, the placement error should be reduced through proper control of the stress of the absorber film rather than by changing the absorber coverage.
Feasibility of utilizing hexamethyldisiloxane film as a bottom antireflective coating for 157 nm lithography
Authors: Lin C. H. , Wang L. A.
Published: July 2002

The feasibility of utilizing a bottom antireflective coating (BARC) layer composed of hexamethyldisiloxane (HMDSO) film for 157 nm lithography is studied. The vaporized liquid HMDSO is used as a coating material in a conventional electron cyclotron resonance-plasma enhanced chemical vapor deposition process. The required optical constants of suitable HMDSO films can easily be tuned by adjusting the gas flow rate ratio of O2 to HMDSO. The swing effect is experimentally shown to be reduced significantly on Si substrates by applying either a single layer BARC or a bilayer BARC. Additionally, the bilayer BARC is shown by simulation to be capable of providing larger thickness-controlled tolerances than a single layer BARC.
Outline of a variable-axis lens with arbitrary shift of the axis in one direction
Authors: Schmid Peter , Rose Harald
Published: July 2002

A sophisticated electrostatic “variable-axis lens” is proposed which allows an arbitrary shift of the axis in one direction. For this purpose we employ a periodic arrangement of the electrodes in a direction perpendicular to the initial axis. The excitations of the electrodes are chosen in such a way that stigmatic imaging is conserved when the axis is shifted. The purely electric field components guarantee a fast dynamic shift of both the axis and the focusing field. Owing to the translational symmetry of the arrangement, the system enables much larger displacements of the axis than the conventional “variable-axis lens.” Moreover, this concept allows the simultaneous shift of many spatially separated lenses. Since the multiple beam system avoids a common crossover of the individual beams, large total currents can be employed.
Induced crystallization as a nonlithographic pattern transfer technique for nanofabrication
Authors: Cabral M. J. , Lye W. K. , Bean J. C. , Reed M. L. , Chraska T. , Mesarovic S. Dj. , Hull R. , Phillips A. B.
Published: July 2002

Controlled crystallization of amorphous films through “nanoprinting” is a novel pattern transfer technique that has been demonstrated for submicron features. Amorphous Ge and indium tin oxide (ITO) films are investigated for their suitability as a pattern transfer layer by direct contact with a patterned printhead. The printhead is heated and brought into contact with the amorphous film, transforming the contacted areas from amorphous to crystalline material. After crystallization, the amorphous regions are selectively etched away, leaving the desired pattern in crystalline material. Theoretical modeling suggests that this technique can be used for pattern transfer of features less than 50 nm.
Passivation of GaAs metal–insulator–semiconductor structures by (NH4)2Sx and by evaporation of SiO2
Authors: Jaouad A. , Aktik Ç.
Published: July 2002

Al–SiO 2 – GaAs structures are prepared and characterized by electrical measurements. The GaAs (100) surfaces are cleaned and passivated by chemical solutions. A passivation treatment based on ammonium polysulfide (NH4)2Sx is applied, then an insulating layer is deposited by electron-beam evaporation of an amorphous SiO2. By adjusting the passivation and the insulator deposition parameters, the accumulation and inversion conditions are observed by a capacitance–voltage (C–V) technique, showing that the Fermi level is unpinned. The interface-states density Dit as calculated using the method of Terman applied to high-frequency C–V characteristics presents a minimum of 1011 cm−2 eV−1.
Field electron emission device using silicon nanoprotrusions
Authors: Sawada Kazuaki , Tabe Michiharu , Ishikawa Yasuhiko , Ishida Makoto
Published: July 2002

Nanometer-scale silicon field emitters with the high packing density have been fabricated successfully by using a self-organized selective oxidation technique. The diameter at the bottom of each nanoemitter was 20–30 nm, and its height was 3–5 nm. The density was approximately 3–5×1011 tips/cm2. Emission characteristics were measured in a diode structure without gate electrodes for simplicity. As a result, it was found that the field emission current was detected at much lower anode voltages than conventional cone-shaped Si emitters. The apex shape was dependent on the oxidation conditions, and the emission current was dependent on the microscopic tip shape. It is expected that the field is significantly enhanced by the nanoprotrusions.
High-frequency metamorphic p-i-n photodiodes and high-electron mobility transistor transimpedance amplifiers: Candidates for fiber-optic communications
Authors: Hoke W. E. , Leoni R. E. , Whelan C. S. , Marsh P. F. , Jang J. H. , Adesida I. , Joshi A. M. , Wang X.
Published: July 2002

Solid source molecular-beam epitaxy was used to grow metamorphic films on GaAs substrates for optical (1.55 μ) p-i-n photodetectors and transimpedance amplifiers which are key components in a fiber-optic receiver. The p-i-n device structure incorporated an In0.53Ga0.47As photoabsorption layer while the transimpedance amplifier contained a metamorphic high-electron mobility transistor structure with an In0.60Ga0.40As channel layer. All layers were arsenide based which simplified material growth. A 10-μm-diam photodiode exhibited a −3 dB bandwidth of 52 GHz, a responsivity of 0.52 A/W corresponding to an external quantum efficiency of 42%, and a dark current of 7 nA at a 10 V reverse bias. The transimpedance amplifier demonstrated a power gain of 16 dB with a −3 dB bandwidth of 45 GHz. The transistors in the amplifier exhibited a dc reliability of 3×106 h at 125 °C. These performances are very promising for the application of metamorphic devices in the next generation 40 Gbit/s fiber-optic communication system.
On the optimum design of the front-end PIN-heterojunction bipolar transistor optoelectronic integrated circuit photoreceiver
Authors: Das N. R. , Deen M. J.
Published: July 2002

In this article, a detailed analysis of the performance of an integrated front-end PIN-heterojunction bipolar transistor photoreceiver has been given and optimum designs are suggested for maximum gain-bandwidth product (GB) and gain-bandwidth-sensitivity measure (GBS) of the device. The present SPICE-based analysis requires the equivalent circuit model of the receiver components. An expression for the impulse response of a PIN photodiode in the frequency domain has been derived to include the effect of transit time on the overall frequency response of the receiver. The models are verified with experimental data. Device parameters are tailored to obtain designs corresponding to maximum GB and GBS. These designs show much improvement in the performance when compared to the published results on unoptimized structures. Bandwidths greater than 40 GHz can be achieved using a simple three-stage amplifier circuit consisting of a common emitter and two emitter–follower circuits. Noise performance is calculated by minimum detectable power at a bit-error rate of 10−9 and the suggested optimum designs show improved noise performance.
Thin-film resistor fabrication for InP technology applications
Authors: Kopf R. F. , Melendes R. , Jacobson D. C. , Tate A. , Melendes M. A. , Reyes R. R. , Hamm R. A. , Yang Y. , Frackoviak J. , Weimann N. G. , Maynard H. L. , Liu C. T.
Published: July 2002

In this study we evaluated both NiCr and TaN thin-film resistor material for use with our InP technology. Thermal stability, sensitivity to oxidation, temperature coefficients, and patterning techniques were compared for the two materials. The film stoichiometry was determined using Rutherford backscattering and Auger electron spectroscopy analysis. Electron-beam evaporation of NiCr (80:20) resulted in films that were rich in Cr (30%), due to a higher vapor pressure of Cr. Thus, it was preferentially evaporated from the source. The TaN, on the other hand, was stoichiometric to within a few atomic %. This was due to better composition control with sputter deposition as opposed to electron (e)-beam evaporation from an alloy source. The NiCr showed a 5% increase in Rs when exposed to O2 plasma, and was stable for anneal temperatures of up to 300 °C. Alternatively, the TaN was stable for O2 plasma exposure, but had an increase in Rs of 5% or 10% when annealed at 300 °C in N2 or air ambients, respectively. From a fabrication point of view, the NiCr was more stable during bake cycles. However, it must be encapsulated to protect it from O2 plasma exposure. It can, therefore, be used earlier on in the process. On the other hand, TaN was more stable during plasma exposure, however, it must not be baked at high temperatures. It can thus be used at the back end of the process. The NiCr thickness required to obtain an Rs of 50 Ω/□ was around 250 Å, as opposed to 800 Å for the TaN. This may have an effect on electromigration issues for high current density applications. In addition, the TaN would be better in applications where resistors with higher Rs are required, such as 200 Ω/□.
Ion implantation effects on the structure and nanomechanical properties of vapor deposited cubic boron nitride films
Authors: Yamada-Takamura Y. , Yoshida T.
Published: July 2002

A few hundred keV C, F, and Si ions were implanted in vapor deposited cBN films with doses ranging from 1012 to 1015 ions/cm2, and implantation effects on the chemical bonding and nanomechanical properties have been investigated. Additionally, implanted-ion concentration and displacement damage were simulated using a Monte Carlo program, TRIM.SP, for the better understanding of the derived experimental results. The experiments and the simulation revealed that when the calculated damage of the implanted cBN film was higher than 0.025 dpa (displacement per target atom), more than 16% of the original cBN was destroyed. This result corresponded well with the hardness decrease observed for these films. On the other hand, when the damage was lower than 0.025 dpa, cBN destruction was less than 7%, and the implanted films showed comparable, or even superior, hardness to as- deposited films.
Abstract: Ion implantation and proton−enhanced diffusion in semiconductors
Authors: Gibbons James F.
Published: July 2002

In a period of less than ten years, ion implantation has become an accepted production process in the semiconductor industry, despite considerable initial skepticism about the merits of the process. More recently, proton−enhanced diffusion has been used to fabricate state−of−the−art microwave bipolar transistors and appears to have a number of other applications, including extensions of the frequency response of GaAs FETs.

The purpose of this paper is to describe the basic physics involved in each of these processes and to show how the relative merits of each lead naturally to a set of applications in which ion implantation, enhanced diffusion, and conventional thermal processes are combined to produce devices with characteristics superior to those previously available.

The principal topics to be presented are the following: (1) Basic operating features of implantation machines with special attention to those characteristics which are required for economic, efficient production; (2) Basic physics of the implantation process with special attention to range distribution theory and experiments, and damage production and annealing; (3) Applications of ion implantation to the production of semiconductor devices including MOSFETs, bipolar transistors, varactors, CCDs, and high−efficiency LEDs; and (4) Basic physics of the proton enhanced diffusion process and its emerging applications in the fabrication of microwave devices.
Abstract: A practical approach to helium leak detector applications
Authors: Briggs Walton E.
Published: July 2002

A helium mass spectrometer leak detector is simply a helium partial pressure gauge, combined with a supporting vacuum system for maintaining a suitable operating pressure. Although calibrated normally in std cc/sec the readout is accurate only when testing small devices directly connected to the leak detector. Locating and measuring leaks in large systems and small hermetically sealed devices are discussed. The use of pressure probe techniques will also be covered.
Abstract: Application of MeV backscattering to thin film diffusion problems
Authors: Campisano S. U. , Foti G. , Grasso F. , Rimini E.
Published: July 2002

The temperature at which mixing processes and compound formation between two metals occur in a thin film structure is strongly decreased with respect to bulk materials. The MeV He+ backscattering technique is well suited with its mass and depth perception to investigate the thermal kinetics of grain boundary diffusion in both miscible and nonmiscible couples of thin films. In the Cu−Pb thin film couple, a nonmiscible system as predicted by the phase diagram, a grain boundary migration of Pb occurs in the temperature range 200−300°C and Pb atoms accumulate at the Cu surface following a t1/2 dependence. In Al−In couples, another nonmiscible system, grain boundary diffusion takes place during deposition with filling of boundaries so that no accumulation is detected after annealing. In the completely miscible In−Pb couples, the slight increase of the substrate temperature during evaporation allows a strong intermixing so that backscattering spectra indicate the presence of both elements on the sample surface.
Synthesis of alloy carbides by the activated reactive evaporation process
Authors: Nimmagadda R. , Bunshah R. F.
Published: July 2002

Several of the carbides of the group IV, V, VI elements exhibit complete solid solubility in each other. Specific compositions of the alloy carbides exhibit melting point maxima. This investigation was concerned with the deposition of alloy carbides using the activated reactive evaporation process. [R. F. Bunshah and A. C. Raghuram, J. Vac. Sci. Technol. 9, 1385 (1972)]. A Ti−6Al−4V alloy rod was evaporated from an eb source in the presence of a partial pressure of C2H2 with all the vapor species being activated or partially ionized using the A.R.E. process. The deposits were characterized by x−ray diffraction and electron microprobe analysis. It was established that an alloy carbide deposit corresponding to a TiC−VC solid solution, with possibly Al present in the microstructure, was produced.
Truncation, potential, and temperature effects in the transform−deconvolution method
Authors: Adams David L. , Landman Uzi , Hamilton John C.
Published: July 2002

Fourier transforms of LEED intensities contain convolution products of functions of the interatomic vectors with data truncation, lattice vibration, and potential windows. The composite and individual effects of the windows in the deconvolution of transforms of LEED intensities are studied using calculated and experimentally measured intensities. In the analysis of LEED intensities from Al(100), lattice motion is found to be of major importance along with data truncation and potential characteristics.