bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance characteristics of displacement-type vacuum pumps
Authors: Hablanian M. H.
Published: July 2002

As recently as 25 years ago, high vacuum pumping was accomplished using mostly diffusion pumps and oil-sealed mechanical pumps. Now, there are alternate technologies available: ion-gettering pumps, turbomolecular pumps, and cryopumps. To be able to make an appropriate selection for a given application, a user should be familiar with properties of each pump. Here, the discussion is limited to mechanical, turbomolecular and vapor jet or diffusion pumps. The following topics are considered: concept of a vacuum pump as a compressor, displacement and pressure ratio characteristics of vacuum pumps, meaning of ultimate pressure and pumping speed in reference to partial pressures, staging problems between high and rough vacuum pumps, steady state, transient and overload conditions, and similarities between diffusion and turbomolecular pumps.
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Authors: Jahrreiss Heribert
Published: July 2002

1986 is the year of the 300th anniversary of Otto von Guericke’s death (11 May 1686). Commemorating O.v.G., the paper deals with his personality, the main scientific contemporary problems, his own basic ideas, and experiments in context with the concepts due to the other cofounders of vacuum physics: Galilei, Torricelli, Pascal, and Boyle. It is shown that some of his concepts are not only of historical interest, but fruitful also in our century.
Elongated microwave electron cyclotron resonance heating plasma source
Authors: Geisler M. , Kieser J. , Räuchle E. , Wilhelm R.
Published: July 2002

The concept as well as the design of a linearly extended microwave electron cyclotron resonance heating (ECRH) plasma source is introduced. A magnet system inside the plasma chamber is used to simultaneously generate the resonant magnetic field, shape and accelerate the plasma. After a discussion of microwave absorption by a low pressure plasma and the influence of magnetic fields of the closed loop type on the motion of charge carriers subjected to a microwave field the design of a so called elongated-mirror-geometry (EMG)-plasma source is introduced. Basic plasma parameters, performance characteristics as well as first results on the gas phase deposition of silicon oxide films are reported.
Metal contacts on Hg1−xCdxTe
Authors: Spicer W. E.
Published: July 2002

The available literature concerning metal contacts on Hg1−xCdxTe is reviewed in order to obtain a systematic overview. The theory and models available predict that, for metal in intimate contact with Hg1−xCdxTe , ‘‘ohmic’’ contact will be easily formed on n-type and rectifying on p-type Hg1−xCdxTe. This is in agreement with experimental results. There is evidence that metal atoms can move into the Hg1−xCdxTe, doping it and thus changing the electrical properties of the contact. Photoemission spectroscopy shows that Hg1−xCdxTe can be strongly disrupted by the deposition of the metal and correlation is found between heats of formation and heats of solution and the extent of this disruption. However, even for cases such as Ag where these bulk thermodynamic parameters are small, evidence is found for disruption of the lattice and movement of the metal into the Hg1−xCdxTe, producing doping. Formation of diffusion barriers and cooling to low temperature (100 K) have been explored as ways to limit this disruption.
Reduction of pumping time for a sputtering system by glow discharge cleaning
Authors: Kagatsume Akiko , Ueda Sinjiroo , Akiba Masakuni , Kawabe Takaya
Published: July 2002

Sputtering systems for semiconductor manufacturing require high-vacuum conditions. Typically it takes a long time to recover high-vacuum conditions after a sputtering system is opened to air. To increase the operating efficiency of the system, the recovery time must be reduced. Therefore, in this study, a glow discharge cleaning technique is applied using a glow-mode plasma source in argon gas. The discharge current distribution inside the sputtering system is measured under various conditions. It was found that nonuniformity was decreased: when the number of electrodes was increased from one to two; when the pressure during the discharge was decreased to 3×10−3 Torr; and when the anode current or anode voltage was increased. By applying these results, a drastic reduction in pumping time is achieved. The pumping time to attain a pressure of 1.5×10−6 Torr is reduced from 17 to 6 h with concurrent use of 3.5 h of discharge cleaning.
High resolution compositional depth profiling
Authors: Hofmann S.
Published: July 2002

High (depth) resolution depth profiling by sputtering in combination with surface analysis techniques critically depends on an appropriate choice of experimental conditions. This requires a thorough understanding of the large number of parameters which generate characteristic deviations between the measured profile and the original shape of the in-depth distribution of composition. These parameters are mainly caused by instrumental factors, composition, crystallinity and morphology of the sample and the specific effects of ion beam–sample interactions. Recent results of Auger electron spectroscopy depth profiling of single- and multilayer structures with optimized experimental conditions, for example high ion beam incidence angle, sample rotation and crater edge profiling, show that a depth resolution in the low nanometer range can be obtained on smooth sample surfaces. The results are compared with predictive models for the dependence of the depth resolution on ion beam energy and incidence angle and on the sputtered depth, revealing the limiting parameters for various systems.
Nonplanar step and terrace configurated surfaces as templates for crystal growth dynamics studies
Authors: Colas E. , Nihous G. C. , Hwang D. M.
Published: July 2002

A model is developed for predicting morphologies resulting from crystal growth on nonplanar surfaces with step and terrace configurations engineered prior to growth. Novel aspects of crystal growth dynamics are revealed by the interplay between diffusion across terraces and over convex corners, which leads to multiple step formation and unique morphologies on (100) and vicinal (100) surfaces. These effects are utilized to generate a variety of quantum wire structure arrays.
Effects of HF solution in the electroless deposition process on silicon surfaces
Authors: Nagahara L. A. , Ohmori T. , Hashimoto K. , Fujishima A.
Published: July 2002

We have investigated the influence of HF concentration on the initial stages of electroless deposition for various metals (Al, Au, Cu, Sn, and Pd) onto silicon using atomic force microscopy. As the HF concentration in the plating solution increased, the rate of metal deposition correspondingly increased for Au, Cu, and Pd. In the case of Au and Cu, uniformly sized nuclei comprised the first deposited layer. However for Al and Sn, deposition occurred only at sporadic sites on the surface and was independent of HF concentration. For all of the metal ion studied, deposition initiated preferentially at flaws on the surface. The electroless process indicates a direct displacement mechanism which results in the simultaneous dissolution of Si as the metal ion is reduced at the surface. For all the metal ions deposited in this manner, metal adhesion to the Si surface was poor.
Effect of substrate temperature on the deposition of polytetrafluoroethylene by an ionization-assisted evaporation method
Authors: Usui H. , Koshikawa H. , Tanaka K.
Published: July 2002

Thin films were deposited from low molecular weight polytetrafluoroethylene source materials by an ionization-assisted evaporation method, and their crystallinity and molecular orientation were studied by x-ray diffraction and infrared spectroscopy. The film properties were largely influenced by the substrate temperature and the molecular weight of the source material. At lower substrate temperatures, the molecules were oriented with the chain axis parallel to the substrate surface, and the film had preferential crystal orientation with the (100) plane of the hexagonal structure parallel to the substrate. With increasing substrate temperature, the molecules lost parallel orientation and the film crystallinity decreased. Such changes took place upon increasing the substrate temperature from 180 to 240 °C when deposited from a source material with a molecular weight of 8500, and from room temperature to 130 °C when the source molecular weight was 1500.
Pulsed laser deposition of Y3Al5O12:Tb photoluminescent thin films
Authors: Hirata G. A. , Lopez O. A. , Shea L. E. , Yi J. Y. , Cheeks T. , McKittrick J. , Siqueiros J. , Avalos-Borja M. , Esparza A. , Falcony C.
Published: July 2002

Transparent-photoluminescent Y3Al5O12:Tb (YAG:Tb) thin films were deposited on single- crystalline sapphire at two different substrate temperatures by means of the pulsed laser deposition technique. The ablation targets were fabricated from YAG:Tb powders obtained with a new ceramic processing technique (combustion synthesis). A KrF excimer laser with an ultraviolet wavelength of 248 nm was used to evaporate the target and to grow the films. Analysis and characterization of the films were performed by scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy, and photoluminescence measurements. As-deposited films were amorphous and deficient in oxygen as compared to the target. Additionally, these films were not luminescent. Postannealing treatments in air for at least 1 hr in the range 800–1200 °C were found to be necessary in order to induce crystallization and oxygenation in the films thus recovering the green photoemission of YAG:Tb with these treatments.
Nanostructural characterization of thin-film transistors using a combination of scanning force microscopy and transmission electron microscopy
Authors: Tsuji S. , Tsujimura T. , Tsujimoto K. , Tsutsui N. , Miura N. , Kuroda K. , Saka H.
Published: July 2002

The nanostructure and morphology of MoTa films deposited on glass substrates as gate metals are studied by combined scanning force microscopy and plan-view transmission electron microscopy (TEM). Hydrogenated amorphous silicon bottom-gate thin-film transistors (TFTs) are used to investigate whether the deposition of each subsequent layer of metal or dielectric is a conformal process. The improvement in the electron mobility of TFTs is discussed in relation to the surface roughness of the bottom-gate metal. The conformability of the nanometer-scale multilayered structure of the TFTs is confirmed by means of cross-sectional TEM. The electron mobility of the TFTs increase with a decrease in the surface roughness of the bottom-gate metal. The improvement in the TFT performance indicates that the smooth surface of the bottom-gate metal is the key factor.
Deposition and x-ray photoelectron spectroscopy studies on sputtered cerium dioxide thin films
Authors: Sundaram K. B. , Wahid P. F. , Melendez O.
Published: July 2002

Cerium dioxide is a rare earth oxide material that can be useful in various optical and electronic applications because of its high refractive index and its dielectric constant. The purpose of this study was to conduct an x-ray photoelectron spectroscopy analysis of sputtered cerium dioxide thin films. The thin films were deposited onto glass substrates using rf magnetron sputtering. A cerium dioxide target was used and various oxygen–argon gas flow ratios under different sputtering power levels were used for deposition. The results presented here characterize the properties of the rf sputtered cerium dioxide thin films under different deposition conditions.
Structural and optical properties of plasma-deposited amorphous hydrogenated oxygenated carbon films
Authors: Durrant Steven F. , de Oliveira Ricardo T. , Castro Sandra G. C. , Bolı́var-Marı́nez Luz Elena , Galvão Douglas S. , Bica de Moraes Mário A.
Published: July 2002

Amorphous hydrogenated oxygenated carbon (a-C:O:H) films were deposited from C6H6/O2/He/Ar mixtures in a deposition system fed rf power. The principal variable was the percentage of oxygen in the feed, Rox. Film structure and composition were investigated as a function of Rox using transmission infrared- and x-ray photoelectron spectroscopy. To some degree, greater values of Rox lead to greater incorporation of oxygen functionalities such as OH, C–O, and C=O into the deposited material. As revealed by ultraviolet-visible spectrophotometry, the optical gap E04 increased from ∼3.1 to ∼3.5 eV as Rox was increased from 0% to ∼50%. Semiempirical methods (PM3 and ZINDO-S/CI) allow modeling of the dependence of E04 on Rox. Broad agreement between the results of the experimental and theoretical analyses was obtained.
Polysilicon thin film transistors fabricated on low temperature plastic substrates
Authors: Carey Paul G. , Smith Patrick M. , Theiss Steven D. , Wickboldt Paul
Published: July 2002

We present device results from polysilicon thin film transistors (TFTs) fabricated at a maximum temperature of 100 °C on polyester substrates. Critical to our success has been the development of a processing cluster tool containing chambers dedicated to laser crystallization, dopant deposition, and gate oxidation. Our TFT fabrication process integrates multiple steps in this tool, and uses the laser to crystallize deposited amorphous silicon as well as create heavily doped TFT source/drain regions. By combining laser crystallization and doping, a plasma enhanced chemical vapor deposition SiO2 layer for the gate dielectric, and postfabrication annealing at 150 °C, we have succeeded in fabricating TFTs with ION/IOFF ratios >5×105 and electron mobilities >40 cm2/V s on polyester substrates.
Molybdenum–ruthenium/beryllium multilayer coatings
Authors: Bajt Saša
Published: July 2002

A newly developed beryllium-based multilayer system consisting of polycrystalline Be and amorphous MoRu layers is presented. The multilayer exhibits many remarkable properties: reflectivity as high as 69.3% at a wavelength of 11.4 nm (achieved with 50 bilayers giving a bandwidth of 0.35 nm), near-zero intrinsic stress, and excellent smoothing properties. As compared with Mo/Si multilayers at 13.4 nm, the shorter wavelength of 11.4 nm is better matched to the spectral output of gas-jet laser produced plasma sources, allowing a much higher optical throughput of the extreme ultraviolet lithography (EUVL) tool. The properties of MoRu/Be are compared to other beryllium-based multilayers, which have been considered for reflective coatings for EUVL optics.
Resonant Auger studies of metallic systems
Authors: Coulthard I. , Antel W. J. , Frigo S. P. , Freeland J. W. , Moore J. , Calaway W. S. , Pellin M. J. , Mendelsohn M. , Sham T. K. , Naftel S. J. , Stampfl A. P. J.
Published: July 2002

Results of resonant Auger spectroscopy experimental are presented for Cu, Co, and oxidized Al. Sublifetime narrowing of Auger spectra and generation of sublifetime narrowed absorption spectra constructed from Auger yield measurements were observed. Resonant Auger yields are used to identify three chemical states of oxidized Al. Partial absorption yield spectra were derived giving detailed electronic information and thickness information for the various chemical states of the bulk metal, the passivating aluminum oxide layer, and the metal–oxide interface region. In addition, the total absorption yield spectrum for the oxidized Al sample was constructed from the partial yield data, supporting the consistency of our method.
Structural properties of GaAs on Si and Ge substrates
Authors: Neumann D. A. , Zhu Xiaomei , Zabel H. , Henderson T. , Fischer R. , Masselink W. T. , Klem J. , Peng C. K. , Morkoç H.
Published: July 2002

We report a detailed x-ray scattering study of GaAs grown on Si and Ge substrates by molecular beam epitaxy. We find that the Q dependence of the peak widths can be completely understood in terms of residual strains in the epitaxial film. This result places lower limits on the domain size and antiphase domain size (if they exist) of 6000 and 4000 Å, respectively. In addition, we find that the GaAs lattice is commensurate with that of the Ge substrate, but that the GaAs lattice is incommensurate with the Si substrate; however, in both cases the GaAs lattice has tetragonal symmetry. We show that the measured lattice parameters and thus the tetragonal distortion can be explained by differential thermal expansion for the Si substrate sample.
Effect of growth sequence on the band discontinuities at AlAs/GaAs (100) and (110) heterojunction interfaces
Authors: Waldrop J. R. , Grant R. W. , Kraut E. A.
Published: July 2002

The valence band discontinuity ΔEv for the AlAs grown on GaAs (AlAs–GaAs) heterojunction interface is compared to the corresponding ΔEv for the GaAs grown on AlAs interface (GaAs–AlAs) for both (100) and (110) crystallographic orientations by using x-ray photoemission spectroscopy (XPS). Molecular-beam epitaxy within the XPS system was used to prepare the samples. The XPS method has the feature that ΔEv differences are measured more accurately than the corresponding absolute magnitudes. For the (100) interface, the value of ΔEv(AlAs–GaAs) is 0.10±0.02 eV larger than ΔEv(GaAs–AlAs). For the (110) interface, ΔEv(AlAs–GaAs) is 0.13±0.04 eV larger than ΔEv(GaAs–AlAs). The average discontinuity magnitudes are: ΔEv(AlAs–GaAs)(100)=0.46 eV; ΔEv(GaAs–AlAs)(100)=0.36 eV; ΔEv(AlAs–GaAs)(110)=0.55 eV; and ΔEv(GaAs–AlAs)(110)=0.42 eV. Thus, both a growth sequence effect and an orientation dependence have been found to be intrinsic characteristics of the (100) and (110) AlAs/GaAs heterojunction interfaces. As a consequence, there is an inherent asymmetry in the potential wells associated with AlAs/GaAs quantum well and superlattice structures.
Effect of nitrogen distribution in nitrided oxide prepared by rapid thermal annealing on its electrical characteristics
Authors: Naito Yasushi , Hori Takashi , Iwasaki Hiroshi , Esaki Hideya
Published: July 2002

Very thin oxides in nm range were nitrided by lamp heated rapid thermal annealing in an ammonia ambient. The nitrided oxides were studied using Auger electron spectroscopy, angular resolved x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and electrical metal–insulator–semiconductor (MIS) characterization. It is found by Auger depth profiling that the thickness of the oxide film does not increase by nitridation. The hydrogen concentration increases monotonically as nitridation proceeds. In the early stages of nitridation, nitrogen piles up at SiOxNy/Si interface and in the final stages it distributes uniformly throughout the film. Fixed charge and interface state densities increase with nitrogen concentration at the interface up to a critical nitrogen concentration (about 9%). Beyond this value, they decrease as nitridation proceeds. Nitrided oxides of the same nitrogen distribution, that were obtained at different nitridation temperatures, show the same electrical MIS characteristics. These results are explained by a model where nitrogen incorporation kinetics and formation of defects relevant to the MIS characteristics are affected by interfacial strain.
Wide range of Schottky barrier height for metal contacts to GaAs controlled by Si interface layers
Authors: Waldrop J. R. , Grant R. W.
Published: July 2002

Metal (Au, Cr, and Ti) contacts to n-type (100) GaAs are described in which the Schottky barrier height φB is controlled by using a very thin Si interface layer to influence the interface Fermi energy EiF. The contact structure consists of a thick metal and an ∼15–30 Å Si interface layer that is heavily either p-type or n-type. A large 1 eV φB is found for the metal–Si(p-type)–GaAs structure and a small 0.5 eV φB for the metal–Si(n-type)–GaAs structure. X-ray photoemission spectroscopy (XPS) was used to obtain EiF and interface composition during initial contact formation; the φB for the thick contacts was measured by I–V and C–V techniques.
Epitaxial growth rate measurements during molecular beam epitaxy
Authors: SpringThorpe A. J. , Majeed A.
Published: July 2002

Apparent oscillations in surface temperature occur during the deposition of heteroepitaxial structures when measured using a narrow optical bandpass pyrometer. The oscillation period can be related to the growth rate of the material being deposited, and provides a convenient method for rapid in situ calibration. For Ga1−xAlxAs alloys the oscillation periods can be directly related to the alloy composition. The pyrometer optics can also be used in conjunction with external light sources so that simultaneous pyrometry and reflectrometry can be carried out at multiple wavelengths.
Scanning tunneling microscopy investigations of polysilicon films under solution
Authors: Carrejo J. P. , Thundat T. , Nagahara L. A. , Lindsay S. M. , Majumdar A.
Published: July 2002

We have investigated the surface morphology of polysilicon films, prepared by low pressure chemical vapor deposition, with scanning tunnel microscope (STM) under very dilute HF solution. Imaging under HF solution eliminates ambiguities in the STM topographs caused by the presence of oxide. The average grain sizes determined from STM topographs were consistent with transmission electron microscopy and scanning electron microscopy studies. The root mean square surface roughness measured from STM topographs was found to increase with the polysilicon film thickness while the sheet resistance was found to decrease with the film thickness. The surface topography of the film was found to have a fractal structure with a surface fractal dimension of 2.35.
Scanning tunneling microscopy studies of phase separation on Si(001) surfaces with periodic step density
Authors: Umbach C. C. , Keeffe M. E. , Blakely J. M.
Published: July 2002

Using photolithography and ultrahigh vacuum annealing, we have produced atomic step arrays on Si(001), where the number of steps per unit length normal to the [110] direction changes periodically. These arrays afford the opportunity to study step phenomena that depend on average step density. A scanning tunneling microscope was used to image the detailed structure of the arrays. A transition in step height—from primarily monatomic to primarily biatomic steps—as a function of surface orientation was observed. Sharp changes in local slope associated with this transition were also observed. The connection with the equilibrium crystal shape is discussed.
Scanning tunneling microscopy and spectroscopy studies of the surface structure and electronic properties of single-crystal Tl–Ba–Ca–Cu–O superconductors
Authors: Zhang Zhe , Lieber Charles M. , Ginley David S. , Baughman Robert J. , Morosin Bruno
Published: July 2002

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to characterize the surface structure and electronic properties of Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 single crystals. Atomic resolution STM images show that 90%–95% of the surface has a near-trigonal structure with a=b=0.24 nm and an a–b angle of 65°. The remaining 5%–10% of the surface consists of a new orthorhombic structure with a=b=0.40 nm. Spatially resolved STS measurements further demonstrate that regions with the 0.24 nm period structure are metallic, while areas with the 0.40 nm period structure are semiconducting.
Deep ultraviolet patterning of monolayer films for high resolution lithography
Authors: Calvert Jeffrey M. , Chen Mu-San , Dulcey Charles S. , Georger Jacque H. , Peckerar Martin C. , Schnur Joel M. , Schoen Paul E.
Published: July 2002

A new process has been developed for high resolution photolithography that employs chemisorbed monolayer films as the surface imaging layers. Organosilane treated surfaces are exposed to patterned deep UV radiation, either from excimer laser or lamp sources. The photochemical process modifies the surface wettability and reactivity of the film. Organosilane films patterned by deep UV radiation are treated with a Pd/Sn catalyst and then metallized with electroless copper and nickel baths to yield metal films several 100 Å thick. The metal is selectively deposited in the unexposed regions of the film to produce a positive tone image. The patterned metal film is then utilized as a plasma hard etch barrier in a reactive ion etch, allowing efficient pattern transfer into the underlying substrate and producing features with linewidths to 0.4 μm. Electrical testing of processed substrates demonstrates compatibility of the process with subsequent device performance, and working transistor test structures have been fabricated. Decoupling the imaging (monolayer surface imaging layer) and resist (metal film) functions of a photoresist allows separate optimization of each function in this scheme. The patterning process is very general and may be applied to a variety of substrate types. Other potential applications include patterned wettability and reactivity of surfaces for selective attachment of other species such as fluorophores or biological moieties.
Circular polarized electron cyclotron resonance source
Authors: Pongratz S. , Gesche R. , Kretschmer K.-H. , Lorenz G. , Hafner M. , Zink J.
Published: July 2002

This paper describes the first results of the new Leybold Leybold circular electron cyclotron resonance (CECR) technology which uses circular polarized microwave excitation for generating a plasma of very high density. At a pressure of 1 μbar, an ion current density of 6 mA/cm2 was measured in a pure chlorine plasma. That reveals in fact an increase of about 30% in ion density compared to the linear polarized electron cyclotron resonance (ECR) source. The appreciable improvement will be demonstrated by etching results of silicon trench with chlorine where an etch rate of 300 nm/min with a uniformity better than ±5% on 200 mm wafer size was obtained. The source has a compact design which enables multichamber processing in a cluster tool environment with the capability for processing wafers up to 200 mm diameter.
Quantitative description of dissolution and dissolution inhibition in novolak and other phenolic resins
Authors: Yeh Tung-Feng , Shih Hsiao-Yih , Reiser Arnost , Toukhy Medhat A. , Beauchemin Bernard T.
Published: July 2002

The dependence of the dissolution rates of phenolic resins on the base concentration of the developer can be described by a dimensionless equation based on a membrane model of novolak dissolution [J. P. Huang, T. K. Kwei, and A. Reiser, Macromolecules 22, 4106 (1989) and R. A. Arcus, Proc. SPIE 631, 124, (1986)]. The resin is characterized by a dissolution threshold c0, which is a limiting base concentration below which dissolution no longer occurs, by a scaling exponent n and by a membrane permeability Pr which refers to a developer of base concentration c = 2c0. Under these reference conditions all resins are in a corresponding state and dissolve with the same dimensionless rate of R/Pr = 0.5. The inhibition effect in an inhibitor/resin pair is represented by a plot of log(Ri/R0) against the inhibitor concentration in the resin matrix, where Ri is the rate of dissolution of the inhibited, R0 the rate of dissolution of the pure resin. The slope of this plot is independent of the inhibitor concentration over a reasonable concentration range and may be termed the inhibition factor and used as a measure of the inherent inhibition capability of the inhibitor in the resin. It is termed the inhibition factor. It is suggested that inhibition factors be compared in conditions where the pure resins dissolve at the same rate. In this study we have chosen a rate of 15 μm/min as the standard condition.
Lateral variation of indium content in InGaAs grown on GaAs channeled substrates by molecular beam epitaxy
Authors: Wakejima A. , Inoue A. , Kitada T. , Tomita N. , Shimomura S. , Hiyamizu S. , Fujii M. , Yamamoto T. , Kobayashi K. , Sano N.
Published: July 2002

Lateral variation of In content in a 1.5 μm thick InxGa1−xAs (x≂0.2) epilayer grown on channeled GaAs (100) substrates having (755)A or (411)A slope regions by molecular beam epitaxy (MBE) was studied by the energy dispersive x-ray spectroscopy, with high spatial resolution (0.6 μm). Significantly peculiar migration of In atoms on the (411)A was observed. Experimental data of this work strongly suggest that In atoms migrate preferentially in one way, that is to say, they migrate much more in the [12̄2̄] direction than in the opposite [1̄22] direction on the (411)A plane during MBE growth. The migration length of In atoms on the (100) plane was 5 μm when InGaAs was grown at Ts=570 °C and V/III=30.
Measurement of the sheet resistance of doped layers in semiconductors by microwave reflection
Authors: Bhimnathwala H. , Borrego J. M.
Published: July 2002

This article presents results obtained using microwave reflection between 26.5 and 36.5 GHz for measuring the sheet resistance of doped layers in semiconductors. The advantage of the technique is that it is nondestructive and has a dynamic range and spatial resolution similar to what it can be obtained with four point resistivity probes. Using this technique, we have been able to measure the sheet resistance of shallow implanted layers on silicon wafers implanted with doses in the range of 1016–1012 ions/cm2. The sheet resistance measured was between 30 and 80 000 Ω/⧠.
Carbonaceous surface layers deposited on TiN coatings by ion implantation
Authors: Franck M. , Blanpain B. , Celis J. P. , Roos J. R. , Pattyn H.
Published: July 2002

TiN coatings deposited by physical vapor deposition have been subjected to a postdeposition treatment involving beam line implantation with 80-keV C+ ions at doses between 1×1017 and 3×1017 ions/cm2. Rutherford backscattering spectrometry measurements showed Gaussian-like implantation-depth profiles extending towards the surface which was found to be covered with carbon. The carbonaceous surface layer was characterized by Raman spectroscopy revealing the typical band features of diamondlike carbon. Simulations of the carbon depth profile indicate that the opaque carbon layer was formed from carbon in excess of the implanted dose. Further experiments suggest that the carbon layer resulted from an ion-beam-assisted deposition process. Fretting wear tests demonstrated lower friction and improved wear resistance of the TiN covered with the diamondlike carbon layer in comparison with as-deposited TiN.
Structural study of a poly(methylmethacrylate) Langmuir–Blodgett film on a graphite surface by scanning tunneling microscope
Authors: Ha Jeong Sook , Roh Hee-Sook , Jung Sang-Don , Park Seong-Ju , Kim Jang-Joo , Lee El-Hang
Published: July 2002

In this study, molecular configurations of three different stereoregular poly(methylmethacrylate) (PMMA) (isotactic, atactic, and syndiotactic PMMA) monolayers, which were transferred onto graphite substrates by the Langmuir–Blodgett (LB) technique, were investigated using scanning tunneling microscope (STM). STM images of monolayer films taken in air in the constant height mode showed various types of film structures. First, polymer films in their different forms always showed long-range ordered chain structures. Second, these polymer chains were generally observed to arrange themselves in parallel chains with no backbone crossovers. However, the packing density of polymer chains on the surface varied with change of scanning area presumably due to the nonuniformity of the LB film and the effect of thermal fluctuation of polymer chains on the film. Third, a monolayer film of isotactic PMMA film showed the coexistence of helical and linear chains in most of the film areas suggesting that the structural transition from the linear chains to 51 single stranded helices occurs at the surface pressure of 8 mN/m.
Much improved interfaces in GaAs/AlAs quantum wells grown on (411)A GaAs substrates by molecular-beam epitaxy
Authors: Shimomura S. , Shinohara K. , Kitada T. , Hiyamizu S. , Tsuda Y. , Sano N. , Adachi A. , Okamoto Y.
Published: July 2002

Effectively atomically flat interfaces over a macroscopic area (200 μm o/) have been achieved in GaAs/AlAs quantum wells (QWs) with well widths of 4.8 to 12 nm grown on (411)A GaAs substrates by molecular-beam epitaxy (MBE). A single and very narrow photoluminescence peak (FWHM)=7.7 meV) was observed at 742.6 nm for the QW with a well width of 4.8 nm at 77 K. The linewidth is comparable to that of growth-interrupted QWs grown on (100)-oriented GaAs substrates by MBE. These results indicate that the surface of GaAs and AlAs grown on the (411)A GaAs substrates are extremely flat and stable on the (411)A plane.
Postfabrication resistance trimming of a superconducting tunnel junction using a focused ion beam
Authors: Barber Z. H. , Blamire M. G. , Dawes N. J.
Published: July 2002

A high current density NbN/MgO/Nb superconducting tunnel junction has been modified using a focused ion beam to trim the junction area following fabrication and measurement. After milling, the exposed edge of the junction was cleaned of resputtered material using a low current ion beam combined with gas assisted etching. Some remaining shorts across the barrier were then removed by anodization. The modified junction showed a resistance increase correlating exactly with the decrease in area and very little change in quality. This technique may be used on fully fabricated circuits to trim accurately the resistance of selected junctions in order to overcome variations in barrier conductance and junction area.
Structural and photoluminescence properties of growth-induced InAs island columns in GaAs
Authors: Solomon G. S. , Trezza J. A. , Marshall A. F. , Harris J. S.
Published: July 2002

InAs quantum dots layers produced by growth-induced islanding are vertically stacked with a variable thickness GaAs spacer layer. Using transmission electron microscopy, dense planar arrays of randomly ordered InAs islands are found to be vertically aligned in columns. We have compared single, 2, 5, and 10 layers of InAs islands and the vertical alignment is maintained. Atomic force microscopy shows the island size is unchanged throughout the layering process. 8 K photoluminescence shows a spectral peak shift and linewidth narrowing that we associate with electronic coupling within the columns. Variations in the GaAs spacer region produce spectral changes that are consistent with this coupling.
Comparison of (Al,Ga)As(110) grown by molecular beam epitaxy with As2 and As4
Authors: Holland M. C. , Stanley C. R.
Published: July 2002

A comparison of Si-doped (Al,Ga)As grown on on-axis GaAs(110) with As2 and As4 is reported, together with a low temperature photoluminescence study of cleaved edge overgrown quantum well structures. Approximately 90% of Si atoms are active as donors under both facet-free and facetted (110) growth conditions with As2, whereas using As4, the proportion is reduced to 40%–60%. It is shown that cleaving at the growth temperature (480 °C) rather than room temperature is essential if the cleaved interface is to be optically active.
Low coverage adsorption of Sb4 on Si(113) studied by scanning tunneling microscopy
Authors: Müssig H.-J. , Da̧browski J. , Arabczyk W. , Hinrich S. , Wolff G.
Published: July 2002

High index surfaces of group-IV crystals are important because high index facets often appear during heteroepitaxial growth of Ge and SiGe islands on Si(001) and Si(111). The Si(113) surface is of a particular interest: Suitable for epitaxy, atomically flat, and thermally stable Si(113) can be easily obtained. Results are reported of scanning tunneling microscopy investigation of the effect of antimony adsorption on Si(113)3×2 at low coverages as a function of annealing temperature. At room temperature, Sb4 molecules are physisorbed in a metastable precursor state and move mainly into areas of high density of antiphase boundaries and other defects where they are chemisorbed. Several cluster formations of different size, shape, and orientation are observed. During annealing at first some of the clusters dissociate and some arrange along [11̄0] and [332̄]. With increasing temperature (about 550 °C), the clusters break and Sb atoms are incorporated into the surface. On the basis of ab initio calculation, an atomic structural model for the resulting 2×2 reconstruction is proposed and verified.
Low dielectric constant film formation by oxygen-radical polymerization of laser-evaporated siloxane
Authors: Fujii Toshiaki , Yokoi Tsuneki , Hiramatsu Mineo , Nawata Masahito , Hori Masaru , Goto Toshio , Hattori Shuzo
Published: July 2002

Polysiloxane thin films were proposed as low dielectric constant interlayer dielectrics for multilevel interconnection of ultralarge scale integration circuits. The films were prepared using oxygen-radical polymerization of siloxane oligomers. A variety of siloxane oligomers were thermally produced by the decomposition of polysiloxane bulk target using CO2 laser irradiation. Oxygen radicals generated by a remote microwave O2 plasma were injected into the vacuum chamber during film deposition. The films deposited with the oxygen radical injection were transformed from polysiloxane to carbon-deficient silicon oxide with increase of substrate temperature as confirmed by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. At a CO2 laser power of 10 W, an O2 pressure of 50 mTorr, a microwave power of 100 W, and a substrate temperature of 100 °C, the dielectric constant of the polysiloxane film was 2.0.
Dual unit scanning tunneling microscope-atomic force microscope for length measurement based on reference scales
Authors: Zhang Haijun , Huang Feng , Higuchi Toshiro
Published: July 2002

The crystalline lattice and periodic grating features have been employed as reference scales for simultaneous calibration between the scanning tunneling microscope (STM) and atomic force microscope (AFM). This article describes the configuration and functions of a dual unit STM-AFM for length metrology. The system was developed on the basis of a dual tunneling unit STM (DTU-STM) in view of the fact that the application of DTU-STM was strongly limited by sample conductivity. In the dual unit STM-AFM, a STM serving as a reference unit and an AFM as a test unit were combined by using one single XY scanner. Both the reference sample and the test sample were installed at the center of the scanner on either surface, and were imaged by STM and AFM units at the same time. The length of the test sample image was measured by counting the periodic features of the reference sample image. We present a detailed discussion about the structure and control of the dual unit STM-AFM. Some comparison results, respectively, using crystalline lattices and periodic grating features as reference scales for length calibration of test samples are also provided. Experiments show a satisfactory matching between the STM unit and the AFM unit when covering a wide scan range from 5 nm to 10 μm. Using different standard reference scales, the system enables nanometer and/or sub-micron accuracy length metrology of microstructures with any conductivity.
Focused ion beam milling: Depth control for three-dimensional microfabrication
Authors: Vasile M. J. , Niu Z. , Nassar R. , Zhang W. , Liu S.
Published: July 2002

Ion milling with a focused ion beam (FIB) is a potential method for making micromolds, which will then be the primary elements in the mass production of micro- or mini-objects by embossing or injection molding. The challenge lies in controlling the ion milling to produce cavities with predefined, arbitrary geometric cross-sections. This work involves programming variations as a function of position into the algorithm that generates the dwell times in the pixel address scheme of a FIB. These variations are done according to whether an axis of symmetry or a plane of symmetry determines the final geometry, and the result is 26 new cross-sectional shapes, such as hemispherical pits, parabolic pits, hemispherical domes, etc. The ion milling control programs were used to generate parabolic cross-section trenches, sinusoidal trenches, sinusoidal cross-section rings on an annulus, and hemispherical domes. We observed reasonable agreement between the shapes ion milled in Si(100) and the expected geometry. The dwell times are generated assuming each pixel has a unique dose and the ion yield is constant with angle of incidence. Deviations from ideality are ascribed to the variation in sputter yield with changing angle of incidence, and to the dwell time control algorithm. Redeposition also compounds the deviation from ideality, but it is difficult to estimate the magnitude of this effect.
Germanium-rich SiGe bulk single crystals grown by the vertical Bridgman method and by zone melting
Authors: Barz A. , Dold P. , Kerat U. , Recha S. , Benz K. W. , Franz M. , Pressel K.
Published: July 2002

Silicon–germanium single crystals with a Si content up to 10 at. % have been grown by the vertical Bridgman technique in a monoellipsoid mirror furnace. Single crystal regions up to 50 at. % have been realized by zone melting in a double ellipsoid mirror furnace. The typical high temperature gradients of radiation heated facilities (grad T up to 100 K/cm or even higher, depending on the sample geometry) reduce the occurrence of constitutional supercooling and stabilize the growth interface. Photoluminescence measurements as well as rocking curves and etch pit densities reveal a high crystal quality. Effective segregation coefficients of Al, Ga, In, P, As, and Sb in Ge1−xSix (x<13 at. %) were determined.
Toward device-quality GaAs growth by molecular beam epitaxy on offcut Ge/Si1−xGex/Si substrates
Authors: Sieg R. M. , Ringel S. A. , Ting S. M. , Samavedam S. B. , Currie M. , Langdo T. , Fitzgerald E. A.
Published: July 2002

The epitaxial growth of GaAs on Si substrates through the use of a Ge/graded Si1−xGex/Si buffer layer would allow monolithic integration of GaAs-based opto-electronics with Si microelectronics. As an initial step toward this goal, this study examines factors which influence the quality of GaAs growth by molecular beam epitaxy (MBE) on bulk Ge substrates. Key findings include the need for an epitaxial Ge smoothing cap deposited in the MBE chamber, the significant detrimental effect of As overpressure on the resultant GaAs crystalline quality, and the efficiency of a very thin (∼3 nm) migration enhanced epitaxy (MEE) nucleation layer at suppressing both anti-phase domain (APD) formation and interdiffusion across the GaAs/Ge heterointerface. Using this developed optimized growth process, APD-free GaAs on Ge is obtained which has undetectable Ga and Ge cross-diffusion, and As diffusion into the substrate at ⩽1×1018 cm−3. Preliminary results for growths on Ge/Si1−xGex/Si substrates are also presented.
Reconstructions of GaN(0001) and (0001̄) surfaces: Ga-rich metallic structures
Authors: Smith A. R. , Feenstra R. M. , Greve D. W. , Shin M. S. , Skowronski M. , Neugebauer J. , Northrup J. E.
Published: July 2002

Reconstructions of GaN(0001) and (0001̄) surfaces are studied by scanning tunneling microscopy and spectroscopy, by electron diffraction, by Auger electron spectroscopy, and using first-principles theory. Attention is focused on Ga-rich reconstructions for each surface, which are found to have a metallic character involving significant overlap between Ga valence electrons. The electron counting rule is thus violated for these surfaces, but they nonetheless form minimum energy structures.
High aspect ratio all diamond tips formed by focused ion beam for conducting atomic force microscopy
Authors: Olbrich A. , Ebersberger B. , Boit C. , Niedermann Ph. , Hänni W. , Vancea J. , Hoffmann H.
Published: July 2002

Conductive (boron doped) all diamond tips are best suited for use as electrical probes for scanning probe experiments due to their hardness, chemical inertness, and resistivity against wear. In order to overcome the problems of image distortion induced by the tip shape the aspect ratio of the diamond tips was increased to about 7:1 by focused ion beam milling, maintaining a tip radius of typically 30 nm at the apex. The application of these sharpened tips to conducting atomic force microscopy for local electrical characterization of thin metal–oxide–semiconductor dielectrics is demonstrated. Excess current flow was detected at the transition region between the gate oxide and the bordering field oxide due to oxide thinning introduced by the local oxidation of silicon process.
Carrier concentration dependence of the scanning capacitance microscopy signal in the vicinity of p–n junctions
Authors: Kopanski J. J. , Marchiando J. F. , Rennex B. G.
Published: July 2002

Scanning capacitance microscopy (SCM) was used to image (1) boron dopant gradients in p-type silicon and (2) identical boron dopant gradients in n-type silicon. The bias voltage dependence of the apparent p–n junction location in the (SCM) images was measured. The theoretical bias voltage dependence of the apparent p–n junction location of the same structures was determined using a two-dimensional, numerical Poisson equation solver. The simulations confirm that, for symmetric step p–n junctions, the apparent junction coincides with the electrical junction when the bias voltage is midway between the voltage that produces the peak SCM response on the p-type side and the voltage that produces the peak response on the n-type side. This rule is only approximately true for asymmetrically doped junctions. We also specify the extent of the region on the junction high and low sides from which valid carrier profiles may be extracted with a simple model.
Diffusion barrier properties of ZrN films in the Cu/Si contact systems
Authors: Takeyama Mayumi B. , Noya Atsushi , Sakanishi Kouichirou
Published: July 2002

A thermally stable Cu/ZrN/Si contact system using a ZrN diffusion barrier of low resistivity was developed. In the contact system, the growth of an oriented ZrN(100) layer on Si(100), and subsequent growth of a Cu(110) layer on ZrN(100) were observed. The obtained contact system was fairly stable after annealing even at 750 °C for 1 h without any diffusion and/or reactions at either the interface of Cu/ZrN or ZrN/Si. It was revealed that the ZrN layer with low electrical resistivity showed a high performance as a diffusion barrier, and was one of the excellent materials for the use in ultralarge scale integration technology.
Notch Inhibition of RAS Signaling Through MAP Kinase Phosphatase LIP-1 During
C. elegans
Vulval Development
Authors: Berset Thomas , Hoier Erika Fröhli , Battu Gopal , Canevascini Stefano , Hajnal Alex
Published: July 2002

During
Caenorhabditis elegans
vulval development, a signal from the anchor cell stimulates the RTK/RAS/MAPK (receptor tyrosine kinase/RAS/mitogen-activated protein kinase) signaling pathway in the closest vulval precursor cell P6.p to induce the primary fate. A lateral signal from P6.p then activates the Notch signaling pathway in the neighboring cells P5.p and P7.p to prevent them from adopting the primary fate and to specify the secondary fate. The MAP kinase phosphatase LIP-1 mediates this lateral inhibition of the primary fate. LIN-12/NOTCH up-regulates
lip-1
transcription in P5.p and P7.p where LIP-1 inactivates the MAP kinase to inhibit primary fate specification. LIP-1 thus links the two signaling pathways to generate a pattern.