bluuebunny/crossref_metadata_2025 huggingface dataset:
Batch fabricated scanning near field optical microscope/atomic force microscopy microprobe integrated with piezoresistive cantilever beam with highly reproducible focused ion beam micromachined aperture
Authors: Grabiec P. , Radojewski J. , Zaborowski M. , Domanski K. , Schenkel T. , Rangelow I. W.
Published: February 2004

In scanning near field optical microscope (SNOM), an optical probe with aperture diameter well below the optical wavelength is moved over the sample. The sample-probe distance control is one of the key problems in SNOM. Our earlier approach allowed for fabrication of the piezo-SNOM/atomic force microscopy (AFM) probe, however, reproductivity of the process and optical quality of the device were not satisfactory. Now we report an innovative processing sequence, which offers highly reproductive batch processing, typical for semiconductor technology and renders it possible to produce cantilevers playing role of an AFM detector as well as a nanoaperture detector. Moreover, illumination of the aperture is easier because of a wide input opening and its big cone angle. The throughput is in the range of 10−5 and higher. Apertures in hollow pyramids have been formed by direct ion beam drilling with a focused beam of 30 keV Ga+ ions. Direct focused ion beam (FIB) drilling is a reproducible process for hole formation at the 30–100 nm diameter range. Formation of smaller apertures is possible if a special FIB drilling/deposition procedure is applied.
Fluoropolymers for 157 nm single-layer resists
Authors: Toriumi M. , Ishikawa T. , Kodani T. , Koh M. , Moriya T. , Yamashita T. , Araki T. , Aoyama H. , Yamazaki T. , Furukawa T. , Itani T.
Published: February 2004

Tetrafluoroethylene-based copolymers with functionalized norbornenes were synthesized using a hydrocarbon and hydrofluorocarbon initiators and their fundamental properties, such as transparency at 157 nm and solubility in a standard alkaline developer were characterized. A high transparency, i.e., absorbance of less than 0.5 μm−1, and the increase of the dissolution rate in the standard alkaline developer were achieved. Positive-working resists formulated by the fluororesins were developed and showed fine patterns of 60 nm dense lines and spaces delineated by the exposure at 157 nm wavelength.
Fabrication of FePt nanoparticles for self-organized magnetic array
Authors: Yang XiaoMin , Liu Chao , Ahner Joachim , Yu Jun , Klemmer Timothy , Johns Earl , Weller Dieter
Published: February 2004

A self-organized array of magnetic nanoparticles can be potentially used to increase the storage density in magnetic recording. One challenge in this approach is to obtain long-range order assemblies of the nanoparticles. One method to solve this problem is to pattern a substrate having circumferential patterns, whose dimensions are within the coherent length of the self-organized array. By patterning the disk into topographically confined circumferential patterns with such dimensions, thermally stable magnetic nanoparticles may be used to fabricate magnetic recording disks. The circumferential patterns in this case are formed on the disk substrate with dimensions of 100–500 nm and depths of 5–20 nm, prepared by electron beam lithography and reactive ion etching techniques. The monodispersed FePt nanoparticles were synthesized by thermal decomposition of iron pentacarbonyl and reduction of platinum salt simultaneously in the presence of surfactant molecules, achieving a size distribution of 3.15±0.20 nm. Our initial experimental results showed that the monodispersed FePt nanoparticles were successfully deposited into the circumferential patterns and they self-organized into a superlattice. The self-assembly of the FePt nanoparticles in the circumferential pattern strongly relied on the line edge roughness (LER) of the circumferential pattern. This suggests that we need to fabricate the circumferential pattern with LER at the length scales of approximate an individual nanoparticle size 3–4 nm in order to improve the assembly quality further. This is another challenge for today’s advanced lithography and etching processes.
Secondary ion mass spectrometry analysis of implanted and rapid thermal processing annealed wafers for sub-100 nanometer technology
Authors: Ehrke U. , Sears A. , Lerch W. , Paul S. , Roters G. , Downey D. F. , Arevalo E. A.
Published: February 2004

The characterization of ultrashallow junctions after implantation and subsequent rapid thermal processing (RTP) annealing is usually done in two ways. The sheet resistance of the junction is measured with a four-point probe and junction depth and dose are evaluated via secondary ion mass spectrometry (SIMS). After ultralow energy beamline implantation in a Varian VIISta 80 single wafer high current implanter the subsequent spike anneal for maximum activation and minimal diffusion was carried out on a Mattson 3000 Plus equipped with the flash-anneal controller. Junction depth profiling was done to monitor the influence of implant conditions and RTP annealing parameters. Measurements of junction depth, total dose, activated dose and uniformity were carried out on FEI Quadrupole SIMS tools. Queued measurements were performed on full wafers and small samples. Calibration of both junction depth and retained dose will be discussed. At very low beam energies (250 eV, oxygen, normal incidence) valuable information about depth profile shape, near surface concentration, and activated dose were obtained.
Crystallographic effects in micro/nanomachining of single-crystal calcium fluoride
Authors: Yan Jiwang , Syoji Katsuo , Tamaki Jun’ichi
Published: February 2004

Single-crystal calcium fluoride (CaF2) is an excellent optical material in the infrared range and the ultraviolet range. It is an indispensable substrate material for the 193 and 157 nm wavelength laser optics for future large-scale semiconductor photolithography systems. Due to its delicate nature, for the most part the CaF2 elements have been fabricated using conventional pitch polishing combined with interferometry and local surface correction to form the desired flat, sphere or aspherical surface. In the present work, the feasibility of generating high quality optical surfaces on CaF2 by single-point diamond turning is examined. The development of this technology may provide the possibility of fabricating aspherical and diffractive optical components in an efficient way. The machining experiments described in this article were done on a high-stiffness, ultraprecision, numerically controlled diamond lathe with a sharply pointed single-crystal diamond tool. The scale of machining was varied from the micrometer level to the nanometer level. It was found that at the micrometer level, machining was significantly affected by the crystal orientation of the workpiece. The crystallographic anisotropy causes nonuniformity of the finished surface texture, microfracture topography and brittle–ductile transition boundary conditions. The results also indicate that by controlling the undeformed chip thickness below a critical value, namely, the minimum critical chip thickness (85 nm), a uniformly ductile-machined surface could be produced. Under the present experimental conditions, a surface with a maximum height (Ry) of 18.5 nm and arithmetical mean roughness (Ra) of 3.3 nm was obtained.
Key role of nanocrystalline feature in porous polycrystalline silicon diodes for efficient ballistic electron emission
Authors: Ichihara Tsutomu , Hatai Takashi , Aizawa Koichi , Komoda Takuya , Kojima Akira , Koshida Nobuyoshi
Published: February 2004

The cold electron emission characteristics of nanocrystalline porous polysilicon (PPS) diodes have been investigated for two PPS diodes prepared under different conditions. The origin of the difference in the emission efficiency and electron energy distribution between the two samples is analyzed in relation to the respective photoluminescence properties. The photoluminescence spectrum in the efficient electron emitter consists of red and blue emission bands corresponding to nanocrystalline silicon and interfacial oxide, respectively, while that in the low-efficiency emitter consists only of a blue band. Too much oxidation results in a reduction of the emission efficiency due to increased electron scattering. It is evident that both the formation of nanocrystalline silicon and its appropriate surface oxidation are key issues for obtaining efficient ballistic emission. These results are consistent with the emission model that electrons are accelerated in the PPS layer by multiple tunneling through interfacial oxide barriers between interconnected silicon nanocrystallites.
Roles of copper mechanical characteristics in electropolishing
Authors: Chang Shih-Chieh , Shieh Jia-Min , Fang Jeng-Yu , Wang Ying-Lang , Dai Bau-Tong , Feng Ming-Shiann
Published: February 2004

We investigated the effect of film stress, hardness, and grain size of copper films on copper electropolishing, which was considered as a next-generation technique in copper multilevel interconnects. The copper electropolishing rate was found to increase with an increase in the tensile stress of copper films. It was suggested that the tensile stress weakened metallic bonds between copper atoms and assisted the copper electropolishing rate, whereas the hardness and grain size of polished copper films did not relate directly to the copper electropolishing rate due to a negligible etching effect and no mechanical stress applied during copper electropolishing in a concentrated phosphoric acid electrolyte.
Properties of Fe-doped semi-insulating GaN structures
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Pearton S. J.
Published: February 2004

The properties of semi-insulating GaN films with the lower part of the film doped with Fe are reported. The 300 K sheet resistivity of the films was 2×1010 Ω/square with an activation energy of the dark conductivity of 0.5 eV. The Fermi level is also pinned at EC−0.5 eV. The concentration of the 0.5 eV traps in the Fe-doped portion of the films was 3×1016 cm−3. Also present is a high concentration of deeper electron traps with the level near 0.9 eV below the bottom of the conduction band and of hole traps with the level near 0.9 eV above the top of the valence band. Intracenter transitions of the Fe3+ center are observed in the photoluminescence spectra from the material.
Development of multiple As delta layer Si reference thin film for shallow junction secondary ion mass spectrometry profiling
Authors: Moon D. W. , Lee H. I. , Kim H. K. , Kim K. J. , Shon H. K. , Won J. Y. , Lee J. C. , Toujou F.
Published: February 2004

To meet the demand for shallow junction secondary ion mass spectrometry (SIMS) profiling, the surface transient Si sputtering effect should be corrected in addition to the improvement of depth resolution. With low-energy grazing incident ions, the SIMS depth resolution can be improved better than 1 nm. For the correction of the surface transient effect, we report that multiple As delta-layer Si thin films characterized with high-resolution transmission electron microscopy and medium-energy ion scattering spectroscopy can be used as a reference thin film. With the reference thin films, the depth scale shift in the surface transient region can be calibrated under each analysis condition. For low-energy Cs+ ion bombardment, the average Si sputtering yield in the surface 5 nm layer can be 70% higher than that in the steady state, which corresponds to a depth scale shift of 2.0 nm to the shallower direction.
Accurate in depth profiling of As and P shallow implants by secondary ion mass spectroscopy
Authors: de Chambost E. , Merkulov A. , Schuhmacher M. , Peres P.
Published: February 2004

The challenge for secondary ion mass spectroscopy is to accurately measure the profile shape for low-energy implants within the first few nanometers as well as to precisely determine the junction depth in the structure after any thermal treatment. Even if knowledge of the exact profile shape is not required for dose measurement, this information becomes essential for process modeling. This article presents results on the accurate determination in depth distribution of shallow As and P implants in Si. Sub-keV impact energy is investigated for O2+ and Cs+ primary ions. An in situ laser interferometer providing a real-time record of the sputter rate is used for the depth scale calibration. Fundamental and instrumental effects limiting the depth resolution, the sensitivity, and the accuracy are discussed.
Improvement of resolution in x-ray lithography by reducing secondary electron blur
Authors: Kise K. , Watanabe H. , Itoga K. , Sumitani H. , Amemiya M.
Published: February 2004

In x-ray lithography, the energy deposition mechanism of secondary electrons generated in the resist and Si substrate is investigated. By reducing resist thickness, the secondary electron blur is reduced because secondary electrons with high energy exit the resist before depositing energy in the lateral direction. Resolution is improved using a thin Cl-containing resist, especially in wavelengths shorter than the K-shell absorption edge of Cl atoms. The secondary electron blur in the wavelength region from 2.5 to 4.0 Å decreases using a 40-nm-thick Cl-containing resist with a bottom layer. By using an x ray in this wavelength region, the 35 nm line-and-space pattern can be resolved at a gap of 10 μm. A higher quality resist pattern can be obtained by increasing the Cl contents in the resist.
Vinyl ethers in ultraviolet curable formulations for step and flash imprint lithography
Authors: Kim E. K. , Stacey N. A. , Smith B. J. , Dickey M. D. , Johnson S. C. , Trinque B. C. , Willson C. G.
Published: February 2004

Until now, acrylates have been the monomers of choice for use for step and flash imprint lithography (SFIL) etch barrier formulations, in part because of the commercial availability of silicon-containing acrylates (necessary for etch resistance), together with their low viscosities and capability for rapid photopolymerization. However, despite many desirable properties, the polymerization of acrylates via radical chain propagation causes some potential issues in the SFIL process as a result of the inhibition of these processes by oxygen. Vinyl ethers are prime candidates to replace acrylates. Their curing proceeds by a cationic mechanism, which is insensitive to oxygen and very rapid, while the vinyl ether group contribution to viscosity is significantly lower than that of an acrylate, silicon-containing vinyl ethers are not widely commercially available, and so were synthesized for this study. As expected, formulations based on these vinyl ethers were lower viscosity and faster curing than the acrylate etch barrier formulations presently employed, while the tensile strength of cured vinyl ether formulations were found to be higher than their acrylate counterparts. In spite of about twice higher template separation force compared with acrylates, the tensile strength of vinyl ether etch barrier formulations is about five times higher than that of acrylate formulations. Therefore, these vinyl ether-based formulations were used to pattern down to 50 nm features using the SFIL process.
Optimized lift-off technique for deposition of high-quality Ti strip on LiNbO3 crystal
Authors: Zhang De-Long , Wong W. H. , Pun E. Y. B.
Published: February 2004

An optimized lift-off technique for deposition of Ti strips onto Z- or X-cut LiNbO3 crystal surfaces is proposed by comparing several pretreatments on the Ti-sputtered substrate before carrying out the lift-off procedure. The best result is obtained for the pretreatment of preserving the Ti-sputtered substrate in a container at a temperature of 50–90 °C for a duration of several hours. Such a pretreatment can strengthen the adhesion of the Ti metal onto the crystal surface to some extent and hence allow the definition of high-quality Ti strips. The experimental results also revealed that the adhesive force of Ti metal onto the crystal surface depends on the cut version of the crystal.
Combination lithography for photonic-crystal circuits
Authors: Schneider Garrett J. , Murakowski Janusz , Venkataraman Sriram , Prather Dennis W.
Published: February 2004

We propose and demonstrate a process for fabricating large-area photonic-crystal slabs with designed defects. The process takes advantage of a property we have observed in certain photoresists. These resists, which under ultraviolet illumination exhibit positive tone, behave as negative resists under electron-beam exposure. Electron-beam exposure is used first to expose defect structures, which renders them insensitive to further exposure. Subsequently, a large area is exposed with a photonic-crystal structure consisting of a regular pattern of holes defined by the interference between several ultraviolet laser beams. Upon chemical developing, a large photonic-crystal region with local patterned defects is created in the resist. The patterned resist is used as an etch mask for etching a slab of high-refractive-index material. In this article, we describe the fabrication process and present fabricated structures.
Investigation of two-dimensional diffusion of the self-interstitials in crystalline silicon at 800 °C and at room temperature
Authors: Giannazzo F. , Mirabella S. , Priolo F. , Goghero D. , Raineri V.
Published: February 2004

The two-dimensional (2D) diffusion of self-interstitials (I) in crystalline Si, both at room temperature and at 800 °C, has been studied by quantitative scanning capacitance microscopy measurements. The 2D I emission from an I source laterally confined down to submicrometer dimensions, obtained by low-energy implantation through a patterned oxide mask, has been observed. At room temperature, I diffusion was monitored by measuring the electrical deactivation of B corresponding to the diffusing interstitial tail and it was demonstrated that this deactivation is due to compensating levels introduced by defects in the Si band gap. At 800 °C I diffusion was monitored by measuring the transient enhanced diffusion of B spikes due to interstitial supersaturation produced during the annealing. In both cases, a dependence of the I depth-penetration on the original source size has been shown.
Optimization of secondary ion mass spectrometry ultra-shallow boron profiles using an oblique incidence O2+ beam
Authors: Giubertoni D. , Barozzi M. , Anderle M. , Bersani M.
Published: February 2004

The features of ultra-shallow junctions indicated by 2001 International Roadmaps require challenging characteristics for secondary ion mass spectrometry (SIMS) instruments: an ultra high depth resolution, minimization of transient width before the steady state and the ability to manage high concentration quantification in the near surface region. In this article a new magnetic sector SIMS, the Cameca Sc-Ultra, has been evaluated in order to profile boron ultra shallow junctions. In this apparatus the use of normal incidence oxygen bombardment is precluded and the primary column allows for a ⩾60° nominal incidence angle. Several approaches varying analytical parameters as energy, incidence angle and oxygen flooding have been tested on boron delta layers samples. In this way a quantitative comparison of different analytical methodologies is possible and the better analytical approach is pointed out. Moreover, an in situ laser depth profile measurement tool has been tested and the advantages and limitation are shown. The minimum impact energy used is 0.5 keV, but the instrument performance can be further improved by using lower impact energy (300 eV), a rotating stage to minimize surface roughness, and a primary column with a nominal angle of 30°. SIMS depth profiles on technological samples have been also carried out and shown.
Electrical and optical properties of hydrogen plasma treated n-AlGaN films grown by hydride vapor phase epitaxy
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Pashkova N. V. , Shlensky A. A. , Baik K. H. , Pearton S. J. , Luo B. , Ren F. , Zavada J. M.
Published: February 2004

Electrical and optical properties and deep level spectra of undoped n-AlGaN films with Al contents of about 40% grown on sapphire by hydride vapor phase epitaxy were studied before and after hydrogenation. The electrical properties prior to hydrogenation are shown to be dominated by deep donors with an activation energy of 0.25 eV and concentration of ∼1018 cm−3. Other deep traps include centers with activation energy of 0.12, 0.3, and 0.45 eV detected by photoinduced current transient spectroscopy and defects giving rise to defect bands near 2.3 and 3.7 eV in microcathodoluminescence spectra. Hydrogen plasma treatment at 250 °C for 0.5 h allows introduction of high concentrations of hydrogen down to a depth of about 0.1 μm and leads to strong suppression of all defects in that region.
Milling of submicron channels on gold layer using double charged arsenic ion beam
Authors: Tseng Ampere A. , Insua Ivan A. , Park Jong S. , Li Bo , Vakanas George P.
Published: February 2004

The capability of using a focused ion beam (FIB) for milling of submicron channel structures on a gold layer is investigated. A double-charged arsenic (As2+) FIB is adopted to assess the effect of the dwell time on the final profiles of the milled structures. A single-pass milling, which creates relatively shallow microchannels, is conducted in order to estimate the corresponding milling yields. The condition to provide a uniform ion flux in milling is first studied. The procedure on conducting the milling experiment is then presented. The atomic force microscope (AFM) is applied for measuring the profiles of the milled channels. Based on the AFM measurements, the milling yields have been estimated and compared with the sputtering yields predicted by a more sophisticated numerical simulation. The milling yield for the relatively shallow microchannels presently considered has been discovered to be roughly equal to the predicted normal-incidence sputtering yield. Consistence has also been found as the present findings have been compared with other channel milling studies, which had used different ion beams and target materials. FIB milling has been shown to be an effective tool for making submicron channels in gold layers.
Characteristics of TaSixNy thin films as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices
Authors: Suh You-Seok , Heuss Greg , Misra Veena
Published: February 2004

Reactively sputtered TaSixNy films have been investigated as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices. The as-deposited TaSixNy films were amorphous over a wide range of compositions. After annealing at 1000 °C, Ta30Si33N37 film became crystalline, however Ta26Si28N52 film remained amorphous. The x-ray photoelectron spectroscopy shows a significant increase of Si–N bonding in the TaSixNy films with increasing N content. The presence of Si–N bonds is attributed to cause the amorphous nature of the high N containing TaSixNy films. The work functions of TaSixNy films were extracted by capacitance–voltage analysis. The work function values for TaSixNy films with varying N contents range from 4.26 to 4.35 eV after forming gas annealing at 400 °C for 30 min, suggesting that TaSixNy films have work functions appropriate for n-type metal-oxide-semiconductor devices. However, it was observed, after 1000 °C anneals, that the work function of TaSixNy films increased to ∼4.8 eV. We believe that the mechanism that causes the work function to increase is the formation of a Ta-disilicide layer at the interface of the electrode and the dielectric. Current–voltage characteristics of the TaSixNy gates showed lower gate leakage compared to the TaSix gates, due to the retarding formation of an interface layer in the TaSixNy/SiO2/p-Si structures.
Fabrication and characterization of a monolithic thin-film edge emitter device with zinc–oxide–tungsten-based thin-film phosphor
Authors: Bhatia Vasuda , Karpov Leonid K. , Weichold Mark H.
Published: February 2004

Advanced applications, such as space and geophysical exploration, medical and military applications, transportation and communications industries, and the goal of hang-on-the-wall television and computer monitors, have driven display technology toward a rapid advancement and development of the flat panel display (FPD) industry. Displays based on the principles of field emission have been regarded as a technology with a potential of replacing cathode ray tubes (CRTs) and liquid crystal displays. A field-emission display (FED) combines the best performance of a CRT in a configuration of a FPD because a FED offers high-power efficiency, high brightness and resolution, wide viewing angles, light weight, tolerance to temperature changes, and instant-on operation. However, commercial application of FEDs has been delayed because of the complex submicron processing involved in the fabrication of microtips for the cathode, early failure of cathodes due to sputter damage from uncontrolled emission current or current runoff, nonavailability of blue phosphors operating in low-voltage regimes, and lack of optimum sealing conditions. This article summarizes the development of a monochromatic monolithic thin-film edge emitter (MT-FEE) device while implementing a thin-film blue-light-emitting phosphor of zinc oxide and tungsten (ZnO:W). The device design reported here overcomes some of the above mentioned drawbacks of conventional FED designs. Performance of the MT-FEE devices was judged by controlling key parameters associated with the technology. Several test structures were fabricated by varying the dielectric, separating anode and cathode lines, in a range of 3–6 μm with emitter configurations as either saw-tooth or rectangular wedges to establish performance of the devices. Stable emission current of an approximate value of 200 nA per pixel was obtained at 300 V for 3 μm devices. Blue light was visible to the naked eye from several excited pixels in the 3 μm devices at voltages as low as 270 V.
Secondary ion mass spectrometry characterization of source/drain junctions for strained silicon channel metal–oxide–semiconductor field-effect transistors
Authors: Duda Erika , Lu Shifeng , Liu Chun-Li , Jiang Zhixiong , Lerma Joe , Barr Alex , Thean Aaron , Orlowski Marius , White Ted , Nguyen Bich-Yen
Published: February 2004

As complementary metal–oxide–semiconductor (CMOS) devices approach the sub-100-nm dimensions in accordance with Moore’s Law, several major technical barriers exist with the formation of ultrashallow junctions. Strained silicon CMOS devices have the advantages of higher carrier mobility and high current drive. The use of silicon germanium substrates for strain in the silicon channel presents many challenges for CMOS integration including maintaining the channel strain and effect on shallow source/drain (SD) junctions. Low energy secondary ion mass spectrometry (SIMS) has been used to study boron and arsenic diffusion behavior in strained silicon and in SiGe. In addition, diffusion of germanium from the relaxed SiGe into the strained silicon layer will be discussed in relationship with SD implant and annealing. SIMS experimental results will also be compared to theoretical simulation results.
Self-annealing effect of electrolessly deposited copper thin films based on Co(II)–ethylenediamine as a reducing agent
Authors: Lee Chang Hwa , Kim Jae Jeong
Published: February 2004

A study on the self-annealing of electrolessly deposited copper films on blanket TiN wafers was carried out for different thicknesses. Decrease of 60%–90% in the sheet resistances of 100–260 nm thick copper films was observed after self-annealing. Changes in the copper films’ microstructure were also investigated, including the enhancement of their (111) orientation and grain growth. The pinning of chlorine was found to be influential for self-annealing and Pd activation for electroless deposition played an important role in self-annealing as to microstructural dislocations and defects. In addition, the thinner copper film was more affected by self-annealing. After deposition at room temperature, elevated temperatures accelerated self-annealing and caused decreases in resistivities. The resistivity of a 260 nm thick copper was reduced to 1.7 μΩ cm at 70 °C.
Local excitation of surface plasmon in structured Au films by atomic force anodic oxidation
Authors: Kim Jeongyong , Kim JunHo , Park Kang-Ho
Published: February 2004

We used a near field scanning optical microscopy (NSOM) to locally excite and detect surface plasmon (SP) in structured Au films by a consecutive process of anodic oxidation of atomic force microscope (AFM) and Au deposition process. Different types of interference patterns with the period close to a half of SP wavelength around and on the array of Au line protrusions are observed in NSOM optical transmission images, depending on the polarization direction of the incident light, which suggests a successful excitation of SP on fabricated nanostructures. The NSOM probes are believed to be somewhat coated with Au during the scans, and these probes are found to be more efficient in exciting SP than uncoated probes. Our result shows that NSOM combined with the AFM anodic oxidation technique provides an efficient and inexpensive method to study the SP excitation on metallic nanostructures.
X-ray and secondary ion mass spectrometry investigation of activation behavior of self-preamorphized silicon substrate
Authors: Suvkhanov Agajan , Mirabedini Mohammad , Hornback Verne , Chen Zhihao
Published: February 2004

The junctions for p-type source/drain and extensions for sub-100 nm technology nodes can be formed by using low energy beamline implantation, plasma doping, or elevated source/drain approaches in conjunction with various thermal processing methods. An important objective for sub-100 nm junction engineering is incorporation and activation of desired level of dopant in the junction region. In this article, the interaction between Si preamorphization implantation and boron implantation has been investigated by using secondary ion mass spectrometry (SIMS), triple crystal x-ray diffraction (XRD), and four point probe measurements. The dopant profile abruptness is found to be a function of boron energy and the Si+ ion dose and energy. Results demonstrate that an increase in Si energy by 10 keV yields ∼100 Å shallower and more abrupt boron profiles. Crystallinity of the implanted layer after thermal treatment has been characterized by the triple crystal XRD technique. The XRD rocking curve data correlated well with Rs and the SIMS measurements indicating lattice damage recovery and dopant activation.
Two-dimensional dopant profiling of ultrashallow junction with off-axis electron holography: A round robin experiment
Authors: Frost B. G. , Thesen A. , Joy D. C. , Foran Brendan , Brand Karin
Published: February 2004

We briefly describe the basics of electron holography, the hologram formation, as well as its acquisition and reconstruction. Our test sample requires a holographic field of view in the medium magnification range of about 20–30 k×. Two of the microscopes (Philips) utilized for this Round Robin experiment feature a Lorentz lens for medium magnification whereas the third one (Hitachi) requires a special lens current setting in its free lens control mode. The phase images from electron holograms reveal potential differences caused by active dopants. The comparison between the phase images reconstructed from our test holograms taken with the different microscopes show excellent agreement.
Actinic mask metrology for extreme ultraviolet lithography
Authors: Kinoshita H. , Haga T. , Hamamoto K. , Takada S. , Kazui N. , Kakunai S. , Tsubakino H. , Shoki T. , Endo M. , Watanabe T.
Published: February 2004

A new actinic mask inspection system has been developed, and simulations were carried out on its imaging performance. Preliminary experiments using the extreme ultraviolet (EUV) microscope developed at NTT have shown that it can resolve 250- and 350-nm-wide lines (on a mask). Furthermore, the type of absorber material used in a mask was found to have some effect on the contrast of mask images taken by EUVM. Our results demonstrate that an at-wavelength microscope is a powerful and useful tool for evaluating mask fabrication processes for EUVL.
Electron beam prebunching in planar cold cathodes with surface current carrying thin films
Authors: Krishnan R. , Cahay M.
Published: February 2004

Electron beam prebunching by direct modulation of the electron current density emitted into vacuum is one of the potential advantages of cold cathodes. We develop a small alternating current signal equivalent circuit of planar cold cathode with negative electron affinity and current carrying thin films at the surface. For a specific InP/CdS/LaS cold cathode, device parameters and biasing conditions are found leading to large (60%) cathode current modulation at a frequency well within the K band.
Dry cleaning technique for particle removal based on gas-flow and down-flow plasma
Authors: Momonoi Yoshinori , Yokogawa Kenetsu , Izawa Masaru
Published: February 2004

A dry-cleaning technique—consisting of down-flow plasma and utilizing gas-flow viscosity—has been developed. This technique is expected to be used for particle cleaning during semiconductor manufacturing. Particles are removed by both the chemical effects of the plasma and the mechanical effects of the viscous friction of the gas flow. Regarding the mechanical effects, the viscous friction is increased by narrowing the gas-flow space along the wafer surface. As for chemical effects, fluorine radical relaxes the adhesion force of particles on the silicon wafer. It has been experimentally found that the removal efficiency of Al2O3 particles on a Si wafer is 98% in 60 s and the etching depth of polysilicon is 0.17 nm. It has been also found that the technique causes no charge-buildup damage.
TGF-ß Signaling in Fibroblasts Modulates the Oncogenic Potential of Adjacent Epithelia
Authors: Bhowmick Neil A. , Chytil Anna , Plieth David , Gorska Agnieszka E. , Dumont Nancy , Shappell Scott , Washington M. Kay , Neilson Eric G. , Moses Harold L.
Published: February 2004

Stromal cells can have a significant impact on the carcinogenic process in adjacent epithelia. The role of transforming growth factor–β (TGF-β) signaling in such epithelial-mesenchymal interactions was determined by conditional inactivation of the TGF-β type II receptor gene in mouse fibroblasts (

Tgfbr2
fspKO

). The loss of TGF-β responsiveness in fibroblasts resulted in intraepithelial neoplasia in prostate and invasive squamous cell carcinoma of the forestomach, both associated with an increased abundance of stromal cells. Activation of paracrine hepatocyte growth factor (HGF) signaling was identified as one possible mechanism for stimulation of epithelial proliferation. Thus, TGF-β signaling in fibroblasts modulates the growth and oncogenic potential of adjacent epithelia in selected tissues.
Genome-Wide RNAi Analysis of Growth and Viability in
Drosophila
Cells
Authors: Boutros Michael , Kiger Amy A. , Armknecht Susan , Kerr Kim , Hild Marc , Koch Britta , Haas Stefan A. , Consortium Heidelberg Fly Array , Paro Renato , Perrimon Norbert
Published: February 2004

A crucial aim upon completion of whole genome sequences is the functional analysis of all predicted genes. We have applied a high-throughput RNA-interference (RNAi) screen of 19,470 double-stranded (ds) RNAs in cultured cells to characterize the function of nearly all (91%) predicted
Drosophila
genes in cell growth and viability. We found 438 dsRNAs that identified essential genes, among which 80% lacked mutant alleles. A quantitative assay of cell number was applied to identify genes of known and uncharacterized functions. In particular, we demonstrate a role for the homolog of a mammalian acute myeloid leukemia gene (
AML1
) in cell survival. Such a systematic screen for cell phenotypes, such as cell viability, can thus be effective in characterizing functionally related genes on a genome-wide scale.
Probing Two-Electron Dynamics of an Atom
Authors: Pisharody S. N. , Jones R. R.
Published: February 2004

Coherent short-pulse laser excitation has been used to control the approximate energy and relative proximity of two valence electrons within the same alkaline-earth atom, thereby providing insight into the dynamical evolution of a three-body Coulomb system. Our time-domain experiments enable direct experimental study of the electron dynamics at the classical limit of a two-electron atom. As an example, we look at the mechanism of autoionization for one two-electron configuration class and find that the doubly excited atom decays through a single violent electron-electron collision rather than a gradual exchange of energy between the electrons.
Superlattices of Iron Nanocubes Synthesized from Fe[N(SiMe
3
)
2
]
2
Authors: Dumestre Frédéric , Chaudret Bruno , Amiens Catherine , Renaud Philippe , Fejes Peter
Published: February 2004

The reaction of the metal-organic precursor Fe[N(SiMe
3
)
2
]
2
with H
2
in the presence of a long-chain acid and a long-chain amine in various proportions produces monodisperse zerovalent iron nanoparticles. These Fe particles display magnetic properties that match those of bulk iron as evidenced by magnetic and Mössbauer measurements. The nanoparticles adopt a cubic shape with edges of 7 nanometers and are incorporated into extended crystalline superlattices containing nanocubes in close proximity and with their crystallographic axes aligned. These superlattices are formed in solution, precipitate in high yield, and may be redissolved and redeposited as two-dimensional arrays.
Cubic AgPb

m

SbTe
2+

m

: Bulk Thermoelectric Materials with High Figure of Merit
Authors: Hsu Kuei Fang , Loo Sim , Guo Fu , Chen Wei , Dyck Jeffrey S. , Uher Ctirad , Hogan Tim , Polychroniadis E. K. , Kanatzidis Mercouri G.
Published: February 2004

The conversion of heat to electricity by thermoelectric devices may play a key role in the future for energy production and utilization. However, in order to meet that role, more efficient thermoelectric materials are needed that are suitable for high-temperature applications. We show that the material system AgPb

m

SbTe
2+

m

may be suitable for this purpose. With
m
= 10 and 18 and doped appropriately,
n
-type semiconductors can be produced that exhibit a high thermoelectric figure of merit material
ZT
max
of ∼2.2 at 800 kelvin. In the temperature range 600 to 900 kelvin, the AgPb

m

SbTe
2+

m

material is expected to outperform all reported bulk thermoelectrics, thereby earmarking it as a material system for potential use in efficient thermoelectric power generation from heat sources.
Role of Microbes in the Smectite-to-Illite Reaction
Authors: Kim Jinwook , Dong Hailiang , Seabaugh Jennifer , Newell Steven W. , Eberl Dennis D.
Published: February 2004

Temperature, pressure, and time have been thought to control the smectite-to-illite (S-I) reaction, an important diagenetic process used for petroleum exploration. We demonstrated that microorganisms can promote the S-I reaction by dissolving smectite through reduction of structural Fe(III) at room temperature and 1atmosphere within 14 days. This reaction typically requires conditions of 300° to 350°C, 100 megapascals, and 4 to 5 months in the absence of microbial activity. These results challenge the conventional concept of the S-I reaction and of reaction kinetic models.
A Broad Look at Tree-Building
Authors: Ronquist Fredrik
Published: February 2004

Inferring Phylogenies
. by Joseph Felsenstein. Sinauer, Sunderland, MA, 2004. 684 pp. Paper, $59.95, £33.99, €48.87. ISBN 0-87893-177-5.

In a work that can serve both as a text and a reference, Felsenstein explains the assumptions and logic that underlie the reconstruction and use of evolutionary trees.
Uses and Abuses of Mathematics in Biology
Authors: May Robert M.
Published: February 2004

In the physical sciences, mathematical theory and experimental investigation have always marched together. Mathematics has been less intrusive in the life sciences, possibly because they have until recently been largely descriptive, lacking the invariance principles and fundamental natural constants of physics. Increasingly in recent decades, however, mathematics has become pervasive in biology, taking many different forms: statistics in experimental design; pattern seeking in bioinformatics; models in evolution, ecology, and epidemiology; and much else. I offer an opinionated overview of such uses—and abuses.
NEUTRON CHARGE RADIUS: RELATIVISTIC EFFECTS AND THE FOLDY TERM
Authors: DE ARAÚJO W. R. B. , FREDERICO T. , BEYER M. , WEBER H. J.
Published: February 2004

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.
ENERGY DISTRIBUTION IN 2D STRINGY BLACK HOLE BACKGROUNDS
Authors: VAGENAS ELIAS C.
Published: February 2004

We utilize Møller's and Einstein's energy–momentum complexes in order to explicitly evaluate the energy distributions associated with the two-dimensional "Schwarzschild" and "Reissner–Nordström" black hole backgrounds. While Møller's prescription provides meaningful physical results, Einstein's prescription fails to do so in the aforementioned gravitational backgrounds. These results hold for all two-dimensional static black hole geometries. The results obtained within this context are exploited in order that Seifert's hypothesis would be investigated.
TEST PARTICLES BEHAVIOR IN THE FRAMEWORK OF A LAGRANGIAN GEOMETRIC THEORY WITH PROPAGATING TORSION
Authors: APREA G. , MONTANI G. , RUFFINI R.
Published: February 2004

Working in the Lagrangian framework, we develop a geometric theory in vacuum with propagating torsion; the antisymmetric and trace parts of the torsion tensor, considered as derived from local potential fields, are taken and, using the minimal action principle, their field equations are calculated. Actually these will show themselves to be just equations for propagating waves giving torsion a behavior similar to that of metric which, as known, propagates through gravitational waves. Then we establish a principle of minimal substitution to derive test particles equation of motion, obtaining, as result, that they move along autoparallels. We then calculate the analogous of the geodesic deviation for these trajectories and analyze their behavior in the nonrelativistic limit, showing that the torsion trace potential ϕ has a phenomenology which is indistinguishable from that of the gravitational newtonian field; in this way we also give a reason for why there have never been evidence for it.
Decreasing size of cardiogenic oscillations reflects decreasing compliance of the respiratory system during long-term ventilation
Authors: Lichtwarck-Aschoff Michael , Suki Bela , Hedlund Anders , Sjöstrand Ulf H. , Markström Agneta , Kawati Rafael , Hedenstierna Göran , Guttmann Josef
Published: February 2004

Part of the energy produced by the heartbeat is transferred to the lung and promotes intrapulmonary gas mixing. It is likely that this transmission in the form of local mechanical disturbances affects and reflects respiratory mechanics. The effects of the cardiogenic oscillations were studied in seven piglets during 7 h of monotonous mechanical ventilation. During the 1st h of ventilation, every heartbeat triggered a noticeable transient increase in lung volume of 14 ml (95% confidence interval = 10-17 ml). After 7 h, the increase in lung volume due to heartbeat significantly decreased to 7 ml (95% confidence interval = 2-9 ml, P < 0.05). During the course of ventilation, overall lung compliance and gas exchange were progressively compromised. We conclude that 1) sufficient mechanical energy is transferred from the beating heart to the lung to increase lung volume, and 2) the ability of the heartbeats to help increase lung volume is reduced during long-term ventilation, which reflects the changes in lung compliance.
Contribution of airway closure to chronic postbronchiolitis airway dysfunction in rats
Authors: Sorkness Ronald L. , Tuffaha Amjad
Published: February 2004

Genetically susceptible Brown Norway rats develop a chronic asthmalike syndrome after recovering from viral bronchiolitis at an early age. We hypothesized that airway closure is an important mechanism of airflow obstruction in postbronchiolitis rats. Rats were studied 8–12 wk after inoculation with Sendai virus or sterile vehicle at 3–4 wk of age. Under light pentobarbital anesthesia, rats were instrumented with an orotracheal catheter and an esophageal pressure monitor and placed in a total body plethysmograph. Lung volumes and forced-expiratory maneuvers were measured using the Boyle's law method and software-controlled valving of positive and negative pressures to elicit lung inflations and rapid deflations; pulmonary resistance was measured during spontaneous tidal breathing; and quasi-static pressure-volume curves were obtained with passive inflations and deflations in fully anesthetized, paralyzed rats. Compared with controls, the postbronchiolitis rats had elevated pulmonary resistance and reduced forced-expiratory volume in 0.2 s. Most of the reduced forced-expiratory volume in 0.2 s was associated with reduced forced vital capacity, indicating premature airway closure as a prominent mechanism. The reduced airflow in postbronchiolitis rats was highly dependent on lung volume, being nearly normal at 70% lung capacity, but sevenfold less than normal at 30% lung capacity. Increased respiratory system hysteresis between functional reserve capacity and total lung capacity was evidence for increased airway closure at normal end-expiratory lung volumes in postbronchiolitis rats. We conclude that airway instability and closure is a prominent mechanism of the chronic airway dysfunction in rats that have recovered from viral bronchiolitis at an early age.
Improved running economy in elite runners after 20 days of simulated moderate-altitude exposure
Authors: Saunders P. U. , Telford R. D. , Pyne D. B. , Cunningham R. B. , Gore C. J. , Hahn A. G. , Hawley J. A.
Published: February 2004

To investigate the effect of altitude exposure on running economy (RE), 22 elite distance runners [maximal O2 consumption (V̇o2) 72.8 ± 4.4 ml·kg-1·min-1; training volume 128 ± 27 km/wk], who were homogenous for maximal V̇o2 and training, were assigned to one of three groups: live high (simulated altitude of 2,000–3,100 m)-train low (LHTL; natural altitude of 600 m), live moderate-train moderate (LMTM; natural altitude of 1,500–2,000 m), or live low-train low (LLTL; natural altitude of 600 m) for a period of 20 days. RE was assessed during three submaximal treadmill runs at 14, 16, and 18 km/h before and at the completion of each intervention. V̇o2, minute ventilation (V̇e), respiratory exchange ratio, heart rate, and blood lactate concentration were determined during the final 60 s of each run, whereas hemoglobin mass (Hbmass) was measured on a separate occasion. All testing was performed under normoxic conditions at ∼600 m. V̇o2 (l/min) averaged across the three submaximal running speeds was 3.3% lower ( P = 0.005) after LHTL compared with either LMTM or LLTL. V̇e, respiratory exchange ratio, heart rate, and Hbmass were not significantly different after the three interventions. There was no evidence of an increase in lactate concentration after the LHTL intervention, suggesting that the lower aerobic cost of running was not attributable to an increased anaerobic energy contribution. Furthermore, the improved RE could not be explained by a decrease in V̇e or by preferential use of carbohydrate as a metabolic substrate, nor was it related to any change in Hbmass. We conclude that 20 days of LHTL at simulated altitude improved the RE of elite distance runners.