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Top 20 Most Read Articles
January 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Electron projection lithography tool development status J. Vac. Sci. Technol. B 20, 2622 (2002); http://dx.doi.org/10.1116/1.1520576 (5 pages) Online Publication Date: 9 December 2002
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In the development of an electron beam projection lithography (EPL) tool, the most important tasks are to develop the high-speed vacuum stage system, reliable vacuum body system, and total control system. Nikon has a long history of over 22 years in precision stage development for its optical lithography tools as well as over 10 years in electron beam (EB) instrument development such as the EB 60 with NTT. Recently, optical lithography stages have been developed based on air bearing and linear motor technologies. It is desirable and of minimum risk to utilize those technologies for the EPL system in order to shorten the total time period of development, but the requirements for the EB stage, body, and system control are much different from their optical counterparts and much more difficult. In this article development and implementation of the EPL vacuum stage system, vacuum body system, vacuum loader system, and control system are discussed and overviewed. © 2002 American Vacuum Society. |
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Band offsets of wide-band-gap oxides and implications for future electronic devices J. Vac. Sci. Technol. B 18, 1785 (2000); http://dx.doi.org/10.1116/1.591472 (7 pages)
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Wide-band-gap oxides such as SrTiO3 are shown to be critical tests of theories of Schottky barrier heights based on metal-induced gap states and charge neutrality levels. This theory is reviewed and used to calculate the Schottky barrier heights and band offsets for many important high dielectric constant oxides on Pt and Si. Good agreement with experiment is found for barrier heights. The band offsets for electrons on Si are found to be small for many key oxides such as SrTiO3 and Ta2O5 which limit their utility as gate oxides in future silicon field effect transistors. The calculations are extended to screen other proposed oxides such as BaZrO3. ZrO2, HfO2, La2O3, Y2O3, HfSiO4, and ZrSiO4. Predictions are also given for barrier heights of the ferroelectric oxides Pb1−xZrxTiO3 and SrBi2Ta2O9 which are used in nonvolatile memories. © 2000 American Vacuum Society. |
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Fabrication of high-resolution multiwall carbon nanotube field-emission cathodes at room temperature J. Vac. Sci. Technol. B 25, 106 (2007); http://dx.doi.org/10.1116/1.2402150 (3 pages) Online Publication Date: 4 January 2007
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Patterned films of multiwall carbon nanotubes (MWCNTs) were fabricated by the “wet” deposition of MWCNT dispersion on a patterned substrate. Films in the form of stripes or lattices of micrometer dimensions and variable thickness were obtained. The films were uniform and adhered strongly to the substrates. Field-emission property of the MWCNT film was investigated. The method can be used at room temperature for the assembly and integration of MWCNTs in the fabrication of nanodevices, including field-emission displays.
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Recent advances in processing of ZnO J. Vac. Sci. Technol. B 22, 932 (2004); http://dx.doi.org/10.1116/1.1714985 (17 pages) Online Publication Date: 26 April 2004
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A review is given of recent results in developing improved fabrication processes for ZnO devices with the possible application to UV light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices. There is also interest in integrating ZnO with other wide band-gap semiconductors, such as the AlInGaN system. In this article, we summarize recent progress in controlling n- and p-type doping, materials processing methods, such as ion implantation for doping or isolation, Ohmic and Schottky contact formation, plasma etching, the role of hydrogen in the background n-type conductivity of many ZnO films, and finally, the recent achievement of room-temperature ferromagnetism in transition-metal (Mn or Co)-doped ZnO. This may lead to another class of spintronic devices, in which the spin of the carriers is exploited rather than the charge as in more conventional structures. © 2004 American Vacuum Society. |
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J. Vac. Sci. Technol. B 25, 43 (2007); http://dx.doi.org/10.1116/1.2404682 (4 pages) Online Publication Date: 29 December 2006
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Experimental results of static and dynamic characteristics for single-layer hole-only devices based on copper phthalcyanine (CuPc) and pentacene are observed in this article. The contribution to injection currents from electrode has been investigated by varying the thickness of the organic film. From the observation of current density versus bias voltage (J-V) characteristics, it is concluded that the space-charge-limited conductivity is the dominant transport mechanism for the organic Schottky diodes. Accordingly, an increase of the organic layer thickness will increase the trapping energy level. However, even with the thin CuPc film down to 50 nm, the dynamic cut-off frequency of the device is still limited to 150 Hz. Low hole mobility and large active area of the device are responsible for the phenomenon. Dramatic enhancement of cut-off frequency up to 11 kHz can be obtained for the pentacene-based Schottky diodes.
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J. Vac. Sci. Technol. B 10, 1237 (1992); http://dx.doi.org/10.1116/1.585897 (30 pages)
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The status of research on both wurtzite and zinc‐blende GaN, AlN, and InN and their alloys is reviewed including exciting recent results. Attention is paid to the crystal growth techniques, structural, optical, and electrical properties of GaN, AlN, InN, and their alloys. The various theoretical results for each material are summarized. We also describe the performance of several device structures which have been demonstrated in these materials. Near‐term goals and critical areas in need of further research in the III–V nitride material system are identified. |
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Low-stress silicon carbonitride for the machining of high-frequency nanomechanical resonators J. Vac. Sci. Technol. B 25, 33 (2007); http://dx.doi.org/10.1116/1.2402153 (5 pages) Online Publication Date: 29 December 2006
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The synthesis of silicon carbonitride by low-temperature plasma-enhanced chemical vapor deposition and the machining of nanomechanical resonators in this material are reported. Films with thickness of 1 μm, 200 nm, and 50 nm were deposited using ammonia, nitrogen, and diethylsilane as precursors. X-ray photoelectron spectroscopy indicated that usage of higher NH3:DES gas flow ratios results in higher nitrogen and low carbon contents in the deposited films. In addition, annealing of the material enabled the full tunability of its residual stress from the compressive to the tensile range. Infrared spectroscopy indicated that desorption of incorporated hydrogen was responsible for those changes. Assaying of resonant cantilevers fabricated from 200-nm-thick films yielded root-modulus-over-density values as high as √(E/ρ) = 8.35×103 m/s, comparable to those of silicon. Doubly clamped beams were also fabricated from 50-nm-thick films of low (σ = 80 MPa) and high (σ = 220 MPa) tensile stresses. Beam resonators fabricated in the lower stress material showed resonance qualities ranging between 3000 and 5000, and resonant frequencies between f = 6.1 MHz and f = 16 MHz. Beam resonators machined in the higher stress material experienced quality factors between 8000 and 23 000 and frequencies between f = 7.6 and 24 MHz. These values correspond to fQ products as high as of 1.5×1011 s−1, exceeding the performance of previously reported silicon resonators.
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J. Vac. Sci. Technol. B 25, 21 (2007); http://dx.doi.org/10.1116/1.2402151 (8 pages) Online Publication Date: 28 December 2006
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A cryogenic etch process using low temperature (T ⩽ −100 °C) and SF6 and O2 gases is presented for fabricating high aspect ratio silicon microstructures, including photonic devices and micro- and nanoelectromechanical systems. The process requires only a single electron beam resist mask and results in open area etch rates of 4 μm/min. Various etch process parameters, including O2 flow, rf forward power, substrate temperature, and chamber pressure were studied, and the resulting effect on the etch quality was evaluated in terms of sidewall verticality and surface roughness. The optimized process uses low temperature (T = −110 °C) and low chamber pressure (P = 7 mTorr) and enables sidewall verticality greater than 89.5° with roughness of 1–10 nm. A silicon etch selectivity of 26:1 was obtained for 380 nm thick electron beam resist. Using the optimized process, a silicon-on-insulator Fabry-Pérot optical cavity with integrated rib waveguides and deeply etched silicon/air distributed Bragg reflector mirrors was fabricated and tested. The device exhibits sharp resonance peaks with full width at half maximum Δλ = 0.45 nm, free-spectral range of 26 nm, finesse F = 58, and quality factor Q = 3400 (at λ0 = 1531.6 nm). The optical measurements and extracted mirror reflectance (R ≈ 95%) confirm the high quality of our optimized etch process.
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J. Vac. Sci. Technol. B 25, L1 (2007); http://dx.doi.org/10.1116/1.2401613 (4 pages) Online Publication Date: 4 January 2007
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A microdeposition technique based on focused ion beam (FIB) sputtering has been developed to overcome the problems of ion radiation damage and high impurity concentration found in metal contacts deposited by FIB-induced deposition from organometallic gas. This damage-free technique is most useful for making metal electrodes onto nonplanar samples such as micron-sized single crystals and nanowires. To demonstrate the capability, four Au wires were connected to an ∼ 200 μm NbSe2 single crystal, and its resistivity versus temperature characteristics were measured. This FIB sputtering microdeposition method with micron-scale spatial resolution can be employed for the deposition of any material.
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J. Vac. Sci. Technol. B 21, 2231 (2003); http://dx.doi.org/10.1116/1.1622676 (31 pages) Online Publication Date: 3 November 2003
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Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication. © 2003 American Vacuum Society. |
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J. Vac. Sci. Technol. B 25, 17 (2007); http://dx.doi.org/10.1116/1.2402144 (4 pages) Online Publication Date: 28 December 2006
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Octadecyltrimethoxysilane (OTMS) self-assembled monolayers have been grafted on micrometric and nanometric areas of SiO2/Si substrates using a process combining nanoimprint lithography and atmospheric chemical vapor deposition. The optimization of the process has lead to monolayer square patterns of OTMS with lateral sizes ranging from 2 μm down to 50 nm. Their coverage uniformity extends on several square millimeters. Their coverage density can be accurately tuned by the deposition time.
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Mechanism of solid-liquid-solid on the silicon oxide nanowire growth J. Vac. Sci. Technol. B 24, 613 (2006); http://dx.doi.org/10.1116/1.2172953 (5 pages) Online Publication Date: 21 February 2006
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The solid-liquid-solid growth mechanism of synthesizing SiOx nanowires is expressed in detail through analyzing the structure and composition of the catalysts and the nanowires. The silicon source for growing nanowires was directly provided from the silicon wafer. A thin catalyst layer of platinum ( ∼ 5 nm) was first deposited on the silicon wafer by sputtering. The platinum film collapsed into dots with diameter about hundreds of nanometers during the thermal process. These dots transformed into crystalline platinum silicide (Pt3Si) and served as nucleation seeds for the silicon oxide nanowire growth. Due to the high process temperature ( ∼ 1100 °C) and long duration time ( ∼ 5 h), the silicon wafer transformed into amorphous silicon oxides and melted into the Pt3Si catalyst dots until supersaturated to form SiOx nanowires. Such nanowires are amorphous and have an average diameter of about 40–60 nm and length of several hundreds of micrometers.
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Photon-beam lithography reaches 12.5 nm half-pitch resolution J. Vac. Sci. Technol. B 25, 91 (2007); http://dx.doi.org/10.1116/1.2401612 (5 pages) Online Publication Date: 3 January 2007
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We have printed dense line/space patterns with half-pitches as small as 12.5 nm in a negative-tone calixarene resist using extreme ultraviolet (EUV) interference lithography. The EUV interference setup which is based on transmission diffraction gratings is illuminated with spatially coherent radiation from a synchrotron source. The results show the extendibility of EUV lithography to printing features measuring less than 15 nm in size. We discuss the potential impact of effects such as photoelectron blur and shot noise in high-resolution EUV lithography.
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Nanofabrication by scanning probe microscope lithography: A review J. Vac. Sci. Technol. B 23, 877 (2005); http://dx.doi.org/10.1116/1.1926293 (18 pages) Online Publication Date: 19 May 2005
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In addition to its well-known capabilities in imaging and spectroscopy, scanning probe microscopy (SPM) has recently shown great potentials for patterning of material structures in nanoscales. It has drawn the attention of not only the scientific community, but also the industry. This article examines various applications of SPM in modification, deposition, removal, and manipulation of materials for nanoscale fabrication. The SPM-based nanofabrication involves two basic technologies: scanning tunneling microscopy and atomic force microscopy. Major techniques related to these two technologies are evaluated with emphasis on their abilities, efficiencies, and reliabilities to make nanostructures. The principle and specific approach underlying each technique are presented; the differences and uniqueness among these techniques are subsequently discussed. Finally, concluding remarks are provided where the strength and weakness of the techniques studied are summarized and the scopes for technology improvement and future research are recommended.
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J. Vac. Sci. Technol. B 25, 74 (2007); http://dx.doi.org/10.1116/1.2406064 (8 pages) Online Publication Date: 2 January 2007
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A gated single carbon nanotube field emitter with magnetic focusing is proposed and simulated using a parallelized Poisson’s equation solver, coupled with the ray tracing of electrons, on an unstructured tetrahedral adaptive mesh. The magnetic focusing for the electrons can be achieved by a vertically downward magnetic focusing field (−Bz) through the use of either external solenoids or permanent magnets around the field-emission array. The simulation results, assuming uniform magnetic field inside a field-emission unit, are compared with those conventional tetrode-type field emitters using an electrostatic focusing structure. The results reveal that the magnetic focusing design can promise much higher emission current, while a much smaller spot size results at the anode. In addition, the magnitude of the applied gate voltage in the range of 60–120 V shows little influence on the electron-beam diameter at the anode. The proposed magnetic focusing method can also possibly reduce the complexity of the fabrication without the electrostatic focusing structure. Noticeably, a distribution, similar to the Airy function, is obtained that shows the dependence of the spot size at the anode on the magnetic flux intensity. Thus, under suitable magnetic focusing conditions, it is possible to produce well-defined microelectron sources for many field-emission applications, such as novel parallel electron-beam lithography or field-emission displays.
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Sub-10 nm imprint lithography and applications J. Vac. Sci. Technol. B 15, 2897 (1997); http://dx.doi.org/10.1116/1.589752 (8 pages)
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New developments, further details, and applications of imprint lithography are presented. Arrays of 10 nm diameter and 40 nm period holes were imprinted not only in polymethylmethacrylate (PMMA) on silicon, but also in PMMA on gold substrates. The smallest hole diameter imprinted in PMMA is 6 nm. All the PMMA patterns were transferred to a metal using a liftoff. In addition, PMMA mesa’s of a size from 45 nm to 50 μm were obtained in a single imprint. Moreover, imprint lithography was used to fabricate the silicon quantum dot, wire, and ring transistors, which showed the same behavior as those fabricated using electron (e)-beam lithography. Finally, imprint lithography was used to fabricate nanocompact disks with 10 nm features and 400 Gbits/in.2 data density—near three orders of magnitude higher than current critical dimensions (CDs). A silicon scanning probe was used to read back the data successfully. The study of wear indicates that due to the ultrasmall force in tapping mode, both the nano-CD and the scanning probe will not show noticeable wear after a large number of scans. © 1997 American Vacuum Society. |
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Effects of SiO2/Si3N4 hard masks on etching properties of metal gates J. Vac. Sci. Technol. B 24, 2689 (2006); http://dx.doi.org/10.1116/1.2382950 (6 pages) Online Publication Date: 9 November 2006
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Reduced etching rates of advanced metal gates (TaN, TiN, and HfN) using SiO2/Si3N4 hard masks are observed in Cl2 plasma. Si and O released from hard masks react with metal surfaces newly exposed to the plasma during the etching, thereby forming metal oxides. The metal oxides formed on the etched surface retard the etch rates. The suppression of etch rates with hard mask is more obvious for TiN than for TaN and HfN, because Ti oxides are readily formed on the etched TiN surface due to their low Gibbs free energies of formation. The surface of TiN degrades with etching time with SiO2 mask, because etching rates of Si oxides and Ti oxides are different in the (TiO2)1−x(SiO2)x residues remaining on the etched surface. In contrast, a conventional poly-Si electrode does not show the mask effects on etch rates and surface roughness.
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Precise positioning of single-walled carbon nanotubes by ac dielectrophoresis J. Vac. Sci. Technol. B 24, 3173 (2006); http://dx.doi.org/10.1116/1.2387155 (6 pages) Online Publication Date: 4 December 2006
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The precise placement of single-walled carbon nanotubes (SWCNTs) in device architectures by ac dielectrophoresis involves the optimization of the electrode geometry, applied voltage and frequency, load resistance, and type of nanotube sample used. The authors have developed a toolkit to controllably integrate SWCNTs in device structures by the use of floating potential metal posts and appropriate electrode geometries, as designed using electric field simulations, and used it to fabricate structures such as crossed nanotube junctions.
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J. Vac. Sci. Technol. B 25, 102 (2007); http://dx.doi.org/10.1116/1.2426976 (4 pages) Online Publication Date: 3 January 2007
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The authors report on the realization of an enhanced process protocol for producing sub-20 nm wide lines with extremely narrow pitches in electron beam resist using a low temperature development process. Linewidths ranging from 10 to 50 nm with a pitch range of 40–250 nm have been fabricated on 8 in. silicon wafers, using a JEOL JBX 6000 FS/E electron beam lithography tool at 50 kV accelerating voltage. ZEP-520A (Nippon Zeon) resist, a nonchemically amplified positive electron beam resist was employed for this effort due to its dry-etch resistance and high-resolution characteristics. The development of the ZEP-520A resist in ZED-N50 developer (Nippon Zeon) has been characterized and optimized for both low and room temperature developer conditions. In addition, standard reactive ion etch technologies have been utilized in conjunction with the low temperature developed ZEP-520A patterns to produce 10 nm range gratings in polysilicon substrates with aspect ratios of 10:1. These gratings are intended for evaluation by angle-dependent and wavelength-dependent optical scatterometry methods for critical dimension measurements. The authors report on the preliminary etch optimization as well as advanced inductively coupled plasma etch characteristics of the pattern transfer.
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Real-time sensing and metrology for atomic layer deposition processes and manufacturing J. Vac. Sci. Technol. B 25, 130 (2007); http://dx.doi.org/10.1116/1.2429672 (10 pages) Online Publication Date: 9 January 2007
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In situ quadrupole mass spectrometry (QMS) has been integrated to an atomic layer deposition (ALD) reactor to achieve real-time chemical diagnostic and wafer-state metrology. The process investigated was tungsten ALD using WF6 and SiH4. The UHV-based substrate-heated ALD reactor incorporated a minireactor chamber to simulate the small reaction volume anticipated for manufacturing tools in order to achieve adequate throughput. Mass spectrometry revealed essential surface reaction dynamics through real-time signals associated with by-product generation as well as reactant introduction and depletion for each ALD half-cycle. The by-product QMS signal was then integrated in real time over each exposure and plotted against process cycle number to directly observe ALD film growth, leading to two valuable metrologies. First, the integrated by-product QMS value changes with cycle number, directly reflecting the nucleation kinetics. Specifically, QMS values increase with cycle number during the nucleation phase and then saturates as the film growth enters its steady-state growth phase. Second, summing the integrated by-product QMS signals over an entire deposition run provides an immediate measure of film thickness. The growth kinetics as measured by QMS is consistent with ex situ film characterization and is strongly dependent on process conditions and reactor chamber status. In the latter case, a clear first wafer effect was apparent when the system was left idle for a few hours, resulting in an apparent QMS signal difference during nucleation phase between the first wafer and nonfirst wafer cases. The dependence of QMS signals on chamber status is attributed to parallel reactions on the chamber wall, where different gas exposure history is encountered. The first wafer effect can be explained in a quantitative manner by considering the chamber wall as an additional wafer inside the ALD reactor. The first wafer effects can be reduced by proper preprocess treatment, and the linear correlation between QMS measurement and film thickness suggests a promising start for QMS-based ALD film thickness metrology.
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