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Top 20 Most Read Articles
September 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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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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Possibility of constructing microwave antenna with carbon nanotubes J. Vac. Sci. Technol. B 25, 1630 (2007); http://dx.doi.org/10.1116/1.2778691 (5 pages) Online Publication Date: 10 September 2007
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The distribution of electrons on a carbon nanotube (CNT) under microwave excitation is analyzed here. Numerical results demonstrate that electrons on CNTs are oscillating under the microwave excitation, which means that the electrons can radiate microwaves with the same frequency. The length of CNTs required for microwave radiation is estimated. Both results reveal that it is possible to construct a microwave antenna with carbon nanotubes or nanotube arrays.
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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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Etching mechanisms of HfO2, SiO2, and poly-Si substrates in BCl3 plasmas J. Vac. Sci. Technol. B 25, 1640 (2007); http://dx.doi.org/10.1116/1.2781550 (7 pages) Online Publication Date: 12 September 2007
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BCl3 based plasmas exhibit promising plasma chemistries to etch high-k materials and, in particular, HfO2, with a high selectivity over SiO2 and Si substrates. The authors report on the mechanisms involved in the etching of HfO2, SiO2, and poly-Si substrates in BCl3 plasmas. X-ray photoelectron spectroscopy analyses help in understanding the mechanism driving the high etch selectivity between HfO2 and silicon-containing substrates. The ion energy plays an important role in the etching mechanisms since it controls a transition between a BCl-like deposition on the substrate and its etching by ionic bombardment. The ion energy threshold above which etching occurs is different from one substrate to another, being lower for HfO2 than for Si substrates. Indeed, BClx deposition forms more easily on poly-Si or SiO2 rather than on HfO2 surfaces, because boron reacts with Si atoms to form Si–B bonds initiating the growth of BClx polymer on Si-containing surfaces, while on HfO2 surfaces, boron is directly involved in the etching and reacts with oxygen to form volatile BOCl etch products.
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Structure shape and stability of nanometric sized particles J. Vac. Sci. Technol. B 19, 1091 (2001); http://dx.doi.org/10.1116/1.1387089 (13 pages)
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Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distributions of single atom energy for every cluster are displayed in order to reveal the effect of surface on the stability of different types and sizes of clusters. We discuss the structure of the particles from ∼1 to ∼100 nm. The mechanisms for stress release as the particles grow larger are reviewed and a mechanism is suggested. Finally, we discuss the parameters that define the shape of a nanoparticle and the possible implications in technological applications. © 2001 American Vacuum Society. |
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Interpretation of atomic friction experiments based on atomistic simulations J. Vac. Sci. Technol. B 25, 1547 (2007); http://dx.doi.org/10.1116/1.2770743 (7 pages) Online Publication Date: 13 August 2007
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Atomic stick-slip experiments on the KBr(100) surface are analyzed using classical zero temperature atomistic simulations. Three different tip models exhibiting atomic stick-slip movement are studied in comparison with the experimental data and the Tomlinson model. The implications of a compliant tip apex for the stick-slip process and the dissipation pathways are discussed.
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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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UV nanoimprint materials: Surface energies, residual layers, and imprint quality J. Vac. Sci. Technol. B 25, 785 (2007); http://dx.doi.org/10.1116/1.2732742 (6 pages) Online Publication Date: 27 April 2007
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UV nanoimprint lithography is attracting more and more interest, because it has the potential of becoming a high-resolution, low-cost patterning technique. The availability of suitable UV curing materials is mandatory for successful imprinting. Within this work, a systematic investigation of commercially available photocuring materials was conducted to provide an overview of the properties of these materials. Their wetting behavior with respect to different substrate surfaces was characterized and their surface tensions were determined from their contact angles against two specifically selected solid surfaces: This method is presented here for the first time. The adhesion properties of the UV curing materials to different substrate surfaces and to the mold were investigated and necessary curing times were estimated. Additionally, the dependence of the residual layer thickness on the viscosity and the initial dispensed volume of UV curing materials was analyzed. It was found that the resist formulation of the UV curing materials strongly influences the surface tension as well as the adhesion to different substrate surfaces. Furthermore, the experiments verified that the thickness of the residual layer for UV curing materials increases with the square root of their viscosity which is predicted by theory. To demonstrate the suitability of the UV curing materials, first imprints with the prototype imprint tool, Nano Patterning Stepper 300 from Süss MicroTec, with pattern sizes down to 50 nm are shown.
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J. Vac. Sci. Technol. B 25, 1593 (2007); http://dx.doi.org/10.1116/1.2769360 (10 pages) Online Publication Date: 17 August 2007
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Blanket films of ultralow dielectric constant (ULK) materials and 193 nm photoresist films have been processed downstream from hydrogen and deuterium-based discharges produced using an inductively coupled plasma reactor. Photoresist ashing rates and ULK modifications have been determined as a function of process parameters. The explored ULK materials differed widely in porosity and carbon content. The effect of processing time, substrate temperature (200–300 °C), and gas composition on the surface and bulk chemical composition of ULK materials was monitored and quantified by ex situ ellipsometry and time-of-flight secondary ion mass spectrometry (SIMS). The stripping rates of 193 nm photoresist films were found to strongly depend on processing temperature and only weakly on the nature of the H2/additive gas mixture. The authors found that hydrogen (or deuterium) fully penetrates the high porosity ULK layer, whereas for low porosity materials, such penetration is limited to a 50 nm near-surface region. SIMS measurements also reveal that H2 (D2) diffusion into carbon-rich ULK layers can cause substantial carbon depletion throughout the penetration region. ULK damage values increase with temperature and injection of gas additives such as argon, helium, and nitrogen to H2 or D2 process gases. For each ULK material, the amount of damage depends on the gas mixing ratio; in general, high percentages of nitrogen in H2/N2 (or D2/N2) mixtures cause the most damage. Overall, the results demonstrate that ULK ashing damage depends strongly on both ULK material properties and H2-based plasma process parameters. In addition, the authors observed in this work a kinetic isotope effect for stripping of 193 nm photoresist films in H2/D2/N2-based discharges. For given ashing process conditions, the photoresist ashing rate decreases by a factor of 1.414 (or square root of 2) in D2 plasma compared to H2 plasma. This can be explained by the influence of the H or D mass on the chemical reaction rate through a change in the frequency of nuclear vibrations of the reacting atoms. The presence of the kinetic isotope effect for gas mixtures provides unambiguous evidence of the rate-limiting role of atomic hydrogen in the fundamental etching reaction. Simultaneously processed ULK materials showed minor film thickness changes (<10 nm) in H2 or D2 discharges, and the ULK damage level does not reflect a kinetic isotope effect. Therefore the H/D isotope effect can be used to separate H2/D2 associated ashing and etching processes from other chemistries or mechanisms.
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Carbon nanotube tip melting with vacuum breakdown in cold cathode J. Vac. Sci. Technol. B 25, 1584 (2007); http://dx.doi.org/10.1116/1.2770744 (4 pages) Online Publication Date: 16 August 2007
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Failure of patterned multiwalled carbon nanotubes during field emission (FE) was systematically studied at different fields using an indigenous FE setup. Here, the findings are reported from the experimental observation of the degradation of carbon nanotube (CNT) based field emitters over a silicon substrate. The CNTs were grown on the patterned silicon substrate using chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) techniques. Scanning electron microscopy (SEM) was employed to observe the effect of different fields over CNTs. The observed current density of 28 mA/cm2 at a field of 5 V/μm from CNTs grown via CVD before giving a high-field treatment remained almost the same until the substrate started melting. Similar observations were made in CNTs grown via PECVD. SEM images clearly reveal that the high-field treatment resulted in melting of silicon substrate at a certain point; at some other points, etching of silicon substrate was also observed. The authors attribute these observations to arcing because the base vacuum was not sufficiently adequate for the applied field. Due to arcing, the localized temperature became so high that the substrate started to melt. The SEM images give an insight into understanding the degradation mechanism of CNT-based field emitters.
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Optimized fabrication of silicon nanofocusing x-ray lenses using deep reactive ion etching J. Vac. Sci. Technol. B 25, 1626 (2007); http://dx.doi.org/10.1116/1.2769361 (4 pages) Online Publication Date: 6 September 2007
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The authors describe an improved production route for silicon nanofocusing lenses for hard x rays using e-beam lithography and deep reactive ion etching. As compared to previous prototypes, these optics have a significantly improved from fidelity, reducing spherical aberrations. Close to an ideal performance for the focusing of hard x rays is achieved with these optics, reaching a lateral beam size of about 50 nm. The lens profile is checked by scanning electron microscopy.
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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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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, 1569 (2007); http://dx.doi.org/10.1116/1.2768605 (5 pages) Online Publication Date: 15 August 2007
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The authors report the fabrication and characterization of a 4.5 in. field emission display (FED) prototype. The FED prototype consists of 14×14 matrix addressable pixels. The pixel is 5 mm in diameter. The characteristics including current-voltage properties, current stability, brightness, and image quality of the display prototype were characterized. The average static brightness of the display prototype is 2500 cd/m2. Characters were displayed in a scanning pulsed driving mode. The adjacent pixels are tangent to each other, making continuous display feature. The results show that the FED prototype has promising potential for high-resolution giant display application.
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Fabrication of magnetic force microscopy probes via localized electrochemical deposition of cobalt J. Vac. Sci. Technol. B 25, L39 (2007); http://dx.doi.org/10.1116/1.2766935 (4 pages) Online Publication Date: 10 August 2007
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Magnetic force microscopy probes were obtained via the solution phase electrochemical deposition of cobalt nanostructures at the probe apexes. Single tips were fabricated in an atomic force microscope fluid cell. Multiple tips were produced in a single batch with an alternating potential in an electrochemical cell. The probes achieve 50 nm spatial resolution.
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Growth of silicon nanowires via gold/silane vapor–liquid–solid reaction J. Vac. Sci. Technol. B 15, 554 (1997); http://dx.doi.org/10.1116/1.589291 (4 pages)
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Silicon nanowires (whiskers) have been grown on Si(111) via the vapor–liquid–solid (VLS) reaction using silane as the Si source gas and Au as the mediating solvent. The silane partial pressure and temperature ranges were 0.01–1 Torr and 320–600 °C, respectively. Growth at high partial pressure and low temperature leads to the growth of Si nanowires as thin as 10 nm. These wires are single crystals but exhibit growth defects such as bending and kinking. Lowering the silane partial pressure leads to an increase in the wire width and a reduction in the tendency to form growth defects. At low pressure, 40–100 nm wide well-formed wires have been grown at 520 °C. The VLS reaction using silane allows the growth of Si wires, which are significantly thinner than those grown previously using SiCl4. © 1997 American Vacuum Society. |
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Optical improvement of photonic devices fabricated by Ga+ focused ion beam micromachining J. Vac. Sci. Technol. B 25, 1609 (2007); http://dx.doi.org/10.1116/1.2770741 (6 pages) Online Publication Date: 24 August 2007
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The authors propose a novel post-focused-ion-beam (FIB) treatment method to improve the optical properties of photonic devices fabricated by the Ga+ FIB technique on the silicon substrate with low temperature liquid annealing process. A conventional micrometric ridge waveguide is first fabricated and then annealed to roughly detect the improvement of its optical properties. Then a nanometric 12-fold photonic quasicrystal waveguide is designed to further study its topography variation as well as the subtle influence on its optical properties with different post-FIB treatments. By comparing the experimental results with the theoretical results that are made by means of the three-dimensional finite-difference time-domain method, the authors find that the proposed low temperature liquid annealing method can efficiently improve the optical properties of photonic devices by decreasing Ga+ contamination, removing redeposited Si–SiO2 composites, and restoring damaged silicon lattice structures caused by Ga+ bombardment in the FIB micromachining.
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Dependence of the quality factor of micromachined silicon beam resonators on pressure and geometry J. Vac. Sci. Technol. B 10, 19 (1992); http://dx.doi.org/10.1116/1.586300 (8 pages)
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An experimental study of damping and frequency of vibrating small cantilever beams in their lowest eigenstate is presented. The cantilever beams are fabricated from monocrystalline silicon by means of micromachining methods. Their size is a few millimeters in length, a few 100 μm in width, and a few 10 μm in thickness. Damping and resonance frequency are studied as a function of the ambient pressure p (1–105 Pa) and the geometry of the beam. The purpose of this research was to obtain design rules for sensors employing vibrating beams. The analysis of the experimental results in terms of a semiqualitative model reveals that one can distinguish three mechanisms for the pressure dependence of the damping: viscous, molecular, and intrinsic. For viscous damping a turbulent boundary layer dominates the damping at high pressures (≊105 Pa), while at smaller pressure laminar flow dominates. In the latter region, this leads to a plateau for the quality factor Q and in the former to Q α √p. The pressure pc at which the transition from laminar flow dominated damping to turbulent flow dominated damping occurs depends on the geometry of the beams. pc is independent on the length and decreases with both, the width and the thickness of the beams. |
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Band gap narrowing of ZnO:N films by varying rf sputtering power in O2/N2 mixtures J. Vac. Sci. Technol. B 25, L23 (2007); http://dx.doi.org/10.1116/1.2746053 (4 pages) Online Publication Date: 13 June 2007
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Band gap narrowing of N-incorporated ZnO (ZnO:N) was achieved by reactive rf magnetron sputtering in O2/N2 mixture ambient. ZnO:N films with various band gaps were realized by varying N concentration, which was controlled successfully by varying the rf powers. When rf power was increased to 200 W, the ZnO:N films exhibited optical band gaps similar to that of Zn3N2 films. Calculations based on first-principles density-functional theory revealed that the band gap narrowing is caused by the mixing of shallower N 2p states with the valence band of ZnO.
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