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Top 20 Most Read Articles
April 2012
The 20 articles with the most full-text downloads during the month, in descending order.
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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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Die singulation technologies for advanced packaging: A critical review J. Vac. Sci. Technol. B 30, 040801 (2012); http://dx.doi.org/10.1116/1.3700230 (27 pages) Online Publication Date: 6 April 2012
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Die singulation, also known as wafer dicing, is reviewed in terms of the brief history, critical challenges, characterization of singulation quality, different singulation technologies and underlying mechanisms, and post-singulation die strength enhancement. Mechanical blade dicing has been the workhorse of die separation in the semiconductor manufacturing process. It faces growing challenges due to the adoption of copper/low-k dielectric interconnect structures, thin and ultra-thin wafers, die attach films, narrow dicing streets, and complex stacked structures on the dicing streets. Key dicing quality characteristics are chipping, delamination, kerf geometry, die side wall damage, die surface contamination, and die strength degradation. Various die singulation technologies have been developed to address these challenges and quality issues, including dicing by thinning, laser based approaches, laser and mechanical hybrid method, and plasma dicing. Die strength is a critical parameter for thin and ultra-thin dies. Post-dicing die strength enhancement is becoming the complement of most dicing technologies to achieve dies with high fracture strength. Plasma dicing has the potential to achieve much higher die strengths than all the other dicing approaches.
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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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Nanoimprint lithography: An old story in modern times? A review J. Vac. Sci. Technol. B 26, 458 (2008); http://dx.doi.org/10.1116/1.2890972 (23 pages) Online Publication Date: 27 March 2008
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Nanoimprint lithography (NIL) is a high throughput, high-resolution parallel patterning method in which a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate on wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. Therefore it is mainly aimed toward fields in which electron beam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. The aim of this review is to play between two poles: the need to establish standard processes and tools for research and industry, and the issues that make NIL a scientific endeavor. It is not the author’s intention to duplicate the content of the reviews already published, but to look on the NIL process as a whole. The author will also address some issues, which are not covered by the other reviews, e.g., the origin of NIL and the misconceptions, which sometimes dominate the debate about problems of NIL, and guide the reader to issues, which are often forgotten or overlooked.
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Recent developments and design challenges in continuous roller micro- and nanoimprinting J. Vac. Sci. Technol. B 30, 010801 (2012); http://dx.doi.org/10.1116/1.3661355 (28 pages) Online Publication Date: 1 December 2011
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As an emerging technology for the manufacture of micro- and nano-scale patterns, continuous imprinting; otherwise known as roll-to-roll or roller imprinting, is attracting interest from researchers around the world because of its inherent advantages of low cost, high throughput, large area patterning. This technology is an evolutionary advance on the more traditional nanoimprint lithography developed in the 1990s, which is considered a batch mode, or dis-continuous patterning approach. In recent years, a number of commercial applications have been discovered which require low cost, large area patterning, particularly displays, optical coatings and films, and biological applications such as anti-fouling surfaces and micro-fluidic devices. This review covers a variety of continuous imprinting approaches, highlights challenges, and surveys progress towards high speed production of micro- and nanoscale features for these applications and others using this platform technology.
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Secondary electron deposition mechanism of carbon contamination J. Vac. Sci. Technol. B 30, 030601 (2012); http://dx.doi.org/10.1116/1.3698602 (3 pages) Online Publication Date: 30 March 2012
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Deposition of a carbonaceous contaminant layer on surfaces exposed to radiation exceeding 7–10 eV is ubiquitous in many fields of research. The mechanism of this deposition process is still debated. A scanning transmission x-ray microscope has been used to create and interrogate carbonaceous deposits with photon energies spanning the C 1s ionization edge. For equal fluence, the rate of carbon deposition is proportional to the x-ray absorption spectrum of the deposited material. The results are consistent with a deposition mechanism involving secondary electrons. Implications of this measurement with regard to future generations of high volume photolithography are discussed.
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Fabrication and performance of graphene nanoelectromechanical systems J. Vac. Sci. Technol. B 29, 050801 (2011); http://dx.doi.org/10.1116/1.3623419 (10 pages) Online Publication Date: 9 September 2011
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As a result of the recent progress in fabricating large-area graphene sheets, graphene-based mechanical devices have become vastly easier to manufacture and now show even greater promise for a range of applications. This article reviews the progress of resonant graphene nanoelectromechanical systems and the possible applications of this technology to signal processing, sensing, and other areas. After discussing recent advances in fabrication and measurement techniques that make graphene resonators a viable technology, the article presents what is known about the performance of graphene mechanical systems. The authors also highlight unresolved questions, such as the source of the dissipation in graphene resonators, and discuss the progress made on these issues to date. The authors conclude with a discussion of important future directions for graphene research and the applications for which graphene nanomechanical devices may be well suited.
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Graphene functionalization and seeding for dielectric deposition and device integration J. Vac. Sci. Technol. B 30, 030801 (2012); http://dx.doi.org/10.1116/1.3693416 (21 pages) Online Publication Date: 19 March 2012
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Graphene has recently attracted wide-spread attention because of its unique transport and physical properties that are appealing for a wide range of electronic applications. Integration with scalable high-κ dielectrics is important for the realization of graphene-based top-gated electronic devices, including next generation THz applications. Atomic layer deposition (ALD), a low temperature deposition method based on two separate self-limiting surface reactions, is a preferred technique to achieve high-quality, conformal, ultrathin dielectric films with precise control of thickness and chemical composition at the atomic scale. Unfortunately, ALD of oxides on graphene is hindered by the inertness of the graphene surface. To alleviate this graphene-oxide incompatibility, several different functionalization and seeding methods have recently been developed to render the graphene more susceptible to the ALD process of high-κ dielectrics including: ozone, wet chemical and fluorine pretreatments, low-k polymer seed, e-beam metal, and oxide seed layers. The ability of each approach to enable conformal, uniform high-κ dielectrics on graphene while maintaining its inherent transport properties for low power, high-frequency device applications is discussed.
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Gas-assisted focused electron beam and ion beam processing and fabrication J. Vac. Sci. Technol. B 26, 1197 (2008); http://dx.doi.org/10.1116/1.2955728 (80 pages) Online Publication Date: 11 August 2008
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Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.
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UV capillary force lithography for multiscale structures J. Vac. Sci. Technol. B 30, 031601 (2012); http://dx.doi.org/10.1116/1.3696696 (4 pages) Online Publication Date: 23 March 2012
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Rapid advances in information technology rely on novel patterning techniques. The authors present a simple UV capillary force lithography process, which allows one to imprint a multiscale system, consisting of 250 nm wide nanobridges and a 8–20 μm wide wiring in one lithography step. An additional annealing step for 5 min at 75 °C improved the capillary rise.
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J. Vac. Sci. Technol. B 30, 033201 (2012); http://dx.doi.org/10.1116/1.3701977 (5 pages) Online Publication Date: 6 April 2012
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A custom double-lamella method is presented for electrochemically etching tungsten wire for use as tips in scanning tunneling microscopy (STM). For comparison, tips were also manufactured in-house using numerous conventional methods and examined using an optical microscope. Both sets of tips were used to obtain STM images of highly oriented pyrolytic graphite, the quality of which varied. The clarity of the STM images was found to be correlated to the optically measured cone angle of the STM tip, with larger cone angles consistently producing atomically resolved images. The custom etching procedure described allows one to create larger cone angles and consequently proved superior in reliably producing high-quality tips.
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Mechanical properties of suspended graphene sheets J. Vac. Sci. Technol. B 25, 2558 (2007); http://dx.doi.org/10.1116/1.2789446 (4 pages) Online Publication Date: 11 December 2007
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Using an atomic force microscope, we measured effective spring constants of stacks of graphene sheets (less than 5) suspended over photolithographically defined trenches in silicon dioxide. Measurements were made on layered graphene sheets of thicknesses between 2 and 8 nm, with measured spring constants scaling as expected with the dimensions of the suspended section, ranging from 1 to 5 N/m. When our data are fitted to a model for doubly clamped beams under tension, we extract a Young’s modulus of 0.5 TPa, compared to 1 TPa for bulk graphite along the basal plane, and tensions on the order of 10−7 N.
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Phase change memory technology J. Vac. Sci. Technol. B 28, 223 (2010); http://dx.doi.org/10.1116/1.3301579 (40 pages) Online Publication Date: 19 March 2010
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The authors survey the current state of phase change memory (PCM), a nonvolatile solid-state memory technology built around the large electrical contrast between the highly resistive amorphous and highly conductive crystalline states in so-called phase change materials. PCM technology has made rapid progress in a short time, having passed older technologies in terms of both sophisticated demonstrations of scaling to small device dimensions, as well as integrated large-array demonstrators with impressive retention, endurance, performance, and yield characteristics. They introduce the physics behind PCM technology, assess how its characteristics match up with various potential applications across the memory-storage hierarchy, and discuss its strengths including scalability and rapid switching speed. Challenges for the technology are addressed, including the design of PCM cells for low reset current, the need to control device-to-device variability, and undesirable changes in the phase change material that can be induced by the fabrication procedure. They then turn to issues related to operation of PCM devices, including retention, device-to-device thermal cross-talk, endurance, and bias-polarity effects. Several factors that can be expected to enhance PCM in the future are addressed, including multilevel cell technology for PCM (which offers higher density through the use of intermediate resistance states), the role of coding, and possible routes to an ultrahigh-density PCM technology.
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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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J. Vac. Sci. Technol. B 14, 4129 (1996); http://dx.doi.org/10.1116/1.588605 (5 pages)
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Nanoimprint lithography, a high‐throughput, low‐cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub‐10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum‐dot, quantum‐wire, and ring transistors. © 1996 American Vacuum Society |
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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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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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Characteristic comparison of AlGaN/GaN enhancement-mode HEMTs with CHF3 and CF4 surface treatment J. Vac. Sci. Technol. B 30, 021201 (2012); http://dx.doi.org/10.1116/1.3680115 (6 pages) Online Publication Date: 1 February 2012
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In this study, enhancement-mode (E-mode) AlGaN/GaN HEMTs that underwent CHF3 and CF4 plasma treatment beneath the gate metal were fabricated. These treatments were applied because, although previous studies have formed AlF3 compound layers after fluorine-based plasma treatment to suppress the polarization-induced charge density, the surface negative charges still influenced the device gate leakage current and trap density. In the device in this study, unlike in previous CF4 plasma-treated GaN E-mode devices, the hydrogen atoms of the CHF3 plasma were introduced to compensate for vacancies by donating an electron to a vacancy acceptor level, thereby reducing the number of vacancy induced traps. Based on the measured subthreshold slope (SS) and the effective interface state density (Dit) results, the SS value of a CHF3-treated HEMT was 80 mV/decade and the Dit was 1.23 × 1012 cm−2. Moreover, the CHF3-treated HEMT exhibited a current gain cut-off frequency, a maximum oscillation frequency, and an output power of 6.7, 26, and 14.8 dBm (302 mW/mm), respectively. The 1/f noise measurement results of the CHF3-treated HEMT indicated that the flicker noise-induced generation-recombination noise and gate leakage-induced generation-recombination noise were also improved. Therefore, the CHF3-treated HEMT has great potential for use in low-distortion power amplifiers and logic control circuits.
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Large area single photon detectors based on parallel configuration NbN nanowires J. Vac. Sci. Technol. B 30, 031204 (2012); http://dx.doi.org/10.1116/1.3699042 (5 pages) Online Publication Date: 3 April 2012
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The authors present superconducting single photon detectors (SSPDs) based on parallel nanostrips with an area up to 40 × 40 μm2. The SSPDs presented here are based on 100 nm wide ultrathin NbN nanostrips with a filling factor of 40%. The devices are fabricated by extending the standard electron beam lithography (EBL) patterning process to those densely structured large areas. By a thorough characterization it is shown that the electrical properties of the parallel SSPDs are comparable with those of smaller devices, as expected, proving in this way that the extended EBL process results in uniform nanostrips also in large area detectors. Furthermore, the estimated maximum count rate of the 40 × 40 μm2 parallel SSPDs was 33 MHz, showing that the parallel nanostrip configuration is much faster when compared with standard meandered serial SSPDs. The successful extension of parallel SSPDs to a large area coverage opens a new route to the use of such detectors also with multimode fibers.
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Reducing damage to Si substrates during gate etching processes by synchronous plasma pulsing J. Vac. Sci. Technol. B 28, 926 (2010); http://dx.doi.org/10.1116/1.3483165 (9 pages) Online Publication Date: 27 August 2010
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Plasma oxidation of the c-Si substrate through a very thin gate oxide layer can be observed during HBr/O2/Ar based plasma overetch steps of gate etch processes. This phenomenon generates the so-called silicon recess in the channel and source/drain regions of the transistors. In this work, the authors compare the silicon recess generated by continuous wave HBr/O2/Ar plasmas and synchronous pulsed HBr/O2/Ar plasmas. Thin SiO2 layers are exposed to continuous and pulsed HBr/O2/Ar plasmas, reproducing the overetch process conditions of a typical gate etch process. Using in situ ellipsometry and angle resolved X-ray photoelectron spectroscopy, the authors demonstrate that the oxidized layer which leads to silicon recess can be reduced from 4 to 0.8 nm by pulsing the plasma in synchronous mode.
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