bluuebunny/crossref_metadata_2025 huggingface dataset:
Endoscopic Criteria for Invasive Depth of Superficial Esophageal Cancer
Authors: MAKUUCHI Hiroyasu , SHIMADA Hideo , MIZUTANI Kyoichi , CHINO Osamu , KISE Yoshifumi , NISHI Takayuki , TANAKA Hikaru , MACHIMURA Takao , MITOMI Toshio , MIWA Takeshi , OSAMURA Yoshiyuki
Published: December 2007

Abstract: The therapeutic strategy for superficial esophageal cancer should be determined by the depth of invasion. Therefore, we endeavored to develop reliable criteria for endoscopic evaluation of the invasive depth of superficial esophageal cancer. Two hundred and fifty nine superficial squamous cell carcinoma cases were enrolled in this study, designed to investigate the relationship between endoscopic classification and the depth of invasion, and also between lesion size and depth of invasion. Almost all 0‐1, 0‐1+0‐llc, O‐llc+0‐lla and 0‐111 lesions invaded the submucosal layer, although 0‐lla and O‐llb lesions were limited to the mucosal layer. The 0‐llc type of lesion showed a wide range of invasive depths from M1 to SM3; in M1 cases with minimal depression the surface appears entirely smooth; in M2 cases the depressed surface is uniformly granular; and M3 cases have slightly larger granules. With submucosal cancer, the depressed surface showed some irregularity and variability in granule size. In the 0‐llc type, 100% of lesions under 10 mm and 80% of those under 30 mm in greatest dimension were mucosal cancer. The accuracy of our criteria for endo‐scopically evaluating the depth of invasion was 80.2%. The accuracy rate, in terms of assignment to group Ml and M2, M3 and SM1, or SM2 and SM3, was 90.6%.
Endoscopic Hemostasis in Patients with Dieulafoy Ulcer
Authors: FUKE Hirofumi , SAITO Kyoko , KAMEI Akira , WAKI Itcho , KOJIMA Yuji , HIGASHIYAMA Hirotaka , SATO Hyoe , TAKARADA Yoshihiro
Published: December 2007

Abstract:Dieulafoy ulcer was defined based on endoscopic findings as an ulcer (1) of 10 mm or less in diameter, (2) of grade Ul‐ll or less and (3) showing vascular protrusion in its floor. We evaluated the clinical background and endoscopic findings of Dieulafoy ulcer and studied the usefulness and problems of endoscopic hemostasis. Patients with Dieulafoy ulcer accounted for 8.7 % of 321 patients with diseases treated by endoscopic hemostasis excluding sclerotherapy. The patients were predominantly males, and their average age was 61 years. An association with other diseases was noted in 21 patients (75%). Therefore, more than 50 % of the patients were treated with NSAIDs such as aspirin. The most frequent site of this disease was the posterior wall of the upper gastric body. In particular, the ulcer was located in the superior duodenal angle. In six of the 28 patients, the ulcer and the exposed vessel were similar in size. Endoscopic hemostasis was successful in 25 patients (89%). Hemostasis was acheived by emergency surgery in two and by transcatheter arterial embolization (TAE) in one. No patient showed recurrence. Most Dieulafoy ulcers can be conservatively treated by endoscopic hemostasis. However, a few cases can not be managed conservatively and shock develops due to fatal massive bleeding. In such patients, the timing of TAE or surgery must be carefully considered.
Endoscopic Resection of Rectal Carcinoids Using Double Snare Polypectomy Technique
Authors: KOYAMA Nobuatsu , YOSHIDA Hatsuo , NIHEI Mitsuhiro , SAKONJI Mitsuaki , WACHI Eiko
Published: December 2007

Abstract: Between 1993 and 1997, 11 patients with rectal carcinoids less than 8 mm in diameter (mean size: 5.5 mm) were endoscopically treated at Tsuboi Hospital. Seven patients were treated by polypectomy or endoscopic mucosal resection. Three of the seven lesions were microscopically diagnosed as having positive submucosal margins. The remaining four showed a distance between the tumor and the resection line(DBTRL) of 0 to 0.33 mm. Then, we attempted endoscopic double snare polypectomy (EDSP) in 1996 and 1997. In four consecutive patients, the tumor was completely resected by this method. The DBTRL ranged from 0.08 to 0.75 mm in four lesions resected by EDSP. With endoscopic resection of these tumors, the incidence of positive margins is high using the conventional single snare methods, even when the lesions are less than 10 mm in diameter. EDSP was useful for total removal of small rectal carcinoids.
Perforating Veins in Recurrent Esophageal Varices after Endoscopic Therapy Visualized by Endoscopic Color Doppler Ultrasonography
Authors: SATO Takahiro , YAMAZAKI Katsu , TOYOTA Jouji , KARINO Yoshiyasu , OHMURA Takumi , SUGA Toshihiro
Published: December 2007

This study was designed to evaluate the detection rate and the direction of blood flow of perforating veins using endoscopic color Doppler ultrasonography (EC‐DUS) in cases of recurrent esophageal varices after endoscopic therapy with complete eradication. Perforating veins were defined as vessels communicating between esophageal varices and paraesophageal veins. The study involved thirty patients with recurrent esophageal varices who had been followed up for more than one year. Seven of them had high risk intramucosal venous dilatation (IMVD) of the esophagus, and 23 had F1 (small straight varices) red color (RC) positive varices. Color flow images of perforating veins were obtained in 18 patients (60.0%). The perforating veins were classified into three types according to flow direction. Type 1 had inflow from paraesophageal veins to esophageal varices, Type 2 had outflow type from esophageal varices to paraesophageal veins, and Type 3 was mixed, showing both inflow and outflow. Of the 18 patients in whom color flow images were obtained, 15 (83.3%) cases were Type 1, none were Type 2, and three (16.7%) were Type 3. All the color flow images in the perforating veins were demonstrated as a continuous wave. In conclusion, perforating veins can be detected at a high rate by ECDUS in cases of recurrent esophageal varices after endoscopic therapy with complete eradication. (Dig Endosc 1999; 11: 236–240)
Laparoscopic Gastrectomy for Early Gastric Cancer after Endoscopic Mucosal Resection
Authors: SHIRAISHI Norio , HAGINO Yoshiaki , YASUDA Kazuhiro , Bandoh Toshio , ADACHI Yosuke , KITANO Seigo
Published: December 2007

Abstract: In 1991, we first performed a simple technique of Iaparoscopy‐assisted Bill‐roth I gastrectomy for patients with mucosal gastric cancer. Endoscopic mucosal resection (EMR) sometimes fails to completely resect the early gastric cancer lesion, nor does it give full histopathology of the resected stomach. The aim of this study was to review the surgical and pathological findings of eight patients who underwent laparoscopic gastrectomy after EMR for early gastric cancer. Of 54 patients with early gastric cancer who were treated with laparoscopic gastrectomy between 1994 and 1998, eight patients underwent surgery after EMR. The resected margin of the EMR specimens was positive in three and suspicious in five; and three underwent laparoscopic wedge resection of the stomach, while five underwent Iaparoscopy‐assisted distal gastrectomy with regional lymph node dissection. All but one resected stomach had residual cancer tissue in the mucosa or submucosa, and three patients had multiple gastric cancers. The results indicated that remnant cancer tissue might be present when the resected margin of the EMR specimen was positive or suspicious. Partial resection or distal gastrectomy under laparoscopy is useful for such patients who have undergone EMR for early gastric cancer. (Dig Endooc 1999; 11:132–136)
Effects of High‐frequency Current on Pacemakers during Endoscopic Gastric Surgery: Experimental Study
Authors: SHIBATA Hil‐oshi , YANO Mituyasii , OKAHISA Toshiya , OKAMURA Seisuke , MUGURUMA Naoki , ITO Susumu
Published: December 2007

Abstract: This study examined the effects of high‐frequency current on pacemakers. Pacemakers were implanted in mongrel dogs, gastric mucosal resection was performed endoscopically using monopolar and bipolar snares, and the times for resection and magnitude of interference current (IC) in the myocardial electrodes were compared. The time for resection was 9.56±2.87 seconds with a monopolar snare and 0.82±0.13 seconds with a bipolar snare (p<0.01). The magnitude of the IC was 0.59±0.26 mV with a monopolar snare and 0.26±0.12 mV with a bipolar snare (p<0.01). The times required for resection and the magnitude of the IC using a bipolar snare in the coagulation mode at an output of approximately 12 W were 1.97±0.65 seconds and 0.03±0.02 mV, respectively, and those in the cutting mode were 1.68±0.50 seconds and 0.07±0.04 mV, respectively. The magnitude of the IC was significantly less (p<0.01), but the time required for resection was longer in the coagulation mode. No abnormalities were noted in the pacemaker mode in any of the 10 pacemakers examined after mucosal resection with high‐frequency current at an output of 300 W. These results suggest that endoscopic therapy using high‐frequency current can be performed more safely with a bipolar snare than with a monopolar snare in patients with pacemakers. In addition, the selection of the endoscope mode is considered to be important. (Dig Endosc 1999; 11: 150–157)
Modification of K+channel–drug interactions by ancillary subunits
Authors: Bett Glenna C. L. , Rasmusson Randall L.
Published: December 2007

Reconciling ion channel α‐subunit expression with native ionic currents and their pharmacological sensitivity in target organs has proved difficult. In native tissue, many K+channel α‐subunits co‐assemble with ancillary subunits, which can profoundly affect physiological parameters including gating kinetics and pharmacological interactions. In this review, we examine the link between voltage‐gated potassium ion channel pharmacology and the biophysics of ancillary subunits. We propose that ancillary subunits can modify the interaction between pore blockers and ion channels by three distinct mechanisms: changes in (1) binding site accessibility; (2) orientation of pore‐lining residues; (3) the ability of the channel to undergo post‐binding conformational changes. Each of these subunit‐induced changes has implications for gating, drug affinity and use dependence of their respective channel complexes. A single subunit may modulate its associated α‐subunit by more than one of these mechanisms. Voltage‐gated potassium channels are the site of action of many therapeutic drugs. In addition, potassium channels interact with drugs whose primary target is another channel, e.g. the calcium channel blocker nifedipine, the sodium channel blocker quinidine, etc. Even when K+channel block is the intended mode of action, block of related channels in non‐target organs, e.g. the heart, can result in major and potentially lethal side‐effects. Understanding factors that determine specificity, use dependence and other properties of K+channel drug binding are therefore of vital clinical importance. Ancillary subunits play a key role in determining these properties in native tissue, and so understanding channel–subunit interactions is vital to understanding clinical pharmacology.
Translational Joints With Clearance in Rigid Multibody Systems
Authors: Flores P. , Ambrósio J. , Claro J. C. P. , Lankarani H. M.
Published: December 2007

A computational methodology for dynamic description of rigid multibody systems with translational clearance joints is presented and discussed in this work. Over the past years, extensive work has been done to study the dynamic effect of the revolute joints with clearance in multibody systems, in contrast with the little work devoted to model translational joints with clearance. In a joint with translation clearance, there are many possible ways to set the physical configuration between the slider and guide, namely: (i) no contact between the two elements, (ii) one corner of the slider in contact with the guide surface, (iii) two adjacent slider corners in contact with the guide surface, and (iv) two opposite slider corners in contact with the guide surfaces. The proposed methodology takes into account these four different situations. The conditions for switching from one case to another depend on the system dynamics configuration. The existence of a clearance in a translational joint removes two kinematic constraints from a planar system and introduces two extra degrees of freedom in the system. Thus, a translational clearance joint does not constrain any degree of freedom of the mechanical system but it imposes some restrictions on the slider motion inside the guide limits. When the slider reaches the guide surfaces, an impact occurs and the dynamic response of the joint is modeled by contact-impact forces. These forces are evaluated here with continuous contact force law together with a dissipative friction force model. The contact-impact forces are introduced into the system’s equations of motion as external generalized forces. The proposed methodology is applied to a planar multibody mechanical system with a translational clearance joint in order to demonstrate its features.
Review of Classical Approaches for Constraint Enforcement in Multibody Systems
Authors: Laulusa André , Bauchau Olivier A.
Published: December 2007

A hallmark of multibody dynamics is that most formulations involve a number of constraints. Typically, when redundant generalized coordinates are used, equations of motion are simpler to derive but constraint equations are present. While the dynamic behavior of constrained systems is well understood, the numerical solution of the resulting equations, potentially of differential-algebraic nature, remains problematic. Many different approaches have been proposed over the years, all presenting advantages and drawbacks: The sheer number and variety of methods that have been proposed indicate the difficulty of the problem. A cursory survey of the literature reveals that the various methods fall within broad categories sharing common theoretical foundations. This paper summarizes the theoretical foundations to the enforcement in constraints in multibody dynamics problems. Next, methods based on the use of Lagrange’s equation of the first kind, which are index-3 differential-algebraic equations in the presence of holonomic constraints, are reviewed. Methods leading to a minimum set of equations are discussed; in view of the numerical difficulties associated with index-3 approaches, reduction to a minimum set is often performed, leading to a number of practical algorithms using methods developed for ordinary differential equations. The goal of this paper is to review the features of these methods, assess their accuracy and efficiency, underline the relationship among the methods, and recommend approaches that seem to perform better than others.
Effect of Ring-Planet Mesh Phasing and Contact Ratio on the Parametric Instabilities of a Planetary Gear Ring
Authors: Canchi Sripathi Vangipuram , Parker Robert G.
Published: December 2007

Parametric excitation of a rotating ring subject to moving time-varying stiffnesses has previously been investigated and given as closed-form expressions in the system parameters. These conditions are applied to identify ring gear parametric instabilities in a planetary gear system. Certain mesh phasing and contact ratio conditions suppress parametric instabilities, and these conditions are presented with examples.
Cs
Br
∕
Ga
N
heterojunction photoelectron source
Authors: Maldonado Juan R. , Liu Zhi , Sun Yun , Schuetter Scott , Pianetta Piero , Pease R. F. W.
Published: December 2007

Experimental results on a new CsBr∕GaN heterojunction photocathode structure are presented. The results indicate a fourfold improvement in photoyield relative to CsBr∕Cr photocathodes. A model is presented based on intraband states in CsBr and electron injection from the GaN (with 1% addition of indium) substrate to explain the observed photoyield enhancement. The photocathode lifetime at high current density (>40A∕cm2) is limited by laser heating of the small illuminated area. Calculations are presented for sapphire and diamond substrates, indicating a factor of 20 reduction in temperature for the latter. The results are encouraging for the realization of a high photoyield photocathode operating at high current density with long lifetime.
Fabrication of ultrahigh aspect ratio freestanding gratings on silicon-on-insulator wafers
Authors: Ahn Minseung , Heilmann Ralf K. , Schattenburg Mark L.
Published: December 2007

The authors report a silicon-on-insulator (SOI) process for the fabrication of ultrahigh aspect ratio freestanding gratings for high efficiency x-ray and extreme ultraviolet spectroscopy. This new grating design will lead to blazed transmission gratings via total external reflection on the grating sidewalls for x rays incident at graze angles below their critical angle (about 1°–2°). This critical-angle transmission (CAT) grating combines the alignment and figure insensitivity of transmission gratings with high broadband diffraction efficiency, which traditionally has been the domain of blazed reflection gratings. The required straight and ultrahigh aspect ratio freestanding structures are achieved by anisotropic etching of ⟨110⟩ SOI wafers in potassium hydroxide (KOH) solution. To overcome structural weakness, chromium is patterned as a reactive ion etch mask to form a support mesh. The grating with period of 574nm is written by scanning-beam interference lithography (SBIL) which is based on the interference of phase-locked laser beams. Freestanding structures are accomplished by etching the handle and device layers in tetramethylammonium hydroxide and KOH solution, respectively, followed by hydrofluoric acid etching of the buried oxide. To prevent collapse of the high aspect ratio structures caused by water surface tension during drying, the authors use a supercritical point dryer after dehydration of the sample in pure ethanol. The authors have successfully fabricated 574nm period freestanding gratings with support mesh periods of 70, 90, and 120μm in a 10μm thick membrane on ⟨110⟩ SOI wafers. The size of a single die is 10×12mm2 divided into four 3×3.25mm2 windows. The aspect ratio of a single grating bar achieved is about 150, as required for the CAT grating configuration.
Surface gate and contact alignment for buried, atomically precise scanning tunneling microscopy–patterned devices
Authors: Fuechsle Martin , Rueß Frank J. , Reusch Thilo C. G. , Mitic Mladen , Simmons Michelle Y.
Published: December 2007

The authors have developed a complete electron beam lithography (EBL)-based alignment scheme for making multiterminal Ohmic contacts and gates to buried, planar, phosphorus-doped nanostructures in silicon lithographically patterned by scanning tunneling microscopy (STM). By prepatterning a silicon substrate with EBL-defined, wet-etched registration markers, they are able to align macroscopic contacts to buried, conducting STM-patterned structures with an alignment accuracy of ∼100nm. A key aspect of this alignment process is that, by combining a circular marker pattern with step engineering, they are able to reproducibly create atomically flat, step-free plateaus with a diameter of ∼300nm so that the active region of the device can be patterned on a single atomic Si(100) plane at a precisely known position. To demonstrate the applicability of this registration strategy, they show low temperature magnetoresistance data from a 50nm wide phosphorus-doped silicon nanowire that has been STM-patterned onto a single atomically flat terrace.
Process characterization of inductively coupled plasma etched silicon nanopillars by micro-Raman
Authors: Laws G. M. , Handugan A. , Eschrich T. , Boland P. , Sinclair C. , Myhajlenko S. , Poweleit C. D.
Published: December 2007

The authors report on the top-down fabrication of silicon nanopillar arrays using electron beam lithography and enhanced plasma etch protocols for producing smoothed sidewalls. They have used cold development (2–4°C) to minimize line edge roughness in the patterned features. Standard reactive ion etch and inductively coupled plasma etch techniques have been used to fabricate nanopillar arrays, 60–100nm in diameter, with aspect ratios up to 20:1. They describe the use of a cyclic plasma oxidation and etch procedure to reduce sidewall roughness of silicon etched by the Bosch® process. The optimization of the smoothing process is demonstrated to produce near roughness free sidewalls. Raman spectroscopy has been used to characterize both the attributes of the nanopillars (including black silicon) and the effects of plasma processing. Preliminary results indicate that the Raman technique can distinguish the quality of the nanopillars (from processing perspective) based on intensity, spectral shifts, and changes in the linewidth. These changes are attributed to an increase in local heating of smoothed nanopillars caused by a modulation in optical absorption.
Figuring and smoothing capabilities of elastic emission machining for low-thermal-expansion glass optics
Authors: Kanaoka M. , Liu C. , Nomura K. , Ando M. , Takino H. , Fukuda Y. , Mimura H. , Yamauchi K. , Mori Y.
Published: December 2007

The use of elastic emission machining (EEM) for fabricating optics from low-thermal-expansion glass for extreme ultraviolet (EUV) lithography is examined. EUV optics require figure accuracy and surface roughness of 0.1nm root mean square (rms) or better. EEM using a rotating-sphere head is demonstrated to achieve this level of surface smoothness after a certain depth of removal dependent on the material being processed. In tests of continuous machining for 12h, no increase in surface roughness is observed, demonstrating the high temporal stability of this noncontact processing method. EEM using a rotating-sphere head is thus confirmed to have sufficient figuring and smoothing capability for the fabrication of EUV optics.
Photoluminescence enhancement in metallic nanocomposite printable polymer
Authors: Reboud V. , Kehagias N. , Striccoli M. , Placido T. , Panniello A. , Curri M. L. , Zelsmann M. , Reuther F. , Gruetzner G. , Sotomayor Torres C. M.
Published: December 2007

A 1.7-fold enhancement in the spontaneous emission intensity of dye chromophore loaded in a printable polymer is achieved by coupling the dye emission to surface plasmons of metallic nanoparticles. The nanocomposite material, embossed into arrays of wires by nanoimprint lithography process, shows good imprint properties. The results prove the potential of the prepared luminescent functional materials for micro- and nanofabrication and suggest the use of nanocomposite materials in prospective nanoplasmonic applications.
Hybrid semiconductor/nanoelectronic circuits: Freeing advanced lithography from the alignment accuracy burden
Authors: Likharev Konstantin K.
Published: December 2007

This is a brief review of the recent work on devices and architectures for hybrid semiconductor/nanoelectronic circuits using an area-distributed “CMOL” interface between its subsystems. Such circuits may provide unprecedented performance in several applications including memories, digital logic circuits, and bioinspired mixed-signal networks, while requiring nanoscale resolution for fabrication of just one simple pattern (a grid of parallel, similar lines) without layer alignment. Detailed calculations have shown that switching to the hybrid circuit technology may allow an extension of the Moore’s law by 10to15years.
Acid distribution in chemically amplified extreme ultraviolet resist
Authors: Kozawa Takahiro , Tagawa Seiichi , Cao Heidi B. , Deng Hai , Leeson Michael J.
Published: December 2007

Acid generators are sensitized by secondary electrons in chemically amplified resists for ionizing radiation. As acid generators react with low-energy electrons (as low as thermal energy), this sensitization mechanism generates a significant blur and an inhomogeneous acid distribution at the image boundary, which results in line edge roughness (LER) formation. The evaluation of resolution blur intrinsic to the reaction mechanisms is important in the optimization of resist processes for extreme ultraviolet (EUV) lithography, especially from the viewpoint of LER. In this study, the authors simulated acid generation induced by EUV photons in poly(4-hydroxystyrene) with 10wt% triphenylsulfonium triflate and clarified the extent of resolution blur in latent acid images and theoretical acid generation efficiency. The average distance between the EUV absorption point and the acid generation point (resolution blur) is 6.3nm. The theoretical acid generation efficiency through the ionization path is 2.6 per EUV photon in the model system. Considering the deprotonation efficiency of polymer radical cations and the contribution of electronic excited states, the acid generation efficiency including the excitation path is 2.0–2.8 in typical resist materials with 10wt% acid generator loading.
Fabrication of two dimensional GaN nanophotonic crystals (31)
Authors: Rong Bifeng , Salemink Huub W. M. , Roeling Erik M. , van der Heijden Rob , Karouta Fouad , van der Drift Emile
Published: December 2007

The authors have investigated chlorine based inductively coupled plasma etching of GaN by using different gas mixtures of Ar, Cl2, and N2. The etch mechanism and N2 role have been studied. We found that both ion energy and ion current density are important. The N2 plays a multiple role in etching GaN, chemical reaction, and ion bombardment. A reliable process to fabricate GaN nanophotonic crystals has been developed. Plasma conditions have been optimized toward a balance of ion current density, ion energy, and chemical species density. As a result, flat bottom, anisotropic photonic crystal with a=215nm d=129nm has been fabricated at an etch rate of 320nm∕min and an etch depth of 650nm. For comparison, an etch rate of 530nm∕min has been obtained in etching trench lines down to 1.61μm deep with a width of 500nm. The developed process has been used to fabricate GaN photonic crystal (PC) waveguides for 1.55μm wavelength. Transmission measurements reveal the ΓM stop band in hole type PC and illustrate the feasibility of the fabrication process.
Focused electron beam induced deposition of nickel
Authors: Perentes A. , Sinicco G. , Boero G. , Dwir B. , Hoffmann P.
Published: December 2007

Focused electron beam induced depositions of nickel-containing materials obtained by using bis(methylcyclopentadienyl)nickel(II) Ni(C5H4CH3)2 and tetrakis(trifluorophosphine)nickel(0) Ni(PF3)4 as precursors, were compared in terms of chemical composition and electrical resistivity. Ni(PF3)4 decomposed into higher Ni content materials than that obtained with Ni(C5H4CH3)2 (typically 40 and 10at.%, respectively). Attempts of increasing the Ni content by injecting controlled flows of molecular oxygen or hydrogen simultaneously to the precursor vapors resulted in all cases in the increase of incorporated oxygen only. The lowest electrical resistivities of 150nm wide lines obtained from Ni(C5H4CH3)2 and Ni(PF3)4 were 1 and 1×10−3Ωcm, respectively. The electrical resistivity of the latter lines showed an e(−T) dependence with temperature, typical of magnetic heterogeneous alloys and granular alloys containing insulating particles. Transmission electron microscopy investigations of a freestanding rod obtained from Ni(PF3)4 showed a nanocrystalline structure of nickel grains surrounded by a partially amorphous cladding.
Influence of the development process on ultimate resolution electron beam lithography, using ultrathin hydrogen silsesquioxane resist layers
Authors: Grigorescu Anda E. , van der Krogt Marco C. , Hagen Cees W. , Kruit Pieter
Published: December 2007

The influence of the development process on the ultimate resolution of electron beam lithography using ultrathin HSQ layers was studied. Different developers, of different types and strengths, were used to develop lines exposed at a variety of doses. Optimum exposures could be found for lines of widths between 7 and 12nm, at a pitch of 20nm. Lines smaller than 5nm could not be fabricated using any of these developers. Changing the development time had no influence on this result. Width versus dose curves are presented for all three developers and a 60s development time. A scaling is presented to enable an easy calculation of the exposure latitude for each linewidth. Using 100keV electron beam lithography, we achieved 6nm isolated features in a 10nm thick HSQ layer on a silicon substrate. We also showed that dense structures (5nm wide at a pitch of 20nm) could be obtained using a 1:5 developer solution of Microposit 351:H2O.
Helium ion microscope invasiveness and imaging study for semiconductor applications
Authors: Livengood Richard H. , Greenzweig Yuval , Liang Ted , Grumski Michael
Published: December 2007

The helium ion gas field ion source is a novel charged particle source technology with potentially greater capabilities than electron beam based tools for imaging and nanomachining [Ward et al., J. Vac. Sci. Technol. B (to be published); Morgan et al., Microscopy Today 14, 24 (2006); V. N. Tondare, J. Vac. Sci. Technol. A 23, 1498 (2005)]. Potential strengths of He ions over electrons (scanning electron microscopy) are improved thin film surface sensitivity, material contrast, IBIC voltage contrast, Rutherford backscattering material contrast, and the ability to utilize in situ electron charge neutralization on floating substrates which have enhanced charging properties (e.g., masks, photoresist). In this article, the authors will discuss and illustrate examples highlighting several of these attributes. Helium ions, unlike electrons, induce collision events in the material lattice. A critical area to understand is the operating conditions and sample types for which the advantages of helium ion imaging can be realized. Dose, beam current, acceleration voltage, and material interaction are all key areas for modeling and empirical analysis to determine potential invasiveness. The focus of the study presented in this article relates to analyzing the potential lattice damage induced in silicon substrate for ion doses ranging from 1×1014to5×1015ions∕cm2. This range represents relatively light dose (fast scan) to intermediate dose (slow scan) imaging applications. Findings for doses in this range (as typically used in image applications) show little to no damage to the silicon lattice. This finding also agrees with SRIM [Ziegler et al., The Stopping and Ranges of Ions in Solids (Pergamon, New York, 1985), Vol. 1] Monte Carlo simulations, which predict that helium ion induced defect densities to be 4×1017to4×1018dis∕cm3. However, it is clear that with higher doses, defect densities will increase to a level that may be invasive to device structures (e.g., metal oxide semiconductor field effect transistor channels or gate oxides).
Influence of temperature on HSQ electron-beam lithography
Authors: Häffner M. , Haug A. , Heeren A. , Fleischer M. , Peisert H. , Chassé T. , Kern D. P.
Published: December 2007

The authors present a study of the influence of temperature on hydrogen silsesquioxane (HSQ) e-beam lithography during drying, developing, and postdevelopment baking. In accordance with the observation that tempering at relatively low temperatures can already lead to noticeable cross-linking, comparable to the effect of e-beam exposure, the authors find that decreasing the prebake temperature below 90°C and drying the HSQ resist at room temperature in vacuum yields better resolution compared with resist that was dried in a furnace or on a hotplate at 90°C or above. Developing the exposed resist not at room temperature (23°C) but at 60°C results in significant contrast enhancement. Further solidification of the developed resist is obtained by baking the material above 300°C. Correlations between these findings and IR data are presented.
Challenges in 1 Teradot∕in.2 dot patterning using electron beam lithography for bit-patterned media
Authors: Yang XiaoMin , Xiao Shuaigang , Wu Wei , Xu Yuan , Mountfield Keith , Rottmayer Robert , Lee Kim , Kuo David , Weller Dieter
Published: December 2007

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots∕in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of ∼2.0 and ∼4.5 Tdots∕in.2, respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm (∼1.5 Tdots∕in.2) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis.
Characterization of ruthenium thin films as capping layer for extreme ultraviolet lithography mask blanks
Authors: Yan Pei-yang , Spiller Eberhard , Mirkarimi Paul
Published: December 2007

In extreme ultraviolet lithography (EUVL), the multilayer (ML) damage-free mask patterning processes and damage-free usage cycle are the keys in obtaining a successful, functional EUVL mask. A robust ML capping layer design will enable a long mask lifetime. In this article detailed investigation on the viability of ruthenium (Ru) thin films as capping layer for EUVL ML mask blanks is presented. The study is focused on Ru capping layer design for high reflectivity and its properties relevant to EUVL mask applications, such as microstructure, stress, optical properties at EUV wavelength, and chemical durability. The authors found that Ru thin films with a crystalline structure present a very high compressive stress which is insensitive to the primary ion deposition source energy. The Ru∕Si interdiffusion layer, however, presents a much lower stress than the of Ru-only film. Amorphization of the Ru film is via atomic composition modification, which the authors believe could be one of the keys in reducing Ru film stress. The ruthenium cap, under a piranha chemical clean, was found to be more durable than Si capped ML blanks, indicating the advantages of using Ru as the EUVL ML mask blank capping layer.
Nonresidual layer imprinting and new replication capabilities demonstrated for fast thermal curable polydimethysiloxanes
Authors: Pina-Hernandez Carlos , Kim Jin-Sung , Fu Peng-Fei , Guo L. Jay
Published: December 2007

Additional capabilities of a thermal curable polydimethylsiloxane based nanoimprinting resist that allows a fast replication (a few seconds) of 70 nm line width structures at low temperatures and low pressures (20 psi) are reported here. Challenging features such as nanopillars and high aspect ratio structures were accurately replicated. Moreover, a composite stamp was fabricated and successfully used to replicate structures from a DVD master. Additionally, it was found that a substrate with surface treatment by fluorinated silane is appropriate to imprint nanogratings with no residual layer. The residual layer can be eliminated on both a hard and a flexible substrate. The stamping of structures without residual layers can be used to create size controlled polymer nanofibers.
58
nm
half-pitch plastic wire-grid polarizer by nanoimprint lithography
Authors: Chen Lei , Wang Jian Jim , Walters Frank , Deng Xuegong , Buonanno Mike , Tai Stephen , Liu Xiaoming
Published: December 2007

Plastic nanowire-grid polarizers based on small period, 58 and 75nm half-pitch, Al gratings are fabricated and studied. Al gratings are made by coating Al on the polymer grating sidewalls at oblique angles. The nanopolymer gratings on plastic film over large area are made by nanoimprint lithography. By optimizing the grating period, grating linewidth, Al coating depth, and thickness, excellent maximum transmittance (Tmax) (80%–90%) and extinction ratio (∼30dB) are achieved.
Time dependent analysis of the resist deformation in thermal nanoimprint
Authors: Hirai Yoshihiko , Onishi Yuki , Tanabe Toshiaki , Nishihata Masayoshi , Iwasaki Takuya , Kawata Hiroaki , Iriye Yasuroh
Published: December 2007

Time evolution of the resist deformation process in the thermal nanoimprint lithography (NIL) has been investigated by both experiment and simulation study. For the numerical simulation, the authors newly developed a simulator using generalized Maxwell model as the viscoelastic constitutive model in conventional finite element method, which handles the complete NIL operations including resist pressing, cooling, and demolding processes. The dependency on the linewidth of the filling rate was investigated by both experiments and simulation and they sufficiently agreed with each other. It is confirmed that narrow pattern (high aspect ratio pattern) was difficult to be filled in a short period under the same imprinting pressure.
Surface energy induced patterning of organic and inorganic materials on heterogeneous Si surfaces
Authors: Tao L. , Crouch A. , Yoon F. , Lee B. K. , Guthi J. S. , Kim J. , Gao J. , Hu W.
Published: December 2007

A surface energy induced patterning (SEIP) method is developed to transfer resist patterns defined by lithography into various functional materials. A Si template is first chemically patterned using conventional lithography and selective attachment of trichlorosilane to achieve spatially different surface energies. Organic materials as well as inorganic films are deposited onto the chemically patterned template, followed by a thermal annealing process. The heterogeneous surface energies on the template induce material microfluidic reflow from the less to the more thermodynamically favorable areas. Using this method, patterned microstructures were achieved with SU-8, diblock copolymer, and aluminum film. In addition, the SEIP template was successfully used for atomic layer chemical vapor deposition to selectively pattern 200nm–2μm wide HfO2 structures.
In situ monitoring and control of material growth for high resolution electron beam induced deposition
Authors: van Dorp W. F. , Hagen C. W. , Crozier P. A. , Kruit P.
Published: December 2007

During electron beam induced deposition on electron transparent membranes, the transmitted annular dark field (ADF) signal can be monitored. A method was developed to use the ADF signal to obtain insight into the growth process and to control the mass of individual nanometer-sized deposits. Arbitrary two-dimensional patterns can be defined. The smallest sampling time of the ADF signal monitoring is presently about 40ms. For arrays of dots that were deposited, the growth of each individual dot was monitored. It is observed that the growth is different for each dot, although the average deposit growth rate is linear with the dwell time. Apart from monitoring the ADF signal during the growth, the amount of deposited mass can be controlled for individual deposits by terminating the growth process when the ADF signal exceeds a threshold value. The dynamic ADF feedback control was applied to reduce variations in deposit mass. This attempt did not succeed, but the method was successfully applied to prevent the occurrence of a proximity effect. When the electron beam irradiates the side of an already existing structure, the amount of deposited material is higher than if the electron beam irradiates an area that is under normal incidence. With the dynamic ADF feedback control, this effect can be compensated in situ and the amount of deposited material that is probed by the beam is constant regardless of the local growth rate. The mass deposition resolution of the feedback system is estimated by assuming a volume and a density of the deposits. It is estimated that the ultimate mass resolution is a single molecule.
Focused ion beam iodine-enhanced etching of high aspect ratio holes in InP photonic crystals
Authors: Callegari V. , Nellen P. M. , Kaufmann J. , Strasser P. , Robin F. , Sennhauser U.
Published: December 2007

The authors investigate the focused ion beam (FIB) fabrication of photonic crystal (PhC) holes in InP combining physical sputtering using 30 keV gallium ions and iodine-enhanced etching at 150 °C with a protective platinum or tungsten layer. The authors show that it is equivalent to conventional dry-etching methods such as inductively coupled plasma reactive ion etching in terms of achievable aspect ratio (>10), surface roughness (12.6 nm rms), and stoichiometry. The protective layers can be selectively removed after fabrication. This new FIB fabrication method lifts the previous constraints of funnel-shaped holes and limited aspect ratios of physical sputtering and reduces the Ga implantation and amorphous layer. Thus, rapid prototyping (5 s fabrication time per hole) of planar PhCs or planar PhC elements, such as PhC Y splitters, becomes feasible.
Effects of surface plasmon resonant scattering on the power conversion efficiency of organic thin-film solar cells
Authors: Chang Y. C. , Chou F. Y. , Yeh P. H. , Chen H. W. , Chang S.-H. , Lan Y. C. , Guo T. F. , Tsai T. C. , Lee C. T.
Published: December 2007

The power conversion efficiencies of organic solar cells fabricated with Ag and Ti nanoparticle arrays using nanosphere lithography are studied. The Ag nanoparticle array exhibits a broad absorption spectrum peaked at 420nm, which spectrally overlaps with the absorption band of the organic absorbing layer centered at 520nm, while no peak presented for the Ti nanoparticle array. Power conversion efficiencies by the solar cells with Ag and Ti nanoparticle arrays are 2.42% and 1.68%, respectively. This efficiency improvement is proposed to originate from the strong surface plasmon resonant scattering of visible light by Ag nanoparticle arrays.
Redeposition characteristics of focused ion beam milling for nanofabrication
Authors: de Winter D. A. M. , Mulders J. J. L.
Published: December 2007

In this article, a new method is presented to measure the focused ion beam induced sputter distribution, obtained with 30keV Ga+ ions. Small holes with diameters ranging from 400to1750nm have been created in a lamella with a thickness of approximately 300nm. Short ion beam pulses sputter small amounts of material from the bottom of the hole that redeposit at the opposite side. Assuming axial spatial symmetry, imaging the hole before and after redeposition yields a quantitative cross section of the sputter distribution. It has been found that at low ion currents (<6pA) and low ion dose (<10+8) the method produces reliable, reproducible results for 30keV Ga+ ions on silicon. The method is compared with SRIM simulations in Si and with previously published results. The simulated and measured results are in good agreement. At the higher dose∕current regime, small Ga droplets are formed, probably as a result of sputtered Ga dopants in Si. As a result of this, the method becomes less accurate and the simulation is no longer valid due to the fact that the substrate milling has to include the many Ga dopants to a certain depth.
Simple fabrication of UV nanoimprint templates using critical energy electron beam lithography
Authors: Joo Jaebum , Jun Kimin , Jacobson Joseph M.
Published: December 2007

Ultraviolet nanoimprint lithography (UV-NIL) is a promising nanoscale patterning method, but the template fabrication processes are expensive and time consuming because a chrome layer is necessary both as a charge dissipation layer to minimize pattern distortion during electron beam patterning and as a physical mask during subtractive quartz etching. In this paper, the authors propose a simple UV-NIL template fabrication scheme based on the direct electron beam patterning of hydrogen silsesquioxane (HSQ) on quartz substrates using critical energy electron beam lithography (CE-EBL). By operating at the critical energy (E2) where the charge balance between incoming and outgoing electrons leaves the surface neutral, charge induced pattern distortion typically seen on quartz is practically eliminated. This template fabrication process eliminates conventional deposition and etching of charge dissipation layers. Quartz with sub-100-nm HSQ structures was used as a UV-NIL template, and SU-8 polymer structures were successfully replicated by a UV nanoimprint process. This simple template fabrication approach may lead to the development of new biological devices, nanoelectronics, and optoelectronics.
Soft x-ray imaging of spin dynamics at high spatial and temporal resolution
Authors: Mesler Brooke L. , Fischer Peter , Chao Weilun , Anderson Erik H. , Kim Dong-Hyun
Published: December 2007

Soft x-ray microscopy provides element specific magnetic imaging with a spatial resolution down to 15 nm. At XM-1, the full-field soft x-ray microscope at the Advanced Light Source in Berkeley, a stroboscopic pump and probe setup has been developed to study fast magnetization dynamics in ferromagnetic elements with a time resolution of 70 ps, which is set by the width of the x-ray pulses from the synchrotron. Results obtained from a 2 μm×4 μm×45 nm rectangular permalloy sample exhibiting a seven domain Landau pattern reveal dynamics up to several nanoseconds after the exciting magnetic field pulse. Domain wall motion, a gyrotropic vortex motion, and a coupling between vortices in the rectangular geometry are observed.
Sub-100-nm three-dimensional nanoimprint lithography
Authors: Unno Noriyuki , Taniguchi Jun , Ishii Yoshiaki
Published: December 2007

In the next generation, there is going to be a strong need for three-dimensional nanoscale patterning technology for various optical devices and dual damascene process. A breakthrough in this field has been made by nanoimprint lithography (NIL) because of its lower cost and process simplicity. In this current study, the characteristics of proximity effect caused by forward scattering of electrons with spin on glass, which is used as a positive-tone inorganic resist, was examined using low-acceleration-voltage (<5kV) electron-beam lithography. As a result, a sub-100-nm three-dimensional nanoimprint mold was fabricated by control-of-acceleration-voltage electron-beam lithography. And by using ultraviolet NIL, a replicated pattern was obtained that approximately corresponded to the fabricated mold.
Impact of glass temperature for thermal nanoimprint
Authors: Scheer H.-C. , Bogdanski N. , Wissen M. , Möllenbeck S.
Published: December 2007

To address the importance of the parameter glass transition temperature Tg for the choice of an adequate process temperature in a thermal nanoimprint process, three polymers with different values of Tg were investigated with respect to their imprint behaviors (poly)vinyl-chloride, (poly)styrene, and (poly)methyl-methacrylate. In order to evaluate the imprint results obtained at different temperatures, the volume of the polymer squeezed into the cavities was observed, and the temperature margins for the appearance of typical pattern size dependent failure types were derived. It turned out that despite the comparable molecular weight of these materials, the imprint temperature has to be chosen at different levels above Tg. Thus, Tg is not sufficient to characterize imprint polymers, and, in addition to the molecular weight, the viscosity at a definite temperature should be known. Tg alone can only indicate a lower limit for the process temperature.