bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on acid generation from polymer
Authors: Yamamoto Hiroki , Kozawa Takahiro , Nakano Atsuro , Okamoto Kazumasa , Tagawa Seiichi , Ando Tomoyuki , Sato Mitsuru , Komano Hiroji
Published: January 2006

In the fabrication beyond the 32nm node, the uniform distribution of acid generators in a resist matrix is a serious concern. The incorporation of acid generators to polymers via covalent bonds has attracted much attention in order to overcome the compatibility problem of acid generators with polymers. We reported the reaction mechanism of acid generation in typical chemically amplified resists for ionizing radiation, such as electron beam and extreme ultraviolet. The simplest way to induce the same reactions in a single-component resist is the halogenation of polymers. We carried out a case study on the acid generation from polymers using brominated poly(4-hyroxystyrene) (Br-PHS). Br-PHS without an acid generator produced hydrogen bromide with the same amount as acid yield of PHS with 1.2mol% (4.1wt%) triphenylsulfonium-triflate. It was confirmed that Br-PHS with hexamethoxy methyl melamine worked as a chemically amplified resist without any acid generators. From the comparison among the acid yields of Br-PHS, PHS, poly(4-bromostyrene) and polystyrene, we concluded that the efficient acid generation from polymers requires a high reactivity with electrons, a high dissociation efficiency of counter anions, and an effective proton source, such as hydroxyl group.
Pumped quantum systems: Immersion fluids of the future?
Authors: Anant Vikas , Rådmark Magnus , Abouraddy Ayman F. , Killian Thomas C. , Berggren Karl K.
Published: January 2006

Quantum optical techniques may yield immersion fluids with high indices of refraction without absorption. We describe one such technique in which a probe field experiences a large index of refraction with amplification rather than absorption, and examine its practicality for an immersion lithography application. Enhanced index can be observed in a three-level system with a tunable near-resonant coherent probe and incoherent pump field that inverts the population of the probe transition. This observation contradicts the common belief that large indices of refraction are impossible without absorption; however, it is well in accord with existing electromagnetic theory and practice. Calculations show that a refractive index ⪢2 is possible with practical experimental parameters. A scheme with an incoherent mixture of pumped and unpumped atoms is also examined, and is seen to have a lower refractive index (∼2) accompanied neither by gain nor loss.
Achromatic spatial frequency multiplication: A method for production of nanometer-scale periodic structures
Authors: Solak Harun H. , Ekinci Yasin
Published: January 2006

Fabrication of periodic structures with resolution below 100nm is required in many emerging applications such as subwavelength optical components, self-assembly templates, or patterned magnetic media. The achromatic spatial frequency multiplication technique that we have developed uses wideband illumination and self-imaging property (Talbot effect) of gratings to create periodic structures. The depth of field is practically unlimited, unlike the Talbot images obtained with monochromatic illumination. The technique requires limited spatial coherence making it suitable for use with sources other than lasers or synchrotrons which are normally used in interference lithography. We demonstrated the feasibility of the method using simulations and exposures in the extreme ultraviolet (EUV) region. One- and two-dimensional patterns with 50nm feature sizes were obtained. The technique is especially suitable for use with EUV light where the newly developed sources (laser or discharge produced plasma) have a rather wide bandwidth and limited spatial coherence. The technique is extendible to the production of much higher-resolution structures with the fundamental limit for the pattern period being equal to one-half of the wavelength.
Iridium/silicon capping layer for soft x-ray and extreme ultraviolet mirrors
Authors: Prisbrey Shon T. , Vernon Stephen P. , Clift W. Miles
Published: January 2006

Iridium terminated silicon spacer layers on Mo∕Si multilayer mirrors fabricated by dc magnetron sputtering are investigated for temporal stability. Samples maintained in atmosphere for periods of more than 3000 hours show: Ir terminating layers >16Å thick are stable, layers with thicknesses between ∼10 and 16 Å are not stable, and thicknesses between ∼7 and 10 Å are stable after a loss in reflectance of ∼1%. Extreme ultraviolet (EUV) reflectance, atomic force microscopy, sputter Auger electron spectroscopy, and x-ray diffraction measurements indicate that the terminating layer is, in reality, an alloy with graded composition that is Ir rich at the surface. The compositional gradient causes a degradation in reflectance from 66% for Si terminated multilayers to ∼63% for Ir terminated samples (thickness 18.7 Å). A sudden onset of oxidation induced silicon transport for deposited layers of Ir ∼10−16Å thick produces a degradation in EUV reflectance upon exposure to atmosphere. Accelerated lifetime testing of Si and Ir (18.7 Å) terminated multilayer mirrors show a ΔR∕R reflectance loss of 0.2% for the Ir terminated sample and ∼3% for the Si terminated sample. Further development on Ir terminated multilayer stacks to increase reflectance is needed.
Magnetoresistance of patterned NiFe thin films with structures modified by atomic force microscope nanolithography
Authors: Watanabe Genta , Koizumi Sinichi , Yamada Tsutomu , Takemura Yasushi , Shirakashi Jun-ichi
Published: January 2006

Surfaces of patterned NiFe strip-shaped thin films of 15–30nm thickness were modified by nanowires of NiFe oxide. The NiFe oxide was fabricated by the atomic force microscopy (AFM) nano-oxidation technique. The anisotropy magnetoresistance was measured in order to study the effect of the nanowires in the magnetization reversal process. The domain wall was pinned at the nanowires of the NiFe oxide. It was indicated that the propagation of domain wall could be controlled by the AFM nanolithography.
Fabrication and characterization of CuO nanorods by a submerged arc nanoparticle synthesis system
Authors: Lo Chih-Hung , Tsung Tsing-Tshih , Chen Liang-Chia
Published: January 2006

The purpose of this study is to investigate an innovative nanorod preparation method, the submerged arc nanoparticle synthesis system. The key parameters such as discharge current, breakdown voltage, pulse duration, and temperature of the dielectric liquid are carefully analyzed in order to obtain more uniform nanorods. The prepared nanorods were systematically characterized by x-ray diffraction, transmission electron microscopy, selected-area electron diffraction, x-ray photoelectron spectroscopy, and the ultraviolet-visible absorption spectrum. The results showed that the CuO nanorods had a diameter of 30–50nm and a longitudinal length of up to 1–2μm. A possible preparation mechanism was also discussed for the growth of the CuO nanorods.
Preparation and characterization of titania nanotubes and hybrid materials derived from them
Authors: Lin Yi-Jun , Wang Leeyih , Chiu Wen-Yen
Published: January 2006

Ti O 2 nanotubes with outer diameters of ∼10nm and lengths of several hundreds nanometer were synthesized by the hydrothermal method. The morphology of the nanotubes was thoroughly examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composition and structure of tubular materials were determined by energy dispersive x-ray spectroscopy, selected area electron diffraction pattern, and x-ray diffraction (XRD). XRD results confirmed that the nanotubes are composed of pure anstase TiO2. Both TEM and the Barrett–Joyner–Halenda methods indicated that the inner diameters of the nanotubes are around 7nm. In addition, the hybrid of poly(3-hexylthiophene) and TiO2 nanotube were prepared by the oxidative polymerization of 3-hexylthiophene in the presence of TiO2 nanotubes. The obtained composites were characterized by SEM, Fourier transformed infrared spectroscopy, and thermal gravimetric analysis.
Nanoscale electron stimulated chemical vapor deposition of Au in an environmental transmission electron microscope
Authors: Ketharanathan Sutharsan , Sharma Renu , Drucker Jeff
Published: January 2006

Nanoscale Au rich dots were deposited on SiO2 and Si3N4 substrates by decomposing an adsorbed organometallic precursor using a focused electron beam. The precursor, dimethyl acetylacetonate gold ((CH3)2(C5H7O2)Au), does not react with either substrate without electron irradiation. Deposited feature diameters are larger than that of the electron beam used for deposition by an amount comparable to the secondary electron escape depth. This result suggests that axial secondary electron emission through the surface of a growing feature limits the minimum attainable feature size. Real-time composition analysis during growth using electron energy-loss spectroscopy indicates that mature features entrain significant carbon.
Modeling of protection schemes for critical surfaces under low pressure conditions: Comparison between analytical and numerical approach
Authors: Asbach Christof , Pui David Y. H. , Kim Jung Hyeun , Yook Se-Jin , Fissan Heinz
Published: January 2006

Nanoparticle contamination is one of the crucial issues for the semiconductor industry on the move towards structure sizes of 50nm and below. In extreme ultraviolet lithography (EUVL), a likely successor to optical lithography, the masks cannot be protected by common pellicles. Different protection methods, such as a “thermophoretic pellicle” [L. Klebanoff and D. J. Rader, US Patent No. 6,153,044 (2000) and US Patent No. 6,253,464 B1 (2001)] have therefore been proposed to protect a face-down mask in an EUV scanner, which might be operated at 50mTorr (6.7Pa). In order to quantify the effectiveness of such protection schemes, we developed an analytical model that allows simple determination of the particle stopping distance as a function of particle and gas properties as well as a thermal gradient that might be employed to make use of a thermophoretic force in order to protect the mask. The analytical results indicate that drag force is most effective in slowing down particles, traveling at high initial velocities. Thermophoresis can add effective protection to particles traveling at low velocities and therefore decrease diffusional deposition. The results from the analytical model were used to check the accuracy of the discrete phase model in FLUENT for particle diameters between 100 and 500nm and pressure levels between 10mTorr (1.3Pa) and 500mTorr (66.7Pa) (corresponding Knudsen numbers 407≤Kn≤102000). The comparison results indicate that with no thermal gradient, the results agree very well with less than 2% deviation. If thermophoresis is included, the absolute deviation generally increases with increasing Knudsen number and with increasing temperature gradient. For a temperature gradient of 10K∕cm and a Knudsen number of 102000 (p=10mTorr,dp=100nm), the deviation reaches almost 50% for 2m∕s initial particle velocity.
Temperature characteristics of stress-induced migration based on atom migration
Authors: Aoyagi Minoru
Published: January 2006

Stress-induced migration is one of the problems associated with the reliability of metal interconnections in semiconductor devices. The physical model of stress-induced migration has been established as that of the migration of vacancies. Vacancies can be considered as holes among atoms constituting interconnections. To clarify the mechanism of stress-induced migration, an atomic migration model is more essential than the physical model. First, we present the stress-induced migration model based on atomic migration using simple calculations in detail. The key issue in this model is the change in elastic potential with atom migration. Second, the presented model is applied in simple cases for analyzing the stress relaxation time due to stress-induced migration. We found that the temperature characteristics of the stress relaxation time have some patterns depending on void surface stress, the stress in an interconnection, and void interval. These patterns reported concerning the interconnection lifetime due to stress-induced migration can be qualitatively explained by the presented model.
Pulse oscillation of self-organized In0.53Ga0.47As quantum wire lasers grown on (775)B InP substrates by molecular beam epitaxy
Authors: Hino H. , Shigenobu A. , Ohmori K. , Kitada T. , Shimomura S. , Hiyamizu S.
Published: January 2006

A self-organized In0.53Ga0.47As∕(In0.53Ga0.47As)2(In0.52Al0.48As)2 quantum wire (QWR) laser was grown on a (775)B InP substrate by molecular beam epitaxy. Threefold 3.6-nm-thick In0.53Ga0.47As QWR layers were used as an active layer, where lateral confinement potential was induced by a nanometer scale interface corrugation of InGaAs∕(InGaAs)2(InAlAs)2 with an amplitude of 7nm and a period of 65nm. Photoluminescence was strongly polarized along the wire direction [P≡(I‖−I⊥)∕(I‖+I⊥)=0.43–0.54] in the temperature range from 12to150K, indicating their good one dimensionality. A 10μm×500μm stripe-contact QWR laser with uncoated cleaved mirrors oscillated with a threshold current density of 5.2kA∕cm2 and a lasing wavelength of 1215nm at 150K under pulsed current condition.
Low damage sputter deposition of tungsten for decanano compound semiconductor transistors
Authors: Cao X. , Macintyre D. S. , Thoms S. , Li X. , Zhou H. , Wilkinson C. D. W. , Holland M. , Donaldson L. , McEwan F. , McLellend H. , Thayne I.
Published: January 2006

This article investigates sputter-induced damage caused by direct current magnetron sputter coating of tungsten on GaAs based high electron mobility transistor layer structures with channels buried less than 20nm from the surface. Van der Pauw structures were used to study the effect of tungsten sputtering on the transport properties of these shallow channels. Using this approach we established that substrate damage can be minimized by using low sputtering currents, a large source to substrate distance, and a high sputtering pressure. Unfortunately such sputtering conditions do not produce the best quality dense films necessary for device fabrication and it was necessary to establish conditions which were a compromise of film quality and substrate damage. Postsputter annealing was found to significantly reduce the damage and a loss of 10% in semiconductor conductivity was obtained for good quality tungsten films.
Simulations of nonuniform embossing: The effect of asymmetric neighbor cavities on polymer flow during nanoimprint lithography
Authors: Rowland Harry D. , King William P. , Sun Amy C. , Schunk P. Randy
Published: January 2006

This article presents continuum simulations of viscous polymer flow during nanoimprint lithography (NIL) for embossing tools having irregular spacings and sizes. Simulations vary nonuniform embossing tool geometry to distinguish geometric quantities governing cavity filling order, polymer peak deformation, and global mold filling times. A characteristic NIL velocity predicts cavity filling order. In general, small cavities fill more quickly than large cavities, while cavity spacing modulates polymer deformation mode. Individual cavity size, not total filling volume, dominates replication time, with large differences in individual cavity size resulting in nonuniform, squeeze flow filling. High density features can be modeled as a solid indenter in squeeze flow to accurately predict polymer flow and allow for optimization of wafer-scale replication. The present simulations make it possible to design imprint templates capable of distributing pressure evenly across the mold surface and facilitating symmetric polymer flow over large areas to prevent mold deformation and nonuniform residual layer thickness.
Immersion zone-plate-array lithography
Authors: Chao David , Patel Amil , Barwicz Tymon , Smith Henry I. , Menon Rajesh
Published: January 2006

An immersion scheme is used to improve resolution, exposure latitude, and depth-of-focus in zone-plate-array lithography (ZPAL). We believe this is the first implementation of an immersion scheme in a maskless lithography system. Replacing air with de-ionized water as the medium between the zone-plate array and the substrate effectively increases the system’s numerical aperture and consequently, enhances its patterning capabilities. The design and fabrication process of an immersion zone plate is described. Its behavior is then characterized through the experimental reconstruction of its point-spread function, and compared to the theoretical model. A wide variety of patterns were printed, demonstrating the improved lithographic performance of immersion ZPAL.
Mask defect inspection using an extreme ultraviolet microscope
Authors: Hamamoto K. , Tanaka Y. , Lee S. Y. , Hosokawa N. , Sakaya N. , Hosoya M. , Shoki T. , Watanabe T. , Kinoshita H.
Published: January 2006

A defect inspection technique on an extreme ultraviolet lithography mask is described. There are two kinds of defects, amplitude defects and phase defects due to the multilayer coating. The technique utilizes a microscope using the same 13.5 nm wavelength as the light used for exposure, and producing a magnified image of defects on a mask. Using this microscope, amplitude defects on practical masks and phase defects are observed. A phase defect was formed by a multilayer coated on a line pattern with a height of 5 nm and width of 90 nm on a glass substrate. Although the detected defect is made beforehand, it is detected by reflection of the light which penetrated inside of a multilayer. These results show that it is possible to detect the internal reflectivity distribution, without depending on surface perturbations.
Reconstruction of pattern images from scanning electron microscope images
Authors: Feng Hanying , Ye Jun , Pease R. Fabian W.
Published: January 2006

As the characteristic feature sizes of integrated circuits continue to shrink, both research and manufacturing are increasingly reliant on the scanning electron microscope (SEM) images. In this article, we propose a robust algorithm that automatically extracts the full edge contours from the SEM images and then converts the SEM images to pattern images even when the SEM images are corrupted by strong noise and lossy compression. This algorithm is expected to have many applications. An example of application—defect self-inspection—based on SEM conversion using this algorithm, is also shown.
Technique for estimating the angle of incidence and depth of focus of an electron beam
Authors: Mizuno Fumio , Amemiya Isao , Taniguchi Kazutake
Published: January 2006

In order to cope with the problems with scanning electron microscopes for semiconductor manufacturing, the ability to measure the focal depth and incident angle of an electron beam is required. A technique for estimating the angle of incidence and the depth of focus has been devised. The main feature of the technique is to employ the specimen with a special pit, which is formed from sidewalls with an accurate tilt angle and a surface structure. In this work, the pit was formed on a (100) silicon-crystal substrate and from four (111) sidewalls with an accurate tilt angle of 54.74° and a step-like surface. The incident angle and focal depth of an electron beam was estimated by using the pit. The estimation result agreed approximately with the expected.
Monolithically integrated circular polarizers with two-layer nano-gratings fabricated by imprint lithography
Authors: Wang Jian Jim , Liu Feng , Deng Xuegong , Liu Xiaoming , Chen Lei , Sciortino Paul , Varghese Ron
Published: January 2006

We developed an integrated circular polarizer based on stacking an aluminum nano-wire grid polarizer with a dielectric nano-grating-based quarter waveplate. The polarizer consists of 65 nm wide and 130 nm tall aluminum wires with a period of 148 nm. For integration, the aluminum nanowires were buried into a silicon dioxide matrix by a trench filling and planarization technology. The buried nanowire polarizer achieved excellent optical performance in a broad wavelength range from 400 nm to >900nm. On top of the buried and planarized nanowire polarizer, a visible quarter waveplate based on a 200 nm period silicon nitride nano-grating was fabricated. Both the 148 nm period aluminum grating and the 200 nm period silicon nitride grating were fabricated by an ultraviolet (UV)-nanoimprint lithography. The ability to integrate multiple nanostructure-based optical layers opens a path for novel integrated optical devices, as well as a new strategy for driving both miniaturization and cost.
History of extreme ultraviolet lithography
Authors: Kinoshita Hiroo
Published: January 2006

Extreme ultraviolet lithography (EUVL) technology was proposed and progressed on both hemispheres in the latter part of the 1980s, independently. Although this technology is a design using a catoptric system instead of refraction lens and the accuracy of subnanometer is demanded for all component engineering, the research and development of Japan and the United States has led to significant breakthroughs in processing and measurement technology over the past 20 years. EUVL is now the most promising next-generation technology for large scale integration fabrication. This article discusses the beginnings of EUVL, what advances are needed, and future prospects.
Fabrication of three-dimensional stamps for embossing techniques by lithographically controlled isotropic wet etching
Authors: Tormen Massimo , Carpentiero Alessandro , Vaccari Lisa , Altissimo Matteo , Ferrari Enrico , Cojoc Dan , Di Fabrizio Enzo
Published: January 2006

The excellent characteristics that nanoimprint lithography (NIL) shows as a two-dimensional patterning technique, such as resolution and throughput, are shared with its three-dimensional (3D) structuring version. Nevertheless, the potentialities of NIL for 3D structuring remain largely unexplored and unexploited, hindered by the difficulties in the fabrication of high quality masters with throughput suitable for practical purposes. We present a technique that allows production of stamps with tightly controlled three-dimensional profiles in the 10nm–100μm scale range. This technique consists of a sequence of lithographic steps alternated with isotropic wet etching processes performed on a quartz substrate. Scanning electron microscopy and atomic force microscopy characterization shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be formed with this method. Quartz stamps have been employed in nanoimprint, hot embossing, or casting processes to shape complex plastic elements. This technique is expected to have many applications in different nanotechnology-related fields such as optics, nanomechanics, microfluidics, and plasmon nano-optics.
Three-dimensional polymer structures fabricated by reversal ultraviolet-curing imprint lithography
Authors: Kehagias N. , Zelsmann M. , Torres C. M. Sotomayor , Pfeiffer K. , Ahrens G. , Gruetzner G.
Published: January 2006

Polymer optical devices could be an alternative to dielectric or semiconductor devices, since they can be fabricated using low-cost processes with high manufacturing output. This article presents results on the fabrication of polymer optical device-like and three-dimensional structures using the imprint and reversal imprint techniques. This last technique offers the unique advantage of printing over nonflat surfaces allowing a layer-by-layer fabrication of three-dimensional structures. Depending on the size and density of the stamp features, a “whole layer transfer” mode or an “inking” mode can be observed. The same printable ultraviolet cross-linkable polymer (mr-L 6000 from Micro Resist Technology) has been used at each repetition of the fabrication process so that the number of layers that can be stacked onto a substrate is no longer limited by the polymer glass transition temperature (Tg), unlike previous results where different polymers with a decreasing Tg had to be used for the successive layers.
4 inch lift-off process by trilayer nanoimprint lithography
Authors: Tallal J. , Berton K. , Gordon M. , Peyrade D.
Published: January 2006

We present the development of a reliable 4 in. lift-off process based on trilayer nanoimprint lithography (NIL). At first, an inductively coupled plasma etching step of the imprinted resist is used to remove the residual resist thickness after NIL for different pattern geometry and density, while maintaining the critical dimensions of the studied patterns. By combining this etching step to a trilayer (NEB22∕Ti∕PMMA) nanoimprint process, reproductible 4 in. wafer lift-off of 250 nm wide metallic patterns was obtained. Finally, local probe indentation measurements are investigated to correlate the mechanical properties of different imprinted polymers to the achievable nanogap replication.
Charting the future (and remembering the past) of optical lithography simulation
Authors: Mack Chris A.
Published: January 2006

Optical lithography modeling began in the early 1970s and represented the first serious attempt to describe lithography not as an art, but as a science. Thirty years later, optical lithography continues to make dramatic advances that enable the profitable continuation of Moore’s Law. Most if not all of these advances would not be possible without the use of lithography simulators. This article will review the history of lithography simulation, describing a few of the milestone events and important lithographic advances that simulation enabled. This historical review will end with a characterization of the current state of lithography modeling and its important applications in chip design, process development, and manufacturing today. Finally, a prediction of future advances in simulation capabilities will be made as well as how these advances will help to move the industry forward.
Lanthanum aluminate by atomic layer deposition and molecular beam epitaxy
Authors: Triyoso D. H. , Li H. , Hegde R. I. , Yu Z. , Moore K. , Grant J. , White B. E. , Tobin P. J.
Published: January 2006

A comparison of physical and electrical characteristics of lanthanum aluminate (LAO) dielectrics formed by atomic layer deposition (ALD) and molecular beam epitaxy (MBE) is investigated in this study. Physical characteristics of LAO deposited with these two deposition methods are compared using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS). Capacitors with TaN and TaSiN gate electrodes were fabricated to assess electrical properties of these LAO films. ALD LAO was deposited using La[N(SiMe3)2]3,Al(CH3)3 and water at 225–275 °C. ALD LAO is stable against Pt and TiN∕W metal gates up to 800 °C. After annealing at 900 °C, interactions between metal gates and dielectrics are observed resulting in nonfunctional devices. MBE LAO film was deposited at room temperature or 200–400 °C in two ways: Using single element targets (La, Al) or a compound target. The LAO∕TaN stack deposited with single element targets showed significant Si up diffusion from the substrate to the dielectric and the metal gate electrode. In addition, nitrogen diffusion from the metal gate into the dielectric was detected. The LAO∕TaN stack deposited with a compound target showed improved thermal stability. No metal out-diffusion and only very slight Si out diffusion was detected after a 900 °C anneal. LAO capacitors show well-behaved capacitance-voltage and leakage current density-voltage characteristics. These results indicate that the method by which lanthanum aluminate films are deposited strongly influenced their thermal stability. Of all the films examined, the most stable films are deposited by MBE using a compound target.
Investigation of surface treatment schemes on n-type GaN and Al0.20Ga0.80N
Authors: Selvanathan Deepak , Mohammed Fitih M. , Bae Jeong-Oun , Adesida Ilesanmi , Bogart Katherine H. A.
Published: January 2006

The effects of SiCl4 reactive-ion-etching (RIE) plasma treatment on n-GaN and n-Al0.20Ga0.80N surfaces, and the subsequent cleaning of the surfaces using ammonium hydroxide (NH4OH), hydrochloric acid (HCl), and buffered oxide etch (BOE) solutions, have been investigated using x-ray photoelectron spectroscopy and Auger electron spectroscopy measurements. Of these cleaning schemes, BOE was found to be the most effective treatment to remove oxides from the surfaces of the SiCl4 plasma treated samples. The SiCl4 plasma treatment of GaN and AlGaN resulted in the blueshift of Ga–N (Ga3d) peaks to higher binding energies corresponding to a shift of the Fermi level (EF) toward the conduction band edge at the surface. It has been reported that this type of shift is caused by the creation of N vacancies, which act as n-type dopant [D. W. Jenkins and J. D. Dow, Phys. Rev. B. 39, 3317 (1989); M. E. Lin, Z. F. Fan, Z. Ma, L. H. Allen, and H. Morkoç, Appl. Phys. Lett. 64, 887 (1994); A. T. Ping, Q. Chen, J. W. Yang, M. A. Khan, and I. Adesida, J. Electron. Mater. 27, 261 (1998)] on the surface due to SiCl4 plasma treatment. This corresponds to an increase in n-type dopant density on the surface. Thus, SiCl4 plasma treatment in a RIE system thins the Schottky barrier heights of n-GaN and n-AlGaN and aids in the formation of ohmic contacts on such surfaces.
Thickness and density evaluation for nanostructured thin films by glancing angle deposition
Authors: Buzea Cristina , Kaminska Kate , Beydaghyan Gisia , Brown Tim , Elliott Chelsea , Dean Cory , Robbie Kevin
Published: January 2006

Thickness evaluation is a particular challenge encountered in the fabrication of nanosculptured thin films fabricated by glancing angle deposition (GLAD). In this article, we deduce equations which allow for accurate in situ thickness monitoring of GLAD thin films deposited onto substrates tilted with respect to the direction of incoming vapor. Universal equations are derived for the general case of Gaussian vapor flux distribution, off-axis sensors, variable substrate tilt, and nonunity sticking coefficient. The mathematical description leads to an incidence angle dependence of thickness and density, allowing for quantitative prediction of porosity in samples with different morphologies and thickness calibrations. In addition, variation of sticking probability with the incidence angle creates a nonmonotonic variation of the film thickness and porosity with the substrate tilt. We discuss the implications of the substrate type, sensor type, and source geometry in a precise quantitative determination of the thickness of thin films fabricated on tilted substrates. Our equations can be particularized for the case of films fabricated at normal incidence.
Direct measurements and analyses of the Coulomb effects in electron projection lithography
Authors: Yamamoto Jiro , Yamashita Hiroshi , Arimoto Hiroshi , Ikeda Junji , Suzuki Shohei , Kawata Shintaro
Published: January 2006

The Coulomb effects have been common problems in electron-beam lithography. In our previous article, we studied the influence of the Coulomb effects on electron projection lithography (EPL) process. In this paper, we analyze the Coulomb effects by direct blur measurements and by simulations. We found that there existed a beam blur around 32 nm at a low beam current (approximately 0μA). We found a relationship between the beam blur and the beam current that was 5.4nm∕μA, and this number agreed with our simulation work as well as with our experiment with resist resolution. We learned that at low current the blur was so small that a blur distribution could be practically ignored. An important finding we had, is that the beam blur did not only depend on the beam current but also on the pattern arrangement. We found the possibility of the existence of the local Coulomb effects and estimated its range to be around 100–120μm on our system. These phenomena should be taken into considerations when making proximity effect correction for highly accurate critical dimension control.
Possible role of oxygen impurities in degradation of nc-TiN∕a-Si3N4 nanocomposites
Authors: Veprek Stan , Karvankova Pavla , Veprek-Heijman Maritza G. J.
Published: January 2006

The recently reported strong effect of minor oxygen impurities on the degradation of mechanical properties of superhard nc-TiN∕a-Si3N4 can be, by analogy with similar effects known in metallic alloys, understood on the basis of a simple size effect of large O2− impurity species incorporated into the Si3N4 interface. The electronic effect of the O2− sites within the Si3N4 interface is also likely to play an important role in weakening the Si–N and, possibly to a lesser extent, also Ti–N bonds. A simple model which assumes that the strength (and hardness) of these materials is approximately proportional to the reciprocal surface coverage of the TiN nanocrystals by oxygen impurities shows a surprisingly good agreement with the measured data.
Design and simulation of ZnO-based light-emitting diode structures
Authors: Han Sang Youn , Yang Hyucksoo , Norton D. P. , Pearton S. J. , Ren F. , Osinsky A. , Dong J. W. , Hertog B. , Chow P. P.
Published: January 2006

Two different types of ZnO-based light-emitting diode structures have been examined using a one-dimensional (1D) simulator that accounts for specific features of the hexagonal semiconductors—strong piezoeffects, existence of spontaneous electric polarization, low efficiency of acceptor activation, and high threading dislocation density (normally, ∼107–109cm−2) in the material. A hybrid ZnO∕CdZnO∕AlGaN∕GaN structure grown on sapphire avoids problems in achieving robust p-type doping in ZnO. An all-ZnO approach employs a MgZnO∕CdZnO∕MgZnO double heterostructure grown on a ZnO substrate. Both structures show a strong sensitivity of emission intensity to doping and layer thicknesses within our simulations.
Pattern matching between a scanning electron microscopy exposed pattern image of large-scale integrated fine structures and computer-aided design layout data by using the relaxation method
Authors: Miura K. , Fujita M. , Nakamae K. , Fujioka H.
Published: January 2006

A pattern matching technique between a scanning electron microscopy (SEM) exposed pattern image of large-scale integrated fine structures and computer-aided design (CAD) layout data based on the relaxation method is proposed wherein circular arc components are utilized. Edges are extracted from the SEM image and corners in the CAD layout are rounded. The edges in the SEM and CAD layout images are divided into three components: horizontal and vertical straight-line segments, and circular arcs. These components are expressed by bounding boxes; the optimal combination between the SEM and CAD components is then searched by using the probabilistic relaxation method. The mean vector among the obtained shift vectors shows the matching point. We applied our method to SEM exposed pattern images and compared the results with those of the conventional cross-correlation method. The results showed that our method has good robustness against change in shape of exposed pattern. The computation time of our method was comparable to the cross-correlation method.
Static and dynamic contact angles of water on photoresist
Authors: Burnett H. , Shedd T. , Nellis G. , Van Peski C.
Published: January 2006

Fluid management issues in an immersion lithography system include the retention of the liquid (i.e., prevention of residual liquid on the wafer) and the possible entrainment of gas bubbles within the immersion fluid. Three key parameters strongly influence the control of fluid within the lens gap: the static liquid/resist contact angle, the contact angle hysteresis, and the dynamic contact angle characteristics. This article presents a comprehensive set of data for these parameters on silicon wafers coated with six different photoresists and describes the experimental apparatus and data reduction techniques used to collect the data. Measurements for six candidate photoresists, one with a top-coat, indicate that air entrainment due to contact line motion is highly unlikely for typical immersion lithography systems. However, significant contact angle hysteresis does exist that may lead to meniscus failure and to the deposition of droplets at low to moderate wafer velocities. In addition, the receding dynamic contact angle can approach zero on some surfaces, leading to liquid film deposition.
Large area and wide dimension range x-ray lithography for lithographite, galvanoformung, and abformung process using energy variable synchrotron radiation
Authors: Utsumi Yuichi , Kishimoto Takefumi
Published: January 2006

We developed an x-ray lithography system for the “lithographite, galvanoformung, and abformung” process using synchrotron radiation at the NewSUBARU facility of the University of Hyogo, Hyogo, Japan. The x-ray lithography system can utilize two different energy regions: one is a high-energy region: from 2 to 12 keV, and the other is a low-energy region from 1 to 2 keV. Each energy region can be selected in accordance with the size and shape of the desired microstructures. Large-area patterning across an A4-size area was successfully performed with a highly uniform pattern thickness. Furthermore, high-aspect-ratio patterning using a high-x-ray-energy region was also achieved using this x-ray lithography system.
Vinyl ether formulations for step and flash imprint lithography
Authors: Kim E. K. , Stewart M. D. , Wu K. , Palmieri F. L. , Dickey M. D. , Ekerdt J. G. , Willson C. G.
Published: January 2006

Acrylates have been used as patterning monomers in step and flash imprint lithography. Vinyl ether formulations have a lower viscosity, faster curing rate, and higher tensile strength than acrylate formulations. However, the lack of commercially available, silicon-containing vinyl ether monomers has required the synthesis of several new vinyl ethers. An ideal monomer has low viscosity and low vapor pressure. The vapor pressure of silicon-containing vinyl ethers was predicted using the Joback-Reid, Lyderson, and Lee-Kesler methods. BVMDSO (1,1,3,3-tetramethyl-1,3-bis(vinyloxymethyl)-disiloxane) has the lowest viscosity of the synthesized silicon-containing vinyl ethers that meet the volatility requirement for a 80 pl dispense volume. The formulation of BVMDSO, CHDVE (cyclohexanedimethanol divinyl ether), and TEGDVE (triethylene glycol divinyl ether) shows good tensile strength and modulus. The formulation of BVMDSO, CHDVE, TEGDVE, and fluorinated acetate can print a 30 nm line because it has a low separation force and high tensile modulus.
Electron beam lithography patterning of sub-10nm line using hydrogen silsesquioxane for nanoscale device applications
Authors: Baek In-Bok , Yang Jong-Heon , Cho Won-Ju , Ahn Chang-Geun , Im Kiju , Lee Seongjae
Published: January 2006

We investigated novel patterning techniques to produce ultrafine patterns for nanoscale devices. Hydrogen silsesquioxane (HSQ) was employed as a high-resolution negative tone inorganic electron beam resist. The nanoscale patterns with sub-10nm linewidth were successfully formed. A trimming process of HSQ by the reactive ion etcher (RIE) played an important role for the formation of 5nm nanowire patterns. Additionally, hybrid lithography was used to produce various device patterns as well as to minimize proximity effects of electron beam lithography (EBL). Finally, we successfully fabricated triple-gate metal oxide semiconductor field effect transistor (MOSFET) with a gate length of 6nm by using the proposed patterning process.
Improving critical dimension accuracy and throughput by subfield scheduling in electron beam mask writing
Authors: Babin Sergey , Kahng Andrew B. , Măndoiu Ion I. , Muddu Swamy
Published: January 2006

Resist heating in high-voltage, high-throughput electron beam (e-beam) mask write is a significant source of critical dimension (CD) distortion. Excessive heating on the reticle determines changes in resist sensitivity, which in turn cause significant CD variation. CD distortions on the reticle are replicated onto the wafer with increased magnitude as determined by the mask error enhancement factor (MEEF). As designs enter the sub-90nm regime, CD variation has a significant impact on performance, performance variation, and product yield. Previous methods for reducing CD distortion include usage of lower e-beam current density, increased delays between electron flashes, and multipass writing. However, all of these methods lower mask writing throughput, which is increasingly becoming a limiting factor in semiconductor industry productivity. In this paper, we propose a novel method for minimizing CD distortion and maximizing mask writing throughput. By scheduling the writing of subfields, we perform simultaneous optimization of mask writing order and e-beam current density. We perform subfield scheduling by evaluating resist temperature of subfield orderings using a fast analytical temperature model. Simulation experiments show that the new subfield scheduling method can reduce the maximum resist temperature up to 12°C over existing sequential writing methods with unchanged mask writing throughput. Alternatively, improved subfield scheduling can enable the use of higher beam current densities, leading to increased writing throughput without compromising CD control.
Copper germanide Ohmic contact on n-type gallium nitride using silicon tetrachloride plasma
Authors: Schuette Michael L. , Lu Wu
Published: January 2006

A Ge∕Cu∕Ge Ohmic contact scheme has been applied to moderately-doped n-GaN, showing specific contact resistivity of 1.1×10−5Ωcm2 and contact resistance equal to 0.26Ωmm. SiCl4 RIE at a dc self-bias of −150V is found to reduce the GaN RMS surface roughness (Rq) from 4.6Åto3.2Å while a −350V treatment slightly increases Rq to 4.1Å. It is demonstrated by x-ray photoelectron spectroscopy that ion bombardment of n-GaN, in conjunction with a hydrochloric acid treatment, reduces surface oxidation and increases the concentration of nitrogen vacancies (VN), a donorlike defect, at the surface. Auger electron spectroscopy depth profiling shows that a 600°C anneal encourages interdiffusion of Ga and Ge such that the heavily-n-doped interfacial region caused by VN is further enhanced. The results therefore suggest that the Ohmic behavior of the Cu3Ge Ohmic contact on n-GaN is due to increased tunneling current at the metal/semiconductor interface caused by the creation of donor-like VN as well as Ge on VGa.
Large-area, infrared nanophotonic materials fabricated using interferometric lithography
Authors: Fan Wenjun , Zhang Shuang , Malloy K. J. , Brueck S. R. J.
Published: January 2006

In this paper, we discuss the characterization and fabrication of two nanophotonic materials for the infrared region by using IL—realizing a negative refractive index material and enhancing transmission through annular metallic coaxial aperture arrays.
Electrical properties of nanocontacts on silicon nanoparticles embedded in thin SiO2 synthesized by ultralow energy ion implantation
Authors: Ben Assayag G. , Shalchian M. , Coffin H. , Claverie A. , Grisolia J. , Dumas C. , Atarodi S. M.
Published: January 2006

In this paper, we present the room temperature current-voltage characteristics of large (100×100μm2) and a nanoscale (100×100nm2) metal-oxide-semiconductor (MOS) capacitor containing few silicon nanocrystals. The layer of silicon crystals is synthesized within the oxide of this capacitor by ultralow energy ion implantation and annealing. Current fluctuations in the form of discrete current steps and sharp peaks are apparent in the static and dynamic I(V) characteristics of the capacitor. These features have been associated to quantized charging and discharging of the nanoparticles and the resulting Coulomb interaction to the tunneling current.
Positioning of carbon nanotubes using soft-lithography for electronics applications
Authors: Plank N. O. V. , Ishida Masahiko , Cheung R.
Published: January 2006

Carbon nanotubes (CNTs) devices have been fabricated using two similar microfabrication processes involving poly(dimethylsiloxane) (PDMS) molecular stamping of 2-thiolpyridine and subsequent self-assembly of CNTs. The two methods allow the fabrication of CNT devices with >90% yield. From Vg=−5to+5V, when Ti–Au electrodes are fabricated on top of the self-assembled CNT films, our devices exhibit p-type field-dependent behavior. When the CNTs have been self-assembled across pre-defined Ti–Au electrodes, metallic conduction has been observed. The electronic properties of our back-gated CNT devices are found to depend upon CNT concentration in the original self-assembly solution. The final structure of the CNT device can affect the field dependency as a result of screening effects at the contact regions, with the 2-thiolpyridine acting as a further screening region.
Subcritical carbon dioxide assisted polymer nanofabrication at low temperatures
Authors: Yang Yong , Lee Ly James , Lu Wu
Published: January 2006

Polymer-based micro/nanoelectromechanical systems have attracted a great deal of interest from industries and academia. The common polymer fabrication methods involve either organic solvents or temperatures above the glass transition temperature, which is undesirable, particularly at the nanoscale. On the basis of different properties near polymer surfaces from those in the bulk, we introduce subcritical fluids [particularly carbon dioxide (CO2)] into polymer surfaces to manipulate the polymer properties at the nanoscale so that we can achieve low temperature polymer nanofabrication. Guided by CO2-enhanced surface dynamics of polymers, we developed a CO2 bonding technique to succeed in low temperature assembly of polymeric nanostructures. This CO2 bonding technique has been applied to seal polymeric nanofluidic biochips and construct well-defined three-dimensional biodegradable polymeric scaffolds for tissue engineering.
Investigation of multilayer structural changes in phase and amplitude-defects correction process
Authors: Lee Seung Yoon , Kim Tae Geun , Park Jae Gun , Song Joo Kyoung , Kim Oh Hyun , Yong Chul-Woong , Ahn Jinho
Published: January 2006

Controlling defects on the extreme ultraviolet lithography (EUVL) mask has become a critical issue among many EUVL element technologies. We have conducted experiments to investigate the correctability of two kinds of major defect types, phase and amplitude defects. Phase defects correctability was addressed by using the electron-beam local heating method and amplitude defects correctability were done by using the focused ion-beam (FIB). Additionally, two kinds of multilayers, Mo∕Si and Mo∕Ru∕Si, were used as substrates to inspect the behavior in a comparative way. As a result, the sink brought by electron-beam (e-beam) localized heating on a planar multilayer surface was about 8 and 13.6 nm in Mo∕Si and Mo∕Ru∕Si multilayers, respectively, under the e-beam dose of 250μC∕cm2. However, the heating effect was limited to within a few layers from the surface. FIB etching was also conducted on a planar surface of a multilayer. There are two types of FIB correction methods, image mode and spot mode. The etched area was relatively large (∼3μm×3μm) in image mode. But in the spot mode, the etched area could be confined to a few tens of nanometers in diameter. This FIB method also caused some damage on the multilayer surface.