bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoconductivity of vertically aligned ZnO nanoneedle array
Authors: Park Dongseok , Yong Kijung
Published: December 2008

A high-density vertically well-aligned ZnO nanoneedle array was fabricated on a ZnO-buffer film on silicon substrates by metal-organic chemical vapor deposition at a growth temperature of 480–500°C. Highly crystalline ZnO nanoneedle arrays showed a strong near-bandedge emission at 380nm in room-temperature photoluminescence. A simple ultraviolet (UV) sensor was fabricated by evaporating a Ag electrode on the ZnO nanoneedle array. The photoresponse results showed very high photocurrent (∼10−4A) from ZnO nanoneedles compared to a single-nanowire sensor (∼10−8A), indicating high sensitivity of the photosensor. It also showed fast rise and decay times in UV-on/off switching measurements.
A new approach to fabricating high density nanoarrays by nanocontact printing
Authors: Gu Jian , Xiao Xiaoyin , Takulapalli Bharath R. , Morrison Michael E. , Zhang Peiming , Zenhausern Frederic
Published: December 2008

The authors introduce a new scheme of nanocontact printing that fabricates nanoarrays using stamps generated by ultraviolet nanoimprint lithography. Array patterns can be generated by this printing technique in a high density (number of features per unit area) fashion with a feature size as low as 30nm and period of 100nm. Sub-500nm alignment accuracy for multilayer printing has been obtained using a traditional contact mask aligner. They also demonstrate that they can image a nanoarray labeled by streptavidin by atomic force microscope.
Copper ion transport induced dielectric failure: Inclusion of elastic drift and consequences for reliability
Authors: Achanta Ravi S. , Plawsky Joel L. , Gill William N.
Published: December 2008

The authors have modeled the copper ion concentration and internal electric field profiles in a SiO2 dielectric by solving the transient nonlinear continuity/Poisson equations. The predicted time-to-failure of the dielectric correlates well with the theory that failure occurs once copper ions accumulate to the point where the induced electric field at the cathode exceeds a critical value. However, the copper ion concentration at the cathode required for failure was much higher than the reported ion solubility, raising doubts about the validity of the model. More realistic values for the required copper ion concentration were obtained by incorporating an “elastic” diffusion term in the continuity equation. Adding this new term and increasing solubility, Ce, to the maximum value reported in the literature reduces the concentration at the cathode to a logically consistent value but does not significantly alter the predicted time-to-failure. The new formulation predicts a higher minimum applied electric field required to induce breakdown. This minimum field is larger than current devices see during operation.
Investigation of negative electron affinity in hydrogen complex deactivated surface of InP:Zn (100)
Authors: Williams M. D.
Published: December 2008

Ultraviolet photoemission spectroscopy is used to investigate the development of negative electron affinity at the surface of hydrogenated Zn-doped InP (100). Hydrogen injected into the material electronically passivates the local carrier concentration. Reverse-biased anneals of the InP under ultrahigh vacuum show a dramatic change in the work function of the material within a set annealing temperature range suggesting the establishment of negative electron affinity at the surface. The strength of the negative electron affinity is 1.08eV. This value is consistent with the deactivation energy of the H–Zn complex (1.14eV) determined previously. Spectral features are also shown to be sensitive to sample temperature. Hydrogen retrapping at the surface limits the effect and it is dependent on whether the surface is smooth or roughened. The electron affinity of the material is thus controlled with defect density and annealing temperature.
Reclamation of a molecular beam epitaxy system and conversion for oxide epitaxy
Authors: Carver Alexander G. , Henderson Walter , Doolittle W. Alan
Published: December 2008

An early 1980s vintage molecular beam epitaxy system, a Varian Gen II system, originally used for HgCdTe epitaxy, was converted into a system capable of growing thin-film complex metal oxides. The nature of some of the alternative oxides requires a thorough cleaning and, in some cases, complete replacement of system components. Details are provided regarding the chemistry of the etchants used, safety requirements for properly handling, and disposal of large quantities of etchants and etch by-products, and components that can be reused versus components that require replacement are given. Following the given procedures, an ultimate base pressure of 2×10−10Torr was obtained. Films grown in the system after reclamation contained no evidence of previously present materials down to the detection limit of secondary ion mass spectrometry.
Surface patterns from block copolymer self-assembly
Authors: Kim Ho-Cheol , Hinsberg William D.
Published: December 2008

It is widely recognized that further extension of optical lithography to even smaller dimensions will be accompanied by rapid increasing cost and difficulty. There is growing interest in devising alternative patterning methods that will support the evolution of microelectronics to the 10nm length scale. Block copolymer lithography, which uses self-assembled microdomains of block copolymers in thin films, can provide arrays of periodic patterns of 10–50nm length scales with a simple process and low cost. While this capability is attractive, the periodic nature of the microdomain patterns places significant restrictions on how block copolymer lithography can be practically implemented. In this review, the authors survey materials and methods for carrying out the controlled assembly of block copolymers in thin films for surface patterning applications. After a brief introduction to block copolymers and their phase behavior, the authors discuss ordering of block copolymer in thin films based on four different thickness categories. Approaches to directed self-assembly are reviewed along with the limitations and challenges of block copolymer lithography. Finally the authors note the circumstances that make it an opportune time to resolve the remaining technological issues facing block copolymer lithography and to demonstrate its utility as an adjunct to traditional photolithography.
Surface water reactivity of polycrystalline MgO and CaO films investigated using x-ray photoelectron spectroscopy
Authors: Craft H. S. , Collazo R. , Losego M. D. , Sitar Z. , Maria J.-P.
Published: December 2008

The authors report a study comparing the surface reactivities of the alkaline earth oxides MgO and CaO with respect to water vapor under ultrahigh and high vacuum conditions. Using x-ray photoelectron spectroscopy and a series of in vacuo exposures spanning ∼10−10Torr vacuum, to 10−6Torr flowing oxygen, the extent of surface hydroxylation was investigated by monitoring the O 1s photoelectron line. After the most aggressive exposures, the MgO surface reacted to form a maximum hydroxyl coverage of ∼1.3 ML (monolayer), while the CaO surface reached a maximum coverage of ∼3.0 ML. Both surface hydroxides could be removed by in vacuo thermal anneals; exposure to 250 and 500°C were required for MgO and CaO, respectively. These results are framed in terms of the suitability of these oxides in complex oxide-compound semiconductor heteroepitaxial multifunctional devices and with respect to understanding the development of surface morphology in epitaxial 111-oriented CaO and MgO thin films.
Tungsten metal gate etching in Cl2∕O2 inductively coupled high density plasmas
Authors: Morel T. , Bamola S. , Ramos R. , Beaurain A. , Pargon E. , Joubert O.
Published: December 2008

Plasma etching of W in a poly-Si∕TiN∕W∕HfO2 gate stack is investigated in Cl2∕O2 based plasmas. Preliminary studies have illustrated the issues induced with the introduction of a metal layer in the gate stack. Based on scanning electron microscopy observations, the authors first show that a mixture of Cl2, O2, and NF3 is required to successfully pattern the W layer without damaging the HfO2, poly-Si, and TiN profiles. For a better understanding of etch mechanisms, W etching is studied on blanket wafers and etch rates are presented and discussed with respect to the plasma parameters. The evolution of the etch rates as a function of O2 ratio in Cl2∕O2 and Cl2∕O2∕NF3 plasmas is interpreted. X-ray photoelectron spectroscopy analyses demonstrate that the introduction of O2 in Cl2 leads to the creation of a thick WOClx deposit on the gate sidewalls. However, the WOCl deposition can be controlled and eliminated by adding fluorine in the plasma during W etching.
Investigation of the oxide-assisted growth mechanism for nanowire growth and a model for this mechanism
Authors: Noor Mohammad S.
Published: December 2008

Oxide-assisted growth (OAG) mechanism produces high-density nonowires (NWs). Salient features of the existing models for this OAG mechanism and the fundamentals underlying this mechanism have been investigated in some detail. A simple, novel, malleable model for the OAG mechanism has been developed, and the concept of droplet used to develop this model has been articulated. The concept takes into consideration the size-dependent melting temperature depression. Two important elements of the model are (1) the attraction between the vapor-phase NW species and the droplet species, which leads to landing of the NW species on the droplet surface, and (2) the diffusion of the NW species through the droplet species to the liquid/solid interface, which leads to supersaturation and nucleation. The present investigation, together with our model, indicates that the assistance of a suitable oxide, the formation of nanoclusters/seeds, and the creation of droplets are all central to the OAG mechanism, which is essentially self-catalytic in nature. Various chemical reactions taking place on the droplet surface and the temperature range for these reactions are also important. The formation of a core and sheath during nucleation are the inevitable results of the use of oxide. The role of the droplet surface tension and the electrostatic forces between the droplet and the reactive (source) NW vapor species are crucial for OAG. Possible participation of a foreign element catalytic agent (FECA) in the NW growth by OAG mechanism has been examined. Based on these investigations, the present model appears to explain many of the OAG-grown NW characteristics. The experimentally observed oxide sheath has been addressed. Also, the basic causes of higher growth rates of the NWs grown by the OAG and FECA-mediated OAG mechanisms have been explained.
Hybridization sensing by electrical enhancement with nanoparticles in nanogap
Authors: Chen Chun-Chi , Ko Fu-Hsiang , Chang Edward Yi , Chang Feng-Chih , Kuo Shiao-Wei
Published: December 2008

In this work, the monolayer of gold nanoparticles within 72nm gap has been proposed to function as a DNA sensor. The authors suggest that the nanoparticles in the nanogap could act as hopping sites which amplify the conductance of hybridized DNA strands. The conductance amplification between single strand and hybridized DNAs through gold nanoparticles is observed. Various concentrations of capture and target DNA are discussed for optimal hybridization sensing purpose. With the help of 1nM capture DNAs, this sensor is able to analyze target DNA sequences at very low concentration of 1fM. Furthermore, by means of adjusting the denature temperature to 60°C, even single mismatch hybridization could be discriminated.
Photomask image enhancement using grating-generated surface waves
Authors: Lafferty Neal V. , Bourov Anatoly , Estroff Andrew , Smith Bruce W.
Published: December 2008

In recent years, the anomalous transmission of subwavelength apertures has become an emergent subject within the physical sciences. While the gain mechanism of these structures is still uncertain, the effect has been observed in several studies. Similar transmission enhancements may be realized for near-wavelength sized photomask structures by including buried grooves in a dual write mask design. Several configurations of one-dimensional transmitting apertures and buried grooves have been investigated under TM illumination using the finite element method. Periodic subwavelength apertures with identical sized nontransmitting assist grooves were used to validate the model against reference data in the near-IR. The method was also used to investigate similar structures featuring a larger than wavelength transmitting aperture. Although transmission through the slot was increased by 1.67×, the primary lithographic benefit was an increase in the magnitude of the primary imaging orders relative to the zeroth diffracted order. A similar approach was extended to structures scaled to 248 nm to show application as a potential lithographic assist feature. A 5.7× transmission increase was observed using aluminum on fused silica configuration using 30 nm slots on a 192 nm pitch.
The effects of molecular weight on the exposure characteristics of poly(methylmethacrylate) developed at low temperatures
Authors: Yan M. , Choi S. , Subramanian K. R. V. , Adesida I.
Published: December 2008

Poly(methylmethacrylate) (PMMA) with various molecular weights exposed using 50keV electron beam have been investigated at subzero developer temperatures. Contrast curves for Methyl Isobutyl Ketone (MIBK):Isopropyl Alcohol (IPA)=1:3 and MIBK:IPA=1:7 developers were determined. The contrast curves for different molecular weight PMMA resists converge into a single curve at lower temperatures. At low temperatures, the line edge roughness and resolution improved. However, minimum line pitch shows no significant improvement while dose latitudes for a particular line pitch increased. It is shown that at low temperatures, linewidth resolution and periodicity are invariant for the different PMMA molecular weights (50K to 2.2M) used in this work.
Decomposition of catechol and carbonaceous residues on TiO2(110): A model system for cleaning of extreme ultraviolet lithography optics
Authors: Jacobson Peter , Li Shao-Chun , Wang Chuandao , Diebold Ulrike
Published: December 2008

High energy photons used to expose photoresists in extreme ultraviolet lithography (92eV, 13.5nm) photoexcite electrons from Mo∕Si multilayer mirror surfaces. Photoemitted electrons participate in the formation of carbonaceous residues on the mirror surface significantly affecting the mirror reflectivity. We explore mitigation strategies utilizing TiO2(110) as a model for the capping layer. Two carbon containing surfaces are examined; an ordered catechol monolayer and a carbonaceous layer. Excimer laser sources (XeF and KrF) coupled with oxidizing gas backgrounds (NO and O2) are shown to be effective for the photocatalytic removal of carbon. Utilizing x-ray photoemission spectroscopy and scanning tunneling microscopy carbon removal is shown to proceed through oxidation of the overlayer.
High and low temperature behavior of Ohmic contacts to AlGaN/GaN heterostructures with a thin GaN cap
Authors: Miller M. A. , Mohney S. E.
Published: December 2008

V/Al/V/Ag contacts that provide low specific contact resistances as well as smooth surfaces and contact edges on AlGaN/GaN heterostructures were recently introduced. In the present study, the contacts are examined in greater detail, including an evaluation of their high temperature stability and their specific contact resistance as a function of measurement temperature. The contacts provide a low specific contact resistance of 5.2×10−7 Ω cm2 and contact resistance of 0.15 Ω mm after aging for 10 h at 500 °C in flowing N2. Furthermore, cross-sectional transmission electron microscopy (TEM) of the aged V/Al/V/Ag contacts shows little change in phase formation compared to the annealed contacts that were not aged. Beneath the annealed V/Al/V/Ag metallization, the AlGaN layer is left intact. On the other hand, cross-sectional TEM images of previously reported V/Al/V/Au and Ti/Al/Ti/Au contacts reveal that both of the Au-bearing metallizations react through a portion of the AlGaN layer and directly contact the underlying GaN. By comparing these TEM images with the observed temperature dependence of the specific contact resistance of all of the contacts measured from 77 to 573 K, conclusions regarding current transport mechanisms were drawn.
Modifications of dielectric films induced by plasma ashing processes: Hybrid versus porous SiOCH materials
Authors: Darnon M. , Chevolleau T. , David T. , Posseme N. , Ducote J. , Licitra C. , Vallier L. , Joubert O. , Torres J.
Published: December 2008

This work focuses on the impact of oxidizing (O2) and reducing plasma ashing chemistries (NH3, CH4) on the modifications of dielectric materials in a porous or an hybrid state (SiOCH matrix+porogen). The plasma ashing processes have been performed on blanket wafers using O2, NH3, and CH4 based plasmas. The modifications of the remaining film after plasma exposures have been investigated using different analysis techniques such as x-ray photoelectron spectroscopy, infrared spectroscopy, x-ray reflectometry, and porosimetric ellipsometry. For the porous material the authors have shown that NH3 and O2 plasmas induce carbon depletion and moisture uptake while the CH4 plasma only leads to important carbon depletion without moisture uptake and to the formation of a thin carbon layer on the surface. For the hybrid material, no significant material modification is evidenced with the O2 plasma while an important methyl depletion and porogen degradation are observed with reducing chemistries such as CH4 and NH3 plasmas. The impact of the porogen on the film modification and the value of the dielectric constant will be presented and discussed.
HBr-based inductively coupled plasma etching of high aspect ratio nanoscale trenches in GaInAsP∕InP
Authors: Zhou Wei , Sultana N. , MacFarlane D. L.
Published: December 2008

The authors report inductively coupled plasma (ICP) dry etching of nanoscale trenches with feature sizes of approximately 140nm wide by 20μm long by 3μm deep in InP with and without quantum wells, based on HBr chemistry. Both focused ion beam and electron beam lithography nanopatterned features are presented with high aspect ratios in excess of 30:1. Importantly, with HBr, hybrid GaInAsP∕InP heterostructures can be anisotropically and vertically etched through with reasonable smoothness at 165°C, which is comparatively lower than what chlorine-based chemistry requires and is therefore beneficial for achieving reliable InP devices. The phenomenon of aspect ratio dependent etching, or reactive ion etch lag, begins to manifest itself when the etch aspect ratio of InP approaches 30:1 using this ICP technique. The application of interest is a novel coupler for integrated photonics.
Effect of the electric field on the form stability of a Schottky electron emitter: A step model
Authors: Bronsgeest M. S. , Kruit P.
Published: December 2008

The stability of the physical shape of an electron emitter (co)determines the stability of the performance of electron-beam equipment. A typical short-term instability of the Schottky electron source is the instability of the (100) facet at the tip end known as “collapsing rings.” This instability causes probe instabilities, but it is known from experiments that this can be prevented by applying high enough extraction voltages. The phenomenon of collapsing rings can be explained with a step-flow model, which is based on variations in equilibrium concentrations of adatoms on the surface. The effect of the extraction voltage can be incorporated by acknowledging the redistribution of the surface charge associated with adatom formation. For operation at constant extraction voltages the adatom formation energy becomes a function of the local charge density. The charge-density distribution on the emitter surface as a function of the applied extraction voltage can be calculated with boundary-element methods. It is shown that, provided the relevant material properties are known, it can be predicted if, for a given tip shape, a collapse is to be expected.
Fabrication of the nanoimprint mold using inorganic electron beam resist with post exposure bake
Authors: Unno Noriyuki , Taniguchi Jun , Shizuno Miyako , Ishikawa Kiyoshi
Published: December 2008

Nanoimprint lithography (NIL) is the preferred technique for next-generation nanometer-scale patterning because of its cost effectiveness and simplicity when compared to conventional technology. The replicated pattern depends on the mold pattern, hence efficient methods for fabricating the fine mold are critically required and have recently become intensive subjects of research. This study reports a new method for the fabrication of a fine mold: this method uses low-acceleration-voltage (4kV) electron beam lithography with spin on glass (SOG), which is used as a positive-tone inorganic resist. Although our SOG process does not contain chemically amplified material, postexposure bake (PEB) was characteristically used in the authors’ process. The PEB process caused the annealing effect for the SOG and also suppressed the proximity effect. Consequently, a line-and-space pattern nanoimprint mold with a sub-50nm spacing was fabricated at 4kV using their process, and ultraviolet NIL was successfully carried out using the fabricated mold.
Ion track lithography and graphitic nanowires in diamondlike carbon
Authors: Krauser J. , Nix A.-K. , Gehrke H.-G. , Hofsäss H. , Trautmann C. , Weidinger A. , Wünsch F. , Bruns J.
Published: December 2008

Ion track lithography is well established and is based on heavy ions of several hundred MeV energy passing through a polymer film and thereby changing the material properties along the trajectory of each ion. By selective chemical track etching, small channels (down to 20–30nm diameter) are formed which can be filled with another material or can serve as mask for further etching steps. Another application uses unetched ion tracks directly for nanostructuring. The authors’ investigations showed that graphitic nanowires are formed along ion tracks in insulating diamondlike carbon films. The diameter of these conducing filaments is in the order of 8nm. In the present article the authors describe a combination of these two possibilities to create several nanodevices such as cold field emission devices, quantum-based electronics, or interconnections in very-large-scale integrated circuits. Since the lithographic structure and the conducting filament are produced by the same ion track, the two parts of the device are self-aligned and need no further adjustment. Furthermore, it should be mentioned that the structure is created by a single ion and therefore is automatically very small in diameter and does not require special beam focusing.
Potential of a rotary stage electron beam mastering system for fabricating patterned magnetic media
Authors: Miyazaki T. , Hayashi K. , Kobayashi K. , Kuba Y. , Ohyi H. , Obara T. , Mizuta O. , Murayama N. , Tanaka N. , Kawamura Y. , Uemoto H.
Published: December 2008

To fabricate master templates of high-density patterned magnetic media, the authors developed a high-resolution and high-throughput rotary stage electron beam mastering system. They accomplished the fabrication of discrete track media groove patterns with 45nm track pitch, and also a dense bit array with both track and bit pitch of 35nm for bit patterned media under the conditions of a bit rate of 1.22MHz∕bit at 50kV acceleration voltage. The high resolution and high throughput are derived from using a continuous stage movement flyback lithography (CSFL) function. CSFL is enabled by differentiated capabilities, such as an electron optical column that achieves a large beam current at a small beam diameter, and a friction-driven slider stage that provides a highly accurate positioning capability and a dynamic focus correction feature and r-theta stage driving. The CSFL capability, working in conjunction with a blankingless beam shift lithography (BLSL), is very effective for fabricating various kinds of servo pattern elements, such as grooves and dots, grooves and right-angled grooves, grooves and half-pitch-shift dot arrays, and various pit length patterns, to construct effective servo patterns.
Experimental validation of full-field extreme ultraviolet lithography flare and shadowing corrections
Authors: Myers A. M. , Lorusso G. F. , Kim I. , Goethals A. M. , Jonckheere R. , Hermans J. , Baudemprez B. , Ronse K.
Published: December 2008

Extreme ultraviolet lithography (EUVL) is the leading candidate for 22nm half-pitch device manufacturing. IMEC has a fully integrated 300mm EUVL process line incorporating an Alpha Demo Tool (ADT) from ASML, aimed to understand issues related to the introduction of EUV technology in high-volume manufacturing. This study experimentally investigates flare and shadowing correction strategies. Experimental characterization of the flare of the ADT is reported, as well as experimental rules for flare variation correction. With respect to shadowing, shadowing corrections are experimentally estimated. Comparisons of experimental data and rigorous simulation are also presented, and a computationally efficient methodology to generate a full-chip flare map is proposed.
Improving organic thin-film transistor performance by nanoimprint-induced chain ordering
Authors: Cui Dehu , Li Huifeng , Park Hyunsoo , Cheng Xing
Published: December 2008

The chain configuration in conjugated polymer films has a significant impact on the electronic and optical properties of polymer semiconductors, which in turn dictate the device performances of polymer electronics. This article presents a new method to control chain orientation in polymer semiconductors by direct nanoimprint. Nanoimprint-induced chain orientation in conjugated polymer imparts strong optical birefringence in patterned microstructures. X-ray diffraction on patterned films exhibits higher level of chain ordering as nanoimprint temperature increases. Polarized absorption spectra show progressive redshift at higher nanoimprint temperature. The carrier mobility in thin-film transistors based on nanoimprinted grating equals to 12 times of that without patterning. Anisotropies of material properties and device performance are observed in all conjugated polymer structures and devices patterned by nanoimprint. It is expected that the unique ability to control chain orientation will enable nanoimprint to play an important role in tailoring the performance of polymer electronics and sensors.
Sputtering limits versus signal-to-noise limits in the observation of Sn balls in a Ga+ microscope
Authors: Castaldo V. , Hagen C. W. , Rieger B. , Kruit P.
Published: December 2008

In principle, a scanning ion microscope can produce smaller probe sizes than a scanning electron microscope because the diffraction contribution is smaller. However, the imaging resolution is often severely limited by the sputtering damage. In this article, an experimental procedure to establish the limit of a focused ion beam system for imaging purposes is proposed. The procedure is based on the observation of the change in geometry (i.e., shrinking) of the features in a Sn-ball sample imaged with a Ga+ beam. Plots of the balls’ diameter versus the irradiation time give a straightforward visual evaluation of the time allowed for the observation of a single feature before the removal of material due to the ion bombardment becomes unacceptable. For each particle, the curve, together with the error band connected with the imaging process, gives the values of uncertainty/resolution due to the two competing processes, collecting of information (for example, from secondary electrons) and damaging of the target. A plot of the uncertainty that is derived from these two processes for different sampling times allows the determination of the limiting factor of the imaging mode in use, and, ultimately, the highest possible resolution obtainable with a given machine for the observation of a certain sample. Together with simulations and theoretical studies, the described procedure will be able to confirm the effectiveness of the new ion sources that are currently being developed.
Abbe singular-value decomposition: Compact Abbe’s kernel generation for microlithography aerial image simulation using singular-value decomposition method
Authors: Chen Charlie Chung Ping , Gurhanli Ahmet , Chiang Tse-Yu , Hong Jen-Jer , Melvin Lawrence S.
Published: December 2008

Abbe’s method and Hopkin’s method are among the most popular microlithography aerial image simulation methods. In particular, Hopkin’s method is generally more popular for the high speed aerial image simulation domain, and it is used in model-based optical proximity correction. This is due to a general perception that Hopkin’s method can generate more compact sets of kernels compared with Abbe’s method, due to the application of a singular-value decomposition (SVD) process to Hopkin’s large transmission cross coefficient matrix. On the other hand, the primitive Abbe’s method is very simple, since it only needs to decompose the source field into independent point sources with a two-dimensional partitioning criteria. Albeit its simplicity, compared with Hopkin’s method, in general, Abbe’s method, generates a larger set of kernels. In this article the authors propose applying SVD to the original Abbe’s kernels, the essential kernels according to their singular values. Experimental results show that the algorithm, the Abbe-SVD method, accomplishes over 68 times of both runtime and memory saving over the traditional Hopkin’s SVD method for kernel generation.
Optical properties of sputtered fluorinated ethylene propylene and its application to surface-plasmon resonance sensor fabrication
Authors: Keathley P. D. , Hastings J. T.
Published: December 2008

The optical properties of sputtered fluorinated ethylene propylene (FEP) thin films (100–400nm) were analyzed using spectroscopic ellipsometry. Glass (similar to BK7) and silicon substrates were used, and deposition rates on glass were found to be on average 37% higher than on silicon. Refractive indices of the deposited films at 630nm ranged from 1.379 to 1.392 on glass and from 1.381 to 1.417 on Si, which roughly corresponds to a 4.3% increase when compared to the bulk material value of 1.335. By using the optical properties of the deposited FEP films, it was shown through modeling that they present a possible alternative when fabricating dual-mode surface-plasmon resonance sensors that can differentiate bulk and surface refractive index changes.
Linewidth uniformity in Lloyd’s mirror interference lithography systems
Authors: O’Reilly Thomas B. , Smith Henry I.
Published: December 2008

Control of linewidth in patterns written with interference lithography (IL) is an important part of process control for many applications, requiring an understanding of how exposure parameters, such as dose and dose modulation, vary across the exposed area, and how a given photoresist will respond to changes in those parameters. This article presents a model of linewidth variation in a common IL system, Lloyd’s mirror, along with some results derived from that model that relate to optimizing the linewidth uniformity that can be achieved for a given application. An extension to a previously reported resist-characterization method that makes it possible to directly measure how changes in dose modulation affect linewidth is also discussed.
Fabrication of metallic nanoslit waveguides with sharp bends
Authors: Lu M. , Ocola L. E. , Gray S. K. , Wiederrecht G. P.
Published: December 2008

Metallic nanoslit waveguides are promising candidates for ultrahigh-density optical interconnections. A variety of devices based on metallic nanoslit waveguides have already been proposed that show a great superiority over conventional photonic devices for compactness. However very few two-dimensional devices have been experimentally demonstrated with in-plane geometries due to fabrication difficulties. In this article, a feasible process is presented using traditional semiconductor fabrication technologies such as mix-and-match lithography and electroplating, which is cable of fabricating complicated 100 nm wide, 800 nm deep gold slit waveguides with multiple sharp right-angle corners. The process can be extended to volume production manufacturing with minor modifications, thus enabling the fabrication of nanoslit photonic circuits and networks.
Fabrication of elastomer pillar arrays with modulated stiffness for cellular force measurements
Authors: Ghassemi S. , Biais N. , Maniura K. , Wind S. J. , Sheetz M. P. , Hone J.
Published: December 2008

The mechanical properties of a cell’s environment can alter behavior such as migration and spreading, and control the differentiation path of stem cells. Here the authors describe a technique for fabricating substrates whose rigidity can be controlled locally without altering the contact area for cell spreading. The substrates consist of elastomeric pillar arrays in which the top surface is uniform but the pillar height is changed across a sharp step. Preliminary results demonstrate the effects on cell migration and morphology at the step boundary.
Improvement in linewidth roughness by postprocessing
Authors: Chandhok Manish , Frasure Kent , Putna E. Steve , Younkin Todd R. , Rachmady Willy , Shah Uday , Yueh Wang
Published: December 2008

In order to meet the linewidth roughness (LWR) requirements for the 16nm node, postprocessing methods need to be investigated to reduce the LWR after the lithography step. We present the results of five different techniques applied to a single extreme ultraviolet photoresist. The results show that rinse has the most promise in achieving the nearly two time LWR improvement needed. However, other techniques such as etch/trim, hardbake, vapor smoothing, and ozonation give at least 10%–20% LWR reduction and could be further optimized. Some of the physical based techniques which melt the photoresist reduce the midspatial frequency (50–10nm period) roughness, whereas chemical based techniques reduce the low order spatial frequencies (∼500–50nm period). Hence, a combination of techniques may be the ultimate solution.
Process variation-aware three-dimensional proximity effect correction for electron beam direct writing at 45nm node and beyond
Authors: Ogino Kozo , Hoshino Hiromi , Machida Yasuhide
Published: December 2008

The simplified electron energy flux (SEEF)model by which the backscattered energy distribution in the multilayered structure is calculated has been applied to the analysis of critical dimension (CD) variations caused by the thickness variations in copper interconnect. The SEEF model defines the reflection, downward transmission, and upward transmission of electron energy fluxes in each layer. Parameters of the SEEF model are expressed as functions of the depth from the substrate surface and are modified by the approximation in regard to the thickness variation. Using this approach, the process window for the dose and thickness variation has been analyzed quantitatively and the necessity of improving the process window has been confirmed especially at 45nm node and beyond. Moreover, a variation-aware proximity effect correction method, in which CD variations caused by process variations are reduced and dose margins for various patterns with the same linewidth are equalized, is proposed. The correction method improves the process window for isolated line pattern and 1:1 line-and-space pattern when the sixth wiring layer is fabricated.
Electrothermal actuation studies on silicon carbide resonators
Authors: Mastropaolo Enrico , Cheung Rebecca
Published: December 2008

The electromechanical behavior of SiC clamped-clamped beam (bridge) resonators with u-shaped aluminium (Al) electrodes on top has been studied as a function of electrode length, width, and spacing. Negative and positive deflections have been observed, indicating a complex interplay exhibited by the combined single material and bimorph characteristics of the resonator structures. It has been found that, both experimentally and theoretically, devices with electrodes applied on the root of the beam have similar or higher displacement amplitudes compared to devices with electrodes covering the half or the entire beam. Moreover, the displacement and vibration amplitudes can be maximized by increasing the electrode width and/or decreasing the spacing.
Improved crystalline quality nonpolar a-GaN films grown by hydride vapor phase epitaxy
Authors: Donskov A. A. , D’yakonov L. I. , Govorkov A. V. , Kozlova Y. P. , Malakhov S. S. , Markov A. V. , Mezhennyi M. V. , Pavlov V. F. , Polyakov A. Y. , Smirnov N. B. , Yugova T. G. , Pearton S. J.
Published: December 2008

Nonpolar a-GaN films were grown by hydride vapor phase epitaxy on r-sapphire. As the thickness of the grown films was increased from 50 to over 250μm, the width of the double-crystal rocking curve for the (11–20) reflection decreased from 2000to500arcsec, indicating a strong decrease in the dislocation density. Microcathodoluminescence mapping of the thick films suggests that the dislocation density is ∼102cm−2, which is more than two orders of magnitude lower than for thin films. The authors also observe a corresponding decrease in the density of residual donors from 1020to1018cm−3, with respective mobility increase from (10–20) to 150cm2∕Vs. The luminescence spectra of the thin films show the presence of intense defect bands attributed in literature to stacking faults. These bands are very strongly suppressed in thick films, which also show about an order of magnitude higher band edge luminescence intensity.
The effects of oxygen plasma on the chemical composition and morphology of the Ru capping layer of the extreme ultraviolet mask blanks
Authors: Belau Leonid , Park Jeong Y. , Liang Ted , Somorjai Gabor A.
Published: December 2008

Contamination removal from extreme ultraviolet (EUV) mask surfaces is one of the most important aspects to improve reliability for the next generation of EUV lithography. The authors report chemical and morphological changes of the ruthenium (Ru) mask surface after oxygen plasma treatment using surface sensitive analytical methods: x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and transmission electron microscopy (TEM). Chemical analysis of the EUV masks shows an increase in the subsurface oxygen concentration, Ru oxidation, and surface roughness. XPS spectra at various photoelectron takeoff angles suggest that the EUV mask surface was covered with chemisorbed oxygen after oxygen plasma treatment. It is proposed that the Kirkendall effect is the most plausible mechanism that explains the Ru surface oxidation. The etching rate of the Ru capping layer by oxygen plasma was estimated to be 1.5±0.2Å∕min, based on TEM cross sectional analysis.
Growth of Si nanowires on micropillars for the study of their dopant distribution by atom probe tomography
Authors: Xu T. , Nys J. P. , Grandidier B. , Stiévenard D. , Coffinier Y. , Boukherroub R. , Larde R. , Cadel E. , Pareige P.
Published: December 2008

This article reports on the growth of Au islands on the Si(111) surface as a function of the Au evaporation rate and the temperature of the surface in ultrahigh vacuum. By controlling the density of the Au islands and their size, it is possible to subsequently grow single vertically oriented Si nanowires on top of (111)-oriented silicon micropillar and analyze their chemical composition at the atomic scale with the femtosecond laser assisted tomographic atom probe. Three-dimensional images of the atom distribution in the nanowire, in particular, the distribution of boron impurities, are obtained and compared to the intended impurity concentration.
Coupling Reactions of Chlorofluoro and Perfluoroalkyl Iodides
Authors: Wlassics Ivan , Tortelli Vito
Published: December 2008

Coupling reactions of chlorofluoro- and perfluoroalkyl iodides Rf-I with Rf = ClCF2CFCl(CF2)3CF2-, ClCF2CFClO(CF2)3CF2-, ClCF2CFCl-, (CF3)2CF- , (CF3)2CFCF2CF2- in the presence of a zinc/solvent system give dimers in good yields. Both homodimerizations (one iodide) and heterodimerizations (two different iodides) have been studied. The effect of temperature and solvent is shown. The zinc mediated dechlorination of vicinal chlorine atoms in the dimers afforded terminal alkenes and dienes.
Probing the Reactivity of the Potent AgF2 Oxidizer. Part 1: Organic Compounds
Authors: Grzybowska Dorota , Malinowski Przemysław , Mazej Zoran , Grochala Wojciech
Published: December 2008

The reactivity of Ag(II)F2 towards a variety of organic compounds of a high degree of fluorination has been investigated. AgF2 readily fluorinates P(C6F5)3 to PF2(C6F5)3, and attacks the isothiocyanate functional group, -NCS, yielding Ag2S. Perfluorinated aliphatic nitriles resist the action of AgF2, but aromatic C6F5CN undergoes a radical-initiated oligomerization; byproducts include C6F6CN• and C6F5N2• (after intramolecular rearrangement following the bimolecular reaction). AgF2 oxidizes higher fluorosulfonic acids (C4F9SO3H, C8F17SO3H) at or close to the room temperature and triflic acid (CF3SO3H) at its boiling point to the corresponding peroxides. CF3COOH and CF3CONH2 are also decomposed in redox reactions, but the gaseous products have not been identified. Surprisingly, AgF2 is kinetically inert to perfluorinated aromatic hydrocarbons and to CCl4, but it decomposes CBr4 with vigorous elimination of Br2. CI4 decomposes explosively in the presence of AgF2. C6F5OH and CF3COOH are readily oxidized with AgF2 but, surprisingly, t-C4F9OH is kinetically resistant under similar conditions. Coordination complexes of perfluorinated aza and oxa Lewis bases (including perfluorinated 15-crown-5 ether) and AgF2 are not formed under the experimental conditions.
Solid Polymer Electrolytes from Crosslinked PEG and Dilithium N,N'-Bis(trifluoromethanesulfonyl)perfluoroalkane-1,ω-disulfonamide and Lithium Bis(trifluoromethanesulfonyl)imide Salts
Authors: Geiculescu Olt E. , Rajagopal Rama V. , Mladin Emilia C. , Creager Stephen E. , Desmarteau Darryl D.
Published: December 2008

The present work consists of a series of studies with regard to the structure and charge transport in solid polymer electrolytes (SPE) prepared using various new bis(trifluoromethanesulfonyl)imide (TFSI)-based dianionic dilithium salts in crosslinked low-molecular-weight poly(ethylene glycol). Some of the thermal properties (glass transition temperature, differential molar heat capacity) and ionic conductivities were determined for both diluted (EO/Li = 30:1) and concentrated (EO/Li = 10:1) SPEs. Trends in ionic conductivity of the new SPEs with respect to anion structure revealed that while for the dilute electrolytes ionic conductivity is generally rising with increased length of the perfluoroalkylene linking group in the dianions, for the concentrated electrolytes the trend is reversed with respect to dianion length. This behavior could be the result of a combination of two factors: on one hand a decrease in dianion basicity that results in diminished ion pairing and an enhancement in the number of charge carriers with increasing fluorine anion content, thereby increasing ionic conductivity while on the other hand the increasing anion size and concentration produce an increase in the friction/entanglements of the polymeric segments which lowers even more the reduced segmental motion of the crosslinked polymer and decrease the dianion contribution to the overall ionic conductivity. DFT modeling of the same TFSI-based dianionic dilithium salts reveals that the reason for the trend observed is due to the variation in ion dissociation enthalpy, derived from minimum-energy structures, with respect to perfluoroalkylene chain length.
Cytotaxonomy ofSimulium siamenseTakaoka and Suzuki (Diptera: Simuliidae) in Thailand
Authors: Kuvangkadilok Chaliow , Lualon Unchulee , Baimai Visut
Published: December 2008

Larval polytene chromosomes of 1824 individuals of Simulium siamense Takaoka and Suzuki from 32 locations in northern, northeastern, eastern, and central Thailand were examined. Differences in sex chromosomes, fixed inversions, and the kind and frequency of floating inversions revealed five cytoforms (A, B, C, D, and E). In contrast to most Simulium species, females of S. siamense are the heterogametic sex (ZW) and males are the homogametic sex (ZZ). Cytoform A differs from the others by having 23 floating inversions and undifferentiated sex chromosomes (W0was undifferentiated from Z0). Cytoforms B, C, and D differ from each other by having different W chromosomes (W1, W2, and W3) in females. Cytoform E is characterized by having two fixed inversions, IS-1 and IIIS-2. Cytoform A is widely distributed throughout the geographic ranges of the species in northern, northeastern, eastern, and central Thailand, whereas cytoforms B, C, and D are restricted to a few locations in central Thailand. Although the larvae of the five cytoforms are morphologically similar, they seem to occupy different ecological habitats, which should be further investigated. At present, no definite conclusion can be drawn as to the taxonomic status of the cytoforms of S. siamense. However, this study indicates that S. siamense is represented by at least five cytoforms, of which cytoform B is the most distinct by having complete sex linkage and no floating inversions.
Association mapping of yellow pigment in an elite collection of durum wheat cultivars and breeding lines
Authors: Reimer S. , Pozniak C. J. , Clarke F. R. , Clarke J. M. , Somers D. J. , Knox R. E. , Singh A. K.
Published: December 2008

Association mapping (AM) is an alternative or complementary strategy to QTL mapping for describing associations between genotype and phenotype based on linkage disequilibrium (LD). Yellow pigment (YP), an important end-use quality trait in durum wheat (Triticum turgidum L. var. durum), was evaluated to determine the ability of AM to identify previously published QTL and to identify genomic regions for further genetic dissection. The YP concentration was determined for 93 durum wheat accessions sampled from a variety of geographic origins. Analysis of population structure using distance- and model-based estimates indicated the presence of five subpopulations. Using subpopulation assignments as covariates, significant (P < 0.05) marker–trait associations for YP were detected on all chromosomes of the durum genome. Using AM, genomic regions housing known YP QTL were confirmed, most notably the group 7 chromosomes. In addition, several markers on the group 1, 2, and 3 chromosomes were identified where QTL have yet to be reported. A phytoene synthase gene, Psy1-B1, a potential candidate gene for YP, was significantly associated with YP and was in strong LD with microsatellite markers on the distal end of 7BL. Our results demonstrated that AM complemented traditional QTL mapping techniques and identified novel QTL that should be the target of further genetic dissection.