bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin-film transistors with amorphous indium gallium oxide channel layers
Authors: Chiang H. Q. , Hong D. , Hung C. M. , Presley R. E. , Wager John F. , Park C.-H , Keszler D. A. , Herman G. S.
Published: December 2006

Indium gallium oxide-based thin-film transistors (TFTs) are formed using rf magnetron sputtering of the channel layer. These TFTs exhibit qualitatively ideal characteristics, including excellent drain current saturation. Various deposition parameters, annealing treatments, and stoichiometries are explored. Varying the oxygen partial pressure is found to have a significant effect on device performance. Decreasing the oxygen partial pressure increases the incremental channel mobility μinc while decreasing (becomes more negative) the turn-on voltage Von. Increasing indium concentration of the channel material increases μinc, while decreasing Von. The maximum value of μinc, ∼27cm2V−1s−1, is obtained by annealing at 600°C, with corresponding Von and drain current on-to-off ratio values of approximately −14V and >106, respectively. Additionally, TFTs subjected to a 200°C postdeposition annealing exhibit μinc and Von of ∼19cm2V−1s−1 and 2V, respectively.
Quantifying release in step-and-flash imprint lithography
Authors: Chan Edwin P. , Crosby Alfred J.
Published: December 2006

Step-and-flash imprint lithography (S-FIL) is a leading candidate as the next-generation lithographic technique for replicating sub-10-nm features. The success of this technique is largely connected to the proper control of the interface formation and separation during the imprinting process. In particular, the release process of the imprinted layer from the master template is not straightforward. During release, the path of interface separation must follow precisely the complex topography of geometric features on the sub-100-nm length scale. While the issue of release is currently being addressed, more work is required to understand the underlying mechanisms in controlling release to increase the robustness of this technique in order to make it industrially viable. In this article, the authors describe a metrology for quantifying release in S-FIL. They show that the surface property and the elastic modulus of the template material control the release characteristics. They demonstrate that substituting the rigid template with a soft, elastomeric template can drastically lower the separation force necessary for release.
Proposal of a new microreactor for vertical chemical operation
Authors: Utsumi Yuichi , Asano Toshifumi , Ukita Yoshiaki , Matsui Katsuhiro , Takeo Masahiro , Negoro Seiji
Published: December 2006

The authors proposed and fabricated a new microreactor stack which would be able to achieve a vertical fluid flow operation for the environment analysis, postgenome analysis, gene diagnosis, and screening of useful materials for medicine manufacture. This reactor is characterized as a simple structure with new aspects of the vertical fluid transportation using a proposed fluid filter with array of micro-through-bores. The deep x-ray lithography process using synchrotron radiation was used for the fabrication of the fluid filter. The feasibility of vertical liquid transportation was investigated using computational fluid dynamics analysis. It is indicated that the vertical liquid transportation is possible using the proposed fluid filter, and high efficiency mixing of liquid was also expected during transportation through the fluid filter. It was confirmed that the fluid flow velocity through the filter can be controlled by varying the load pressure around several kilopascals. A rapid enzyme reaction was successfully carried out and product concentration was observed using ultraviolet absorption spectroscopy. It was demonstrated that the proposed chemical reactor had a good vertical fluid flow operation performance for unit chemical operation.
Reverse transfer of nanostencil patterns using intermediate sacrificial layer and lift-off process
Authors: Park Chan Woo , Vazquez Mena Oscar , van den Boogaart Marc A. F. , Brugger Jürgen
Published: December 2006

We propose a new process by which patterns produced by nanostencil lithography can be reversed, so that the final pattern on the substrate has the same contrast (filled or empty) as that of the stencil. In this process, the stencil pattern is first formed on an intermediate sacrificial layer, and then transferred onto the underlying substrate in a reverse manner. Using this process, we can form various pattern structures that cannot be produced by the normal stencil process, such as an array of pores or multiple parallel bridges. Because a bridge in the stencil is transferred also as a bridge on the substrate, we can not only avoid the widening of a narrow bridge pattern by the stress-induced bending of the membrane, but also reduce the width of the bridge even further using the pattern blurring. Using SiO2 as an intermediate layer, we have fabricated various reversed Cr patterns on Si, including an array of 800nm circular pores and a 100-nm-wide and 150-nm-long nanobridge.
Mobility study of a new naphthalenetetracarboxylic diimide derivative
Authors: Yang D. , Shrestha R. P. , Li Y. X. , Yan L. , Irene E. A.
Published: December 2006

New naphthalenetetracarboxylic diimide derivative based thin film organic transistors (OTFTs) have been fabricated on a variety of dielectrics: SiO2, polyethylene, and polyvinylidene fluoride trifluoroethylene. Resulting inverted gate OTFTs were found to be p channel with Au contacts. In situ annealing studies revealed densification and significant mobility improvement. The mobility of as-deposited films was around 10−4cm2V−1s−1 for the best material and this could be improved by two orders of magnitude by a judicious annealing regimen and using a low static dielectric constant material for the gate dielectric.
Vertical-via interconnection for infrared antennas
Authors: Mandviwala T. A. , Lail B. A. , Boreman G. D.
Published: December 2006

The authors present fabrication process details and test data for a vertical-via interconnection suitable for low-frequency signal extraction from infrared antenna-coupled sensors. Electrical readout of the signal from an antenna-coupled bolometer was accomplished using two 300nm diameter Au via structures that extended 300nm in the vertical direction. These vertical vias passed through two isolation layers of SiO2 and through a 1500×600nm2 cutout in a ground plane. Electromagnetic isolation of the antenna from its associated electrical-readout bondpads at 28.3THz in the infrared was demonstrated by mapping the two-dimensional spatial response of the antenna and comparing it to spatial response data from a similar structure without the intervening ground plane.
Immersion lithography for laser mask writing
Authors: Bassett Derek W. , Bonnecaze Roger T.
Published: December 2006

The viability of fluid management in immersion lithography for laser mask writing is demonstrated. The so-called “drag-a-drop” method is proposed, where a droplet of fluid is held between the moving lens and the mask due to surface tension forces without the need of a fluid circulation system. Theoretical calculations and experimental measurements show that a stable droplet can be held onto a 6mm diameter lens, typical in size for laser mask writing, translating at velocities up to 600mm∕s. Experiments also show that the stability of the droplet is greatly enhanced by the addition of a hydrophobic topcoat on the surface of the mask. Receding edge instabilities with the deposition of droplets similar to those seen in 193nm immersion lithography and a new advancing edge instability with complete drop breakup were seen at sufficiently high velocities. A stability map is presented that predicts the onset of these two instabilities as a function of the dimensionless capillary number, a ratio of the viscous forces to surface tensions forces, and Weber number, a ratio of inertial forces to surface tension forces. Moving the lens and attached droplet off and on the edge of the mask during the scanning process can be done repeatedly with no fluid loss. The constancy of the index of refraction of the droplet is an important consideration for immersion lithography. The index can change due to changes in temperature and composition. Calculations and experiment with 193nm immersion indicate that maintaining a constant index of refraction in laser mask writing with the drag-a-drop system is feasible. The application of immersion lithography appears to be a viable means of increasing the resolution of laser mask writing.
Electron-beam lithography of Co∕Pd multilayer with hydrogen silsesquioxane and amorphous Si intermediate layer
Authors: Wi Jung-Sub , Lee Tae-Yon , Jin Kyung-Bae , Hong Dae Hoon , Shin Kyung Ho , Kim Ki-Bum
Published: December 2006

We propose a patterning method to form nanostructures of a Co∕Pd multilayer by using electron-beam lithography with an amorphous silicon (a-Si) layer and two-step etching process. On the Co∕Pd multilayer, a-Si is sputter deposited and hydrogen silsesquioxane (HSQ), the electron-beam resist, is spin coated sequentially. We found that an a-Si intermediate layer between the Co∕Pd underlayer and HSQ overlayer improves adhesion of HSQ on the metallic underlayer after electron-beam dosing and chemical development; it also increases etch selectivity between the Co∕Pd multilayer and its overlayers. We demonstrate that a Co∕Pd multilayer can be patterned successfully as a nanowire array using the suggested process.
Fabrication and characterization of novel cross point structures for molecular electronic integrated circuits
Authors: Chen Wei , Liu Xueqing , Tan Zhongkui , Likharev Konstantin K. , Lukens James E. , Mayr Andreas
Published: December 2006

Molecular electronic devices have the potential to dramatically increase the density and performance of integrated circuits. In order to realize this potential, reliable and scalable fabrication of nanoscale molecular electronic devices is essential. The authors have developed a new type of cross point structure in which the molecules are self-assembled between two metallic electrodes separated by an aluminum oxide layer. The gap between the electrodes is only a few nanometers wide and is defined by the aluminum oxide layer thickness, so it can be adjusted to match the length of the molecules with high (subnanometer) precision. This fabrication method applies to the study of transport properties of single molecules and at the same time is compatible with processes used in electronic industry, so that it may be used in the future to integrate molecular devices with silicon-based integrated circuits. Since the molecular self-assembly is the last step of the process, damage to molecules can be minimized. The authors have achieved a relatively high yield of high-quality support structures even at this early stage of technology development. Preliminary experimental data for electron transport through self-assembled oligo-phenylene-ethynylene-based molecules are compatible with the general theory of sequential single-electron tunneling.
Three-dimensional patterning using fine step motion in synchrotron radiation lithography
Authors: Fukuda M. , Deguchi K. , Suzuki M. , Utsumi Y.
Published: December 2006

A simple method of fabricating blazed diffraction gratings using synchrotron radiation lithography was developed that employs an ordinary binary mask with a line-and-space pattern, a step-and-expose procedure that provides a linear cumulative-dose distribution, and a thick resist with a linear sensitivity curve. This method enables the fabrication of blazed gratings with a grating pitch of 1μm and a blaze angle of 15°–40°. The angle and pitch can be changed by changing the dose from step to step and/or by using mask spaces of different widths.
Contactless capturing of particles in liquid using pulsed alternating dielectrophoresis
Authors: Luo Cheng-Ping , Heeren Andreas , Henschel Wolfgang , Fleischer Monika , Kern Dieter P.
Published: December 2006

Dielectrophoresis is an effective method for manipulation of particles in a medium, which can be achieved by applying electrical potentials to appropriately arranged electrodes. In the case of positive dielectrophoresis, the particles will move to regions of strong electric field and be captured at the edge or the surface of the electrodes, usually. The drawback thereby is that the particles may attach to the electrodes, leading to unwanted side effects. Negative dielectrophoresis moves them away from high field regions. In this article, the authors present a new method for contactless capturing of particles by using pulsed alternating dielectrophoresis. A signal sequence consisting of two pulsed ac voltages of different frequencies is applied to the electrodes. Each of them generates either positive or negative dielectrophoresis, respectively. With appropriate settings of dwell times and amplitudes, the particles are attracted toward the electrodes without attaching to them. Furthermore, the average distance from the electrodes can be tuned. Their experiments show that latex beads could be kept at a distance of up to about 20μm from the electrodes.
Predicting electron projection lithography mask membrane image placement errors
Authors: Boruszewski M. J. , Engelstad R. L. , Sakaue H. , Arimoto H. , Eguchi H.
Published: December 2006

Electron projection lithography (EPL) has been identified as a viable candidate of the next-generation lithography technologies for moderate-volume production of systems-on-a-chip for the sub-65nm nodes. EPL is especially suited for the fabrication of contact structures. The development of a low-distortion mask is essential for meeting the stringent requirements at these lower nodes. This research focuses on quantifying in-plane distortions (IPDs) due to mask fabrication and the effects of different mounting schemes in the e-beam writer and exposure tools for a 200mm EPL stencil mask. In order to quantify the IPD of the freestanding membranes, three-dimensional finite element (FE) models have been developed and benchmarked with experimentally measured data. Metrology measurements in both the membrane-side up and membrane-side down configurations can be used to correct for image placement errors (due to the fabrication and chucking of the mask) by compensating for IPD during the exposure process. To correct for higher order distortions associated with pattern specific errors, FE models were generated to simulate the entire process flow, including chucking. As a sample test case, a stencil pattern was replicated uniformly over the membrane arrays. The actual mask was fabricated and metrology measurements were taken. Selected membranes were experimentally measured to compare with FE results and the data correlated well in both direction and magnitude. Results illustrate that FE modeling and simulation can be used to predict mask distortions due to fabrication. Such techniques can be instrumental in meeting the stringent error budget required at the lower lithographic nodes.
Analysis of acid yield generated in chemically amplified electron beam resist
Authors: Kozawa Takahiro , Shigaki Takumi , Okamoto Kazumasa , Saeki Akinori , Tagawa Seiichi , Kai Toshiyuki , Shimokawa Tsutomu
Published: December 2006

Acid-related matters are a critical issue in a chemically amplified resist, in which photo- or radiation (ionizing radiation)-generated acids drive pattern formation reactions in exposed areas. The photosensitization of resist materials has been formulated by Dill et al. [IEEE Trans. Electron. Dev. 22, 445 (1975)]. The applicability of the formulation by Dill et al. to acid generation in chemically amplified photoresists has been proven by many researchers. The acid yields in photoresists are predicted well by the formulation of Dill et al. However, the formulation of Dill et al. cannot be applied to chemically amplified resists for ionizing radiation such as electron beams and extreme ultraviolet rays because polymer ionization significantly contributes to acid generation in these resists. In this study, the authors formulated acid generation in a chemically amplified resist for ionizing radiation. By the analysis of the dependence of acid yield on acid generator concentration, the details of acid generation paths were clarified.
Comparison of parameters for Schottky and cold field emission sources
Authors: Schwind G. A. , Magera G. , Swanson L. W.
Published: December 2006

Total energy distribution (TED) measurements were carried out for point electron sources operating in the cold field (T=300K) and Schottky (T=1800K) emission regimes. The full width at half maximum (FWHM) values of the TED’s for both emission regimes were found to increase significantly above the respective theoretical values as the emitter radius (a) was decreased and as the angular current density (I′) was increased. This increase in the FWHM arises from the stochastic electron-electron interactions in the beam commonly known as the Boersch [Z. Phys. 139, 115 (1954)] effect. A method was devised to extract the magnitude of the Boersch effect from the experimental TED’s. The TED’s were investigated as a function of I′ and a. In addition, the reduced brightness for both emitters was calculated from the virtual source size and I′ values as a function of the FWHM values.
Time-dependent exposure dose of hydrogen silsesquioxane when used as a negative electron-beam resist
Authors: Clark Nathaniel , Vanderslice Amy , Grove Robert , Krchnavek Robert R.
Published: December 2006

Hydrogen silsesquioxane (HSQ) is used as a high-resolution, negative-tone, inorganic electron-beam resist for use in nanoimprint lithography. Previous studies show that 1week long exposure delay in air decreases sensitivity and enhances the contrast of HSQ [F. C. M. J. M. van Delft, J. Vac. Sci. Technol. B 20, 2932 (2002)]. In this work, the authors report that the electron-beam dose required for high-resolution (sub-50-nm) HSQ patterning is shown to be very sensitive to the time the sample has been at room temperature. For example, a sample written with nanoscale features at constant e-beam dose will increase in size approximately 66% per hour of time at room temperature. The minimum feature size for a given dose depends on the ambient conditions the sample was stored in (air, nitrogen, vacuum). Samples stored in vacuum are not exempt from the feature broadening. Long e-beam writing times for large-area patterning of nanoscale features will likely suffer from this time dependence unless the exposure dose is varied during the e-beam writing. The experiments relating the various ambient conditions and the minimum feature size under dose control are presented.
Effect of cold development on improvement in electron-beam nanopatterning resolution and line roughness
Authors: Ocola L. E. , Stein A.
Published: December 2006

This article presents the results about the effect of cold development on the improvement in patterning resolution and line edge roughness for electron-beam lithography resists. Cold development shows improved resolution and contrast for resists that are exposed by polymer chain scission. It does not work for chemically amplified resists. A discussion on why this works for resists like ZEP 520 and PMMA and not for positive chemically amplified resists (such as UV113) is presented. Results for 13 nm structures obtained after metal liftoff using a 30 kV e-beam tool using ZEP 520 resist are shown. These results have impact in the photomask industry and other manufacturers that require squeezing out as much resolution out of their existing tools and materials. It is found that, even with the improvement by cold development, there is a “shot noise” of 2% uncertainty limit that is not surpassed for resists exposed at 100kV. This explains why high throughput and high resolution electron-beam nanolithography is not possible.
Electron-beam patterning and process optimization for magnetic sensor fabrication
Authors: Xiao Shuaigang , Yang XiaoMin
Published: December 2006

Electron-beam lithography has been widely applied to define critical features in magnetic recording thin-film heads. To be a viable resist candidate for read sensor fabrication, e-beam resists need to be optimized in three major aspects—resolution, etching resistance, and strippability. Here the authors investigated four typical resists for their applicability in the production of sub-50nm read sensors and extendibility into sub-30nm regime, including a negative-tone chemically amplified resist (CAR), a negative-tone non-CAR, a positive-tone CAR, and a positive-tone non-CAR. Pattern design for positive-/negative-tone resists, resist resolution capability, sloped resist pole profile, underlayer preparation for Si-containing imaging layer, hybrid lithography for low-sensitivity non-CARs, and process issues in ion-beam etching of sensor stacks are discussed in detail. Finally, 20nm giant magnetoresistive sensor fabrication was demonstrated.
Highly porous silicon membrane fabrication using polymer self-assembly
Authors: Black C. T. , Guarini K. W. , Breyta G. , Colburn M. C. , Ruiz R. , Sandstrom R. L. , Sikorski E. M. , Zhang Y.
Published: December 2006

A combination of diblock copolymer self-assembly and state-of-the-art semiconductor device fabrication methods is used to create highly uniform suspended porous silicon membranes. Integration of these two processing techniques is key to realizing manufacturable high quality devices. Three different methods are shown for adjusting membrane pore dimensions between 10 and 35 nm, allowing device optimization for specific applications.
Modeling of linewidth measurement in scanning electron microscopes using advanced Monte Carlo software
Authors: Babin S. , Borisov S. , Ivanchikov A. , Ruzavin I.
Published: December 2006

Accurate measurement of linewidth is a critical problem in sub-100nm semiconductor manufacturing, where required accuracy is below 1nm. Critical dimension scanning electron microscopes (CD-SEMs) are usually used for such measurements. A cross correlation of CD-SEMs, while demonstrating a good relative trend, is often subjected to a significant absolute linewidth error. There is no proven algorithm for absolute edge detection in CD-SEMs. In this article, the authors demonstrate that edge detection depends greatly on parameters of SEM settings, such as beam diameter, and pattern properties, such as the wall angle of a pattern. When both the signal and pattern are known, an offset for a specific SEM algorithm can be found. An algorithm for automatic edge detection in CD-SEMs can be tuned for beam parameters and the type of pattern. A SEM signal was simulated using the advanced Monte Carlo software CHARIOT. Input data for the modeling were three dimensional microstructures and e-beam parameters. A known pattern was then compared to a simulated signal. Such a comparison allowed to define the edge position and calibrate a SEM so that any system- and pattern-dependent errors could be removed.
Distortion of chucked extreme ultraviolet reticles from entrapped particles
Authors: Ramaswamy V. , Engelstad R. L. , Turner K. T. , Mikkelson A. R. , Veeraraghavan S.
Published: December 2006

Successful imaging of patterns with critical dimensions less than 45nm with extreme ultraviolet lithography (EUVL) requires stringent controls on all sources of image placement (IP) errors. Among the potential sources of IP error is the mechanical distortion of the patterned mask when mounted in the exposure tool. An EUVL reticle can exhibit both in-plane distortion and out-of-plane distortion due to the presence of debris lodged between the mask and the electrostatic chuck. Even particles with a compressed height as small as 100nm have the potential to consume a significant portion of the IP error budget. To alleviate this problem, a thorough understanding of the response of the reticle∕particle∕chuck system during electrostatic chucking is essential. This article describes experimental indentation testing to characterize relevant nanoscale material properties and the subsequent use of the data in finite element models that simulate the system response under typical chucking conditions.
Two-dimensional Bragg grating lasers defined by electron-beam lithography
Authors: DeRose Guy A. , Zhu Lin , Choi John M. , Poon Joyce K. S. , Yariv Amnon , Scherer Axel
Published: December 2006

Two-dimensional Bragg grating (2DBG) lasers with two quarter-wave slip line defects have been designed and fabricated by electron-beam lithography and reactive ion etching. Unlike conventional two-dimensional photonic crystal defect lasers, which use a large refractive index perturbation to confine light in a plane, the 2DBG structures described here selectively control the longitudinal and transverse wave vector components using a weak index perturbation. Two line defects perpendicular to each other are introduced in the 2DBG to define the optical resonance condition in the longitudinal and transverse directions. In this article, we describe the lithography process used to pattern these devices. The 2DBG lasers were defined using polymethylmethacrylate resist exposed in a Leica Microsystems EBPG 5000+ electron-beam writer at 100kV. A proximity correction code was used to obtain a uniform pattern distribution over a large area, and a dosage matrix was used to optimize the laser design parameters. Measurements of electrically pumped 2DBG lasers showed modal selection in both the longitudinal and transverse directions due to proper design of the grating and defects, making them promising candidates for single-mode, high power, high efficiency, large-area lasers.
Atomic force microscopy local anodic oxidation of thin Si3N4 layers for robust prototyping of nanostructures
Authors: Fernandez-Cuesta Irene , Borrisé Xavier , Pérez-Murano Francesc
Published: December 2006

Local anodic oxidation by atomic force microscopy (AFM) of thin silicon nitride layers deposited on silicon wafers allows the definition of stamps for nanoimprint lithography. The study of the mechanism and kinetics of the AFM induced oxidation shows that the patterns on silicon nitride can be generated faster and at lower voltages than directly on silicon surfaces. Stamp fabrication is completed by chemical wet etching of the samples after the AFM patterning, resulting in a robust process because of the excellent properties of silicon nitride as a mask for selective wet etching. As a demonstrator, a stamp for nanoimprint lithography is fabricated that will be used for the realization of biosensors based on interdigitated nanoelectrodes.
Exposure dose effects on the reaction-diffusion process in model extreme ultraviolet photoresists
Authors: Lavery Kristopher A. , Vogt Bryan D. , Prabhu Vivek M. , Lin Eric K. , Wu Wen-Li , Satija Sushil K. , Choi Kwang-Woo
Published: December 2006

The effect of exposure dose on the latent image deprotection profile in a model extreme ultraviolet (EUV) photoresist polymer, poly(hydroxystyrene-co-d9-tert-butyl acrylate), is measured with neutron reflectometry. As the photoacid concentration is increased by exposure dose, the spatial extent of propagation increases but eventually becomes self-limited by the products of the reaction. A long-range deprotection path occurs with diffusion length between 10 and 100Å, while an additional subnanometer short-range deprotection length scale proceeds monotonically with dose. These measurements show that the photoacid diffusion length into unexposed regions of a photoresist is limited even in the absence of base quencher additives. These fundamental data can be used to highlight materials effects on photoresist processing and to improve quantitative models for EUV photoresists needed at the sub-32-nm half pitch lithography.
Suppression of surface segregation of silicon dopants during molecular beam epitaxy of (411)A In0.75Ga0.25As∕In0.52Al0.48As pseudomorphic high electron mobility transistor structures
Authors: Sagisaka H. , Kitada T. , Shimomura S. , Hiyamizu S. , Watanabe I. , Matsui T. , Mimura T.
Published: December 2006

The authors achieved considerable suppression of surface segregation of Si dopants in In0.75Ga0.25As∕In0.52Al0.48As high electron mobility transistor (HEMT) structures grown on (411)A InP substrates by molecular beam epitaxy (MBE). The (411)A HEMT structures were conventionally grown at a high substrate temperature (Ts) of 540°C in order to form the extremely flat (411)A heterointerfaces. This results in considerable surface segregation of Si dopants. Surface segregation of Si dopants was suppressed by lowering growth temperature of the top InAlAs barrier layer (TB) down to 450°C with keeping Ts of 540°C for other parts. Sheet carrier concentration (Ns) of two-dimensional electron gas (2DEG) was measured as a function of thickness (Lb) of the top InAlAs barrier for TB=450 and 540°C samples. Observed Ns of the TB=540°C sample vanished when Lb approached to 7nm, while 2DEG with of Ns∼2×1012cm−2 remained for the TB=450°C sample. Surface segregation of Si-sheet-doped (411)A InAlAs layers grown at TB was also characterized by secondary ion mass spectrometry measurements. Si segregation length (λSi:1∕e decay length of Si concentration) observed for TB=450°C sample was 2.3nm, which is 56% smaller than that for TB=540°C (λSi=5.2nm).
Anisotropic high aspect ratio etch for perfluorcyclobutyl polymers with stress relief technique
Authors: Rahmanian Nazli , Kim Seunghyun , Nordin Gregory P.
Published: December 2006

The authors have developed an anisotropic, high aspect ratio (18:1) etch for perfluorocyclobutyl (PFCB) polymers with trenches as narrow as 800nm using a CO∕O2 etch chemistry in an inductively coupled plasma reactive ion etcher. Anisotropy is achieved by carbon sidewall passivation. The motivation for this etch development is to use the air trenches as very compact waveguide splitters [S. Kim et al., Opt. Eng. 45, 054602 (2006)]. The authors report a new trench widening mechanism due to tensile stress of the PFCB films and a method of avoiding this widening through the use of additional stress relief trenches on both sides of the desired trench.
Characterization and optimization of a P-channel poly(o-methoxyaniline) based thin film transistor
Authors: Shrestha Roshan P. , Yang Dongxing , Li Yuxiang , Yan Li , Irene Eugene A.
Published: December 2006

Poly(o-methoxyaniline) based thin film organic transistors (OTFT’s) have been fabricated on a variety of dielectrics: SiO2, polyethylene, and polyvinylidene fluoride trifluoroethylene. Resulting inverted gate OTFT’s were found to be P channel with Au contacts. The mobility was measured to be around 10−3cm2V−1s−1 for as-deposited thin film OTFT structures but could be improved by an order of magnitude by doping, annealing, and decreasing the static dielectric constant of the gate dielectric.
Coulomb blur in a multi-electron-beam system
Authors: Sohda Yasunari , Kamimura Osamu , Ohta Hiroya
Published: December 2006

Coulomb blur in a multi-electron-beam system with a single column was investigated by simulations and experiments in 1024 two-dimensional electron beams with double lens-doublet optics. Monte Carlo simulation showed three main points. First, in spite of a high current density, Coulomb blur and energy broadening were the same as those in the case of a shaped beam covering a multi-electron-beam area. The Coulomb blur for a 50keV electron beam at 1μA total beam current was simulated as 20nm, which was less than half of that in the case of a single beam. Second, the Coulomb blur is slightly nonuniform depending on the distance from the beam center. Third, the decrease in the Coulomb blur by beam blanking is similar to that by beam absence at the objective plane. In addition, Coulomb blurs of the axial beam were estimated by experiments at various currents. The results show that the experimental blurs were in good agreement with the simulated blurs. In conclusion, the authors clarified that multiplying the number of beams is effective for decreasing Coulomb blur at the same total current.
Time of flight secondary ion mass spectroscopy investigation of ultralow-k dielectric modifications in hydrogen and deuterium plasmas
Authors: Lazzeri P. , Stueber G. J. , Oehrlein G. S. , McGowan R. , Busch E. , Pederzoli S. , Bersani M. , Anderle M.
Published: December 2006

Photoresist stripping processes based on hydrogen reductive chemistry have emerged as attractive replacements of the conventional treatments performed using O2 plasma. H2 discharges and plasma processes based on gas mixtures containing H2 provide, in fact, adequate stripping rates while reducing the chemical modifications of the porous ultralow-k (ULK) dielectric materials employed in interconnect technology. In this work the authors investigate the chemical modification of a number of organosilicate low-k dielectrics interacting with remote H2 plasma. The materials include both spin-on and plasma-enhanced chemical vapor deposited dielectrics with k, porosity, and chemical composition spanning on a broad range of values. The mechanisms of plasma∕dielectric reaction and the depth of interaction are evaluated by means of time of flight secondary ion mass spectrometry. In order to study the nature of the plasma∕dielectric interactions and the chemical modifications introduced in the ULK materials, deuterium (D2) is used to substitute for H2 in the discharge. Although the plasma-generated radicals interact strongly with the materials, negligible stoichiometry modifications are observed during exposure of silica-rich ULK materials. On the other hand, the dielectrics with higher carbon content undergo major compositional changes. The chemical damage introduced by H2-based discharges depends strongly on the formulation of the organosilicate material. The substrate temperature is also seen to affect the influx of plasma species. This acts on the extent of material modifications. Nevertheless, the nature of plasma∕dielectric interactions does not vary for processes performed in the temperature range of 200–300°C.
Effects of SiO2∕Si3N4 hard masks on etching properties of metal gates
Authors: Hwang Wan Sik , Cho Byung-Jin , Chan Daniel S. H. , Bliznetsov Vladimir , Yoo Won Jong
Published: December 2006

Reduced etching rates of advanced metal gates (TaN, TiN, and HfN) using SiO2∕Si3N4 hard masks are observed in Cl2 plasma. Si and O released from hard masks react with metal surfaces newly exposed to the plasma during the etching, thereby forming metal oxides. The metal oxides formed on the etched surface retard the etch rates. The suppression of etch rates with hard mask is more obvious for TiN than for TaN and HfN, because Ti oxides are readily formed on the etched TiN surface due to their low Gibbs free energies of formation. The surface of TiN degrades with etching time with SiO2 mask, because etching rates of Si oxides and Ti oxides are different in the (TiO2)1−x(SiO2)x residues remaining on the etched surface. In contrast, a conventional poly-Si electrode does not show the mask effects on etch rates and surface roughness.
Threshold voltage adjustment on spherical, single-crystal silicon substrates by focused ion beam implantation
Authors: Zomorrodian V. , Craver B. , Radhakrishnan G. , Patel M. , Charlson E. J. , Ruchhoeft P. , Wolfe J. C.
Published: December 2006

The development of spherical, rather than planar, imaging arrays would enable compact wide field-of-view cameras by reducing the size and complexity of the optical components. One approach is to fabricate the sensors and readout integrated circuits directly on a spherical shell machined from a single-crystal silicon substrate. Several significant advances in processing these substrates have already been reported. This article addresses one of the fundamental electronic issues: a threshold voltage correction procedure that accounts for the dependence of oxide thickness, fixed oxide charge, and interface trapped charge on crystallographic orientation and the variation of implant depth and projected dose on substrate geometry. Substrates with 15mm radius of curvature and 25mm diameter were machined from a B-doped (3Ωcm) (100) silicon ingot. The threshold voltage of as-formed capacitors varied from −0.4V in the center to −2.0V at a radius of 10mm. A 110keV B+ focused ion implantation system was used to adjust threshold voltage point by point with 1mm resolution. The authors demonstrate, for the first time, the ability to correct threshold voltage to within 0.12V over an 83° field of view.
Spatial light modulator for maskless optical projection lithography
Authors: Watson G. P. , Aksyuk V. , Simon M. E. , Tennant D. M. , Cirelli R. A. , Mansfield W. M. , Pardo F. , Lopez D. O. , Bolle C. A. , Papazian A. R. , Basavanhally N. , Lee J. , Fullowan R. , Klemens F. , Miner J. , Kornblit A. , Sorsch T. , Fetter L. , Peabody M. , Bower J. E. , Weiner J. S. , Low Y. L.
Published: December 2006

Spatial light modulators (SLMs) designed to replace photomasks for optical lithography have been designed, fabricated, and tested. These microelectromechanical devices are fabricated with alternating polycrystalline Si and sacrificial SiO2 layers that are patterned by a 193nm wavelength scanner to dimensions as small as 150nm. Aerial image simulations were used to define the mechanical requirements of the devices. Piston motion of electrically actuated devices was measured with an optical profilometer. The measurements were fit to a simple equation to within 1nm precision, which is adequate for defining 50nm features lithographically. Transient response measurements show that one version of the SLM responds to actuation as quickly as 20μs, fast enough for current 193nm wavelength excimer laser sources.
Transmission electron microscopy: A linewidth measurement technique for lithography
Authors: Warren John B. , Stein Aaron
Published: December 2006

The authors describe preparation methods for patterning high resolution e-beam resists on electron beam transparent samples that facilitate the direct comparison of linewidth measurements from transmission and scanning electron microscopy imaging of the same feature. A goniometer-equipped JEOL 1200EX transmission electron microscope (TEM) with a resolution of 0.45nm (120keV) and a JEOL SEM 6500F scanning electron microscope (SEM) with a resolution that varies from 1.5nm (15keV)to5.0nm (1keV) are used to acquire digital images suitable for linewidth measurements. This comparison emphasizes the differences between TEM images based on mass-absorption contrast and surface topology sensitive SEM images when making linewidth measurements.
Submicron three-dimensional structures fabricated by reverse contact UV nanoimprint lithography
Authors: Kehagias N. , Reboud Vincent , Chansin G. , Zelsmann M. , Jeppesen C. , Reuther F. , Schuster C. , Kubenz M. , Gruetzner G. , Sotomayor Torres C. M.
Published: December 2006

The fabrication of a three-dimensional multilayered nanostructure is demonstrated with a newly developed nanofabrication technique, namely, reverse contact ultraviolet nanoimprint lithography. This technique is a combination of reverse nanoimprint lithography and contact ultraviolet lithography. In this process, a UV cross-linkable polymer and a thermoplastic polymer are spin coated onto a patterned hybrid metal-quartz stamp. These thin polymer films are then transferred from the stamp to the substrate by contact at a suitable temperature and pressure. The whole assembly is then exposed to UV light. After separation of the stamp and the substrate, the unexposed polymer areas are rinsed away with acetone leaving behind the negative features of the original stamp with no residual layer.
Direct wiring of carbon nanotubes for integration in nanoelectromechanical systems
Authors: Bauerdick S. , Linden A. , Stampfer C. , Helbling T. , Hierold C.
Published: December 2006

The authors present the use of electron beam induced deposition (EBID) for direct wiring of carbon nanotubes (CNTs). Since this technique is a maskless, direct patterning method, EBID is applicable to suspended nanotubes potentially integrated in predefined nanoelectromechanical systems (NEMS). The authors developed a process including CNT adsorption from solution on prepatterned planar samples, evaluation and localization of CNTs by scanning force microscopy, preparation of GDSII layouts, and contacting CNTs by EBID of tungsten. EBID was performed in an integrated e-beam lithography and nanoengineering workstation using tungsten hexacarbonyl as precursor. With well controlled exposure conditions, a resistivity on the order of 10−2Ωcm has been achieved. Moreover, electrical measurements on CNTs contacted by EBID tungsten leads clearly show transistorlike behavior. First tests on EBID metal lead integration on alumina NEMS structures were carried out. Thus EBID can enable a top metallization of CNTs on suspended NEMS structures, which should enhance also the mechanical stability between the lead and the CNT.
Layer thickness-induced lens distortions during thermal nanoimprint
Authors: Scheer H.-C. , Bogdanski N. , Möllenbeck S. , Wissen M. , Nishilata M. , Hirai Y.
Published: December 2006

Arrays of convex spherical lenses with heights in the micrometer range and diameters of 100 and 200μm, respectively, were imprinted into thin layers of polystyrene by thermal imprint. The masters were prepared by gray tone lithography and dry etching. They feature three distinct lens heights, so that during imprint into medium layer thickness three different situations prevail: imprint into thick layers, imprint into thin/adequate layers, and imprint into highly thinned layers. Only during imprint in such highly thinned layers slight recovery was detected combined with stretching-induced polymer layer breakup. For all other cases the replication quality was good and did not show recovery effects. This is in contrast to the imprint of flat stamps into layer thickness of similar sizes. Differences detected in height of the replicated lenses compared to the master are due to thermal expansion in the thermal nanoimprint lithography process. Negligible residual layers were obtained at only slightly changed curvature radius.
Custom design of optical-grade thin films of silicon oxide by direct-write electron-beam-induced deposition
Authors: Wanzenboeck Heinz D. , Fischer Markus , Svagera Robert , Wernisch Johann , Bertagnolli Emmerich
Published: December 2006

This work describes a rapid fabrication approach of thin silicon oxide films on confined areas by electron-beam-induced deposition. This maskless direct-write process utilizes a localized chemical vapor deposition (CVD) on specific areas utilizing a focused electron beam. The deposition from siloxane vapor in the presence of oxygen is initiated by the energy of an electron beam of 1nm diameter. By scanning the beam, thin films with arbitrary geometries and three-dimensional structures were deposited. In contrast to blanket deposition with conventional methods such as thermal CVD or plasma-enhanced CVD, the lateral confined layers can be fabricated at room temperature. With a maskless process, the final structure is fabricated within a single process step. The process was optimized towards a high deposition rate and high material purity. The influence of process parameters on the deposition efficiency is discussed. A characterization of the chemical composition and of the surface roughness was performed with auger electron spectroscopy, energy-dispersive x-ray, and atomic force microscopy, respectively. The optical properties were investigated by transmission measurement at 248nm. The correlation to processing conditions and the growth mechanism induced by the electron beam is discussed. This work illustrates the flexibility of this maskless method and the potential to control material properties via the process parameters. The fabrication of exemplary structures such as three-dimensional silicon oxide pillars and transparent films illustrates the application potential of this versatile direct-write method.
Effects of Zn content on structural and transparent conducting properties of indium-zinc oxide films grown by rf magnetron sputtering
Authors: Park Jae-Soung , Song Ju-Il , Heo Young-Woo , Lee Joon-Hyung , Kim Jeong-Joo , Lim W. T. , Stafford L. , Norton D. P. , Pearton S. J.
Published: December 2006

Indium-zinc oxide (IZO) films were grown on glass substrates by rf magnetron sputtering using targets of 50mol% In2O3–50mol% In2O3(ZnO)3 and In2ZnkOk+3 (k=3, 4, 5, and 7) at room temperature and 300°C. The difference in Zn content between the films and the sputter targets varied with the growth temperature. The structural, electrical, and optical properties of the IZO films were investigated as a function of Zn content. The crystal structure of IZO films grown at room temperature changed from amorphous to crystalline at a Zn content (Zn∕(Zn+In)) of 68at.%. IZO films grown at 300°C using a target of 50% In2O3–50% In2O3(ZnO)3 had a Zn content of 40at.% and its x-ray diffraction peaks were matched with those of ITO. As the Zn content in IZO thin films grown at 300°C increased from 40to74at.%, the conductivity and optical band gap energy decreased.
Multiple level nanochannels fabricated using reversal UV nanoimprint
Authors: Yang B. , Pang S. W.
Published: December 2006

There is a wide range of applications for three-dimensional (3D) nanochannels in biomedical systems and fluidic control. In this article, a simple and versatile technique to create 3D nanochannels with width from 200nm to 2μm is demonstrated using sequentially stacked reversal UV nanoimprint of SU-8. Its advantages include controllable channel profile, low pressure and temperature for imprints, and flexibility in designing 3D channels by stacking. In a typical reversal UV imprint, SU-8 is spin coated on a glass mold and then transferred onto Si substrates by an UV imprint process at low temperature of 55°C, low pressure of 2MPa, and UV exposure of 1–4s. While reversal UV imprinting top SU-8 layer onto bottom SU-8 layer, the UV exposure and imprint sequence of the top SU-8 layer and its effect on channel profile control are investigated. It has been found that initially UV-cured top SU-8 layer is preferred for good channel profile control because UV-cured SU-8 layer is prevented from flowing down into bottom SU-8 layer.
Influence of mold depth on capillary bridges in nanoimprint lithography
Authors: Chaix N. , Landis S. , Hermelin D. , Leveder T. , Perret C. , Delaye V. , Gourgon C.
Published: December 2006

Nanoimprint lithography (NIL) processes are often plagued by different kinds of defects. The so-called capillary bridge is related to capillary forces between the stamp surface and the polymer during the pressing process. These defects affect both the printed and unprinted areas of the polymer film. Implementation of NIL as an industrial process requires that these defects be understood and minimized. As such, establishing a relationship between capillary bridge growing and pressing conditions, specifically the mold to polymer distance, is a key step. Two NIL stamps with various feature depths (12–224nm) were studied in this work to establish a link between bridge formation and mold filling. Printing processes were performed using small forces to guarantee contact between the mold and resist without totally filling stamp cavities. The resulting capillary bridges were characterized as a function of cavity depth and printing temperature. Results indicate that the number of defects is strongly influenced by the cavity size for depths <80nm as well as printing temperature.