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Rutile tin oxide (SnO2 ) is a wide band gap (3.6 eV at 300K [1]) n-type semiconductor material. It is widely used as sensing elements in gas sensors [2]. The sensing mechanism is generally attributed to the significant change in the electrical resistance of the material associated with the adsorption/desorption of oxygen on the semiconductor surface [3]. The formation of oxygen adsorbates (O2 − or O− ) results in an electron-depletion surface layer due to the electron transfer from the oxide surface to oxygen [4]. Recent studies [5, 6] have shown that use of tin oxide nanocrystals significantly improves the dynamic response and the sensitivity of sensors since the electron depletion may occur in the whole crystallite. Here we report on the fabrication and characterization of a miniaturized gas sensor based on tin oxide nanocrystals. A simple, convenient and low-cost mini-arc plasma source is used to synthesize high-quality tin oxide nanoparticles in aerosol phase at atmospheric pressure. The nanoparticle sensor is then fabricated by electrostatic assembly of product tin oxide nanoparticles onto e-beam lithographically patterned interdigitated electrodes. The microfabricated nanoparticle sensor exhibits good sensitivity and dynamic response to low-concentration ethanol vapor and hydrogen gas diluted in air.Copyright © 2007 by ASME and Argonne National Laboratories

Fresnel zone plates are widely used as x-ray nanofocusing optics. To achieve high spatial resolution combined with good focusing efficiency, high aspect ratio nanolithography is required, and one way to achieve that is through multiple e-beam lithography writing steps to achieve on-chip stacking. A two-step writing process producing 50 nm finest zone width at a zone thickness of 1.14 μm for possible hard x-ray applications is shown here. The authors also consider in simulations the case of soft x-ray focusing where the zone thickness might exceed the depth of focus. In this case, the authors compare on-chip stacking with, and without, adjustment of zone positions and show that the offset zones lead to improved focusing efficiency. The simulations were carried out using a multislice propagation method employing Hankel transforms.

Nanoscale geometry assisted proximity effect correction (NanoPEC) is demonstrated to improve PEC for nanoscale structures over standard PEC, in terms of feature sharpness for sub-100 nm structures. The method was implemented onto an existing commercially available PEC software. Plasmonic arrays of crosses were fabricated using regular PEC and NanoPEC, and optical absorbance was measured. Results confirm that the improved sharpness of the structures leads to increased sharpness in the optical absorbance spectrum features. We also demonstrated that this method of PEC is applicable to arbitrary shaped structures beyond crosses.

Optimizing the photochemistry in extreme ultraviolet (EUV) photoresists due to EUV exposures may enable faster, more efficient resists, leading to a greater throughput in manufacturing. Since the fundamental reaction mechanisms in EUV resists are believed to be due to electron interactions after incident 92 eV photons (13.5 nm) generate photoelectrons during ionization events, understanding how these photoelectrons interact with resist components is critical for optimizing the performance of EUV resists and EUV lithography as a whole. The authors will present an experimental method to measure the cross section of incident electron induced decomposition of three different photoacid generators (PAGs). To study the photoelectrons generated by the EUV absorption and measure their effect within resists, photoresists were exposed to electron beams at electron energies between 80 and 250 eV. The reactions between PAG molecules and electrons were measured by using a mass spectrometer to monitor the levels of smal...

Extreme ultraviolet (EUV) photons expose photoresists by complex interactions starting with photoionization that create primary electrons (∼80 eV), followed by ionization steps that create secondary electrons (10 to 60 eV). Ultimately, these lower energy electrons interact with specific molecules in the resist that cause the chemical reactions which are responsible for changes in solubility. The mechanisms by which these electrons interact with resist components are key to optimizing the performance of EUV resists. A resist exposure chamber was built to probe the behavior of electrons within photoresists. Resists were exposed under electron beam and then developed; ellipsometry was used to identify the dependence of electron penetration depth and number of reactions on dose and energy. Additionally, our group has updated a robust software that uses a first principles-based Monte Carlo model called low-energy electron scattering in solids (LESiS) to track secondary electron production, penetration depth, and reaction mechanisms within materials-defined environments. LESiS was used to model the thickness loss experiments to validate its performance with respect to simulated electron penetration depths to inform future modeling work.

The optical properties of BaTiO3 two dimensional photonic crystal (PhC) nanocavities were investigated. Two types of nanocavities consisting of dopants and vacancies with PhC periodicities ranging from 200 to 550 nm were evaluated. The images from laser scanning confocal microscopy show the optical scattering of the PhC cavities is highly wavelength dependent. An optical intensity reversal is observed when the wavelength of probe light shifts by 29 nm. Meanwhile, intensity contrast between the nanocavity and its adjacent PhCs is enhanced as the PhC periodicity becomes shorter than the probe wavelength. To determine the photonic band structures fluorescence from dye covered PhCs were imaged and analyzed. A strong enhancement of fluorescence is observed for the PhC with a period of 200 nm. Upon comparison to the 2D finite difference time domain calculations, the enhancement is attributed to strong light localization within the PhC nanocavity. As a result, the in-plane lightwave propagation is prohibited that results in an increase in the vertical light scattering.

We studied collective surface plasmon excitations in chains of gold nanoparticles. The resonance frequency of these excitations is a function of the distance between the particles and polarization of the incident light. The near-field coupling between the particles in a chain leads to a cosine squared angular dependence between the polarization of the incident light and the axis connecting the particles. The far-field coupling between the particles results in a sine squared angular dependence. When the incident light is polarized along the chain, the near-field coupling exhibits a red shift, while the far-field exhibits a blue shift of the collective plasmon mode with respect to the mode of the non-interacting particles. We experimentally determined the particle separation for which the resonance frequency in the extinction spectra is polarization-independent.

Miniaturized gas sensors or electronic noses to rapidly detect and differentiate trace amount of chemical agents are extremely attractive. In this paper, we report on the fabrication and characterization of a functional tin oxide nanoparticle gas sensor. Tin oxide nanoparticles are first synthesized using a convenient and low-cost mini-arc plasma source. The nanoparticle size distribution is measured online using a scanning electrical mobility spectrometer (SEMS). The product nanoparticles are analyzed ex-situ by high resolution transmission electron microscopy (HRTEM) for morphology and defects, energy dispersive X-ray (EDX) spectroscopy for elemental composition, electron diffraction for crystal structure, and X-ray photoelectron spectroscopy (XPS) for surface composition. Nonagglomerated rutile tin oxide (SnO2) nanoparticles as small as a few nm have been produced. Larger particles bear a core-shell structure with a metallic core and an oxide shell. The nanoparticles are then assembled onto an e-beam lithographically patterned interdigitated electrode using electrostatic force to fabricate the gas sensor. The nanoparticle sensor exhibits a fast response and a good sensitivity when exposed to 100 ppm ethanol vapor in air.

In this work, we investigate the feasibility of using a surface-tethered heptapeptide sequence as the basis for a ferroelectric-actuated component in a nanofluidic device. The fluorescently-labeled peptide sequence, (CISLLHSTC) is shown by fluorescence microscopy to selectively coat the PZT patterned channel floors. The peptide binding strength to PZT is determined over a range of flow rates in the patterned channel by imaging the fluorescence intensity of the coated channel and monitoring the output spectroscopically. The peptide is found to be stripped from the PZT at flow rates exceeding 5mL/h. Initial results demonstrating the possibility of covalently integrating the short peptide sequence to larger biological components such as antibodies are also presented.

Summary form only given. Combinatorial phage display methods have been used to identify a circularly constrained heptapeptide sequence, ISLLHST, that strongly associates with a perovskite ferroelectric, lead zirconium titanate, Pb(ZrxTi1-x)O3 (PZT). The affinity and selectively of binding to polycrystalline MOCVD deposited PZT thin films supported on Si/SiO2/Pt substrates were determined by titering and immunofluorescence microscopy, and the peptide was shown to selectively bind PZT in the presence of Pt, Si, Au, and several different photoresists. Ferroelectric properties were determined by measurement of the P-E hysteresis loop on unmodified and phage bound PZT thin films, and no change in the coercive field, Ec , or the saturation polarization, Ps was observed after contacting the PZT with aqueous buffer or phage binding. Since this preliminary characterization indicates that the PZT is compatible with biological chemistry, work is currently underway to develop a gated nanofluidic device using this chemistry. This is being accomplished by using electron beam lithography to etch nanochannels (~100 nm in width) in photoresists deposited on these PZT substrates. The base of these channels can be modified using the PZT-specific peptide, and by incorporating metallic electrodes into this structure, the charge of the functionalized PZT can be manipulated, forming the basis for such a device

The integration of biomolecules with inorganic materials to create functional composites represents a critical step in the development of next-generation biosensors, micro/nanofluidic devices, and biochips that require a combination of abiotic (inorganics) and biotic (proteins, DNA, antibodies) components. Toward this end, we have previously applied combinatorial phage display techniques to identify a constrained heptapeptide sequence (CISLLHSTC) that selectively binds to a perovskite ferroelectric (MOCVD-deposited lead zirconium titanate, PZT). In this work, we examine the binding of this heptapeptide sequence, prepared by solid phase peptide synthesis to sol-gel PZT. In particular, the surface roughness has been examined and the long-term stability of the PZT films in biological buffered aqueous solutions by atomic force microscopy, X-ray diffraction and P-E hysteresis loop. In addition, the selectivity of the peptide binding to PZT has been determined by immunofluorescence microscopy and the nature of peptide binding to the PZT surface is probed by X-ray photoemission spectroscopy.

This paper describes the use of a unique combination of an environmentally stable chemically amplified photoresist (UV113, Shipley) and a copolymer of methyl styrene and chloromethyl acrylate P(MS/CMA) resist (ZEP520, Zeon), without any additional intermediate layers, in the fabrication of micro- and nanochannels. The two resists used are innocuous to each other during the designed process flow, providing flexibility, high resolution, greater throughput and ease of use. We have also determined that the maximum channel length is limited by diffusion and mass transport effects, and that sub-100 nm nanochannels can be obtained with 30 micron lengths.

Noncontact scanning force microscopy topography measurements of exposed and undeveloped photoresists are reported. A negative chemically amplified photoresist, SAL605, was patterned by electron beam direct writing of 1 μm line linear gratings, and 5 mm pads. A relief image of exposed unbaked resist has been observed of the order of a few A, and then monitored as a function of time after exposure. This relief image undergoes a topography transformation with postexposure bake (PEB), yielding a ridge located at the exposed–unexposed region interface, extending several nanometers in vertical and about one micrometer laterally. The effect has been investigated as a function of PEB time and exposure dose. Correlations of the observed phenomena with optical film thickness monitoring techniques and previously reported data on the photoresist chemical changes during exposure and PEB are discussed. Two independent mechanisms contributing to the image formation are identified. The data show that the local chemistry ...

We introduce a new design of tilted linear zone plates, which are named tapered tilted linear (TTL) zone plates. The purpose of the design is to increase efficiency while at the same time keeping the focal plane perpendicular to the optical path. In order to accomplish this, the zone radius and number of zones must become a function of position along the structure. Simulation work described in this paper shows improved optical performance over regular tilted linear zone plates.

Electron beam lithography still represents the most effective way to pattern materials at the nanoscale, especially in the case of structures, which are not indefinitely repeating a simple motif. The success of e-beam lithography depends on the availability of suitable resists. There is a substantial variety of resist materials, from PMMA to calixarenes, to choose from to achieve high resolution in electron-beam lithography. However, these materials suffer from the limitation of poor sensitivity and poor contrast.In both direct-write and projection e-beam systems the maximum beam current for a given resolution is limited by space-charge effects. In order to make the most efficient use of the available current, the resist must be as sensitive as possible. This leads, naturally, to the use of chemically amplified (CA) systems. Unfortunately, in the quest for ever smaller feature sizes and higher throughputs, even chemically amplified materials are limited: ultimately, sensitivity and resolution are not independent. Current resists already operate in the regime of < 1 electron/nm2. In this situation detailed models are the only way to understand material performance and limits.Resist requirements, including sensitivity, etch selectivity, environmental stability, outgassing, and line-edge roughness as they pertain to, high-voltage (100 kV) direct write and projection electron-beam exposure systems are described. Experimental results obtained on CA resists in the SCALPEL® exposure system are presented and the fundamental sensitivity limits of CA and conventional materials in terms of shot-noise and resolution limits in terms of electron-beam solid interactions are discussed.

Diffractively coupled plasmonic resonances possess both ultra-sharp linewidths and giant electric field enhancement around plasmonic nanostructures. They can be applied to create a new generation of sensors, detectors, and nano-optical devices. However, all current designs require stringent index-matching at the resonance condition that limits their applicability. Here, we propose and demonstrate that it is possible to relieve the index-matching requirement and to induce ultra-sharp plasmon resonances in an ordered vertically aligned optical nano-antenna phased array by transforming a dipole resonance to a monopole resonance with a mirror plane. Due to the mirror image effect, the monopole resonance not only retained the dipole features but also enhanced them. The engineered resonances strongly suppressed the radiative decay channel, resulting in a four-order of magnitude enhancement in local electric field and a Q-factor greater than 200.

This paper will discuss aspects of resist properties required for nanolithography using high-energy electrons. A comprehensive image formation model is presented for positive and negative chemically amplified resists where most aspects have been considered (from exposure through development) for e-beam nanolithography (EPL, DWL). A series of optimization studies are performed using the modulation of soluble site density after PEB as a metric to characterize resist imaging performance. Base loading, blocking fraction and acid diffusion properties are investigated. Slower acid diffusion near regions with deprotected sites dominates during PEB and contributes to a sharp image modulation. Electron beam exposed nanostructures exhibit spatial fluctuations of soluble sites in the material left after development, which may alter etch resistance and pattern collapse. Soluble site fluctuations arise from the low statistics involved in the image formation and are significant contributors to the sidewall roughness.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Optimization of phenolic chemically amplified resist platforms has lead to the development of new resists, capable of high throughput SCALPEL exposure. A positive resist, XP9947A, has exhibited 100 nm and 80 nm dense line resolution with good sensitivity and dose latitude. The influence of DUV absorption and 100 KV e-beam absorption to the optimization process is discussed. The nature of 100 KV e-beam absorption enables a greater freedom of resist design than encountered for DUV resists.

We have dramatically increased the sensitivity of a technique for the rapid inspection of EUV multilayer-coated mask blanks. In this technique an EUV sensitive resist is applied directly to a mask blank which is then flood exposed with EUV light and partially developed. Reflectivity defects in the mask blank result in mounds in a partially developed positive resist that appear as high contrast objects in a standard Nomarski microscope. The use of a higher contrast resist is shown experimentally to result in the creation of dramatically taller mounds. A simple model for the exposure and development of the resist has been developed and the predictions of the model compare well with the experimental results.

A manufacturable process for fabricating alignment marks that are compatible the SCALPEL lithography system is described. The marks were fabricated in a SiO 2 /WSi 2 structure using SCALPEL lithography and plasma processing. The positions of the marks were detected through e-beam resist in the SCALPEL proof of lithography (SPOL) tool by scanning the image of the corresponding mask mark over the wafer mark and detecting the backscattered electron (BSE) signal. Scans of 1 μm line-space patterns yielded mark positions that were repeatable within 20 nm 3σ with a dose of 4 μC/cm 2 and signal-to-noise of 32 dB. An analysis shows that the measured repeatability is consistent with a random noise limited response combined with SPOL machine factors. By using a digitally sequenced mark pattern, the capture range of the mark detection was increased to 13 μm while maintaining 36 nm 3σ precision. Further improvements in mark detection repeatability are expected when the SCALPEL electron optics is fully optimized.

High acceleration voltage electron beam exposure is one of the possible candidates for post-optical lithography. The use of electrons, instead of photons, avoids optical related problems such as the standing wave issues. However, resists must conform to certain needs for the SCALPEL system, such as exposure in a vacuum chamber with 100kv electron beams. Taking into account the challenging requirements of high resolution, high sensitivity, low bake dependency and no outgassing, TOK has been able to develop resists to meet most of the SCALPEL system needs. However, due to the nature of chemical amplification and the PEB dependency, as is the case with DUV resist which varies for different features, we must recommend different resist for multiple features such as dense lines, isolated lines and contact holes. TOK has designed an electron beam negative resist, EN-009, which demonstrate 100nm pattern resolution. The dose to print on the SCALPEL system is 5.0(mu) C/cm2. The electron beam positive resist, EP-004M, has been designed for line and space patterns. The dose to print on the SCALPEL system is 8.25(mu) C/cm2. The processing conditions are standard, using 0.26N developer. These are the lowest exposure energies reported to date for similar resolution on this exposure tools.

This article reviews technology issues in scaling conventional planar transistors to a physical gate length of 30nm that are expected to produce an effective channel length of 10 nm. Gate fabrication features direct write e-beam lithography to form a ring structure capable of exploring the practical limits of gate processing while requiring only a single level of lithography. Other processing elements include ultra-thin gate dielectric formation (∼ 0.6nm); highly selective transformer coupled plasma (TCP) etching; and low energy ion implantation. DC electrical results obtained for high performance n-MOS and p-MOS type nanotransistors made using this process are discussed as are simulations of sub-threshold currents for n-MOS transistors with physical gate lengths down to 26nm

Ordered arrays of high-aspect-ratio micro/nanostructures in semiconductors stirred a huge scientific interest due to their unique one-dimensional physical morphology and the associated electrical, mechanical, chemical, optoelectronic, and thermal properties. Metal-assisted chemical etching enables fabrication of such high aspect ratio Si nanostructures with controlled diameter, shape, length, and packing density, but suffers from structure deformation and shape inconsistency due to uncontrolled migration of noble metal structures during etching. Hereby the authors prove that a Ti adhesion layer helps in stabilizing gold structures, preventing their migration on the wafer surface while not impeding the etching. Based on this finding, the authors demonstrate that the method can be used to fabricate linear Fresnel zone plates.

In this paper, the authors present microfluidic mixers containing complex curvilinear and several tens of microns deep three-dimensional (3D) geometries used to decrease mixing lengths in passive microfluidic systems. In order to create these 3D geometries, the authors use ion beam micromachining (IBμM) and address redeposition and exposure strategy effects that follow this type of fabrication. Results of this work clearly demonstrate that fabrication of 3D microfluidic mixers using IBμM is achievable for real practical applications. In order to scale up to the tens of microns width and depth, and hundreds of microns in length fabrication, high current is required. This raises unique challenges of redeposition handling. This was achieved by realizing that redeposited silicon can be removed with an extended buffered oxide etch. In addition, data management and writing strategies not encountered in electron beam lithography have to be considered when designing the solid to be milled. Both designs, straight 3D and serpentine 3D mixers, were significantly faster mixers than the standard focusing mixer with no 3D texturing. This demonstrates that adding programmed depth variations to existing microfluidic devices can open new opportunities in microfluidic research and IBμM.

The authors report experimental data on the dose contribution of backscattered electrons on a silicon substrate. The backscattered electron intensity, i.e., the relative dose contribution from backscattered electrons with respect to direct write dose, is not constant, but varies with the percentage of the total dose received by backscattered electrons. In order to measure the backscattered electron contribution, the position and number of electrons are controlled by electron beam lithography. The dose contribution is measured using a negative electron beam resist, which quantifies the electron interactions in a nanoscale volume on the surface of the substrate. The data presented here will lead to improvements in proximity effect correction algorithms and ultimately improve pattern creation using electron beam lithography.

We report the observation of a highly antisymmetric magnetoresistance in GaMnAs specimens with lateral nano-constrictions. The experiments were carried out on samples with an in-plane easy axis of magnetization, in in-plane applied magnetic field. We attribute this behavior to the formation of isolated nano-sized islands at the nano-constrictions, whose magnetization can undergo out-of-plane reorientation during switching. The change in resistance is up to 50%, which cannot be explained by the normal anisotropic magnetoresistance in GaMnAs. We propose tunneling anisotropic magnetoresistance as the most likely mechanism for this effect.

We demonstrate a practical sensing platform, consisting of SnO(2) nanoparticle-decorated semiconducting single-walled carbon nanotubes assembled on gold electrodes via a dielectrophoretic process, for highly sensitive CO detection with fast response at room temperature. The highest sensitivity obtained was 0.27 and the response time was ∼2 s for 100 ppm CO detection. The lower detection limit was ∼1 ppm. These results indicate that the sensing performance of our device is among the best of CO sensors implemented with SWNTs. Further, we observed a significant increase in sensitivity to 0.67 after subjecting the device to an electrical breakdown at 8 V. We also proposed a theoretical model to reveal the relationship between the sensitivity and the gas concentration. The new model not only resulted in a nice fit to our data, but also allowed us to estimate the contact resistance between an individual SWNT and the gold electrodes.

Deposits of aggregated silver particles were grown from aqueous silver-nitrate solution by electron-beam induced deposition in a liquid cell in a scanning electron microscope. Electron energies of 2, 5, and 20 keV were evaluated and found to produce distinguishably different deposits. Optimal energies exist for maximum growth rate and for minimum feature sizes. The physical structure of the deposits was found to evolve with increasing thickness as silver particles grow larger and develop more structure. Optical absorbance measurements and Raman spectroscopy on adsorbed dye suggest appropriate silver purity for using this fabrication method in nano-optics applications.

The authors have measured the range and intensity of backscattered electrons in silicon from a 100 keV source using a process independent method. Backscattered electrons contributed to the total dose of features written in a negative tone electron beam resist. Instead of measuring the height of the resist and using a contrast curve to convert the resist height to dose, the heights of the features were made equal by adjusting the backscattered contribution through dose assignments. Creating features of equal height eliminated the need to use a contrast curve to convert from resist height to total dose. Also, it allowed for measurements of the backscattered contribution from larger distances. Using a circularly symmetric torus pattern, the three-dimensional backscatter problem was reduced to a 1-dimensional Gaussian form. The authors measured the range of the backscattered electrons, β, to be 31.08 ± 0.06 μm. By varying the writing dose of the pattern, we determined the backscatter coefficient, η, to be 0.63 ± 0.03.

We report the fabrication of horizontally aligned ultrananocrystalline diamond (UNCD) nanowires (NWs) via two different approaches. First, with the top-down approach by using electron beam lithography (EBL) and reactive ion etching (RIE) with a photo resist layer as an etch mask. Using this approach, we demonstrate fabrication of 50 µm long UNCD NWs with widths as narrow as 40 nm. We further present an alternative approach to grow UNCD NWs at pre-defined positions through a selective seeding process. No RIE was needed either to etch the NWs or to remove the mask. In this case, we achieved UNCD NWs with lengths of 50 µm and smallest width of 90 nm respectively. Characterization of these nanowires by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that the UNCD NWs are well defined and fully released, with no indication of residual stress. Characterization using visible and ultraviolet (UV) Raman spectroscopy indicates that in both fabrication approaches, UNCD NWs maintain their intrinsic diamond structure.

We report far-field experimental optical extinction spectra of linear chains of gold nanocylinders with interparticle separations close to the particle's surface plasmon resonance (SPR) wavelength λSPR. The spectra reveal non-monotonic shift of the SPR peak position with increase in the distance d. The non-monotonic λSPR(d) dependence is rationalized considering electromagnetic coupling between the particles in the dipole approximation. Simple expressions for the modified SPR frequencies are obtained using the dipole scattered field and taking into account both the retardation and phase lag effects.

We have measured the intensity of backscattered 100 keV electrons on a silicon substrate as a function of distance up to 50 μm from the source. The intensity of backscattered electrons was determined by measuring the thickness changes in pre-exposed, isolated 100 nm crosses in a negative resist using atomic force microscopy. The electron backscattered range was measured to be 31.08 ± 0.30 μm and showed deviation from Gaussian behavior for radii larger than 30 μm. This method produces an accurate measurement of the backscattered range because it is process independent and covers a large data range.

The etch resistance of electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and ZEP520A, is increased significantly by sequential infiltration synthesis (SIS). This process infiltrates the bulk of the resist film with alumina, rendering it resistant to plasma etching. The enhanced etch resistance eliminates the need for an intermediate hard mask and the associated process costs and pattern fidelity losses. Furthermore, the improvement is realized with no degradation to the line-edge roughness of lithographically defined patterns. The enhancement in etch resistance is especially strong at the edges of the printed lines, owing to diffusion of the SIS precursors from the resist sidewalls. These improvements enable the anisotropic transfer of sub-100 nm patterns deeply into silicon without the need for an intermediate hard mask.

A distinctive feature of resist exposure by energetic helium ions or neutral atoms is that critical exposure densities are very low, about 100 times smaller than for electrons. Thus, particle distributions are sparse, leading to significant statistical fluctuations in the deposited energy density even in polymethylmethacrylate (PMMA), a relatively insensitive, nonchemically amplified resist. The impact is first seen as roughness in the region of partial exposure on a feature’s edge where the bunching of just a few particles may cause the energy density to shift above or below the resist development threshold. As feature size is reduced, however, fluctuations in the total number of particles (shot noise) become larger as a fraction of average dose, potentially causing over- and underexposure of the entire feature. This article presents an integrated study of image noise in helium lithography that compares shape variations in neutral particle mask images with the predictions of a Monte Carlo model. The mode...

This article describes a postdevelopment, additional electron exposure to enhance the etch selectivity and improve pattern transfer fidelity of an electron beam resist, ZEP 520A, through chemical changes of the resist. After the critical features were patterned and developed, the resist was exposed at 5 kV accelerating voltage to a second dose of electrons ranging from 300 to 300 000 μC/cm2. The etch rate of the resist decreased by approximately 25% in a CHF3 and O2 plasma. More critically, the fidelity of the pattern transfer was improved. Infrared and Raman spectroscopies were used to characterize the resist before and after electron beam exposure for doses up to 3000 μC/cm2. The carbonyl bonding in the polymer showed significant changes after electron beam exposure that can be associated with improvement in the etch performance of this resist.This article describes a postdevelopment, additional electron exposure to enhance the etch selectivity and improve pattern transfer fidelity of an electron beam resist, ZEP 520A, through chemical changes of the resist. After the critical features were patterned and developed, the resist was exposed at 5 kV accelerating voltage to a second dose of electrons ranging from 300 to 300 000 μC/cm2. The etch rate of the resist decreased by approximately 25% in a CHF3 and O2 plasma. More critically, the fidelity of the pattern transfer was improved. Infrared and Raman spectroscopies were used to characterize the resist before and after electron beam exposure for doses up to 3000 μC/cm2. The carbonyl bonding in the polymer showed significant changes after electron beam exposure that can be associated with improvement in the etch performance of this resist.

Etch resistance of two commonly used lithography resists is increased significantly by sequential infiltration synthesis (SIS). Exposing films to trimethyl-aluminum and water with long dosage times infiltrates the bulk of the film with alumina, which renders them dramatically more resistant to plasma etching with no degradation to the patterns. Enhanced etch resistance eliminates the need for an intermediate hard mask and the concomitant costs and pattern fidelity losses. Moreover, by allowing for thinner resist films, this approach can improve the final pattern resolution.

We have performed experiments to study the kinetics of dissolution of the positive chemically amplified resist AZ-PF (Hoechst AG). The resist dissolution in exposed regions was shown to have non-linear time dependence, with a delay time strongly dependent on prebake and post- exposure bake conditions. Effect of the presence of a low-solubility surface layer on patterning of submicron features as well as on roughness of the developed film has been demonstrated.

The study of photoelectron effects in X-ray Lithography motivates the need for modeling codes to simulate these effects to have an estimate of the influence of x-ray generated photoelectrons in the exposure of resists. We have performed a series of Monte Carlo simulations to study the spatial distribution of photoelectrons in a resist, PMMA, and parametrized this distribution with a set of energy-dependent gaussians for monochromatic X-rays within an energy range of 0.5 KeV to 2.5 KeV. We discuss the effects of the the redistribution of the photoelectron kinetic energy as a function of the electrons generated by the x-ray absorption in various atomic species.

X-ray zone plates are diffractive focusing optics composed of concentric rings of phase-shifting material with a changing period along their radii. Hard x-ray zone plates operate primarily in a range of photon energies from 3 to 30 keV. In order to achieve needed resolution and efficiency, high-aspect-ratio structures are typically patterned and fabricated by gold electroforming into a dielectric mold. Ideally, the molds would be mechanically stable and radiation resistant. Ultrananocrystalline diamond offers a solution with a set of physical properties that suggests that the material can be fabricated to desired requirements. The authors present here the first results for the fabrication of hard x-ray zone plates using an ultrananocrystalline diamond mold for electroforming gold and discuss future developments for creating an optimized focusing optic.

In this article, the authors present microfluidic mixers containing three-dimensional (3D) geometries used to decrease mixing lengths in passive microfluidic systems. In order to create these 3D geometries, the authors use ion beam lithography and micromachining and address charging, redeposition, and stitching error effects that follow this type of fabrication. Prior to mixer fabrication, simulations were run and results were compared between a common straight mixer and two other mixers designed by the authors. The simulation results have shown that 3D geometries can generate lateral velocities and lower mixing lengths down to approximately 70 μm.

High-fidelity surface enhanced Raman spectra (SERS) of Rhodamine 6G and 2-mercaptopyrimidine liquid solutions are measured using a microfluidic delivery system constructed on a flat silver substrate. Microscopic plasmon lenses patterned in the silver film focus surface plasmons into a subwavelength spot which yields the light amplification required for SERS. The system provides an efficiency similar to traditional colloidal substrates, and allows multiple sample loading. We find that the main contribution to the spectra comes from the molecules directly attached to the silver surface, which gives strong evidence for the chemical enhancement of SERS.

We demonstrate a high-performance gas sensor using partially reduced graphene oxide (GO) sheets obtained through low-temperature step annealing (300 °C at maximum) in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally reduced GO showed p-type semiconducting behavior in ambient conditions and were responsive to low-concentration NO2 diluted in air at room temperature. The sensitivity is attributed to the electron transfer from the reduced GO to adsorbed NO2, which leads to enriched hole concentration and enhanced electrical conduction in the reduced GO sheet.

(Pb)(Zr0.52Ti0.48)O3 (PZT) films were fabricated on LaNiO3 (LNO)/In2O3 90%SnO210% (ITO) layered transparent electrodes on glass substrates using chemical solution deposition. The structural, electrical, and optical properties of semitransparent Pd/PZT/LNO/ITO and transparent ITO/LNO/PZT/LNO/ITO capacitors fabricated on glass substrates were studied. X-ray diffraction revealed an improved crystalline structure of PZT on ITO-buffered glass substrates by interposing a LNO layer between PZT and ITO. Atomic force microscopy showed a smoother surface topography for the LNO/ITO layered electrode on glass, as compared to that of the single ITO layer on glass. The remnant polarization (Pr) of the Pd/PZT/LNO/ITO/glass capacitors and transparent ITO/LNO/PZT/LNO/ITO/glass capacitors was estimated from P-E hysteresis loops. The Pd/PZT/LNO/ITO capacitors on glass revealed significant improvement in the Pr as compared to PZT film based capacitors with ITO electrodes only. Excellent optical transmittance was observed for...

Superconducting niobium nitride wires and ribbons with transverse dimensions down to tens of nanometers were synthesized by annealing NbSe3 nanostructure precursors in flowing ammonia gas at temperatures up to 1000°C. Their critical temperatures increase with increasing annealing temperatures and reach 9–11.2K when sintered at 950°C or above. X-ray diffraction analyses identified Nb4N5 and Nb5N6 phases, dominating at annealing temperatures below and above 950°C, respectively. Transport measurements show magnetoresistance oscillations at temperatures near the superconducting transition due to vortex-row confinement effects and voltage jumps in current-voltage characteristics at low temperatures attributed to hot-spot behavior.

Combinatorial phage display methods have been used to identify a heptapeptide sequence, ISLLHST, that strongly associates with a perovskite ferroelectric, Pb(ZrxTi1−x)O3 (PZT). The selectively of peptide binding to polycrystalline metalorganic chemical vapor deposition deposited PZT thin films were determined by titering and immunofluorescence microscopy. Ferroelectric properties were determined by measurement of the P-E hysteresis loop on unmodified and phage bound PZT thin films. No change in the coercive field, Ec, or the saturation polarization, Ps was observed. The remnant polarization, PR, however, showed a minor reduction after exposure to aqueous buffer and/or phage binding, possibly due to association of compensating surface charges on the PZT.

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 n...

The need for stimuli-responsive components in microfluidic systems has led to the development of hydrogel-based patterned microstructures. The most commonly practiced means for fabricating micropatterned hydrogels is based on in situ photopolymerization using 365nm UV light in a liquid medium. This approach has been found to be very successful for patterning hydrogel-based features with tens or hundreds of microns resolution, but its main drawback lies in having to contain the liquid prepolymer mixture within the device for irradiation. We instead propose an alternate approach that uses direct-write electron-beam radiation to cross-link a dry, spin-coated thin film of linear polymer. After exposure, the linear polymer is dissolved in water leaving behind the cross-linked regions. When immersed in water, the cross-linked regions assume the properties of hydrogel and undergo naturally thermoreversible swelling and shrinking. This direct-writing approach can be used to fabricate hydrogel-based nanostructures...