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The strong attenuation of extreme ultraviolet (EUV) radiation by organic materials necessitates the use of a thin layer imaging (TLI) process for EUV lithography. Several TLI processes have been identified for potential use for EUVL, and the common theme in these approaches is the transfer of the aerial image to a thin layer of refractory-containing material, which is then used as a dry O 2 etch mask during a subsequent pattern transfer to the device layer. One TLI process that has been extensively examined for EUVL is the silylated top-surface imaging (TSI) technology, which is discussed in this paper. Using a new disilane silylation reagent, dimethylaminodimethyldisilane (DMDS) and 13.4 nm exposure, the TSI process has been used to print 100 nm lines and spaces at equal pitch and 70 nm lines and spaces at a higher 1:2 pitch. The line edge roughness for the printed lines has been determined using a custom image analysis program and, as expected, varies with the particular EUV exposure system and numerical aperture. Exposures done with 193 nm lithography and the TSI process using DMDS are also shown for comparison to the EUV results.

A method for in-plane imaging of large objects as compared to the RF coil is proposed based on the use of a single specially designed surface coil, without using B(0) gradients. A constant B(1) gradient was generated along the main axis of a ladder-shaped coil, and RF-encoding along the direction of the gradient made it possible to obtain spin-density profiles. Successive acquisitions of profiles obtained by translation of the NMR coil resulted in distorted images-due to the presence of non-zero gradients perpendicular to the constant gradient-that were successfully processed using a mathematical treatment based on linear combinations of calculated altered images from single-pixel objects. Copyright 2000 Academic Press.

We present a coherence domain imaging modality based on the spectral analysis of the output of an interferometer. It features no moving parts and combines the imaging of sub-surface morphology with surface spectroscopic imaging.

Strong resist photoabsorption at wavelengths below 248 nm necessitates the use of a thin layer imaging (TLI) scheme for microlithography using 193 nm, 157 nm, or 13.4 nm radiation. Previous to this work, a TLI process commonly known as silylated top surface imaging (TSI) was developed by a Sandia/AT and T team for use in extreme ultraviolet lithography (EUVL) at 13.4 nm. Using this bilayer process, 0.13 {micro}m resolution with 87{degree} sidewalls in 0.7 {micro}m of resist was achieved for EUV exposures. New imaging layer polymers, silylation reagents and crosslinkers, and process conditions were screened for improvement in this TSI process with the ultimate goal of demonstrating a resist technology capable of 0.10 {micro}m critical dimension (CD). The results of these attempted improvements to the TSI process are described in this report.

Top-surface imaging process by silylation (TIPS) has been suggested as an attractive solution to cope not only with limitation of resolution and process latitudes but also with line width variations due to reflections over steps. However this technique has not received a wide acceptance as a production worthy process until now, because of the stringent requirements on suitable silylation and dry development equipment that have good uniformity and good reproducibility. In a parametric study of TIPS dry development steps, we found the most important factors in the first step and the second step respectively. The optimized process demonstrated good etch rate uniformity and excellent 0.17 micrometer dense and isolated pattern of gate and islands pattern of capacitor in 1 G bit DRAM device. Their profiles were vertical and uniform within a wafer, while the proximity effect between dense and isolated pattern of gate remained 0.01 micrometer. In islands pattern, wider process margins of both local depth of focus (LDOF) and exposure latitude (EL) could be obtained and excellent 3(sigma) value of critical dimension (CD) uniformity within a wafer confirmed better applicability to 1 G bit DRAM and beyond. When silylated resist patten was transferred into substrate layer CD bias and uniformity could be controlled less than 0.02 micrometer. There were also no residues after both photoresist strip and induced polymer removal step. From these studies. TIPS process using cluster tool of silylation system made by LRC and TCP TM 9400 TM SE etcher for dry development was demonstrated a production worth process for the sub-0.20 micrometer lithography in terms of obtaining finer pattern without pattern problems and a reliable process for 1 G bit DRAM and beyond.

The purpose of this study was to measure the accuracy of a three-dimensional surface imaging system (3-D SIS) in comparison to a 3-laser system by analyzing the setup errors obtained from a RANDO Phantom and head and neck cancer patients. The 3-D SIS used for the evaluation of the setup errors was a C-RAD Sentinel. In the phantom study, the OBI setup errors without the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. Furthermore, the setup errors with the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. After comparison of the CBCT, setup correction about 1 mm was performed in a few cases. The probability of the error without the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 75.00% vs. 35.00% on the X-axis, 80.00% vs. 40.00% on the Y-axis, and 80.00% vs. 65.00% on the Z-axis. Moreover, the probability of the error with the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 70.00% vs. 15.00% on the X-axis, 75.00% vs. 25.00% on the Y-axis, and 70.00% vs. 35.00% on the Z-axis. These results showed that the 3-D SIS has a lower probability of setup error than the 3-laser system for the phantom. For the patients, the setup errors of the 3-laser system vs. the 3-D SIS were measured. The probability of the error exceeding more than 1 mm in the 3-laser system vs. the 3-D SIS was shown to be 81.82% vs. 36.36% on the X-axis, 81.82% vs. 45.45% on the Y-axis, and 86.36% vs. 72.73% on the Z-axis. As a result, the 3-D SIS also exhibited a lower probability of setup error for the cancer patients. Therefore, this study confirmed that the 3-D SIS is a promising method for setup verification.

We have studied the surface morphology of single‐crystal bulk superconductors in the Tl‐Ca‐Ba‐Cu‐O system by scanning tunneling microscopy, observing surface etching phenomena in air at room temperature, including the formation of lines and pits.

We have investigated the effect of line edge roughness (LER) of active patterns used for shallow trench isolation to the electrical performance of MOS transistor applicable for 1 giga-bit DRAM. Three different processes for resist patterning were applied for comparative analysis to form the active pattern in MOS transistor; the first method applied a conventional single layer resist (SLR) process, the second TIPS with two step dry development, and the third another TIPS with three step dry development. The third process adopted an additional step to break-through thin silicon dioxide which may contribute to the LER. The LER data of an active pattern before and after nitride substrate etching and their profiles were investigated among these processes. The third method shows the almost same LER and CD uniformity of the active pattern as those of SLR. The electrical properties. Only, threshold voltage variation of MOS transistor by the second method shows the worse results than those of SLR. Considering the ratio of LER in isolated active pattern with channel width of 0.3 micrometers to its average CD value, we think that its ratio should be controlled well below 7 percent for TIPS to make an useful technology for real device. Based on these studies, we believed that the well-controlled TIPS process using three step dry development is a strong candidate for device production of ArF and EUV lithography, if the advantages of TIPS technology over the SLR process are considered in the respect of lithography.

The advantages of surface-imaging photoresist processes have been well documented in the literature: greater resolution, wider focus budget, and less sensitivity to topography and reflections from the substrate. The diffusion enhanced silylated resist (DESIRE) is a good example of a surface-imaging process. In previous papers we have presented characterization data for this process, and discussed some of the issues involved in its implementation in a manufacturing environment. More recently we have reviewed integration issues evolving from the interactions between the equipment, materials, and process. In this paper we continue our discussion of process integration issues focusing on: (1) electrical discharge, or arcing, during dry-development, and (2) line-width uniformity. Arcing is a very serious problem because of its catastrophic effect on yield. Thus far we have determined that the substrate and equipment influence the occurrence of arching, but further work remains to be done to determine all the possible causes. In previous papers we showed that the linewidth can be controlled across the wafer, and from wafer-to-wafer. By optimizing the magnetic field uniformity in our initial process set up, we were able to control the linewidth to within +/- 8% for 0.63 micrometers lines. However, to maintain this control over time, modifications in the silylation reactor had to be made. Additional improvements in the linewidth uniformity require us to go back and make modifications to the dry-develop reactor to improve the magnetic field uniformity further. These two examples illustrate the need to take a comprehensive or process integration approach to successfully implement this process.

A variety of analytical and process control techniques have been employed during process development activities for a 0.5 micrometers deep UV positive tone surface imaging process. Examples of applications of these methods for identification of primary positive tone surface imaging issues and process optimization for enhancement of ultimate resolution are described. Advantages and limitations for each technique are discussed.

This paper describes the silylation properties and the lithographic performance of ArF (193 nm) surface imaging process with bis(dimethylamino)methylsilane [B(DMA)MS]. The silicon concentration of silylated region with B(DMA)MS in liquid phase is much higher (2 times) than that for the conventional silylation with dimethylsilyldimethylamine (DMSDMA) in vapor phase. The excellent resolution of 0.12 micrometers L/S and practical DOF (1.0 micrometers in a range for 0.18 micrometers L/S) have been achieved using ArF exposure system with a conventional binary mask under a normal illumination. Further, the resolution of 0.088 micrometers has been obtained with a Levenson-type phase shifting mask.

Sub-micron resist features obtained by surface imaging and dry development have been used as masks in the pattern transfer of multilevel metal stacks in a single-wafer multichamber etcher. The calibration of such a negative working submicron lithographic process, derived from a g-line wafer stepper having a specified resolution of 1 micron, is described. Surface imaging was initiated by silylation of a proprietary resist using HMDS, while dry development was performed in a single-stage oxygen process in a conventional reactive ion etcher. Metal etch processes are outlined in conjunction with their effect on resist integrity and removal and the need for post-development deep-UV hardening. While not being part of the two-layer demonstrator, submicron 'via' hole definition in polyimide interlayer dielectric is demonstrated in a single-stage dry development/pattern transfer process.

A variety of different approaches were used in an effort to improve the photospeeds of single component TSI resists based on poly(4-hydroxystyrene). The variations included molecular weights, co-monomer partners, and selected substituents. The factors that were studied dramatically affected silylation rates, in one case by as much as an order of magnitude. However, when the silylation times were adjusted to compensate for the rate differences and silylation depths, only minimal differences in photospeed were observed. The apparent contrast measured by swelling upon silylation was very poor ((gamma) equals 1.5) while the contrast measured after etching was quite high, approximately ten times that of the silylation value.

The practical limits of i-line top surface imaging process using a novolak based photoresist were investigated dependent on exposure techniques such as conventional and off-axis illumination. Ultimately, quarter micron small geometry was clearly delineated and depth of focus (DOF) latitude of 1.5micrometers and 2.7micrometers was achieved respectively for 0.25micrometers and 0.30micrometers lines and spaces pattern by annular illumination of 0.50NA. To compensate proximity effect caused by pattern density, sub-resolution auxiliary pattern was firstly optimized for off- axis illumination of quadrapole and annular. As a result, critical dimension (CD) difference between dense and isolated pattern in 0.30micrometers reduced to half-level compared to that of non-auxiliary pattern. It was found that desilylation phenomenon was critically affected by the kind of photopolymer reacted with silicon source and molecular weight of silylation agent. Novolak based polymer maintained superior silylation durability to polyvinyl phenolic (PVP) resin. New silylation process concept which is dual silylation method was developed to utilize PVP's merits in the silylation process against desilylation. Dry development lithography of i-line was feasible to practical application of prototype 256 mega bit DRAM which demands 0.30micrometers patterning with a reproducibility.

We have developed a novel scanning near-field ultrasound holography (SNFUH) technique which combines the nanometer-scale spatial resolution of conventional scanning probe microscope (SPM) with the surface and subsurface imaging capabilities [1]. This technique fills the critical void in characterization and investigation of the static and dynamic mechanics of nanoscale systems and address emerging issues in imaging and analysis of diverse “embedded” nano and microscale structures, and engineered systems. The SNFUH development integrates three major approaches: a unique combination of scanning probe microscope platform (which enjoys excellent lateral and vertical resolution) coupled to microscale ultrasound source and detection (which facilitates “looking” deeper into structures, section-by-section) and a novel holography approach (to enhance phase resolution and phase coupling in imaging). Existing far-field ultrasonic or acoustic microscopy techniques [2] suffer from spatial resolution limitations. Moreover, all far field microscopies lack: resolution Limitations due to Rayleigh limit: 0.51λ/N.A., coupling fluid attenuation ~ f 2 , and impedance mismatches. Recently ultrasonic force microscopy [3-4] has been widely used to map the elastic properties of soft and hard surfaces. In SNFUH approach, a high frequency (~ 100’s of KHz to several MHz) acoustic wave is launched from the bottom of the specimen, while another wave is launched on the AFM cantilever, albeit at a slightly different frequency. The interference of these two waves would nominally form so-called “beats” and “product frequencies” which is monitored by the AFM tip, which itself acts as an antenna for both phase and amplitude of the beats and product frequencies. As the specimen acoustic wave gets perturbed by sub-surface (and surface) features, especially its phase, the local acoustic interference is very effectively monitored by the AFM tip. Thus, within the near-field regime (which enjoys superb lateral and vertical resolution), the acoustic wave (which is nondestructive and sensitive to mechanical/elastic variation in its “path”) is fully analyzed, point-bypoint, by the AFM acoustic antenna in terms of phase and amplitude. The efficacy of SNFUH for in-vitro biological imaging and indentifying the buried structures is demonstrated on acoustically active liposomes (AAL) which contains small amount of air. AAL have oil layer in which therapeutics can be dissolved, the lipid shell and the air-bubbles interior. These liposomes have potential to carry drugs, ease of conjugation with antibodies, peptides and their acoustic activity could enable them to respond to ultrasound stimulation by releasing their contents and has been reported elsewhere [5]. Figure 1 depicts a high resolution and remarkably high contrast from AAL, and shows embedded air-bubbles embedded in them. Here, we demonstrated direct and real-space in-vitro imaging of the presence of air-bubbles and proteins inside liposome’s without any labels or sectioning of cells, and under physiologically viable conditions. Figure 2 shows another potential application of SNFUH approach in direct imaging of

A combination of Surface Imaging resist with a Low Voltage EBL is suggested and it is referred to a suitable EBL-equipment

High resolution imaging of wheat and potato starch granule surfaces has been performed using low-voltage scanning electron microscopy and atomic force microscopy. The complimentary images of uncoated granules demonstrate that the two starch types possess substantially different surface topologies; potato starch has many protrusions (100-300 nm in diameter), above a flatter surface containing 20-50 nm structures, whilst wheat starch possesses far fewer protrusions and generally has a smoother surface composed of approximately 20 nm structures. The protrusions are believed to be carbohydrate in nature and thus represent the ends of amylopectin side-chain clusters at the granule surface.

Application of Scanning Acoustic Microscopy for nondestructive evaluation of mechanical properties of objects having non-planar surface reveal two kinds of contrast. Images of ceramic bearing balls (Chow et al., 1991) and the images of steel spheres (Kolosov et al., 1991) exhibit the shape of a light spot which diameter is proportional to the diameter of the spheres. In contrary, acoustic micrographs of steel bearing ball obtained by (Weglein, 1981) and cavities in alumina (Poirier et al., 1984) exhibited a fringe pattern associated with a V(z) curve (Poirier et al., 1984). In this paper we present the theoretical explanation of this phenomena using the approximation of the uneven surface by an inclined plane (Weise et al., 1994). The dependence of the contrast of surface images on the wave length, radius of surface curvature and the aperture angle of the lens is investigated. The conditions for different kinds of contrast are obtained.

A method for full-field surface profiling in the tandem scanning confocal microscope has been previously described. The technique utilizes chromatic aberration to produce an extended and color coded focal volume. Planes at different axial depths within this volume correspond to the foci of different wavelengths through the intentionally aberrant system. To determine the height of any point within the field, the confocal detection system must be capable of identifying the wavelength of the most intensely reflected light from that point. Hence the relative sensitivity of the detector and the spectral response of the imaging system are important parameters. We have utilized xenon and mercury arc sources and compared results with various types of objective lens. One potential limitation of this microscope is the fact that the introduction of longitudinal chromatic aberration affects the correction of the optics for plan imaging, i.e., introduces spherical aberrations, but the technique is rapid and produces results well correlated with more conventional techniques. To allow detailed study of the use of a chromatic 3-D probe for surface imaging we have designed and constructed a stage- scanned instrument which uses on-axis optics and is therefore free from spherical aberrations and can be corrected optimally. The instrument is described and results presented for single pass 3-D imaging.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Submicrometer IR surface imaging was performed with a resolution better than the diffraction limit. The apparatus was based on an IR optical parametric oscillator laser and a commercial atomic force microscope and used, as the detection mechanism, induced resonant oscillations in an atomic force microscopy (AFM) cantilever. For the first time to our knowledge this was achieved with top-down illumination and a benchtop IR source, thus extending the range of potential applications of this technique. IR absorption and AFM topography images of polystyrene beads were recorded simultaneously with an image resolution of 200 nm.

Summary The design of a scanned-cantilever-type force microscope is presented which is fully integrated into an inverted high-resolution video-enhanced light microscope. This set-up allows us to acquire thin optical sections in differential interference contrast (DIC) or polarization while the force microscope is in place. Such a hybrid microscope provides a unique platform to study how cell surface properties determine, or are affected by, the three-dimensional dynamic organization inside the living cell. The hybrid microscope presented in this paper has proven reliable and versatile for biological applications. It is the only instrument that can image a specimen by force microscopy and high-power DIC without having either to translate the specimen or to remove the force microscope. Adaptation of the design features could greatly enhance the suitability of other force microscopes for biological work.

Techniques commonly used to determine silicon penetration depth during deep UV surface imaging lithography are compared to a method referred to as plasma etch 'staining.' This methodology is described in detail and the results compared and correlated to Rutherford Backscattering Spectroscopy (RBS) and ellipsometric (film swelling) measurements. Effects of the staining parameters on the resulting silicon depth are also discussed.

Creation of three-dimensional representations of surfaces from images taken at two or more view angles is a well-established technique applied to optical images and is frequently used in combination with scanning electron microscopy (SEM). The present work describes specific steps taken to optimize and enhance the repeatability of three-dimensional surfaces reconstructed from SEM images. The presented steps result in an approximately tenfold improvement in the repeatability of the surface reconstruction compared to more standard techniques. The enhanced techniques presented can be used with any SEM friendly samples. In this work the modified technique was developed in order to accurately quantify surface geometry changes in metallic bond coats used with thermal barrier coatings (TBCs) to provide improved turbine hot part durability. Bond coat surfaces are quite rough, and accurate determination of surface geometry change (rumpling) requires excellent repeatability. Rumpling is an important contributor to TBC failure, and accurate quantification of rumpling is important to better understanding of the failure behavior of TBCs.

Surface microscopy of individual biological cells is essential for determining the patterns of cell migration to study the tumor formation or metastasis. This paper presents a correlated and effective theoretical and experimental technique to automatically address the biophysical and mechanical properties and acquire live images of biological cells which are of interest in studying cancer. In the theoretical part, a distributed-parameters model as the comprehensive representation of the microcantilever is presented along with a model of the contact force as a function of the indentation depth and mechanical properties of the biological sample. Analysis of the transfer function of the whole system in the frequency domain is carried out to characterize the stiffness and damping coefficients of the sample. In the experimental section, unlike the conventional atomic force microscope techniques basically using the laser for determining the deflection of microcantilever's tip, a piezoresistive microcantilever serving as a force sensor is implemented to produce the appropriate voltage and measure the deflection of the microcantilever. A micromanipulator robotic system is integrated with the MATLAB(®) and programmed in such a way to automatically control the microcantilever mounted on the tip of the micromanipulator to achieve the topography of biological samples including the human corneal cells. For this purpose, the human primary corneal fibroblasts are extracted and adhered on a sterilized culture dish and prepared to attain their topographical image. The proposed methodology herein allows an approach to obtain 2D quality images of cells being comparatively cost effective and extendable to obtain 3D images of individual cells. The characterized mechanical properties of the human corneal cell are furthermore established by comparing and validating the phase shift of the theoretical and experimental results of the frequency response.

We present an imaging technique using an optically trapped cigar-shaped probe controlled using holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be taken in a manner analogous to scanning probe microscopy (SPM), with automatic closed loop feedback control provided by analysis of the probe position recorded using a high speed CMOS camera. The probe is held using two optical traps centred at least 10 µm from the ends, minimizing laser illumination of the tip, so reducing the chance of optical damage to delicate samples. The technique imparts less force on samples than contact SPM techniques, and allows highly curved and strongly scattering samples to be imaged, which present difficulties for imaging using photonic force microscopy. To calibrate our technique, we first image a known sample--the interface between two 8 µm polystyrene beads. We then demonstrate the advantages of this technique by imaging the surface of the soft alga Pseudopediastrum. The scattering force of our laser applied directly onto this sample is enough to remove it from the surface, but we can use our technique to image the algal surface with minimal disruption while it is alive, not adhered and in physiological conditions. The resolution is currently equivalent to confocal microscopy, but as our technique is not diffraction limited, there is scope for significant improvement by reducing the tip diameter and limiting the thermal motion of the probe.

Deep UV photochemical patterning of chemisorbed metal-binding (ligating) organosilane films has been previously used to demonstrate sub-0.5 micrometers patterned additive metallization by electroless deposition. Significant photospeed advantages have now been obtained using a two step process in which an organosilane film is first patterned and then functionalized to impart the ability to metallize. This is achieved by photochemical patterning of a film which lacks a ligating group, but which is optimized for photospeed. The pattern of chemical functions so created is then reacted with an organic ligand which selectively places the ligand functionalities on the surface. Treatment with an aqueous Pd catalyst followed by electroless plating deposits metal in patterns defined by the irradiation step. Using several chemical approaches based upon this concept, metal patterns have been fabricated to 0.5 micrometers feature width at doses of 50 mJ/cm2 at 193 nm.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fullerene thin films have been prepared on Au(111) substrates by sublimation from fullerene powders with different C60 / C70 ratios. Scanning tunneling microscopy (STM) images of the film surfaces show a hexagonal lattice built-up of two types of ball-shaped molecules (differing in diameter and corrugation). The ratio of smaller to larger balls compares well with the C60/ C70 ratio determined by high pressure liquid chromatography (HPLC) on hexane solutions of the respective fullerene powders. STM images show defects such as vacancies, interstitials and boundaries between different stacking domains (ABC and CBA). Dynamic displacement of C70 molecules and vacancies is observed.

A multichannel scanning system for magnetic surface imaging composed of 16 magnetoresistive sensors has been developed. A gray scale, from 0 to 255, was used to represent the magnetic signal detected by each sensor when the sample was moved above the scanner. Measurements and calibration were performed using magnetic surfaces with different shapes and samples with similar profiles, but different magnetization intensities. The system was sufficiently sensitive to detect gradients and discontinuities on the magnetic map. The 16 channel images were numerically processed to obtain a smooth representation of the magnetic map using the LabView™ Image Vision package.

G- and i-line diazonaphthoquinone/novolak photoresist films are surface imaged with g-line, i-line and deep-UV steppers. Following optical exposure, the resist film is treated with aqueous solutions which deposit a catalyst for electroless metal deposition. Wet development of the exposed and catalyzed photoresist results in selective removal of catalyst along with the exposed portion of the underlying photoresist. Upon immersion in an aqueous electroless plating solution, metal is selectively deposited on the unexposed photoresist which is still bearing catalyst to yield a positive-tone plasma etch mask. Oxygen magnetron-enhanced reactive ion etching (O2 MERIE) provides high polymer etch rates (approximately equals 1 micrometers /min) with excellent selectivity (> 300:1) to 70-170 angstrom Ni films. In addition, large ion fluxes produce highly anisotropic etch profiles for faithful pattern transfer. The process has achieved 0.30 micrometers resolution with a 6:1 aspect ratio at 248 nm (0.35 NA). Printing of 0.40 micrometers lines and spaces has been achieved at i-line (0.45 NA) over Al steps.

A variety of novolac-based polymers and blends with photoactive compounds were studied for their suitability as resists in a 193-nm positive-tone silylation process. The addition of photoactive compound was found to reduce the sensitivity of the resist and to hinder the diffusion of the silylating agent. Pure meta-cresol novolacs and polyvinylphenols, both of which can be polymerized to high (> 10,000) molecular weights show the best sensitivity for this process. Diffusion rates correlate with the molar volume of the silylating agent, although the activation energy does not. Resolution of 0.2-micrometers line-and-space gratings has been achieved with the polyvinylphenol and meta-cresol novolac resins.

We have been working towards a 3 dimensional structural understanding of the Nuclear Pore Complex (NPC) with a view to investigating structural alterations associated with the molecular mechanism of transport across the nuclear envelope. FEISEM allows direct visualisation of changes in individual NPCs which will complement information from TEM 3D reconstructions. FEISEM has produced significant new information on the more peripheral elements of the NPC, most notably the nuclear pore basket or ‘fishtrap’ and the nuclear envelope lattice. NPC baskets have been recognised in both avian and insect species as well as amphibia and are likely to be evolutionarily conserved. In the salivary gland nuclei ofChironomusdifferent configurations of basket structure have been recognised undergoing interaction with Balbiani Ring particles during mRNA export. (Fig 1).The ability to observe and directly compare large numbers of NPCs on isolated NEs from either the cytoplasmic or nucleoplasmicface, at equivalent biological resolution to TEM has enabled us to access internal NPC organisation by surface imaging.

Optical imaging of fluorescent objects embedded in a tissue simulating medium was characterized using non-contact based approaches to fluorescence remittance imaging (FRI) and sub-surface fluorescence diffuse optical tomography (FDOT). Using Protoporphyrin IX as a fluorescent agent, experiments were performed on tissue phantoms comprised of typical in-vivo tumor to normal tissue contrast ratios, ranging from 3.5:1 up to 10:1. It was found that tomographic imaging was able to recover interior inclusions with high contrast relative to the background; however, simple planar fluorescence imaging provided a superior contrast to noise ratio. Overall, FRI performed optimally when the object was located on or close to the surface and, perhaps most importantly, FDOT was able to recover specific depth information about the location of embedded regions. The results indicate that an optimal system for localizing embedded fluorescent regions should combine fluorescence reflectance imaging for high sensitivity and sub-surface tomography for depth detection, thereby allowing more accurate localization in all three directions within the tissue.

A hydrogen silisesquioxane (HSQ) bilayer process and a top surface imaging (TSI) process are investigated for application as low-voltage electron beam resist systems. Namatsu, van Delft, and others have reported printing exceptionally small features using high-voltage electron beam exposure of HSQ at high-exposure doses (~2000 µC/cm2 at 100 kV). The shallow penetration depth of low-voltage electrons results in greatly reduced dose requirements, and smooth, high-resolution images are generated at 1 kV with an exposure dose of less than 60 µC/cm2. HSQ's high silicon content enable it to be used in a bilayer form utilizing reactive ion etching with an oxygen plasma, thus generating high aspect ratio images. TSI has been studied in the past by numerous researchers at low voltages using various TSI schemes. We investigate the use of a chemically amplified TSI resist process based on poly (t-BOC-hydroxystyrene). The effect of base quencher loading in the resist formulation on line edge roughness and resolution is investigated, and is found to have a dramatic influence. High-resolution, high aspect ratio images are printed down to 40 nm, and exhibit only moderate levels of line edge roughness. Furthermore, proximity effects at 1, 2, and 3 kV are examined and compared to simulation.

Focused ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering, and proximity effects. However, combining the FIB lithography with top surface imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This article reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation, and oxygen dry etching. The negative resist image by dry etching is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that the Ga+ ion beam dose in the range of 1–50 μC/cm2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of a positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30 keV ...

Top surface imaging systems based on vapor phase silylation have been investigated for use at a variety of wavelengths. This approach to generating high aspect ratio, high resolution images held great promise particularly for 193 nm and EUV lithography applications. Several 193 nm top surface imaging (TSI) systems have been described that produce very high resolution (low k factor) images with wide process latitude. However, because of the line edge roughness associated with the final images, TSI systems have fallen from favor. In fact, TSI does not appear in the strategy or plan for any imaging technology at this time. Most of the 193 nm TSI systems that have been studied are based on poly(p-hydroxystyrene) resins. These polymers have an unfortunate combination of properties that limit their utility in this application. These limiting properties include (1) high optical density, (2) poor silylation contrast, and (3) low glass transition temperature of the silylated material. These shortcomings are relate...

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