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Rapid advances in nanoscience rely on continuous improvements of material manipulation at near-atomic scales. Currently, the workhorse of nanofabrication is resist-based lithography and its various derivatives. However, the use of local electron, ion, and physical probe methods is expanding, driven largely by the need for fabrication without the multistep preparation processes that can result in contamination from resists and solvents. Furthermore, probe-based methods extend beyond nanofabrication to nanomanipulation and to imaging which are all vital for a rapid transition to the prototyping and testing of devices. In this work we study helium ion interactions with the surface of bulk copper indium thiophosphate CuM(III)P2X6 (M = Cr, In; X= S, Se), a novel layered 2D material, with a Helium Ion Microscope (HIM). Using this technique, we are able to control ferrielectric domains and grow conical nanostructures with enhanced conductivity whose material volumes scale with the beam dosage. Compared to the copper indium thiophosphate (CITP) from which they grow, the nanostructures are oxygen rich, sulfur poor, and with virtually unchanged copper concentration as confirmed by energy-dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) imaging contrast as well as scanning microwave microscopy (SMM) measurements suggest enhanced conductivity in the formed particles, whereas atomic force microscopy (AFM) measurements indicate that the produced structures have lower dissipation and are softer as compared to the CITP.

The conventional SEM must operate with a pressure in the sample chamber below ~10−4 Pa (~10−6 torr), a condition determined by the need to satisfy four key instrumental operating conditions

Electron beams have made possible the development of the versatile, high performance electron microscopes described in the earlier chapters of this book. Techniques for the generation and application of electron beams are now well documented and understood, and a wide variety of images and data can be produced using readily available instruments. While the scanning electron microscope (SEM) is the most widely used tool for high performance imaging and microanalysis, it is not the only option and may not even always be the best instrument to choose to solve a particular problem. In this chapter we will discuss how, by replacing the beam of electrons with a beam of ions, it is possible to produce a high performance microscope which resembles an SEM in many respects and shares some of its capabilities but which also offers additional and important modes of operation.

While X-ray analysis can be performed in the Variable Pressure Scanning Electron Microscope (VPSEM), it is not possible to perform uncompromised electron-excited X-ray microanalysis. The measured EDS spectrum is inevitably degraded by the effects of electron scattering with the atoms of the environmental gas in the specimen chamber before the beam reaches the specimen. The spectrum is always a composite of X-rays generated by the unscattered electrons that remain in the focused beam and strike the intended target mixed with X-rays generated by the gas-scattered electrons that land elsewhere, micrometers to millimeters from the microscopic target of interest.

Summary Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field–scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3–1 times λ), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided. SCANNING 36:338–346, 2014. © 2013 Wiley Periodicals, Inc.

Over the past fifty years the scanning electron microscope (SEM) has established itself as the most versatile and productive tool for imaging and microanalysis in many areas of science and technology, and some seventy-thousand instruments generate millions of micrographs every day. Scanning electron microscopes do, however, have one fundamental limitation in that the only experimental variable available to the operator is the choice of the accelerating voltage. Although the ability to vary beam energy is both necessary and important, it is an unfortunate fact that changing the beam energy also alters many aspects of performance: imaging resolution, relative strength of different signal components, depth of beam penetration, capabilities of the various analytical systems, and the severity of charging and beam-induced damage. This makes it difficult or impossible to optimize the interaction of interest.

Summary Generally, in scanning electron microscopy (SEM) imaging, it is desirable that a high-resolution image be composed mainly of those secondary electrons (SEs) generated by the primary electron beam, denoted SEI. However, in conventional SEM imaging, other, often unwanted, signal components consisting of backscattered electrons (BSEs), and their associated SEs, denoted SEII, are present; these signal components contribute a random background signal that degrades contrast, and therefore signal-to-noise ratio and resolution. Ideally, the highest resolution SEM image would consist only of the SEI component. In SEMs that use conventional pinhole lenses and their associated Everhart–Thornley detectors, the image is composed of several components, including SEI, SEII, and some BSE, depending on the geometry of the detector. Modern snorkel lens systems eliminate the BSEs, but not the SEIIs. We present a microfabricated diaphragm for minimizing the unwanted SEII signal components. We present evidence of improved imaging using a microlithographically generated pattern of Au, about 500 nm thick, that blocks most of the undesired signal components, leaving an image composed mostly of SEIs. We refer to this structure as a “spatial backscatter diaphragm.” SCANNING 35:1-6, 2013. © 2012 Wiley Periodicals, Inc.

The scanning electron microscope (SEM) has become the most widely used of all advanced imaging tools because it offers a unique range of capabilities. It can resolve and image objects with sizes ranging from millimeters to below 1 nm; it offers multiple ways to generate, collect, and display signals; the images produced contain information about the topography, chemical composition, and the magnetic, electrostatic, and crystallographic properties of the sample; and it can generate characteristic x-ray emission from the specimen to provide a quantitative chemical analysis. Unfortunately, one thing that it will be unable to do is maintain its competitive edge in the 21st century. This is because electrons are electromagnetic ‘‘waves’’ and thus the smallest spot, ‘‘d,’’ into which an electron beam can be focused has a diameter of the order of: d 1⁄4 k=a ð1Þ

A combination of the 'semi-empirical' model for secondary electron production and the TRIM routines which describe ion stopping power, scattering, and transport, has been used to construct a Monte Carlo simulation (IONiSE) that can quantitatively interpret the generation of secondary electrons (SE) from materials by fast helium ions. This approach requires that the parameters of the semi-empirical model be determined by fitting to experimental yield data but has the merit that, unlike more fundamental models, it can be applied with equal ease to both pure elements and complex compounds. The application of the model to predict the topographic yield variation of helium generated SE as a function of energy and material, and to investigate the ratio between SE generated by incident and backscattered ions, is demonstrated.

Electron beam-induced deposition (EBID) provides a simple way to fabricate submicron- or nanometer-scale structures from various elements in a scanning electron microscope (SEM). The growth rate and shape of the deposits are influenced by many factors. We have studied the growth rate and morphology of EBID-deposited nanostructures as a function of the tungsten hexafluoride (WF6) and tetraethylorthosilicate (TEOS) precursor gas pressure and growth time, and we have used Monte Carlo simulations to model the growth of tungsten and silicon oxide to elucidate the mechanisms involved in the EBID growth. The lateral radius of the deposit decreases with increasing pressure because of the enhanced vertical growth rate which limits competing lateral broadening produced by secondary and forward-scattered electrons. The morphology difference between the conical SiO(x) and the cylindrical W nanopillars is related to the difference in interaction volume between the two materials. A key parameter is the residence time of the precursor gas molecules. This is an exponential function of the surface temperature; it changes during nanopillar growth and is a function of the nanopillar material and the beam conditions.

The phase-contrast imaging of atomic lattices has now become commonplace for both Transmission Electron Microscopes (TEM) and Scanning Transmission Electron Microscopes (STEMs). Recently, however, bright-field STEM images of multi-wall carbon nanotubes (MWCNTs) recorded from an ultra-high resolution (UHR) in-lens field-emission scanning electron microscope (FE-SEM) operating at 30keV have also demonstrated lattice fringe resolution. One example of such an image containing multiple examples of fringe detail is shown in figure 1. The carbon lattice fringes were analyzed and their origin confirmed by the application of the FFT algorithms in the SMART image analysis program. The resulting power spectrum after thresholding to remove background noise (Figure 2) confirms that phase detail in the image extends down to about 5 Angstroms (0.5nm) and that well defined diffraction spots corresponding to a spacing of 3.4 Angstroms (0.34nm) generated by the (002) basal plane spacing of the graphite lattice are present.

A field-emission scanning electron microscope (FESEM) equipped with the standard secondary electron (SE) detector was used to image thin (70-90 nm) and thick (1-3 microns) sections of biological materials that were chemically fixed, dehydrated, and embedded in resin. The preparation procedures, as well as subsequent staining of the sections, were identical to those commonly used to prepare thin sections of biological material for observation with the transmission electron microscope (TEM). The results suggested that the heavy metals, namely, osmium, uranium, and lead, that were used for postfixation and staining of the tissue provided an adequate SE signal that enabled imaging of the cells and organelles present in the sections. The FESEM was also used to image sections of tissues that were selectively stained using cytochemical and immunocytochemical techniques. Furthermore, thick sections could also be imaged in the SE mode. Stereo pairs of thick sections were easily recorded and provided images that approached those normally associated with high-voltage TEM.

Experimental nanotips have shown significant improvement in the resolution performance of a cold field emission scanning electron microscope (SEM). Nanotip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nanotips offer higher brightness and smaller electron source size. An electron microscope equipped with a nanotip electron gun can provide images with higher spatial resolution and with better signal-to-noise ratio. This could present a considerable advantage over the current SEM electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field-emission critical dimension (CD) SEM was used as an experimental test platform. Substitution of tungsten nanotips for the regular cathodes required modification of the electron gun circuitry and preparation of nanotips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nanotips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nanotips. Nanotip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nanotip clearly demonstrated an improvement in the performance of the test SEM. This and the results of the theoretical assessment gave support for the installation of the nanotips as the next step and pointed to potentially even better performance. Images taken with experimental nanotips showed a minimum two-fold improvement in resolution performance than the specification of the test SEM. The stability of the nanotip electron gun was excellent; the tip stayed useful for high-resolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to take full advantage of the nanotip electron emitters.

Low voltage scanning electron microscopy (LVSEM) has become the imaging technique of choice for many applications because it offers surface specific information, and both control of charging and a reduction of damage to labile specimens. However fundamental limitations such as the electron wavelength, lens aberrations, and gun brightness, severely limit the performance of the LVSEM, and in addition some capabilities such as microanalysis are difficult or impossible. New technologies, including aberration correction and brighter electron sources are now available, and novel spectroscopic approaches are in development. Together these advances could significantly enhance the performance of the LVSEM. The advent of ultra-high performance ion column imaging systems offers interesting competition to the LVSEM for both imaging and analysis. [DOI: 10.1380/ejssnt.2006.369]

The development of the microcalorimeter energy-dispersive X-ray spectrometer (µ-cal EDS) offers a significant advancement in X-ray microanalysis, especially for electron beam instruments. The benefits are especially pronounced for low voltage (≤5 kV) X-ray microanalysis in the field emission scanning electron microscope (FE-SEM) where the high energy resolution of the µ-cal EDS minimizes the peak overlaps among the myriad of K, L, M and N lines in the 0–5 keV energy range. The availability of L- and M-shell X-ray lines for microanalysis somewhat offsets the absence of X-ray lines traditionally used above 5 keV energy. The benefits and challenges of the µ-cal EDS will be discussed, including P/B ratio for characteristic X-rays, collection angle, count rate capability and the impact of polycapillary X-ray optics on microanalysis.

A simple method is described to determine the effective gas path length when incident electrons scatter in the gas above the specimen. This method is based on the measurement of a characteristic x-ray line emitted from a region close to the incident beam. From various experimental measurements performed on various microscopes, it is shown that the effective gas path length may increase with the chamber pressure and that it is also often dependent of the type of x-ray bullet.

Specimens that charge under electron beam irradiation in the scanning electron microscope (SEM) can be stabilized by choosing the beam energy to be such a value that the sum of the secondary and backscatter electron yields is unity, as this establishes a dynamic charge balance. We show here that for pure elements, the energies El and E2, for which charge balance occurs, are related directly to the atomic number of the material. Although generally there is no comparable relation for compounds, we also show that for polymers, the E2 energy is related both to the ratio of the number of valence electrons to molecular weight and to the electro-negativity of the monomer units that form the polymer.

We describe a novel, all dry approach that uses direct epitaxial growth for nanostructure fabrication. The two major requirements for achieving direct epitaxial growth are the ability to generate and to subsequently maintain and control spatial and chemical selectivity in the film growth process. The spatial selectivity is generated by pattering a surface adsorption layer on Si(100) using scanning electron beam lithography. This artificial lateral variation in surface reactivity is used as a template in subsequent epitaxy. Selective epitaxial growth on the resulting patterns is achieved by supersonic molecular jet epitaxy. Systematic investigation of the effects of various patterning and growth parameters on spatial and chemical selectivity at a sub- 100-nm feature scale using hydrogen terminated and nitrogen terminated growing Si(100) surfaces are presented.

Low voltage scanning electron microscopy (LVSEM) is the application of the SEM at beam energies below 5 keV. The fall in electron beam range compared to its magnitude at higher energies leads to significant changes in the beam interaction volume and in the secondary and backscattered electron yields. The topographic and beam penetration contrast effects which dominate images at high energies are replaced by detector collection efficiency contrast effects giving images which are less three dimensional but which contain more detailed information on the surface morphology and, in some circumstances, the surface chemistry of the specimen. In order to observe non-conducting specimens a state of charge balance must be obtained to obviate imaging artifacts. This requires an optimized choice of the incident beam energy, sample tilt, beam current and magnification for each sample. The high stopping power of electrons at low energy can result in enhanced radiation damage. However, because of the small electron range such damage is confined to a thin, near surface, region of the specimen. The combination of a field emission gun and a high performance lens allows the probe size of the instrument to be made almost independent of the chosen beam energy over the range 1–30 keV and probable advance in electron sources and electron optics promise still better levels of performance for the LVSEM.

A major concern in both scanning electron and scanning ion microscopy is that of sample charging, but strategies to eliminate this problem are available.

The scanning electron microscope (SEM) has become the most widely used high-performance microscope. However because of the fundamental limitations of electron beams the new technology of ion beam microscopy is being developed

Every microscope requires a high brightness, reliable, stable source of illumination in order to function, and both the quality and the quantity of the illumination provided will determine, and ultimately limit, the performance of the instrument. Each type of microscope will have its own type of illuminating source. For a high-performance scanning electron or ion microscope, the most desirable property of the beam source is that the source must have a high brightness.

The CD-SEM has been the tool of choice for the imaging and metrology of semiconductor devices for the past three decades but now, with critical dimensions at the nanometer scale, electron beam instruments can no longer deliver adequate performance. A scanning microscope using a He+ ion beam offers superior resolution and depth of field, and provides enhanced imaging contrast. Device metrology performed using ion beam imaging produces data which is comparable to or better than that from a conventional CD-SEM although there are significant differences in the experimental conditions required and in the details of image formation. The charging generated by a He+ beam, and the sample damage that it can cause, require care in operation but are not major problems.

Single-wall carbon nanotubes (SWNT) were grown to micron lengths by laser-annealing nanoparticulate soot containing short (∼50 nm long) nanotube “seeds.” The “seeded” nanoparticulate soot was produced by restricting the time spent by an ablation plume inside an 800 °C oven following laser vaporization of a C–Ni–Co target. The soot collected from the laser vaporization apparatus was placed inside graphite crucibles under argon, and heated by a CO2 laser. In situ pyrometry was used to estimate the sample temperature. Length distributions of SWNT bundles in the unannealed and annealed samples were measured by transmission electron microscopy and field emission scanning electron microscopy. Annealing treatments exceeding 1600 °C produced no increase in nanotube length, while lower temperatures in the 1000–1300 °C range were optimal for growth. These experiments indicate that SWNT grow by the conversion of condensed phase nanomaterial during annealing, a similar mechanism to that proposed for growth during normal laser–vaporization production.

Although Scanning Electron Microscopes (SEM) have improved greatly over the last decade the techniques usually employed to measure their performance have not changed significantly in half a century. In particular, describing the imaging performance of an SEM by a single number - its 'resolution' - provides no useful information about its real world imaging capabilities nor about any of the factors that might limit that usefulness of the SEM for tasks such as metrology. The Contrast Transfer Function (CTF) discussed here analyses the way in which the SEM processes signal components of different spatial frequencies. The resultant plot provides information on the noise limited spatial resolution limit, predicts how this will vary with noise level, and provides a powerful general diagnostic capability. This type of measurement, which has become standard practice for transmission electron microscopes, can be performed using the public domain software package IMAGE-J, is rapid, and requires only a specimen offering a broad and flat Fourier spectrum. The capabilities of this approach are demonstrated by a number of examples.

Recent advances in instrumentation have produced the first commercial examples of what can justifiably be called high-resolution scanning electron microscopes. The key components of such instruments are a cold field emission gun, a small-gap immersion probe-forming lens, and a clean dry-pumped vacuum. The performance of these microscopes is characterized by several major features including a spatial resolution, in secondary electron mode on solid specimens, which can exceed 1 nm on a routine basis; an incident probe current density of the order of 10 6 A/cm 2 ; and the ability to maintain these levels of performance over an accelerating voltage range of from 1 to 30 keV. This combination of high resolution, high probe current, low contamination and flexible electron-optical conditions provides many new opportunities for the application of the SEM to materials science, physics, and the life sciences.

SUMMARY Current scanning electron microscopes, equipped with field emission guns and high-performance immersion lenses, can achieve spatial resolutions of the order of 1 nm in both secondary and backscattered imaging modes over a wide range of operating energies. The generation and interpretation of images with nanometre-scale resolution relies on a detailed knowledge, and application, of electron-solid interactions. This paper develops the practical steps required to produce a high-resolution image, and discusses the principles which govern image interpretation. Attention is focused primarily on materials which are low in atomic number and density, such as biological tissue, but the results apply after appropriate scaling of the physical parameters to most other materials.

Noise is the single most important limiting factor in scanning electron microscopy. Because of the presence of noise, we are forced to operate the SEM to maximize the available beam current and the beam dose (current × time) at the expense of degraded image resolution, increased charging, and more sample damage. Recent developments in high-performance electron guns, aberration correctors, and lenses are all part of an attempt to attain control of the noise while still achieving ever higher levels of resolution. In this chapter, we will examine noise in the SEM, its origin and properties, its measurement, and how the properties of the detectors used for the collection of secondary emission (SE) electrons and backscatter electrons (BSE) signals affect the noise.

Electron-beam-induced deposition (EBID) and etching (EBIE) provides a simple way to fabricate or etch submicron or nanoscale structures of various materials in a direct-write (i.e.nonlithographic) fashion. The growth rate or the etch rate are influenced by many factors such as beam energy, beam current, temperature of the substrate material, pressure of the chamber, and geometry of the gas injector etc. The mechanism of EBID and EBIE involves the interaction of the incident electron beam or emitted electron from the target material. The role of these electrons is still not completely understood although the contribution of low energy secondary electrons (SE) has been assumed to be the dominant contributor of EBID and EBIE based on its overlap with the dissociation cross section. We have studied the growth and etching phenomenon under various biasing conditions to investigate how low voltage biasing of the substrate affects secondary electron trajectories and subsequently modifies electron-beam-induced deposition and etching.SCANNING 29: 000–000, 2007. © 2007 Wiley Periodicals, Inc.

A scanning ion microscope (SIM) is analogous to a scanning electron microscope (SEM) but utilizes a beam of helium ions, with energy of 10 to 25 keV , instead of electrons. The SIM potentially offers several advantages for device critical dimension metrology as compared to the more familiar CD-SEM. These include a high brightness source which is sub-nanometer in size, an enhanced secondary electron yield, restricted beam penetration, and superior image contrast and information content. Possible problems include pervasive positive charging, ion implantation, and a lack of detailed experimental and theoretical knowledge about low energy ion interactions with solids. Comparison of line profiles across structures made by electron induced and ion induced secondary electrons show that there are some significant differences between them which arise from the different modes of interaction in the two cases. As a result the algorithms employed for line width determination will require revision in order to produce data which is consistent with CD-SEM data.

The monoatomic hydride layer on silicon was used as a prototype for resistless electron beam lithography. Arbitrary patterns with linewidths below 60 nm have been achieved. The variation of the linewidth with electron energy, electron dose, and substrate thickness was studied to determine the mechanisms that govern surface hydrogen desorption and subsequent pattern formation. Unlike in resist based lithography, no resolution enhancement was observed with decreasing substrate thickness. The experimental data in combination with Monte Carlo simulations of the backscattered and transmitted electrons suggest that surface hydrogen desorption and pattern formation are not strongly related to the backscattered electrons and the secondary electrons (energies

To examine the practical limits and effects of low voltage operation, studies of electron beam lithography (EBL) in the low (few keV) to ultra-low (E < 500eV) energy range, employing commonly used resists such as PMMA was done, and the results were compared to those from conventional high voltage processing. The direct writing was performed at low energies by our homemade scan generator and a Schottky field emission gun scanning electron microscope (SEM), used in cathode-lens mode for ultra-low voltage operation. The exposure characteristics and sensitivity of the system at these energies have been investigated using an advanced Monte Carlo simulation method. Our modeling of the lithographic process showed a significant increase in resolution and process latitude for thinner resists.

Summary The electron backscattering coefficient of liquid water has been determined for electrons in the energy range 15–30 keV using QuantomixTM capsules. Values of the mean atomic number for water estimated from a fit to the backscatter yield, the mean ionization potential of water and from Monte Carlo simulations, show that the scattering behaviour of water is not anomalous despite the effects of hydrogen bonding. Computations of the electron range, and of the mean depth for backscattering, in water as a function of incident beam energy show that water and vitreous ice are good media for imaging purposes.

In the variable pressure scanning electron microscope (VP-SEM) the incident electrons pass through a gaseous environment and the beam is scattered by these interactions. We show here that the experimental intensity profile of the scattered beam can be described as Gaussian in form to a high level of accuracy. This provides a rapid means of accounting for the effects of beam scatter in imaging and microanalysis because the standard deviation of the Gaussian is a simple function of parameters such as working distance, beam energy, gas type and pressure.

ISMI metrology in collaboration with the University of Tennessee and Oak Ridge National Laboratory has begun investigating applications of high‐energy scanning electron microscope metrology to a semiconductor environment. The initial findings show potential for overlay metrology, non‐visible defect detection and an expanded definition of line edge roughness measurements. While this is a preliminary experiment to estimate the efficacy of high‐energy scanning electron microscopes for overlay metrology, the initial conclusion is that, at a minimum, a high‐energy scanning electron microscope has good potential as a reference measurement system for overlay, defect, and line edge roughness diagnostics.

The performance of the conventional low‐energy CD‐SEM is limited by the aberrations inherent in the probe forming lens. Multi‐pole correctors are now available which can reduce or eliminate these aberrations. An SEM equipped with such a corrector offers higher spatial resolution and more probe current from a given electron source, and other aspects of the optical performance are also improved, but the much higher numerical aperture associated with an aberration corrected lens results in a reduction in imaging depth of field.

Secondary electron spectra have been collected from both pure elements and from compounds examined under conditions approximating those found in a scanning electron microscope. Despite the presence of substantial surface contamination these spectra are found to be reproducible and characteristic of the underlying material. Typically the peak in such spectra is found to be at an energy of about 5 eV, and 50% of the total secondary electron emission falls within the range 0-12 eV. These data may be of value for the design of detectors for scanning microscopy and might have applications for microanalysis.

Because a photomask is typically a block of quartz partially covered a thin metal coating it charges significantly under an electron beam making CD metrology difficult and often imprecise. A solution to this problem can be found by performing the measurement in the presence of a low pressure of gas in a variable pressure scanning electron microscope (VPSEM). The gas is ionized by the emitted secondary electrons so producing both positive and negative ions which drift to the charged surface and neutralize it. This process is self controlling and requires no critical adjustments by the operator. With charging removed metrology can then be performed over a wide range of beam energies using either secondary or backscattered electron signals with excellent precision and accuracy. The presence of the gas atmosphere also eliminates beam induced contamination effects. If a chemically active precursor gas is injected into the system then the electron beam can also be used to edit and repair damaged masks.

Voltage profiles of the source-drain region of a CMOS transistor with 75nm gate architecture taken from an off-the-shelf Intel PIII processor are presented. The sample preparation using a dual beam system is discussed as well as details of the electron optical setup of the microscope. Special attention is given to the analysis of the reconstructed holograms.

It is important to be able to measure the parameters, such as spatial resolution, astigmastism, signal-to-noise ratio, and drift and instability, that characterize the performance of a scanning electron microscope. These quantities can be determined most reliably by a Fourier analysis of digital micrographs from the instrument, recorded under conditions of interest. A program designed to implement all of the necessary steps in an automated manner has been developed as a 'macro' for the popular, and freely available, NIH Image and SCION Image programs.

Conventional scanning electron microscopes are now close to the limit of their performance for tasks such as the metrology of sub-micron design rule devices. In order to overcome these limits we have designed, and are presently testing, a low voltage point source microscope operated with a nanotip field emitter and without any electron optical lenses. The microscope is designed such that can be operated in the transmission mode as well as in a reflection mode. The ultra-sharp field emitter delivers emission currents of several nanoamps at energies less than 100 eV. The magnification of the object wave is achieved by placing the specimen in the divergent electron beam from the nanotip and observing the object wave using a microchannel plate (MCP) at a great distance from the sample. Images obtained that way are out of focus images. As no lenses are present a special procedure for scaling the magnification has been developed. Since electrons from a point source are highly coherent the out of focus images of the sample are interferograms. Electrons diffracted at an edge of the specimen cause Fresnel fringes in the image plane. An electrically charged holey carbon foil acts in the same way on the electrons as the Youngs double slit experiment and results in an interference pattern consisting of parallel fringes. A comparison between the transmission mode and the perfection mode shows great similarities with respect to the magnification and the interference pattern. An electron gun needed in the transmission mode is the most important difference between the two modes of operation. The experimental results at a reflection of 45 degrees are in good agreement with our simulation. Following our simulations a reflection angle of 90 degrees is most promising for easiest image interpretation.

A recent study of secondary electron (SE) spectra in an Auger spectrometer demonstrated unique features indicative of the chemical nature of the tested material. The scanning electron microscope (SEM) naturally generates SEs; therefore, in this paper, we combine the concept of using differential voltage contrast (DVC) with SE spectroscopy to identify the chemical nature of a material. It is demonstrated that this method reveals the uniqueness of electron energy distribution in the conduction band of a solid or, what is the same, the uniqueness of a build-up of the outer electron shell system, and avoids errors due to the changes in the angular distribution or yield of the SE in the SEM. A theory of this new microanalytical method is developed. The experimental limitations of the SEM for this type of study are examined as well.

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

The charging of polymeric resist materials during electron beam irradiation leads to significant problems during imaging and lithography processes. Charging occurs because of charge deposition in the polymer and charge generation/trapping due to formation of electron-hole pairs in the dielectric. The presence of such charge also results in the phenomena of electron beam-induced conductivity (EBIC). Electron beam-induced conductivity data have been obtained for three commercial e-beam resists under a variety of dose rate and temperature conditions. From the observed values of induced conductivity under varying conditions significant information about the generation of electron-hole pair and the transport of charge in the resist can be obtained. Three electron beam resists, EBR900, ZEP7000, and PBS are examined by an external bias method. The difference in resist chemistry is considered to play the role in the initial state EBIC behaviors among three resists even though the way that it affects the behaviors is not clear. A comparison of the power consumption comparison is proposed as a measure to give a preliminary estimate of the carrier concentration and carrier drift velocity differences among the resists. A simple single trap model with constant activation energy is proposed and provides good agreement with experiment.

Conventional scanning electron microscopes are now close to the limit of their performance for tasks such as the metrology of sub-micron design rule devices. In order to overcome these limits we are investigating the use of in-line electron holography for device metrology. This device will use ultralow energy electrons (50-250eV) emitted from a nano-tip electron source. Out of focus holograms of a mesh were simulated and reconstructed in the transmission mode of the microscope whereas in the reflection mode a sample consisting of only two points was used. In both operation modes of the microscope it is possible to change the distance from the point source (crossover of a lens) to the sample and the distance from the sample to the detector plane such that the magnification is kept constant. Series of simulated holograms consisting of only a few points reveal the distances resulting in the easiest interpretable images. When in-line holography is performed using electrons, the beams are deflected by the electric field between point source and sample. Ray tracing of the electrons performed by solving the appropriate Laplace equation can help to determine an optimum geometry for the microscope.

Ultra-low energy (ULV) scanning electron microscopy is performed in the range between 20 eV and 100 eV. By the use of a retarding field cathode lens assembly ULV imaging with a spatial resolution in the nanometer range has been achieved. This performance is close the predicted theoretical value but is limited by astigmatism and signal to noise considerations. The modes of signal formation at ULV are well suited for metrology and this type of operation may offer reduced beam damage and charging artifacts.