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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.

With the semiconductor industry moving into the 65nm technology node, the metrology of the critical dimension (CD) becomes an important part for the industry. Metrology relies not only on the precision, but also on the accuracy of the tools like the high performance CD-SEMs. A major area of concern affecting the accuracy of the high performance CD-SEMs is the magnification calibration. The purpose of the research is to address this area of concern by fabrication of magnification calibration artifact by using direct write electron beam lithography. A calibration artifact has been fabricated in negative resist Hydrogen Silsesquioxane (HSQ) onto a silicon substrate, thereby decreasing the contamination on the substrate. The design of the artifact has been corrected for the proximity effects, giving a 2-D dense grid structure with 100nm pitch. Pitch determination using optical metrology tools and the inbuilt laser interferometer in the electron beam lithography tool is being evaluated for making the artifact traceable to some national standards. Once the traceability is achieved, mass production at low cost using Nanoimprint technology is feasible.

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.

Although electron beams with energies of a few keV can excite fluorescent X-ray production from solids, ion beams of comparable energy cannot do so. The reason for this situation is that it is the velocity of the incident particle, rather than its energy, which determines whether an ionization event can be generated. SCANNING 29: 1–4, 2007. Copyright © 2007 Wiley Periodicals, Inc.

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

Prototype field emission devices have been fabricated in the 300-1000 eV range using vertically aligned carbon nanofibers as the field emitter. The devices are fabricated using a self-aligned process for the extraction gate opening and the focus grid opening is defined lithographically. Field emission tests of the completed devices are carried out in a vacuum chamber with a phosphor anode and show that the emission follows Fowler-Nordheim characteristics. A technique to selectively grow fibers with W in digitally addressable field-emission array (DAFEA) prototype devices is demonstrated by nanoscale electron beam induced deposition (EBID). A non-organometallic precursor, WF/sub 6/, is used to deposited metallic W fibers. Vacuum electrical testing revels that electrons are successfully extracted from the W nanofiber tip and have been used to draw lines in PMMA coated glass substrates in the DEAL lithography testbed. This growth technique can be used to repair DAFEA emitters thus providing a means to produce a reliable massive parallel e-beam write head.

It is important to be able to quantify the imaging performance of CD-SEMs for such purposes as verifying the specification, rechecking after a routine maintenance, or for tool matching. To perform tests such as these it is necessary to have both appropriate software for image analysis and suitable test samples. A package of 2-D Fourier transform and analysis software, designed as a plug-in for the shareware IMAGE-Java program, has been developed and is freely available on line. The requirement for a reproducible and well characterized sample has been met by using direct-write electron beam lithography to fabricate suitable Fresnel zone plate structures.

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.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

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.

Lithographic processes for printing device structures on integrated circuits (ICs) are the fundamental technology behind Moore's law. Next-generation techniques like maskless lithography or ML2 have the advantage that the long, tedious and expensive process of fabricating a unique mask for the manufactured chip is not necessary. However, there are some rather daunting prblems with establishing ML2 as a viable commercial technology. The data rate necessary for ML2 to be competitive in manufacturing is not feasible with technology in the near future. There is also doubt that the competing technologies for the writing mechanisms and corresponding photoresist (or analogous medium) will be able to accurately produce the desired patterns necessary to produce multi-layer semiconductor devices. In this work, we model the maskless printing system from a signal processing point of view, utilizing image processing algorithms and concepts to study the effects of various real-world constraints and their implications for a ML2 system. The ML2 elements are discrete devices, and it is doubtful that their motion can be controlled to the level where a one-for-one element to exposed pixel relationship is allowable. Some level of sub-element resolution can be achieved with gray scale levels, but with the highly integrated manufacturing practices required to achieve massive parallelism, the most effective elements will be simple on-ofrf switches that fire a fixed level of energy at the target medium. Consequently gray-scale level devidces are likely not an option. Another problem with highly integrated manufacturing methods is device uniformity. Consequently, we analyze the redundant scanning array concept (RSA) conceived by Berglund et al. which can defeat many of these problems. We determine some basic equations governing its application and we focus on applying the technique to an array of low-energy electron emitters. Using the results of Monte Carlo simulations on electron beam profiles, we determine an empirical "impulse response" for each emitter and thus determine how each emission manifests itself in the final printed lithographic pattern. We apply methods to determine the best printable image for a variety of RSA geometries, including different levels of redundancy and achieved printer element spacing. We use concepts of total printing error to help quantify the printing quality. Through simulation, we report the effects of dead or missing elements. We also present some error analysis to account for non-ideal array positioning. Ultimately, we believe that printing quality should be the grounds for determining the necessary data rates to support competitive manufacturing with ML2 devices.

The purpose of this paper is to define standard methods for effective and efficient image-based dimensional metrology for microlithography applications in the manufacture of integrated circuits. This paper represents a consensual view of the co-authors, not necessarily in total agreement across all subjects, but in complete agreement on the fundamentals of dimensional metrology in this application. Fundamental expectations in the conventional comparison-based metrology of width are reviewed, with its reliance on calibration and standards, and how it is different from metrology of pitch and image placement. We discuss the wealth of a priori information in an image of a feature on a mask or a wafer. We define the estimates of deviations from these expectations and their applications to effective detection and identification of the measurement errors attributable to the measurement procedure or the metrology tool, as well as to the sample and the process o fits manufacture. Although many individuals and organizations already use such efficient methods, industry-wide standard methods do not exist today. This group of professionals expects that, by placing de facto standard meth-odologies into public domain, we can help reduce waste and risks inherent in a "spontaneous" technology build-out, thereby enabling a seamless proliferation of these methods by equipment vendors and users of dimensional metrology. Progress in this key technology, with the new dimensional metrology capabilities enabled, leads to improved perform-ance and yield of IC products, as well as increased automation and manufacturing efficiency, ensuring the long-term health of our industry.

Phase defects in extreme UV lithography masks made from Mo/Si multilayer thin films can be removed by heating the metal multilayer to produce a localized phase transition. The experimental situation has been simulated using a Monte Carlo method to determine the deposition of energy from the incident electrons, and the resultant elevation of temperature has been found by solving the thermal diffusion equation. The effects of operating parameters such as beam energy, beam current, and beam spot size have been investigated. It is shown that the effect of surface radiation cooling is negligible, and that only a steady state solution needs to be considered.

Electron-beam-stimulated etching has been investigated as a clean, alternative method for nanoscale selective processing. Primarily fluorine-based precursors have been used to etch a variety of technologically relevant materials. Empirical data reveals that with decreasing the electron beam energy increases the material removal rate, however the effective beam width increases. Both of these observations are consistent with the fact that cross-sections for electron-gas scattering increases with decresaing beam energy. Monte Carlo models of the electron-gas and electron-solid interactions have been performed to better udnerstand the fundamentals of the process. Finally, specific application to soft transmission electron microscopy sample preparation is made.

Quantitative X-ray microanalysis requires the use of many fundamental constants related to the interaction of the electron beam with the sample. The current state of our knowledge of such constants in the particular areas of electron stopping power, X-ray ionization cross-sections, X-ray fluorescence yield, and the electron backscattering yield, is examined. It is found that, in every case, the quality and quantity of data available is poor, and that there are major gaps remaining to be filled.

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.

We need only to consider our own bodies as an example to realize the complexity of biological material. Our body is three-dimensional and composed primarily of light elements, most of which are organized into a mixture of periodic and aperiodic structures. These structures range from simple molecules and macromolecules to complex heteropolymers, all bathed in an aqueous solution of ions and electrolytes. We are thermodynamically unstable, live at ambient temperatures and pressures, and are sensitive to ionizing radiation.

Chapter 9 presented the procedures for performing quantitative electron probe x-ray microanalysis for the casef an ideal specimen. The ideal specimen surface is flat and highly polished to reduce surface roughness to a negligible level so that electron and x-ray interactions are unaffected by geometric effects. Such a highly polished surface has a short-range surface topography (sampled at distances less than 1 μm) that is reduced to an amplitude of a few nanometers and the long-range topography (sampled at distances greater than 100 μm) that is reduced to 100 nm or less. These ideal specimens satisfy three “zeroth” assumptions that underlie the conventional EPMA technique: 1. The only reason that the x-ray intensities measured on the unknown differ from those measured on the standards is that the compositions of specimen and standard are different. Specifically, no other factors such as surface roughness, size, shape, and thickness, which can be generally grouped together as “geometric” factors, act to affect the intensities measured on the unknown. 2. The specimen is homogeneous over the full extent of the interaction volume excited by the primary electron beam and sampled by the primary and secondary x-rays. Because x-rays of different excitation energies are generated with different distributions within the interaction volume, it is critical that the specimen has a uniform composition over the full region. If a thin surface layer of different composition than the underlying bulk material is present, this discontinuity is not properly considered in the conventional matrix correction analysis procedure. 3. The specimen is stable under the electron beam. That is, the interaction volume is not modified through loss of one or more atomic or molecular species by the electron beam over the time period necessary to collect the x-ray spectrum (EDS) or peak intensities (WDS). Biological and polymer specimens are likely to alter composition under electron bombardment.

This chapter outlines a variety of sample preparation procedures for imaging and x-ray analysis of hard materials in the SEM. Several special and relatively new techniques, such as the use of focused ion beams for preparation of cross sections of various materials, are also discussed.

From the basic description in Chapter 4, the SEM image formation process can be summarized as a geometric mapping of information collected when the beam is sequentially addressed to an x–y pattern of specific locations on the specimen. When we are interested in studying the fine-scale details of a specimen, we must understand the factors that influence SEM image resolution. We can define the limit of resolution as the minimum spacing at which two features of the specimen can be recognized as distinct and separate. Such a definition may seem straightforward, but actually applying it to a real situation becomes complicated because we must consider issues beyond the obvious problem of adjusting the beam diameter to the scale of the features of interest. The visibility of a feature must be established before we can consider any issues concerning the spatial scale. For a feature to be visible above the surrounding general background we must first satisfy the conditions contained within the threshold equation (4.26). For a specified beam current, pixel dwell time, and detector efficiency, the threshold equation defines the threshold contrast, the minimum level of contrast (C = ΔS/S max) that the feature must produce relative to the background to be visible in an image presented to the viewer with appropriate image processing.

Obtaining a low-magnification (

This chapter outlines a variety of sample preparation procedures for performing scanning electron microscopy and x-ray microanalysis of polymer materials. Typical specimen preparation methods will be described and shown in a range of applications that are encountered every day in academic and industrial laboratories. The reader new to the study of polymer materials is directed to Chapter 12 of the Enhancements section on the accompanying CD, which provides background material for this chapter. The topics found on the CD are an introduction to polymer materials, E12.1, and polymer morphology, E12.2, and a description of some typical processes used to produce materials from polymers, E12.3. The book by Sawyer and Grubb (1996) is comprehensive, providing details of specimen preparation methods, dozens of practical examples, and references that describe both the structure and the microscopy of polymers.

Low-temperature specimen preparation is not to be considered solely in the context of hydrated biological systems, although much of what will be discussed here will be directed toward these types of samples. Low temperatures are an essential prerequiste for studying naturally frozen materials such as snow and ice and frozen foods such as ice cream (Fig. 14.1). The technology is central to the preparation of aqueous systems such as paints, suspensions, emulsions, solutions, soils, clays, muds, and cements; of any nonaqueous liquid systems such as oils and organic liquids; and even of gases, vapors, and volatile materials. In addition, as has been shown in Chapter 12, low temperatures may play an important part in the preparation of plastics, polymers, and elastomers. The common physical parameter of these diverse samples is that they all can be solidified, provided the temperature is below their melting point. Once solidified they can then be further manipulated for subsequent examination and analysis in electron beam instruments.

As discussed in Chapters 5 and 6, the x rays emitted from a specimen bombarded with the finely focused electron beam of the scanning electron microscope (SEM) or electron-probe microanalyzer (EPMA) can be used to identify which elements are present (qualitative analysis). With the proper experimental setup and data-reduction procedures, the measured x rays can also be used to quantitatively analyze chemical composition with an accuracy and precision approaching 1%. This chapter provides an overview of the basic principles and techniques used for determining chemical composition, on the micrometer scale, with the SEM and EPMA. Our intention is to provide the conceptual basis for an understanding of the x-ray microanalytical data-reduction procedures that today are almost always incorporated into black-box computer-based, integrated analysis systems with which the analyst interacts as a user. As a user, the analyst depends on the knowledge and skill of programmers to have devised an accurate, robust analytical procedure from the diverse approaches available in the literature. Despite the apparent disconnection which has arisen between the analyst as user and the underlying physics as incorporated into the algorithms of the software, it is nevertheless extremely important to grasp the underlying physical principles to become a sophisticated analyst rather than a mere user.

The specimen can be thought of as an electrical junction into which flows the beam current i B. The phenomena of backscattering of the beam electrons and secondary electron emission represent currents flowing out of the junction, i BSE and i SE, respectively. For a copper target with an incident beam energy of 20 keV, η is approximately 0.3 and δ is approximately 0.1, which accounts for 0.4, or 40%, of the beam current. The remaining beam current must flow from the specimen to ground to avoid the accumulation of charge in the junction (Thevenin’s current theorem). The balance of the currents is then given by $$ \eqalign{ & \sum {{i_{in}}} = \sum {{i_{out}}} \cr & {\rm{ }}{i_B} = {i_{BSE}} + {i_{SE}} + {i_{SC}}, \cr} $$ (15.1) where i SC is the specimen (or absorbed) current. For the example of copper, i SC = 0.6i B. Thus, even with a conducting specimen such as a metal, an electrical connection must be established to conduct this substantial current from the specimen to ground (typically the specimen stage is wellgrounded). Because all materials (except superconductors) have the property of electrical resistivity ρ, the specimen has a resistance R ( R = ρ l / A, where l is the length of the specimen and A is the cross section). The passage of the specimen current i SC through this resistance will cause a potential drop across the specimen, V = i SC R. For a metal, ρ is typically of the order of 10-6 ohm-cm, so that a specimen 1 cm thick with a crosssectional area of 1 cm2 will have a resistance of 10-6 ohm, and a beam current of 1 nA (10-9 A) will cause a negligible potential of about 10-15 V to develop across the specimen.

The electron beam generates x-ray photons in the beam–specimen interaction volume beneath the specimen surface. X-ray photons emerging from the specimen have energies specific to the elements in the specimen; these are the characteristic x-rays that provide the SEM’s analytical capabilities (see Fig. 6.1). Other photons have no relationship to specimen elements and constitute the continuum background of the spectrum. The x-rays we analyze in the SEM usually have energies between 0.1and 20 keV. Our task in this chapter is to understand the physical basis for the features in an x-ray spectrum like that shown in Fig. 6.1.

The CD‐SEM, which has been the major tool for critical dimension metrology for the last twenty years, now faces severe challenges to its utility and predominance. The problems that must be solved are outlined, and the possible scenarios for progress are described.