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Monte Carlo electron trajectory simulations have been adapted to run on a parallel supercomputer. The increased speed achieved by parallelization of the Monte Carlo code results in the ability to model small probability events easily. The techniques for parallelization of the algorithm are presented here along with examples of applications. The applications include the calculation of the X-ray spatial resolution in thin films, backscattered electron imaging of voids in Al metallizations and X-ray production in thin-film specimens.

The spatial resolution of X-ray microanalysis in thin foils is defined in terms of the incident electron beam diameter and the average beam broadening. The beam diameter is defined as the full width tenth maximum of a Gaussian intensity distribution. The spatial resolution is calculated by a convolution of the beam diameter and the average beam broadening. This definition of the spatial resolution can be related simply to experimental measurements of composition profiles across interphase interfaces. Monte Carlo calculations using a high-speed parallel supercomputer show good agreement with this definition of the spatial resolution and calculations based on this definition. The agreement is good over a range of specimen thicknesses and atomic number, but is poor when excessive beam tailing distorts the assumed Gaussian electron intensity distributions. Beam tailing occurs in low-Z materials because of fast secondary electrons and in high-Z materials because of plural scattering.

Calculations of Mott elastic scattering cross section of electrons for most elements of the periodic table up to element number 94 in the energy range 20 eV–20 keV have been performed. The Dirac equation transformed to a first‐order differential equation was solved numerically. The influence of the choice of atomic potential on the scattering factor was studied in comparison to a simple muffin‐tin approximation of the atomic potential in solids. The application of calculated cross sections to a conventional Monte Carlo model for electron scattering using modified Bethe equation is described and results concerning the electron backscattering for different atomic potentials are compared.

This case study describes a success in technology transfer out of Sandia National Laboratories that resulted in commercialization supporting both the laboratories' national security mission and economic development. This case exemplifies how the process of technology innovation stretches from national legislation to laboratory management to entrepreneurs, and then out into the community where the technology must be developed and commercialized if innovation is to occur. Two things emerged from the research for this case study that have implications for technology transfer and commercialization from other national laboratories and may also be relevant to technology commercialization out of other federal laboratories and universities. The first is the very clear theme that partnerships were critical to the ultimate successful commercialization of the technology--partnerships between public and private research groups as well as between business development groups. The second involves identifiable factors that played a role in moving the process forward to successful commercialization. All of the factors, with two significant exceptions, focused on technology and business development directly related to creating research and business partnerships. The two exceptions, a technology with significant market applications, and entrepreneurs willing and able to take the risks and accomplish the hard work of technology innovation, weremore » initiating requirements for the process.« less

The committee regards Sandia's Microelectronics and Photonics Program as a vital and strategic resource for the nation. The Microsystems (MEMS) and Chem Lab programs were assessed as unique and best-in-class for the development of significant application areas. They contribute directly to the Sandia mission and impact the development of new commercial areas. The continued development and integration of Radiation hard silicon integrated circuits, micromechanical systems, sensors, and optical communications is essential to the national security mission. The quality of the programs is excellent to outstanding overall. MEMS and Chem Lab activities are examples of outstanding programs. The committee was pleased to see the relationship of the microelectronics development programs to applications in the mission. In a future review the committee would like to see Sandia's research programs and a vision for connectivity to potential national security needs. (This review may be based on analysis and assumptions about the strategic needs of the nation.) In summary, the Microelectronics and Photonics capability affords Sandia the opportunity to deliver exceptional service in the national interest across broad technology areas. The presentations were excellent and well integrated. We received ample pre-reading materials, expectations were well set and the documents were high quality. The committee was provided an agenda with sufficient time among us and some selected one-on-one time with the researchers. The composition of the committee held representation from industry, universities and government. Committee contributions were well balanced and worked as a team. However, the committee was disappointed that no member of Sandia executive management was able to be present for the readout and final debriefing. (A late, higher priority conflict developed.) The members of the EST Program and the committee put substantial effort into the review but a written report like this one is not a substitute for direct feedback in helping SNL leadership assess the value of these programs.

Nonconducting samples invariably need some sort of treatment before they can be examined and analyzed under optimal conditions in electron-beam instruments that rely on an emitted signal to provide information. The treatment is necessary to eliminate or reduce the electric charge that builds up rapidly in a nonconducting specimen when it is scanned by a beam of high-energy electrons. Figs. 4.63a–c and 4.64a–c show examples of pronounced and minor charging as observed in the SEM. In addition to charging phenomena, which result in image distortion, the primary beam also causes thermal and radiation damage, which can lead to a significant loss of material from the specimen. In many situations the specimen may acquire a sufficiently high charge to decelerate the primary beam, and the specimen may even ultimately act as an electron mirror (see Fig. 4.62).

The versatility of scanning electron microscopy and of x-ray micro-analysis is derived in large measure from the rich variety of interactions that the beam electrons undergo in a specimen. These interactions can reveal information on the specimen’s composition, topog­raphy, crystallography, electrical potential, local magnetic field, and other properties. The electron—specimen interactions can be divided into two classes.

Specimen preparation for SEM and EPMA is in many ways still as much of an art as a science. This chapter outlines a variety of procedures used to prepare inorganic materials for SEM and EPMA, and supplemented by laboratory exercises (Lyman et al., 1991), will provide the micros- copist and analyst with the starting point for most specimen-preparation problems for inorganic materials. This chapter specifically addresses the preparation of metals; ceramic and geological materials; sands, soils, and clays; electronic devices and packages; semiconductor materials; and particles and fibers. In addition, specimen preparation for both microstructural and microchemical characterization are discussed.

This chapter will consider the formation and interpretation of SEM images. One of the most surprising aspects of scanning electron microscopy is the apparent ease with which SEM images of three- dimensional objects can be interpreted by any observer, including young children with no prior knowledge of the instrument. This aspect of the SEM is often taken for granted, and yet it is one of the most important reasons for the great utility and wide acceptance of the instrument. SEM images are routinely presented in textbooks and popular scientific articles with little or no mention of the type of microscopy employed in preparing the image or of the complex way in which the image was constructed. It can safely be assumed that the reader will automatically perceive the true nature of the specimen without any instruction on the origin of the image. For this to be true, the SEM imaging process must in some way mimic the natural experience of human observers in visualizing the world around them. Such a situation is somewhat surprising in view of the unusual way in which the image is formed, which seems to differ greatly from normal human experience with images formed by light and viewed by the eye. In the SEM, high-energy electrons are focused into a fine beam, which is scanned across the surface of the specimen.

An overview of the basic principles and techniques used to determine chemical composition, on the micrometer scale, with the SEM and EPMA was presented in Chapter 8. We outlined the approach to quantitation, the need for matrix corrections, and the physical origins of the matrix effects. The x-ray production process and the use of φ(ρz) curves to describe x-ray production were introduced. Finally, we discussed the three major matrix effects, atomic number (Z), absorption (A), and fluorescence (F) and showed, on a conceptual basis, how they are calculated. This chapter presents the more detailed theory and equations which can be used to determine the three major matrix corrections for quantitative analysis of flat polished specimens. The two commonly used correction schemes, the ZAF and φ (ρz) methods, will be described separately although the two schemes are, in many ways, closely related.

As discussed in Chapter 6, qualitative analysis is based on the ability of a spectrometer system to measure characteristic line energies and relate those energies to the presence of specific elements. This process is relatively straightforward if.

The distribution of copper in aluminum thin films is examined with respect to how the copper can influence electromigration behavior. Al-Cu thin films annealed in the single phase region, to just below the solvustemperature, have 0-phase Al2Cu precipitates at the aluminum grain boundaries. The grain boundaries between precipitates are depleted in copper. Al-Cu thin films heat treated at lower temperatures, within thetwo phase region, also have 0-phase precipitates at the grain boundaries but the aluminum grain boundariescontinuously become enriched in copper, perhaps due to the formation of a thin coating of 0-phase at the grain boundary. Here, it is proposed that electromigration behavior of aluminum is improved by addingcopper because the 0-phase precipitates may hinder aluminum diffusion along the grain boundaries. It was also found that resistivity of Al-Cu thin films decrease during accelerated electromigration testing prior to failure. Pure Al films did not exhibit this behavior. The decrease in resistivity is attributed to theredistribution of copper from the aluminum grain matrix to the 0-phase precipitates growing at the grain boundaries thereby reducing the number of defects in the microstructure.

The purpose of this laboratory is to prepare samples of metals, ceramics, and geological and microelectronic specimens for examination and analysis in the transmission electron microscope (TEM) and analytical electron microscope (AEM). Material forms include bulk, thin films, and particles. To achieve suitable electron transparency, and meet various requirements for electron diffraction and microanalysis, the thin region of the specimen must be

The SE signal collection efficiency of the conventional E-T detector is limited by the asymmetry of the collection field resulting from the detector position and from the surface potential of rough specimens. Specimen biasing should be routinely applied to optimize signal collection for a given specimen and imaging situation. The voltage supply must be of extreme stability which can be provided by dry batteries such as 45-V farm batteries. Two batteries connected in series provide for an easy change of polarity. There is no rule to predict the effect of specimen biasing on signal collection. The bias modifies only the accelerating voltage of the probe and the collection field of the collector. Thus, SE components will still be collected. (Note: Only a grounded specimen grid which shields the specimen from all other biased surfaces allows establishment of a positive field between the grid and the specimen for the absorption of SE-I+II as described in experiments of Section 12.3.)

This laboratory is designed to give you a feel for the amount of care and time that must go into any measurement involving trace elements. The trace element concentration range is often defined as concentrations below 0.5 wt% for most elements and below 1 wt% for the light elements. The example used here is the measurement of small amounts of phosphorus (P) in FeNi alloys. More details on these techniques may be found in SEMXM, Chapters 7 and 8.

This laboratory demonstrates: (1) the two major types of contrast in SEM images, known as atomic number contrast and topographic contrast, (2) the factors affecting the quality of the image and how they ultimately limit the image resolution, and (3) the effects of electronic signal processing on the visibility of features in the image. More details and references may be found in SEMXM, Chapters 3 and 4.

This laboratory explores some of the principal phenomena observed at low beam energies. Images prepared at “conventional” beam energies, e.g., 15 keV and above, are compared with low-beam-energy images, e.g., 5 keV and below. The possibility of examining uncoated insulators by taking advantage of enhanced emission of secondary electrons at low energy is also examined.

This laboratory demonstrates: (1) election gun saturation and alignment; (2) the measurement of beam current, beam size, and beam convergence; (3) the concept of electron gun brightness; and (4) the effects of these parameters on depth-of-field and resolution. More details and references can be found in SEMXM, Chapter 2.

The purpose of this laboratory is to prepare samples of metallic, ceramic, polymeric, and biological specimens for examination and analysis in the SEM. The organization is such that under each type of material sample preparations are discussed for surface topography (e.g., fracture surface), microstructural analysis (e.g., phase morphology), and x-ray microanalysis. Special procedures for semiconductor devices, polymers, and biological samples are also considered. The objective is to provide a brief outline and enough general references to enable the reader to produce all of the specimens used in this workbook. The outlined methods should not be considered comprehensive, however, and the reader is strongly urged to consult the references listed. For further discussion, see SEMXM, Chapters 9–12.

There are two main objectives of this laboratory: (1) to study the differences observed in EDS and WDS x-ray spectra obtained from particles and rough surfaces as compared to bulk targets, and (2) to test the comparative accuracies of (a) conventional quantitative analysis methods, (b) the peak-to-background method, and (c) the particle ZAF method when applied to particles. More details may be found in SEMXM, Chapter 7.

The purpose of this laboratory is to demonstrate quantitative x-ray microanalysis as practiced on an electron column instrument equipped with an energy-dispersive spectrometer (EDS) and a computer-based multichannel analyzer (MCA). Although the difficult calculations of quantitative x-ray microanalysis are performed automatically in the MCA, the analyst must be aware of the responsibility to select operating conditions that optimize accuracy and precision. As with the WDS, increasing the accelerating voltage will improve the x-ray count rate and peak-to-background ratio and therefore the precision and sensitivity, respectively. However, increasing the beam voltage will also increase the absorption of lower-energy x-ray lines such as aluminum. More details may be found in SEMXM, Chapters 3, 5, and 7.

This first laboratory is designed to acquaint the beginning SEM operator with the steps for taking a micrograph. The steps are described without reference to a particular instrument. Please consult the manufacturer’s operation manual or an instructor before proceeding.

The objective of this laboratory session is to introduce the principal method of obtaining electron diffraction information from regions smaller than the limit of conventional selected area diffraction (SAD), about 0.5 μm in diameter. The technique is termed convergent beam electron diffraction (CBED). We will see that CBED patterns can be used to generate much more information than can be obtained from SAD patterns.

This laboratory is concerned with use of the digital computer to aid in the acquisition, display, and interpretation of various digital images obtained with the scanning electron microscope, e.g., secondary electron, backscattered electron, x-ray, etc. We will be concerned with all aspects of SEM imaging from the generation of the signal, when the electron beam interacts with the specimen surface, to the perception and interpretation of this information in the mind of the observer. Indeed, we will view all steps involved as an information channel which has certain imperfections and nonlinearities that must be examined. This aspect of microscopy is a rapidly developing area and consequently it is difficult to condense all of the important concepts into a single laboratory exercise. Nevertheless, the topics covered in the following experiments should give a sense of the power of this new tool for the microscopist. For more details see ASEMXM, Chapter 5, and references [1–4] at the end of the laboratory.

The light element regime traditionally defined as the elements Be through F (Z = 4 to 9) has posed many difficulties for the analyst. Poor detectability due to low count rates caused by insufficient beam current at low voltage and small spot sizes has made microanalysis very difficult Adequate matrix correction procedures are just being developed and quantification is difficult without very good standards. Contamination of the sample during analysis often makes the results questionable. These problems are slowly but surely being corrected in today’s modern electron microprobes. New WDS crystals and recent ultra-thin-window (UTW) have contributed to improved detectability; modern electron columns have much better low-voltage performance; and finally, today’s SEMs and microprobes are designed with anticontamination devices. However, with all these improvements, the measurement and subsequent quantification of light elements is far from routine. This laboratory will illustrate operational aspects of light element analysis background measurements, peak overlap problems, and quantitation techniques. More details may be found in SEMXM, Chapter 8.

This laboratory demonstrates the operation of a wavelength-dispersive x-ray spectrometer (WDS) fitted to a scanning electron microscope (SEM) or electron probe microanalyzer (EPMA). The WDS has important advantages over the energy-dispersive spectrometer (EDS) in terms of the peak-to-background ratio, improved elemental sensitivity, and better energy resolution of characteristic x-ray peaks to avoid peak overlaps. Comparisons of the major characteristics of the WDS and EDS detectors will be made. More detailed background information may be found in SEMXM, Chapters 5–8.

The aim of this laboratory is to introduce the principles and practice of quantitative x-ray microanalysis in the AEM using an energy-dispersive spectrometer (EDS). Since it is important to recognize the limitations of the technique as well as the relative ease of quantification, some effects due to spurious x-rays in the EDS spectrum will be identified in the first experiment. More details may be found in PAEM, Chapters 4 and 5.

The modern energy-dispersive x-ray spectrometer (EDS) coupled with a computer-based multichannel analyzer (MCA) provides a powerful analytical facility in the SEM lab. The purpose of this laboratory is to introduce the student to the wide range of analytical capabilities of the EDS/MCA system and to illustrate the basic appearance and characteristics of electron-excited x-ray spectra. Procedures for both qualitative and quantitative analysis will be examined. More detail on these subjects can be found in SEMXM, Chapters 6, 7, and 8.

The aim of this laboratory session is to introduce the scanning transmission electron microscope (STEM), used in this and other analytical electron microscopy (AEM) laboratory sessions, and to demonstrate the various imaging modes available. The experimental control that the operator has over the information in the image will be emphasized. More details may be obtained in PAEM, Chapter 3 and D. B. Williams, Practical Analytical Electron Microscopy in Materials Science, Philips Electron Optics, Mahwah, New Jersey, 1984.

The purpose of this laboratory is to demonstrate quantitative x-ray microanalysis as practiced on an electron column instrument equipped with a wavelength-dispersive spectrometer (WDS) and appropriate detector electronics. Although the calculation of composition is performed automatically in the computer, the analyst must be aware of the responsibility to select operating conditions that optimize accuracy and precision. The experimental measurements will show that increasing the beam voltage will increase x-ray count rate and the peak-to-background ratio and therefore the precision and sensitivity. But, at the same time, higher voltages dramatically increase the absorption of lower-energy (longer-wavelength) x-ray lines. More details may be found in SEMXM, Chapters 3, 5, and 7.

Experiment 23.1: Recording Dot Maps. (a) Adjustment of CRT recording dot. Various WDS iron x-ray images obtained with different settings of the CRT dot brightness reveal the subjective nature of the analog dot mapping procedure. A dim recording dot (Figure A23.1b) provides a very weak image even where the iron concentration is high and no information at all where the iron concentration is low. The optimum dot brightness image (Figure A23.1c) carries more information but the image is weak and noisy in the iron-poor regions because the total number of x-rays recorded in the 100-sec scan is inadequate to provide the necessary image statistics. Note that both characteristic and bremsstrahlung x-rays of the same energy are recorded since no background correction is applied in the analog WDS scan. The highest intensity dot produces an image (Figure A23.1d) in which the x-ray pulse locations are most easily evident, but the image is not satisfactory because blooming of the dot image causes a loss of resolution and contrast, obscuring fine scale details.

The purpose of this laboratory is to understand voltage contrast (VC) and electron beam induced contrast (EBIC) as important tools for the examination of semiconductor materials which aid in the production of microcircuit devices. More details may be found in ASEMXM, Chapter 2.

Experiment 8.1: E-T Detector Collection Efficiency. The solid angle and efficiency of a specific E-T detector for direct collection of BSEs is: (a) Area, A, of scintillator (cm2) = 1.5 cm2. (b) Distance, r, from specimen to scintillator (cm) = 4 cm. (c) Solid angle, Ω = A/r2 = 1.5/16 = 0.094 steradians. (e) For a specimen set normal to the beam (0° tilt), approximate take-off angle = 45°.

Secondary electron (SE) images of various specimens will be taken at different magnifications and accelerating voltages and will be compared to the BSE image. High-resolution SE-I image features will be demonstrated and the SE-I imaging conditions defined. This technique has been developed since the publication of SEMXM and so additional explanatory material is given in Section 11.1. More details can be found in references [1–3].

The objective is to acquaint the microscopist with the crystallographic and contrast effects of electron channeling. The initial emphasis is on channeling experiments which can be performed on any conventional scanning electron microscope: large area channeling patterns of single crystals and channeling contrast images to reveal the crystalline microstructure of polycrystalline materials. The optional advanced experiments on covering area electron channeling patterns can only be carried out on an SEM which is equipped with special scanning and/or electron optical modifications. More detail on this topic may be found in ASEMXM, Chapter 3.

The modern energy-dispersive x-ray spectrometer (EDS) coupled with a computer-based multichannel analyzer (MCA) provides a powerful analytical facility in the SEM lab. The purpose of this laboratory is to introduce the student to the basic concepts of energy-dispersive x-ray spectrometry and to examine some of the spectral artifacts inherent in the technique. More details and references can be found in SEMXM, Chapter 5.

The aim of this laboratory session is to demonstrate the use of a magnetic prism electron spectrometer to perform electron energy loss spectrometry (EELS). The main characteristics of the energy loss spectrum will be discussed as well as the effect of instrumental and specimen parameters on the spectrum. Quantitative elemental analysis will be demonstrated and if time permits an example of EELS imaging will be shown. More details can be found in PAEM, Chapters 7 and 8.

The spatial resolution of x-ray microanalysis in a thin foil is determined by the size of the beam-specimen interaction volume. This volume is a combination of the incident electron beam diameter (d) and the beam broadening (b) due to elastic scatter within the specimen. Definitions of spatial resolution have already been proposed on this basis but all present a worst case value for the resolution based on the dimensions of the beam emerging from the exit face of the foil.

SUMMARY A new procedure has been developed to produce thin foils of uranium and its alloys for transmission electron microscopy. The procedure is a two-step electrochemical cleaning-thinning process which produces self-supporting discs. This procedure was used to produce thin foils of the most important alloys of uranium.