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Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

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.

Laser vaporization (LV) is a remarkably versatile technique for the catalytically-aided synthesis of nanomaterials, such as single-wall carbon nanotubes (SWNT). SWNT show remarkable promise for future generations of electronics and structural materials, however their application and commercialization has been hampered by a lack of control over the synthesis process, and low production quantities. Time-resolved in situ spectroscopic investigations of the laser-vaporization SWNT-synthesis process are described which are yielding some of the first direction determinations of carbon nanotube growth mechanisms and rates necessary to evaluate strategies for controllable synthesis and large-scale production. Our measurements indicate that SWNT grow over extended annealing times during the LV process by the conversion of condensed phase nanoparticle feedstock. These measurements were extended to grow carbon nanotubes by CO2- laser-annealing heat treatments of carbon and metal nanoparticle mixtures, offering an alternative synthesis approach to vapor- phase methods. These results present opportunities for scaled-up production of nanomaterials compatible with commercial high- power-laser technology.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

Electron-beam tools have been an important part of the semiconductor industry since its beginnings especially in the area of metrology and are a major contributor towards the goals of process control and yield enhancement. However, in order to stay on the Moore's Law curve instrument performance must be improved by a factor of two every two or three years and with the proximity of fundamental physical limits such major improvements in performance become increasingly difficult to obtain. This paper examines the opportunities that exist for continued improvement, and considers what other options are available for tools to replace the CD-SEM and its associates.

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.

We show simulation images of projection microscope, which uses parallel beam to the sample, detecting secondary electrons, photoelectrons and mirror electrons using electrons and UV/X-ray sources as probe beam. The results show we can see image for square and dense line patterns without charging and damage in the objects. This research can be used for quantitative analysis for projection microscope using multi beam source to get comprehensive information of many characteristics of objects as well as topographic information.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

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.

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. The in-line holograms are formed in a point projection microscope using ultra-low energy electrons (50-250eV) emitted from a nano-tip electron source. Holograms in the transmission mode and in the reflection mode of the microscope as well are possible. Since these in-line holograms are equivalent to out of focus micrographs acquired in a transmission electron microscope with a field emission gun we can reconstruct the original wave front by means of Fourier optics. The resolution of the point projection microscope is given by the sharpness of the emitter. We investigate the electric potential of the emitter using off-axis electron holography in a transmission electron microscope and compare the results to simulations obtained by solving the appropriate Laplace equation.

Charging effects on secondary electron (SE) profiles with bias voltage in deep contact holes are investigated. We show first in detail the SE beam profiles for operating conditions such as scanning time, current and landing energy, the brightness of the bottom of the contact hole depends on the charge of SE yield with incident energy. We conclude that we can enhance the contrast of the beam profile by optimizing the applied bias voltage.

Single-wall carbon nanotubes are formed by Nd:YAG laser vaporization of a graphite/(1 at. % Ni, 1 at. % Co) target into flowing argon (500 Torr) within a quartz tube furnace (1000 degree(s)C). Here, this process is investigated for the first time with time-resolved laser-induced luminescence imaging and spectroscopy of Co atoms, C 2 and C 3 molecules, and clusters. These measurements under actual synthesis conditions show that the plume of vaporized material is segregated and confined within a vortex ring which maintains an approximate 1 cm 3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 microsecond(s) ) and cobalt (2 ms). This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs during several seconds of time from a feedstock of mixed nanoparticles in the gas-suspended plume. By adjusting the time spent by the plume within the high- temperature zone using these in situ diagnostics, single- walled nanotubes of controlled length were grown at an estimated rate of 0.2 micrometers /s. Ex situ annealing of short, 100-200 nm-long SWNT seeds collected after limited growth inside the hot oven resulted in continued growth of longer SWNT bundles, supporting the condensed phase conversion mechanism for SWNT growth.

The continued dominance of electron-beam instruments as the tool of choice for metrology is threatened by the requirements demanded for sub-100nm device structures. The key factors required for effective metrology are identified, the limitations of existing instruments are considered, and a new type of microscope tool for metrology which avoids this limitation is proposed.

Laser vaporization (LV) is a remarkably versatile technique for the catalytically-aided synthesis of nanomaterials, such as single-wall carbon nanotubes (SWNT). SWNT show remarkable promise for future generations of electronics and structural materials, however their application and commercialization has been hampered by a lack of control over the synthesis process, and low production quantities. Time-resolved in situ spectroscopic investigations of the laser-vaporization SWNT-synthesis process are described which are yielding some of the first direct determinations of carbon nanotube growth mechanisms and rates necessary to evaluate strategies for controllable synthesis and large-scale production. Our measurements indicate that SWNT grow over extended annealing times during the LV process by the conversion of condensed phase nanoparticulate feedstock. These measurements were extended to grow carbon nanotubes by CO2-laser-annealing heat treatments of carbon and metal nanoparticle mixtures, offering an alternative synthesis approach to vapor-phase methods. These results present opportunities for scaled-up production of nanomaterials compatible with commercial high-power laser technology.Laser vaporization (LV) is a remarkably versatile technique for the catalytically-aided synthesis of nanomaterials, such as single-wall carbon nanotubes (SWNT). SWNT show remarkable promise for future generations of electronics and structural materials, however their application and commercialization has been hampered by a lack of control over the synthesis process, and low production quantities. Time-resolved in situ spectroscopic investigations of the laser-vaporization SWNT-synthesis process are described which are yielding some of the first direct determinations of carbon nanotube growth mechanisms and rates necessary to evaluate strategies for controllable synthesis and large-scale production. Our measurements indicate that SWNT grow over extended annealing times during the LV process by the conversion of condensed phase nanoparticulate feedstock. These measurements were extended to grow carbon nanotubes by CO2-laser-annealing heat treatments of carbon and metal nanoparticle mixtures, offering an alt...

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

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

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

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

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

Electron holography performed in a transmission electron microscope, has been used to measure the width of 90° domain walls in tetragonal BaTiO3, and to determine the magnitude and distribution of the polarization across these walls. The walls are found to be between 15 and 25 A in width. The polarization and its measured variation are in good agreement with other estimates. Fringe splitting has been observed in some holograms and it is suggested that this is due to the presence of charged oxygen vacancies on the walls.

The charging of the workpiece in electron beam direct writing processes has been identified as a problem that disturbs the electron beam and causes pattern displacement error. In this paper the electron beam deflection caused by surface charging is evaluated by the SIMION and MATHEMATICA simulation programs. Isolated charged patterns of different geometry are simulated as electrodes with given potentials in SIMION to calculate the extent of beam deflection, while secondary electron emission yield and beam dosage are assigned in MATHEMATICA programming for determination of surface potential and spatial field, from which the beam deflection is then calculated. The simulation results are in good agreement with each other and they are compared with values available in literature. The initial charge content along with the pattern dimensions chosen in simulation are found to be the major factors that determine the extent of beam deflection. The limitation of SIMION simulation on the beam deflection is also discussed.

Charging effects on beam deflection of incident electrons in electron beam lithography are investigated. We show first in detail how the non-unity yield of electron generation in insulator resists leads to local charging accumulation and affects the beam deflection of incident electrons as charging develops. Then the amounts of beam deflection are identified for various operating and resist dimension conditions, and then we conclude that the beam deflection should be avoided for more accurate manufacturing semiconductor devices by the control of charging effects.

The 1999 International Technology Roadmap for Semiconductors describes the critical measurement challenges for all areas of wafer processing in the Metrology Roadmap. The roadmap indicates that the research and development community must advance microscopy, especially scanning electron microscopy, in the near term and simultaneously develop alternate technology for IC generations with sub 100 nm feature sizes. In this paper, the issues such as loss of depth of focus that are facing CD-SEM are described. In addition, some of key challenges for overlay are briefly mentioned.

The performance of scanning electron beam instruments such as CD-SEMs can be defined in terms of parameters such as the beam probe size, the spatial resolution, and the signal to noise ratio of the image. A knowledge of these quantities is important in verifying the fact that an instrument meets its specification, and subsequently for tracking and optimizing its performance during use. Analytical methods based on the power spectrum (2-D Fourier transform analysis) of images are now beginning to be used for these purposes but care must be exercised to ensure reliable and meaningful results. Two new methods are suggested which can offer more detailed information about the microscope performance while avoiding the pitfalls of the simpler technique. Code implementing these tests, written as a plug-in macro for the well known NIH Image program, is available on-line.

The polarisation of x-ray photons can be determined by measuring the direction of emission of a K-shell photoelectron. Effective exploitation of this effect below 10 keV would allow development of a highly sensitive x-ray polarimeter dedicated in particular to x-ray astronomy observations. Only with the advent of finely segmented gas detectors was it possible to detect polarisation sensitivity based on the photoelectric effect in this energy range. Simulation and measurements at 5.4 and 8.04 keV with a microgap gas counter, using both a polarised and an unpolarised x-ray source, showed that the photoelectron track in a neon-based gas mixture retains the memory of the polarisation of the incoming photons. Possible experiments aimed at galactic/extragalactic sources and solar flares are considered and their sensitivity to these sources is calculated., Comment: 45 pages included 13 figures; (Accepted for publication in : Nuclear Instruments and Methods in Physics Research A)

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

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.

Secondary electron spectra have been obtained from a variety of materials under vacuum conditions similar to those encountered in a conventional scanning electron microscope. Although secondary emission is restricted to the near surface region of a sample, and so would be expected to be affected by the presence of a film of contamination, it is shown that the modifications to the secondary electron spectrum are generally minor in nature and do not make it impossible to associate the spectrum with the underlying material. Secondary electron spectroscopy may provide a method to add a materials classification category to defect review.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Valid Conventions throughout the Book. 1. The History of the Electron Biprism. 2. Principles and Theory of Electron Holography. 3. Optical Characteristics of a Holography Electron Microscope. 4. Practical Electron Holography. 5. Quantitative Electron Holography. 6. The Reconstruction of Off-Axis Electron Holograms. 7. Electron Holography of Electromagnetic Fields. 8. On Recording, Processing and Interpretation of Low Magnification Electron Holograms. 9. High Resolution Off-Axis Electron Holography. 10. Off-Axis Stem Holography. 11. Focus Variation Electron Holography. 12. Applications of Electron Holography. 13. Electron Holography using Diffracted Electron Beams (DBH). 14. Electron Holography at Low Energy. 15. A Plus or Minus Sign in the Fourier Transform? Bibliography. Index.

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.

The scanning electron microscope (SEM) has many advantages for tasks for as metrology and defect review compared to other competitive technologies, but the level of performance required to meet the specifications proposed for the next generation of devices will raise some significant problems that must be overcome. These include theoretical limits on the spatial resolution, practical limits to performance set by the electron-optical characteristics of the SEM, and the dynamic response of the instrument to signal information. Unwanted artifacts of the electron-solid interaction such as charging and radiation damage must also be considered as potential restrictions to performance.

The scanning electron microscope (SEM) represents the most promising tool for metrology, defect review, and for the analysis of ULSI structures, but both fundamental problems such as electron-solid interactions, and practical considerations such as electron-optical constraints, are now setting a limit to performance. This paper examines the directions in which an advanced SEM might be developed to overcome these constraints. The SEM also offers considerable promise as a tool for the high spatial resolution X-ray microanalysis, especially for those situations where a thin cross-section is not practical and first surface analysis is required. The ways in which this capability can be incorporated in an advanced SEM are examined.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005