SEM at Low Beam Voltage

1984 ◽  
Vol 42 ◽  
pp. 440-443
Author(s):  
James Pawley
Keyword(s):  
Low Voltage ◽  
Probe Diameter ◽  
Small Probe ◽  
Beam Voltage ◽  
Practical Constraints

Operation of the SEM with V0 = l-3kV (LVSEM) was early recognized to reduce charging artefacts and increase topographic contrast. This early promise was not pursued because several theoretical and practical considerations made it difficult to produce a small probe diameter (d0) at low voltage. Recently, the necessity of using low V0 to image uncoated semiconductors without damaging them has prompted a re-evaluation of LVSEM. This re-evaluation has taken the form of efforts to eliminate the practical constraints and to alleviate the theoretical ones. In the process, some heretofore neglected theoretical advantages of LVSEM have emerged. These problems and possibilities will now be discussed in more detail.

scholarly journals Low-voltage scanning electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 488-491
Author(s):  
J. B. Pawley ◽  
M. P. Winters
Keyword(s):  
Electron Probe ◽  
Current Flow ◽  
Low Voltage ◽  
Semiconductor Industry ◽  
X Rays ◽  
Probe Diameter ◽  
Small Probe ◽  
Important Improvement ◽  
Voltage Scanning ◽  
Beam Damage

There are two reasons for the renewed interest in using the SEM at beam voltages, Vb, around 1kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage. The second reason postulates that the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in topographic spatial resolution if only a sufficiently small probe diameter can be obtained. We shall treat these two areas separately and then mention some of the strategies that have been adopted to make LVSEM work.Surfaces are very important in the manufacture of modern semiconductor devices and the ability of the electron probe to induce current flow (EBIC), to detect variations in surface voltage, Vs, and to excite characteristic x rays in addition to its ability to image topography in an easily understandable way guaranteed the SEM a major role in programs of semiconductor development and failure analysis. There were two problems, however, charging and beam-induced damage to the specimen.

Low-voltage high-resolution SEM of biological samples

1989 ◽  
Vol 47 ◽  
pp. 72-73
Author(s):  
James B. Pawley
Keyword(s):  
Secondary Electron ◽  
Low Voltage ◽  
Focal Length ◽  
Semiconductor Industry ◽  
Focal Length Lens ◽  
Small Probe ◽  
Beam Voltage ◽  
Recent Developments ◽  
Topographical Feature ◽  
Beam Damage

There are three reasons for the recent upsurge of interest in using the SEM at a beam voltage (Vo) around 1 kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage obtainable at low VoThe second reason derives from the belief that, given instrumentation capable of producing a sufficiently small probe, the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in real topographic spatial resolution.The third reason is that recent developments in instrumentation have shown that by coupling a cold field-emission source with a short focal length lens, it is indeed possible to obtain small probe diameters at low voltage. Although they are considerably larger than probes obtained at higher voltage, they are nonetheless smaller than the smallest topographical feature yet imaged in the secondary electron (SE) mode. (Fig 1)

High resolution at low voltage: A new approach

1989 ◽  
Vol 47 ◽  
pp. 76-77
Author(s):  
Arthur V. Jones
Keyword(s):  
Low Voltage ◽  
Emission Sources ◽  
New Approach ◽  
Design Concepts ◽  
Probe Diameter ◽  
Low Voltage Operation ◽  
Sufficient Intensity ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Immersion Type

With the introduction of field-emission sources and “immersion-type” objective lenses, the resolution obtainable with modern scanning electron microscopes is approaching that obtainable in STEM and TEM-but only with specific types of specimens. Bulk specimens still suffer from the restrictions imposed by internal scattering and the need to be conducting. Advances in coating techniques have largely overcome these problems but for a sizeable body of specimens, the restrictions imposed by coating are unacceptable.For such specimens, low voltage operation, with its low beam penetration and freedom from charging artifacts, is the method of choice.Unfortunately the technical dificulties in producing an electron beam sufficiently small and of sufficient intensity are considerably greater at low beam energies — so much so that a radical reevaluation of convential design concepts is needed.The probe diameter is usually given by

High Power Density Multi-Mosfet-Based Series Resonant Inverter for Induction Heating Applications

2016 ◽  
Vol 7 (1) ◽  
pp. 107 ◽  
Author(s):  
M. Saravanan ◽  
A. Ramesh Babu
Keyword(s):  
Conversion Efficiency ◽  
Induction Heating ◽  
High Frequency ◽  
Low Voltage ◽  
Resonant Inverter ◽  
Power Simulation ◽  
Series Resonant ◽  
Series Resonant Inverter ◽  
State Resistance ◽  
Practical Constraints

Induction heating application uses uniquely high frequency series resonant inverter for achieving high conversion efficiency. The proposed work focus on improving the practical constraints in requiring the cooling arrangements necessary for switching devices used in resonant inverter due to higher switching and conduction losses. By introducing high frequency Multi- MOSFET based series resonant inverter for the application of induction heating with the following merits such as minimum switching and conduction losses using low voltage grade  of automotive MOSFET’s and higher conversion efficiency with high frequency operation. By adding series combination of low voltage ratedMulti MOSFET switches, temperature variation according to the on-state resistance issues can be avoided by sharing the voltage across the switches depends on number switches connected in the bridge circuit without comprising existing system performance parameter such as THD, power factor, output power. Simulation results also presents to verify that the proposed system achieve higher converter efficiency.

scholarly journals Ultra-High Velocity Ratio in Magnetron Injection Guns for Low-Voltage Compact Gyrotrons

Electronics ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 1587
Author(s):  
Dun Lu ◽  
Wenjie Fu ◽  
Xiaotong Guan ◽  
Tongbin Yang ◽  
Chaoyang Zhang ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Space Charge ◽  
High Velocity ◽  
Low Voltage ◽  
Simulation Optimization ◽  
Velocity Ratio ◽  
Space Charge Effects ◽  
Charge Effects ◽  
Beam Voltage ◽  
Interaction Efficiency

Low-voltage compact gyrotron is under development at the University of Electronic Science and Technology of China (UESTC) for industrial applications. Due to the low operating voltage, the relativistic factor is weak, and interaction efficiency could not be high. Therefore, a magnetron-injection gun (MIG) with an extremely high-velocity ratio α (around 2.5) is selected to improve the interaction efficiency. As beam voltage drops, space charge effects become more and more obvious, thus a more detailed analysis of velocity-ratio α is significant to perform low-voltage gyrotrons, including beam voltage, beam current, modulating voltage, depression voltage, cathode magnetic field, and magnetic depression ratio. Theoretical analysis and simulation optimization are adopted to demonstrate the feasibility of an ultra-high velocity ratio, which considers the space charge effects. Based on theoretical analysis, an electron gun with a transverse to longitudinal velocity ratio 2.55 and velocity spread 9.3% is designed through simulation optimization. The working voltage and current are 10 kV and 0.46 A with cathode emission density 1 A/cm2 for a 75 GHz hundreds of watts’ output power gyrotron.

Micro Auger analysis using a field emission source

1978 ◽  
Vol 36 (1) ◽  
pp. 516-517
Author(s):  
P.E. Bovey ◽  
I.R.M. Wardell ◽  
P.M. Williams
Keyword(s):  
Field Emission ◽  
High Current Density ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Emission Source ◽  
Auger Analysis ◽  
Sem Image ◽  
Probe Diameter ◽  
Small Probe ◽  
Experimental Vessel

The use of a high brightness field emission source holds clear promise in the area of micro Auger analysis of surfaces. The high current density and small probe diameter obtainable from the field emitter (30 n A into 300Ǻ, for example) offer the possibility of recording Auger spectra from areas less than 300Ǻ, as previously demonstrated . Furthermore, the ultra high vacuum technology necessary for a reliable field emission source, is wholly compatible with the type of vacuum experimental vessel customary in surface analysis applications.We describe here results obtained with an HB50A Auger Microprobe in which an environmental cell, introduced on a bellows movement into the experimental vessel, permits heating to 800°C in an atmosphere of 0.1 torr of gas. The sample under study was pure polycrystalline iron.This was reacted with methane at 750°C in situ for 12 hours. The carbon resulting from cracked methane, dissolved in the iron to such an extent that, on cooling to 600˚C, precipitation occured. Figure 1 shows an SEM image of a characteristic precipitate, recorded with the sample held at 600˚C at a magnification of 2,000 X.

State of the development of multipole correctors for a probe-forming system and a high-resolution 200kV TEM

1995 ◽  
Vol 53 ◽  
pp. 596-597
Author(s):  
M. Haider ◽  
J. Zach
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Limiting Factors ◽  
Objective Lens ◽  
Probe Diameter ◽  
Physical Limit ◽  
Low Energies ◽  
Routine Basis ◽  
Electron Microscopes

The development of modern high resolution electron microscopes has shown the emergence of new modern microscopes which are easy to operate and, more importantly, with which one can attain high resolution on a routine basis. However, the physical limit set by the inherent aberrations of electron lenses could not be overcome by simply optimising the geometry of the pole pieces. The only direct way to get rid of the aberrations of the round lenses is to use a corrector with which the resolution limiting aberrations can be compensated.For the observation of uncoated biological surfaces we started a project to develop a Low Voltage Scanning Electron Microscope (LVSEM). The main problem with using low energies is to design electron optics with which one can achieve high resolution in the range of 1 nm at energies of 1 keV and below. Hence, the two main axial aberrations of such a probe forming system: the chromatic and the spherical aberration Cc and C3, respectively, have to be considered as the limiting factors of the probe diameter. Therefore, the compensation of these two aberrations is the best choice as one does not want to run into other limitations if, for example, the geometry of the objective lens is scaled down in order to obtain small aberration coefficients.

Low-voltage SEM update

1986 ◽  
Vol 44 ◽  
pp. 654-657
Author(s):  
J.B. Pawley ◽  
W.R. Scala
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Low Energy ◽  
Special Issue ◽  
Significant Progress ◽  
Beam Voltage ◽  
Signal Collection ◽  
Upper Stage ◽  
Micro Lens ◽  
Made In

The advantages of operating an SEM at low beam voltage (Vo) are now widely recognized and significant progress has been made in overcoming the practical limitations to high resolution operation with Vo = 1-2 kV. A Symposium on Low Voltage SEM (LVSEM) was held at the 1984 EMSA meeting and several of the papers presented there were later collected for a special issue of the Journal of Microscopy. The purpose of this contribution is to outline three developments in instrumentation for LVSEM that have recently appeared. These include: 1) The new pole-pieces on the upper stage of the ISI DS-130c which permit it to produce very low aberration coefficients with low energy beams. 2) The replacement of the final lens of the Hitachi S-800, field emission SEM with an immersion lens to create the new S-900; 3) The development of the micro-lens for mounting in the chamber on a conventional’ SEM to produce both low aberration coefficients and a favorable geometry for signal collection.

The limitations of quantitative EDS analysis at low voltage

1996 ◽  
Vol 54 ◽  
pp. 476-477
Author(s):  
C. E. Nockolds
Keyword(s):  
Quantitative Analysis ◽  
Low Voltage ◽  
Low Energy ◽  
X Rays ◽  
Considerable Effort ◽  
Beam Voltage ◽  
Absorption Correction ◽  
Transition Series ◽  
Very High ◽  
High Absorption

There are several reasons for carrying out x-ray microanalysis at low beam energies. In conventional electron probe microanalysis with wavelength dispersive spectrometers (WDS) there has been a considerable effort in recent years to improve the accuracy of quantitative analysis of the “light” elements B, C, N and O. The shapes of the low energy K x-rays and the L x-rays of the first transition series metals are also being studied with the aim of determining the chemical environments of the atoms in a sample. In most materials these soft x-rays suffer from very high absorption, and reducing the depth of the interaction volume by lowering the beam voltage to 5kV or below leads to a much reduced absorption correction. In scanning electron microscopy the introduction of thin window energy dispersive spectrometers (EDS) has made it possible to look at low energy x-rays and here the main interest in working at low voltages is in the improvement of the resolution of analysis.In this paper the limitations of SEM/EDS low voltage analysis will be examined, and possible solutions to some of the problems explored. It will be assumed that the aims are to achieve quantitative analysis at the best possible spatial resolution.

Characterization of the Interface in a TiC Reinforced Ti-6%A1-4%V Composite Using Monte Carlo Simulations and FEGSEM.

1997 ◽  
Vol 3 (S2) ◽  
pp. 527-528
Author(s):  
Raynald Gauvin ◽  
Priti Wanjara ◽  
Robin A.L. Drew ◽  
Steve Yue
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Metallic Matrix ◽  
Weight Ratio ◽  
Specimen Preparation ◽  
Ion Milling ◽  
Small Probe ◽  
Low Energy Electrons

Metal matrix composite (MMC) materials are promising materials because of their higher specific mechanical properties (e.g. strength-to-weight ratio) relative to conventional metallic alloys. However, during the processing of these materials, the development of an interfacial reaction zone between the reinforcing material (generally a ceramic) and the metallic matrix may occur, which typically degrades the mechanical properties of these materials if not controlled. Since these interfaces are generally quite small (from 5 to 500 nm), Transmission Electron Microscopy (TEM) is the technique of choice for characterization because of its outstanding spatial resolution. However, specimen preparation for TEM (e.g. ion milling) is quite difficult for MMC materials, due to the combination of two completely different material types, specifically a hard and brittle reinforcement phase incorporated in a relatively soft metallic matrix. Also, since there is only a small amount of the material which is transparent to electrons after specimen preparation, TEM as a materials characterization technique suffers from a lack of statistical robustness, which is a serious drawback.To characterize materials with a spatial resolution close to that of TEM, low voltage field emission scanning electron microscopy is an option because of the small interaction volume of low energy electrons, as well as the small probe size of these microscopes (typically < 5 nm).

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