Monte Carlo simulations of the ion-cascade process in the ESEM

1996 ◽  
Vol 54 ◽  
pp. 834-835
Author(s):  
B.L. Thiel ◽  
I.C. Bache ◽  
A.L. Fletcher ◽  
P. Meredith ◽  
A.M. Donald
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Cascade Process ◽  
Secondary Electrons ◽  
Monte Carlo Calculations ◽  
Steady State Kinetic ◽  
Electron Cascade ◽  
State Kinetic ◽  
Primary Electrons ◽  
Environmental Sem

Our Monte Carlo simulations and experimental measurements show the Townsend Gas Capacitor (TGC) model to be highly inappropriate for describing the electron cascade process in the Environmental SEM (ESEM). Previous workers have described the signal collected by the Gaseous Secondary Electron Detector (GSED) as having contributions from secondary as well as backscattered and primary electrons, all being amplified by gas cascade. Although these models are qualitatively correct, they require a more sophisticated description of Townsend’s First Ionisation Coefficient, α. Figure 1 illustrates the short-comings of the TGC models when compared to experimentally obtained amplification curves. (Details of the amplification measurements made with various imaging gases will be given elsewhere, along with specifics of the Monte Carlo Calculations.)The major flaw in applying the TGC model to the ESEM stems from the assumption that the secondary electrons and their environmental daughters reach a steady-state kinetic energy distribution en-route to the detector.

Effects of Space Charge on ESEM Gas Amplification

1997 ◽  
Vol 3 (S2) ◽  
pp. 609-610 ◽  
Author(s):  
B.L. Thiel ◽  
M.R. Hussein-Ismail ◽  
A.M. Donald
Keyword(s):  
Electric Field ◽  
Electrostatic Field ◽  
Secondary Electron ◽  
Sample Surface ◽  
Cascade Process ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Space Charges ◽  
Cascade Amplification ◽  
Environmental Sem

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.

scholarly journals Estimating Step Heights from Top-Down SEM Images

2019 ◽  
Vol 25 (4) ◽  
pp. 903-911 ◽  
Author(s):  
Kerim Tugrul Arat ◽  
Jens Bolten ◽  
Aernout Christiaan Zonnevylle ◽  
Pieter Kruit ◽  
Cornelis Wouter Hagen
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Semiconductor Industry ◽  
Step Edge ◽  
Step Height ◽  
Top Down ◽  
Sem Images ◽  
Force Microscopy ◽  
Atomic Force ◽  
Primary Electrons

AbstractScanning electron microscopy (SEM) is one of the most common inspection methods in the semiconductor industry and in research labs. To extract the height of structures using SEM images, various techniques have been used, such as tilting a sample, or modifying the SEM tool with extra sources and/or detectors. However, none of these techniques focused on extraction of height information directly from top-down images. In this work, using Monte Carlo simulations, we studied the relation between step height and the emission of secondary electrons (SEs) resulting from exposure with primary electrons at different energies. It is found that part of the SE signal, when scanning over a step edge, is determined by the step height rather than the geometry of the step edge. We present a way to quantify this, arriving at a method to determine the height of structures from top-down SEM images. The method is demonstrated on three different samples using two different SEM tools, and atomic force microscopy is used to measure the step height of the samples. The results obtained are in qualitative agreement with the results from the Monte Carlo simulations.

Quantum-trajectory Monte Carlo method for study of electron–crystal interaction in STEM

2015 ◽  
Vol 17 (27) ◽  
pp. 17628-17637 ◽  
Author(s):  
Z. Ruan ◽  
R. G. Zeng ◽  
Y. Ming ◽  
M. Zhang ◽  
B. Da ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Electron Scattering ◽  
Secondary Electron ◽  
Quantum Trajectory ◽  
Cascade Process ◽  
Electron Cascade ◽  
Electron Crystal

A quantum trajectory Monte Carlo method is developed to simulate electron scattering and secondary electron cascade process in crystalline specimen.

Measurements of the range of secondary electrons in low-Z materials

1984 ◽  
Vol 42 ◽  
pp. 356-357
Author(s):  
A. Muray ◽  
M. Isaacson ◽  
E. Kirkland
Keyword(s):  
Monte Carlo ◽  
Sample Surface ◽  
Mean Free Path ◽  
Simple Analytical Model ◽  
Si Substrate ◽  
Secondary Electrons ◽  
Monte Carlo Calculations ◽  
Escape Depth ◽  
Small Probe ◽  
Pattern Size

Previously, calculations of the resolution of SEM secondary electron images due to the escape depth of these electrons utilized Monte-Carlo calculations to simulate the “edge brightness effects” seen in high resolution magnification images obtained with small probe sizes (e.g.,). Similar Monte-Carlo calculations have been made to try to deduce the energy dissipation profiles in PMMA due to secondary electrons. We are trying to develop a simple analytical model which might allow us to get a better feel for the salient features with which the secondary electrons limit the pattern size in microfabrication and spatial resolution in the SEM.For our initial measurements, we have fabricated the structure shown in figure 1. The thickness of both the PMMA and Si substrate are less than one mean free path for inelastic scattering (of 100 keV electrons) thick. A 10 Å diameter beam of convergence angle of 15 mrad is incident normal to the sample surface.

Monte Carlo Simulations of Crystalline TATB

1995 ◽  
Vol 418 ◽  
Author(s):  
Thomas D. Sewell
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Physical Properties ◽  
Structural Parameters ◽  
Lattice Energy ◽  
Atomistic Model ◽  
Lattice Constants ◽  
Preliminary Results ◽  
Monte Carlo Calculations ◽  
The Individual

AbstractWe are performing constant-NPT Monte Carlo calculations of the physical properties of crystalline TATB. Our approach is to employ an atomistic model in which the individual molecules are treated as semi-rigid entities. Each molecule is allowed to undergo rigid translations and rotations, and in some cases limited intramolecular flexibility is conferred on the molecules via exocyclic torsions. Additionally, the size and shape of the simulation box is allowed to vary. Our immediate interest is in computing the density, lattice energy, lattice constants, and other structural parameters as a function of temperature. Preliminary results indicate that simulations involving only two molecules suffice for calculations of the energy and density, but that more molecules are required to compute the lattice constants. Intramolecular flexibility is important, particularly at higher temperatures.

scholarly journals Monte Carlo Calculations Applied to SLOWPOKE Full-Reactor Analysis

2012 ◽  
Vol 1 (2) ◽  
pp. 43-46 ◽  
Author(s):  
T.S. Nguyen ◽  
G.B. Wilkin ◽  
J.E. Atfield
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Third Party ◽  
Fuel Burnup ◽  
Mcnp Code ◽  
Monte Carlo Calculations ◽  
Transport Calculation ◽  
Enriched Uranium ◽  
Good Agreement

Monte Carlo simulations are applied to the full-reactor analysis of the SLOWPOKE design. The temperature reactivity feedback calculated by using the MCNP code for either the high enriched uranium (HEU) or low enriched uranium (LEU) core is in good agreement with the experimental data, with a k-eff bias of +3.3 mk for a HEU core and +6 mk for a LEU core. Two methods that are based on existing third-party codes have been developed for use in core following: 1) MCNP (for the transport calculation) in conjunction with WIMS-AECL (for fuel burnup advancement), and 2) SERPENT (that combines both transport and burnup capabilities). Both methods show very good agreement with the experimental data for core excess reactivity and detailed power distributions versus burnup and reactivity shim.

Low-voltage EDS of magnesium ferrite Dendrites in a FEG-SEM

1996 ◽  
Vol 54 ◽  
pp. 478-479
Author(s):  
Matthew T. Johnson ◽  
Ian M. Anderson ◽  
Jim Bentley ◽  
C. Barry Carter
Keyword(s):  
Monte Carlo ◽  
Quantitative Analysis ◽  
Monte Carlo Simulations ◽  
Cross Section ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Magnesium Ferrite ◽  
X Ray ◽  
Interaction Volume ◽  
Ferrite Spinel

Energy-dispersive X-ray spectrometry (EDS) performed at low (≤ 5 kV) accelerating voltages in the SEM has the potential for providing quantitative microanalytical information with a spatial resolution of ∼100 nm. In the present work, EDS analyses were performed on magnesium ferrite spinel [(MgxFe1−x)Fe2O4] dendrites embedded in a MgO matrix, as shown in Fig. 1. spatial resolution of X-ray microanalysis at conventional accelerating voltages is insufficient for the quantitative analysis of these dendrites, which have widths of the order of a few hundred nanometers, without deconvolution of contributions from the MgO matrix. However, Monte Carlo simulations indicate that the interaction volume for MgFe2O4 is ∼150 nm at 3 kV accelerating voltage and therefore sufficient to analyze the dendrites without matrix contributions.Single-crystal {001}-oriented MgO was reacted with hematite (Fe2O3) powder for 6 h at 1450°C in air and furnace cooled. The specimen was then cleaved to expose a clean cross-section suitable for microanalysis.

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