Quantitative secondary electron energy filtering in a scanning electron microscope and its applications

Kazemian, P.; Mentink, S.A.M.; Rodenburg, Cornelia; Humphreys, C. J.

doi:10.1016/j.ultramic.2006.06.003

Cited by 57 publications

(55 citation statements)

References 20 publications

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“…The crossovers of plots of I SE were observed between Cu and Cr at 420 eV, and Cu and Fe at 630 eV. Considering SE energy distribution N(E, E p ) and the detector acceptance, I SE is generally written as [4] .(1) In this study, we adopt standard SE spectra N ref (E, E p ) given by Goto et al [7,8] to substitute N(E, E p ). By introducing an approximation that G has weak θ dependence, SE intensity with standard spectra I ref can be calculated as, ,…”

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“…detector acceptance G (E, θ). In most cases, however, G(E, θ) is not known clearly except few results obtained by simulation [4]. Thus, if we develop a simple and easy method to estimate G(E, θ), it is very useful to analyze SE image contrast.…”

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Estimation of Energy Acceptance of SE Detectors in Scanning Electron Microscopy

Kumagai¹,

Sekiguchi²

2013

Microsc Microanal

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In modern scanning electron microscopy (SEM), spectroscopic signal detection has been attracting increasing attention, because it has potential to emphasize the image contrast of our interest by selecting signal electron energy [1]. According this point, we have studied secondary electron (SE) image formation in aspect of SE energy [2,3]. Since SE detector set in actual SEM collects a part of electrons emitted from specimen with energy E and emission angle θ, we have to understand possible combinations of E and θ to be detected, i.e. detector acceptance G (E, θ). In most cases, however, G(E, θ) is not known clearly except few results obtained by simulation [4]. Thus, if we develop a simple and easy method to estimate G(E, θ), it is very useful to analyze SE image contrast. As a first step to do this, we have evaluated the energy acceptance of an annular in-lens SE detector set in so-called "Gemini column." We fabricated a specimen consists of several metal layers, and studied their SE image contrast comparing with standard SE spectrum to deduce energy acceptance of the SE detector.A model specimen was fabricated by depositing layers of Cr, Fe, Cu, Ag, Au (200 nm thick each) and Pt (300 nm thick) onto p-Si substrate. After the cross section polishing with Ar + ion beam, the specimen was put in SEM chamber as immediately as possible. We used an UHV-SEM equipped with field emission electron gun (Omicron Nanotechnologies, Germany), for SE observation. The SE detector to be evaluated was an annular in-lens SE detector located inside of the electron gun column [5,6]. The vacuum of SEM chamber was kept lower than 10 -7 Pa, which enables us to observe specimens without contamination.The experimental results are shown in Fig. 1. A series of SE images of the model specimen is shown in Fig. 1(a), which is taken at primary electron energy E p from 200 eV to 5 keV at constant beam current. Working distance, brightness and contrast were fixed. Figure 1(b) shows the plots of SE image intensity I SE extracted from Fig. 1(a). Intensity order is shown in Fig. 1(c). The crossovers of plots of I SE were observed between Cu and Cr at 420 eV, and Cu and Fe at 630 eV. Considering SE energy distribution N(E, E p ) and the detector acceptance, I SE is generally written as [4] .(1) In this study, we adopt standard SE spectra N ref (E, E p ) given by Goto et al [7,8] to substitute N(E, E p ). By introducing an approximation that G has weak θ dependence, SE intensity with standard spectra I ref can be calculated as, ,where E L and E U is lower and upper limit of integration as shown in Fig 2(a). Thus, by finding E L and E U , with which I ref reproduces intensity relationship in the plots of I SE , we can estimate the energy acceptance of SE detector.We found that with E L = 14 eV and E U = 30 eV, I ref reproduces not only the order of the intensities of I SE , 1196

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Estimation of Energy Acceptance of SE Detectors in Scanning Electron Microscopy

Kumagai¹,

Sekiguchi²

2013

Microsc Microanal

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“…As an example of this effort, this paper will describe the use of energy filtering of the secondary electron (SE) signal using an immersion lens SEM. Applications of this technique include visualizing dopant contrast [2] and improving the sensitivity of passive voltage contrast, Figure 1, as well as the potential for increasing the contrast between key materials of interest by exploiting the different SE energy distributions from different materials (see for example, [3] for experimental measurements of SE spectra).To better understand the complete imaging process Monte-Carlo simulations have been undertaken that include a 3D modeling of the SEM column, including the electromagnetic fields, so that the trajectories of the emitted SE and back-scattered electrons (BSE) from the beam-sample interaction can be accurately followed back into the SEM detection system [4]. Once such a model is in place virtual experiments can be carried to determine the optimum beam and detector conditions for a particular sample type.…”

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Low-Energy Secondary Electron Filtering with Immersion Lens SEM

Young

Bosch²,

Unčovský

et al. 2009

Microsc Microanal

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The scanning electron microscope (SEM) offers a rich array of different electron-beam induced signals with which to create the final micrograph. So in parallel with efforts to improve the beam resolution [1], it is also important to find ways to make the best use of these induced signals to bring out the desired information about the sample. As an example of this effort, this paper will describe the use of energy filtering of the secondary electron (SE) signal using an immersion lens SEM. Applications of this technique include visualizing dopant contrast [2] and improving the sensitivity of passive voltage contrast, Figure 1, as well as the potential for increasing the contrast between key materials of interest by exploiting the different SE energy distributions from different materials (see for example, [3] for experimental measurements of SE spectra).To better understand the complete imaging process Monte-Carlo simulations have been undertaken that include a 3D modeling of the SEM column, including the electromagnetic fields, so that the trajectories of the emitted SE and back-scattered electrons (BSE) from the beam-sample interaction can be accurately followed back into the SEM detection system [4]. Once such a model is in place virtual experiments can be carried to determine the optimum beam and detector conditions for a particular sample type. Such simulations can investigate the signal based on particular SE energies or trajectory angles from the sample, and also to simulate the actual image expected.This modeling has been applied to the energy filtering of the SE signal. Low-pass, high-pass and band-pass filtering can be carried out depending upon the beam, sample and detector conditions. In each case, the magnetic field of the immersion lens SEM combined with an in-lens detector play the crucial role in enabling the filtering. Figure 2 shows modeled results for a low pass filter where with in-lens detector parameter M=-2V the electrons up to ~5 eV are transmitted, while a value of M=-16V allows a wider range (~16 eV). The modeling showed that by adjustment of M it was possible to go from zero to full transmission of the SE range, with Fig.2 just being representative examples. Figure 1 shows experimental results for a high pass filter on a voltage contrast sampleby adjusting the starting point of the range from 1 eV to 2 eV it was possible to change which of the contacts appear bright or dark in the image.

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Electron Probe Techniques

Walker¹

2014

Handbook of Spectroscopy

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Excitation of surfaces with electrons is accompanied by the release and detection of secondary electrons or photons and only a limited number of techniques use detection of neutrals or ions, for example, electron-stimulated desorption. To the first group, detecting secondary electrons, belongs Auger electron spectroscopy (AES) that is the workhorse technique for characterizing the elemental constituents of a surface. Another popular technique is electron energy loss spectroscopy (EELS) that can provide information regarding the electronic and optical dielectric properties of a surface. As for photon excitation, energy dispersive X-ray spectroscopy (EDXS) is in common use, although the volume to which it is sensitive is typically a micron or more below the surface and so not as surface sensitive as many techniques. More recently, developed techniques such as scanning tunneling spectroscopy can provide details of the electronic structure at very high spatial resolution. Certain techniques can use a spin-polarized source beam or detect spin-polarized emission. These techniques often find uses in the analysis of magnetic samples.Individual techniques are presented in alphanumerical order.Total (or target) current spectroscopy (TCS) is similar to DAPS, but it is a very low-energy technique (0-15 eV) and all the secondary electrons originate from the valence band. Auger Electron Spectroscopy18.2.1 ApplicationsEMS is used to determine electron momenta and energies within solids and (for the low-energy primary electrons) to shed light on the role of exchange coupling and spin-orbit coupling in the dynamic interaction of low-energy electrons in the valence band of solids. Electron Probe Microanalysis18.5.1 ApplicationsEPMA is typically used in metallurgy, microelectronics, and corrosion science. Electron-Stimulated Desorption18.6.1

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Quantitative secondary electron energy filtering in a scanning electron microscope and its applications

Cited by 57 publications

References 20 publications

Estimation of Energy Acceptance of SE Detectors in Scanning Electron Microscopy

Estimation of Energy Acceptance of SE Detectors in Scanning Electron Microscopy

Low-Energy Secondary Electron Filtering with Immersion Lens SEM

Electron Probe Techniques

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