Material contrast in SEM: Fermi energy and work function effects

Cazaux, J.

doi:10.1016/j.ultramic.2009.12.002

Cited by 54 publications

(34 citation statements)

References 48 publications

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“…As less beam damage is observed we utilize the increased applicable electron dose for electron spectroscopy. Here we record either spectra of SE to obtain "work function / electron affinity contrast" [4,5], or spectra of BSE. The DELTA-SEM facilitates ESI in a similar way to energy loss imaging and spectroscopy in TEM.…”

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confidence: 99%

DELTA - A Novel Ultra-Low Voltage SEM for Electron Spectroscopic Imaging

et al. 2018

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In the last few years, low-voltage TEM [1] was instrumental for changing paradigms of imaging using low energy electrons. For very thin and highly conductive samples low-voltage TEM is clearly advantageous, but one faces increasing ionization and thus increased beam damage for less conductive samples [2]. This conundrum can be overcome by further reducing electron energy and using SEM detection mechanisms instead of TEM or STEM.Based on the DELTA-technology [3] we demonstrate here the possibility of conventional SE and BSE imaging as well as electron spectroscopic imaging (SEM-ESI) at electron landing energies down to 50 eV, well below typical beam damaging energies. Such ultra-low landing energies require aberration correction and the development of new filter and detector technologies if high resolution SEM-ESI needs to be achieved. A novel SEM prototype combining all these technologies has now been developed in the framework of our DELTA-project. The correction of spherical and chromatic aberrations allows even for electrons at ultra-low energies high resolution imaging (better than 1nm at 50 eV). As less beam damage is observed we utilize the increased applicable electron dose for electron spectroscopy. Here we record either spectra of SE to obtain "work function / electron affinity contrast" [4,5], or spectra of BSE. The DELTA-SEM facilitates ESI in a similar way to energy loss imaging and spectroscopy in TEM. Fig. 1 shows the current DELTA-SEM prototype with its complex electron optics made possible by the Delta-shaped beam splitter and the electrostatic electron mirror. This SEM allows energy-filtered imaging (Fig. 2) using an electrostatic energy filter combined with a scintillator electron detector (DELTADetector ® design). Electrons of different energy range contribute selectively to the final image when the electric field in the DELTA-detector is varied. Fig. 3 shows an example of imaging and SE spectroscopy of semiconducting organic materials. Their SE intensity, compared to the gold substrate, and their ESI spectra correlate with the relative conductivity of the materials.Even more interesting than spectral imaging with SEs is the use of BSEs. While SE signals are higher than BSE signals at conventional landing energies, BSE gains on SE at very low energies. Fig. 4 shows the typical intensity profiles for BSE and SE of Al at 100 eV and 500 eV landing energies. Thus, at lower energies the BSE signal can be studied in detail: The zero-loss peak as the signal of immediate backscattering is trivial, whereas the spectrum at low energy loss can be interpreted as multiple elasticinelastic scattering. For Al the excitation of the surface plasmon can be identified (cf. Fig. 4).At present we work on the deconvolution of the energy spread function of the DELTA-SEM [5] and use landing energies down to 50 eV for spectral imaging of organic materials. Model simulations and experiments on the bulk heterojunction of organic solar cells [6] indicate the possibility to distinguish different materials and to utilize S...

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confidence: 99%

DELTA - A Novel Ultra-Low Voltage SEM for Electron Spectroscopic Imaging

et al. 2018

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“…It seems doubtful that these effects are of decisive importance, although they undoubtedly make their own contribution to the mechanism of the formation of potential contrast in the SEM. Calculations and experiments confirm that contamination actually increases the work function of SEs in a Si crystal; i.e., it decrease the signal, but sur face oxidation reduces the work function, thereby increasing the SE signal [13,14].…”

Section: Introductionmentioning

confidence: 85%

Image contrast of impurity regions of semiconductor crystals in scanning electron microscopy

Рау

Tagachenkov

2013

Bull. Russ. Acad. Sci. Phys.

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“…Enhanced dopant contrast using a through-the-lens system at a low extraction voltage was reported and attributed to the different angular distributions of SEs emitted from different doping regions. 6,7 In addition, efforts for quantitative analysis include energy-filtered SE imaging 8,9 and Monte Carlo simulations. 10,11 However, limited studies have been done for heterostructures, 12,13 in spite of their importance for device applications including photovoltaics, light-emitting diodes (LEDs), and high electron mobility transistors.…”

Section: Secondary Electron Dopant Contrast Imaging Of Compound Semicmentioning

confidence: 99%

Secondary electron dopant contrast imaging of compound semiconductor junctions

Chung

Myers-Ward

Nyakiti

et al. 2011

Journal of Applied Physics

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Secondary electron imaging combined with immersion lens and through-the-lens detection has been used to analyze various semiconductor junctions. Dopant contrast imaging was applied for multi-doped 4H-SiC, growth-interrupted n þ /p and n/n þ homoepitaxial interfaces, and an AlGaAs/ GaAs p-n junction light-emitting diode structure. Dopant contrast was explained by the local variation in secondary electron escape energies resulting from the built-in potential difference. The effect of varying electron affinity on contrast for the heterostructures is also discussed. The contrast profile of the n-doped AlGaAs compared reasonably well to the simulated valence bandedge energy using a previously determined efficiency of dopant ionization.

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Material contrast in SEM: Fermi energy and work function effects

Cited by 54 publications

References 48 publications

DELTA - A Novel Ultra-Low Voltage SEM for Electron Spectroscopic Imaging

DELTA - A Novel Ultra-Low Voltage SEM for Electron Spectroscopic Imaging

Image contrast of impurity regions of semiconductor crystals in scanning electron microscopy

Secondary electron dopant contrast imaging of compound semiconductor junctions

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