Optimization of the SEM Working Conditions: EsB Detector at Low Voltage

Abstract

Material contrast in scanning electron microscopy (SEM) is studied for several kinds of samples with an energy selective backscattered (EsB) electron detector using low voltage. The working conditions are optimized for every specimen and the contrast is quantified, in order to investigate the influence of the most important parameters on the performance: the primary beam voltage, the grid voltage of the EsB detector, and the working distance. Furthermore, strategies to avoid undesirable beam-induced sample damage like shrinkage in organosilicate glass (OSG) thin films or charging in polymer samples are discussed. in a OSG thin film on Si substrate after 3 min. scan with high magnification at Ep ¼ 20 kV. The EsB image (d) shows no shrinkage with Ep ¼ 1 kV.A. Garitagoitia Cid et al./Optimization of the SEM Working Conditions: EsB. Fig. 11. Blend of PS-PMMA with SiO 2 nanoparticles distributed on the surface. InLens images (a) and (c) shows charging and the polymers are not distinguishable. The corresponding EsB images (b) and (d) provide the material contrast between the PS (dark phase) and the matrix of PMMA. The SiO 2 nanoparticles can be clearly distinguished from the organic material.

In-Column Backscattered Electron Microscopy for a Rapid Identification of the Number of Layers in MoS2 Nanosheets: Implications for Electronic and Optoelectronic Devices

“…For MoS 2 , the EsB imaging at V acc = 1 kV produces the layer number-sensitive superior image contrast. The use of low V acc in SEM imaging causes an incident PE–sample interaction to occur on the surface and/or near-surface region of the sample, enabling the acquisition of detailed sample surface information and thereby making it suitable for studies of ultrathin films . Therefore, during the EsB imaging of MoS 2 at V acc = 1 kV, BSEs are produced by the elastic scattering of incident PEs with the nuclei of Mo and S atoms.…”

“…The surface charging effect can be problematic in the SEM imaging of semiconducting or insulating samples at a low V acc because the electrical fields generated by the sample charging easily affect the paths of low-energy SEs, leading to signal distortion and creating noisy and unstable images (InLens SE images of graphene and MoS 2 at V acc = 1 kV in Figure d). However, BSEs have high energy ranging from 50 eV to the incident PE energy . This high energy characteristic of BSE imaging (i.e., EsB imaging) reduces the sensitivity to surface charging effects, enabling the acquisition of less noisy and more stable EsB images.…”

“…The use of low V acc in SEM imaging causes an incident PE−sample interaction to occur on the surface and/or near-surface region of the sample, enabling the acquisition of detailed sample surface information and thereby making it suitable for studies of ultrathin films. 53 Therefore, during the EsB imaging of MoS 2 at V acc = 1 kV, BSEs are produced by the elastic scattering of incident PEs with the nuclei of Mo and S atoms. In general, the yield of BSEs, that is, the ratio between the number of emitted BSEs and that of incident PEs, depends on the atomic number of the sample atoms; the higher the atomic number (or the heavier the atom), the brighter the contrast.…”

“…However, BSEs have high energy ranging from 50 eV to the incident PE energy. 53 This high energy characteristic of BSE imaging (i.e., EsB imaging) reduces the sensitivity to surface charging effects, enabling the acquisition of less noisy and more stable EsB images. Furthermore, the EsB detector's grid voltage can be precisely adjusted to filter out low-energy SEs, ensuring that only high-energy BSEs contribute to the EsB image.…”

Comparative study of image contrast in scanning electron microscope and helium ion microscope

“…To collect SEs and form images, HIM and SEM are equipped with either an Everhart‐Thornley (ET) detector or an annular InLens detector (Griffin, ). To collect the backscattered particles, an energy selective backscattered (EsB) detector (Garitagoitia Cid et al ., ) and a microchannel plate detector (MCP) detector can be used in SEM and HIM, respectively. Compared with SEM, the HIM imaging has several advantages, such as a better lateral resolution, a larger depth of field, better surface sensitivity and material contrast and a unique charging compensation mechanism (Scipioni et al ., ; Hill & Faridur Rahman, ; Kostinski & Yao, ).…”