Image creation mechanism in beam deceleration method using a semi-in-lens FE-SEM

Abstract number
European Microscopy Congress 2020
Corresponding Email
[email protected]
PST.4 - Spectroscopies in Electron, X-ray and Ion Microscopy
Tatsuro Nagoshi (1), Naoto Kuga (1), Yasuyuki Okano (1), Hidetoshi Nishiyama (1)
1. JEOL Ltd.

Beam Deceleration

Detection System

Scanning Electron Microscope

Abstract text

In a field emission scanning electron microscope (FE-SEM), a beam deceleration (BD) method, in which a negative bias voltage is applied to a sample, is effective for high resolution imaging with an electron beam at a low accelerating voltage [1]. It is however difficult to select secondary electrons and backscattering electrons (SE and BSE) depending on the purpose. In this study, we clarified the relationship between the sample bias voltage and the image by using the BD method.

JSM-7610FPlus (JEOL Ltd.) has a detector with a retractable enhanced plate in the semi-in lens type objective lens (OL) (Fig. 1). The enhanced plate has an aperture (a diameter of 1.5 mm) through which an electron beam passes. SE and BSE accelerated by the sample bias voltage move upward to wind around the optical axis because of a magnetic field of the OL, collide with the enhanced plate, and can be converted to SE (Converted SE). The converted SE can be detected by the detector. SE and BSE travel closer to the optical axis as the sample bias voltage increases. In addition, the SE with lower energy travels closer to the optical axis than the BSE with higher energy. If we want to observe the surface structure of the sample, the bias voltage should be smaller. In this case, most of the SE collide with the enhanced plate and the converted SE can be detected. For topological information, it is useful to detect the BSE with low emission angle and eliminate collision of SE with the enhanced plate by increasing the sample bias voltage.

In this study, we investigated how SEM images are changed by changing the sample bias voltage. The sample is an evaporated gold film prepared by thickly depositing gold to cover a carbon substrate and heating it at a high temperature. The landing energy of the electron beam was 1 keV. Figure 2 shows SEM images of the sample taken at the sample bias voltages of (a) -1 kV, (b) -3 kV, and (c) -5 kV. As shown in the zoomed image of Fig. 2(a), fine gold particles (white spots) on the surface of the film were observed brightly. The result shows that the SE mainly collids with the enhanced plate. The topological information of the gold film as well as the surface structure information such as particles were acquired at -3 kV as shown in Fig. 2(b). At a sample bias voltage of -5 kV, the topological information was mainly obtained as shown in Fig. 2(c). This result shows that BSE detected at a low emission angle mainly contributes to the SEM image.

As described above, it was found that the information of the SEM image depends on the sample bias voltage. In the conference, we will explain the image creation mechanism in the BD method.


[1] Osamu Terasaki et al., Novel Structural Characterisations of Insulating and Electron Beam Sensitive Materials Employing Low Voltage High Resolution Scanning Electron Microscopy, JEOL NEWS, Vol.48, No.1, 21-31 (2013).