Tactful Use of Low Angle Electrons in Scanning Electron Microscope

The charge effect is one of the important reasons for the unexpected scanning electron microscope (SEM) images, such as distortion, drift, bright spots and bright lines. Secondary electrons imaging is beneficial for the topographical contrast, but easily affected by charge effect, while backscattered electrons imaging behaves better to avoid charge effect with shortcoming of mainly presenting material contrast. In this paper, Apreo 2S is used to explore the optimal combinations of the use cases, detectors and work distance to regulate the detected electrons. Considering about the secondary electrons, Optiplan use case combined with T2 detector is applied and the work distance is decreased to collect low angle secondary electrons, thus leading to weakened charge effect. From the point of backscattered electrons, at low magnification, Optiplan use case combined with ETD detector can be used to obtain high-resolution images with good topographic contrast. At high magnification the best quality image is acquired under Immersion use case combined with T1 detector at short work distance.