Optimizing electron channeling contrast imaging condition in scanning electron microscope

Abstract

The electron channeling contrast imaging (ECCI) is a technique that makes use of the influence of back scattered electrons (BSE) by the relative orientation of crystalline lattice and incident electron beam [1]. The ECCI in scanning electron microscope (SEM) is especially useful to image the crystallographic defects such as dislocations, stacking faults and twin boundaries [2]. In this contribution the amount of channeling contrast in the total BSE signal is quantified and its dependence on different working conditions is explored. An example of the ECCI on an epitaxial GaN thin film is shown in Figure 1. The sample is investigated using ZEISS GeminiSEM 500 FE‐SEM with a PIN‐diode BSE detector under the objective lens. By adjusting the strength of the scanning coil it is possible to move the pivot point of scanning electron down to the surface of the sample, forming the selected area channeling pattern (SACP) [1]. The intensity variation of BSE signal can be extracted by the line profile across the Kikuchi line, shown as the red dotted line in the figure. The relative variation of BSE signal in SACP with respect to average signal can thus be used as a quantification of channeling contrast. The amount of channeling contrast is influenced by the properties of incident electron beam and the detector. In principle, the energy and convergence angle of the incident electron beam determines the channeling pattern itself, while the position and energy response of the detector influence the amount of channeling contrast. In this study a large parameter space is explored to optimize the channeling contrast, including electron beam energy, working distance, convergence angle and position of detectors. As an example, the influence of electron beam energy to channeling contrast is summarized in Figure 2. The SACPs are shown in the right part of the figure. The position of the lines as well as intensity variations within the pattern changes significantly between different energies. However, quantification of the channeling contrast shows a clear trend of increasing channeling contrast at lower electron beam energy.