Spatial resolution of electron backscatter diffraction in a FEG-SEM

摘要

Crystallographic information can be determined for bulk specimens in a SEM by utilizing electron backscatter diffraction (EBSD), which is also referred to as backscatter electron Kikuchi diffraction. This technique provides similar information to that provided by selected area electron channeling (SAEC). However, the spatial resolutions of the two techniques are limited by different processes. In SAEC patterns, the spatial resolution is limited to (approximately)2 (mu)m by the motion of the beam on the specimen, which results from the angular rocking of the beam and the aberration of the probe forming lens. Therefore, smaller incident probe sizes provide no improvement in spatial resolution of SAEC patterns. In contrast, the spatial resolution for EBSD, which uses a stationary beam and an area detector, is determined by (1) the incident probe size and (2) the size of the interaction volume from which significant backscattered electrons are produced in the direction of the EBSD detector. The second factor is influenced by the accelerating voltage, the specimen tilt, and the relative orientation of scattering direction and the specimen tilt axis. This study was performed on a Philips XL30/FEG SEM equipped with a TexSEM Orientation Imaging Microscopy (OIM) system. The signal from the EBSD detector (SIT camera) is flat- fielded and enhanced in a MTI frame storage/image processor. The Schottky FEG source provides the fine probe sizes ((approximately)10 nm) desired with sufficient probe current ((approximately)1 nA) needed for image processing with the low signal/noise EBSD signal.