Method and apparatus for correcting magnetic field distortions in electron backscatter diffraction patterns obtained in an electron microscope

Abstract

A system and method for correcting automatically the distortions in electron background diffration (EBSD) patterns which result from magnetic fields produced by some scanning electron microscopes (SEMs) used for collecting such patterns from polycrystalline sample materials. The method may be implemented as a software program running on a computer which is part of a conventional system for obtaining and analyzing EBSD patterns to obtain crystallographic information about the sample material. The method includes a calibration procedure and a correction procedure. In the calibration procedure, a distorted EBSD pattern obtained from a calibration sample is displayed on an operator display and user interface. Using an input device, an operator defines segment endpoints along a Kikuchi band in the distorted EBSD pattern image. From the user defined segment endpoints, correction parameters are calculated based on a mathematical curve (e.g., cubic spline) fitting the endpoints. The correction parameters may also be corrected automatically, without user intervention. The correction parameters are saved and may be used to correct magnetic field distortions in all subsequent EBSD patterns obtained using the SEM geometry for which the calibration procedure is run. In the correction procedure, the correction parameters are employed to shift lines of pixels in the distorted EBSD pattern image by an amount defined by the correction parameters to correct the distortion in the EBSD pattern image. Thus corrected EBSD pattern images may be displayed to a operator of the system and saved for subsequent EBSD pattern analysis using conventional EBSD pattern analysis techniques.