Modern Scanning Electron Microscopy. 3. Electron Probe

— A review of the electron-probe parameters of a scanning electron microscope and of methods for their measurements is given. Three definitions of the concept of the electron-probe diameter are presented. It is shown that the definition of the probe diameter as the size of the effective square beam with a uniform electron-density distribution is most convenient. A method for measuring the probe diameter using blade diaphragms is analyzed. The drawbacks of this method are shown. Methods for measuring the probe diameter by means of test objects with rectangular groove profiles, by means of those with trapezoidal profiles and large side-wall inclination angles, and by means of two coordinates and one certified test object size are given. Methods for measuring the electron-density distribution in the low-voltage microscope probe, the vertical probe profile, and the probe nonorthogonality with respect to the measured-object plane are described. A method for experimentally determining the probe-diameter dependence on the electron-beam current is presented. It is shown that, for tungsten cathodes, the theory of electron-probe formation does not coincide with experiments. The influence of probe focusing on the relief image in the scanning electron microscope operating in all modes is described. It is concluded that it is necessary to focus the microscope in the high-voltage mode when recording slow secondary electrons even in the case where measurements are conducted in the mode of backscattered-electron recording.