Monte Carlo simulation and theoretical calculation of SEM image intensity and its application in thickness measurement

The intensity profiles of backscattered and secondary electrons from a pure Mg sample have shown a variation with sample thickness and acceleration voltage in the range of 5-30 kV, depending on the specimen holder used. The intensities of backscattered electron (BSE) and secondary electron (SE) signals increases with the sample thickness until saturation when using a scanning transmission electron microscopy (STEM) holder with a closed tube below the sample. However the SE signal increases to the maximum and then decreases with the sample thickness when using a transmission Kikuchi diffraction (TKD) holder with no shielding below the sample whereas the BSE signal again increases until saturation. The influence of the holder on the SE signals is caused by the fact that secondary electrons emitted from the bottom surface could be detected only when using the TKD holder but not the STEM holder. The experimental results obtained are consistent with the Monte Carlo simulation results. Application of the magnitude of the SE and BSE signals to measurement of sample thickness has been considered and the BSE image profile shows a reasonably good accuracy.