Reflected and transmitted secondary electron images of thin Si₃N₄ window

Reflected and transmitted secondary electron images of Si₃N₄ window are obtained in scanning electron microscopy (SEM) by using SEM and scanning transmission electron microscopy (STEM) holders. The figure of Si₃N₄ window becomes distinguishable as the accelerating voltage increases. However, the brightness of Si₃N₄ window relative to the surroundings in images for SEM and STEM holders is completely opposite. It changes from dark to bright, which means the number of detected secondary electron increases. The difference of the two kinds of image is caused by the fact that secondary electrons emitted from the bottom surface can also be detected when using STEM holder. The images are consistent with Monte Carlo simulation results. Image figures are sensitive to accelerating voltages and sample thicknesses. Therefore, more characteristics of thin sample could be analyzed via combining the two kinds of image.