In recent silicon transistors, fluctuation of the gate threshold voltage due to statistical variation in the number of dopant atoms has been pointed out to be a serious problem. For this reason, characterization methods are required which can detect individual dopant atoms within the transistor. In this paper, we present a technique for visualizing individual arsenic (As) atoms in a doped silicon crystal using our developed spherical aberration corrected scanning transmission electron microscope (STEM) with a convergent electron probe with a half angle of 30 mrad to view very thin doped silicon crystals from the [001] direction. The STEM images show the distribution of As dopant atoms within a 2.7 nm defocusing range around the focal position. It was found that in a highly doped silicon wafer following rapid thermal annealing, clustering of As atoms was extremely rare.
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