Detection of arsenic dopant atoms in a silicon crystal using a spherical aberration corrected scanning transmission electron microscope

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.