Energy-filtered imaging in a field-emission scanning electron microscope for dopant mapping in semiconductors

Two-dimensional dopant mapping using secondary electrons in a scanning electron microscope (SEM) is a useful and rapid technique for studying dopant distributions with high spatial resolution in semiconductor materials and devices. However, the technique has a major drawback: although p-n junctions and differently doped p-type regions can be imaged, the contrast from differently doped n-type regions is extremely low, hence, such regions cannot normally be detected. We demonstrate that energy filtering of the secondary electrons substantially enhances the contrast of differently doped n-type regions, so that they are easily differentiated and mapped. This is because the contrast is based on the shift of energy spectra from n and p regions rather than secondary electron yield differences that lead to the conventional dopant contrast. We have used a standard commercially available Schottky field emission gun SEM for our work. Energy-filtered secondary electron imaging in a SEM therefore provides a rapid technique for the imaging and mapping of both p-type and n-type dopants. Our initial results indicate that a spatial resolution of <6 nm can be expected for favorable specimens. (C) 2002 American Institute of Physics.