| Abstract: | Contrast plays a crucial role both in qualitative and quantitative imaging in scanning microscopy. Usual methods of obtaining high contrast images in the scanning electron microscope (SEM) involve performing specific operations on the video signal already produced by the SEM. In this article, the concept of in situ differential imaging in the SEM is discussed. In this imaging modality, a true differential image of the sample is generated simultaneously with the normal video. The signal can be obtained at low and high video band-widths, thus allowing low contrast objects to be readily imaged. Various methodologies developed to perform in situ differential imaging are reviewed. A characteristic of all these techniques is their sensitivity to edges, a feature which is extensively used in a number of applications. The ability to obtain feature enhancement in any desired direction is another important attribute of this approach. Examples are given on the use of the method in general imaging as well as in the metrology of critical dimensions. |
