Identification of superfine precipitates and crystalline defects in silicon using TEM phase-contrast imaging

Abstract

Very large (≥1000Å in size) precipitates, and crystalline defects, such as dislocation loops or twins, can be identified in a straightforward manner using the conventional electron diffraction contrast in bright field/dark field (BF/DF) mode in a transmission electron microscope (TEM) On the other hand, superfine precipitates and crystallographic defects, whose sizes are ≤ 100Å, can be difficult to identify by the BF/DF technique. For example, the distinction between a small and a large dislocation loop (similar arguments hold for precipitates, too) is the way the elastic stress is distributed around the dislocation. The elastic stresses around a large loop have the same general form as that for a straight dislocation line. Hence, the BF and DF images of a large loop have the same general characteristics of the image of a straight dislocation line.[1] However, the image characteristics of a small dislocation loop are derived using the infinitesimal loop approximation of a dislocation line to describe the stress field of the small loop.[2] Hence, the image characteristics of a small loop can be complex with black/white or black/black dot contrast. In this article, we report a technique for distinguishing superfine precipitates and defects using the phase contrast imaging technique in the TEM without going through the time consuming and sometimes ambiguous BF/DF technique. This technique was applied to identify interfacial defects in homoepitaxial silicon films deposited by rapid thermal chemical vapor deposition (RTCVD).