Profiling semiconductor multilayer structures by CBED and CBIM techniques

Abstract

Strain and composition profiles are of great importance in understanding properties of semiconductor multilayers, increasingly so as layer dimensions decrease. Recent advances in measuring these profiles have been achieved using convergent beam electron diffraction (CBED) and convergent beam imaging (CBIM) techniques. In both methods a converging incident beam allows us to map rocking curve information approximately parallel to the incident beam direction as the Ewald sphere is scanned through a given reflection. CBIM may be usefully compared with the large angle technique of CBED (LACBED). Both methods essentially utilise the same illumination condition with the incident probe brought to a focus in a plane appreciably removed from the specimen (fig 1). In CBIM an in-focus image of the specimen is recorded. In LACBED the object plane is that of the minimum probe and the diffraction pattern is recorded; this means that the illuminated area is mapped onto each diffraction disc. In both methods the smallest probe is important, defining the area of angular uncertainty (effectively angular resolution) in CBIM, and the spatial resolution in LACBED.