Imaging, spectroscopy and spectroscopic imaging with an energy filtered field emission TEM

Energy filtered microscopy using a post column filter has been applied in a variety of materials characterisation problems to demonstrate its use with a field emission transmission electron microscope. We have shown that the technique, when combined with sample preparation methods such as the focussed ion beam technique, enables the imaging of large fields of view for general analysis and also high resolution mapping so that interfaces and grain boundaries can be studied. The general microstructure of semiconductor devices is initially investigated with elemental mapping and energy loss fine structure analysis. From the B K edge detected in an interlevel dielectric glass layer of a device, the trigonal coordination of B (present at 2–4wt.%) was deduced. The chemistry of 14nm wide oxynitride composite dielectric layers (composed of a silicon oxide–silicon nitride–silicon oxide or O–N–O sandwich, each layer only a few nm in thickness) in a dynamic random access memory (DRAM) was also studied with elemental maps of oxygen and nitrogen. The intensity profiles and images of these two elements showed two very well resolved oxygen layers and a central N layer. Changes in the energy loss fine structure at the Si L2–3 edge in elemental Si, Si nitride and Si oxide were also used to map different areas of a DRAM transistor and spectroscopic images were thus obtained showing features arising from the change in chemical state of Si. Finally the expected resolution of energy filtered microscopy is discussed for various imaging conditions and used to analyse Fe segregation observed at grain boundaries and triple junctions.