PROFILING STRAIN IN THIN BURIED LAYERS BY CONVERGENT BEAM ELECTRON DIFFRACTION TECHNIQUES. D. Cherns Physics Department, University of Bristol, Bristol, BS8 1TL UK

Convergent beam electron diffraction (CBED) provides a powerful method of recording crystal rocking curves. In contrast to X-ray rocking curves, electron rocking curves are not restricted to low order reflections and have spatial resolutions down to about 1 nm. The method has now been used to profile strain and composition in a range of semiconductor multilayer structures in both plan-view and cross-sectional geometries.

Electron rocking curves have been most usefully recorded using the large angle CBED (LACBED) method which shows spatial variations directly. LACBED also provides a means of filtering out most of the phonon- and some of the plasmon-generated inelastic background, giving useful rocking curve detail up to a tilt of more than 10deg. from the Bragg orientation. Studies of Si/SiGe multilayers in a plan-view geometry have shown that layer strains may be determined to~20% accuracy (1). Corresponding studies on cross-sectional samples (2) suggest a similar sensitivity; in this case strainrelaxation must be taken into account. Work on single buried layers in InP/InGaAs in plan-view has shown that, using low order reflections, strains may be analysed for layers down to 1 monolayer in thickness (3). Recently we have extended these studies to high order reflections which are more sensitive to layer srains. Results obtained for thin Ge layers in Si indicate that strain can thereby be profiled across Ge islands where 3-D growth has occurred.

(1) D. Cherns, R. Touaitia, A. R. Preston, C. J. Rossouw and D. Houghton, Phil. Mag. A64 (1991) 597.

(2) X-F. Duan, D. Cherns and J. W. Steeds, Phil. Mag. A70 (1994) 1091.

(3) N. Grigorieff, D. Cherns, M. J. Yates, M. Hockly, S. D. Perrin and M. R. Aylett, Phil. Mag. A68 (1993) 121.