MEASUREMENT OF STRESS AND RELAXATION IN SI1-XGEX LAYERS BY RAMAN LINE SHIFT AND X-RAY-DIFFRACTION

Epitaxial Si1-xGex layers, grown by molecular beam epitaxy (MBE) and by chemical vapor deposition (CVD) on Si(001) substrates, with thicknesses between 20 and 50 nm and Ge contents from 4% to 23% were investigated by micro Raman backscattering, x-ray double crystal diffractometry, and transmission electron microscopy. A quite simple phenomenological model was developed to derive the Raman shift of the Si-Si mode as a function of the germanium content for the two limiting cases, the pseudomorphically strained layer, and the alloy-like stress-free layer. A measure for the degree of relaxation can be obtained from the measured Raman shift and from the independently determined germanium content, using the results of the model. The degree of relaxation was determined for a number of CVD- and MBE-grown Si1-xGex layers. The as-grown pseudomorphic layers relax partially after annealing at 900-degrees-C. The Raman scattering allows the monitoring of the development of relaxation during the semiconductor device processing.