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

Epitaxial Si1-xGex layers, grown by molecular beam epitaxy (MBE) and b y chemical vapor deposition (CVD) on Si(001) substrates, with thicknes ses between 20 and 50 nm and Ge contents from 4% to 23% were investiga ted by micro Raman backscattering, x-ray double crystal diffractometry , and transmission electron microscopy. A quite simple phenomenologica l 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 pse udomorphically strained layer, and the alloy-like stress-free layer. A measure for the degree of relaxation can be obtained from the measure d Raman shift and from the independently determined germanium content, using the results of the model. The degree of relaxation was determin ed for a number of CVD- and MBE-grown Si1-xGex layers. The as-grown ps eudomorphic layers relax partially after annealing at 900-degrees-C. T he Raman scattering allows the monitoring of the development of relaxa tion during the semiconductor device processing.