Strain relaxation of SiGe islands on compliant oxide

The relaxation of patterned, compressively strained, epitaxial Si0.7Ge0.3 films transferred to borophosphorosilicate (BPSG) glass by a wafer-bonding and etch-back technique was studied as an approach for fabricating defect-free Si1-xGex relaxed films. Both the desired in-plane expansion and undesired buckling of the films concurrently contribute to the relaxation. Their relative role in the relaxation process was examined experimentally and by modeling. Using x-ray diffraction, Raman scattering and atomic force microscopy, the dynamics of in-plane expansion and buckling of Si0.7Ge0.3 islands for island sizes ranging from 10 mumx 10 mum to 200 mumx200 mum for anneal temperatures between 750 and 800 degreesC was investigated. Lateral relaxation is favored in small and thick islands, and buckling is initially dominant in large and thin islands. Raising the temperature to lower viscosity of the oxide enhances the rate of both processes equally. For very long annealing times, however, the buckling disappeared, allowing larger, flat, and relaxed islands to be achieved. Cross-sectional transmission electron microscopy observation on a relaxed Si0.70Ge0.30 island revealed no dislocations, confirming that SiGe relaxation on BPSG is a good approach to achieve high quality relaxed SiGe. (C) 2002 American Institute of Physics.