Strain measurement in heteroepitaxial layers-Silicon on sapphire

An x-ray diffraction technique is presented for the determination of the strain tensor in an epitaxial layer grown on a crystallographically distinct substrate. The technique utilizes different diffracting planes in the layer and in a reference crystal fixed to the layer, and is illustrated by application to an similar to 4000 angstrom (001) silicon layer grown on a (01 (1) over bar2) sapphire wafer. The principal strains were measured, and the measured strain normal to the layer was found to agree with the normal strain calculated from the measured in-plane strains within the experimental uncertainty of strain measurement. The principal stresses in the plane of the silicon film, calculated from the measured strains were -0.92 +/- 0.16 GPa in the [100] direction and -0.98 +/- 0.17 GPa in the [010] direction.