Study of relaxed Si0.7Ge0.3 buffers, grown on patterned silicon substrates, by Raman spectroscopy

We have carried out micro-Raman spectroscopy to characterize Ge concentration and strain in relaxed Si0.7Ge0.3, buffer layers grown on patterned silicon substrates. Different epitaxial layer stacks, annealing steps and Ge composition were used to achieve different relaxation in the strain relaxed buffer layers. A detailed consideration of Raman frequencies and the relative intensities of the, various phonon modes can be used to monitor composition and strain. We show that this method is also suitable for a device layer stack with a strained Si layer on top of the relaxed SiGe buffer layer and we compare it with another proposal for determining of the Ge content using the Si-Si LO Raman frequencies of the Si cap layer and the relaxed SiGe layer. The potential and the accuracy of the various methods in comparison to high resolution x-ray diffraction measurements are discussed. Finally, we demonstrate, that micro-Raman can be used as an in-line monitoring tool to determine the uniformity of Ge concentration and strain with a lateral resolution of 1-2 mum.