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Surface-sensitive strain analysis of Si/SiGe line structures by Raman and UV-Raman spectroscopy

Strained silicon is applied to the transistor channel of leading-edge CMOS devices, significantly increasing carrier mobility and requiring measurement techniques to characterize strain. In the investigation reported here, we apply Raman spectroscopy using excitation by both visible and UV light in conjunction with finite-element analysis to analyze the strain distribution adjacent to embedded silicon-germanium (SiGe) line structures in silicon wafers. In agreement with the modeling results, a strong strain depth gradient is obtained for the silicon lines, whereas the strain within the SiGe regions depends weakly on the depth. We show further how the stress tensor and its distribution in both SiGe and Si regions is modified when changing the geometry of the line structures. For the strained Si line region, a sensitive dependence of the stress state on the geometry is obtained.