In this paper, intensity enhancements of the Raman signal from strained silicon films utilizing the tip enhanced Raman spectroscopy (TERS) effect are reported. Specially shaped metallized atomic force microscopy tips have been prepared by sputter deposition of thin silver films onto sharpened quartz tips and subsequent focused ion beam (FIB) modification. Raman signal enhancements of more than 20%, which are attributed to the strained silicon film of 70nm thickness only, have been obtained due to approaching the TERS tips the laser spot. On samples with patterned trench structures prepared by FIB milling, lateral sample scans have been performed. These scans revealed a resolution of strained silicon lines with center-to-center distances below 250nm, well below the classical optical diffraction limit. Based on an analysis of the stress state in the strained silicon structures, relaxation effects close to the trench edges have been investigated. The described approach of nano-Raman spectroscopy is promising for strain characterization in devices, e.g., in field-effect transistor structures.
Embedded-SiGe is shown to be fully compatible with strained-SOI substrates. Despite a lack of lateral lattice mismatch between the SiGe and strained-SOI, the resulting drive current improvement from embedded-SiGe is identical for strained-SOI and standard SOI control (where a lateral lattice mismatch is present). This result isolates the vertical lattice mismatch as the source of stress generation from embedded-SiGe. The concept of a critical length of SiGe beyond the vertical Si-SiGe interface is introduced to explain the observed experimental results, and is confirmed by various SiGe epitaxial fill-height and stress relaxation experiments.
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