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.
In semiconductor industry, process control and physical failure analysis were dominated by light and electron microscopy as well as surface analysis techniques including X-ray photoelectron spectroscopy (XPS) until the end of the last century. During the past decade, X-ray diffraction (XRD) and X-ray reflectivity (XRR) have been successfully applied in out-of-fab analytical labs. In addition to XRF and TXRF, some additional X-ray techniques -e.g. XRD, XRR and XPS -have been moved or are in the process to be moved from lab-based studies to in-line applications, using cleanroom compatible thin film characterization tools in wafer fabs. Lab-based smallangle X-ray scattering (SAXS) tools are applicable for pore size characterization in porous thin films. Advanced transmission X-ray microscopy (TXM) and X-ray computed tomography (XCT) systems with sub-100 nm resolution are currently being evaluated for their use in out-of-fab analytical labs. Apart from the on-site use of laboratory X-ray sources, synchrotron-radiation sources have been used in all fields of X-ray techniques: diffraction (SR-XRD), spectroscopy (SR-XPS, XAFS) and microscopy (SR-TXM/XCT). The high brightness and collimation of SR beams provide unique possibilities, e.g. for in-situ X-ray microdiffraction, photoelectron emission microscopy (PEEM) and in-situ TXM/XCT.In this paper, we demonstrate the high potential of the X-ray techniques for semiconductor industry, we describe potential implementations of these techniques for current and future applications, particularly for advanced process development and process monitoring, and we provide an outlook showing that we are living in a decade which is characterized by a breakthrough in the industrial application of Xray techniques. The application focus of this review is on the study of two types of nanostructures with typical dimensions less than 100 nm: artificial nanolayers and nanostructures caused by thin film deposition and patterning (litho/etch) processes as well as nanostructured materials, i. e. thin film materials with a "sub-structure" on sub-100 nm length scale.
We have investigated silicon-germanium (SiGe) line structures employing metallic apertures in combination with Raman spectroscopy to obtain high-spatial strain resolution below the diffraction limit. The apertures were cut into specifically shaped electrochemically etched tungsten tips, which were adjusted within the Raman laser beam on the sample surface by a tuning fork atomic force microscope. With this setup, line structures on patterned SiGe films with a center-to-center distance down to 200 nm were resolved in the Raman scans, evidently indicating a resolution clearly below the far-field Raman resolution of about 600 nm for the used instrument. This setup allows improved local strain analysis by Raman spectroscopy and shows potential for further near-field Raman applications.
Local stress fields in strained silicon structures important for CMOS technology are essentially related to size effects and properties of involved materials. In the present investigation, Raman spectroscopy was utilized to analyze the stress distribution within strained silicon (sSi) and silicon-germanium (SiGe) island structures. As a result of the structuring of initially unpatterned strained films, a size-dependent relaxation of the intrinsic film stresses was obtained in agreement with model calculations. This changed stress state in the features also results in the appearance of opposing stresses in the substrate underneath the islands. Even for strained island structures on top of silicon-on-insulator (SOI) wafers, corresponding stresses in the silicon substrate underneath the oxide were detected. Within structures, the stress relaxation is more pronounced for islands on SOI substrates as compared to those on bulk silicon substrates
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