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Raman spectra for two incident-scattered radiation polarization configurations, ss and sp , recorded on the (a) 50-nm and (b) 200-nm-stripe structure. The positions of the Si optical phonon mode originating from the c -Si substrate and the s Si nano-stripes are denoted by arrows and labelled “ c Si” and “sSi,” respectively.
Source publication
We report on the experimental determination of the biaxial stress characteristic of the strain state present in strained silicon nano-stripes on insulator structures. Conventional confocal backscattering Raman spectroscopy being insensitive to the tensorial nature of strain, a methodology based on the use of polarized oblique incidence backscatteri...
Citations
... Raman spectroscopy is an efficient tool to measure residual stress by correlating the effects with the optical change in the materials [1][2][3][4][5][6][7]. Moreover, it is a nondestructive and noncontact method, characterized by a high spatial resolution, and has already been widely used to investigate silicon, such as in cubic crystals [8,9], microelectronic devices [10][11][12][13], and nanostrips [14]. ...
The growing interest in improving optoelectronic devices requires continuous research of the materials and processes involved in manufacturing. From a chemical point of view, the study of this sector is crucial to optimize existing manufacturing processes or create new ones. This work focusses on the experimental evaluation of residual stresses on samples that are intended to simulate part of the structure of an optoelectronic device. It represents an important starting point for the development of optoelectronic devices with characteristics suitable for future industrial production. Silicon chips, with a thickness of 120 μm, were soldered onto copper and alumina substrates, using different assembly parameters in terms of temperature and pressure. Using Raman spectroscopy, the stress evaluation was estimated in a wide temperature range, from −50 to 180 °C. Silicon chips soldered with AuSn alloy on copper substrates demonstrated at 22 °C a compressive stress, developed in the center of the assembly with a maximum value of −600 MPa, which reached −1 GPa at low temperatures. They present a stress distribution with a symmetric profile with respect to the central area of the chip. The silicon chip assembled on a ceramic substrate without pressure turned out to be extremely interesting. Even in the absence of pressure, the sample did not show a large shift in the Raman position, indicating a low stress.
... To this end, a "dry" alternative is required. While oblique backscattering approaches have been explored, 18,19 the most efficient scattering configuration for detection of the forbidden TO mode is when incident light is tilted away from the normal axis and the scattered light is collected normally ( Fig. 1(b)). For p-polarized incident light, the E in⊥ amplitude responsible for the TO mode excitation scales with the incidence angle ( i ). ...
Raman spectroscopy is an effective tool for stress and compositional metrology in the semiconductor industry. However, its application towards decoupling a complex stress state in semiconductor materials requires the use of liquid immersion lenses that are process line incompatible. In this work, a practical design concept for off-axis Raman spectroscopy is presented. By tilting the incident light away from the normal incident axis, forbidden Raman modes can be accessed allowing determination of the in-plane stress tensor in semiconductor materials. Further, we benchmark off-axis Raman spectroscopy against oil-immersion Raman spectroscopy for stress characterization in 20 nm-wide strained Ge fin field-effect transistor channels. We demonstrate that off-axis Raman allows anisotropic stress metrology without reliance on liquid immersion lenses, highlighting its viability in the process line. The stress state is validated through nanobeam diffraction measurements.
Square-shaped Ce0.8Gd0.2O2 (GDC) membranes are prepared by microstructuring techniques from (111)-oriented, polycrystalline GDC thin films. The strain state of the membranes is investigated by micro-Raman mapping using polarized excitation light. Using circularly polarized excitation, the maps of the Raman shifts reveal circular contour lines in concordance with the quadratic shape of the membrane and with optical investigations of the residual strain distribution. In contrast, asymmetric contours of the maps of the Raman shifts exhibiting a two-fold symmetry are found when using linearly polarized excitation. The contour plots for a linear polarization perpendicular or parallel to the local curvature are rotated by 90°. This behavior is caused by the polarization dependence of three overlapping Raman modes arising from the splitting of the triply degenerate F2g mode due to strain. The contribution of their Raman intensity to the overall Raman signal depends on the measurement geometry and the polarization of the incoming and scattered light. Varying the polarization of the incoming excitation light results in different averaging of the Raman-active modes contributing to the broad Raman signal observed. These results clearly demonstrate that polarization-dependent Raman measurements have the potential to yield additional insight into the local strain distribution in free-standing oxide membranes.
In this review, a review a of the applications of micro-Raman spectroscopy (μRS) to characterize the residual strain and/or stress in electronic packaging is presented. Micro-Raman spectroscopy is considered as an effective tool for residual stress evaluation in semiconductor devices at the microscale level due to its nondestructive, noncontact feature with high spatial resolution. In this review, a comparison of μRS to the other measurement techniques, such as DIC, micro moiré and XRD has been illustrated. The range of problems in semiconductor packaging that can be characterized by μRS has been discussed. The basics of μRS in stress/strain measurement is described and the recent progress of residual stress measurement including shear stress component is discussed in detail. Two case studies for the use of μRS in electronic packaging are presented, including in the application of through silicon via (TSV) and flip chip assembly. Finally, several challenges for the future development of μRS are discussed.
In advanced transistor technology, Silicon-Germanium alloy (SiGe) is being used as a replacement for Si channels to achieve higher mobility. Among the various characterization techniques μ-Raman spectroscopy is a promising candidate due to a good spatial resolution and low detection threshold. This study presents the evaluation of the technique for the measurement of Ge concentration and comparison to other metrology techniques. As a first step to evaluate the μ-Raman capability, we considered a simple case of thin SiGe films from 12nm down to 4 nm thickness. Assuming an epitaxial pseudomorphic structure, the Ge content has been extracted for all samples with an average 0.3% stability and at least 1% accuracy as confirmed by high resolution X-ray diffraction (HRXRD) and secondary ion mass spectrometry analysis (SIMS). We then studied a more complex structure of SiGe on fully depleted-silicon on insulator (FD-SOI) as being critical for the development of condensation process of advanced transistor technology. Since μ-Raman requires prior knowledge of the structural state of the layer, we discuss the interest to combine μ-Raman measurements with X-rays diffraction in order to extract the Ge composition on such stacks. μ-Raman shows a real potential for thin SiGe film characterization and it does not suffers of the lack of precision for very thin films as HRXRD does, however there are still some developments to be made before using it as a metrology technique. Moreover, it could be interesting to couple the technique with HRXRD measurement. The approach to control SiGe condensation process on FD-SOI might suggest interesting experiment. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
