Multiwavelength micro-Raman Spectroscopy Research Articles

Detection of Ge and Si Intermixing in Ge/Si Using Multiwavelength Micro-Raman Spectroscopy

To meet various physical property requirements of materials for advanced application, for specific devices, combinations of Si/Ge, Ge/Si, Si1-xGex/Si, are frequently introduced in the device fabrication process. Epitaxy, condensation and annealing processes are commonly used. Since a small variation in composition, strain and crystallinity can result in reduced device performance or failure, the composition, strain and crystallinity must be carefully monitored and controlled throughout the manufacturing process. We report the detection of Ge and Si intermixing in epitaxially grown Ge/Si after successive thermal anneals using multiwavelength Raman spectroscopy. We have studied the dependence of Ge and Si intermixing on annealing temperature and Raman excitation wavelength. Very strong dependence of signal-to-noise (S/N) ratio measurements on excitation wavelength and film structure was observed. Suitable excitation wavelengths must be chosen to properly detect and characterize Si and Ge intermixing, based on the stacking order of epitaxial films and thicknesses.

Detection of Ge and Si Intermixing in Ge/Si Using Multiwavelength Micro-Raman Spectroscopy

To meet various physical property requirements of materials for advanced application specific devices, combinations of Si/Ge, Ge/Si, Si1-xGex/Si are frequently introduced in the device fabrication process. Epitaxy, condensation and annealing processes are commonly used. Since a small variation in composition, strain and crystallinity can result in reduced device performance or failure, the composition, strain and crystallinity must be carefully monitored and controlled throughout the manufacturing process.In this study, we report the detection of Ge and Si intermixing in epitaxially grown Ge/Si after successive thermal anneals using multiwavelength Raman spectroscopy. We have studied dependence of Ge and Si intermixing on annealing temperature and Raman on excitation wavelength. Very strong excitation wavelength and film structure dependence of signal-to-noise (S/N) ratio of measurements was observed. Suitable excitation wavelengths must be chosen to properly detect and characterize Si and Ge intermixing, based on the stacking order of epitaxial films and thicknesses.Figure 1 shows 514.5nm excited Raman spectra from reference Si, reference Ge and epitaxially grown Ge/Si wafers before and after thermal annealing. As grown Ge/Si wafers showed very distinct Ge and Si Raman peaks. Si and Ge intermixing was found in one annealing condition. Ge epitaxial was converted to Si1-xGexafter annealing.S/N ratio of measurements and their dependence on excitation wavelength and film structure dependence will be discussed. Excitation wavelength selection guidelines will be proposed.

Clarification of Stress Field Measured by Multiwavelength Micro-Raman Spectroscopy in the Surrounding Silicon of Copper-Filled Through-Silicon Vias

Recently, micro-Raman spectroscopy has become popular in the near-surface silicon stress measurement around copper-filled through-silicon vias. Because the stress σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Raman</sub> measured by the micro-Raman spectroscopy is a combined result of all of the stress components, interpretation of this stress becomes obscure. Ryu et al. has claimed that σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Raman</sub> is approximately biaxial and hence it is proportional to σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> + σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sub> . On the other hand, Wilson et al. has claimed that σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> + σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</sub> should be close to zero and hence σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Raman</sub> is directly proportional to σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> . In view of the dilemma as proposed by different research groups, this paper aims to provide insight into the origin of this stress so that it can be understood and used properly.

Multiwavelength Raman characterization of silicon stress near through-silicon vias and its inline monitoring applications

Characterization of silicon stress near copper (Cu)-filled through-silicon via(s) (TSVs) was demonstrated using high-resolution micro-Raman spectroscopy. For depth profiling of Si stress distribution near TSVs, a polychromator-based, multiwavelength excitation Raman measurement with different probing depths was used. The design concept of the polychromator-based, multiwavelength micro-Raman spectroscopy system, including the importance of the high-spectral resolution and multiwavelength excitation capability in three-dimensional (3-D) Si stress characterization, was described. Silicon stress near Cu-filled TSVs, with various sizes and layouts, was measured and analyzed before and after Cu annealing steps. Main factors impacting Si stress near Cu-filled TSVs are analyzed based on Raman characterization results on various types of TSV structures, layouts, and Cu annealing conditions. Large variations in Si stress in TSV arrays were measured in wafers with poor Cu fill characteristics and in wafers annealed in nonoptimized conditions. The Cu annealing sequence and annealing conditions are found to be significantly important for managing Si stress and the reliability of Cu-filled TSVs. Substantially lower Si stress was measured near Cu-filled TSVs with voids. Multiwavelength micro-Raman spectroscopy can be used as a very effective noncontact, nondestructive, inline TSV process and Si stress monitoring technique.

Non-contact monitoring of Ge and B diffusion in B-doped epitaxial Si1-xGex bi-layers on silicon substrates during rapid thermal annealing by multiwavelength Raman spectroscopy

B-doped, thin Si1-xGex bi-layers with different Ge content and B concentrations were epitaxially grown on Si(100) device wafers. Diffusion behavior of Ge and B atoms during rapid thermal annealing were monitored by multiwavelength micro-Raman spectroscopy. Raman spectra indicating possible Ge and B redistribution by thermal diffusion was observed from B-doped, thin Si1-xGex bi-layers on Si(100) wafers after rapid thermal annealing at 950°C or higher. Significant Ge and B diffusion in Si1-xGex bi-layers and Si substrates was verified by secondary ion mass spectroscopy. Pile up of B atoms at the surface and at the boundary between Si1-xGex bi-layers was observed in the early stages of thermal diffusion.

Contactless monitoring of Ge content and B concentration in ultrathin single and double layer Si1-xGex epitaxial films using multiwavelength micro-Raman spectroscopy

Non-contact monitoring of Ge content and B concentration in single and double Si1-xGex epitaxial layers on Si(100) device wafers was attempted using high-resolution, multiwavelength micro-Raman spectroscopy. The Ge content and B concentration determined by secondary ion mass spectroscopy (SIMS) depth profiling showed very strong correlation with the position and full-width-at-half-maximum of the Si-Si peak from the Si1-xGex epitaxial layers as determined by Raman measurements. High resolution X-ray diffraction (HRXRD) characterization was done for all wafers to determine Ge and B sensitivity and form comparisons with Raman and SIMS analysis. The non-destructive, in-line monitoring of Ge content and B concentration of single and double Si1-xGex epitaxial layers with thickness ranging from 5 ∼ 120 nm, on small area monitoring pads, was successfully demonstrated by multiwavelength micro-Raman spectroscopy during epitaxial process optimization, material property verification, and quality control applications.

Stress evolution in surrounding silicon of Cu-filled through-silicon via undergoing thermal annealing by multiwavelength micro-Raman spectroscopy

Three-dimensional stress development was observed in silicon surrounding the Cu-filled through-silicon via (TSV) structures undergoing the thermal annealing process. We show here, using a multiwavelength micro-Raman spectroscopy system, that the behavior of stress development in silicon after annealing step is dependent on the initial stress state as well as the geometry and directionality of the TSV array. The warping of stress curve for postannealed state with a reference of preannealed state is distinctively observed. Furthermore, the introduction of stress-free point is also attributed to the destructive stress interaction from different geometry and direction and initial stress state.

Strain Stability in Nanoscale Patterned Strained Silicon-On-Insulator

Nowadays, strain engineering plays a key role in boosting the performance of Si-based nanoelectronics. So far a tremendous progress has been made in establishing methods for strain manipulation in Si nanodevices. This has brought up further challenges in terms of development of reliable probes to characterize the strain on the nanoscale. In this paper, we discuss strain imaging using multi-wavelength micro-Raman spectroscopy. As a model system, we investigate the strain behavior upon nanoscale patterning of ultrathin strained silicon-on-insulator (SSOI). We show that valuable details on the strain depth distribution can be obtained by combining deep UV and visible Raman microprobes. Additionally, we also demonstrate that strain mapping with high lateral resolution can be achieved using UV-Raman with glycerin-immersed high numerical aperture objective lens. Results from nano-beam electron diffraction and peak-pairs analysis of high-angle annular dark field images are also presented. Detailed 3D finite element simulations of edge-induced strain relaxation in SSOI nanostructures augment our experimental studies.

Study of CNTs and nanographite grown by thermal CVD using different precursors

Carbon nanotubes (CNTs) are obtained by chemical vapor deposition (CVD) on uncoated silicon and quartz substrates. The process of synthesis involves the co-evaporation of a carbon precursor and a metal catalyst in a nitrogen atmosphere in a high temperature furnace. Beside the formation of CNTs, by varying few parameters, other carbon structures can be deposited, such as a nanographite layer. In particular we believe that our version of thermal CVD is an economic and efficient process in alternative to other methods for the growth of nanographite. The morphology and structure of our samples were characterized by multi-wavelength Micro-Raman spectroscopy, SEM and HR-TEM analyses. We found that our CNTs have an average diameter of 80nm, with length between few and hundreds of micrometers. Brunauer–Emmett–Teller (BET) analysis was used to calculate the specific surface area and porosity. Furthermore, we have performed an hydrogen storage experiment on our CNTs samples, finding an adsorption capacity of about 1.7wt%, at 14bar and 190°C.