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The stress dependence of the room-temperature cathodoluminescence (CL) spectrum of N-doped cubic silicon carbide is analyzed in a field-emission-gun scanning electron microscope by using the electron beam as an excitation source for luminescence emission. The results have stated that the stress assessment technique is available in conventional scanning electron microscopy (SEM) devices coupled with CL spectrometers for the nondestructive evaluation of residual stresses in N-doped 3C-SiC-based devices.

This study is aimed at establishing a method of polarized/confocal Raman spectroscopy capable of quantitatively assessing crystallographic orientation in wurtzitic GaN with a micron-scale resolution. First, Raman selection rules are explicitly put forward from a theoretical viewpoint in their complete form; then, experimentally retrieved intensities of the Raman signal as a function of Euler angles are fitted to the obtained theoretical dependencies in order to quantify a set of Raman tensor elements using experiments on known crystallographic planes of a wurtzitic GaN single-crystal. According to the above two procedures, a spectroscopic algorithm, incorporating the use of Raman tensor elements and Euler angles in tandem, becomes available for estimating unknown crystallographic orientations. As an application of the developed method, a confocal Raman probe was used to non-destructively unfold the relative orientation of a wurtzitic GaN epilayer with respect to (0001)-oriented sapphire substrate. The microscopic distribution of tilt/twist angles in space for the GaN lattice could be measured in a bulk region of the sample with no cut or other sample manipulations being necessary. Polarized/confocal Raman spectroscopy provides a practical and convenient tool for characterizing on the micron scale the interfacial disorder that affects energy transport phenomena at GaN/substrate interfaces. [ABSTRACT FROM AUTHOR]

A spatial and tensor deconvolution procedure is proposed for the analysis of cumulative Raman frequency shifts recorded in silicon surface zones containing a Blister-type contact stress field. The procedure is further applied to the quantitative determination of the three independent values of phonon deformation potentials for the Si lattice. Phonon potentials are experimentally obtained for an (110) oriented Si single-crystal containing a pyramidal (Vickers) indentation print. A cross-polarized laser microprobe operating at a visible wavelength enabled us to precisely retrieve the three independent phonon potentials for Si. The presented method requires a minimum amount of material and can be applied with a single measurement set, while previously published characterizations required the availability of relatively large and differently oriented samples. The proposed experimental method is particularly suitable for in situ assessments of phonon deformation potentials in thin/opaque samples with high refractive index. [ABSTRACT FROM AUTHOR]

Two cathodoluminescence piezospectroscopic (CL/PS) approaches for measuring the residual stress distribution in thin films are critically examined and compared using an intrinsic GaN film sample (2.5 μm in thickness) grown on a (0001)-oriented sapphire substrate. The first approach invokes an analytical model to fit experimental stress distributions as retrieved in both film and substrate at the edge of an artificially created cross section of the sample. Such an edge-stress distribution takes into account both the thermal expansion mismatch between the film and substrate and the mechanistics of film growth process. In the second approach, we directly and nondestructively measure the bulk residual stress field from the sample top surface on the film side using an increase in electron beam voltage (maintaining a constant beam power) as a means for screening the film subsurface. In this latter case, the combined effects of self-absorption and misfit dislocations on the GaN spectrum severely affect the CL/PS assessments; therefore, they need to be analyzed separately from the effect of stress. After spectral deconvolution of the obtained stress profiles, according to either in-plane or in-depth response functions of the electron probe for both film and substrate, cross-section and top-surface stress data were compared and discussed in an effort to substantiate the feasibility of spatially resolved CL/PS approach for the examination of residual stress distributions in film structures. [ABSTRACT FROM AUTHOR]

Underlying physics has been put forward and an experimental verification given for in situ determination of deformation potentials in Si-doped GaAs through a quantitative assessment of micro-/nanoscopic surface stress fields. Highly localized spectroscopic stress assessments could be achieved using a field emission scanning electron microscope as an energy source for stimulating cathodoluminescence emission from a Si-doped GaAs wafer. The deformation potentials were obtained from the local (elastic) residual strain fields stored in the neighborhood of an indentation print. The three independent GaAs deformation potentials could be obtained from a single measurement set and from mixed strain fields including tensile and compressive strains, while all the previously published characterizations were made in compression and on different samples. For these reasons, the deformation potentials determined in this study may prove more reliable and valid in a wider strain range as compared to those from previously published study. The proposed experimental method is suitable for in situ assessments of epitaxially grown thin-film materials and other zinc-blende-like III-V semiconductor heterostructures and alloys. [ABSTRACT FROM AUTHOR]

A spatially resolved cathodoluminescence piezospectroscopic analysis is attempted for the high-resolution evaluation of the stress field developed ahead of the tip of an equilibrium crack propagating in a semiconductor. GaN was selected for this assessment as a paradigm semiconductor material. Quantitative measurements of in-plane luminescence probe response function (PRF) were preliminarily performed at different acceleration voltages upon scanning across a straight and atomically sharp interface between GaN and gold metal. Then, based on the knowledge of PRF, the convoluting effect due to the finite size of the electron probe could be corrected and an improved plot of the crack-tip stress field could be retrieved by a computer-aided data restoration procedure. The crack-tip stress intensity factor KI obtained by the cathodoluminescence piezospectroscopic method was compared with that obtained on the same crack path according to high-resolution measurements of crack-tip opening displacement. This study not only shows that a nanometer-scale spatial resolution can be experimentally achieved in a stress analysis of semiconductor materials but also that a stress data treatment based on experimental PRF is a viable approach to greatly reduce the error involved with the finite size of the electron probe. [ABSTRACT FROM AUTHOR]

A piezospectroscopic (PS) cathodoluminescence (CL) study has been carried out on a Cu-Ta/SiOx (carbon-doped) model chip prepared on a Si substrate. The PS approach was applied to CL spectra arising from optically active point defects in dielectric silica. The red CL emission arising from nonbridging oxygen hole centers (NBOHC) in the carbon-doped SiOx dielectric layer was calibrated and used as a stress sensor. This approach enabled us to locate the trace of the residual stress tensor, as locally developed during manufacturing process in the dielectric interlayers between Cu-Ta interconnects. A minimally invasive electron beam allowed probing local residual stress fields with an improved spatial resolution as compared to more conventional photostimulated PS techniques applied to the Si substrate. In addition, a two-dimensional deconvolution procedure was attempted to retrieve the “true” residual stress distribution piled up between adjacent Cu-Ta lines, according to a theoretical model for embedded structural elements. As probed on the nanometer scale by the NBOHC sensor, the interfaces were found under a substantially enhanced residual stress, characteristic for low-temperature Si/SiOx growth in the presence of metallic interconnects. CL/PS spectroscopy represents an improved tool to quantitatively monitor the residual stresses developed at SiOx/metal interfaces, thus opening the possibility to systematically engineer the interface itself in search for high-reliability Si-based devices. [ABSTRACT FROM AUTHOR]

A microscopic procedure has been proposed for evaluating the stress dependence of the (room-temperature) cathodoluminescence (CL) excitonic band emitted from the (0001) crystallographic plane of GaN in a field-emission-gun scanning electron microscope. The room-temperature near-band-gap emission (generally referred to as the excitonic band) mainly consisted of a band arising from free exciton (FX). However, an asymmetric morphology was found for the band, which thus needed to be deconvoluted into the main FX band and a shoulder. The spectral location at intensity maximum of the overall excitonic band under stress-free conditions was observed at room temperature at around 365 nm. Experimentally measured spectral shifts were precisely retrieved nearby the tip of a Vickers indentation microcrack, while CL intensity probe response functions were collected at different acceleration voltages at a sharp interface between a GaN film and its sapphire substrate. Based on these assessments, the magnitude of the piezospectroscopic coefficient (i.e., the spectral shift rate versus the trace of a biaxial stress tensor) Π=1.35±0.01 nm/GPa of the excitonic (cumulative) band of GaN could be evaluated. This study not only emphasizes the importance of microscopic piezospectroscopic calibration procedures for precise residual stress assessments in GaN-based devices, but also the need of deconvoluting the electron probe for minimizing the error involved with its finite size. [ABSTRACT FROM AUTHOR]

A spatially resolved cathodoluminescence piezospectroscopic analysis used for evaluating the stress field developed ahead of the tip of an equilibrium crack propagating in a semiconductor. The analysis has shown that a nanometer-scale spatial resolution can be achieved in stress analysis of semiconductor materials and also that a stress data treatment based on experimental probe response function (PRF) is a viable approach to reduce the error involved with the finite size of the electron probe.

A piezospectroscopic (PS) cathodoluminescence (CL) study is counducted on a Cu-Ta/Si[O.sub.x] (carbon-doped) model chip that is prepared on a Si substrate. CL/PS spectroscopy has represented an improved tool to quantitatively monitor the residual stresses developed at Si[O.sub.x]/metal interfaces.

The deformation potentials have been experimentally determined for the direct gap of n-Al0.25Ga0.75As and compared to experimental and theoretical literature values. Highly localized spectroscopic stress assessments could be achieved using a field-emission electron gun as the energy source for stimulating cathodoluminescence (CL) emission from an epitaxial thin film sample. The three independent deformation potentials for the zinc-blende-type crystal structure could be obtained from a single set of CL measurements in small material volumes of the order of the μm3, while all previously published characterizations required samples of a relatively large size (i.e., of the order of mm3). [ABSTRACT FROM AUTHOR]