Alexandre Crisci

Micro-Raman scattering from undoped and phosphorous-doped (111) homoepitaxial diamond films: Stress imaging of cracks

We report postgrowth micro-Raman stress imaging of cracks in (111) homoepitaxial diamond films. Undoped and phosphorous-doped diamond thin films grown by microwave plasma-enhanced chemical-vapor deposition on Ib (111)-oriented diamond substrates have been studied by confocal micro-Raman spectroscopy. For comparison purposes, a film grown on a (100) Ib substrate was also examined. Thanks to the confocal optics, the Raman signal arising from the epilayer could be discriminated from that arising from the substrate. As was already reported, the (111) films exhibited substantial tensile stress, indicated by a downshift in the Raman peak and by spontaneous cracking in films grown thicker than 5μm. The sixfold symmetry of the cracks supported that the films were homoepitaxial. A high compressive stress was also detected at the substrate near surface, and a partial stress relaxation was observed to occur in the vicinity of the cracks. Possible origins of the high tensile stress observed in the (111) homoepitaxial...

Strain in epitaxial Si/SiGe graded buffer structures grown on Si(100), Si(110), and Si(111) optically evaluated by polarized Raman spectroscopy and imaging

We report on the characterization, thanks to Raman spectroscopy and imaging of tensely strained Si films pseudomorphically grown on (001), (110), and (111) SiGe virtual substrates. The samples studied here are those described in the work of Destefanis et al. [J. Appl. Phys 106, 043508 (2009)]. They consist in 17-nm-thick strained Si layers grown at 650 °C with SiH4 as a gaseous precursor on top of polished SiGe virtual substrates of various surface orientations. We first derived the exact component array of the strain/stress field along the different growth directions. Because the relation between strain or stress and the Raman frequencies are complex, we also derive the strain-shift coefficients for the different substrate orientations considered in this work and the polarization selection rules. Visible and near-UV Raman spectroscopies were used to extract the in-plane lattice parameter of the SiGe virtual substrates and the tensile strain in the thin Si epitaxial layers on top. We have notably investig...

Structural properties of tensily strained Si layers grown on SiGe(100), (110), and (111) virtual substrates

We have studied the structural properties of tensily strained Si (t-Si) layers grown by reduced pressure–chemical vapor deposition on top of SiGe(100), (110), and (111) virtual substrates (VSs). Chemical mechanical planarization has been used beforehand to eliminate the as-grown surface crosshatch on all orientations and reduce by 10 up to 100 times the surface roughness. A definite surface roughening has occurred after the epitaxy of t-Si on (110) and (111). For the lowest Ge contents investigated, top Si(100) and (110) layers are locally “defect-free” whereas numerous {111} stacking faults are present in the t-Si(111) layers. For higher Ge content SiGe VS, a degradation of the crystallographic quality of (110) and (111) t-Si layers has been evidenced, with the presence of dislocations, stacking faults, and twins. Quantification of the strain level in the t-Si layers has been carried out using visible and near-UV Raman spectroscopy. The Ge contents in the VS determined by Raman spectroscopy were very clo...

Thermal Alumina Scales on FeCrAl: Characterization and Growth Mechanism

High temperature oxidation resistance of alumina-forming materials is connected to the growth of dense, stable and protective alumina scales. Depending on temperature, impurities present in the base alloys, presence of water vapour in the oxidizing atmosphere, the alumina scales are composed of alpha-alumina (which is the stable phase obtained for temperatures over 1000°C) or of transient alumina (γ,θ,δ obtained for lower temperatures). It is generally considered that γ- Al2O3 grows when T<850°C, that θ-Al2O3 is present for 850°C<T<1000°C and that α-Al2O3 is stable when T exceeds 1000°C. The exact role played by transient alumina formation and/or transformation on the high temperature performances of alumina-forming materials is not exactly defined. Many works proposed that transient alumina phases grew during the first steps of the oxidation process and transformed into the stable phase after further oxidation. The transformation of transient phases in the stable alphaphase is generally accompanied by a volume contraction of around 14 %. In order to get better oxidation resistance, the formation of transient alumina is not wished, because: 1) their growth rate is generally higher than that of alpha-alumina with, as a consequence, a huge Al consumption, detrimental for the material resistance after long exposures, 2) the change in volume during the transformation of transient phases into alpha-alumina can generate stresses in the oxide scale and can weaken its adherence to the underlying substrate, leading to massive spallation. The present study deals with the coupling of different characterization tools in order to precisely identify the transient phases grown on FeCrAl materials. The use of scanning electron microscope (SEM-FEG), transmission electron microscope (TEM), Photoluminscescence Spectroscopy(PLS), X-ray photoelectron spectrometry (XPS) and X-ray diffraction at different glancing angles (XRD) on model materials oxidized at two temperatures (850 and 1100°C) could help the identification of transient phases. These techniques gave a better understanding of the alumina scale growth mechanism.

Practical Aspects of Carbon Content Determination in Carburized Steels by EPMA

The carbon contents in carburized steels were investigated by electron probe microanalysis (EPMA) for a range of carbon levels in the solid solution less than 1 wt%. This article describes the difficulties encountered with the classic analytical procedure using the k ratio of X-ray intensities and the phi(rhoz) model. Here, a suitable calibration curve method is presented with emphasis on the metallographic study of standard specimens and on the carbon decontamination of samples.

Raman Imaging Analysis of SiC Wafers

Recent improvements in the implementation of the technique make Rama n spectroscopic imaging possible. Different systems have been developed to reduc e recording and display times to reasonable levels. In this study, we have performed Raman imagin g measurements for different 4HSiC wafers, and some test experiments performed on defective sam ple will be presented. Results were qualitatively interpreted in terms of residual strain fie lds and variations in the carrier concentration in the vicinity of the defects. Introduction In view of its excellent thermal, mechanical, chemical and el ectrical properties, silicon carbide (SiC) is an important semiconductor material for high-temperatur e and high-power devices and for a variety of other applications as well. Although SiC technology has re ched the market-place, the frequent occurrence of defects or nonuniform electrical propert ies is still a serious and persistent problem. Because of these nonuniform properties, some bulk measurements ma y be difficult to interpret, and more local probes are necessary to characterize bot h the structural and electrical properties in SiC wafers. It is known that micro-Raman spectroscopy is a powerful technique for the characterization of SiC: it is non destructive and requires no special preparation of the sam ples. Polytype identification by Raman scattering is possible. Moreover, the Raman parameters suc h a intensity, width, peak frequency and polarization of the strong and weak Raman bands provide fruit ful information both on the structural and the electronic properties of the samples [1]. Finally, recent improvements in the implementation of the technique make Raman spectroscopic imagin g possible. Different systems have been developed to reduce recording and display times to r ea onable levels, and it is now technically possible to produce Raman images with spatial resolut ion better than 1 μm within some hours. Such spectrometers have been used in our group to look for strain fields or impurities in diamond coatings or crystals [2,3]. Other systems have been used to study strain fields or impurities in semi-conducting materials like GaN [4] or SiGe[5]. In this study, we have performed Raman imaging measurements f or different 4H-SiC wafers, and some test experiments performed on defective samples will be presented. First, the method has been used as a full wafer mapping tool, with a rather low spatial resolution ( ≈500μm). Examination of the spectra yielded spatial maps of the carrier concentration. Second, defects (micropipes in particular) were optically detected and studied w ith micron resolution. Results were qualitatively interpreted in terms of residual strain fields and variations in the carrier concentration in the vicinity of the defects. Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 353-356 doi:10.4028/www.scientific.net/MSF.433-436.353

Raman Imaging Characterization of Structural and Electrical Properties in 4H SiC

Raman imaging measurements have been used to determine the spatial distribution of the doping level in n-type 4H-SiC wafers. The carrier concentration and mobility were determined from the line shape analysis of the LO phonon-plasmon coupled mode, using know procedures. The application of the method for mapping of the doping level at the wafer scale as well as in the vicinity of defects, for example micropipes, is demonstrated. Introduction Raman scattering is a powerful technique for the characterization of SiC. It is known that polytype identification by Raman scattering is possible [1]. Moreover, the Raman parameters such as intensity, width, peak frequency and polarization of Raman bands provide fruitful information both on the structural and the electronic properties of the samples [1,2]. The use of modern instrumentation now allows obtaining Raman maps or images within a few hours. Such spectrometers were used in our group to look for parasitic phases, strain fields, impurities... in diamond coatings or crystals [3,4]. They were also used to study the spatial distribution of defects or dopants in 4H SiC wafers [5-7]. As already mentioned, an important feature of Raman spectroscopy in semiconductors is that it provides information on the electrical properties. In this study, n-type 4H-SiC wafers were examined, and the carrier concentration and mobility were determined from the line shape analysis of the LO phonon-plasmon coupled mode, using know procedures [1,2]. The present method will be used as a full wafer mapping tool with a rather low spatial resolution, 100-500 μm, depending on the samples. It will also be used to image the electrical properties of samples in the vicinity of defects, micropipes in particular, with true micron resolution.

Local strain measurements in shallow trench insulator structures using near-ultraviolet Raman spectroscopy: Simulation and experiment

Shallow trench insulator (STI) stress induced in active lines has been investigated both by near-ultraviolet (UV) Raman spectroscopy and mechanical modelization. Two different STI processes have been compared. The influence of the linewidth is also studied. After adjusting some instrumental and material parameters, all components of the stress tensors have been determined accurately. The polarization of the incoming light is discussed, showing that the selection rules are no longer respected at the edges of the STIs. Some of the limitations in spatial resolution of the Raman spectroscopy have been overcome, making use of the mechanical model and taking benefit from the higher spatial resolution of the UV excitation. In turn, the mechanical model has been refined from comparisons with experiments. It is therefore suggested that coupling these techniques may provide a relevant method to measure stress in the silicon for the integrated circuit industry. From a practical viewpoint, it is demonstrated that the use of the subatmospheric chemical vapor deposition process allows significant reduction of the compressive stress in the center of the active lines.

Growth and Characterization of Thick Polycrystalline AlN Layers by HTCVD

Thick polycrystalline AlN layers were grown at low pressure using high temperature chemical vapor deposition (HTCVD). The experimental setup consists of a graphite susceptor heated by an induction coil surrounding a vertical cold wall reactor. The reactants used were ammonia (NH(3)) and aluminum chloride (AlCl(x)) species formed in situ via chlorine (Cl(2)) reaction with high purity aluminum wire. AlN films were deposited on a 55 mm diameter graphite susceptor between 1200 and 1600 degrees C. AlN layers have been characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electron backscattered diffraction. The influence of temperature on growth rate, surface morphology, grain size, and crystalline structure is presented. Growth rates of up to 230 mu m/h have been reached. A nonpolar preferred orientation of AlN films is stabilized at a higher temperature. The potential of investigation in this new range of experimental conditions, i.e., high temperature and high growth rate, as well as deposition of nonpolar AlN crystals, is very promising for epitaxial growth and extends the field of applications

PEALD ZrO2 Films Deposition on TiN and Si Substrates

a STMicroelectronics 850 rue Jean Monnet 38926 Crolles, France. b SIMaP, Grenoble-INP-CNRS-UJF, 1130 rue de la piscine 38402 Saint Martin d’Heres, France. c CMTC, Grenoble-INP, 1260 rue de la piscine 38402 Saint Martin d’Heres, France. d ESRF 6 rue Jules Horowitz 38043 Grenoble, France. e CEA-LETI, Minatec 17 rue des Martyrs 38054 Grenoble, France. f LPCML, Universite Lyon 1 UMR 5620, CNRS, 10 rue Andre-Marie Ampere 69622 Villeurbanne, France.