Role of SiCl4_4 addition in CH3_3F/O2_2 based chemistry for Si3_3N4_4 etching selectively to SiO2_2, SiCO and Si

International audienceDry etching of amorphous silicon nitride (Si3N4) selectively toward silicon dioxide (SiO2), silicon oxicarbide (SiCO) and crystalline silicon (c-Si) in an Inductive Coupled Plasma (ICP) reactor using CHF3/O2/He chemistry with SiCl4 addition is studied. Plasma exposure of c-Si, SiO2 and SiCO leads to an oxide deposition. The deposition rate is the same for all these materials and increases linearly with the amount of SiCl4 added. On the other side, Si3N4 etching is observed at very small amount of SiCl4 added (2sccm) while oxide deposition takes place at higher SiCl4 flow (10sccm). Quasi-in situ Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) investigation shows oxifluoride SiOxFy deposition on c-Si and SiCO while a thin F-rich reactive layer is observed on Si3N4. The oxidation of Si3N4 surface followed by CHF3/O2/He chemistry with small SiCl4 addition showed that oxidation state plays a significant role on the etching / deposition equilibrium. In addition, it is found that oxifluoride deposition on Si3N4 is driven by ion energy, with deposition observed at 0 V substrate bias voltage while etching is observed for values superior to 150 V. All these results show that a competition takes place between silicon oxifluoride deposition and etching, depending on substrate material, surface oxidation and ion energy. Based on some additional Optical Emission Spectroscopy (OES) data, we proposed some insights to explain the different etching and deposition behaviors observed. It is focused on the crucial role of ion energy and the nitrogen presence in Si3N4 leading to formation of CN and HCN, helping to get a thinner reactive layer and to evacuate etch by-products on Si3N4 while an oxifluoride build-up on the other materials

Estimation de l’indice foliaire et de la biomasse du blé et des adventices par imagerie visible et machine learning : vers un nouvel indicateur non destructif de la compétition culture-adventices ?

Prod 2019-245h équipe EA équipe SPE GESTAD AGROSUP Prod 2019-245h équipe EA équipe SPE GESTAD AGROSUPNational audienceCette étude propose d’estimer précocement par imagerie deux variables clés dans la gestion des cultures et dans la compétition culture-adventices : l’indice foliaire (LAI) et la biomasse aérienne sèche (BM). Une expérimentation a été conduite au champ pendant la phase végétative d’une culture de blé. Pour chaque peuplement (culture de blé, adventices), les taux de couverture du sol par la végétation (TCc, TCw) ont été déduits du traitement d’image basé sur une technique de machine learning. LAI et BM ont été mesurés de façon destructive. Puis, une calibration a été réalisée entre TC et LAI d’une part et entre TC et BM d’autre part. Ce travail pourrait, à terme, faciliter le diagnostic de l’agriculteur dans sa gestion durable de la flore adventice avec la création d’un nouvel indicateur non destructif de la compétition culture-adventices construit à partir de simples images visibles. This study proposes to estimate very early the leaf area index (LAI) and aerial dry biomass (BM) of crop and weeds by an image approach (RGB images). A field experiment was conducted during the vegetative phase of wheat. For each stand (crop, weeds), the vegetation cover ratios (TCc, TCw) were deduced from visible images and machine learning techniques. LAI and BM were measured with destructive methods. Then, a calibration was performed between TC and LAI and between TC and BM. This work could facilitate the diagnosis of the farmer for a sustainable weed management because it aims to create a new non-destructive indicator of crop-weed competition using simple visible images

Gate spacers etching of Si3_3N4_4 using cyclic approach for 3D CMOS devices

International audienceIn this work, we optimize a CH$_3$F/O$_2$/He/SiCl$_4$ chemistry to etch silicon nitride gate spacers for 3D CMOS devices in a 300mm inductivelycoupled plasma reactor. The chemistry has high directivity and high selectivity to Si and SiO$_2$. A cyclic approach, which alternates thischemistry with a CH$_2$F$_2$/O$_2$/CH$_4$/He plasma, is investigated. Using $quasi\ in\ situ$ x-ray photoelectron spectroscopy and ellipsometry measurements,etching mechanisms are proposed to explain the results obtained. As a result of process optimization, silicon nitride spacers with verticalprofile and a small critical dimension loss of 3 nm as well as complete spacers removal on sidewalls of the active area are obtained on3D patterns, confirming the advantages of this approach

Downscaling large-scale climate variability using a regional climate model: the case of ENSO over Southern Africa

International audienceThis study documents methodological issues arising when downscaling modes of large-scale atmospheric variability with a regional climate model, over a remote region that is yet under their influence. The retained case study is El Niño Southern Oscillation and its impacts on Southern Africa and the South West Indian Ocean. Regional simulations are performed with WRF model, driven laterally by ERA40 reanalyses over the 1971-1998 period. We document the sensitivity of simulated climate variability to the model physics, the constraint of relaxing the model solutions towards reanalyses, the size of the relaxation buffer zone towards the lateral forcings and the forcing fields through ERA-Interim driven simulations. The model's internal variability is quantified using 15-member ensemble simulations for seasons of interest, single 30-year integrations appearing as inappropriate to investigate the simulated interannual variability properly. The incidence of SST prescription is also assessed through additional integrations using a simple ocean mixed-layer model. Results show a limited skill of the model to reproduce the seasonal droughts associated with El Niño conditions. The model deficiencies are found to result frombiased atmospheric forcings and/or biased response to these forcings, whatever the physical package retained. In contrast, regional SST forcing over adjacent oceans favor realistic rainfall anomalies over the continent, although their amplitude remains too weak. These results confirm the significant contribution of nearby ocean SST to the regional effects of ENSO, but also illustrate that regionalizing large-scale climate variability can be a demanding exercise

Following the phase transitions of iron in 3D with X-ray tomography and diffraction under extreme conditions

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Martensitic-like microstructures across the isostructural phase transitions in Cerium

International audienceThe isostructural gamma – alpha phase transition in elemental cerium is an electronic transition caused by a delocalization of the 4f electrons. This affects the bonding properties of Ce atoms and leads to a large volume collapse reaching 17% in the low pressure regime (¡ 2 GPa). While great attention has been drawn on the electronic description of this transition, attempts to understand the mesoscale mechanisms of this structural transition and their consequences in terms of microstructure remain scarce. We have investigated this transition by means of combined X-ray Computed Tomography and Energy Dispersive X-ray Diffraction on polycrystalline samples. Our experimental observations reveal a platelet-shape microstructure across the transition and up to the critical point, which have been associated to displacive mechanisms. Based on continuum mechanics modeling and ab initio calculations, we propose that here, this microstructure is initiated by elastic instability and shear anisotropy in the ¡100¿ directions

Quantitative 4D X-ray microtomography under extreme conditions: a case study on magma migration

International audienceX-ray computed tomography (XCT) is a well known method for three-dimensional characterization of materials that is established as a powerful tool in high-pressure/high-temperature research. The optimization of synchrotron beamlines and the development of fast high-efficiency detectors now allow the addition of a temporal dimension to tomography studies under extreme conditions. Presented here is the experimental setup developed on the PSICHE beamline at SOLEIL to perform high-speed XCT in the Ultra-fast Tomography Paris–Edinburgh cell (UToPEc). The UToPEc is a compact panoramic (165° angular aperture) press optimized for fast tomography that can access 10 GPa and 1700°C. It is installed on a high-speed rotation stage (up to 360° s −1 ) and allows the acquisition of a full computed tomography (CT) image with micrometre spatial resolution within a second. This marks a major technical breakthrough for time-lapse XCT and the real-time visualization of evolving dynamic systems. In this paper, a practical step-by-step guide to the use of the technique is provided, from the collection of CT images and their reconstruction to performing quantitative analysis, while accounting for the constraints imposed by high-pressure and high-temperature experimentation. The tomographic series allows the tracking of key topological parameters such as phase fractions from 3D volumetric data, and also the evolution of morphological properties ( e.g. volume, flatness, dip) of each selected entity. The potential of this 4D tomography is illustrated by percolation experiments of carbonate melts within solid silicates, relevant for magma transfers in the Earth's mantle