Influence of the synthesis conditions of silicon nanodots in an industrial low pressure chemical vapor deposition reactor

Experiments conducted in an industrial tubular low pressure chemical vapor deposition (LPCVD) reactor have demonstrated the reproducibility and spatial uniformity of silicon nanodots (NDs) area density and mean radius. The wafer to wafer uniformity was satisfactory (density and radius standard deviations <10%) for the whole conditions tested except for low silane flow rates, high silane partial pressures and short run durations(<20 s). Original synthesis conditions have then been searched to reach both excellent wafer to wafer uniformities along the industrial load of wafers and high NDs densities. From previous results, it was deduced that the key was to markedly increase run duration in decreasing temperature and in increasing silane pressure. At 773 K, run durations as long as 180 and 240 s have thus allowed to reach NDs densities respectively equal to 9 1011 and 6.5 1011 NDs/cm2 for the two highest silane pressures tested in the range 60–150 Pa

Development of an original model for the synthesis of silicon nanodots by Low Pressure Chemical Vapor Deposition

Using the Computational Fluid Dynamics code Fluent, a simulation model of an industrial Low Pressure Chemical Vapor Deposition reactor has been developed for the synthesis of silicon nanodots from silane SiH4 on silicon dioxide SiO2 substrates. A comparison between experimental and simulated deposition rates has shown that classical kinetic laws largely over-estimated these deposits. So, an original heterogeneous kinetic model is proposed as a first attempt to quantify the temporal evolution of deposition rates and of surface site numbers, as a function of operating conditions and of the chemical nature of substrate sites, for the early stages of silicon deposition. Contributions of silane and of the homogeneously born silylene SiH2 to nucleation and growth have been considered on different surface sites, silanol Si–OH, siloxane Si–O–Si and fresh silicon bonds. Simulations have revealed that for the conditions tested, the classical heterogeneous kinetic laws over-estimate, by more than 60%, silicon deposition during the first stages. The assumption that silylene and more largely all the unsaturated species formed in the gas phase contribute in priority to nucleation has been validated. Nucleation appears as a mandatory step to form the first fresh Si sites to allow deposition to occur from silane via growth phenomena

LPCVD synthesis of silicon nanodots from silane and for flash mamory devices

The increase of microelectronic device potentialities essentially derives from the reduction of feature size down to the nanometer scale. Multinanocrystals memories are one illustration of this trend. A multi-field study is reported, aiming to better understand phenomena involved in silicon nanocrystals elaboration. A first objective is to better control the density and the size of silicon nanocrystals formed during Low Pressure Chemical Vapor Deposition (LPCVD). Some experimental results will be presented, aiming a reliable estimation of densities and sizes of nanocrystals using several techniques: ellipsometry measurements, SEM and TEM image analysis. These experimental data have been simulated at the reactor scale using the Computational Fluid Dynamics (CFD) code FLUENT. A new kinetic scheme has been developed, which considers the various chemisorption sites existing on SiO2 substrates. This new modelling approach allows to correlate in transient mode the local composition of the gas phase near the substrate with the various sites number and with the density and the size of nanocrystals

Formulation Mixte Vitesse-Déplacement pour Viscoélasticité - Confrontation Expérimentale et Numérique

National audienceL'objectif de ce travail est de modéliser le comportement des matériaux polymère injectés sous sollicitations dynamiques par une approche monolithique. Basé sur les équations de Navier-Stokes, nous proposons une méthode des éléments finis mixtes avec une interpolation P1+/P1 utilisant le déplacement (ou la vitesse) et la pression en tant que principales variables. La technique implémentée utilise un maillage composé de triangles (2D) ou de tétraèdres (3D) [6]. Le but de cette approche est de modéliser le comportement viscoélastique des matériaux polymère où les milieux visqueux et élastiques sont mélangés en utilisant une approche multiphasique en vitesse et déplacement. L'idée de base est d'utiliser une formulation mixte (u, v, p) avec un modèle de fermeture F(du / dt,v) = 0 , où les deux champs u et v représentent les principales variables de la déformation et de la vitesse de déformation.See http://hal.archives-ouvertes.fr/docs/00/59/26/75/ANNEX/r_ABQP7S30.pd

Évaluation du stress : application à la détection des chutes

National audienceThis paper deals with the association of several physiological parameters in order to estimate a stress level that can be use in the detection of falls or the evaluation of fear of falling among elderly people

Interopérabilité et automatisme dans les etudes du Bâtiment

Les professionnels constatent des difficultés dans l’exploitation de la norme ISO dite « IFC » d’échange de données du Bâtiment, ainsi que dans la maquette numérique des projets (BIM)telle qu’elle existe aujourd’hui. Deux disciplines qui selon les auteurs sont devenues inséparables dans la conception des ouvrages. Ajouter de l’information numérique dans cette maquette ne résout pas l’essentiel attendu : son partage et sa synthèse2 entre les métiers. Pour relever le défi d’une veritable interopérabilité dans les échanges de données entre métiers, qui supposent des procédures automatisées, les auteurs imaginent un outil logiciel

Variational multiscale large eddy simulation and anisotropic mesh adaptation for transient and turbulent flows

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