Redistribution of Metallic Impurities in Si during Annealing and Oxidation: W and Fe

International audienceAtomic redistribution of W and Fe in Si were studied using secondary ion mass spectrometry and transmission electron microscopy. W diffusion experiments performed during isothermal annealing and during Si oxidation show that W atoms should use at least two different diffusion mechanisms. Experimental diffusion profiles can be well simulated by considering the simultaneous use of three different W diffusion mechanisms: the dissociative and the kick-out mechanisms, as well as an original mechanism based on the formation of a W-Si self-interstitial pair located on the interstitial Si sub-lattice. Fe redistribution was studied during the oxidation of a Fe-contaminated Si wafer. Fe is shown to be first pushed-out in Si by the mobile SiO 2 /Si interface, and thus to form Fe silicides at this interface. The silicide precipitates, which can exhibit a core-shell structure, appear to move with the SiO 2 /Si interface thanks to an oxidation/dissolution mechanism in the SiO 2 and a nucleation/growth mechanism in the Si matrix. Furthermore, the rate difference between Si and Fe silicide precipitate oxidation leads to the formation of Si pyramidal defects at the SiO 2 /Si interface

Atomic redistribution of implanted Fe and associated defects around moving SiO 2 /Si interfaces

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First stages of Ni reaction with the Si(Ge) alloy

International audienceThe Si(Ge) alloy is currently used in the Complementary Metal Oxide Semiconductor (CMOS) technology, improving device performances, decreasing power consumption, and allowing stress engineering in Sibased devices. If Si(Ge) is used in transistors' source, drain and gate, it is necessary to create ohmic contacts between the first-level metal and Si(Ge). In the current Si-based CMOS technology, ohmic contacts are created via the reaction of a thin Ni(Pt) layer with doped-Si, aiming to form a thin NiSi layer on the Si substrate. A similar process should be used on Si(Ge). In this work, the first stages of Ni reaction with Si(Ge) is investigated using high resolution transmission electron microscopy and laser-assisted atom probe tomography. The first stage of Ni/Si(Ge) reaction leads to the formation of a germanosilicide layer made of Nip(Si1-xGex)(q) nano-grains exhibiting different structures and compositions. The formation of Nip(Si1-xGex)(q) phases occurs at temperatures as low as 60 degrees C. The germano-silicide grains exhibit coherent interfaces with the Si(Ge) layer, and during their growth, a fraction of the Ge atoms initially located in Si(Ge) is pushed from the Nip(Si1-xGex)(q)/Si(Ge) interface into the Si(Ge) layer, leading to Ge accumulation at this interface. This phenomenon can cause Ge accumulation up to 100%, promoting the incorporation of Ge-pure nanometric inclusions inside the germano-silicide layer. (C) 2016 Elsevier B. V. All rights reserved

An economical and non polluting technique for the growth of GaAs on GaAs and Ge

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Mechanism of β-FeSi 2 precipitates growth-and-dissolution and pyramidal defects' formation during oxidation of Fe-contaminated silicon wafers

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New insights into thermomechanical behavior of GeTe thin films during crystallization

International audienceIn this work, we reexamine Ge rejection in Ge-rich GeTe thin films with a slight deviation from stoichiometry using a unique combination of in situ measurements: curvature and x-ray diffraction as well as electrical resistance and x-ray diffraction and reflectivity during annealing. This unique combination of several experiments performed simultaneously on a synchrotron beamline allows to monitor in situ, during the crystalliza-tion and phase transformation, the microstructure, the strain and the stress changes, as well as electrical properties of GeTe films. Structural, electrical and thermomechanical evolutions of the GeTe thin films upon annealing are shown to follow three different steps. Stage I, before crystallization, is characterized by a tensile stress variation and a small decrease of the mass density. Stage II corresponds to the rhombohedral aGeTe phase crystallization leading to an abrupt tensile stress jump (+72 MPa), a mass density increase, and followed by a slight compressive stress evolution. During stage III, Ge crystallization is observed leading to a compressive stress jump (À54 MPa), an abrupt increase in aGeTe lattice spacing and diffracted intensity, whereas aGeTe diffraction peak widths decrease. During cooling a thermoelastic behavior is observed. A detailed analysis of stage III (Ge precipitation and crystallization) is performed and discussed regarding structural , stress, microstrain, electrical and thermomechanical properties. In particular, this study reveals that crystalline Ge precipitation results in important changes (volume of the unit cell, homogeneity of lattice spacing, average stress. . .) in the surrounding GeTe matrix. Different scenarios are proposed to understand these results

Stress Buildup Upon Crystallization of GeTe Thin Films: Curvature Measurements and Modelling

International audiencePhase change materials are attractive materials for non-volatile memories because of their ability to switch reversibly between an amorphous and a crystal phase. The volume change upon crystallization induces mechanical stress that needs to be understood and controlled. In this work, we monitor stress evolution during crystallization in thin GeTe films capped with SiOx, using optical curvature measurements. A 150 MPa tensile stress buildup is measured when the 100 nm thick film crystallizes. Stress evolution is a result of viscosity increase with time and a tentative model is proposed that renders qualitatively the observed features

Fantasmagories du Moyen Âge

Arthur et ses chevaliers de la Table Ronde, Tristan et Yseut, mais aussi Jeanne d'Arc et Charles VII, le poète Villon sont autant de figures du passé médiéval dans lesquelles se reconnaît notre époque. Cet âge reculé se révèle être une source privilégiée d'inspiration avec laquelle les artistes engagent une relation à chaque fois renouvelée. Ainsi en est-il de la littérature des XIXe et XXe siècles, du Romantisme à l'Oulipo et en particulier la fantasy sous l'ombre tutélaire du grand Tolkien. Les supports d'un nouvel imaginaire médiéval sont multiples et fertiles, qu'il s'agisse de l'illustration inspirée de l'art des manuscrits, des études historiques scientifiques aux élucubrations fantaisistes et ésotériques. La chanson contemporaine, l'agencement des jardins ou bien les jeux de rôles, ces univers actuels nous proposent un jeu de miroir avec l'époque médiévale. Ce livre nous invite à un étrange et fécond dialogue entre les siècles