Stress transfer in ultimate transistors through SiN deposits: study by electron holography and finite element modelling

Longtemps considérées comme pénalisantes, les contraintes sont aujourd'hui utilisées sciemment pour fabriquer des transistors CMOS de dernière génération car elles permettent d'augmenter très sensiblement la mobilité des porteurs dans le silicium et donc la vitesse des dispositifs type MOS. L'utilisation de couches fortement contraintes qui, déposées sur un transistor, introduisent une déformation élastique dans la région électriquement active du dispositif, est une solution très prometteuse. A cette fin, les couches amorphes de Nitrure de Silicium (SiN) sont particulièrement intéressantes car elles sont peu couteuses à fabriquer et compatibles avec les technologies MOS. Cependant, l'optimisation de ce procédé de mise sous contrainte impose de connaître précisément les propriétés mécaniques de ces couches. Celles-ci étant très dépendantes des conditions d'élaboration et donc des lieux de production, ces propriétés sont en général pas connues. La récente invention de l'Holographie Electronique en Champ Sombre (Dark Field Electron Holography, DFEH), qui permet de mesurer des distributions de déformations avec un champ de vue de l'ordre du micromètre, une résolution spatiale nanométrique et une très bonne précision (10-4), ouvre de nouvelles perspectives dans ce domaine. Le but de ce travail de thèse était d'étudier, en couplant des mesures DFEH à des Modélisations par Eléments Finis (FEM), les déformations transférés par des couches de SiN amorphe déposées sous des conditions communément utilisées dans l'industrie microélectronique. Dans un premier temps, j'ai étudié les déformations introduites dans des structures modèles composées de motifs de Silicium recouvert par un dépôt de SiN. Ce faisant, j'ai pu développer le concept générique de "capteur de déformation". L'idée est d'utiliser un matériau cristallin bien connu comme un "capteur" pour étudier les déformations cristallines introduites en son sein par une couche déposée. La confrontation avec des simulations par éléments finis (FEM) permet ensuite de déterminer les caractéristiques mécaniques (contrainte interne et module de Young) de ces couches déposées. Pour me rapprocher de la structure réelle de dispositifs MOS, j'ai ensuite étudié puis expliqué les déformations introduites par un réseau de lignes de poly-Si déposé sur un substrat de silicium, lui-même recouvert par une couche de SiN contraint. Doté de cette méthodologie, j'ai finalement étudié la distribution des déformations dans de " vrais " dispositifs MOSFETs (type "n" et "p") réalisés en technologie "28 nm". Plus précisément, je me suis attaché à comprendre l'effet des différentes étapes technologiques sur la distribution des déformations dans des dispositifs " complets ". J'ai ainsi pu mettre en évidence que l'introduction de certains " éléments " (spacers, contacts) ou la réduction de "taille" peuvent sensiblement affecter/réduire les effets bénéfiques espérés grâce à cette approche technologique.For long time considered as detrimental, stress is now an integral feature of ultimate MOS technology because it considerably increases the carrier mobility in silicon, hence it can be used to boost device performances. The use of highly stressed layers deposited over the transistor for introducing an elastic deformation in the electrically active region of the device is a very promising solution. For that, silicon nitride (SiN) amorphous layers are particularly interesting because they are cheap and compatible with MOS technology. However, the optimization of this method for stress transmission requires the precise knowledge of the mechanical properties of these layers. Being highly dependent on the fabrication parameters and thus on the production sites, these properties are generally unknown. The recent invention of Dark Field Electron Holography (DFEH), which allows strain fields to be mapped over micro-scale fields of view, with nanometric spatial resolution and high precision (10-4), opens new perspectives in this field. The aim of this thesis was to investigate, by combining DFEH measurements and Finite Element Modelling (FEM), the strain transferred by amorphous SiN layers deposited under conditions commonly used in the microelectronics industry. At first, I studied the strain introduced in model structures composed of silicon patterns covered by a SiN deposit. While doing this, I have developed the generic concept of "strain sensor". The idea is to use a well-known crystalline material as a "sensor" to study the crystal deformations introduced by a deposited layer. The comparison with finite element simulations (FEM) allows one to determine the mechanical properties (internal stress and Young's modulus) of these deposited layers. Then, to get closer to the actual structure of MOS devices, I studied and explained the strain introduced by an array of poly-Si lines deposited on a silicon substrate, covered by a stressed layer of SiN. Using this approach, I finally studied the strain distribution in "real" MOSFET devices ("n" and "p" types) made by the "28 nm" technology node. More precisely, I sought to understand the effect of the different technological steps on the final strain distribution in "complete" devices. I was able to show that the introduction of some "components" (spacers, contacts) or the reduction of "size" can significantly affect/reduce the beneficial effects expected using this technological approach

SiNx:Tb3+--Yb3+, an efficient down-conversion layer compatible with a silicon solar cell process

SiN x : Tb 3+-Yb 3+, an efficient down-conversion layer compatible with silicon solar cell process Abstract Tb 3+-Yb 3+ co-doped SiN x down-conversion layers compatible with silicon Photovoltaic Technology were prepared by reactive magnetron co-sputtering. Efficient sensitization of Tb 3+ ions through a SiN x host matrix and cooperative energy transfer between Tb 3+ and Yb 3+ ions were evidenced as driving mechanisms of the down-conversion process. In this paper, the film composition and microstructure are investigated alongside their optical properties, with the aim of maximizing the rare earth ions incorporation and emission efficiency. An optimized layer achieving the highest Yb 3+ emission intensity was obtained by reactive magnetron co-sputtering in a nitride rich atmosphere for 1.2 W/cm${}^2$ and 0.15 W/cm${}^2$ power density applied on the Tb and Yb targets, respectively. It was determined that depositing at 200 {\textdegree}C and annealing at 850 {\textdegree}C leads to comparable Yb 3+ emission intensity than depositing at 500 {\textdegree}C and annealing at 600 {\textdegree}C, which is promising for applications toward silicon solar cells.Comment: Solar Energy Materials and Solar Cells, Elsevier, 201

Diagnóstico de las nuevas tecnologías empleadas para el diseño de mezclas asfálticas densas en caliente MDC-2

El presente trabajo pretende brindar alternativas de modificación de las Mezclas Asfálticas Densas en Caliente, empleadas para la pavimentación de las vías en Colombia, mecanismos que actualmente generan un impacto ambiental negativo debido a la utilización de los materiales pétreos, los cuales debido a su ubicación no cumplen con las especificaciones técnicas o son de difícil acceso en algunas zonas de nuestro país. Es por ello que estudios realizados han demostrado que la fabricación de mezclas con asfalto convencional no han sido suficientes para soportar la acción del tránsito y el clima, por lo tanto se ha recomendado emplear modificadores o aditivos en las mezclas, con el fin de mejorar las características o propiedades geológicas tanto del cemento asfáltico como de las mezclas asfálticas, así como emplear desechos de materiales que generan un alto impacto en el ambiente

Transfert de contraintes dans les tranisitors ultimes via des dépôts SiN (étude par holographie électronique et modélisation par éléments finis)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Vibrational density of states and thermodynamics at the nanoscale: the 3D-2D transition in gold nanostructures

International audienceSurface enhanced Raman scattering (SERS) is generally and widely used to enhance the vibrationalfingerprint of molecules located at the vicinity of noble metal nanoparticles. In this work, SERS isoriginally used to enhance the own vibrational density of states (VDOS) of nude and isolated goldnanoparticles. This offers the opportunity of analyzing finite size effects on the lattice dynamics whichremains unattainable with conventional techniques based on neutron or x-ray inelastic scattering. Byreducing the size down to few nanometers, the role of surface atoms versus volume atoms becomedominant, and the “text-book” 3D-2D transition on the dynamical behavior is experimentallyemphasized. “Anomalies” that have been predicted by a large panel of simulations at the atomic scale,are really observed, like the enhancement of the VDOS at low frequencies or the occurrence of localizedmodes at frequencies beyond the cut-off in bulk. Consequences on the thermodynamic properties atthe nanoscale, like the reduction of the Debye temperature or the excess of the specific heat, have beenevaluated. Finally the high sensitivity of reminiscent bulk-like phonons on the arrangements at theatomic scale is used to access the morphology and internal disorder of the nanoparticles

Ultra-low-energy Ion Beam Synthesis for Nanotechnology and Nanostructures

International audienc

Epitaxial Growth of a Gold Shell on Intermetallic FeRh Nanocrystals

International audienceIn contrast with bimetallics, multimetallic nanoparticle (NPs) can combine different chemical orders in the same NP, whichfavors an enhanced tuning of their properties. In this work, trimetallic (Fe, Rh, Au) nanocrystals with controlled composition and chemicaldistribution were grown through a physical vapor deposition route using a two-step process. First FeRh nanocrystals, 8.5 nm of mean diameter,were formed according to a Volmer−Weber growth mode. The growth conditions were tuned so as to achieve the atomic scale chemical orderdisplayed by the intermetallic B2-FeRh phase. Then the gold layer was deposited at a lower temperature. Evidence is given for the completecoverage of the gold shell, which grows epitaxially over the B2-FeRh core exposed facets. These different features are particularly promising forfurther applications

Equilibrium shape of core(Fe)–shell(Au) nanoparticles as a function of the metals volume ratio

International audienceThe equilibrium shape of nanoparticles is investigated to elucidate the various core–shell morphologies observed in a bimetallic system associating two immiscible metals, iron and gold, that crystallize in the bcc and fcc lattices, respectively. Fe–Au core–shell nanoparticles present a crystalline Fe core embedded in a polycrystalline Au shell, with core and shell morphologies both depending on the Au/Fe volume ratio. A model is proposed to calculate the energy of these nanoparticles as a function of the Fe volume, Au/Fe volume ratio, and the core and shell shape, using the density functional theory-computed energy densities of the metal surfaces and of the two possible Au/Fe interfaces. Three driving forces leading to equilibrium shapes were identified: the strong adhesion of Au on Fe, the minimization of the Au/Fe interface energy that promotes one of the two possible interface types, and the Au surface energy minimization that promotes a 2D–3D Stranski–Krastanov-like transition of the shell. For a low Au/Fe volume ratio, the wetting is the dominant driving force and leads to the same polyhedral shape for the core and the shell, with an octagonal section. For a large Au/Fe ratio, the surface and interface energy minimizations can act independently to form an almost cube-shaped Fe core surrounded by six Au pyramids. The experimental nanoparticle shapes are well reproduced by the model, for both low and large Au/Fe volume ratios

Morphology and symmetry driven by lattice accommodation in polycrystalline bcc-fcc core-shell metallic nanoparticles

Bcc-fcc multi-metallic nanoparticles associating a single-crystal core (Fe, FeCo alloys…) with a polycrystalline noble metal shell (Au, AuAg alloys …) are perfectly symmetrical or more irregular, even dramatically dissymmetrical, yet presenting a good crystalline organization. Here a combination of experimental analysis and theoretical symmetry analysis is proposed, in order to provide a unified description of the observed morphologies (Fe-Au and Fe-AuAg systems), whatever their symmetry, and predict some morphology variability in a population of nanoparticles. First the central role of the crystal lattice accommodation is comprehensively analyzed from the experimental Fe-AuAg system. The two possible bcc-fcc epitaxial relationships generate a core-shell interface in the shape of a truncated rhombic dodecahedron. This results in two different types of grains in the shell which are elastically accommodated between them by an equal distribution of twins and low angle grain boundaries, however at the cost of internal stresses. At the same time, a symmetry breaking results from two possible growth variants originating from the Nishiyama-Wasserman epitaxial relationships. The shell grains fit together in a nano-puzzle-like organization, resulting in a large number of possible arrangements distributed in 13 different point groups of symmetry, all of lower order than the core symmetry (highest order of cubic symmetry). If the variants are randomly distributed, the probability for the nanoparticle to be asymmetric (group 1) is 80%. The dissymmetrical development of the nanoparticles is then discussed. Extending this approach to other core shapes succeeds in predicting dissymmetrical or dramatically off-centered morphologies experimentally observed in Fe-Au nanoparticles

Morphology and symmetry driven by lattice accommodation in polycrystalline bcc-fcc core-shell metallic nanoparticles

Bcc-fcc multi-metallic nanoparticles associating a single-crystal core (Fe, FeCo alloys…) with a polycrystalline noble metal shell (Au, AuAg alloys …) are perfectly symmetrical or more irregular, even dramatically dissymmetrical, yet presenting a good crystalline organization. Here a combination of experimental analysis and theoretical symmetry analysis is proposed, in order to provide a unified description of the observed morphologies (Fe-Au and Fe-AuAg systems), whatever their symmetry, and predict some morphology variability in a population of nanoparticles. First the central role of the crystal lattice accommodation is comprehensively analyzed from the experimental Fe-AuAg system. The two possible bcc-fcc epitaxial relationships generate a core-shell interface in the shape of a truncated rhombic dodecahedron. This results in two different types of grains in the shell which are elastically accommodated between them by an equal distribution of twins and low angle grain boundaries, however at the cost of internal stresses. At the same time, a symmetry breaking results from two possible growth variants originating from the Nishiyama-Wasserman epitaxial relationships. The shell grains fit together in a nano-puzzle-like organization, resulting in a large number of possible arrangements distributed in 13 different point groups of symmetry, all of lower order than the core symmetry (highest order of cubic symmetry). If the variants are randomly distributed, the probability for the nanoparticle to be asymmetric (group 1) is 80%. The dissymmetrical development of the nanoparticles is then discussed. Extending this approach to other core shapes succeeds in predicting dissymmetrical or dramatically off-centered morphologies experimentally observed in Fe-Au nanoparticles