Développement du pompage de charges pour la caractérisation in-situ de nanocristaux de Si synthétisés localement dans SiO2 par implantation ionique basse énergie et lithographie stencil

Le regain d'attention des industriels pour les mémoires non volatiles intégrant des nanocristaux, illustré par l'introduction sur le marché de la Flexmemory de Freescale en technologie 90 nm, incite à poursuivre des études sur ce type de systèmes. Pour cela, nous avons mis au point des cellules mémoires élémentaires, à savoir des transistors MOS dont l'oxyde de grille contient une grille granulaire formée par un plan de nanocristaux de silicium (Si-ncx) stockant la charge électrique.Ce travail présente les principaux résultats issus de ces travaux, ceux-ci allant du procédé de fabrication à la caractérisation fine des dispositifs mémoires. Le parfait contrôle de l'élaboration de la grille granulaire de Si-ncx par implantation ionique à très basse énergie (ULE-IBS) est accompagné de caractéristiques mémoires répondant aux normes industrielles d'endurance et d'une discrimination des pièges responsables du chargement. Le stockage majoritaire par les Si-ncx est démontré, ce qui est essentiel pour la rétention de la charge. Nous avons développé une technique électrique permettant d'extraire à la fois la quantité de charge stockée par les Si-ncx mais également leurs principales caractéristiques structurales (taille, densité, position dans l'oxyde). Cette extension de la technique électrique de pompage de charges , non destructive et in-situ permet de suivre l'état du composant en fonctionnement et de caractériser des pièges (e.g. les Si-ncx) pour la première fois au-delà de 3 nm de profondeur dans l'oxyde. Ces résultats ont été validés par des observations TEM. La résolution du pompage de charge étant le piège unique, nous avons alors couplé l'ULE-IBS avec la lithographie Stencil pour réduire latéralement le nombre de Si-ncx synthétisés. Cette technique nous permet pour le moment de contrôler la synthèse locale à la position désirée dans l'oxyde de poches de Si-ncx de 400 nm. La synthèse de quelques Si-ncx est envisagée à très court terme. Nous serons alors en mesure de fabriquer des mémoires à nombre choisi de nanocristaux (par SM-ULE-IBS), dont les propriétés structurales (taille, densité, position) et électriques (quantité de charge stockée) seront vérifiées par pompage de charge, offrant ainsi des outils puissants pour la fabrication et la caractérisation de mémoires à nombre réduit de nanocristaux, notamment pour des longueurs de grilles inférieures à 90 nmThe aim of this thesis has been to fabricate and electrically characterize elementary memory cells containing silicon nanocrystals (Si-ncs), in other words MOSFET which insulating layer (SiO2) contains a Si-ncs array storing the electrical charge. We have shown that we perfectly control the synthesis of a 2D array of 3-4 nm Si-ncs embedded into the MOSFET oxide by low-energy ion implantation (1-3 keV) Reaching this goal implied two key steps: on the one hand develop a reliable MOSFET fabrication process incorporating the Si-ncs synthesis steps and on the other hand develop tools and methods for both memory window and Si-ncs array itself characterizations. We have developed an in-situ characterization technique based on the well-known charge pumping technique, allowing for the first time the extraction of traps depth (e.g. the Si-ncs array) further than 3 nm into the oxide layer leading to the characterization of both position of these Si-ncs into the SiO2 matrix and their structural properties (diameter, density). These results have been confirmed by EF-TEM measurements. Finally, we have worked on the improvement of controlled local synthesis of Si-ncs pockets by combining low-energy ion implantation and stencil lithography. We reduced the size of these pockets down to about 400 nm using this parallel, low cost and reliable technique and identified the limiting effect for the pockets size reduction. These results pave the way for memory cells containing a few Si-ncs with a well-defined position into the oxide and a well-controlled number of ncsTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Structured ZnO-based contacts deposited by non-reactive rf magnetron sputtering on ultra-thin SiO2/Si through a stencil mask

In this paper, we study the localized deposition of ZnO micro and nanostructures deposited by non-reactive rf-magnetron sputtering through a stencil mask on ultra-thin (10 nm) SiO2 layers containing a single plane of silicon nanocrystals (NCs), synthetized by ultra-low energy ion implantation followed by thermal annealing. The localized ZnO-deposited areas are reproducing the exact stencil mask patterns. A resistivity of around 5×10−3 Ω cm is measured on ZnO layer. The as-deposited ZnO material is 97% transparent above the wavelength at 400 nm. ZnO nanostructures can thus be used as transparent electrodes for Si NCs embedded in the gate-oxide of MOS devices

Couches supportées et membranes ultraminces à base de silicium (fabrication et spectrométrie raman-brillouin)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

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

International audienc

Amorphization, recrystallization and end of range defects in germanium

International audienceThe controlled doping of germanium by ion implantation is a process which requires basic research before optimization. For this reason, we have experimentally studied by transmission electron microscopy both the kinetics of amorphization and of recrystallization of Ge during ion implantation (Ge, P and B) and further annealing. As in Si, the crystalline to amorphous phase transition occurs through the linear accumulation of damage with the dose until a certain threshold is reached above which the material turns amorphous. We show that the Critical Damage Energy Density (CDED) model can be used in germanium to predict the existence, position and extension of amorphous layers resulting from the implantation of ions for almost all mass/energy/dose combinations reported here and in the literature. During annealing, these amorphous layers recrystallize by solid-phase epitaxy following an Arrhenius-type law which we have determined. We observe that this regrowth results in the formation of extended defects of interstitial type. During annealing these defects evolve in size and density following an Ostwald ripening mechanism which becomes non-conservative (defects “evaporate”) as the temperature is increased to 600 °C. These results have important implications for the modeling of diffusion of implanted dopant in Ge. Transient diffusion may also exist in Ge, driven by an interstitial component usually not evidenced under equilibrium conditions

Hybrid systems with Ag nanocrystals and Si nanostructures synthesized by ultra-low-energy ion beam synthesis

International audienceHybrid systems based on silicon and silver nanocrystals (Si-NCs and Ag-NCs) are of considerable interest in photon conversion solar cells. Due to their plasmonic properties, Ag-NCs strongly increase the photoluminescence emission intensity of Si-NCs located in their vicinity, allowing, in principle, to solve the problem of their low emission yield. In this work, we have elaborated 2D networks of Ag-NCs and amorphous Si nanoparticles in a controlled way by using Ultra-Low-Energy Ion-Beam-Synthesis. In the proposed synthesis scheme, a 2D layer of Si-NCs is first obtained by implanting Si+ ions at ultra low energy (from 1 to 3 keV) in a SiO2 layer with subsequent high temperature thermal annealing. Then, Ag+ ions are implanted in the same matrix at energies between 3 and 10 keV and crystalline Ag-NCs are formed during the implantation step. Several configurations with either 2D arrays or a large band of Ag-NCs have been obtained following the Ag+ implantation energy. Enhancement of the PL emission from Si nanostructures, which is related to the presence of Ag-NCs, has been observed under specific arrangement of the two embedded subsystems. In this type of synthesis, a combination of physical phenomena including ion mixing, implantation damage, point defect, and thermal diffusion has been taken into account in order to explain and thus control the structural and the optical characteristics of the system

Ultra-low-energy ion-beam synthesis of nanometer-separated Si nanoparticles and Ag nanocrystals 2D layers

International audience2D networks of Si and Ag nanocrystals have been fabricated in the same SiO2 matrix by Ultra-Low-Energy Ion-Beam-Synthesis. Our synthesis scheme differs from a simple sequential ion implantation and its key point is the control of the matrix integrity through an appropriate intermediate thermal annealing. Si nanocrystal layer is synthesised first due to high thermal budget required for nucleation, while the second Ag nanocrystal plane is formed during a subsequent implantation due to the high diffusivity of Ag in silica. The aim of this work is to show how it is possible to overcome the limitation related to ion mixing and implantation damage to obtain double layers of Si-NCs and Ag-NCs with controlled characteristics. For this, we take advantage of annealing under slight oxidizing ambient to control the oxidation of Si-NCs and the Si excess in the matrix. The nanocrystal characteristics and in particular their position and size can be adjusted thanks to a compromise between the implantation energy, the implanted dose for both Si and Ag ions and the intermediate annealing conditions (atmosphere, temperature and duration)

Scaling size of the interplay between quantum confinement and surface related effects in nanostructured silicon

International audienceSi nanocrystals (NCs) embedded in a SiO2 matrix provide an exemplar curved nanostructured interface to evidence the competition between surface states and quantum confinement (QC) effects. The study of the energy band alignment as a function of NCs size (<5 nm) clarifies their interplay and identifies, with subnanometric resolution, three different regimes. Primarily QC affects the conduction band, then surface effects pin the conduction states, and finally QC starts to modify the valence band. A way to study how different nanoscale configurations compete with pure quantum properties is established

Silicon crystallization in nanodot arrays organized by block copolymer lithography

cited By 2International audienceAsymmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymers are used to fabricate nanoporous PS templates with different pore diameter depending on the specific substrate neutralization protocol. The resulting polymeric templates are used as masks for the subsequent deposition of a thin (h = 5 nm) amorphous Si layer by electron beam evaporation. After removal of the polymeric film and of the silicon excess, well-defined hexagonally packed amorphous Si nanodots are formed on the substrate. Their average diameter (d &lt; 20 nm), density (1.2 × 1011 cm−2), and lateral distribution closely mimic the original nanoporous template. Upon capping with SiO2 and high temperature annealing (1050 °C, N2), each amorphous Si nanodot rearranges in agglomerates of Si nanocrystals (d &lt; 4 nm). The average diameter and shape of these Si nanocrystals strongly depend on the size of the initial Si nanodot

Experimental investigation of the vibrational density of states and electronic excitations in metallic nanocrystals

cited By 12International audienceAn investigation of the vibrational density of states (VDOS) in silver nanocrystals is performed using Raman scattering. A specific sample architecture, setup configuration, and original elaboration process are used in order to take simultaneously advantage of spectrally and spatially localized surface plasmon resonance, optical amplification, and dark-field spectroscopy. Disentangling the contributions of atom vibrations and electron-hole excitations (i.e., the so-called "background" in surface-enhanced Raman scattering) is performed. The extracted VDOS is successfully compared with theoretical ones obtained by atomic scale simulations. The effects of size, strain, and disorder on the VDOS are analyzed; in particular, the strain effect is investigated experimentally using the geometrical phase analysis coupled with high-resolution transmission electron microscopy. This work offers an opportunity to examine thermodynamic properties, like specific heat, at the nanoscale