Study of defects induced by excimer laser annealing in silicon

La micro-électronique est un domaine exigeant, en constante évolution, motivé par le secteur applicatif et les besoins des utilisateurs. La réalisation de jonctions ultra-minces et fortement dopées est un enjeu majeur pour la poursuite de son évolution, et notamment pour son composant de base, le transistor MOS. Dans ce contexte, de nouvelles techniques de dopage permettant d'obtenir des jonctions ultra-minces ont été développées. Le recuit par laser nanoseconde (LTA) en mode " melt " est une de ces techniques. En effet, il permet une très forte activation locale (en surface et en profondeur) et une distribution uniforme des dopants. Ce procédé utilisé en laboratoire depuis les années 1980 dans la fabrication des cellules solaires offre également de nouvelles possibilités technologiques comme le développement d'architectures 3D. Néanmoins, des dégradations électriques de paramètres sensibles aux défauts tels que la mobilité et le courant inverse d'un transistor MOS ou la durée de vie des porteurs dans le cas de cellule photovoltaïque ont été observées. Dans ce contexte, cette thèse propose une étude rigoureuse des défauts générés par recuit laser en deux volets. Le premier volet traite de l'impact du recuit laser sur les propriétés physiques du silicium et repose essentiellement sur des caractérisations approfondies par spectroscopie infrarouge et photoluminescence d'échantillons silicium non intentionnellement dopés soumis à diverses conditions de recuits par impulsions laser à excimère. L'étude met en évidence la formation de défauts suite au procédé de recuit laser. Leur identification a permis d'affirmer l'introduction d'impuretés d'oxygène et de carbone durant le recuit. A partir de cette identification, le suivi en profondeur par spectroscopie de masse à ionisation secondaire de chacune des impuretés a été effectué révélant une augmentation de la concentration et de la diffusion des impuretés avec l'augmentation de la densité d'énergie du laser et/ou du nombre de tirs. A haute énergie laser, les profils de concentration d'oxygène montrent la présence d'un pic immobile (en concordance avec la solubilité limite de l'oxygène dans le silicium liquide) associé à des cavités de silicium observées par microscopie électronique en transmission (MET). L'origine de ces impuretés est discutée ; la caractérisation de véhicules tests dédiés a permis de définir l'oxyde natif comme étant leurs sources. Le second volet permet de répondre au second objectif qui consiste à évaluer l'impact du recuit laser sur les propriétés électriques de composants à base de silicium et s'appuie sur la caractérisation de diodes Schottky et PN préalablement fabriquées. Les résultats obtenus constituent un moyen supplémentaire pour, non seulement localiser les défauts électriquement actifs, mais également les identifier. Les caractéristiques courant-tension des diodes montrent systématiquement l'impact du recuit sur le courant de fuite, paramètre sensible aux défauts. Plus spécifiquement, le courant de fuite se dégrade avec l'augmentation de la densité d'énergie. Ces mesures électriques ont permis également de mettre en évidence la présence de défauts localisés à l'interface liquide/solide, défauts ayant un fort impact sur les propriétés électriques des diodes. Les résultats sont en accord avec la littérature qui suggère la présence de lacunes à cette interface. Pour aller plus loin, des mesures de DLTS ont été effectuées et dévoilent, selon la localisation (zone fondue ou interface), des signatures singulières laissant présager plusieurs types de défauts.The micro-electronic domain is constantly evolving in response to the continuous emerging of new application fields as well as new users' needs. The fabrication of heavily-doped regions for ultra-shallow junctions is a major issue to ensure its evolution. In this context, new doping techniques allowing to obtain ultra-shallow junctions have been developed. Nanosecond laser annealing in "melt mode" is one of these techniques. Indeed, it allows a very strong local activation (on surface and in depth) and a uniform distribution of doping. This process used in laboratory since the 1980s for the realization of solar cells offers also new technological possibilities such as the development of 3D architectures. However, degradation of several parameters sensitive to laser-induced defects were observed, such as carrier mobility and reverse current in MOS transistors or carrier lifetime in the case of photovoltaic cells. In this context, this thesis proposes a rigorous study of the defects generated by laser annealing in two parts. The first part analyses the impact of the laser annealing on the physical properties, thanks to infrared and photoluminescence spectroscopy characterizations of bare silicon samples submitted to different annealing conditions. The study highlights the formation of defects following the laser process. Their identification allowed to confirm the introduction of oxygen and carbon impurities during the annealing. From this identification, the impurities were followed in depth by secondary ion mass spectrometry allowing to reveal an increase of their concentration and diffusivity when increasing the laser energy density and/or the number of laser pulses. At high energy, the oxygen concentration profiles show the presence of an immobile peak (in agreement with the known solubility limit value in liquid silicon) which are related to silicon cavities observed by transmission electron microscopy. The origin of these impurities is also discussed and the characterization of dedicated test vehicles allowed to identify the native oxide as the source of the impurities. The objective of second part is to evaluate the impact of laser annealing on the electrical properties of silicon devices thanks to the characterization of PN and Schottky diodes. The obtained results provide an additional mean to localize the electrically active defects but also to identify them. The current-voltage characteristics of diodes systematically show an impact of the annealing on the leakage current, which is a strongly defect-sensitive parameter. More specifically, the leakage current deteriorates with increasing the laser energy. These measurements have allowed also to highlight the presence of defects at the liquid/solid interface, defects which also have a strong impact on diodes electric properties. The results are in agreement with the literature which suggests the presence of vacancies at the interface. To go further on this study, DLTS measurements have been carried out and reveal, depending on their localization (melt zone or liquid/solid interface), singular signatures suggesting several types of defects

Etude des défauts induits par recuit laser excimère dans le silicium

National audienceThe micro-electronic domain is constantly evolving in response to the continuous emerging of new application fields as well as new users' needs. The fabrication of heavily-doped regions for ultra-shallow junctions is a major issue to ensure its evolution. In this context, new doping techniques allowing to obtain ultra-shallow junctions have been developed. Nanosecond laser annealing in "melt mode" is one of these techniques. Indeed, it allows a very strong local activation (on surface and in depth) and a uniform distribution of doping. This process used in laboratory since the 1980s for the realization of solar cells offers also new technological possibilities such as the development of 3D architectures. However, degradation of several parameters sensitive to laser-induced defects were observed, such as carrier mobility and reverse current in MOS transistors or carrier lifetime in the case of photovoltaic cells. In this context, this thesis proposes a rigorous study of the defects generated by laser annealing in two parts. The first part analyses the impact of the laser annealing on the physical properties, thanks to infrared and photoluminescence spectroscopy characterizations of bare silicon samples submitted to different annealing conditions. The study highlights the formation of defects following the laser process. Their identification allowed to confirm the introduction of oxygen and carbon impurities during the annealing. From this identification, the impurities were followed in depth by secondary ion mass spectrometry allowing to reveal an increase of their concentration and diffusivity when increasing the laser energy density and/or the number of laser pulses. At high energy, the oxygen concentration profiles show the presence of an immobile peak (in agreement with the known solubility limit value in liquid silicon) which are related to silicon cavities observed by transmission electron microscopy. The origin of these impurities is also discussed and the characterization of dedicated test vehicles allowed to identify the native oxide as the source of the impurities. The objective of second part is to evaluate the impact of laser annealing on the electrical properties of silicon devices thanks to the characterization of PN and Schottky diodes. The obtained results provide an additional mean to localize the electrically active defects but also to identify them. The current-voltage characteristics of diodes systematically show an impact of the annealing on the leakage current, which is a strongly defect-sensitive parameter. More specifically, the leakage current deteriorates with increasing the laser energy. These measurements have allowed also to highlight the presence of defects at the liquid/solid interface, defects which also have a strong impact on diodes electric properties. The results are in agreement with the literature which suggests the presence of vacancies at the interface. To go further on this study, DLTS measurements have been carried out and reveal, depending on their localization (melt zone or liquid/solid interface), singular signatures suggesting several types of defects.La micro-électronique est un domaine exigeant, en constante évolution, motivé par le secteur applicatif et les besoins des utilisateurs. La réalisation de jonctions ultra-minces et fortement dopées est un enjeu majeur pour la poursuite de son évolution, et notamment pour son composant de base, le transistor MOS. Dans ce contexte, de nouvelles techniques de dopage permettant d'obtenir des jonctions ultra-minces ont été développées. Le recuit par laser nanoseconde (LTA) en mode " melt " est une de ces techniques. En effet, il permet une très forte activation locale (en surface et en profondeur) et une distribution uniforme des dopants. Ce procédé utilisé en laboratoire depuis les années 1980 dans la fabrication des cellules solaires offre également de nouvelles possibilités technologiques comme le développement d'architectures 3D. Néanmoins, des dégradations électriques de paramètres sensibles aux défauts tels que la mobilité et le courant inverse d'un transistor MOS ou la durée de vie des porteurs dans le cas de cellule photovoltaïque ont été observées. Dans ce contexte, cette thèse propose une étude rigoureuse des défauts générés par recuit laser en deux volets. Le premier volet traite de l'impact du recuit laser sur les propriétés physiques du silicium et repose essentiellement sur des caractérisations approfondies par spectroscopie infrarouge et photoluminescence d'échantillons silicium non intentionnellement dopés soumis à diverses conditions de recuits par impulsions laser à excimère. L'étude met en évidence la formation de défauts suite au procédé de recuit laser. Leur identification a permis d'affirmer l'introduction d'impuretés d'oxygène et de carbone durant le recuit. A partir de cette identification, le suivi en profondeur par spectroscopie de masse à ionisation secondaire de chacune des impuretés a été effectué révélant une augmentation de la concentration et de la diffusion des impuretés avec l'augmentation de la densité d'énergie du laser et/ou du nombre de tirs. A haute énergie laser, les profils de concentration d'oxygène montrent la présence d'un pic immobile (en concordance avec la solubilité limite de l'oxygène dans le silicium liquide) associé à des cavités de silicium observées par microscopie électronique en transmission (MET). L'origine de ces impuretés est discutée ; la caractérisation de véhicules tests dédiés a permis de définir l'oxyde natif comme étant leurs sources. Le second volet permet de répondre au second objectif qui consiste à évaluer l'impact du recuit laser sur les propriétés électriques de composants à base de silicium et s'appuie sur la caractérisation de diodes Schottky et PN préalablement fabriquées. Les résultats obtenus constituent un moyen supplémentaire pour, non seulement localiser les défauts électriquement actifs, mais également les identifier. Les caractéristiques courant-tension des diodes montrent systématiquement l'impact du recuit sur le courant de fuite, paramètre sensible aux défauts. Plus spécifiquement, le courant de fuite se dégrade avec l'augmentation de la densité d'énergie. Ces mesures électriques ont permis également de mettre en évidence la présence de défauts localisés à l'interface liquide/solide, défauts ayant un fort impact sur les propriétés électriques des diodes. Les résultats sont en accord avec la littérature qui suggère la présence de lacunes à cette interface. Pour aller plus loin, des mesures de DLTS ont été effectuées et dévoilent, selon la localisation (zone fondue ou interface), des signatures singulières laissant présager plusieurs types de défauts

Self-Propagating Reaction Mechanisms in TiB2 Integrated Al/CuO Nanothermites

International audienceUnary nanoscale metallic fuels such as Al, Ti, Mg, Zr, and B with an oxidizer have been massively explored in reactive energetic formulations commonly used in explosives and propellants owing to their high combustion energy. While Al has routinely been preferred, its low melting point and the resultant sintering effects curtail the reaction surface area. Despite the high gravimetric and volumetric enthalpies of B, low combustion rates and poor diffusion across the liquid boron oxide barrier restrict its use as a fuel. Although Ti oxidation can be induced at low temperatures, its high sensitivity limits the integration in nanolaminates. To overcome some of these common limitations imposed by single fuel thermites, binary fuel systems are seen as a very desirable strategy to prepare insensitive safe to handle nanothermites exhibiting fast energy release and high propagation rates. Whereas TiB2 may not be the most obvious choice of fuel, the fuel-oxidizer surface synergistic effects brought by its integration in Al/CuO nanolaminates resulted in enhanced reactivity characterized by relatively faster burn rate and shorter ignition delay. Beyond the excellent heat conducting properties, TiB2 demonstrated a strong affinity towards oxygen boosting low temperature CuO decomposition concomitantly forming TiO and boron oxide, following which Al underwent oxidation via both liquid boron oxide and vapor phase oxygen. There is however a lack of fundamental understanding of the self-propagating mechanisms in such ternary thermites due to the complexity associated with the material heterogeneities and multiphase flow occurring during combustion. Herein, sputter-deposited ternary Al-TiB2/CuO nanolaminates are fabricated as model structures, and a high-speed imaging system is utilized to study the flame-front propagation at sub-millimeter scales. DC magnetron sputtering is specially chosen to obtain precisely controlled layer-by-layer structures. To assess the extent of variation in the combustion regime, TiB2:Al molar ratio is varied between 0 and 1. We examine the entire material life cycle of Al-TiB2 bi-fuel component comprising of microfabrication, placement of TiB2 in Al/CuO multilayer stack as well as the individual effects of Al and TiB2 on the self-propagating combustion mechanism. While the individual placement of TiB2 nanolayer in the stack only slightly affects the ignition and the combustion properties, the measure attests to be critical in precluding nano-structural losses. Finally, various combustion stages and flame front behaviors are discussed, followed by a scenario of the combustion process

Etude des défauts induits par recuit laser excimer sur silicium

National audienceLe recuit par laser (LTA) est une technique bien adaptée pour la réalisation de jonctions ultra minces et ultra dopées. En effet, ce type de recuit est très prometteur car il permet une très forte activation des dopants de manière localisée (en surface et en profondeur) et une distribution uniforme des dopants

Influence of in-situ x-ray exposure on the magnetotransport properties of NPB and MADN based blue OLED structures

International audienceMagnetic Field Effects (MFE) on Organic Semiconductors (OSC) have a large fundamental and technological interest presently due to the development of organic electronics devices like OLED (organic light emitting diodes) or OPV (organic photovoltaic). Up to now, the largest observed MFE[1] have been reported for OLED-type devices. They are related to the interaction between excited states (singlet, triplet) and charge carriers, either free or trapped.[2] The origin of the magneto-conductance (MC) is still controversial and depends on the device structure. In particular, the materials choice plays an important role, as well as film thickness, fabrication process, temperature. For example, x-ray exposure during the deposition of metal layers with an electron gun may modify optoelectronic properties of OSC and MC, as reported by several authors.[3, 4] They are assumed to cause punctual trap defects in OSC films. We contribute to this issue in this work. We have decided to compare two HTL organic materials, NPB and MADN, since they display almost the same HOMO and LUMO with huge differences in published values for hole mobility which are respectively 10-4 and 3.10-7 cm 2 /V.s for NPB and MADN.[5, 6] We have prepared devices with an OSC single-layer, ITO anode and Al cathode. For photoluminescence (PL) experiments, similar OSC single layers were deposited on bare silicon substrates. All organic layers of one sample set were grown during the same evaporation run, then individually x-ray treated at various acceleration voltages of the e-gun. In the case of NPB, we report a dramatic dependence of current onsets that increase with the e-gun voltage (typically from 4 to 8 V for 100 nm NPB respectively pristine and 5 kV exposed). X-ray exposure is less significant for MADN-based devices with a shift from 4 to 5 V. However, they gave the optimal MFE with up to +6.3 % at 300 mT applied magnetic field for a 4 kV exposed sample. We also report a neat dependence of MFE on the voltage conditioning of the samples, i.e. applying direct polarization to the device. All these results strongly support the fact that MFE is governed by a combination of extrinsic x-rays-induced local defects in OSC layers. We will analyze the observed effects in terms of trap formation, occupancy and polaron-triplet exciton coupling according to present models and the obtained PL spectra

Structural and Electrical Characterizations of BiSb Topological Insulator Layers Epitaxially Integrated on GaAs

Topological insulators (TIs) are known as promising materials for new nanoelectronics and spintronics applications thanks to their unique physical properties. Among these TIs, bismuth antimony alloys (Bi1–xSbx) remain the most interesting because their electronic band structure can be controlled by changing the stoichiometry, the thickness, or the temperature. However, integrating these materials on an industrial substrate remains a challenge. Here, we investigate the growth, structural, and electrical properties of BiSb materials epitaxially deposited on industrial GaAs(001) substrates. We report the influence of key growth parameters such as temperature, antimony composition, thickness, and growth rate on the crystal quality. We manage to optimize the growth conditions while keeping the Bi1–xSbx composition within the TI range. Despite the large lattice mismatch and different crystalline matrices between the deposited material and the substrate, we successfully grow high-quality BiSb(0001) films. For optimized growth conditions, n-type semiconductor behavior of the BiSb layer is demonstrated at temperatures above 100 K. The material band gap calculated from our transport measurements corresponds to that mentioned in the literature. A change of the carrier type from bulk electrons to surface holes is observed when decreasing the temperature below 55 K. Hole mobilities up to 7620 cm2/(V·s) are extracted. This is, to our knowledge, the first demonstration of TI integrated on an industrial substrate keeping its protected surface states

Backside Fault Localization and Defect Physical Analysis of Degraded Power HEMT p-GaN Transistors Stressed in DC and AC Switching Modes

International audienceAbstract This paper describes a backside approach methodology for sample preparation, fault localization and physical defect analysis on p-GaN power HEMT electrically stressed in DC voltage surge and AC switching mode. The paper will show that preparation must be adapted according to the defect position (metallurgy, dielectric layers, epitaxy, etc.) which depends on the type of stress applied. In our life-operation mode amplified electrical stress reliability study, the failure analysis will help us to reveal the weakest parts of the transistor design in relation to the type of applied stress. The failure analysis presented in this paper is composed of electrical characterization, defect localization with PEM and LIT, FIB Slice&View, TEM analysis and frontside conductive AFM after a deep HF

Diodes Schottky diamant fonctionnant à 200°C

International audienceLes caractéristiques courant-tension jusqu'à 200 °C de diodes Schottky diamant verticales et pseudo-verticales réalisées dans le cadre du projet DIAMONIX2 sont présentées dans cet article. Sur les différents échantillons testés le taux de fonctionnalité est supérieur à 75 % et atteint même 100 % pour l'un d'entre eux. Pour les diodes verticales la densité de courant atteint 488 A/cm 2 à 200 °C et pour les diodes pseudo-verticales une densité de courant supérieure à 1000 A/cm² à 200 °C est obtenue. En inverse sur toutes les diodes fonctionnelles le courant de fuite mesuré est inférieur à 10-7 A/cm 2 à 50 V. Toutefois, la hauteur de barrière de 1,96 eV et le coefficient de non-idéalité de 1,77 sont certainement causés par une densité de charges importante à l'interface diamant/contact Schottky. La reproductibilité des caractéristiques et le fort taux de fonctionnalité à 200 °C est mis en avant dans cet article

Defect investigation of excimer laser annealed silicon

International audienceIn this paper, we study the effect of excimer laser annealing on silicon and specifically the oxygen impurities induced versus laser energy density. We show that oxygen penetration from the native oxide occurs during laser annealing, which increases with increasing laser energy. At higher laser energies, oxygen precipitation occurs well below the surface, which is confirmed both by SIMS and optical spectroscopy analyses. The precipitates do not affect the dopant activation in the epitaxial layer

Evaluating depth distribution of excimer laser induced defects in silicon using micro-photoluminescence spectroscopy

International audienceLaser Thermal Annealing (LTA) has been demonstrated to be an effective method to create heavily doped regions required for ultra-shallow junctions, in which dopants are typically introduced by ion implantation. More generally, laser annealing is very attractive due to the localised nature of the annealing process (both on the wafer surface and in depth), allowing dopants to be activated while preserving the integrity of the surrounding areas. Similarly, it is generally accepted that the laser induced damage, if any, is also localised and is reduced when using ultrashort pulses. However, the depth distribution of the laser induced damage has been rarely investigated in detail, with few works reporting on the subsurface doping and damage in laser-doped Si solar cells [1, 2]