Etude expérimentale de l'interdiffusion Ge-Si à partir de sources solides Germanium sur Silicium. Application à la formation de couches graduelles Si1-xGex pour les transistors pMOSFETs

As Silicon limits are reached, Ge-based materials are expected to be progressively introduced in the fabrication of advanced microelectronic devices. SiGe layers are already used as Source/Drain regions to induce uniaxial compressive stress in the Si channel, which results in the enhancement of hole mobility in PMOS. In this work, we study an alternative method for the fabrication of shallow SiGe regions, in which a pure Ge layer is deposited on a Si substrate and the Ge in-diffusion is induced by a subsequent anneal. The optimisation of such a technology requires the accurate measurement of the Ge concentration in the full range of Ge composition and the understanding of the Si-Ge interdiffusion occurring during the formation of the SiGe layers. Pure Ge(:B) layers were grown on Si substrates by CVD. We present a novel SIMS MCs2+ methodology for the accurate measurement of the Ge diffused profiles. Boltzmann-Matano analysis was used to extract the interdiffusion coefficients. Si-Ge interdiffusion is found to be strongly dependent on the Ge concentration. Also, an effect of dislocations near the Ge/Si original interface is suggested by our results. A physical model including the various observed effects is proposed, that gives a very good agreement with experiments. We also show that the effect of the in-situ B doping of the pure Ge layer is to reduce the interdiffusion. Finally, we suggest that the use of polycristalline Ge films is a promising route for the formation of gradual Si1-xGex layers.Dans la course à la miniaturisation des dispositifs de la microélectronique, les alliages SiGe sont des matériaux remarquables pour poursuivre l'amélioration des performances des composants de type CMOS, le Silicium atteignant aujourd'hui ses limites physiques. En effet, une méthode originale pour appliquer une contrainte de compression uniaxiale au canal de conduction Silicium, afin d'augmenter la mobilité des trous des transistors pMOS, consiste à remplacer le Silicium dans les régions Source et Drain par des couches SiGe pseudomorphiques. L'utilisation de sources solides sacrificielles de Germanium peut être une solution pour la fabrication de telles structures. Dans ce travail, nous avons ainsi étudié l'interdiffusion Ge-Si, induite par recuit thermique à haute température, à partir d'hétérostructures Ge/Si dont la couche de Germanium est déposée par CVD. Le développement de la méthodologie SIMS MCs2+, que nous réalisons dans cette thèse, assure la caractérisation chimique de couches graduelles Si1-xGex dans la gamme complète de concentrations (0 d x d 1). Nous montrons que l'interdiffusion Ge-Si est fortement dépendante de la composition en Germanium mais également des défauts structuraux formés aux interfaces Ge-Si. Nous avons alors développé un modèle qui permet de reproduire fidèlement les profils expérimentaux. L'effet du dopage Bore tend à réduire légèrement l'interdiffusivité. Finalement, nous montrons que l'utilisation de couches de Germanium polycristallin est prometteuse pour la fabrication de couches graduelles Si1-xGex. En effet, elle permet de réduire la densité de défauts structuraux initialement présents dans les films monocristallins

P-doped region below the AlGaN/GaN interface for normally-off HEMT

International audienceDevelopment of a new design for enhancement-mode AlGaN/GaN HEMT is presented. The normally-off operation was achieved by burying a p-GaN region below the AlGaN/GaN interface only below the gate. Simulation results show that the proposed technique is capable of shifting the threshold voltage to positive values, making the HEMT normally-off. To address the advantages and drawbacks of the proposed structure a comparison with the normally-off Gate injection transistor (GIT) was performed. The proposed structure seems to be more effective when it comes to the p-doping concentration required to achieve normally-off operation and offers superior confinement for the two dimensional electron gas. On the other hand, the low forward gate voltage limits the increase of the threshold voltage

Scalable normally-off MIS-HEMT using Fluorine implantation below the channel

International audienceA new normally-off Metal-Insulator- Semiconductor High-Electron-Mobility-Transistor (MIS-HEMT) is proposed. The design is based on the implantation of fluorine ions in the GaN layer below the gate electrode under the AlGaN/GaN interface. Sensitivity analyses are carried out, showing the effects of the fluorine concentration and the thickness of the insulator on the threshold voltage. The limitations and scalability of this technique are pointed out

Dynamic of power-GaN-HEMT electrical parameters: Why DC characterization might be misleading

International audiencePower GaN HEMT components offer very interesting performances (high voltage, high current, low on-resistance, fast switching), but the GaN material has some defects that can lead to carrier trapping, which induces dynamic electrical phenomena. Thereby, static measurement of the GaN HEMT components requires some reconsideration. In this work, we analyze how the typical static electrical parameters evolve as a function of time and how much they deviate from the DC measurements

Enhancement mode HEMT using fluorine implantation below the channel

International audienceGallium nitride based high electron mobility transistors (HEMT) are powerful candidates for high frequency and high power applications. While switching applications demand normally-off operation, these devices are normally-on. Recent normally-off HEMTs were demonstrated by implanting fluorine above the channel, in the barrier layer. During implantation, fluorine ions penetrate into the channel and cause mobility degradation. In this paper, we propose and simulate an alternative approach in which fluorine ions are implanted below the channel of the HEMT rather than above it. The simulation tool ATLAS is calibrated using experimental data from a real HEMT device. Simulation results have shown that implanting fluorine ions below the channel is capable of achieving normally-off operation. When compared to the implantation in the barrier layer, the proposed approach offers better confinement for the two dimensional electron gas (2DEG) below the gate, eliminates the scattering of fluorine ions with channel electrons and is more efficient when it comes to the fluorine concentration required to achieve a desired threshold voltage. This technique neither affects the breakdown voltage nor the off-state current

Un interrupteur GaN HEMT normally-off grâce à des ions fluor implantés sous l'interface AlGaN/GaN

National audienceAlGaN/GaN HEMTs are very promising candidates for high frequency applications with high power and low noise. Unfortunately, while switching applications strongly demand normally-off operation, conventional HEMTs are normally-on. For the sake of achieving normally-off HEMTs, several structures have been proposed. One of the major normally-off HEMTs uses fluorine implantation in the AlGaN layer. We suggest in this work the implantation of fluorine ions under the AlGaN/GaN interface only below the gate electrode rather than implanting in the AlGaN layer. Simulation results show that the proposed method is capable of achieving normally-off operation and more effective when it comes to the fluorine concentration required to obtain the desired threshold voltage. Neither the vertical breakdown voltage, nor the off-state current are affected by this approach.Les HEMTs en AlGaN/GaN sont des candidats prometteurs pour les applications forte puissance, haute fréquence et faible bruit. Grâce au champ électrique critique élevé du GaN et à la haute mobilité électronique dans le gaz bidimensionnel (2DEG) du HEMT, ce composant peut afficher des tenues en tension et des fréquences de commutation élevées ainsi que des résistances à l'état passant faibles, dépassant ainsi les limites des composants conventionnels en silicium. Alors que les applications de commutation de puissance nécessitent très souvent des composants normally-off, les HEMTs conventionnels ont un fonctionnement normally-on. C'est pourquoi plusieurs structures de HEMTs normally-off ont été proposées récemment dans la littérature, l'une d'entre elles utilisant l'implantation de fluor dans la couche d'AlGaN. Dans ce travail, nous suggérons d'implanter les ions fluor non pas dans l'AlGaN mais dans la couche de GaN, sous l'interface AlGaN/GaN et seulement sous l'électrode de grille. Les résultats de simulations montrent que la méthode proposée permet d'obtenir un fonctionnement normally-off. En outre, cette méthode semble être plus efficace, notamment en terme de concentration du fluor implanté, qui est le paramètre d'ajustement permettant d'obtenir la tension de seuil souhaitée

HEMT with fluorine implanted below the AlGaN/GaN interface for normally-off operation

2 pagesInternational audienceAlGaN/GaN HEMTs are promising candidates for high frequency applications with high power and low noise. While switching applications demand normally-off operation, conventional HEMTs are normally-on. To achieve normally-off HEMTs, several structures have been proposed. One of the major normally-off HEMTs uses fluorine implantation in the AlGaN layer. We suggest in this work the implantation of fluorine ions under the AlGaN/GaN interface only below the gate electrode rather than implanting in the AlGaN layer. Simulation results show that the proposed method is capable of achieving normally-off operation and is more effective when it comes to the fluorine concentration required to obtain a desired threshold voltag

Hybrid normally-off AlGaN/GaN HEMT using GIT technique with a p-region below the channel

International audienceGallium nitride based High Electron Mobility Transistors (HEMT) are powerful candidates for high frequency and high power applications. Unfortunately, while switching applications demand normally-off operation, these devices are normally-on. In this paper, after calibrating the simulator using experimental data, we address the advantages and drawbacks of two normally-off HEMT devices: the previously proposed Gate Injection Transistor (GIT) and our newly proposed HEMT with a p-GaN region below the channel. Afterwards, an hybrid normally-off HEMT is proposed, combining both techniques, aiming to merge their advantages and remedying their drawbacks

Mesure de résistance dynamique de HEMT en GaN à l'échelle de la centaine de nanosecondes

International audienceLes nouveaux composants HEMT en GaN de puissance offrent des performances très intéressantes (haute tension, courant élevés, faible résistance à l'état passant, commutation rapide). Toutefois, le matériau GaN contient encore quelques défauts qui constituent des pièges de porteurs, conduisant à des phénomènes dynamiques qui peuvent être difficiles à mesurer, en particulier aux temps courts. Afin de pouvoir étudier ces phénomènes, nous avons mis au point un banc expérimental permettant de mesurer l'évolution de la résistance à l'état passant du composant en fonction du temps, quelques dizaines de nanosecondes après sa mise en conduction pour des tensions bloquées jusqu'à 1200V. L'utilisation de ce nouvel outil est illustrée sur des composants commerciaux. Des hypothèses sont proposées pour expliquer le comportement observé

Développement technologique d'un HEMT normally-off avec une grille à barrière P-GaN

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