3C-SiC — From Electronic to MEMS Devices

Since decades, silicon carbide (SiC) has been avowed as an interesting material for high-power and high-temperature applications because of its significant properties including its wide bandgap energy and high temperature stability. SiC is also professed as an ideal candidate for microsystem applications due to its excellent mechanical properties and chemical inertia, making it suitable for harsh environments. Among the 250 different SiC polytypes, only 4H, 6H and 3C-SiC are commercially available. The cubic structure, 3C-SiC, is the only one that can be grown on cheap silicon substrates. Hence, 3C-SiC is more interesting than any other polytype for reducing fabrication costs and increasing wafer diameter. This huge property has been evidenced for more than 30 years using chemical vapor deposition. Despite this key achievement and the growing interest for silicon carbide, no 3C-SiC-based devices can be found on the market whereas 4H-SiC-based devices are more and more largely commercialized. Even so, important headways have been reached for electrical and microelectromechanical systems (MEMS) applications. Therefore, the purpose of this chapter is to address concerns related to electronic applications and MEMS fabrication of 3C-SiC-based devices, trying to give a broad overview on specific issues and challenging solutions

Activation des dopants implantés dans le carbure de silicium (3C-SiC et 4H-SiC)

Ces travaux de thèse sont consacrés à l étude de l activation des dopants implantés dans le carbure de silicium. L objectif est de proposer des conditions d implantation optimisées pour réaliser le dopage de type n dans le 3C-SiC et de type p dans le 4H-SiC.Nous avons tout d abord étudié les implantations de type n dans le 3C-SiC. Pour cela, des implantations de N, de P et une co-implantation N&P avec les recuits d activation associés ont été étudiés. L implantation d azote suivie d un recuit à 1400C-30min a permis une activation proche de 100% tout en conservant une bonne qualité cristalline. Une étude sur les propriétés électriques des défauts étendus dans le 3C-SiC a également été réalisée. A l aide de mesures SSRM, nous avons mis en évidence l activité électrique de ces défauts, ce qui rend difficile la réalisation de composants électroniques sur le 3C-SiC.Nous avons ensuite réalisé une étude du dopage de type p par implantation d Al dans le 4H-SiC, en fonction de la température d implantation et du recuit d activation. Nous avons pu montrer qu une implantation à 200C suivie d un recuit à 1850C-30min donne les meilleures résultats en termes de propriétés physiques et électriques.This work was dedicated to the activation of implanted dopants in 3C-SiC and 4H-SiC. The goal is to propose optimized process conditions for n-type implantation in 3C-SiC and for p-type in 4H-SiC.We have first studied the n-type implantation in 3C-SiC. To do so, N, P implantations, N&P co-implantation and the associated annealings were performed. The nitrogen implanted sample, annealed at 1400C-30 min evidences a dopant activation rate close to 100% while maintaining a good crystal quality. Furthermore, the electrical properties of extended defects in 3C-SiC have been studied. Using the SSRM measurements, we have evidenced for the first time that these defects have a very high electrical activity and as a consequence on future devices.Then, we have realized a study on p-type doping by Al implantation in 4H-SiC with different implantation and annealing temperatures. Al implantation at 200C followed by an annealing at 1850C-30min lead to the best results in terms of physical and electrical properties.TOURS-Bibl.électronique (372610011) / SudocSudocFranceF

Etude de la croisssance CVD des films minces de 3C-SiC et élaboration du cantilever AFM en 3C-SiC avec pointe Si intégrée

Parmi les polytypes les plus connus du carbure de silicium (SiC), le polytype cubique (3C-SiC), est le seul qui peut croitre sur des substrats silicium. L hétérostructure 3C-SiC/Si est intéressante non seulement pour son faible coût de production mais aussi pour la conception de Systèmes Micro-Electro-Mécaniques ( MEMS ). La valeur élevée du module de Young du 3C-SiC, comparé à celui du silicium, permettrait à des cantilevers submicroniques, fabriqués à partir de films minces de 3C-SiC, de vibrer à ultra-hautes fréquences (>100MHz). Cette haute fréquence de résonance est la clé pour obtenir un système AFM non-contact ultra-sensible et rapide. Cependant, il n existe pas de cantilever en SiC disponible sur le marché en raison de la difficulté à élaborer des films minces de 3C-SiC de bonne qualité, la technique de synthèse la plus utilisée étant le Dépôt Chimique en phase Vapeur (CVD). La raison première de cette difficulté à obtenir un matériau de bonne qualité réside essentiellement dans l important désaccord de maille et la différence de dilatation thermique entre le 3C-SiC et Si qui génèrent des défauts cristallins à l interface et jusqu à la surface du film de 3C-SiC, la zone la plus défectueuse se localisant auprès de l interface .Among aIl the well known polytypes ofihe silicon carbide (SiC), the cubic polytype (3C-SiC) is the only one that min be grown on silicon substrates. This heterostructure 3C SiC/Si ta interesting not only for its low production cost but also for the design of tise Micro-Electro-Mechanical Systems (MEMS). The high value ofthe Young s modulis the 3C-SiC, compared to the silicon, allows submicronic cantilevers, fabrmcated from tIse 3C-SiC thin filins, to resonate at ultra-high frequency (>100MHz). The high resonant frequency is the key to obtain s fast, ultra-sensitive non-contact AFM systein.However, there isn t any SiC cantilevers available on the market because of the difficulty to elaborate gond quality 3C-SiC thin films, with tIse Chemical Vapor Deposition (CVD) technique being tIse most frequently used synthesis technology. Tise first reason of tIse difficulty with the CVD technology to obtain gond quality thin film rests essentially in the important lattice mismatch and the difference in thermal expansion coefficient existing between 3C SiC and Si which generate crystalline defects at the interface and propagating tilI the 3C-SiC filin surface, with the inost defective zone localizing near the interface .TOURS-Bibl.électronique (372610011) / SudocSudocFranceF

Investigation of the Young's Modulus and the Residual Stress of 4H-SiC Circular Membranes on 4H-SiC Substrates

International audienceThe stress state is a crucial parameter for the design of innovative microelectromechanical systems based on silicon carbide (SiC) material. Hence, mechanical properties of such structures highly depend on the fabrication process. Despite significant progresses in thin-film growth and fabrication process, monitoring the strain of the suspended SiC thin-films is still challenging. However, 3C-SiC membranes on silicon (Si) substrates have been demonstrated, but due to the low quality of the SiC/Si heteroepitaxy, high levels of residual strains were always observed. In order to achieve promising self-standing films with low residual stress, an alternative micromachining technique based on electrochemical etching of high quality homoepitaxy 4H-SiC layers was evaluated. This work is dedicated to the determination of their mechanical properties and more specifically, to the characterization of a 4H-SiC freestanding film with a circular shape. An inverse problem method was implemented, where experimental results obtained from bulge test are fitted with theoretical static load-deflection curves of the stressed membrane. To assess data validity, the dynamic behavior of the membrane was also investigated: Experimentally, by means of laser Doppler vibrometry (LDV) and theoretically, by means of finite element computations. The two methods provided very similar results since one obtained a Young's modulus of 410 GPa and a residual stress value of 41 MPa from bulge test against 400 GPa and 30 MPa for the LDV analysis. The determined Young's modulus is in good agreement with literature values. Moreover, residual stress values demonstrate that the fabrication of low-stressed SiC films is achievable thanks to the micromachining process developed

Porosity and thickness characterization of porous Si and oxidized porous Si layers – an ultraviolet-visible-mid infrared ellipsometry study

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Optimized plasma-polymerized fluoropolymer mask for local porous silicon formation

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Realization of minimum number of rotational domains in heteroepitaxied Si(110) on 3C-SiC( 001)

Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth

Evaluation technologique de structures 3D dans le silicium pour la réalisation de composants de puissance

La verticalisation des composants de puissance, nécessaire pour acheminer des fortes densités de courant, est bien connue. Il n empêche que la circulation des courants perpendiculairement à la surface dans les composants de puissance limite aujourd hui leur intégration. Dans cette problématique, une rupture technologique, associée à un concept nouveau de l électronique, les structures 3D, voit le jour avec ce travail de thèse. Il s agit de concevoir, dans un premier temps, des structures électroniques connues, dans lesquelles la circulation du courant est parallèle à la surface de la plaquette en utilisant toute l épaisseur de celle-ci. L intérêt de ce travail tient en premier lieu dans le gain important en densité d intégration des composants de puissance qu autorise l approche 3D. De plus, ce concept s inscrit en rupture au niveau des technologies du silicium, ouvrant ainsi la voie à de nouveaux développements dépassant largement le cadre de l électronique de puissance. La première partie de ce document introduit et formalise le concept 3D. Elle propose de plus une analyse de la faisabilité technologique des éléments de base de l intégration 3D. Le développement des étapes technologiques de base (gravure, photolithographie, dépôt et dopage) adaptées à des structures 3D y est donc décrit. La seconde partie de ce travail présente la conception et la fabrication d'un prototype de composant de puissance 3D, un transistor MOSFET, permettant d'évaluer l'application de l'ensemble des technologies 3D développées. Finalement, cette étude permet de statuer sur la maturité technologique requise pour que le concept 3D offre les gains théoriques espérés.Vertical through-wafer current conduction is a well know configuration used to conduct high current in power devices. However, the perpendicular current conduction to the power devices surface limits its integration factor. In this context, a technological breakthrough associated with a new electronic concept, the 3D structures, appear in this thesis work. Firstly, it consists in conceiving standard electronics structures, in which the current flow is parallel to the wafer surface, in the whole wafer thickness. This work was conducted to show the potential high integration capability of power devices with this 3D approach. Moreover, this concept dealing with a tremendous modification in silicon technologies, paves the way to new developments going beyond the power electronics domain. The first part of this document introduces and formalizes the 3D concept. It proposes a capability analysis of basic technological steps of 3D integration. The main technological developments (etching, photolithography, deposition and doping) adapted to 3D structures are described. The second part of this work presents the design and fabrication of a 3D power device prototype, a 3D MOSFET, which allows an evaluation of the technology developments implementation. Finally, this study defines the technological maturity required to observe someday the level of integration expected from this 3D concept.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF