A l’heure actuelle, le marché de l’électronique de puissance est dominé par les composants silicium. Néanmoins, de nouveaux matériaux comme le nitrure de gallium ont émergé dans ce domaine grâce à leurs propriétés intéressantes. Ces nouveaux composants sont principalement réalisés sur des substrats silicium ce qui induit certaines problématiques lors de leur fabrication ou au niveau de leurs performances. Nous nous sommes intéressés dans cette thèse à des approches d’un point de vue du substrat dans l’objectif de résoudre ces problématiques. Ce travail a permis notamment de mettre en place une succession de procédés technologiques afin de remplacer le substrat silicium de fabrication par d’autres matériaux pour améliorer les performances de ces composants. Cette approche a notamment permis de transférer des composants fonctionnels sur un substrat cuivre. L’impact électrique et thermique du remplacement du substrat initial par un nouveau matériau a été étudié. Ce travail ouvre ainsi la voie du report de composants en nitrure de gallium réalisés sur des substrats silicium de diamètre 200 mm ou plus. / New materials such as gallium nitride (GaN) emerge as promising candidates for power electronics. The current trend is to fabricate the AlGaN/GaN power devices directly on (111) silicon substrates. It makes the expitaxy of the GaN challenging and affects the device performances. In this work, we focus on substrate approaches to solve these problems. A transfer process was developed to replace the silicon substrate by another material to enhance electrical performances of the devices. Especially, GaN devices were transferred on copper substrates without electrical degradation. Electrical and thermal characterizations were performed to study the impact of the transfer. This work offers a first approach on the transfer of GaN devices from 8 or even 12 inches silicon substrates.

Temperature sensing in harsh environment is desired in many areas, such as coal gasification, aerospace, etc. Single crystal sapphire is an excellent candidate for construction of harsh environment sensors due to its superior mechanical and optical properties even at temperature beyond 1600°C. The temperature inside a coal gasifier can be as high as 1200°C. And there is dramatic temperature gradient between the inner and outer layers of the gasifier refractory. Previous work has been done at Virginia Tech's Center for Photonics Technology to design and fabricate a sapphire wafer based Fabry-Perot interferometer (FPI) sensor for temperature sensing in coal gasifiers. The sensor head is based on the use of sapphire wafer which is attached to a lead-in sapphire fiber to be applied in the ultrahigh temperature region; and the sapphire fiber is spliced to a multi-mode fused silica fiber for quality signal transmission in lower temperature areas. One of the challenges encountered by this approach is the shear force to the sapphire fiber, which is caused by the differential thermal expansion between the inner and outer layers of the gasifier refractory. This shear force may be so significant to break the sensor probe. This thesis proposed a free space based interrogation sensing system to address that problem. In this free space based interrogation sensing system, only the sensor head is placed in the inner refractory wall, while all the other parts of the system are placed in the outer refractory or outside the gasifier at the ambient room temperature. An optical frequency domain reflectometry (OFDR) based multiplexed technique is applied in the sensor design to realize temperature measurement at multiple locations along the optical path. In this work, three sapphire wafers based multiplexed temperature sensor is fabricated and calibrated in laboratory. This multiplexed high temperature sensor shows linear response in the range of 20°C ~ 1000°C, with a sensitivity of 1.602?10??/°C and a resolution of 1.3°C. / Master of Science

De nos jours, l’industrie de la microélectronique cherche à développer des composants toujours plus performants tout en réduisant la consommation d’énergie. Les solutions planaires ayant atteint leurs limites, desstructures 3D furent développées afin d’empiler verticalement les circuits. Cela nécessite une parfaite maitrise des différents procédés d’assemblage au sein desquels le collage direct de couches minces d’oxyde de silicium déposées par PECVD constitue une alternative intéressante en ce sens qu’elle permet l’élaboration à basse température de structures intégrant des couches isolantes composées d’oxyde de silicium.Le collage direct d’oxyde de silicium obtenu par voie thermique fut largement étudié par le passé. Cependant, l’utilisation d’oxyde de silicium obtenu par voie de dépôt PECVD fut jusqu’ici peu répandu dans les structures collées. L’objet de notre étude fut d’évaluer les particularités de l’oxyde de silicium déposé dans le cadre du collage direct ainsi que les mécanismes spécifiques mis en jeu lors du scellement de l’interface de collage. Le collage direct s’effectuant par la mise en contact de ces surfaces à température ambiante, puis étant généralement suivi d’un recuit de consolidation, des mécanismes particuliers auront lieu dans le volume de l’oxyde ainsi qu’à l’interface de collage permettant de différencier le comportement des oxydes déposés en collage.Dans cette étude, nous avons assemblés différentes configurations d’oxydes et montré l’influence primordiale de l’eau sur le collage direct. Il est apparu que, dès la température ambiante, cette dernière impactait déjà le collage en modifiant les propriétés physicochimiques et mécaniques de la subsurface de l’oxyde. A plus haute température, l’eau migre du volume de l’oxyde vers l’interface de collage permettant la fermeture de l’interface de collage en exacerbant les propriétés de l’oxyde précités. L’eau résultant de la fermeture de l’interface de collage est alors soit stockée à l’intérieur de cavités se formant à l’interface de collage, soit évacuée dans la subsurface de l’oxyde suivant la typologie de celui-ci. Il a également été montré que l’oxydedéposé disposait d’un profil de concentration d’eau relativement équilibré et qu’il pouvait contenir une quantité importante d’eau. Ces constations ont permis l’élaboration de structures bicouches optimisées pour le collage direct. La compréhension de ces différents mécanismes apporte un nouvel éclairage dans l’utilisation des procédés de collage direct pour les applications du futur. / Nowadays, the microelectronics industry is seeking to develop ever more efficient components while reducing energy consumption. Planar solutions having reached their limits, 3D structures were developed to vertically stack the circuits. This requires a perfect control of the different assembly processes in which the direct bonding of thin layers of silicon oxide deposited by PECVD constitutes an interesting alternative in the sense that it allows the elaboration at low temperature of structures integrating insulating layers composed of silicon oxide.The direct bonding of silicon oxide obtained by thermal oxidation has been widely studied in the past. However, the use of deposited PECVD silicon oxides has not been so far widespread in bonded structures. The purpose of our study was to evaluate the particularities of the silicon oxide deposited in the direct bonding framework as well as the specific mechanisms involved during sealing of the bonding interface. Since direct bonding takes place by bringing these surfaces into contact at room temperature and then generally followed byconsolidation annealing, special mechanisms will take place in the oxide volume and at the bonding interface to differentiate the behaviour of the PECVD deposited silicon oxides in bonding.In this study, we assembled different oxide configurations and showed the primordial influence of water on direct bonding. It appeared that, from the ambient temperature, the water was already impacting the bonding by modifying the physicochemical and mechanical properties of the oxide subsurface. At higher temperatures, the water migrates from the oxide volume to the bonding interface allowing the closing of the bonding interfaceby exacerbating the above oxide properties. The water resulting from the closing of the bonding interface is then either stored inside cavities forming at the bonding interface or discharged into the oxide subsurface dependingon the type of oxide. It was also shown that the deposited oxide had a relatively balanced water concentration profile and could contain a significant amount of water. These findings have led to the development of two-layerstructures optimized for direct bonding. Understanding these different mechanisms provides new insights into the use of direct bonding processes for future applications.

Direct wafer bonding has been identified as an en-abling technology for microelectromechanical systems (MEMS). As the complexity of devices increase and the bonding of multiple patterned wafers is required, there is a need to understand the factors that lead to bonding failure. Bonding relies on short-ranged surface forces, thus flatness deviations of the wafers may prevent bonding. Bonding success is determined by whether or not the surface forces are sufficient to overcome the flatness deviations and deform the wafers to a common shape. A general bonding criterion based on this fact is developed by comparing the strain energy required to deform the wafers to the surface energy that is dissipated as the bond is formed. The bonding criterion is used to examine the case of bonding bowed wafers with etch patterns on the bonding surface. An analytical expression for the bonding criterion is developed using plate theory for the case of bowed wafers. Then, the criterion is implemented using finite element analysis, to demonstrate its use and to validate the analytical model. The results indicate that wafer thickness and curvature are important in determining bonding success and that the bonding criterion is independent of wafer diameter. Results also demonstrate that shallow etched patterns can make bonding more difficult while deep features, which penetrate through an appreciable thickness of the wafer, may facilitate bonding. Design implications of the model results are discussed in detail. Preliminary results from experiments designed to validate the model, agree with the trends seen in the model, but further work is required to achieve quantitative correlation. / Singapore-MIT Alliance (SMA)

Le collage direct consiste en la mise en contact de deux surfaces suffisamment lisses et propres pour créer une adhérence entre-elles, et ce sans apport de matière à l'interface des matériaux. Ce procédé est réalisable à l'échelle industrielle et compatible avec les procédés de la microélectronique. Il trouve son principal intérêt dans la réalisation de substrats innovants. Le plus célèbre d'entre eux est le substrat SOI (pour « Silicon On Insulator »). Depuis quelques années, une nouvelle voie s'est ouverte dans le collage direct en l'élargissant au collage de couches métalliques ce qui permet de répondre à de nouvelles applications en offrant par exemple conduction électrique et dissipation thermique. Ce travail de thèse a pour objectif d'analyser le comportement du collage direct de couches métalliques et de poser les premiers éléments de modélisation. La compréhension de ces fondamentaux est indispensable pour optimiser le procédé et permettre une intégration de cette technologie dans un grand nombre de dispositifs. Dans cette étude, des procédés de collage direct de couches de tungstène et de titane ont été développés à la lumière des pré-requis établis pour le collage direct. La caractérisation physico-chimique des interfaces de collage et de leur évolution en température ont permis de mettre en évidence le rôle clé de l'oxyde métallique. Il est montré que les mécanismes de collage sont gouvernés par des phénomènes de diffusion aux joints de grains et par l'instabilité de la couche d'oxyde piégée à l'interface de collage. Par ailleurs, les propriétés mécaniques et électriques des interfaces ont été étudiées. Enfin, la compréhension du comportement des interfaces en fonction de certains paramètres conduit à quelques recommandations pour réussir l'intégration du collage direct métallique. / Direct wafer bonding refers to a process by which two mirror-polished wafers are put into contact and held together at room temperature without any additional materials. This technology is feasible at an industrial scale and compatible with the microelectronic processes. Wafer bonding finds many interests applied to innovative substrates realization. Therefore the use of direct wafer bonding is growing and extending to various materials. Since few years direct bonding involving metallic layers presents many interests as it can offer, for example, vertical electrical conduction or heat dissipation. The aim of this work is to analyze the bonding behavior and to propose a first model describing the bonding driving forces. A precise understanding of these mechanisms is essential for the optimization and the technological integration of the process in various devices. In this study, tungsten and titanium bonding processes were developed. Physical and chemical bonding interfaces characterizations have highlighted the key role of the metallic oxide. We showed that bonding mechanisms are driven by grain boundary diffusion phenomena and the interface trapped oxide layer instability. Moreover, mechanical and electrical properties were also studied. Finally, the bonding behavior understanding in function of define parameters lead to some recommendations for the bonding process integration achievement.

Lors de l'assemblage de wafers par adhésion moléculaire, un mince film d'air est piégé entre les deux wafers, créant ainsi un système fluide/structure couplé.La qualité finale de l'assemblage dépend fortement de la dynamique de ce système.L'initiation et la propagation du collage ont été étudiées, en régime transitoire, en utilisant un modèle de plaques minces couplée avec l'équation de Reynolds. La résolution numérique de l'équation, ainsi que la mesure optique du déplacement vertical de la plaquette durant le collage, nous a permis de valider le modèle et de mieux comprendre la dynamique du collage.Dans la continuité de cette étude, nous avons proposé une expression analytique de la courbure finale de l'assemblage en fonction des forces en jeu pendant le collage, ceci en utilisant à nouveau la théorie des plaques minces et en considérant l'exitence d'un saut de déformation transverse le long de l'interface collée.Ce modèle a été validé par une expérience, impliquant le collage de wafers d'épaisseur différentes et en prenant soin de contrôler l'ensemble des forces agissant sur ces wafers. Nous observons une influence importante du film d'air sur la forme finale des wafers.En complément, un modèle du travail d'adhésion a été développé prenant en compte, à la fois, la rugosité d'interface et la quantité d'eau adsorbée. La différence de répartition de l'eau à l'interface de collage, nous permet d'expliquer les résultats expérimentaux montrant des valeurs d'énergie de séparation supérieure à celle de l'adhésion.Enfin, nous proposons une nouvelle méthode de mesure du travail d'adhésion pour la géométrie entière des wafers, utilisant la mesure de la taille d'une bulle cylindrique intentionnellement créée, par un petit objet, à l'interface de collage. / The direct wafer bonding process involves a coupled physical system, formed by the elastic deformation of the wafers and a thin layer of fluid trapped in-between the two wafers.Dynamics of the system during the contacting step has many practical consequences on the quality of the assembled stack.A model for the bonding dynamics is formulated using the thin plate theory and the Reynolds equation. The transient equation is solved numerically, allowing to study both the initiation and the propagation of the bonding. The model is supported by the measurement of the vertical movement of the wafer during the bonding, using an original setup involving optical sensors.Subsequently, an analytical model for the final curvature of the bonded stack is derived, as a function of the different load components acting on the wafers during the bonding, using the thin plate theory and by considering a transverse strain discontinuity locked at the bonding interface.Experimental validation is performing using two different wafer thicknesses. The measured bonded wafer profiles are well described by the model.In addition, a model for the work of adhesion is developed, taking into account both the interface roughness and the amount of adsorbed water.The interface energy controlling the adhesion is found different than for the separation because of the different distribution of water along the interface, in agreement with the experimental observations. At last, a new method to accurately measure the work of adhesion for the entire wafers geometry is proposed, using an elongated bubble intentionally created at the bonding interface and by measuring the induced wafer deflection.

<p>Microengineering has developed a broad range of production techniques to reduce size, increase throughput, and reduce cost of electrical and mechanical devices. The miniaturisation has also entailed entirely new opportunities.</p><p>In this work, a piezoresistive silicon sensor measuring mechanical deformation has been designed and fabricated with the help of microengineering. Due to the large variety of used processes, this device can serve as a survey of techniques in this field. Four basic process categories are recognised: additive, subtractive, modifying, and joining methods.</p><p>The last category, joining methods, has previously been the least investigated, especially when it comes to compatibility with the other categories. The adaptability of wet chemical etching to established silicon wafer bonding technique has been investigated. Further, phenomena related to oxygen plasma pre-treatment for direct bonding has been investigated by blister bond adhesion tests, X-ray photoelectron spectroscopy, and atomic force microscopy.</p><p>Wafer bonding has been adapted to monocrystalline quartz. For wet chemical pre-treatment, characteristics specific for quartz raise obstacles. Problems with limited allowable annealing temperature, low permeability of water released in the bond at annealing, and electrostatic bonding of particles to the quartz surface, have been studied and overcome. The influence of internal bond interfaces on resonators has been investigated.</p><p>Chemical polishing of quartz by ammonium bifluoride has been experimentally investigated at high temperatures and concentrations. Chemometrical methods were used to search for optimum conditions giving the lowest surface roughness. These extreme conditions showed no extra advantages.</p><p>Adhesion quantification methods for wafer bonding have been comprehensively reviewed, and augmentations have been suggested. The improved techniques’ usefulness for three areas of use has been forecasted: general understanding, bonding scheme optimisation, and quality control. It was shown that the quality of measurements of all commonly used methods could be dramatically improved by small means.</p>

Microengineering has developed a broad range of production techniques to reduce size, increase throughput, and reduce cost of electrical and mechanical devices. The miniaturisation has also entailed entirely new opportunities. In this work, a piezoresistive silicon sensor measuring mechanical deformation has been designed and fabricated with the help of microengineering. Due to the large variety of used processes, this device can serve as a survey of techniques in this field. Four basic process categories are recognised: additive, subtractive, modifying, and joining methods. The last category, joining methods, has previously been the least investigated, especially when it comes to compatibility with the other categories. The adaptability of wet chemical etching to established silicon wafer bonding technique has been investigated. Further, phenomena related to oxygen plasma pre-treatment for direct bonding has been investigated by blister bond adhesion tests, X-ray photoelectron spectroscopy, and atomic force microscopy. Wafer bonding has been adapted to monocrystalline quartz. For wet chemical pre-treatment, characteristics specific for quartz raise obstacles. Problems with limited allowable annealing temperature, low permeability of water released in the bond at annealing, and electrostatic bonding of particles to the quartz surface, have been studied and overcome. The influence of internal bond interfaces on resonators has been investigated. Chemical polishing of quartz by ammonium bifluoride has been experimentally investigated at high temperatures and concentrations. Chemometrical methods were used to search for optimum conditions giving the lowest surface roughness. These extreme conditions showed no extra advantages. Adhesion quantification methods for wafer bonding have been comprehensively reviewed, and augmentations have been suggested. The improved techniques’ usefulness for three areas of use has been forecasted: general understanding, bonding scheme optimisation, and quality control. It was shown that the quality of measurements of all commonly used methods could be dramatically improved by small means.

This paper discusses basic issues of micromachined ultrasonic transducers, including their design and fabrication. First, the acoustic fundamentals of ultrasonic transducers are introduced, and relevant simulation methods are illustrated. Following these topics, important aspects of silicon micromachining are presented. Based on this knowledge, two distinctive micromachining processes for transducer fabrication are proposed. One of them, the bulk process, has been proved to be successful, whereas for the second one, a surface process, some improvements are still needed. Besides these works, an innovative direct bonding technology is also developed. This technology constitutes the basis of the bulk process. Of course, it can also be used for the packaging of other MEMS devices.

Le collage direct est maintenant utilisé par un nombre croissant d'applications en microélectronique (Elaboration de SOI, technologie imager Back Side Illumination, technologies 3D...). C'est une technique d'assemblage permettant de coller deux surfaces sans apport de matière adhésive. Principalement utilisée pour le collage de wafers, elle vient en complément de techniques telles que l'épitaxie ou le dépôt de couches minces. Ce collage s'effectue sous certaines conditions : il faut que les surfaces soient suffisamment propres, planes et lisses pour qu'il y ait une adhésion spontanée à température et pression ambiante. Enfin, un traitement thermique est appliqué pour augmenter l'énergie d'adhérence. Pendant le processus de fabrication, il peut apparaître des défauts de collage qui sont essentiellement dus à un piégeage de particules. Ces défauts se présentent sous la forme de bulles d'air. Finalement, les défauts de collage et l'énergie de collage sont les deux caractéristiques à partir desquelles est déduite une qualité de collage.Aujourd'hui, la technique utilisée pour la mesure d'énergie de collage est le clivage au coin. C'est une technique qui consiste dans un premier temps à séparer partiellement deux wafers par une lame, et dans un second temps, à calculer l'énergie de collage à partir d'une équation comportementale qui intègre la longueur de décollement. Mis à part le fait qu'elle permette la mesure d'énergie seulement sur quelques points, il se trouve que c'est une technique destructive. Un contrôle non destructif serait très intéressant pour l'industrie microélectronique et spécialement pour les lignes d'inspection. De plus, les procédés de fabrication microélectronique n'étant pas uniforme, avoir la possibilité d'obtenir une cartographie d'énergie de collage serait un atout majeur. A ce jour, aucune technique respectant ces deux exigences n'est connue. L'objectif de cette étude est d'utiliser la microscopie acoustique pour mesurer l'énergie de collage.Dans cette étude, un modèle inspiré de la "méthode des matrices hybrides" a été développé afin de modéliser des collages de différentes qualités. Le résultat de la modélisation montrera que le coefficient de réflexion acoustique de la structure collée est influencé par la qualité d'interface. En se plaçant dans des conditions précises, une méthode expérimentale est alors réalisée pour la mesure de la qualité d'interface. En parallèle, des wafers de Silicium réalisés par collage direct ont été spécialement conçus pour valider la méthode. Sur ce principe, des cartographies bidimensionnelles d'énergie de collage sont réalisées.Dans un second temps, la technique est améliorée afin d'augmenter la résolution latérale. Pour cela, un transducteur ayant une lentille est utilisé pour focalisé les ondes ultrasonores en points du collage. Une étude théorique est tout d'abord menée en utilisant le modèle du "spectre angulaire" afin de simuler la diffraction par la lentille. Enfin, des cartographies expérimentales confirmeront la faisabilité de mesures d'énergie de collage hautes résolutions. / Direct bonding is used for many applications in microelectronics (SOI Silicon-On-Insulator technology, imager back side illumination technology, 3D technology...). It is a processes that consists in an assembly of two surfaces without any adhesive material. It is primarily used to bond silicon wafers and it is complementary with other microelectronics technique such as epitaxy, thin film deposition... Bonding requires special wafer surface conditions and preparations. The surfaces have to be clean, flat and smooth to obtain a spontaneous adhesion at ambient temperature and atmospheric pressure. A heat treatment is applied to increase the adherence energy. During the manufacturing process, bonding defects may appear which are due to trapping of particles. These bonding defects are essentially formed of air. Finally, bonding defects and bonding energy are the two main characteristics from which is deduced the bonding quality.Nowadays, the main technique that is used to measure the direct bonding energy is the double cantilever beam (DCB). The method consists in firstly partially separating the two wafers by a blade, and secondly calculating the bonding energy from an equation that integrates the debonding lenght. The major disadvantage of this technique is its destructiveness. Furthermore it is only possible to make measurements on few points.Thus a non-destructive characterisation could be very interesting especially for an industrial in-line inspection. Moreover, having the possibility to obtain a mapping of the bonding energy could lead to interesting development. Up to know, no technique can reach the both requirements. The aim of this work is to use the acoustic microscopy to measure the direct bonding energy.In this study, a model based on "hybrid matrix method" has been developed to model bonding with different qualities. The results of the modelling show that the acoustic reflection coefficient of the bonded structure is influenced by the quality of the interface. From these results, an experimental method is proposed to perform quality of the interface measurements from the reflection coefficients acquired under normal incidence. In parallel, silicon wafers have been bonded to validate the method. Finally, once the method validated, two-dimensional mappings of the interface quality are realised.Secondly, the technique is improved to increase the lateral resolution. For this, a transducer having a lens is used to focus the ultrasonic waves on the bonded structure. A theoretical study is conducted using the model of the "angular spectrum" to simulate the diffraction lens. Finally, experimental mapping confirm the feasibility of measuring bonding energy of high resolutions.