Les diélectriques solides sont les éléments constitutifs de base des isolants utilisés dans les composants ou les systèmes du génie électrique et de l'électronique de puissance. Principalement à cause des tendances à la miniaturisation, ces isolants sont soumis à des contraintes sans cesse croissantes (électriques, mécaniques et thermiques) qui peuvent dégrader ou induire un vieillissement prématuré des diélectriques. Ceci peut conduire à la défaillance ou à un claquage de la structure, phénomènes qui l'on doit prendre en compte et étudier. De manière plus précise, la charge globale stockée à l'intérieur du matériau diélectrique, généralement dénommée charge d'espace, est directement liée à ces processus de dégradation. Ainsi, il devient alors nécessaire d'analyser le comportement de la charge d'espace lorsque le matériau est contraint dans des conditions proches d'un environnement réel d'utilisation. Parmi les techniques existantes, la (F)LIMM est une méthode thermique dédiée à l'analyse de la charge d'espace dans des fines couches diélectriques (avec une épaisseur comprise entre 5µm et 50µm), avec la possibilité de réaliser des cartographies en 3-D lorsque le faisceau laser est focalisé à la surface de l'échantillon étudié. Les premières caractérisations par cette technique étaient liées à la détermination de la distribution de la charge d'espace dans des films minces qui avaient été préalablement soumis à un champ électrique continu, puis analysés hors tension (volt-off). Cette procédure dite " off-line ", et mise en œuvre pendant la dépolarisation de l'échantillon, est restée longtemps la seule façon d'analyser la charge d'espace. De nouveaux développements sont devenus nécessaires plus récemment pour apporter des réponses au domaine industriel pour lequel une caractérisation du comportement dans des conditions d'utilisation réelles faisait défaut. Dans ce but, une version " sous tension " ou " on-line " du banc expérimental (F)LIMM conventionnel a été développée. Ainsi, la mesure du courant (F)LIMM se réalise maintenant de manière simultanée à l'application d'un champ électrique continu externe sur l'échantillon. Outre la mesure in-situ et l'analyse sous tension, ces nouveaux développements présentent un avantage supplémentaire consistant en la possibilité d'évaluer et de calibrer les profils de température. Dans ce travail, les modifications expérimentales réalisées sur le banc test de mesure sont tout d'abord détaillées et validées. Puis, la procédure de calibration du model thermique proposé est expliquée et testée. Ainsi, la simulation les courants (F)LIMM devient possible et l'on constate une bonne adéquation avec les courants expérimentaux enregistrés. Enfin, quelques applications à des films polymères minces en PEN et en PP sont décrites. Les résultats obtenus prouvent alors que ces évolutions expérimentales et théoriques sont efficaces pour l'étude du comportement de la charge d'espace " sous tension ". / Solid dielectrics are basic elements of most insulations used in devices or systems in electrical engineering or in power electronics. Mainly due to current trends in downsizing, these insulations being subjected to increasing stresses (electrical, mechanical or thermal) may degrade and age dielectrically. This may lead to failure and breakdown, which have to be addressed. More specifically, the global charge store inside the dielectric and generally called space charge is directly linked to these degradation processes. It is therefore necessary to analyze this space charge behavior when the material is at the same time stressed under conditions close to those of the real environment of use. Among many existing techniques, the (F)LIMM is a thermal wave method dedicated to the space charge analysis of thin dielectric films (with a thickness from 5µm to 50µm), with a possibility of 3-D cartographies when the beam is focused onto the sample under study. Its first characterizations were related to the determination of the space charge distribution in thin films that were first submitted to an external DC field and next analyzed in a volt-off way (no voltage applied). This off-line procedure remained the only way of space charge investigations for quite a while. New developments became necessary in order to provide answers to the industry for which a characterization close to the actual conditions of use was lacking. For this purpose, an on-line version of the conventional (F)LIMM set-up was developed. It allows a measurement of the (F)LIMM current when simultaneously a DC bias field is applied to the sample. This development presents, apart from allowing an in-situ and on-line analysis, another important advantage, namely the possibility for assessing or calibrating the temperature profile. In this work, the experimental modifications made to the measuring test rig are first detailed and validated. Then, the calibration procedure of the thermal model developed is explained and tested. As a consequence, the possibility of simulating the (F)LIMM currents is possible and shows a very good agreement with the experimental registered ones. Finally, some applications to PEN and PP polymer thin films are described and results got prove the efficiency of these new developments for space charge on-line investigation.

Les multiferroïques sont des matériaux dans lesquels plusieurs propriétés ferroïques peuvent coexister, e. g. ferromagnétisme et ferroélectricité. La recherche de tels matériaux fait l'objet d'une activité croissante en raison de l’enjeu majeur qu’ils représentent dans de nombreux domaines (mémoires, spintronique…). Les matériaux qui possèdent les propriétés nécessaires pour des applications futures sont cependant peu nombreux. Des niobates de formule Ba2LnFeNb4O15 (Ln = lanthanide), de structure bronze quadratique (TTB) susceptibles de présenter un ordre ferroélectrique et un ordre magnétique ont été synthétisés. Les propriétés magnétiques des céramiques proviennent d'une phase secondaire, faisant d’eux des composites multiferroïques. Leur souplesse cristallochimique permet de contrôler les propriétés composites par substitutions cationiques dans la matrice TTB. Afin de compléter l'étude cristallochimique, la croissance de monocristaux de TTB a été entreprise avec succès. / Multiferroics are materials which possess several ferroic properties, e.g. ferroelectricity, ferromagnetism. The search for multiferroics arises a growing activity, due to their potential applications in memories, spintronic… Yet the materials displaying the adequate properties for future application are very few. Niobates with the formula Ba2LnFeNb4O15, potentially ferroelectric and ferromagnetic, have been synthesized. The magnetic properties of the ceramics are related to a secondary phase, thus making them composite multiferroics. Their crystal-chemical flexibility allows for the composites properties tuning by cationic substitutions into the TTB framework. To complete the crystal-chemical study, the growth of TTB single-crystals was successfully engaged.

A challenging application space exists for high-aspect-ratio, high-fidelity dielectrics in micro-electro-mechanical system (MEMS), microelectronic, and photonic applications. Photosensitive polymers are widely used in these fields because they are relatively easy to process and pattern, and have good mechanical properties. Photosensitive polynorbornene (PNB)-based dielectrics have been shown to have high sensitivity, excellent photodefinition properties, and high mechanical strength making them suitable for MEMS, microelectronic packaging, and photonic applications. PNB-based dielectrics can be functionalized with epoxide, carboxylic acid, or fluorinated alcohol groups. Epoxy or carboxylic acid groups can be used to provide cross-linkable sites, resulting in improved chemical and thermal properties while fluorinated alcohol groups can provide solubility in aqueous base. The focus of this study has been on the epoxy-based cross-linking of ultraviolet and electron beam (e-beam) sensitive negative-tone PNB-based dielectrics. The impact of multifunctional epoxy-based additives on the cross-linking, photolithographic properties, and adhesion properties of the photosensitive PNB dielectric was investigated. High aspect ratio features of 13:1 (height:width) were produced in 40 µm thick films (a single coat) with straight side-wall profiles and high fidelity. Contrast values as high as 33.4 were obtained at doses below 15 mJ/cm2. To evaluate the polymer's suitability to MEMS and microelectronics applications, epoxy cross-linking reactions were studied as a function of processing condition through Fourier transform infrared spectroscopy (FTIR), nanoindentation, swelling and dielectric measurements. The fully cross-linked films had an elastic modulus of 2.9 GPa and hardness of 0.18 GPa which can improve the mechanical compliance of the packaging device. To explore the feasibility of the PNB dielectric as a highly sensitive e-beam resist for nano scale fabrication, the e-beam initiated reaction between PNB cross-linking sites and the multifunctional epoxy cross-linkers was investigated. In this study, the interaction of an e-beam with the PNB mixture and its compounds was investigated. The contrast, photodefinability, and e-beam activation of the components in the PNB formulations were studied. The PNB polymer had very high e-beam sensitivity and contrast. It was shown that the addition of a photoacid generator (PAG) to the polymer-epoxy mixture enhanced the contrast and sensitivity. Formulations with the additional cross-linker showed improved contrast, sensitivity, and substrate adhesion. 100 nm structures with 13.5 nm line edge roughness (LER) were fabricated. The influence of the developing time, the developer concentration, PEB, and film thickness on the contrast and sensitivity were studied. Structures with contrast values as high as approximately 8 were fabricated at doses as low as 0.38 µC/cm2. The acid-catalyzed epoxy ring opening reaction of the PNB dielectric was studied using FTIR spectroscopy. The photo and thermal acid generation initiated epoxy ring opening reactions and subsequent cross-linking of polymer. Additionally, polymer properties were characterized as a function of processing conditions for this polymer system. It was shown that thermal cure conditions have a substantial impact on the mechanical and electrical properties of the polymer. The rate and ultimate conversion of the epoxy ring opening reaction increased with increasing cure temperature, resulting in a higher degree of cross-linking at cure temperatures above 140°C. Degradation reactions occurred at temperatures above 160°C, indicating loss of epoxide cross-linking groups and linkages. These hypotheses were supported by electrical and mechanical property studies. It was shown that curing the PNB polymer at 160°C for 1 h after develop resulted in full epoxy ring opening and highest cross-link density. This sample showed lower dielectric constant (3.9), residual stress (20 MPa), and solvent swelling (3.1%). Variable frequency microwave (VFM) processing of the PNB dielectric was studied to investigate the rapid curing of the polymer at lower temperatures. The FTIR results showed that the microwave reaction rates were higher at each isothermal cure temperature compared to convective heating, indicating that the rapid VFM curing of PNB at low temperatures is feasible. The PNB film was fully cross-linked after 15 min VFM cure at the low temperature of 150˚C. The shortest time to fully cure the polymer was found to be 5 min at 160°C. Also, the feasibility of rapid VFM curing of PNB in air was studied. All samples VFM-cured (140˚C-180˚C) in air showed no signs of oxidation. The electrical and mechanical properties of VFM-cured films were characterized and compared with thermally cured films to determine the effectiveness of the VFM processing. VFM-cured samples showed higher degree of cross-linking than thermally-cured samples, which was congruent with the FTIR results. Improved or equivalent properties were obtained for VFM-cured samples at shorter cure cycles and lower cure temperatures compared to thermally-cured films. The PNB dielectric was also used as an overcoat material to make micro and nano fluidic channels. In this work, incorporation of advanced micro/nano fluidics with high-sensitivity photonic sensors was demonstrated. 500 nm to 50 µm channels were fabricated by thermal decomposition of epoxy-based PNB polymers. Microdisks with quality factors of over 106 were presented in complementary metal-xide-semiconductor (CMOS) compatible SiN on oxide technology. These ultra-high quality factor SiN resonators were demonstrated in the visible range for the first time. The fluidic structures were interfaced with photonics for index and florescence sensing. This study was a collaboration with Dr. Ehsan Shahhosseini from the Photonics Group at Georgia Tech.

This thesis deals with the investigations on the atomic composition, chemical surface states and microstructural features of barium titanate and other electronic ceramics namely barium polytitantes, calcium manganites and magnesium calcium titanate by surface analytical techniques. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and interfacial characteristics, the thesis describes the synthesis of the ceramics and the methodology of the different surface analytical techniques utilized such as backscattering spectrometry (BS), an ion beam analysis (IBA) technique, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS). The XPS investigations on the chemical surface states of polycrystalline barium titanate having well-defined electrical characteristics reveal the prevalence of Ba in two distinct chemical environments : the one corresponding to the lower binding energy is related to the dielectric while the other having higher binding energy is correlated to semiconducting properties of the ceramics. Processes such as abrasion or polishing make the surfaces more reactive and susceptible to atmospheric contamination. Sputter cleaning causes surface modification leading to changes in the Ba (3d) and Ti (2p) spectra. Studies on the surface atomic composition by BS and microstructural features of doped barium titanate ceramics reveal their interfacial characteristics in terms segregation of dopants or metal ion constituents. Surfaces of these ceramics exhibit cationic as well as anionic nonstoichiometry depending on the processing steps involved. Ceramics synthesized by oxalate precursor route are Ti-rich while those prepared by gel-to-crystallite method are Ba-rich. These are correlated to the chemical processes and background impurities which in turn control the microstructures. Barium titanate substitued with > 1 at. % Mn are deficient in oxygen and exist as the hexagonal polymorph. Acceptors segregate at the grain boundaries accompanied by the enrichment of Ti leading to PTCR or GBLC characteristics. The oxygen nonstoichiometry prevailing in the surface regions of differently processed calcium manganites is investigated by way of depth profile measurements involving 16O(a,a) 16O resonant scattering. These studies reveal extensive compositional heterogeneity across the surface layers particularly in the manganite specimens annealed in lower po2 leading to the stabilization of brownmillerite phase. Two of the microwave dielectric ceramics namely dibarium nona-titanate and barium tetra-titanate with suitable variations in Ba:Ti ratios have been synthesized by the carbonate-gel precipitation. The corresponding dense ceramics have high permittivity (~ 52) and low temperature coefficient of permittivity (TCK ~ 5 ppm /0C). Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ + La3+. The resulting (Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The microarea elemental distribution and chemical surface state studies reveal the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. The discontinuous changes in the local site symmetry of the cationic substituents in these ceramics have been investigated by the photoluminescence spectra using Pr3+ as the emission probe.

Die ITRS (International Technology Roadmap for Semiconductors) sagt voraus, dass die fortlaufende Miniaturisierung der Transistoren und Verdrahtungen auch neue Isolationsmaterialien mit äußerst niedrigen (ultralow) Dielektrizitätskonstanten k erfordern wird. Die Miniaturisierung der Bauteile der ULSI (Ultra Large Scale Integration) führt zu starken Anforderungen an die Fertigung der kritischen Bereiche (backend-of-line, BEoL). Die ITRS deutet darauf hin, dass die k-Werte bis zu 2.0 für die 45 nm Technologie reduziert werden müssen, und zu noch niedrigeren k-Werten (k  1.5) für die nachfolgenden Jahre. Ergänzend zur äußerst niedrigen dielektrischen Konstante müssen die Isolatoren auch über entsprechende mechanische Eigenschaften verfügen. Die vorliegende Arbeit stellt Forschungen vor, die das Ziel haben, mittels modernen ab-initio und halbempirischen theoretischen Methoden neuartige Isolationsmaterialien für zukünftige mikroelektronische Anwendungen zu entwerfen. Die umfangreichen eingesetzten Rechenmethoden wurden verwendet, um strukturelle und physikalische (mechanische, dielektrische und elektronische) Eigenschaften von entworfenen Zwischenschichtsdielektrika zu bestimmen. Eine neue Art von Materialien wird vorgestellt, die als ein möglicher Kandidat für isolierende ultralow-k dünne Schichte zwischen Metallleiterbahnen in zukünftigen CMOS (Complementary Metal-Oxide-Semiconductor) Technologien fungieren sollen. Die Struktur der neuartigen Materialien wird durch ein Modell beschrieben, das ein geordnetes dreidimensionales Netzwerk (Mosaikstruktur) darstellt. Dies besteht aus drei Hauptkomponenten: Knoten, Kanten und Topologie der Anordnung. Fullerenmoleküle (C60) werden als Knoten des Netzwerkes verwendet. Die Knoten werden durch Verknüpfermoleküle entlang der Kanten der Mosaikzelle angekoppelt. Dies wird durch kovalente Bindungen realisiert. Als Verknüpfermoleküle werden Kohlenwasserstoff- Kettenmoleküle verwendet. Einfache kubische, flächenzentrierte kubische und diamantähnliche Topologien werden für Anordnungen des Netzwerkes betrachtet. Das Innere einer Netzwerkzelle repräsentiert eine Nanopore der Größe in Bereich von 1 nm. Zunächst werden am Beispiel fluorierter Fullerene Probleme der molekularen Polarisierbarkeit untersucht. In Molekülen mit ionischem Beitrag zur Bindung kann der Beitrag der Kernverschiebungen (wegen des äußeren Feldes) zur statischen Polarisierbarkeit entscheidend sein. Mittels der Finite Field Methode wird die Struktur mit und ohne ein endliches äußeres elektrisches Feld optimiert. Dabei wird die Optimierung durch Minimierung der Gesamtenergie durchgeführt und die molekulare Polarisierbarkeit aus dem induzierten Dipolmoment bestimmt. In C60Fn erhöht meistens das Fluorieren die Polarisierbarkeit. Nur für n = 2 und 18, wobei das Molekül ohne ein äußeres Feld ein sehr großes Dipolmoment hat, wird die Polarisierbarkeit verringert. Für große Werte n (n = 20, 36 und 48) wird die Polarisierbarkeit pro zusätzliches Fluoratom wegen Kernverschiebungen deutlich erhöht. Die Modifizierung der Knoten des Netzwerkes wird betrachtet und die Anwendbarkeit des Additivitätsmodells diskutiert. Die Dielektrizitätskonstante des reinen flächenzentrierten kubischen Fullerengitters beträgt etwa 4.4. Die Einführung der Verknüpfermoleküle zwischen benachbarten Fullerenmolekülen und die gleichzeitige Verwendung von auf Kohlenstoffatomen basierten käfigförmigen Molekülen reduziert die Dichte des Materials. Dies ergibt eine beträchtliche Verringerung der makroskopischen Polarisierbarkeit des Materials. Die Struktureinheit, die aus zwei Fullerenmolekülen und einem Kohlenwasserstoff-Verknüpfermolekül besteht, wird mittels quantenchemischer Methoden (DFTB Molekulardynamik) optimiert. Es werden die Dichte der lokalen Dipole und elektronische Effekte betrachtet, um die effektive Dielektrizitätskonstante des Modells abzuschätzen. Die Berechnungen zeigen, dass k-Werte von etwa 1.4 erreicht werden können, wenn C6H12 Kettenmoleküle verwendet werden, um die C60-Moleküle im Netzwerk mit diamantähnlicher Symmetrie zu verknüpfen. Weiterhin werden molekulare Cluster mit angelegten periodischen Randbedingungen für einfache kubische und diamantähnliche Topologien konstruiert. Kombinationen der klassischen und quantentheoretischen Methoden werden eingesetzt, um die Struktur zu optimieren, Kompressionsmodule zu berechnen und die dielektrischen Eigenschaften der fullerenbasierten Materialien zu berechnen. Dies hat das Ziel, ultralow-k Isolatoren mit entsprechenden mechanischen Eigenschaften zu finden. Es wird die kovalente Verknüpfung der C60 Moleküle untersucht und sowohl die Länge und chemische Zusammensetzung des Verknüpfermoleküles als auch die Verknüpfungsgeometrie variiert. Gemäß dem entworfenen Modell werden Strukturen mit einfacher kubischer und diamantähnlicher Topologie des Netzwerkes als vielversprechende Kandidaten betrachtet. Die (statische) Dielektrizitätskonstanten k und Kompressionsmodule B sind für einige vorgeschlagene Materialien im Bereich von k = 1.7 bis 2.2 und beziehungsweise von B = 5 bis 23 GPa. Das Clausius-Mossotti Modell wird zur Bestimmung der Dielektrizitätskonstante der entworfenen Strukturen verwendet. In den nächsten Schritten der Arbeit werden die Wege der Verbesserungen für das vorgeschlagene Modell betrachtet. Es wird analysiert, auf welche Art Verknüpfermoleküle an die Knoten gebunden werden können, um die mechanischen und dielektrischen Eigenschaften der generierten ultralow-k Strukturen zu verbessern. Es gibt zwei mögliche verschiede Arten, die Verknüpfermoleküle > C = C < und > C – CH2 – CH2 – C < an das Käfigmolekül C60 anzukoppeln. Die Berechnungen zeigen, dass es im gegenwärtigen Verbesserungsschritt möglich ist, für die einfache kubische Topologie Eigenschaftskombinationen mit k = 2.2 und B = 33 GPa zu bekommen. In der vorliegenden Arbeit wurde eine theoretische Methode ¬¬– sogenannter molekularer Entwurf – entwickelt und erfolgreich angewandt. Die theoretische Behandlung ist kompliziert, weil Wechselwirkungen im atomaren Skalabereich und auf einem strukturellen Niveau von 1 nm zusammen betrachtet werden müssen. Dies Verfahren erfordert die Anwendung komplementärer theoretischen Methoden, um das gesamte Problem beschreiben zu können. Die Methoden schließen klassische, kontinuierliche theoretische und quantenchemische Näherungen ein. Der Vorteil dieser Methode ist, dass verschiedene mögliche Kandidaten für ultralow-k Dielektrika theoretisch getestet werden können, ohne teure und zeitaufwendige Experimente durchzuführen. / The International Technology Roadmap for Semiconductors (ITRS) predicts that continued scaling of devices will require insulating materials with ultralow dielectric constant k. The shrinking of device dimensions of ultra-large-scale integrated (ULSI) chips imposes strong demands on the backend of the line (BEoL) interconnect structures. The ITRS indicates that the k values need to be reduced to 2.0 for the 45 nm technology node or below (k  1.5) in the next few years. Additionally to extremely low dielectric constants, the insulating materials must have also suitable mechanical properties. The work represents research, which is aimed to support molecular design and investigations of modelled novel insulating materials for future application in microelectronics by means of theoretical ab-initio and semiempirical methods. A wide range of computational methods were used to estimate structural and physical (mechanical, dielectrical and electronic) properties of the designed interlayer dielectrics (ILDs). A new class of materials is presented that is supposed to be a potential candidate for isolating ultralow-k thin films between metal on-chip interconnects in future CMOS technology nodes. The structure of the novel materials is described by a model that assumes an ordered three-dimensional network (mosaic structure) consisting of three main components: nodes, edges and topology of arrangement. Fullerene (C60) molecules are used as the nodes of the network. The nodes are connected by linker molecules along the edges of the mosaic cells through a covalent bonding. Hydrocarbon chain molecules are used as the linkers. Simple cubic, face-centred cubic and diamond-like topologies of the network are considered. The interior of a network cell represents a nanopore of a 1-nm scale. At first problems of molecular polarizability are investigated considering the case of fluorinated fullerenes. In molecules with ionic contribution to the binding, the contribution of nuclear displacements (due to the external field) to the static polarizability can be decisive. Using the finite field method, the structure is optimized with and without a finite external electric field by a total energy minimization and the polarizability is calculated from the induced dipole moment. In C60Fn, fluorination mostly increases the molecular polarizability. Only for n = 2 and 18, where the molecule without an external field has a very large dipole moment, fluorination does decrease it. For large n (n = 20, 36, and 48), the polarizability per added F atom due to nuclear displacements is increased by a factor of about 2. The modification of the nodes of the network is considered and the validity of the additivity model is discussed. The dielectric constant of the pure fullerene face-centred cubic lattice is about 4.4. The introduction of bridge molecules between neighbouring fullerene molecules and the simultaneous usage of cage-like molecules based on carbon atoms reduces the density of the material. This results in a considerable decrease of the macroscopic polarizability of the material. The structural units of the models consisting of two fullerenes and a hydrocarbon bridge molecule are optimized by means of quantum chemical methods (DFTB molecular dynamics). The density of local dipoles and electronic effects are considered to estimate the effective dielectric constant of the models. It is shown that k values of about 1.4 can be obtained if C6H12 chain molecules are used to connect C60 molecules on a network with diamond-like symmetry. Further, molecular clusters with applied periodic boundary conditions are constructed for simple cubic and diamond-like topologies. Combinations of classical and quantum-theoretical approaches are used to optimize the structure, to calculate bulk moduli, and for the assessment of the dielectric properties of fullerene-based materials with the goal to find ultralow-k insulators with suitable mechanical properties. The covalent linking of C60 molecules is studied and the length and chemical composition of the linker molecule as well as the linkage geometry is varied. According to the molecular design-based model, structures with simple cubic and diamond-like topology of the network are proposed as promising candidates. The (static) dielectric constants k and elastic bulk moduli B of the proposed materials are in the range of k = 1.7 to 2.2 and B = 5 to 23 GPa, respectively. The Clausius-Mossotti-Model is used to estimate dielectric constants of the designed structures. In the next steps of the work the ways of improvements for the proposed model are considered. The way to connect linker molecules to the node molecules is analyzed, in order to improve the mechanical and dielectric properties of the generated ultralow-k structures. Two different types of bonding linker molecules to the cage C60 molecule with the > C = C < and > C – CH2 – CH2 – C < linker molecules are possible. It is shown that at the present improvement step it is possible to get property combinations with dielectric constant of k = 2.2 and bulk modulus of B = 33 GPa for the simple cubic topology. In this work a theoretical method called molecular design is developed and successfully applied. The theoretical treatment is difficult since interactions both on the atomic scale and on the structural level of 1 nm must be considered. This approach requires the application of complementary theoretical methods to describe the complex problems. The methods include classical, continuum theoretical and quantum-chemical approximations. The advantage of the present approach is that various possible candidates for ultralow-k dielectrics can be tested theoretically without performing expensive and time-consuming experiments.

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Materials, Processes, and Characterization of Extended Air-gaps for the Intra-level Interconnection of Integrated Circuits Seongho Park 157 pages Directed by Dr. Paul A. Kohl and Dr. Sue Ann Bidstrup Allen The integration of an air-gap as an ultra low dielectric constant material in an intra-metal dielectric region of interconnect structure in integrated circuits was investigated in terms of material properties of a thermally decomposable sacrificial polymer, fabrication processes and electrical performance. Extension of the air-gap into the inter-layer dielectric region reduces the interconnect capacitance. In order to enhance the hardness of a polymer for the better process reliabilities, a conventional norbornene-based sacrificial polymer was electron-beam irradiated. Although the hardness of the polymer increased, the thermal properties degraded. A new high modulus tetracyclododecene-based sacrificial polymer was characterized and compared to the norbornene-based polymer in terms of hardness, process reliability and thermal properties. The tetracyclododecene-based polymer was harder and showed better process reliability than the norbornene-based sacrificial polymer. Using the tetracyclododecene-based sacrificial polymer, a single layer Cu/air-gap and extended Cu/air-gap structures were fabricated. The effective dielectric constant of the air-gap and extended air-gap structures were 2.42 and 2.17, respectively. This meets the requirements for the 32 nm node. Moisture uptake of the extended Cu/air-gap structure increased the effective dielectric constant. The exposure of the structure to hexamethyldisilazane vapor removed the absorbed moisture and changed the structure hydrophobic, improving the integration reliability. The integration processes of the air-gap and the extended air-gap into a dual damascene Cu metallization process has been proposed compared to state-of-the-art integration approaches.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. 66-73. Document électronique également accessible en format PDF. CaQCU

Θέμα της παρούσας ερευνητικής εργασίας είναι η μελέτη διατάξεων MOS σε υπόστρωμα Ge τύπου –p. Ως διηλεκτρικό πύλης χρησιμοποιήθηκε Al2O3 και ως μέταλλο πύλης Pt. Τέτοιες διατάξεις οι οποίες αποτελούνται από υπόστρωμα Ge στο οποίο εναποτίθεται διηλεκτρικό υψηλής διηλεκτρικής σταθεράς (high-k dielectric) εμφανίζουν ιδιαίτερο ερευνητικό και τεχνολογικό ενδιαφέρον για τους παρακάτω κυρίως λόγους: (i) Το Ge εμφανίζει υψηλότερη ευκινησία φορέων έναντι αυτής του Si. Eπομένως η χρήση υποστρωμάτων Ge στις διατάξεις MOS θεωρείται πλεονεκτική έναντι της χρήσης υποστρωμάτων Si, τα οποία μέχρι σήμερα έχουν μονοπωλήσει τις τεχνολογικές εφαρμογές και κατ’ επέκταση την έρευνα γύρω από αυτές. (ii) Η χρήση υλικών υψηλής διηλεκτρικής σταθεράς, όπως το Al2O3, ως διηλεκτρικά πύλης φέρεται πλέον ως ιδιαίτερα ελπιδοφόρα για την μελλοντική κατασκευή λειτουργικών διατάξεων MOS. (iii) Πρόσφατες μελέτες έχουν αποδείξει ότι, κατά την ανάπτυξη Al2O3 στα υποστρώματα Ge, στη διεπιφάνεια Ge/Al2O3, δημιουργείται ένα λεπτό στρώμα οξειδίου του γερμανίου, το οποίο αποτελεί βασική προϋπόθεση για την κατασκευή λειτουργικών CMOS δομών. Η ανάπτυξη των υμενίων Al2O3 στα υποστρώματα Ge έγινε με την τεχνική Eναπόθεσης Ατομικού Στρώματος (Atomic Layer Deposition- ALD), η οποία είναι μια από τις πιο διαδεδομένες και πολλά υποσχόμενες τεχνικές στον τομέα της Μικροηλεκτρονικής. Βασικά πλεονεκτήματα της μεθόδου αυτής έναντι άλλων μεθόδων εναπόθεσης (CVD, MBE κ.λπ.), είναι η άριστη ποιότητα και ομοιογένεια των αναπτυσσόμενων υμενίων, καθώς και ο απόλυτος έλεγχος του πάχους τους. Στόχος της εργασίας αυτής, είναι η μελέτη των ηλεκτρικών ιδιοτήτων δομών p-Ge/Al2O3/Pt, καθώς και της διεπιφάνειας Ge/Al2O3. Παρασκευάστηκαν δομές με πάχος διηλεκτρικού (Al2O3) 5nm, 10nm,15nm και 25nm σε θερμοκρασία εναπόθεσης 300oC. Ο δομικός χαρακτηρισμός των δειγμάτων έγινε με φασματοσκοπία XPS (X-ray Photoelectron Spectroscopy), ενώ ο ηλεκτρικός τους χαρακτηρισμός έγινε με τη μέθοδο της Διηλεκτρικής Φασματοσκοπίας Ευρέως Φάσματος (Broadband Dielectric Spectroscopy-BDS) στην περιοχή συχνοτήτων από 100Ηz έως 1ΜΗz. Τα αποτελέσματα της μελέτης του δομικού χαρακτηρισμού έδειξαν, ότι αυξανομένου του πάχους του υμενίου Al2O3, το πάχος του αναπτυσσόμενου Οξειδίου του Γερμανίου (GeOx) αυξάνεται. Παράλληλα υπάρχει ένδειξη πιθανής αλλαγής της στοιχειομετρίας του GeOx. Ο ηλεκτρικός χαρακτηρισμός των δομών αυτών, πραγματοποιήθηκε με παράμετρο αφενός μεν το πάχος του Al2O3 σε θερμοκρασία περιβάλλοντος, αφετέρου δε με παράμετρο τη θερμοκρασία, στην περιοχή θερμοκρασιών από 78Κ - 200Κ. Ελήφθησαν οι χαρακτηριστικές C-V και C-f, από τις οποίες προκύπτουν τα συμπεράσματα που αφορούν στην ηλεκτρική συμπεριφορά των δομών αλλά και στην ποιότητα της διεπιφάνειας Ge / Al2O3. Σε όλες τις δομές, ανεξαρτήτως του πάχους του Al2O3, οι χαρακτηριστικές C-V παρουσιάζουν την τυπική συμπεριφορά της δομής MOS, με διάκριτες τις τρεις περιοχές συσσώρευσης, απογύμνωσης και αναστροφής φορέων. Οι χαρακτηριστικές C-V σε θερμοκρασία περιβάλλοντος παρουσίασαν, σε όλα τα πάχη, φαινόμενα γένεσης – επανασύνδεσης φορέων, τα οποία εμφανίζονται υπό τη μορφή “γονάτων” στην περιοχή απογύμνωσης/ασθενούς αναστροφής. Τα φαινόμενα αυτά συνδέονται άμεσα με το μικρό ενεργειακό χάσμα του Ge και το μεγάλο πλήθος ενδογενών φορέων αγωγιμότητας που χαρακτηρίζει το Ge στη θερμοκρασία περιβάλλοντος. Αυτά τα φαινόμενα δεν παρατηρούνται στις χαμηλές θερμοκρασίες. Επιπλέον, από τις μετρήσεις C-f και εφαρμόζοντας τη μεθόδου αγωγιμότητας (conductance method), η οποία εφαρμόστηκε σε όλες τις θερμοκρασίες, προέκυψαν οι τιμές της πυκνότητας των διεπιφανειακών καταστάσεων, Dit’s, των δομών αυτών. Από τα αποτελέσματα αυτά, προκύπτει το συμπέρασμα ότι οι τιμές των Dit’s στη θερμοκρασία περιβάλλοντος εμφανίζονται αυξημένες σε σχέση με τις αντίστοιχες στις χαμηλές θερμοκρασίες. Η υπερεκτίμηση αυτή, η οποία μπορεί να φτάσει και τις 2 τάξεις μεγέθους, οφείλεται στην εμφάνιση των “γονάτων” στη χαρακτηριστική C-V. Επομένως το πραγματικό πλήθος των διεπιφανειακών καταστάσεων υπολογίζεται από την ανάλυση των πειραματικών μετρήσεων στις χαμηλές θερμοκρασίες. Επιπλέον, προκύπτει το συμπέρασμα ότι, η πυκνότητα διεπιφανειακών καταστάσεων, Dit’s στις δομές με το μικρότερο πάχος είναι μικρότερη από την αντίστοιχη σε παχύτερες δομές. Η συμπεριφορά αυτή έρχεται σε αντίθεση με την αναμενόμενη και η ερμηνεία της, πιθανώς να συνδέεται με τα αποτελέσματα της φασματοσκοπίας XPS σύμφωνα με τα οποία, αυξανομένου του πάχους του Al2O3, υπάρχουν ενδείξεις μεταβολής της στοιχειομετρίας του Οξειδίου του Γερμανίου. / The subject of the present research work is the study of MOS structures on p- type Ge substrates. Al2O3 was used as gate dielectric and Pt as metal gate. Such devices, which are comprised by Ge substrate on which a high -k dielectric material is deposited, are of high scientific and technological interest for the following reasons: (i) Ge shows higher carrier mobility compared to that of Si. Therefore, the use of Ge substrates in MOS devices is considered advantageous compared to Si substrates, which up to date have been used exclusively for technological applications. (ii) The use of high -k materials seems to be more promising for the construction of functional MOS structures. (iii) Recent results have shown that a thin layer of Ge oxide builds up at the Ge/Al2O3 interface during the deposition of Al2O3 on Ge. This is a basic requirement for the operation of CMOS devises. In the current work, Al2O3 films were deposited on Ge substrates by Atomic Layer Deposition (ALD). ALD is one of the most widespread and very promising techniques in microelectronics. Basic advantages of this method, compared to other deposition techniques (e.g. CVD, MBE and others), are the quality and homogeneity of the films as well as the absolute control of their thickness. The purpose of the present work is the study of the electrical properties of Ge/ Al2O3 /Pt structures as well as of the quality of the Ge/ Al2O3 interface. Structures with Al2O3 thickness of 5 nm, 10 nm, 15 nm and 25 nm were prepared, at deposition temperature of 3000C. The structural characterization of the samples was performed by means of X-Ray Photoelectron Spectroscopy –XPS whereas the electrical characterization was performed with the Broadband Dielectric Spectroscopy- BDS in the frequency range from 100 Hz to 1 MHz. The XPS results suggest that the thickness of the Ge oxide (GeOx), grown during deposition, increases by increasing the thickness of the deposited Al2O3 films. Furthermore, there is evidence of possible change in the stoichiometry of GeOx. The electrical behaviour of these structures was determined using as parameters either the thickness of Al2O3 at room temperature or the temperature at constant thickness. Measurements were performed in the range of 78 oC to 200 oC. C-V and C-f characteristics were constructed, from which conclusions are drawn regarding the electrical behaviour of the structures and the quality of the interface Ge/ Al2O3. The C-V characteristics of all samples, show the typical behaviour of a MOS structure with the three distinct regions of accumulation, depletion and inversion, regardless the thickness of Al2O3. The C-V characteristics at room temperature show generation-recombination phenomena, which are demonstrated through “humps” in depletion / weak inversion regime. These phenomena are intimately connected with the small energy gap and the large density of intrinsic conductivity carriers of Ge. These “humps” do not appear at low temperatures, below 170K, indicating that “generation-recombination” phenomena have been suppressed by reducing temperatures. Furthermore, from C-f measurements the values of the interfacial trap density (Dit) were determined through the conductance method, in all temperatures. The Dit values at room temperature seem to be overestimated compared to those at low temperatures due to the “generation- recombination” phenomena. Therefore, the actual density of interfacial traps is determined from the analysis at low temperatures. Furthermore, the Dit values of the Al2O3 -10nm structure are lower compared to those of the Al2O3 -25nm structure. This behavior, which is in contradiction to the expected one, is connected with the XPS results, according to which there is evidence of change in the stoichiometry of Ge oxide as the thickness of Al2O3 is increased.

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