Thesis (Master)--İzmir Institute of Technology, İzmir, 2005 / Keywords: Capacitance-voltage spectroscopy, high dielectric constant insulators, tantalum pentoxide. Includes bibliographical references (leaves 92-97)

<p> Nanoscale patterning research is motivated by two objectives: (i) tool development and (ii) scientific opportunities at small length scales. The first objective focuses on designing techniques that can be used to fabricate features as small as possible. Synthetic strategies of nanomaterials can be classified into two categories; bottom-up and top-down. The top-down approach involves reducing the size of a bulk material into nanoscale patterns, while the bottom-up approach refers to the build up of a material from the bottom, i.e. particle-by-particle. This particle maybe an atom, a molecule or even a cluster. In this work, two different top-down approaches were applied to create patterns in the nanoscale. </p> <p> Direct selective metal deposition on semiconductors is of interest to electronic device technology, in particular for interconnects and Schottky devices. In this study, we investigated selective Cu electrodeposition on patterned tantalum oxide thin films. Cyclic voltammetry studies showed that tantalum oxide thin films of thicknesses higher than a certain critical value have insulating properties while oxide films of thicknesses less than this value are semiconductors. For the purpose of this study, tantalum oxide patterns of different thicknesses were created by electrochemical oxidation. Based on the aforementioned behavior of insulating and semiconducting tantalum oxide films, Cu lines were selectively electrodeposited on the tantalum oxide thin films patterns forming Schottky junctions. The process demonstrated in this work is compatible to standard processes for semiconductor device fabrication while permitting flexible prototyping for research at the nanoscale. </p> <p> The second method used to pattern nanoscale features on tantalum lead to the discovery of the first highly ordered nanoporous metal (template) prepared by electrochemical oxidation. The nanoporous tantalum has pores not only of high regularity and high diameter monodispersity, but also of tunable diameters in the range 27-55 nm. The template that has the highest hardness among other porous templates can be used for nanoparticles fabrication. The compatibility of the new porous tantalum template with semiconductor industry makes it a candidate for many potential technological applications. </p> / Thesis / Master of Science (MSc)

Neste trabalho estudou-se a influência da substituição de TiO2 por Ta2O5 nas propriedades estruturais e eletrocatalíticas do sistema RuO2/Ta2O5. Uma investigação sistemática das propriedades estruturais, morfológicas, eletroquímicas e eletrocatalíticas para a produção de O2 em meio ácido foi conduzida usando ânodos de composição nominal Ti/(x)RuO2(1 – x)Ta2O5 (x = 0,1; 0,3; 0,5; 0,8), preparados por decomposição térmica (450 e 500 oC por 1h sob fluxo de 5 L min-1 de O2) das misturas precursoras preparadas em isopropanol (Aldrich). Os sais de cloretos precursores foram (RuCl3.xH2O e TaCl5 – Aldrich). Análises da composição e da morfologia da camada de óxidos foram feitas antes e após os testes acelerados de vida (TAV), através das técnicas de EDX (Energia dispersiva de raios-X) e MEV (Microscopia eletrônica de varredura) respectivamente. A microscopia mostrou estrutura de “barro-rachado" para a maioria dos filmes. As análises de EDX evidenciaram uma redução do conteúdo do Ru após o TAV. Os dados sobre a estrutura foram obtidos por DRX (Difração de raios-X) e mostraram forma rutílica para o RuO2 e ortorrômbica para Ta2O5. Os voltamogramas cíclicos deste sistema em meio ácido (0,5 mol dm-3 de H2SO4) apresentaram as bandas características da dupla Ru(III) / Ru(IV). Em baixos sobrepotenciais, o coeficiente de Tafel, b, apresenta valores entre 40 mV e 60 mV. Os valores de resistência ôhmica (0,5 – 2,0 W) sugerem que a queda ôhmica do sistema pode ser atribuída principalmente à resistência da solução. A atividade eletrocatalítica apresentou uma forte dependência em relação ao conteúdo de RuO2 no filme, aumentando conforme o aumento da quantidade de RuO2 na composição. A estabilidade do sistema foi avaliada pelo TAV, utilizando eletrólise a corrente constante (750 mA cm-2 e T = 80 oC em solução de H2SO4 0,5 mol dm-3). As análises dos resultados mostraram uma relação entre o tempo de operação do eletrodo e a quantidade do componente ativo (RuO2). A substituição de titânio por tântalo (x = 0,5) apresentou uma melhora considerável (54%) no tempo de operação destes óxidos. Estes resultados apontam o sistema Ru/Ta como um recobrimento bastante promissor para operação em condições drásticas. / In this work it was investigated the structural and electrochemical properties of the RuO2/Ta2O5 system. A systematic investigation of structural, morphologic, electrochemical and eletrocatalytic properties for O2 evolution from acidic solutions was conducted using anodes of nominal composition Ti/(x)RuO2(1 + x) Ta2O5 (x = 0.1; 0.3; 0.5; 0.8), prepared from appropriate mol ratio by thermal decomposition (450 and 500 oC for 1 h under O2-flux of 5 L min-1) from alcoholic (isopropanol – Aldrich) solutions of the precursors mixtures (RuCl3.xH2O and TaCl5 - Aldrich). Analyses of the composition and the morphology of the oxide layer were investigated before and after accelerated life tests (ALT), through EDX techniques (Energy Dispersive X-rays) and SEM (Scanning Electron Microscopy) respectively. SEM results showed typical mud-flat-cracking morphology for the majority of the films. EDX analyses even after total deactivation evidenced the reduction of the content of Ru in the coating. Structure data have been obtained by XRD (X-rays diffraction) and which showed the rutile-type struture for RuO2 and orthorhombic one for Ta2O5. Cyclic voltammograms of this system where registered in acidic solutions (0.5 mol dm-3 of H2SO4). The observed peak has been attributed to the solid-state redox transition of Ru(III)/Ru(IV). At low overpotentials, Tafel slope, b, ranges from 40 - 60 mV. The RW-values found (0.5 – 2.0 W), are in agreement with other RuO2-based oxide electrodes. This is a good evidence that the ohmic drop of the system can be attributed mainly to solution resistance. The eletrocatalytic activity shows a strong dependence with the RuO2 content in the film. The stability of the electrodes are evaluated by the ALT, performed at 0.5 mol dm-3 in aqueous H2SO4 (750 mA cm-2 and T = 80 oC). The results shows a straight relation between the ALT-values and the amount of active component (RuO2) presented in the coating. Changing TiO2 by Ta2O5 (x = 0.5) showed a considerable improvement (54%) in the ALT-values of these oxides. These results it is a good indication that Ru/Ta system might be a promising coating to operate under drastic conditions.

Au cours des dernières années, la synthèse ciblée du butadiène en utilisant le bioéthanol a suscité une attention sans précédent en raison de l'intérêt croissant aux matières premières biosourcées ainsi que de la demande croissante en butadiène.Un processus pertinent dans ce contexte est le processus d'Ostromyslensky, qui s’effectue en deux étapes, comprenant la déshydrogénation de l'éthanol en acétaldéhyde en une étape séparée , suivie de la production de butadiène dans la deuxième étape par réaction d'acétaldéhyde avec de l'éthanol supplémentaire. Bien que la viabilité économique et la faisabilité de ce procédé d’éthanol en butadiène (ETB) soient bien établies, il reste de la place pour de meilleures performances catalytiques et une meilleure sélectivité. Dans cet effort, notre objectif était de développer une famille de catalyseurs sur silice à base de silice bien définis, basés sur la chimie organométallique de surface (SOMC) et de les tester lors de la conversion d'EtOH / AA en BD. Le premier ensemble de pré-catalyseurs a été synthétisé en traitant le [(=SiO)2TaHx] précédemment connu avec du N2O en tant qu'oxydant doux. La deuxième famille de catalyseurs a été préparée par calcination de l'espèce alkyl de tantale à 500°C. Les pré-catalyseurs ont été caractérisés par FTIR, RMN SS, UV-vis-DRS, DRX, EXAFS et HR-STEM. On a découvert que les pré-catalyseurs SOMC oxydés au N2O avaient principalement isolé des espèces [(SiO)2Ta (OH)x] peuplant la surface, tandis que la famille des pré-catalyseurs synthétisés par calcination mettait en évidence un mélange d’espèces de surface, y compris des agrégations de type cordes. Les tests catalytiques sur ces catalyseurs ont donné des résultats prometteurs, présentant une catalyse supérieure dans la transformation d'EtOH / AA en BD en termes de sélectivité en BD et de rendement par rapport à l'état de la technique. Outre l'excellente sélectivité, une gamme étroite de distribution du produit et une formation négligeable de coke ont été observées. Les espèces de TaOx isolées sur le pré-catalyseur oxydé au N2O ont montré une activité nettement meilleure et se sont révélées être les sites actifs de cette conversion par rapport à l'agrégation en chaîne de centres de tantale sur le matériau calciné. Sur la base de ces études DRIFT et in situ sur les catalyseurs, un mécanisme préliminaire pour cette conversion a été proposé / In the recent years on-purpose synthesis of butadiene using bioethanol has gained unprecedented attention owing to rise in interest for bio-based feedstock along with the steeply increasing demand for butadiene (BD). In this regard a relevant process is the Ostromyslensky’s two-step process, involving dehydrogenation of ethanol to acetaldehyde in a separate step, followed by butadiene production in the second stage by co-feeding ethanol and acetaldehyde. Although the economic viability and feasibility of this ethanol to butadiene (ETB) process is well established, there is a room for better catalytic performances and selectivity. In this endeavour our aim was to develop a family of well-defined Ta-based silica-supported catalysts through Surface Organometallic Chemistry (SOMC) and test them in the conversion of EtOH/AA to BD. The first set of pre-catalysts was synthesized by treating the previously known [(=SiO)2TaHx] with N2O as mild oxidant. The second family of catalysts was prepared by calcination of the tantalum alkyl species at 500°C. The pre-catalysts were characterized by FTIR, SS NMR, UV-vis-DRS, XRD, EXAFS and HR-STEM. The N2O oxidized SOMC pre-catalysts were found to have mostly isolated [(=SiO)2Ta(OH)x] species populating the surface whereas the family of pre-catalysts synthesized via calcination evidenced a mixture of surface species, including string-like aggregations.Catalytic tests over these catalysts generated promising results exhibiting superior catalysis in the transformation of EtOH/AA to BD in terms of both BD selectivity and yield compared to the state of the art. In addition to the excellent selectivity a narrow range of product distribution and negligible coke formation was observed. Isolated TaOx species on the N2O oxidized pre-catalyst showed markedly better activity and were found to be the active sites in this conversion compared to the string-like aggregation of tantalum centres on the calcined material. Based on this and in-situ DRIFT studies over the catalysts a preliminary mechanism for this conversion was proposed

Neste trabalho estudou-se a influência da substituição de TiO2 por Ta2O5 nas propriedades estruturais e eletrocatalíticas do sistema RuO2/Ta2O5. Uma investigação sistemática das propriedades estruturais, morfológicas, eletroquímicas e eletrocatalíticas para a produção de O2 em meio ácido foi conduzida usando ânodos de composição nominal Ti/(x)RuO2(1 – x)Ta2O5 (x = 0,1; 0,3; 0,5; 0,8), preparados por decomposição térmica (450 e 500 oC por 1h sob fluxo de 5 L min-1 de O2) das misturas precursoras preparadas em isopropanol (Aldrich). Os sais de cloretos precursores foram (RuCl3.xH2O e TaCl5 – Aldrich). Análises da composição e da morfologia da camada de óxidos foram feitas antes e após os testes acelerados de vida (TAV), através das técnicas de EDX (Energia dispersiva de raios-X) e MEV (Microscopia eletrônica de varredura) respectivamente. A microscopia mostrou estrutura de “barro-rachado” para a maioria dos filmes. As análises de EDX evidenciaram uma redução do conteúdo do Ru após o TAV. Os dados sobre a estrutura foram obtidos por DRX (Difração de raios-X) e mostraram forma rutílica para o RuO2 e ortorrômbica para Ta2O5. Os voltamogramas cíclicos deste sistema em meio ácido (0,5 mol dm-3 de H2SO4) apresentaram as bandas características da dupla Ru(III) / Ru(IV). Em baixos sobrepotenciais, o coeficiente de Tafel, b, apresenta valores entre 40 mV e 60 mV. Os valores de resistência ôhmica (0,5 – 2,0 W) sugerem que a queda ôhmica do sistema pode ser atribuída principalmente à resistência da solução. A atividade eletrocatalítica apresentou uma forte dependência em relação ao conteúdo de RuO2 no filme, aumentando conforme o aumento da quantidade de RuO2 na composição. A estabilidade do sistema foi avaliada pelo TAV, utilizando eletrólise a corrente constante (750 mA cm-2 e T = 80 oC em solução de H2SO4 0,5 mol dm-3). As análises dos resultados mostraram uma relação entre o tempo de operação do eletrodo e a quantidade do componente ativo (RuO2). A substituição de titânio por tântalo (x = 0,5) apresentou uma melhora considerável (54%) no tempo de operação destes óxidos. Estes resultados apontam o sistema Ru/Ta como um recobrimento bastante promissor para operação em condições drásticas. / In this work it was investigated the structural and electrochemical properties of the RuO2/Ta2O5 system. A systematic investigation of structural, morphologic, electrochemical and eletrocatalytic properties for O2 evolution from acidic solutions was conducted using anodes of nominal composition Ti/(x)RuO2(1 + x) Ta2O5 (x = 0.1; 0.3; 0.5; 0.8), prepared from appropriate mol ratio by thermal decomposition (450 and 500 oC for 1 h under O2-flux of 5 L min-1) from alcoholic (isopropanol – Aldrich) solutions of the precursors mixtures (RuCl3.xH2O and TaCl5 - Aldrich). Analyses of the composition and the morphology of the oxide layer were investigated before and after accelerated life tests (ALT), through EDX techniques (Energy Dispersive X-rays) and SEM (Scanning Electron Microscopy) respectively. SEM results showed typical mud-flat-cracking morphology for the majority of the films. EDX analyses even after total deactivation evidenced the reduction of the content of Ru in the coating. Structure data have been obtained by XRD (X-rays diffraction) and which showed the rutile-type struture for RuO2 and orthorhombic one for Ta2O5. Cyclic voltammograms of this system where registered in acidic solutions (0.5 mol dm-3 of H2SO4). The observed peak has been attributed to the solid-state redox transition of Ru(III)/Ru(IV). At low overpotentials, Tafel slope, b, ranges from 40 - 60 mV. The RW-values found (0.5 – 2.0 W), are in agreement with other RuO2-based oxide electrodes. This is a good evidence that the ohmic drop of the system can be attributed mainly to solution resistance. The eletrocatalytic activity shows a strong dependence with the RuO2 content in the film. The stability of the electrodes are evaluated by the ALT, performed at 0.5 mol dm-3 in aqueous H2SO4 (750 mA cm-2 and T = 80 oC). The results shows a straight relation between the ALT-values and the amount of active component (RuO2) presented in the coating. Changing TiO2 by Ta2O5 (x = 0.5) showed a considerable improvement (54%) in the ALT-values of these oxides. These results it is a good indication that Ru/Ta system might be a promising coating to operate under drastic conditions.

A novel high-k gate dielectric material, i.e., hafnium-doped tantalum oxide (Hf-doped TaOx), has been studied for the application of the future generation metal-oxidesemiconductor field effect transistor (MOSFET). The film's electrical, chemical, and structural properties were investigated experimentally. The incorporation of Hf into TaOx impacted the electrical properties. The doping process improved the effective dielectric constant, reduced the fixed charge density, and increased the dielectric strength. The leakage current density also decreased with the Hf doping concentration. MOS capacitors with sub-2.0 nm equivalent oxide thickness (EOT) have been achieved with the lightly Hf-doped TaOx. The low leakage currents and high dielectric constants of the doped films were explained by their compositions and bond structures. The Hf-doped TaOx film is a potential high-k gate dielectric for future MOS transistors. A 5 àtantalum nitride (TaNx) interface layer has been inserted between the Hf-doped TaOx films and the Si substrate to engineer the high-k/Si interface layer formation and properties. The electrical characterization result shows that the insertion of a 5 àTaNx between the doped TaOx films and the Si substrate decreased the film's leakage current density and improved the effective dielectric constant (keffective) value. The improvement of these dielectric properties can be attributed to the formation of the TaOxNy interfacial layer after high temperature O2 annealing. The main drawback of the TaNx interface layer is the high interface density of states and hysteresis, which needs to be decreased. Advanced metal nitride gate electrodes, e.g., tantalum nitride, molybdenum nitride, and tungsten nitride, were investigated as the gate electrodes for atomic layer deposition (ALD) HfO2 high-k dielectric material. Their physical and electrical properties were affected by the post metallization annealing (PMA) treatment conditions. Work functions of these three gate electrodes are suitable for NMOS applications after 800°C PMA. Metal nitrides can be used as the gate electrode materials for the HfO2 high-k film. The novel high-k gate stack structures studied in this study are promising candidates to replace the traditional poly-Si-SiO2 gate stack structure for the future CMOS technology node.

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第24622号 / 工博第5128号 / 新制||工||1980(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 小林 圭 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Thin films are an enabling technology for a wide range of applications, from microprocessors to diffusion barriers. Nanolaminate thin films combine two (or more) materials in a layered structure to achieve performance that neither film could provide on its own. Atomic layer deposition (ALD) is a chemical vapor deposition technique in which film growth occurs through self limiting surface reactions. The atomic scale control of ALD is well suited for producing nanolaminate thin films. In this thesis, ALD of two nanolaminate systems will be investigated: Al₂O₃-Ta₂O₅ and ZnO-SnO₂. Al₂O₃ and Ta₂O₅ are high κ dielectrics that find application as gate oxides for field effect devices such as metal oxide semiconductor field effect transistors and thin film transistors. Al₂O₃-Ta₂O₅ nanolaminate films of a fixed composition and total thickness, but with varied laminate structures, were produced to explore the influence of layer thickness on dielectric behavior. Layer thickness was found to have little impact on the dielectric constant but a strong impact on the leakage current. Thick layered nanolaminates (with 2.5 to 10 nm layers) performed better than either pure material. Showing structure provides a means of tailoring nanolaminate properties. ZnSnO is an amorphous oxide semiconductor used to make transparent TFTs. Although ALD is naturally suited to the production of nanolaminates, the deposition of homogenous ternary compounds is still uncommon. For very thin depositions, nucleation behavior can dominate, resulting in ALD growth rates different than for thicker films. Initial work on ALD of the ZnO-SnO₂ system is presented, focusing on nucleation and growth of each material on the other. It was found that both ZnO and SnO₂ inhibit the growth of one another and a method was developed to characterize the average growth rate for few cycle depositions. / Graduation date: 2011

<p>Due to the constantly decreasing dimensions of electronic devices, the conventional dielectric material in transistors and capacitors, SiO₂, has to be replaced by a material with higher dielectric constant. Some of the most promising candidates are tantalum oxide,Ta₂O₅, zirconium oxide, ZrO₂ and hafnium oxide, HfO₂.</p><p>This thesis describes new chemical vapour deposition (CVD) and atomic layer deposition (ALD) processes for deposition of Ta₂O₅, ZrO₂ and HfO₂ using the metal iodides as starting materials. The layer-by-layer growth in ALD was also studied in real time with a quartz crystal microbalance (QCM) to examine the process characteristics and to find suitable parameters for film deposition.</p><p>All the processes presented here produced high-purity films at low deposition temperatures. It was also found that films deposited on Pt substrates generally crystallise at lower temperature, or with lower thickness, than on silicon and single-crystalline oxide substrates. Films grown on MgO(001) and α-Al₂O₃(001) substrates were strongly textured or epitaxial. For example, monoclinic HfO₂ deposited on MgO(001) were epitaxial for deposition temperatures of 400-500 C in ALD and 500-600 C in CVD. Electrical characterisation showed that the crystallinity of the films had a strong effect on the dielectric constant, except in cases of very thin films, where the dielectric constant was more dependent on layer thickness.</p>

Due to the constantly decreasing dimensions of electronic devices, the conventional dielectric material in transistors and capacitors, SiO2, has to be replaced by a material with higher dielectric constant. Some of the most promising candidates are tantalum oxide,Ta2O5, zirconium oxide, ZrO2 and hafnium oxide, HfO2. This thesis describes new chemical vapour deposition (CVD) and atomic layer deposition (ALD) processes for deposition of Ta2O5, ZrO2 and HfO2 using the metal iodides as starting materials. The layer-by-layer growth in ALD was also studied in real time with a quartz crystal microbalance (QCM) to examine the process characteristics and to find suitable parameters for film deposition. All the processes presented here produced high-purity films at low deposition temperatures. It was also found that films deposited on Pt substrates generally crystallise at lower temperature, or with lower thickness, than on silicon and single-crystalline oxide substrates. Films grown on MgO(001) and α-Al2O3(001) substrates were strongly textured or epitaxial. For example, monoclinic HfO2 deposited on MgO(001) were epitaxial for deposition temperatures of 400-500 C in ALD and 500-600 C in CVD. Electrical characterisation showed that the crystallinity of the films had a strong effect on the dielectric constant, except in cases of very thin films, where the dielectric constant was more dependent on layer thickness.