Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 138-143). Also available on the Internet.

Thesis (M.S.)--Rochester Institute of Technology, 2005. / Typescript. Includes bibliographical references (leaves 109-113).

Le développement du marché des appareils de communication nomades, a nécessité l'intégration de composants passifs et actifs sur du silicium via des montages « hybrides ».Ceci a amené le LMP partenaire de l'entreprise STMicroelectronics à rechercher des solutions pour une intégration « monolithique ». Le silicium micro/mésoporeux est un candidat potentiel pour satisfaire les exigences de cette intégration. Ce travail traite de la réalisation de caissons profonds de silicium poreux sur silicium résistif de type P 30-50 Ω.cm et N 37-46Ω.cm. L'utilisation de l'acide acétique comme solvant industriellement compatible nous a permis de réaliser des structures micro/mésoporeuses. L'intégrité mécanique de nos échantillons a été étudiée via la mesure de la porosité en fonction de l'épaisseur. Ainsi des caissons poreux avec des épaisseurs de plus de 400 µm et 50 % de porosité ont été fabriqués.La réalisation d'une couche N⁺ sur du silicium type N 37-46 Ω.cm a permis la mise en œuvre de doubles couches composées d'une dizaine de micromètres de micro/mésoporeuse sur une couche de 200 µ.m de silicium macroporeux. Des changements importants ont été observés par addition d'une très faible quantité d'un tensioactif (triton X-I00®) a notre solution électrolytique et où des doubles couches ont été obtenues sur silicium type P 30-50 Ω.cm. / The rapid expansion of wireless devices caused a tremendous demand of the development of active and passive devices integration on silicon via « hybrid » systems. The search of a« monolithic » integration has led the LMP in partnership with STMicroelectronics to focus on this topic. Micro/Mesoporous silicon is a good candidate to fulfill the requirements to achieve this purpose. The present work deals with the realization of thick porous silicon layers on low doped P type (30-50 Ω.cm) and N type Si (37-46 Ω.cm). The use of a particular solution based on HF-H₂O and acetic acid allowed the implementation of micro/mesoporous Si structures. The mechanical integrity is studied via the porosity and the PS layer thickness.Thus layers with a thickness up to 400 µm have been implemented with a porosity of 50 % on P Type Si samples. Double layers with micro/mesoporous layer of tenth micrometers on a macroporous layer stack up to 200 µm have been realized on N-Type Si samples via the realization of an N⁺ layer by phosphorous implantation. Important changes occurred when a tiny amount of surfactant (triton X-I00®) has been introduced into our organic electrolyte and allowed the implementation of double layers on P type Si.

Ces travaux de thèse ont pour but l’évaluation et le développement de briques technologiques en silicium poreux répondant à la problématique de l’intégration monolithique 3D rattachée au concept du “more than Moore” : d’une part l’intégration sur silicium de composants passifs RF, d’autre part, la réalisation de chemins traversants d’interconnexion à fort facteur d’aspect par voie électrochimique. Dans un premier temps, différents substrats mixtes silicium / silicium poreux sont réalisés. Des inductances en cuivre, réalisées sur un substrat mésoporeux de 200 µm de profondeur et de porosité proche de 60%, atteignent des facteurs de qualité à 20 GHz jusqu’à 55% supérieurs à ceux mesurés sur silicium massif. Une perspective d’industrialisation de ce type d’application est à l’étude dans le cadre d’une thèse CIFRE. La gravure de matrices de pores à fort facteur d’aspect, bien qu’encore difficilement localisable en termes de qualité de périphérie, fait d’autre part l’objet de développements, notamment pour la fabrication de condensateurs à haute densité capacitive et de contacts d’interconnexions en cuivre. / Those thesis works deal with the evaluation and the development of porous silicon technological step in order to answer some of the monolithic integration challenges bring by the “more than Moore” problematic in microelectronics industry: on one hand, the integration on silicon of passive RF devices, on the other hand, realization by electrochemical etching of through silicon via. In a first time, several mixed porous silicon / silicon substrat are realized. Copper inductors, realized on 200 µm thick and 60% porosity mesoporous layer, show a quality factor superior to 55% to the one obtained on massive silicon. Industrialization perspectives are on the line via a CIFRE PhD convention. In a second time, several electrochemical etching process are evaluated. Among them, high aspect ratio macropore array etching, although poorly localizable, allows many perspectives: copper via and high density capacitor.

SILVA, Francisco Wellery Nunes. Transporte eletrônico em semicondutores porosos baseado na equação de Schrodinger dependente do tempo. 2012. 77 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-04-23T21:11:22Z No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-04-29T17:38:22Z (GMT) No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) / Made available in DSpace on 2015-04-29T17:38:23Z (GMT). No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) Previous issue date: 2012 / We propose in this work a theoretical study, of the properties of a electronic pulse, injected under a external bias, on a porous silicon layer, so that we could define fundamentally the shape of T X V and R X V curves, where T is the transmission coefficient and R is the reflection coefficient of the wave packet, trough the porous region. With this, we could make a simple calculation and obtain information about the electrical current in this material, using the very simple model I=Q/t, where we defined the time of transmission, as the time interval necessary for the electronic pulse to be consumed completely. This kind of approach is already known in the literature, propose by Lebedev and co-workers (1998). Using the definition of charge carrier mobility, we obtained information about it, since the principal aim of this work is the electronic transport in this kind of material, that despite a strong research on porous silicon, since the beginning of the nineties, the transport properties still remains a relatively unexplored area. The major incentive for this study is due to the strong possibility of application of this material in new optoelectronic devices such as LEDs. Along the development of this dissertation, we applied well known techniques for the computational modelling such as effective mass theory, for example, associated with methods like the periodic boundary conditions, and the absorbing boundary conditions. Treating of a quantum system, we begin all the work solving the time dependent Schröedinger equation. To do this task, we have used the numerical method known as Split-Operator, in order to obtain the solutions for this equation. Initially, the calculations in this dissertation where based in an isotropic effective mass, in order to optimise the calculation parameters. After this, we made calculations using an anisotropic effective mass for the different valleys of silicon. All these things leads us to believe that this work have a great importance regarding the contribution to the understanding of transport in electronic systems based on porous silicon, to maintain for some time the applications of this kind of material that was so revolutionary in the twentieth. / Neste trabalho, propomos um uma pesquisa teórica onde estudamos as propriedades de um pulso eletrônico em uma camada de silício poroso, injetado sob uma certa voltagem externa V. Desta forma, podemos definir fundamentalmente a forma das curvas T X V e R X V, onde T é o coeficiente de transmissão e R é o coeficiente de reflexão do pacote de onda através da região porosa. Aliado a estes dados, podemos fazer um cálculo simples e obter informações a respeito da corrente elétrica que atravessa o material, utilizando o modelo I=Q/t, onde definimos o tempo como o intervalo necessário para que o pulso seja consumido completamente, como proposto por Lebedev e colaboradores (1998). Utilizando a definição para mobilidade de portadores de carga, obtivemos informações sobre a mesma, pois este trabalho foca-se principalmente no estudo do transporte eletrônico neste tipo de material poroso, que apesar de um estudo intenso em silício poroso desde o início da década de noventa, as propriedades de transporte ainda permanecem um pouco inexploradas. O principal incentivo para que estudemos este material é devido à grande possibilidade da criação de dispositivos em opto-eletrônica tais como LEDs (Light Emissor Diode). Ao longo do desenvolvimento, empregamos técnicas já bem conhecidas para a modelagem de semicondutores, como a teoria da massa efetiva, por exemplo, associadas a técnicas de modelagem computacional, como o emprego de condições periódicas de contorno e condições de contorno absorvente. Por se tratar de um sistema quântico, tudo parte da solução da equação de Schrödinger dependente do tempo, e para executar esta tarefa fizemos uso de um método numérico conhecido como Split-Operator. Assim obtemos as soluções para a equação. Inicialmente, os cálculos realizados neste trabalho foram baseados em uma massa efetiva isotrópica, a fim de otimizar os parâmetros de cálculo, e só em seguida foram feitos cálculos baseando-se em massa efetiva anisotrópica para os diversos vales do silício poroso. Tudo isto nos leva a crer que este trabalho possui uma grande importância no que diz respeito à contribuição para o entendimento do transporte eletrônico em sistemas baseados em silício poroso, de forma a manter por mais algum tempo a aplicação deste tipo de material que foi tão revolucionário no século XX.

SILVA, Francisco Wellery Nunes. Transporte eletrônico em semicondutores porosos baseado na equação de Schrodinger dependente do tempo. 2012. 77 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-16T21:34:35Z No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-10-20T20:59:54Z (GMT) No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) / Made available in DSpace on 2015-10-20T20:59:54Z (GMT). No. of bitstreams: 1 2012_dis_fwnsilva.pdf: 12829801 bytes, checksum: 1fca3d2dc15fc07961d7231c6087fe50 (MD5) Previous issue date: 2012 / We propose in this work a theoretical study, of the properties of a electronic pulse, injected under a external bias, on a porous silicon layer, so that we could define fundamentally the shape of T X V and R X V curves, where T is the transmission coefficient and R is the reflection coefficient of the wave packet, trough the porous region. With this, we could make a simple calculation and obtain information about the electrical current in this material, using the very simple model I=Q/t, where we defined the time of transmission, as the time interval necessary for the electronic pulse to be consumed completely. This kind of approach is already known in the literature, propose by Lebedev and co-workers (1998). Using the definition of charge carrier mobility, we obtained information about it, since the principal aim of this work is the electronic transport in this kind of material, that despite a strong research on porous silicon, since the beginning of the nineties, the transport properties still remains a relatively unexplored area. The major incentive for this study is due to the strong possibility of application of this material in new optoelectronic devices such as LEDs. Along the development of this dissertation, we applied well known techniques for the computational modelling such as effective mass theory, for example, associated with methods like the periodic boundary conditions, and the absorbing boundary conditions. Treating of a quantum system, we begin all the work solving the time dependent Schröedinger equation. To do this task, we have used the numerical method known as Split-Operator, in order to obtain the solutions for this equation. Initially, the calculations in this dissertation where based in an isotropic effective mass, in order to optimise the calculation parameters. After this, we made calculations using an anisotropic effective mass for the different valleys of silicon. All these things leads us to believe that this work have a great importance regarding the contribution to the understanding of transport in electronic systems based on porous silicon, to maintain for some time the applications of this kind of material that was so revolutionary in the twentieth. / Neste trabalho, propomos um uma pesquisa teórica onde estudamos as propriedades de um pulso eletrônico em uma camada de silício poroso, injetado sob uma certa voltagem externa V. Desta forma, podemos definir fundamentalmente a forma das curvas T X V e R X V, onde T é o coeficiente de transmissão e R é o coeficiente de reflexão do pacote de onda através da região porosa. Aliado a estes dados, podemos fazer um cálculo simples e obter informações a respeito da corrente elétrica que atravessa o material, utilizando o modelo I=Q/t, onde definimos o tempo como o intervalo necessário para que o pulso seja consumido completamente, como proposto por Lebedev e colaboradores (1998). Utilizando a definição para mobilidade de portadores de carga, obtivemos informações sobre a mesma, pois este trabalho foca-se principalmente no estudo do transporte eletrônico neste tipo de material poroso, que apesar de um estudo intenso em silício poroso desde o início da década de noventa, as propriedades de transporte ainda permanecem um pouco inexploradas. O principal incentivo para que estudemos este material é devido à grande possibilidade da criação de dispositivos em opto-eletrônica tais como LEDs (Light Emissor Diode). Ao longo do desenvolvimento, empregamos técnicas já bem conhecidas para a modelagem de semicondutores, como a teoria da massa efetiva, por exemplo, associadas a técnicas de modelagem computacional, como o emprego de condições periódicas de contorno e condições de contorno absorvente. Por se tratar de um sistema quântico, tudo parte da solução da equação de Schrödinger dependente do tempo, e para executar esta tarefa fizemos uso de um método numérico conhecido como Split-Operator. Assim obtemos as soluções para a equação. Inicialmente, os cálculos realizados neste trabalho foram baseados em uma massa efetiva isotrópica, a fim de otimizar os parâmetros de cálculo, e só em seguida foram feitos cálculos baseando-se em massa efetiva anisotrópica para os diversos vales do silício poroso. Tudo isto nos leva a crer que este trabalho possui uma grande importância no que diz respeito à contribuição para o entendimento do transporte eletrônico em sistemas baseados em silício poroso, de forma a manter por mais algum tempo a aplicação deste tipo de material que foi tão revolucionário no século XX.

Um novo processo de fabricação de dispositivos de emissão de campo (FE) em silício (Si) é apresentado nesta tese, baseado na potencialidade de utilização da técnica de microusinagem denominada HI-PS (Hydrogen Ion Porous Silicon), que trata da combinação entre processos de implantação de hidrogênio e silício poroso. Por meio do procedimento proposto, foram obtidos dispositivos com 2500 emissores (micropontas de Si) integrados e não integrados ao anodo e contidos em uma área de 2,8 x 2,8 mm² (3,2.10\'POT.4\' pontas/cm²). As micropontas de Si fabricadas apresentaram altura de 10 µm, com diâmetro do ápice em torno de 150 nm. A separação entre os emissores (50 µm), na configuração não integrada dos dispositivos, foi limitada pela resolução da máscara litográfica utilizada. Foram propostas etapas de otimização estrutural das micropontas após sua formação, e aplicadas tanto na configuração do sistema anodo-catodo integrado como não integrado. Como resultado destas etapas, constatou-se a redução do ápice das microestruturas para dimensões inferiores a 100 nm. Os dispositivos FE integrados foram obtidos com uma distância de separação entre o anodo e o catodo de aproximadamente 12 µm, distância definida pelas dimensões da máscara litográfica, porém não limitada pelo processo aplicado. Destacam-se, entre as vantagens da utilização da técnica HI-PS em relação às tecnologias usuais de manufatura dos dispositivos FE, a baixa complexidade do processo proposto e a utilização de apenas uma etapa litográfica para obtenção do sistema anodo-catodo integrado e auto alinhado. Para efetuar as caracterizações dos dispositivos, foram implementados uma câmara de vácuo específica, que permite alterar a distância entre as estruturas do anodo e do catodo não integradas, sem a necessidade de se retirar a amostra da câmara, e três sistemas para ensaios elétricos, sendo um destes sistemas desenvolvido especificamente para caracterização elétrica de dispositivos FE. As caracterizações elétricas foram efetuadas por meio de curvas I-V, I-t e V-d, sendo esta última utilizada para extrair o campo elétrico macroscópico E, que foi utilizado como parâmetro de comparação entre amostras submetidas a diferentes processos de otimização estrutural e de recobrimento superficial dos emissores por Al. Todas as amostras caracterizadas apresentaram variação de corrente exponencial com o potencial aplicado, de acordo com o esperado pela teoria proposta por Fowler-Nordheim (F-N). Dispositivos com otimização estrutural ou deposição de Al apresentaram melhores características de emissão (menor valor de E), de acordo com o aprimoramento do modelo de F-N sugerido na literatura para superfícies otimizadas. Constatou-se, pelos gráficos de F-N, o comportamento diferenciado dos emissores de Si tipo p em comparação com outros materiais, estabelecendo uma relação entre as variações da inclinação da curva traçada às distintas fontes de elétrons do Si. Frente aos resultados obtidos, conclui-se que a técnica Hi-PS é altamente promissora para fabricação de emissores microusinados em Si para aplicações em dispositivos FE. / This thesis presents a new silicon (Si) field emission devices (FE) fabrication process based on the potential of the HI-PS (Hydrogen Ion Porous Silicon) micromachining technique, which is a combination of hydrogen implantation and porous silicon. Devices with 2500 emitters (Si microtips), integrated and non-integrated to the anode, enclosed in an area of 2.8 x 2.8 mm² (3.2 x 10\'POT.4\' tips/cm²), were obtained from the proposed technique. The fabricated Si microtips show 10 µm in height, with apex diameter of about 150 nm. The separation distance between emitters (50 µm), considering the non-integrated devices design, was limited by the resolution of the lithographic mask applied. Microtips structural improvement process steps were proposed and applied in both anode-cathode design (integrated and non-integrated). As a result, a reduction in tip apex diameter to dimensions lower than 100 nm was verified. The integrated FE devices were obtained with an anode-cathode separation of about 12 µm, which distance was defined by lithographic mask dimensions, but not limited by the process applied. The outstanding advantages of the HI-PS technique in comparison with usual technologies for FE devices fabrication are the low complexity of the process proposed and the use of a single lithographic step to obtain a selfaligned and integrated anode-cathode system. A dedicated vacuum chamber, which allows the changing of the separation distance between non-integrated anodecathode structures without the need of removing the sample out the chamber, and three systems for electrical test, being one of them developed specifically for FE devices electrical characterization, were implemented. The electrical characterizations were performed by means of I-V, I-t and V-d curves, being the last one used to extract the macroscopic electrical field E, which was applied as comparison parameter between samples obtained from distinct structural improvement process and samples with emitters surface coated with Al. All samples characterized showed exponential-like behavior of current with the potential applied, as expected from theory proposed by Fowler-Nordheim (F-N). Devices with structural improvement or Al coating showed better emission characteristics (lower E value), according with the modified F-N model suggested in the literature for optimized surfaces. From the F-N plots, the distinct behavior of p type Si emitters was verified in comparison with different materials, establishing a relationship between the slope variations of the curve obtained and the electrons source of the Si. Based on the results obtained, the HI-PS technique is very promising to fabricate Si micromachined emitters for use in FE devices.

Nanopartículas luminescentes de silício poroso (NPSi) foram projetadas e preparadas por métodos de corrosão eletroquímica seguidas de ultrasonicação, em substratos de silício tipo-p, dopados com boro e com resistividades que variam de 10-20 e 1-10 ômega cm em soluções eletrolíticas compostas por ácido fluorídrico (HF) em etanol absoluto (C^2H^5OH). As condições de processamento envolvem a variação da densidade de corrente \"J\" tempo de anodização \"t\" e o controle da concentração do HF. Técnicas de microscopia eletrônica de varredura (MEV), espectroscopia de absorção UV-Vis, espectroscopia de fluorescência, difração de raios-X e medidas de potencial zeta e tamanho de partícula foram usados para investigar as propriedades morfológicas e ópticas do material resultante. Nanopartículas com diâmetros de até 150 nm foram obtidas após filtragem através de filtros de membrana. A oxidação química em soluções de peróxido de hidrogénio e ácido sulfúrico permitiu a obtenção de Nanoparticulas com emissão de fluorescência na região verde (532 nm), vermelho (630 e 650 nm) e infravermelho próximo (862 e 980 nm) do espectro eletromagnético. A associação de NPSi com RGDfV foi estudada por espectroscopia de ressonância magnética nuclear de próton (H-RMN). Um aumento na distribuição do tamanho e a intensidade de fluorescência foi observado após a funcionalização com RGDfV. Os efeitos citotóxicos do RGDfV e NPSi foram confirmados por ensaios de viabilidade celular pelo método MTT usando células de melanoma murino B16-F10 como modelo biológico. Estudos iniciais de internalização de PcCIAI por eletroporação foram realizados para futuros estudos de transfecção de moléculas de interferência (siRNA). / Luminescent porous silicon nanoparticles (NPSi) were synthesized by electrochemical etching followed by ultra-sonication of 1-10 and 10-20 ohm.cm resistive p-type silicon wafers in electrolytic solutions composed by hydrofluoric acid (HF) in absolute ethanol (C2H5OH), by changing current density (J), etching time (t) and HF concentration. Scanning electron microscopy (SEM), X-ray diffraction, dynamic ligth scattering (DLS), zetasize measurement, UV-Vis absorption spectroscopy and fluorescence spectroscopy were used to investigate the morphological and optical properties of the resulting material. Nanoparticles with diameter up to 150 nm were obtained after filtered through filtration membrane. The chemical oxidation in oxidizing solutions composed by hydrogen peroxide in sulfuric acid allowed the isolation of nanoparticles with fluorescence properties as expected, with emission in green (532 nm), red (630 and 650 nm) and near infrared (862 and 980 nm) region of the electromagnetic spectrum. The association of NPSi with RGDfV was studied by nuclear magnetic resonance spectroscopy (H-NMR). The increase on size distribution and fluorescence intensity was observed after functionalization with RGDfV. The citotoxicity effects of RGDfV and NPSi was confirmed by MTT assays using B16-F10 melanoma murine cells, as a biological model. Initial studies of internalization PcClAl by electroporation were performed for future studies of transfection of interfering molecules (siRNA).

In the recent years, there has been a growing interest in micro- and nano-structured composite systems due to their wide use in microelectronics, optoelectronics, magneto-optical devices, high-density data storage, sensors, biomedical devices, and many other areas. Of particular interest is application in the integrated circuit (IC) industry. Here the need for miniaturization has led to new architectures that combine disparate technologies. This has been achieved through innovations in packaging technologies such as 3D integration for high interconnection density, low power, high data throughput, good signal integrity and reliability, and low cost. One of the key active manufacturing technologies for 3D integration is through silicon vias (TSVs), which involves etching of deep vias in a silicon substrate that are filled with an electrodeposited metal, and subsequent removal of excess metal by chemical mechanical planarization (CMP). Electrodeposition often results in undesired voids in the TSV metal fill as well as a thick overburden layer. These via plating defects can severely degrade interconnect properties and lead to variation in via resistance, electrically open vias, and trapped plating chemicals that present a reliability hazard. Thick overburden layers result in lengthy and expensive CMP processing. We are proposing a technique that pursues a viable method of depositing a high quality metal inside vias with true bottom-up filling, using an additive-free deposition solution. The mechanism is based on a novel concept of electrochemical oxidation of backside silicon that releases electrons, and subsequent chemical etching of silicon dioxide for regeneration of the surface. Electrons are transported through the bulk silicon to the interface of the via bottom and the deposition solution, where the metal ions accept these electrons and electrodeposit resulting in the bottom-up filling of the large aspect ratio vias. With regions outside the vias covered bydielectric, no metal electrodeposition should occur in these regions, which minimizes the metal CMP step and reduces the overall processing times and costs. Hence, inherent bottom-up filling is financially advantageous because it will eliminate a large portion of the metal overburden and associated planarization costs. Additive-free deposition is preferable from both lower production cost and quality management perspectives since it results in higher reliability of deposited metal. Our new bottom-up technique was initially examined and successfully demonstrated on blanket silicon wafers and shown to supply electrons to provide bottom-up filling advantage of through-hole plating and the depth tailorability of blind vias. In order to understand the driving mechanism and limits of this process, we have also conducted a fundamental study that investigated the effect of various process parameters on the characteristics of deposited Cu and Ni and established correlations between metal filling properties and various electrochemical and solution variables. A copper sulfate solution with temperature of about 65 °C was shown to be suitable for achieving stable and high values of current density that translated to copper deposition rates of ~2.4 μm/min with good deposition uniformity. The importance of backside silicon oxidation and subsequent oxide etching on the kinetics of metal deposition on front side silicon has also been highlighted. Further, a process model was also developed to simulate the through silicon via copper filling process using conventional and contactless electrodeposition methods with no additives being used in the electrolyte solution. A series of electrochemical measurements were employed and integrated in the development of the comprehensive process simulator. The experimental data not only provided the necessary parameters for the model but also validated the simulation accuracy. From the simulation results, the “pinch-off” effect was observed for the additive-free conventional deposition process, which further causes partial filling and void formation. By contrast, a void-free filling with higher deposition rates was achieved by the use of the contactless technique. Moreover, experimental results of contactless electrodeposition on patterned wafers showed fast rate bottom-up filling (~3.3 μm/min) in vias of 4 μm diameter and 50 μm depth (aspect ratio = 12.5) without void formation and no copper overburden in the regions outside the vias. Efforts were also made to extend the use of the contactless technique to other applications such as synthesis of porous silicon, which is known to be an excellent material with fascinating physical and chemical properties. We were able to fabricate porous silicon with a morphological gradient using a novel design of the experimental cell. The resulted porous silicon layers show a large distribution in porosity, pore size and depth along the radius of the samples. Symmetrical arrangements were attributed to decreasing current density radially inward on the silicon surface exposed to surfactant containing HF based etchant solution. The formation mechanism as well as morphological properties and their dependence on different process parameters, such as HF concentration, solution pH, surfactant concentration, current density and wafer resistivity, has been investigated in detail. In the presence of surfactants, an increase in the distribution range of porosity, pore diameter and depth was observed by increasing HF concentration or lowering pH of the etchant solution, as the formation of pores was considered to be limited by the etch rates of silicon dioxide. Gradient porous silicon was also found to be successfully formulated both at high and low current densities. Interestingly, the morphological gradient was not developed when dimethyl sulfoxide (instead of surfactants) was used in etchant solution potentially due to limitations in the availability of oxidizing species at the silicon-etchant solution interface. In the last part of the dissertation, we have discussed the gradient bottom up filling of Cu in porous silicon substrates using the contactless electrochemical method. The radially symmetric current that gradually varied across the radius of the sample area was achieved by utilizing the modified cell design, which resulted in gradient filling in the vias. Effect of different deposition parameters such as applied current density, copper sulfate concentration and etching to deposition area ratio has been examined and discussed. Increasing the current density from 10 to 15 mA/cm2 resulted in bottom up deposition with less sharp gradients. Further, the study on the effect of copper sulfate concentration highlighted the importance of mass transfer in this process, as either bottom-up deposition or gradient filling could not be achieved at lower CuSO4 concentrations (0.1 and 0.25 M). Additionally, the filling gradient of deposited Cu was obtained with etching to deposition area ratio of 1.6 and 2.7, while a more uniform deposition was observed when the ratio was increased to 3.8. This suggested that the gradient filling may only be accomplished within a certain range of the etching to deposition area ratios.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20001号 / 工博第4245号 / 新制||工||1657(附属図書館) / 33097 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 作花 哲夫, 教授 安部 武志, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM