Dynamic wet etching of silicon through isopropanol alcohol evaporation

In this paper, Isopropanol (IPA) availability during the anisotropic etching of silicon in Potassium Hydroxide (KOH) solutions was investigated. Squares of 8 to 40 m were patterned to (100) oriented silicon wafers through DWL (Direct Writing Laser) photolithography. The wet etching process was performed inside an open HDPE (High Density Polyethylene) flask with ultrasonic agitation. IPA volume and evaporation was studied in a dynamic etching process, and subsequent influence on the silicon etching was inspected. For the tested conditions, evaporation rates for water vapor and IPA were determined as approximately 0.0417 mL/min and 0.175 mL/min, respectively. Results demonstrate that IPA availability, and not concentration, plays an important role in the definition of the final structure. Transversal SEM (Scanning Electron Microscopy) analysis demonstrates a correlation between microloading effects (as a consequence of structure spacing) and the angle formed towards the (100) plane.This work was supported by FCT (Fundação para a Ciência e Tecnologia) in the scope of the project PTDC/EBB-EBI/120334/2010 and by FEDER funds through the “Eixo I do Programa Operacional Fatores de Competitividade” (POFC) QREN, project reference COMPETE: FCOMP-01-0124-FEDER-020241. First author thanks FCT for scholarship grant SFRH/BD/74975/2010. INESC-MN and acknowledges Pest-OE/CTM/LA0024/2011 project

Fabrication of Silicon Based Micro and Nano Devices

微纳米材料表现出许多传统材料所不具备的新特性，随着科学技术的不断进步，纳米技术已然成为了最热门的研究领域之一。集成度的提高依赖于微纳米器件的尺寸的进一步缩小，微纳米加工技术的提高是器件尺寸缩小的基础。微纳米加工技术主要可以归为三类：平面工艺、探针工艺以及模型工艺。平面工艺是指利用光刻将图形转移到光刻胶并采用刻蚀或者沉积技术等将图形转移到基片表面形成结构复杂的微纳米器件，主要工艺包括光刻、刻蚀、薄膜沉积等。探针工艺是不仅可以指采用传统探针(扫描电镜探针、原子力显微镜探针)在基片表面加工出微纳米结构，还包括采用聚焦离子束、激光束等在基片表面剥离形成微纳结构。模型工艺是指使用微纳米量级的模具复制出相...Micro-nano structures exhibited lots of novel characters, which traditional materialsdo not have. Nanotechnology has become one of the most popular research areas. The increase of integration level depends on the further miniaturization of the micro-nano devices, The improvement of micro-nano processing technology is the basis for device size reduction. Micro-nano processing technology can be clas...学位：工学硕士院系专业：信息科学与技术学院_微电子学与固体电子学学号：2312014115310

Development of a microfluidic device for patterning multiple species by scanning probe lithography

Scanning Probe Lithography (SPL) is a versatile nanofabrication platform that leverages microfluidic “ink” delivery systems with Scanning Probe Microscopy (SPM) for generating surface-patterned chemical functionality on the sub-100 nm length scale. One of the prolific SPL techniques is Dip Pen Nanolithography™ (DPN™). High resolution, multiplexed registration and parallel direct-write capabilities make DPN (and other SPL techniques) a power tool for applications that are envisioned in micro/nano-electronics, molecular electronics, catalysis, cryptography (brand protection), combinatorial synthesis (nano-materials discovery and characterization), biological recognition, genomics, and proteomics. One of the greatest challenges for the successful performance of the DPN process is the delivery of multiple inks to the scanning probe tips for nano-patterning. The purpose of the present work is to fabricate a microfluidic ink delivery device (called “Centiwell”) for DPN (and other SPL) applications. The device described in this study maximizes the number of chemical species (inks) for nanofabrication that can be patterned simultaneously by DPN to conform the industrial standards for fluid handling for biochemical assays (e.g., genomic and proteomic). Alternate applications of Centiwell are also feasible for the various envisioned applications of DPN (and other SPL techniques) that were listed above. The Centiwell consists of a two-dimensional array of 96 microwells that are bulk micromachined on a silicon substrate. A thermoelectric module is attached to the back side of the silicon substrate and is used to cool the silicon substrate to temperatures below the dew point. By reducing the temperature of the substrate to below the dew point, water droplets are condensed in the microwell array. Microbeads of a hygroscopic material (e.g., poly-ethylene glycol) are dispensed into the microwells to prevent evaporation of the condensed water. Furthermore, since poly-ethylene glycol (PEG) is water soluble, it forms a solution inside the microwells which is subsequently used as the ink for the DPN process. The delivery of the ink to the scanning probe tip is performed by dipping the tip (or multiple tips in an array) into the microwells containing the PEG solution. This thesis describes the various development steps for the Centiwell. These steps include the mask design, the bulk micromachining processes explored for the micro-fabrication of the microwell array, the thermal design calculations performed for the selection of the commercially available thermoelectric coolers, the techniques explored for the synthesis of the PEG microbeads, and the assembly of all the components for integration into a functional Centiwell. Finally, the successful implementation of the Centiwell for nanolithography of PEG solutions is also demonstrated

Design and fabrication of silver microelectrodes for biomedical applications

Tese de doutoramento em Engenharia BiomédicaO cancro é uma das maiores causas de mortalidade e morbilidade em países desenvolvidos em todo o mundo. É geralmente precedido por alterações pré-cancerígenas e a sua deteção precoce, especialmente numa fase de displasia, é um dos grandes objetivos da medicina moderna, visto que as probabilidades de tratamento aumentam consideravelmente nesta fase. Estudos in-vitro demonstraram que alterações no pH a nível do ambiente intra- e extracelular podem estar correlacionadas com a proliferação de células tumorais em diferentes estados. Contudo, medições in-situ das propriedades eletroquímicas das células podem ser desafiantes e requerer equipamento complexo ou dispendioso. A ambição desta tese consiste no desenvolvimento de ferramentas inovadoras para o diagnóstico celular in-vitro e in-situ, com base em elétrodos micrométricos “solid-state” com capacidade de leitura de pH. Este sistema deverá, preferencialmente, ser compatível e permitir a integração de componentes “lab-on-chip” subsequentes, maioritariamente de processos óticos para posterior análise química e biológica. O protótipo proposto consiste numa matriz de 9600 microelétrodos “solid-state” com pontas nanométricas. O processo de fabricação consiste na padronização de um molde negativo para as pontas individuais de cada microelétrodo, seguido de um aumento na altura do perfil (para um maior “aspect-ratio” e capacidade de penetração) através da adição de um Photoresist, preenchimento do molde com Prata através de um processo inovador de Eletrodeposição “Through-Silicon”, e finalmente a transferência do perfil para um substrato de vidro com compatibilidade com processos óticos. Os resultados finais demonstram a prova de conceito da viabilidade do processo e dos múltiplos desenvolvimentos em engenharia de processos, apesar de estudos e otimizações subsequentes serem necessárias em diversas áreas do projeto de forma a melhor compreender os princípios e mecânicas por detrás de alguns aspetos dos processos inovadores.Cancer is one of the major causes of mortality and morbidity in developed countries worldwide. It is usually preceded by precancerous changes and its early detection, especially at the dysplasia stage, is one of the major goals in modern medicine, as the chances of a successful treatment are increased at this stage. In-vitro studies have demonstrated that pH changes in both the intracellular and extracellular environment of a tissue can be correlated with tumor cell proliferation at different stages. However, in-situ measurements of the electrochemical properties of cells can be challenging and require complex or costly equipment. In this thesis, the ambition is to develop a novel tool for in-vitro and in-situ cell diagnosis, based on solid-state micrometric electrodes with pH sensing capabilities. This system should, optimally, be compatible and allow integration with subsequent lab-on-chip components, mainly optical processes for further biological and chemical analysis. The proposed prototype consists in an array of 9600 solid-state microelectrodes with nanometric tips. The fabrication process includes the patterning of a negative mold for the individual microelectrode tips, followed by an increase in height (for higher aspect-ratio and deeper penetration capability) through the addition of a Photoresist, filling of the mold with Silver through a novel Through-Silicon Electrodeposition process, and finally transferring the pattern to a Glass substrate with optical processing compatibility. The end results demonstrates a proof-of-concept of the process feasibility and the multiple achievements in process engineering, although further studies and optimization are required in different areas of the project as to better understand the mechanics and principles behind some of the novel aspects of the processes.This thesis had the support of Fundação para a Ciência e Tecnologia under a Doctoral Scholarship -SFRH/BD/90121/201

Design Of Microhotplate Based Gas Sensing System [TK7875. Z21 2008 f rb].

The purpose of this research is to design, fabricate and characterize a microhotplate based gas sensing system. Tujuan kajian ini adalah untuk merekabentuk, fabrikat dan mencirikan system pengesan gas berasaskan microhotplate

Fabrication Techniques for III-V Micro-Opto-Electro-Mechanical Systems

This thesis studies selective etching techniques for the development of AlxGa1-xAs micro-opto-electro-mechanical systems (MOEMS). New MEMS technology based on materials such as AlxGa1-xAs enables the development of micro-systems with embedded active micro-optical devices. Tunable micro-lasers and optical switching based on MOEMS technology will improve future wavelength division multiplexing (WDM) systems. WDM vastly increases the speed of military communications and sensor data processing. From my designs, structures are prepared by molecular beam epitaxy. I design a mask set for studies of crystal plane selectivity. I perform a series of experiments on the selective removal of GaAs and AlAs. I convert AlAs and Al0.98Ga0.02As layers within the test structures to AlOx and Al0.98Ga0.02Ox and perform selective etching experiments on these sacrificial oxide layers. The etchants and materials studied showed high selectivity for removal of all materials studied. Results suggest that any of these material layers are useful as sacrificial layers for general MOEMS technology. I design, fabricate, and characterize prototype III-V MOEMS. Using AlOx sacrificial layers, I investigate a new technique for transplanting microcavity light-emitting devices. I successfully transplant arrays of light-emitting diodes. Finally, I discuss ideas on how this work forms the basis for nano-electro-mechanical systems (NEMS) fabrication in III-V materials

Chemical vapor deposition of thin films for ULSI interconnect metallization

We have studied the kinetics of copper chemical vapor deposition (CVD) for interconnect metallization using solution delivery of Cu(hfac)2 (Cu(II) hexafluoroacetyl-acetonate) dissolved in isopropanol. We observe a growth rate of 17.7 „b 1.5 nm/min at reference conditions of 300„aC substrate temperature, 0.025 Torr Cu(hfac)2 partial pressure, 1.6 Torr isopropanol (reducing agent), and 80 Torr H2 (carrier gas). The film resistivity approaches the bulk value of copper for film thickness greater than 100 nm. Reaction order experiments show first-order kinetics with respect to Cu(hfac)2 partial pressure and zero-order with respect to isopropanol. A series reaction mechanism including three kinetically significant steps (adsorption of Cu(hfac)2, dissociation of (hfac) ligand, and desorption of (hfac)) is used to describe the observed kinetic results. The proposed rate determining step is the dissociation of (hfac) ligand when the pressure ratio of Cu(hfac)2 to isopropanol is low, and becomes the desorption of (hfac) when the pressure ratio is high. We also examined a low temperature chemical vapor deposition process for the growth of tantalum thin films using SiH4 reduction of TaF5. Using a temperature of 350„aC and reactant partial pressures of 0.2 Torr TaF5 and 0.3 Torr SiH4, we obtain a growth rate of 2.2 ¡Ó 1.7 nm/min. The XPS analysis results show that the Ta film is Si free, but contains relatively high oxygen concentration because of residual gas contamination. Lastly, we have studied a batch CVD process for palladium seed layer deposition using H2 reduction of Pd(hfac)2 (Pd(II) hexafluoroacetylacetonate). Nano-sized Pd particles with nuclei density between 1 to 14 clusters/ƒÝm2 are observed using AFM. The quality of the Pd seed layer is examined by depositing electroless copper film. We have investigated the influence of CVD operating conditions (deposition time, activation temperature, and precursor concentration) on the activity of the Pd seed layers (i.e., by monitoring visual appearance and deposition rates of the ELD Cu films). At the optimized conditions we can deposit uniform Cu films at a rate of 3.4 „b 1.4 nm/s. Additional work is needed to improve the resistivity and adhesion of the films

FABRICATION OF MAGNETIC TWO-DIMENSIONAL AND THREE-DIMENSIONAL MICROSTRUCTURES FOR MICROFLUIDICS AND MICROROBOTICS APPLICATIONS

Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production. This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications

Design and Characterization of a Fluidic FET for Flow Control in Micro and Nanochannels

L'obiettivo di questa tesi è caratterizzare il comportamento di Fluidic FET (Fluidic Field Effect Transitor ) per il controllo del flusso in micro e nano canali. Un equivalente modello elettrico è stato sviluppato per calcolare la variazione nel potenziale di parete (potenziale ζ) quando una differenza di potenziale è applicata tra le pareti del canale e il fluido. In particolare sono stati generalizzati diversi modelli presenti in letteratura con lo scopo di considerare l'effetto della concentrazione e del pH dell'elettrolita, dello spessore dell'ossido e della temperatura nella relazione tra il potenziale ζ e la tensione applicata all'elettrodo di gate. Un modello numerico del movimento del fluido all'interno del microcanale verrà utilizzato per lo studiare l'effetto della presenza di una variazione a gradino del potenziale. Verrà inoltre illustrato il processo di fabbricazione di dispositivi FFET, focalizzandosi sia sulla preparazione dei microcanali sia sulla deposizione del metallo e dell'ossido su lastrine di vetro. Verrano presentati i risultati degli esperimenti di monitorizzazione della corrente (current monitoring) per osservare gli effetti della tensione di gate nel movimento del fluido. Infine verranno comparati i risultati sperimentali e delle simulazioni numerich