Progress in the microelectronics industry is driven by smaller and faster transistors. As feature sizes in integrated circuits become smaller and liquid chemical waste becomes an even greater environmental concern, gas expanded liquids (GXLs) may provide a possible solution to future device fabrication limitations relative to the use of liquids. The properties of GXLs such as surface tension can be tuned by the inclusion of high pressure gases; thereby, the reduced surface tension will allow penetration of cleaning solutions into small features on the nanometer scale. In addition, the inclusion of the gas decreases the amount of liquid necessary for the photoresist and etch residue removal processes. This thesis explores the role of CO2-based GXLs for photoresist and etch residue removal. The gas used for expansion is CO2 while the liquid used is methanol. The cosolvent serving as the removal agent is tetramethyl ammonium hydroxide (TMAH) which upon reacting with CO2 becomes predominantly tetramethyl ammonium bicarbonate (TMAB).

A MEMS-based micro-electro-discharge machining technique that is enabled by the actuation of micromachined planar electrodes defined on the surfaces of the workpiece is developed that eliminates the need of numerical control machines. First, the planar electrodes actuated by hydrodynamic force is developed. The electrode structures are defined by patterning l8-µm-thick copper foil laminated on the stainless steel workpiece through an intermediate photoresist layer and released by sacrificial etching of the resist layer. The planer electrodes are constructed to be single layer structures without particular features underneath. All the patterning and sacrificial etching steps are performed using dry-film photoresists towards achieving high scalability of the machining technique to large-area applications. A DC voltage of 80-140 V is applied between the electrode and the workpiece through a resistance-capacitance circuit that controls the pulse energy and timing of spark discharges. The parasitic capacitance of the electrode structure is used to form a resistance capacitance circuit for the generation of pulsed spark discharge between the electrode and the workpiece. The suspended electrodes are actuated towards the workpiece using the downflow of dielectric machining fluid, initiating and sustaining the machining process. Micromachining of stainless steel is experimentally demonstrated with the machining voltage of 90V and continuous flow of the fluid at the velocity of 3.4-3.9 m/s, providing removal depth of 20 µm. The experimental results of the electrode actuation match well with the theoretical estimations. Second, the planar electrodes are electrostatically actuated towards workpiece for machining. In addition to the single-layer, this effort uses double-layer structures defined on the bottom surface of the electrode to create custom designed patterns on the workpiece material. The suspended electrode is electrostatically actuated towards the wafer based on the pull-in, resulting in a breakdown, or spark discharge. This instantly lowers the gap voltage, releasing the electrode, and the gap value recovers as the capacitor is charged up through the resistor. Sequential pulses are produced through the self-regulated discharging-charging cycle. Micromachining of the stainless-steel wafer is demonstrated using the electrodes with single-layer and double-layer structures. The experimental results of the dynamic built-capacitance and mechanical behavior of the electrode devices are also analyzed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of micro-ribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the top surfaces of the ribs, and does not penetrate into the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For micro-ribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This thesis presents numerical results of a study exploring the momentum and thermal transport in a parallel plate microchannel with such microengineered walls. The liquid-vapor interface (meniscus) in the cavity regions is approximated as flat in the numerical analysis. Two conditions are explored with regard to the cavity region: 1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and 2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled through the velocity and shear stress matching at the interface. Predictions reveal that significant reductions in the frictional pressure drop (as large as 80%) can be achieved relative to the classical smooth channel Stokes flow. In general, reductions in the friction factor-Reynolds number product (fRe) are greater as the cavity-to-rib length ratio is increased (increasing shear-free fraction), as the relative module length (length of a rib-cavity module over the channel hydraulic diameter) is increased, as the Reynolds number decreases, and as the vapor cavity depth increases. The thermal transport results predict lower average Nusselt (Nu) numbers as the cavity-to-rib length ratio is increased (increasing shear-free fraction), as the relative module length (is increased, and as the Reynolds number decreases with little dependence on cavity depth. The ratio of Nu to fRe was evaluated to characterize the relative change in heat transfer with respect to the reduction in driving pressure. Results show that the benefits of reduction in driving pressure outweigh the cost of reduction in heat transfer at higher Reynolds numbers and narrower relative channel widths.

In the field of photolithography for micro-chip manufacturing, the photo-mask is used to print desired patterns on a proper photo-resist on wafer. The most common type of photo-mask is binary amplitude mask made an opaque layer of chrome. The principle and potential application of hybrid photo-mask with diffractive phase element and binary amplitude is presented in this dissertation paper from both numerical modeling and experimental research. The first important application is the characterization of aberration in the stepper system using hybrid diffractive photo-mask. By utilizing multiple diffractive illumination conditions, it is possible to characterize Zernike wave front aberration coefficients up to any desired order. And, the second application is the use of binary phase grating mask for analog micro-optics fabrication. This approach of using binary phase grating mask for fabricating analog micro-optics turned out to be a very effective alternative for gray-scale mask technology. Since this is a pure phase only mask, it doesn't cause any scattered noise light like half-tone mask and it results in smooth desired resist profile. The benefits and limitations of hybrid diffractive photo-mask approach for both applications are discussed.

Multiple laser beam interference allows to produce periodic light patterns in the order of the wavelength of light. A simulation program helps to identify different patterns and to investigate the influence of changing parameters such as e.g. the angle of incidence or the polarization. A positive photoresist (Shipley S1805) is used to create two-dimensional metallic photonic crystals by UV interference lithography.

Hydrogen terminated silicon surfaces play an important role in the integrated circuit (IC) industry. Ultra-pure water is extensively used for the cleaning and surface preparation of silicon surfaces. This work studies the effects of ultra-pure water on hydrogen passivated silicon surfaces in a short time frame of 120 minutes using fourier transform infrared spectroscopy – attenuated total reflection techniques. Varying conditions of ultra-pure water are used. This includes dissolved oxygen poor media after nitrogen bubbling and equilibration under nitrogen atmosphere, as well as metal contaminated solutions. Both microscopically rough and ideal monohydride terminated surfaces are examined. Hydrogen terminated silicon is also used as the sensing electrode for a potentiometric sensor for ultra-trace amounts of metal contaminants. Previous studies show the use of this potentiometric electrode sensor in hydrofluoric acid solution. This work is able to shows sensor function in ultra-pure water media without the need for further addition of hydrofluoric acid. This is considered a boon for the sensor due to the hazardous nature of hydrofluoric acid. Thin carbon films can be formed by spin coating photoresist onto silicon substrates and pyrolyzing at 1000 degrees C under reducing conditions. This work also shows that the electroless deposition of palladium and platinum may be accomplished in hydrofluoric acid solutions to attain palladium and platinum nanoparticles on a this film carbon surface for use as an electrode. Catalysis of these substrates is studied using hydrogen evolution in acidic media, cyclic voltammetry, and catalysis of formaldehyde. X-ray diffractometry (XRD) is used to ensure that there is little strain on palladium and platinum particles. Iridium is thought to be a prime candidate for investigation as a new generation copper diffusion barrier for the IC industry. Copper electrodeposition on iridium is studied to address the potential of iridium as a copper diffusion barrier. Copper electrodeposition is studied using a current-transient technique to obtain insight into the nucleation and growth mechanism. Copper on iridum was annealed up to 600 degrees C. X-ray photoelectron spectroscopy and XRD confirm that electrodeposited copper exists in a metallic state. XRD shows that copper exists in the characteristic face-centered cubic (111) form. XRD also confirms the stability of the copper-iridium interface with no new peaks after annealing, which is indicative that no interaction occurs. Scanning electron microscopy, and Scotch ® Tape peel tests confirm the uniformity and strength of copper on iridium even after annealing to 600 degrees C.

L’objectif de ce travail de thèse est de préparer des microélectrodes à base carbone, montrant des propriétés électrochimiques adéquates pour réaliser des dispositifs microfluidiques qui pourraient servir à la détection de polluants en milieu aqueux. Ce travail décrit la réalisation d’électrodes carbonées de graphène, résine pyrolysée et diamant sur support SiC, permettant leur structuration et intégration dans un procédé d’étapes technologiques . L’élaboration de ces éléments implique la mise en œuvre de techniques utilisées dans la microélectronique : les procédés de mise en forme tels que la lithographie et la gravure sèche, mais aussi des techniques de dépôt ou encore de traitements thermiques. Cette thèse expose également l’élaboration d’électrodes composites à base de fibres de carbone et de polydiméthylsiloxane (PDMS) pour la réalisation de dispositifs microfluidiques simples et peu onéreux, permettant l’analyse électrochimique en flux continu. Les propriétés électrochimiques (cinétique, surface active, réversibilité, domaine d’électroactivité…) ainsi que physiques (rugosité, résistivité électrique…) de ces matériaux ont été déterminées. L’objectif principal de ce travail de caractérisation étant de définir les conditions optimales de synthèse menant à des matériaux viables pour des applications électrochimiques et bioélectrochimiques. Les performances de ces électrodes pour la détection électrochimique d’espèces en solution ont été étudiées sur des modèles de molécules redox et confrontées à la littérature. La biocompatibilité de ces électrodes a également été vérifiée à travers la réalisation de biocapteurs enzymatiques pour la détection de l’acétylthiocholine. L’activité de l’enzyme acétylcholinestérase (AChE) déposée à la surface de nos différentes matériaux carbonés a été conservée et a permis l’utilisation de ces électrodes modifiées comme transducteurs pour la détection de l’acétylthiocholine. / This thesis work is aimed at preparing novel carbon based microelectrodes, revealing adequate electrochemical characteristics for the realization of microfluidic devices which could apply for the detection of biological pollutants in aqueous environment. This work describes the realization of carbon based electrodes made of grahene, pyrolyzed photoresist films, and diamond on silicon carbide, allowing their structuration and integration in a process formed by multiple technological steps. The elaboration of these elements implies the use of technics used in microelectronics. Processes of patterning such as lithography and dry etching, but also deposition technics or even thermal treatments were used. This thesis also shows the elaboration of carbon microfibers and polydiméthylsiloxane (PDMS) based composite electrodes for the realization of simple and cheap microfluidic devices for electrochemical analysis in continuous flow. The electrochemical properties (kinetics, active surface, reversibility, potential range…) but also physical properties (rugosity, electrical resistivity…) of these materials have been determined. The main aim of the characterizations work has been to determine the optimal synthesis conditions leading to viable materials for electrochemical and bioelectrochemical applications. The performances of these electrodes for electrochemical detection of species in solution were investigated on classical redox molecules used in literature for comparison. The biocompatibility of these electrodes was also verified through the realization of enzymatic biosensors for the detection of acétylthiocholine. The activity of the enzyme acetylcholinesterase’s (AChE), deposited on the surface of our different carbon materials, was kept and permitted the use of these modified electrodes as transducers for acetylthiocholine detection.

This study concentrates on two of the main processes involved in the fabrication of electrostatic valve assembly, thick resist photolithography and wet chemical etching of a polyamide film. The electrostatic valve has different orifice diameters of 25, 50, 75 and 100 µm. These orifice holes are to be etched in the silicon wafer with deep reactive ion etching. The photolithography process is developed to build a mask of 15 µm thick resist pattern on silicon wafer. This photo layer acts as a mask for deep reactive ion etching. Wet chemical etching process is developed to etch kapton polyamide film. This etched film is used as a stand off, gap between two electrodes of the electrostatic valve assembly. The criterion is to develop the processed using standard industry tools. Pre post etch effects, such as, surface roughness, etching pattern, critical dimensions on the samples are measured with Veeco profilometer.

Microfluidics refers to manipulation, precise control, and behavior of fluids at the micro and nanoliter scales. It has entered the realm of science as a way to precisely measure or mix small amounts of fluid to perform highly controlled reactions. Glass and polydimethylsiloxane (PDMS) are common materials used to create microfluidic devices; however, glass is difficult to process and PDMS is relatively hydrophobic. In this study, SU-8, an epoxy based (negative) photoresist was used to create various electrokinetic microfluidic chips. SU-8 is commonly used in microelectromechanical design. Spin coating of various SU-8 formulations allows for 1 μm to 100 μm thick layers with aspect ratios reportedly as high as 50:1. Case studies were performed to understand the curing/crosslinking process of SU-8 by differential scanning calorimetry. Supplier (MicroChem) recommended parameters were then altered to allow for adequate development of microfluidic channels, while maintaining enough molecular mobility to subsequently bond the SU-8 to a secondary substrate. Three SU-8 layers were used to create fully (SU-8) enclosed microfluidic channels. An (1) SU-8 2050 fully cured base layer was used as a platform on silicon to build from, (2) an SU-8 2050 partially cured layer for developing microfluidic channels , and (3) an SU-8 2007 uncured layer for bonding a secondary substrate to enclose the microfluidic channels. Bond quality was verified by optical and scanning electron microscopy, which resulted in a nearly 100% bond with little to no reflow of SU-8 into channels. Working pressures (ΔP across the capillary) of 15.57 lb/in2 (max detection) were obtained with no fluid leaks. Electroosmotic flow and steaming potential measurements failed. Electrophoretic behavior of glass particles was observed and particle velocities were compared by the application of 200 volts and 300 volts, across a channel length of 2 cm. Particle velocities obtained ranged from 100 μm/s to 1500 μm/s.