<p>Bonding techniques intended for assembling space microsystems are studied in this work. One of the largest problems in bonding pre-processed semiconductor wafers are the severe process restrictions imposed by material compatibility issues. Plasma processes have shown to be good for sensitive materials integration why the influence of different plasma parameters on the bondability of wafers is particularly studied. Conventional wet chemical and field-assisted methods are also examined. The resulting bond quality is assessed in terms of mechanical strength, homogeneity, and yield.</p><p>The effect of spaceflight environment on the reliability of wafer bonds is also investigated. Both high and low temperature annealed bonds are found to be very robust. Effects observed are that low temperature bonds are reinforced by thermal cycling in vacuum and that high temperature bonds degrade slightly by low dose γ irradiation.</p><p>Adhesion quantification is important for all bonding. Development of accurate quantification methods is considered necessary since most methods at hand are limited. This work includes the development of the blister test method. Former test structures are improved to be more practical to work with and to yield low experimental scatter. A physical stress model for the improved structure is suggested with which successful predictions of fracture for different test specimen configurations are made. The blister test method is used throughout this work to assess the strength of wafer bonds. The physics background and modelling of other common test methods are also thoroughly analysed. The methods’ practical capabilities and limitations are commented; origin and mitigation of measurement errors are discussed. It is shown that all methods can be significantly improved by small means.</p><p>Weibull statistics is introduced as a tool to characterise wafer bonds. This method is suitable to use in brittle materials design as the inherent variability in strength can be properly accounted for.</p>

Bonding techniques intended for assembling space microsystems are studied in this work. One of the largest problems in bonding pre-processed semiconductor wafers are the severe process restrictions imposed by material compatibility issues. Plasma processes have shown to be good for sensitive materials integration why the influence of different plasma parameters on the bondability of wafers is particularly studied. Conventional wet chemical and field-assisted methods are also examined. The resulting bond quality is assessed in terms of mechanical strength, homogeneity, and yield. The effect of spaceflight environment on the reliability of wafer bonds is also investigated. Both high and low temperature annealed bonds are found to be very robust. Effects observed are that low temperature bonds are reinforced by thermal cycling in vacuum and that high temperature bonds degrade slightly by low dose γ irradiation. Adhesion quantification is important for all bonding. Development of accurate quantification methods is considered necessary since most methods at hand are limited. This work includes the development of the blister test method. Former test structures are improved to be more practical to work with and to yield low experimental scatter. A physical stress model for the improved structure is suggested with which successful predictions of fracture for different test specimen configurations are made. The blister test method is used throughout this work to assess the strength of wafer bonds. The physics background and modelling of other common test methods are also thoroughly analysed. The methods’ practical capabilities and limitations are commented; origin and mitigation of measurement errors are discussed. It is shown that all methods can be significantly improved by small means. Weibull statistics is introduced as a tool to characterise wafer bonds. This method is suitable to use in brittle materials design as the inherent variability in strength can be properly accounted for.

Les biocapteurs sont utilisés quotidiennement pour déterminer la présence de molécules biologiques dans une matrice complexe, comme l’urine pour les tests de grossesses ou le sang pour les glucomètres. Les techniques courantes pour la détection des autres maladies nécessitent fréquemment le marquage de l’analyte avec une autre molécule, ce qui est à éviter pour fin de simplicité d’analyse. Ces travaux ont pour but la maximisation de la sensibilité d’une surface d’or ou d’argent nanotrouée, afin de permettre la détection de la liaison de molécules biologiques par résonance des plasmons de surface localisés (LSPR), en utilisant la spectroscopie de transmission. Un biocapteur portable, rapide et sans marquage pour quantifier des analytes d’intérêt médical ou environnemental pourrait être construit à partir de ces travaux. Dans l’objectif d’étudier de nombreuses configurations pour maximiser la sensibilité, le temps et le coût des méthodes de fabrication de nanostructures habituelles auraient limité le nombre de surfaces nanotrouées pouvant être étudiées. Un autre objectif du projet consiste donc au développement d’une technique de fabrication rapide de réseaux de nanotrous, et à moindres coûts, basée sur la lithographie de nanosphères (NSL) et sur la gravure au plasma à l’oxygène (RIE). La sensibilité à la variation d’indice de réfraction associée aux liaisons de molécules sur la surface du métal noble et la longueur d’onde d’excitation du plasmon de surface sont influencées par les caractéristiques des réseaux de nanotrous. Dans les travaux rapportés ici, la nature du métal utilisé, le diamètre ainsi que la périodicité des trous sont variés pour étudier leur influence sur les bandes LSPR du spectre en transmission pour maximiser cette sensibilité, visant la fabrication d’un biocapteur. Les surfaces d’argent, ayant un diamètre de nanotrous inférieur à 200 nm pour une périodicité de 450 nm et les nanotrous d’une périodicité de 650 nm démontre un potentiel de sensibilité supérieur. / Biosensors are used daily to determine the presence of biomolecules in a complex matrix, like urine for pregnancy test or blood with a glucometer. The usual biodetection methods require the addition of a tag on the analyte, which is to be avoided to design a simple analytical method. The objective of this work is to maximize the sensitivity of a gold or silver nanohole arrays to detect the biomolecules liaisons close to the metal surface by localized surface plasmon resonance (LSPR) in transmission spectroscopy. A portable and effective biosensor to quantify analytes could be built based on this work, without a tagging step. To achieve the objective of evaluating numerous configurations for maximal sensitivity, the time and cost of the usual nanostructures fabrication methods would have limited the number of nanohole arrays in metal surface that could have been studied in this project. This fact motivated another objective of this project, the development of a fast and low cost fabrication method for nanohole arrays using nanospheres lithography (NSL) followed by reactive ions etching (RIE). The plasmon sensitivity and wavelength excitation are influenced by the nanohole arrays characteristics. In the work presented here, the chemical composition of the metal surface, the diameter and the periodicity of the nanohole arrays are shown to the influence the LSPR bands. The transmission maximum and minimum position of some LSPR bands are sensitive to refractive index change, which can be exploited in a biosensor format to detect biomolecules. The optimization of these nanohole arrays characteristics allows the maximization of this sensitivity to build a biosensor. The best index refraction sensitive results were with silver surfaces, with nanohole diameters smaller than 200 nm for a periodicity of 450 nm and the nanoholes with a periodicity of 650 nm show a potential for an increased sensitivity.

Plasma pretreatments are environmentally benign and energy efficient processes for modifying the surface chemistry of materials. In an effort to improve the strength of the titanium alloy/FM-5 polyimide adhesive joint for aerospace applications, oxygen plasma pretreatments and novel thin plasma polymerized (PP) films were investigated as adhesion promoters. Plasma treatments were carried out using custom-built, low pressure, radio frequency, inductively coupled plasma reactors. Ti-6Al-4V coupons were plasma treated and used to prepare miniature single lap shear (SLS) joints. The effects of plasma pretreatments on surface chemistry were studied using x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier transform infrared analysis (FTIR), and contact angle measurements. Relationships between composition, mechanical properties, and adhesion of PP films on Ti-6Al-4V and silicon wafers were investigated. The nanomechanical properties (modulus, hardness and adhesion) were studied using atomic force microscopy (AFM) nanoindentation and nanoscratch testing. A design of experiments (DOE) three factorial model was used to optimize the parameters for oxygen plasma treatments. Oxygen plasma pretreatments enhanced joint strength by cleaning the titanium surface and creating an extended oxide layer. Nanoindentation of oxygen plasma treated substrates showed no change in the surface mechanical properties due to the oxygen plasma treatment. This suggested that the improved SLS strength of the oxygen plasma pretreated substrates was due to the cleaning of the substrate and the removal of carbonaceous contaminants, rather than any changes in the morphology of the oxide layer. PP acetylene films were predominantly carbon, with oxygen as the other main constituent (incorporated mostly as C-O and C=O). For all SLS specimens tested, the adhesion between PP acetylene and FM-5 adhesive was adequate. However, the strength of SLS joints was limited by the adhesion of the PP acetylene to the Ti-6Al-4V substrate. The effects of a large number of plasma parameters, such as substrate pretreatment, carrier gas, input power, flow rate and film thickness were investigated. All samples failed at the PP film/Ti-6Al-4V interface or within the PP acetylene film, and thicker PP films yielded lower SLS strengths. PP films deposited at lower power exhibited higher hardness and reduced modulus than films deposited at higher power. Overall, thinner films exhibited higher hardness and reduced Young's modulus than thicker films. PP films of higher hardness yielded higher critical loads at debond (thickness normalized) during the nanoscratch test. Thin films were developed via the vapor plasma polymerization of titanium(IV) isobutoxide (TiiB). XPS results suggested that titanium was incorporated into the film as TiO2 clusters dispersed in an organic matrix. No evidence for Ti-C was obtained from the XPS spectra. PP films of TiiB were much more compliant than PP acetylene films. This behavior was attributed to decreased fragmentation and lower crosslinking that occurred during PP TiiB film deposition. These PP films did not exhibit sol-gel-like qualities, and because of the way titanium was incorporated into the films, a more appropriate name for these films might be "titanium dioxide-doped plasma polymerized films." / Ph. D.

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