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The aluminum oxide growth rate for aluminum protected with 2.4 nm of aluminum fluoride has been determined. We show that a 2.4 nm aluminum fluoride layer does not prevent aluminum from oxidation but does significantly retard the oxide growth – decreasing the oxide layer thickness from 1 nm in less than an hour to 0.9 nm over 116 hours. Additionally, the optical constants for aluminum oxide growing under an aluminum fluoride barrier layer have been determined – showing an increase in absorption at high energies for Al2O3 forming at room temperature as compared to highly ordered Al2O3 formed at high temperatures.

Irreversible thermodynamics is a widely-applicable toolset that extends thermodynamics to describe systems undergoing irreversible processes. It is particularly useful for describing macroscopic flow of system components, whether conserved (e.g., particle number) or non-conserved (e.g., spin). We give a general introduction to this toolset and calculate the entropy production due to bulk and interfacial flow. We compare the entropy production and heating rate of bulk and interfacial transport, as well as interfacial charge and spin transport. We then demonstrate the power and applicability of this toolset by applying it to three systems. We first consider metal oxide growth, and discuss inconsistency in previous theory by Mott. We show, however, that Mott's solution is the lowest order of a consistent asymptotic solution, with the ion and electron concentrations and fluxes going as power series in t^-k/2, where k = 1, 2, .... We find that this gives corrections to the "parabolic growth law" that has oxide thickness going as t^1/2; the lowest order correction is logarithmic in t. We then consider the effect on spin of electric currents crossing an interface between a ferromagnet (FM) and non-magnetic material (NM). Previous theories for electrical potential and spin accumulation neglect chemical or magnetic contributions to the energy. We apply irreversible thermodynamics to show that both contributions are pivotal in predicting the spin accumulation, particularly in the NM. We also show that charge screening, not considered in previous theories, causes spin accumulation in the FM, which may be important in ferromagnetic semiconductors. Finally, we apply irreversible thermodynamics to thermal equilibration in a thin-film FM on a substrate. Recent experiments suggest that applying a thermal gradient across the length of the system causes a spin current along the thickness; this spin current is present much farther from the heat sources than expected. We find that, although the interaction between the separate thermal equilibration processes increases the largest equilibration length, thermal equilibration does not predict a length as large as the experimentally measured length; it does predict, however, a thermal gradient along the thickness that has the shape of the measured spin current.

Oxide formation on metallic surfaces is a common phenomenon which occursnaturally or intently. Depending on the metallic oxide, they can be viewed as either nuisances or conveniences depending on the effects of the oxide. Formed oxides may also potentially smooth surfaces of metallic alloys since a portion of the surface in contact with the oxygen will be converted into the oxide via the metal-oxygeninteraction, leading to a smoother surface underneath the formed oxide. It was found that oxide formation was most significant when metallic Vibenite® alloys were treated at 1000°C for a minimum of 3 hours with an oxygen flow into the oven of 10 L/min. This signifies the importance of a minimum temperature limit as well as an increased oxygen pressure within the oven the samples are being treated in, which concurs with various studies referred to in the report. The oxides were also somewhat successfully identified using analysis methods such as XPS, XRD and Raman spectroscopy with supporting evidence from simulated Thermo-Calc approximations. Thepost-treatment surfaces of the samples, after having their oxide layers removed, were confirmed to have undergone surface smoothing using the optical analysis method of VSI. The results of this report indicate validity in the use of the oxide formation technique for surface smoothing and strongly suggests further study in material optimised heat-treatments for different metallic alloys with the purpose of surface refinement

Wafer bonding is important in microelectromechanical systems (MEMS) manufacturing, enabling wafer-level encapsulation and packaging. In this project, different pre-treatments of the polycrystalline silicon surface for eutectic gold-silicon (AuSi) bonding were studied with respect to the resulting bond strength. Native oxides or other surface layers can decrease the interaction between Au and Si, leading to weaker bonds. Different etching methods were investigated to remove native oxide. Spectroscopic ellipsometry (SE), water contact angle measurements and Fourier transform infrared spectroscopy (FTIR) were used to analyze the surfaces. SE measurements showed that the oxide layer grew 5 Å the first 4 hours after HF etch, rinse and dry, but then grew less than this during the following 6 weeks. The measured oxide growth was similar for wafers with other pre-treatments. Through contact angle measurements, it was demonstrated that the different etching methods resulted in different outermost surface layers. None of the contact angles were changed much over several weeks, indicating subsequent oxide growth occurred below a stable outermost layer. For wafer bonding, wafers with bond frame structures were used. After wafer bonding, the bond frames were analyzed with infrared (IR) microscopy and the bonds were shear tested for bond strength. The shorter the exposure time to ambient air atmosphere before bond, the stronger the bond in general. Furthermore, the wafers stored in nitrogen atmosphere exhibited higher bond strengths than the wafers stored in air for the same amount of time, confirming that the growing oxide was the reason for the decreased bond quality during wafer storage. HF (wet/vapor) etched wafers in general had slightly stronger bonds than the other wafers and the wafers etched with HF vapor had the highest average bond strength of all. The IR images showed that white areas in the bond frames were related to decreased bond strength, and that wafers that had longer storage time on average had more white in the bond frames. As a conclusion, to achieve as strong bonds as possible, the waiting time between wafer pre-treatments and bonding should be minimized, and in the waiting time it is beneficial to store the wafers in nitrogen atmosphere. In this study most wafers stored 2 weeks in nitrogen had good bond quality and even wafers stored 3 days in air had acceptable bond strengths. However, using HF to etch away the oxide before bond is preferable compared to the other etching methods, not only to have larger average bond strength, but also to have less bond strength decrease during waiting time before bond. / I tillverkning av mikroelektromekaniska system (MEMS) är skivbondning viktigt för inkapsling och förpackning av mikrosystem på skivnivå. I detta projekt studerades olika förbehandlingar av polykristallina kiselytan, inför eutektisk AuSi-bondning, med avseende på resulterande bondstyrka. Nativoxid eller andra ytskikt kan minska interaktionen mellan guld (Au) och kisel (Si), vilket leder till svagare bond. Flera olika etsmetoder undersöktes för att ta bort nativoxid. Spektroskopisk ellipsometri (SE), mätningar av vattenkontaktvinkel och Fouriertransform infraröd spektroskopi (FTIR), användes för att analysera ytorna. Resultaten från SE-mätningarna visade att oxiden växte 5 Å under de 4 första timmarna efter HF-ets, skölj och tork, men växte sedan mindre än detta under de följande 6 veckorna. Den uppmätta oxidtillväxten var liknande för skivorna med andra förbehandlingar. Kontaktvinklarna var olika för olika förbehandlingsmetoder, vilket visar att de hade olika yttersta ytskikt. Ingen av kontaktvinklarna ändrades mycket under flera veckor, vilket indikerar att den följande oxidtillväxten skedde under ett stabilt yttersta lager. För skivbondning andvändes skivor med bondramar längs chip-kanterna. Dessa bondramar var gjorda av polykristallint Si respektive Au på skivorna som skulle bondas. Efter bondning analyserades bondramarna med infraröd (IR) mikroskopi och skjuvtester gjordes för att bestämma bondstyrkan. Ju kortare tid skivorna exponerades till omgivande luft, desto starkare bond i allmänhet. Dessutom uppvisade skivorna som lagrats i kväveatmosfär högre bondstyrkor än de skivor som lagrats i luft, vilket bekräftar att den växande oxiden var orsaken till den minskade bondkvaliteten under skivlagring. HF-etsade skivor (HF- dipp och HF-ånga) hade något starkare bond än de andra skivorna och de skivor som etsats med HF-ånga hade allra högst genomsnittlig bondstyrka. IR-bilderna visade att vita områden i bondramarna var relaterat till minskad bondstyrka och att skivor som hade längre lagringstid i genomsnitt hade mer vitt i bondramarna. Slutsatsen är att för att uppnå så hög bondstyrka som möjligt ska tiden mellan förbehandlingar och bond minmeras, och under väntetiden är det till fördel att skivorna förvaras i kväveatmosfär. I den här studien hade skivor som förvarats 2 veckor i kväve bra bondkvalitet och även skivor som stått 3 dagar i luft hade godtagbara bondstyrkor. Att använda HF för att etsa bort oxid är dock bättre än att använda någon av de andra etsmetoderna, inte bara för att få högre genomsnittliga bondstyrkor, utan också för att få mindre minskning av bondstyrkan under väntetiden inför bondning.

Ce travail de thèse s’est inscrit dans un cadre fondamental d’étude de la formation contrôlée d’oxydes en couches ultra-minces. Un bâti ultra-vide dédié à la croissance contrôlée de ces oxydes et à leur analyse in-situ (STM-STS, AES et LEED) a été développé. Par une méthode originale de phases alternées de dépôt d’une monocouche atomique de Mg et oxydation à RT, les mécanismes impliqués dans la formation de deux systèmes à fort potentiel applicatif : MgO/Si(100) et MgO/Ag(111) ont été étudiés .Le système MgO/Si(100) a révélé la formation d’une couche ultra-mince de Mg2Si à l’interface entre le MgO et le substrat. En bon accord avec les calculs thermodynamiques réalisés, une cristallisation de cette couche interfaciale dans un processus de dissociation partielle du Mg2Si en MgO à température ambiante a été observée. Identifiée ex-situ par TEM, la relation d’épitaxie associée à cette cristallisation a permis de conclure à la formation d’une hétérostructure MgO / Mg2Si (11-1) / Si(001), témoignant d’une grande qualité d’interface avec le silicium et de la formation d’une couche ultra-mince et amorphe de MgO homogène et isolante (gap de 6 eV).Pour le système MgO/Ag(111), nos résultats expérimentaux couplés aux calculs ab initio de nos partenaires du LAAS ont révélé l’absence de formation d’un alliage de surface ainsi qu’une croissance « liquid-like » du magnésium à RT. Un double empilement O/Mg/O/Mg/Ag(111) suivi d’un recuit UHV à 430°C a ensuite permis la stabilisation d’une couche ultra-mince polaire de MgO(111) qui a été caractérisée par LEED et STM-STS. Les propriétés physico-chimiques et origines possibles de stabilité de cet oxyde polaire ont ensuite été discutées. / This PhD work was dedicated to studying the fundamental mechanisms driving the controlled growth of ultra-thin oxide films. An experimental set-up was designed to finely control the growth parameters under UHV conditions while allowing the study of such oxide layers in situ with STM-STS, AES and LEED. Using an original method based on alternate cycles of Mg monolayer adsorption and RT oxidation, we focused on the formation of systems exhibiting a wide range of potential applications: MgO/Si(100) and MgO/Ag(111). The MgO/Si(100) system revealed the growth of an ultra-thin Mg2Si layer at the interface between the MgO and the silicon. In agreement with thermodynamic calculations, a crystallization of this interlayer driven by a partial decomposition of the Mg2Si to a MgO oxide was shown to occur at RT. From ex situ TEM experiments, the involved epitaxial relationship highlighted the formation of an MgO / Mg2Si (11-1) / Si(001) heterostructure. A sharp interface with the silicon was formed, as much as an ultra-thin and amorphous MgO layer exhibiting both a good homogeneity and a high insulating character (bandgap of 6 eV).In the MgO/Ag(111) system, no interfacial alloy formation and a « liquid-like » growth for the Mg were evidenced at RT, using our experimental results coupled with the ab initio calculations performed by our co-workers at LAAS laboratory. Later, a double-layering O/Mg/O/Mg/Ag(111) grown at RT followed by UHV annealing at 430°C resulted in the stabilization of a polar MgO(111) ultra-thin film, which was characterized using LEED and STM-STS. The physicochemical properties of this polar oxide and the potential origin of its stability were discussed.