Doctor of Philosophy(PhD) / Biomedical materials are being extensively researched, and many different types such as metals, metal alloys, and polymers are being used. Currently used biomedical materials are not perfect in terms of corrosion resistance, biocompatibility, and surface properties. It is not easy to fabricate from scratch new materials that can fulfill all requirements and an alternative approach is to modify the surface properties of current materials to cater to the requirements. Plasma immersion ion implantation (PIII) is an effective and economical surface treatment technique and that can be used to enhance the surface properties of biomaterials. The unique advantage of plasma modification is that the surface properties and functionalities can be enhanced selectively while the favorable bulk attributes of the materials such as strength remain unchanged. In addition, the non-line of sight feature of PIII is appropriate for biomedical devices with complex geometries such as orthopedic implants. However, care must be exercised during the plasma treatment because low-temperature treatment is necessary for heat-sensitive materials such as polymers which typically have a low melting point and glass transition temperature. Two kinds of biomedical materials will be discussed in this thesis. One is nickel titanium (NiTi) alloy which is a promising orthopedic implant material due to its unique shape memory and superelastic properties. However, harmful ions may diffuse from the surface causing safety hazards. In this study, we investigate the properties and performance of NiTi after nitrogen and oxygen PIII in terms of the chemical composition, corrosion resistance, and biocompatibility. The XPS results show that barrier layers mainly containing TiN and TiOx are produced after nitrogen and oxygen PIII, respectively. Based on the simulated in vitro and electrochemical corrosion tests, greatly reduced ion leaching and improved corrosion resistance are accomplished by PIII. Porous NiTi is also studied because the porous structure possesses better bone ingrowth capability and compatible elastic modulus with human bones. These advantages promote better recovery in patients. However, higher risks of Ni leaching are expected due to the increased exposed surface area and rougher topography than dense and smooth finished NiTi. We successfully apply PIII to porous NiTi and in vitro tests confirm good cytocompatibility of the materials. The other type of biomedical materials studied here is ultra-high molecular weight polyethylene (UHMWPE) which is a potential material for use in immunoassay plates and biosensors. In these applications, active antibodies or enzymes attached to a surface to detect molecules of interests by means of specific interactions are required. Moreover, the retention of enzyme activity is crucial in these applications. Therefore, the aim of this study is to investigate the use of PIII to prepare UHMWPE surfaces for binding of active proteins in terms of the binding density and ‘shelf life’ of the treated surfaces. Argon and nitrogen PIII treatments are attempted to modify the surface of UHMWPE. Horseradish peroxidase (HRP) is selected to conduct the protein binding test since it is a convenient protein to assay. Experimental results show that both PIII treated surfaces significantly improve the density of active HRP bound to the surface after incubation in buffer containing HRP. Furthermore, the PIII treated surfaces are found to perform better than a commercially available protein binding surface and the shelf life of the PIII treated surfaces under ambient conditions is at least six months. In conclusion, a biocompatible barrier layer on NiTi and a protein binding surface on UHMWPE is synthesized by PIII. The surface properties such as corrosion resistance and functionality on these two different types of substrates are improved by PIII.

Doctor of Philosophy(PhD) / Biomedical materials are being extensively researched, and many different types such as metals, metal alloys, and polymers are being used. Currently used biomedical materials are not perfect in terms of corrosion resistance, biocompatibility, and surface properties. It is not easy to fabricate from scratch new materials that can fulfill all requirements and an alternative approach is to modify the surface properties of current materials to cater to the requirements. Plasma immersion ion implantation (PIII) is an effective and economical surface treatment technique and that can be used to enhance the surface properties of biomaterials. The unique advantage of plasma modification is that the surface properties and functionalities can be enhanced selectively while the favorable bulk attributes of the materials such as strength remain unchanged. In addition, the non-line of sight feature of PIII is appropriate for biomedical devices with complex geometries such as orthopedic implants. However, care must be exercised during the plasma treatment because low-temperature treatment is necessary for heat-sensitive materials such as polymers which typically have a low melting point and glass transition temperature. Two kinds of biomedical materials will be discussed in this thesis. One is nickel titanium (NiTi) alloy which is a promising orthopedic implant material due to its unique shape memory and superelastic properties. However, harmful ions may diffuse from the surface causing safety hazards. In this study, we investigate the properties and performance of NiTi after nitrogen and oxygen PIII in terms of the chemical composition, corrosion resistance, and biocompatibility. The XPS results show that barrier layers mainly containing TiN and TiOx are produced after nitrogen and oxygen PIII, respectively. Based on the simulated in vitro and electrochemical corrosion tests, greatly reduced ion leaching and improved corrosion resistance are accomplished by PIII. Porous NiTi is also studied because the porous structure possesses better bone ingrowth capability and compatible elastic modulus with human bones. These advantages promote better recovery in patients. However, higher risks of Ni leaching are expected due to the increased exposed surface area and rougher topography than dense and smooth finished NiTi. We successfully apply PIII to porous NiTi and in vitro tests confirm good cytocompatibility of the materials. The other type of biomedical materials studied here is ultra-high molecular weight polyethylene (UHMWPE) which is a potential material for use in immunoassay plates and biosensors. In these applications, active antibodies or enzymes attached to a surface to detect molecules of interests by means of specific interactions are required. Moreover, the retention of enzyme activity is crucial in these applications. Therefore, the aim of this study is to investigate the use of PIII to prepare UHMWPE surfaces for binding of active proteins in terms of the binding density and ‘shelf life’ of the treated surfaces. Argon and nitrogen PIII treatments are attempted to modify the surface of UHMWPE. Horseradish peroxidase (HRP) is selected to conduct the protein binding test since it is a convenient protein to assay. Experimental results show that both PIII treated surfaces significantly improve the density of active HRP bound to the surface after incubation in buffer containing HRP. Furthermore, the PIII treated surfaces are found to perform better than a commercially available protein binding surface and the shelf life of the PIII treated surfaces under ambient conditions is at least six months. In conclusion, a biocompatible barrier layer on NiTi and a protein binding surface on UHMWPE is synthesized by PIII. The surface properties such as corrosion resistance and functionality on these two different types of substrates are improved by PIII.

Malgré son grand potentiel, l’énergie photovoltaïque n’arrive pas encore à trouver une grande place dans le paysage énergétique mondial. Elle se heurte à deux problèmes de taille : le coût et le rendement. Les cellules solaires à base du silicium multicristallin (mc-Si) perdent beaucoup de leur rendement à cause de la présence des impuretés métalliques. Plusieurs recherches ont montré que les cavités induites par implantation ionique sont efficaces dans le piégeage des impuretés. Mais les techniques utilisées dans l’implantation n’ont pas permis à ce procédé de se développer dans l’industrie à cause de leur coût élevé. Le plasma immersion ion implantation (PIII) est une technique bas coût qui permet d’implanter de grandes surfaces. Elle est utilisée dans le traitement de surface à l’échelle industrielle, mais à ce jour aucune étude n’a montré son utilisation dans le piégeage des impuretés dans le silicium. Dans cette thèse nous avons créé des cavités dans le mc-Si par implantation d’hydrogène par PIII. Plusieurs techniques de caractérisation ont été utilisées afin d’étudier le mécanisme de formation de ces cavités. La MET, la photoluminescence et les positons ont été utilisées pour avoir un maximum d’informations sur la nature et l’évolution des défauts créés par implantation d’hydrogène. Nous avons également étudié la différence entre les cavités formées par PIII et celles formées par implantation classique. Les cavités formées ont été utilisées, par la suite, pour le piégeage des impuretés métalliques présentes dans le mc-Si (Cu, Fe, Cr et Ni). Les résultats obtenus par SIMS ont monté l’efficacité de notre procédé dans le piégeage des impuretés métalliques. / Extraction of silicon metal impurities to be used for photovoltaic by plasma immersion ion implantation (PII)

Doctor of Philosophy (PhD) / This thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface.

This thesis details the design and development of a solid-state, high power modulator for driving plasma ion implantation systems. A plurality of modulators can be stacked in a Marx geometry to allow complete voltage (implantation energy) scalability. Unlike a classic Marx modulator, the design employs actively controlled charging and discharging paths. This allows maximum modulation flexibility and efficiency. A hybrid Marx bank - pulse transformer configuration was commissioned in a 20keV 12A plasma ion implantation system for the purpose of photonics research. <p>The design portion of this work is accompanied by an investigation, extension and discretization of the Lieberman analytical model of plasma ion implantation dynamics. The model predicts final implantation concentrations as well as system operational limits in specific plasma conditions. A new extension to the model accounts for subtle time-of-flight effects on accelerating ions. Agreement between modeled and measured ion currents is good.<p>Finally, a collection of material processing experiments conducted with the plasma ion implantation system since its inauguration in February 2006 is briefly presented. In it, a new silicon-based light emitting diode is introduced.

This thesis details the design and development of a solid-state, high power modulator for driving plasma ion implantation systems. A plurality of modulators can be stacked in a Marx geometry to allow complete voltage (implantation energy) scalability. Unlike a classic Marx modulator, the design employs actively controlled charging and discharging paths. This allows maximum modulation flexibility and efficiency. A hybrid Marx bank - pulse transformer configuration was commissioned in a 20keV 12A plasma ion implantation system for the purpose of photonics research. <p>The design portion of this work is accompanied by an investigation, extension and discretization of the Lieberman analytical model of plasma ion implantation dynamics. The model predicts final implantation concentrations as well as system operational limits in specific plasma conditions. A new extension to the model accounts for subtle time-of-flight effects on accelerating ions. Agreement between modeled and measured ion currents is good.<p>Finally, a collection of material processing experiments conducted with the plasma ion implantation system since its inauguration in February 2006 is briefly presented. In it, a new silicon-based light emitting diode is introduced.

Doctor of Philosophy (PhD) / This thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface.

Cette thèse est centrée sur le développement de modèles numériques pour simuler le comportement physique des plasmas présents dans un réacteur d'implantation ionique à immersion plasma. Ces modèles ont pour but d'estimer l'impact des réglages opérationnels du réacteur sur les paramètres plasma pertinents pour l'implantation, comme le flux ionique sur le substrat et la distribution en énergie des ions. La géométrie complexe du réacteur rend difficile sa modélisation d'un seul tenant, du fait des importants gradients temporels et spatiaux attendus pour les densités ioniques et la température électronique. Une stratégie de simulation en deux étapes a donc été adoptée : - Un modèle quasi-homogène, couplé à un module de chimie en volume élaboré, permet de représenter des deux portions de la source plasma et d'obtenir l'évolution de la composition du plasma en fonction de la puissance radiofréquence injectée. - Un modèle unidimensionnel de type PIC-MC permet de décrire la dynamique de la gaine ionique qui se forme près du substrat du fait du potentiel imposé, ainsi que de déterminer la distribution de l'énergie d'impact des ions et les flux d'implantation correspondants. Au final, ces travaux de recherche ont permis d'aboutir à une meilleure compréhension de l'impact des paramètres opérationnels du réacteur sur le flux ionique et la distribution en énergie des ions arrivant sur le substrat. La connaissance des couplages physiques entre la source plasma et la chambre d'implantation autorise l'optimisation du processus de dopage, puisque les paramètres opérationnels peuvent être réglés de manière à minimiser la profondeur de dopage après implantation. / Numerical models have been developped to simulate the plasma present inside a plasma immersion ion implantation reactor. Their goal is to estimate the impact of the reactor’s settings on the plasma parameters relevant for ion implan-tation. The complex geometry of the reactor renders its modelling difficult, because of the stiff spatial and temporal gradients expected, so a two-step simulation stra-tegy was adopted : – A global model of the plasma source, coupled to a detailed volume chemistry module, allows to determine the time evolution of the plasma composition according to the radio-frequency power injected in the source.– A 1D PIC-MC model of the sheath facing the substrate describes the dyna-mics of the expanding sheath and allows to determine the ion impact energy distribution function and corresponding implantation profiles. Determination of the couplings between the plasma source and the implantation chamber makes possible to optimize the doping process, since the reactor’s opera-tional settings can then be adjusted to minimize the doping depth after implanta-tion.

Le dopage du silicium par implantation ionique pour le photovoltaïque est une application relativement récente dont l'essor se heurte encore aujourd'hui aux coûts élevés d'intégration au sein des lignes de fabrication des cellules solaires. L'implantation ionique par immersion plasma promet de répondre aux futures exigences du secteur en termes de coûts et de productivité.Ces travaux de thèse ont permis le développement de procédés d'implantation ionique par immersion plasma de l'équipement PULSION®, conçu par IBS, dédiés à la fabrication de cellules solaires en silicium monocristallin. Dans un premier temps, nous montrons qu'il permet la réalisation de profils de dopage d'émetteur de type n variés, répondant aux exigences des cellules solaires à haut rendement. Les émetteurs fabriqués sont caractérisés de manière chimique, physique et électrique afin de démontrer leur excellente qualité. L'intégration de l'implantation ionique des émetteurs au sein d'un processus de fabrication industriel et peu coûteux, développé par l'INES sur silicium monocristallin de type p, permet d'atteindre des rendements de conversion supérieurs à 19,3%, soit un gain de plus de 0,5% par rapport aux rendements obtenus avec des cellules usuelles à émetteurs dopés par diffusion POCl3.La réalisation d'émetteurs de type p est également étudiée dans ce mémoire afin de préparer la transition technologique vers les cellules solaires sur silicium monocristallin de type n. Confirmant les atouts et le potentiel de la technologie d'implantation ionique par immersion plasma, les travaux menés au cours de cette thèse débouchent sur la conception d'un prototype industriel PULSION® dédié au photovoltaïque. / Ion implantation is a major process technology for manufacturing integrated circuits. However, silicon doping by ion implantation for photovoltaics is a relatively recent application, and its growth still faces high costs of integration into solar cell production lines. Plasma-immersion ion implantation (PIII) promises to meet the future industry requirements in terms of costs and productivity.This thesis work has led to the development of processes dedicated to silicon-based solar cell manufacturing using the plasma-immersion ion implanter – PULSION® – designed by IBS. First, we show that PIII enables the realization of various doping profiles for phosphorus-doped emitters which fit the requirements of high-efficiency solar cells. Emitters thus fabricated are chemically, physically and electrically characterized to demonstrate their excellent quality. Those emitters, implanted through plasma immersion and integrated into a low cost solar cell manufacturing line from INES on monocrystalline silicon, enable to raise the conversion efficiency, obtained with conventional POCl3-diffused solar cells, by more than 0.5% absolute to reach efficiencies above 19.3%.Fabrication of p-type boron implanted emitters is also studied in order to improve conversion efficiencies of p-type silicon based solar cells, but also in order to anticipate the technological shift from p-type to n-type silicon material. Thanks to this thesis work, the strength and potential of PIII for photovoltaic applications have been proven and this has convinced IBS to design a PULSION® equipment dedicated to solar cell manufacturing.

Šio darbo literatūros apžvalgoje aptariami plazmos tipai, plazmos charakteristikos bei sąveika su medžiaga. Aptariama plazminės implantacijos technologija. Trumpai apibūdinama vandens garų plazma ir jos panaudojimas. Apžvelgiama titano oksido struktūra bei jo panaudojimas katalizatorių gamybai, kurie gali būti skirti skaldyti vandens molekules ir gaminti vandenilį. Darbe paaiškinamas magnetroninis nusodinimas bei jo privalumai. Darbo metu buvo oksiduojamas titanas vandens garų plazmoje. Titano oksidacija priklauso nuo daugybės plazmoje vykstančių procesų (adsorbcija, sulaikymas, vakansijų susidarymas ir pan.). Titano oksido panaudojimas yra labai platus dabartiniu metu. Aptariama šio eksperimento technologija bei atliekama oksiduotų titano dangų analizė. SEM, XRD, AES, GDOES analizės metodais buvo tiriama titano dangos oksidacija ir aiškinamas oksidacijos mechanizmas. / Types of plasma, characteristics and plasma interaction with solids are discussed in the literature review of this paper. Also, the plasma immersion ion implantation are described. Water vapour plasma are briefly discussed. Titanium oxide structure and it‘s usage for catalyst which could split water molecules are reviewed. Magnetron deposition are explained in this paper. The titanium film was oxidized by water vapour plasma on experiment. The oxidation of titanium depends on many processes in plasma (adsorption, trapping, formation of oxygen vacancies and etc.). Appliance of titanium oxide is very large in recent times. Experimental technology are discussed and plasma treated films are analysed. Titanium oxidation was analysed by SEM, XRD, AES, GDOES. Oxidation mechanism was explained in this paper.