Mass-spectroscopy and modeling of capacitive coupled hydrogen plasmas

This work presents the characterization of a radio-frequency, capacitively coupled, symmetric, hydrogen plasma. Both steady-state operation and the time-prole of the afterglow when RF power is terminated are investigated. Fluxes of the hydrogen ions, H+ , H+2, H+3, at the grounded electrode are measured with an energy-resolved mass spectrometer. Spatial proles of the electron density are measured using a hairpin probe. Particle-in-cell simulations including a complex hydrogen chemistry are performed which enable direct comparison to the experiment. In the steady-state operation, the electron density increases with both power and pressure, and the ion flux magnitudes and energy distributions are found to vary with power. The H+3 ion flux decreases with power and pressure, whereas the H+ and H+2 ion fluxes increase with power and pressure, with approximately equal fluxes at the highest pressure/power combination of 30.0 Pa and 750V peak-to-peak. In conjunction with the PIC results, it is determined that the H+3 ion remains the dominant ion in the plasma for all investigated parameter space, and that the strong variation in ion flux magnitudes and energy-distributions are due to fast-ion induced chemistry occurring in the sheath at the grounded electrode. A simple theoretical model is developed in order to estimate the electron temperature at the sheath edge if the IEDFs and electron density are known. Investigations of the afterglow include time-evolution of the H+3 ion energy distribution, spatio-temporal proles of the electron density, and particle-in-cell simulations. The measured H+3 ion flux energy distribution persists substantially longer into the afterglow than is seen in the PIC simulations. This unusual result is explained in the hypothesis of super elastic collision of vibrationally excited hydrogenmolecule with an electron resulting in energy transfer to the electron. The mechanics such super-elastic collisions are not included in the PIC simulation, and this is consistent with the discrepancy between the simulation and the experiment. Electron density measurements show a substantial increase in the density, as much as a factor of four, sharply rising immediately after the RF voltage is switched off. Small density rises, of order 10%, are seen in the simulation. An analysis showing the validity of the measurements, and two hypothesis to explain the density rise are presented. A method for determining the electron temperature time-prole in the afterglow is introduced

バイポーラPBII&D法によるDLC膜の三次元作成およびプラズマ挙動解析に関する研究

学位の種別:課程博士University of Tokyo(東京大学

Development of planar langmuir probes for supersonic plasma flows

Langmuir probes are a long established tool for the investigation and char- acterization of plasmas. Diagnostic use of planar Langmuir probes in sta- tionary low temperature plasmas is a well understood and long established technique. When the plasma possesses a drift velocity greater than the ion sound speed the flow is considered to be supersonic. Under such conditions the theory for Langmuir probes is less than satisfactory. Where the flow is supersonic the Mach probe theory of Hudis and Lidsky [1] can be applied for a magnetized plasma. However in the case of an unmagnetized plasma there is no satisfactory theory. It has been observed that in orientating a planar Langmuir probe parallel to the direction of flow, the ion current due to the flow is eliminated. Under such conditions the behaviour of the plasma’s in- teraction with the probe bears close resemblance to the conditions seen in plasma immersion ion implantation (PIII). This thesis describes the adaptation’s made to PIII analytical model’s to take advantage of these similarities and its use to then describe the ion current of planar Langmuir probes in unmagnetized plasmas possessing a supersonic flow. In adapting a suitable analytical model for planar Langmuir probes under such conditions, extensive use of both 1D and 2D hybrid particle in cell (PIC) simulations have been made. Additionally the work required the development of a 2D hybrid PIC code where the probe is embedded within the grid. This allowed the investigation of the impact of edge effects on the analytical model’s performance. The theory for and structure of the 2D code is also presented as part of this work. Three different probe orientations are considered, firstly the parallel case, the other two concerns the near parallel cases of the probe surface orientated both into and away from the direction of flow. The model’s performance under these conditions is evaluated and discussed. Finally the use of this model in allowing a planar Langmuir probe to act as a Mach probe is also considered. In testing the success of the analytical model against experimental data, comparisons are made between the models results and those of the 2D hybrid PIC. The experimental results used for this work were for xenon plasma with a range of moderately supersonic velocities and a highly supersonic silver laser ablated plasma plume

Investigation of Ion and Electron Kinetic Phenomena in Capacitively Coupled Radio-Frequency Plasma Sheaths: A Simulation Study

Stochastic heating is an important phenomenon in low-pressure radio-frequency (RF) capacitive discharges. Recent theoretical work on this problem using several different approaches has produced results that are broadly in agreement in-so-far as scaling with the discharge parameters is concerned, but there remains some disagreement in detail concerning the absolute size of the effect. Here we report a simulation study for single and dual frequency capacitive discharges with two main aims. In the case of single frequency discharge, this work investigates the dependence of stochastic heating on various discharge parameters by scaling of these parameters with the help of particle-in-cell (PIC) simulation. This research work produces a relatively extensive set of simulation data that may be used to validate theories over a wide range of parameters. The analytical models are satisfactory for intermediate current density amplitude ˜ J0 (or control parameter H) and in agreement with PIC results. However in extreme cases new physical effects appear (like field reversal, electron trapping, reflection of ions etc.) and the simulation results deviate from existing analytical models. The dependence of stochastic heating on applied frequency is also investigated. The second aim is to study any evidence of wave emission with a frequency near the electron plasma frequency at the sheath edge. This is the result of a progressive breakdown of quasi-neutrality close to the electron sheath edge. These waves are damped during their propagation from the sheath towards the bulk plasma. The damping occurs because of the Landau damping or some related mechanism. This research work reports that the emission of waves is associated with a field reversal during the expansion phase of the sheath. Trapping of electronsnear to this field reversal region is observed. Calculation shows that these waves are electron plasma waves. In the dual frequency case, this research has produced a relatively extensive set of simulation data and shown that the dual-frequency analytical model is in agreement for wide range of parameters. However, in extreme cases, new phenomena like the presence of strong field reversal and the reflection of ions appear and the simulation results deviate from the analytical model. A further aim is the investigation of the presence of strong wave phenomena during the expanding and collapsing phase of the low frequency sheath. The characteristics of waves in the dual-frequency case is entirely different from the single-frequency case. The presence of electron trapping near to the field reversal regions is also observed at multiple times of an RF period. The frequency of these waves are calculated and to be of the order of the plasma frequency

Simulation de profils de gravure et de dépôt à l’échelle du motif pour l’étude des procédés de microfabrication utilisant une source plasma de haute densité à basse pression

En lien avec l’avancée rapide de la réduction de la taille des motifs en microfabrication, des processus physiques négligeables à plus grande échelle deviennent dominants lorsque cette taille s’approche de l’échelle nanométrique. L’identification et une meilleure compréhension de ces différents processus sont essentielles pour améliorer le contrôle des procédés et poursuivre la «nanométrisation» des composantes électroniques. Un simulateur cellulaire à l’échelle du motif en deux dimensions s’appuyant sur les méthodes Monte-Carlo a été développé pour étudier l’évolution du profil lors de procédés de microfabrication. Le domaine de gravure est discrétisé en cellules carrées représentant la géométrie initiale du système masque-substrat. On insère les particules neutres et ioniques à l’interface du domaine de simulation en prenant compte des fonctions de distribution en énergie et en angle respectives de chacune des espèces. Le transport des particules est effectué jusqu’à la surface en tenant compte des probabilités de réflexion des ions énergétiques sur les parois ou de la réémission des particules neutres. Le modèle d’interaction particule-surface tient compte des différents mécanismes de gravure sèche telle que la pulvérisation, la gravure chimique réactive et la gravure réactive ionique. Le transport des produits de gravure est pris en compte ainsi que le dépôt menant à la croissance d’une couche mince. La validité du simulateur est vérifiée par comparaison entre les profils simulés et les observations expérimentales issues de la gravure par pulvérisation du platine par une source de plasma d’argon.With the reduction of feature dimensions, otherwise negligible processes are becoming dominant in microfabricated profile evolution. Improved understanding of these different processes is essential to improve the control of the microfabrication processes and to further decrease of the feature size. To help attaining such control, a 2D feature scale cellular simulator using Monte-Carlo techniques was developed. The calculation domain is discretized in square cells representing empty space, substrate or mask of the initial system. Neutral and ion species are inserted at simulation interface from their respective angular and energy distributions functions. Particles transport to the feature surface is calculated while taking into account ion reflection on sidewall and neutral reemission. The particles-surface interaction model includes the different etching mechanisms such as sputtering, reactive etching and reactive ion etching. Etch product transport is also taken into account as is their deposition leading to thin film growth. Simulation validity is confirmed by comparison between simulated profiles and experimental observations issued from sputtering of platinum in argon plasma source

High Yield Production and Biofunctionalization of Plasma Polymerized Nanoparticles for Applications in Biomedicine

The advent of nanoparticle technology in the medical and pharmaceutical sectors offers significant potential in the quest for more effective healthcare solutions. Surface biofunctionalization, the engineering of nanoparticle surfaces for targeted biomedical applications, is critical for the development of personalized medicine in the delivery of diagnostic and therapeutic agents. However, the transition from laboratory research to commercial scale production faces substantial challenges in ensuring scalability of synthesis methods, consistent nanoparticle quality and addressing safety concerns related to toxicity. The commercial viability of nanoparticle-based medical products requires the precedence of translation into clinical settings warranting their integration into cellular environments while maintaining bioactivity. Traditional methods for nanoparticle synthesis and functionalization often fall short from achieving this aim due to inconsistencies in particle sizes, high production costs, reagent toxicity and subsequent complex wet-chemical processing. This thesis introduces plasma polymerization as a high-throughput method for producing surface- active polymeric nanoparticles, through a more environmentally friendly, dry synthesis process. Chapter 1 introduces polymer nanoparticles in nanomedicine, focusing on surface functionalization for improved diagnostics and therapeutics, and overcoming biological barriers for targeted delivery. Chapter 2 outlines methodologies. Chapter 3 discusses enhanced collection yield while maintaining properties for surface treatment, demonstrated through biofunctionalization of plasma polymerized nanoparticles (PPNs) with non-cytotoxic covalent bonds. Chapter 4 confirms this via in vitro studies. Chapter 5 studies long-term stability, showing bioactivity after a year. The final chapter details PPN synthesis, validating a continuum fluid model to enhance predictive accuracy