Study of the effects of deuterium implantation upon the performance of thin-oxide CMOS devices

The use of ultra thin oxide films in modem semiconductor devices makes them increasingly susceptible to damage due to the hot carrier damage. Deuterium in place of hydrogen was introduced by ion implantation at the silicon oxide-silicon interface during fabrication to satisfy the dangling bonds. Deuterium was implanted at energies of 15, 25 and 35 keV and at a dose of 1x1014/cm2. Some of the wafers were subjected to N2O annealing following gate oxide growth. It was demonstrated that ion implantation is an effective means of introduction of deuterium. Deuterium implantation brings about a clear enhancement in gate oxide quality by improving the interface characteristics. N2O annealing further improves device performance. A reduction of electron traps with deutenum was also observed. A combination of deuterium implantation at 25 keV and a dose of 1x1015/cm2, followed by annealing in N2O was observed to have the most positive influence on device behavior. Concurrently, MEMS microheaters being fabricated for an integrated VOC sensor were also tested for their temperature response to an applied voltage. Different channel configurations and materials for the conducting film were compared and the best pattern for rapid heating was identified. Temperature rises of upto 390° C were obtained. The temperature responses after coating spin-on glass in the microchannels were also measured

Plasma induced damage to Si and SiGe devices and materials

This thesis studied the plasma-induced damage to Si and strained Si1-xGex, and the resulting change in device characteristics. The energetic particles (ions, electrons and photons) in plasma reactor present a potentially hostile environment for processing VLSI devices. An inductively coupled plasma (ICP) reactor was used to study its damage effects to thin gate oxides. Electrical characterizations by C-V, ramped voltage breakdown (RVB) and deep-level transient spectroscopy (DLTS) measurement, and x-ray photoelectron spectroscopy (XPS) analysis were employed to investigate the damages to thin gate oxides and Si/SiO2 interface. The shift of flat band voltage, the reduction of breakdown voltage and the creation of high interface trap density were found to be in good agreement with the creation of suboxidation states at Si/SiO2 interface. It is observed that device damage is well associated with the reactor operating conditions. The major mechanism responsible for damage appeared to be high energy electron charging which occurred when only the ICP power was activated, without any rf bias to the wafercarrying electrode. Energetic particle bombardment damage was dominant when the wafer-carrying electrode\u27was biased and the damage was considerably higher for rf bias power grater than 35W. The effect of plasma processing to the strained Si1-xGex layer of p+ - n diode has been investigated. The effect of SF6 plasma, used to etch an overlying Si film stopping at the strained Si1-xGex film, on the electrical properties of an underlying Si1-xGex/Si heterojunction device was studied. The changes of C-V and I-V characteristics, such as higher depletion capacitance and lower diffusion current were attributed to ion bombardment and radiation-induced bonding change, such as creation of interface charges and recombination centers. The TEM analysis revealed the dislocation loops in Si/Si1-xGex/Si outside the aluminum contact region due to the ion bombardment stress. The O2 plasma ashing has moderate effect to Si1-xGex device when the device was protected by aluminum contact layer. The C-V profiling techniques on SiGe MOS structures were used to investigate the change of valence band discontinuity (ΔEv) at the Si/SiGe interface before and after plasma exposure and high temperature annealing. Wet and plasma etched samples were annealed at 500, 600, 700 and 800°C for 60 seconds. It was observed that the accuracy of extracting the changes of ΔEv using the C-V profiling was strongly influenced by the release of electrons from the traps at SiO2/Si interface, which were created during the low-pressure CVD SiO2, deposition. The device simulations have been used to confirm this finding. By carefully analyzing the C-V profile at slight depletion region the band gap modifications at back Si/SiGe interface due to process-induced damage could be evaluated. The dry etched sample was partially relaxed after 700°C annealing while wet etched sample was partially relaxed after 800°C annealing. Dry etched sample demonstrated a faster relaxation mechanism as compared to its wet etched counterpart due to the creation of dislocation loops by dry etching process. The C-V method is a simple, fast and efficient approach to estimate any band-gap modification in SiGe due to process-induced damage, but the measurements and simulations in slight depletion region should be carried out with special care and high resolution

Enabling control of matter at the atomic level: atomic layer deposition and fluorocarbon-based atomic layer etching

The diminishing size of devices has necessitated the development of new patterning, deposition and etch techniques at ever-finer resolution, now approaching the atomic scale. Current trends in device manufacturing impose stringent requirements on nanoscale processing techniques, in terms of material properties and dimensional control. At the required nanoscale dimensions, additionally, surface composition and damage will be as important as physical dimensions for the desired functionality. Ultimately, the deposition and removal of arbitrary materials with single atomic layer precision are required. In this work I will present the insights of my work into fabrication processes and characterization techniques needed in the era of controlling matter at the atomic level using atomic layer deposition (ALD) and atomic layer etching (ALE). To address the challenges in atomic scale manufacturing, a solid understanding of materials and their physical and chemical interactions is required. In this work, the synergy between materials and different fabrication processes is investigated. By studying how ALD performs on spacer defined double patterning (SDDP) I demonstrate the engineering of sub-10 nm features. SDDP is generally limited in resolution due to lack of nanoscale processes at sub-10 nm dimensions. Here, I establish how thermal ALD allows for conformal deposition of a titanium dioxide spacer layer without damaging or modifying any substrate. In conclusion, the first successful fabrication of 7.5 nm titanium oxide features using SDDP is made possible by atomic scaled processes. While ALD has become productive enough to become a mainstream technology, the etch counterpart ALE has been more challenging. Indeed, removing material one atomic layer at a time is a complex scientific problem, especially when directional etching is required. In my work, a major goal was to develop methodologies that would allow the use of existing plasma etching tools for ALE. In this context, this work establishes and evaluates a cyclic fluorocarbon (FC) based approach for ALE of silicon dioxide, characterizes the mechanisms involved, and evaluates the impact of processing parameters. Using a cyclical FC and argon plasma process it is possible to atomically etch silicon oxide in a conventional plasma etch tool with minimal modifications. Plasma-based ALE allows for the directional etching required for deep narrow structures. For the first time, using the FC-based ALE processes, aspect ratio independent etching and high fidelity pattern transfer have been achieved. This result is obtained through a detailed study of the impact of plasma parameters on the SiO2 etch performance and using this information to achieve self-limiting behavior. Overall, this work proves how new technology nodes are enabled by ALD and ALE as part of the increasing trend toward the atomic scale processing.Die fortschreitende Miniaturisierung von Halbleiterschaltkreisen erfordert die Entwicklung neuartiger Strukturierungs-, Abscheidungs- und Ätzmethoden. Die dafür erforderliche Auflösung nähert sich heutzutage atomaren Maßstäben. Die derzeitigen Trends in der Fabrikation von elektronischen Schaltkreisen stellen strenge Anforderungen an die verwendeten Nanostrukturierungsmethoden, in Bezug auf Kontrolle der Materialeigenschaften und der Strukturabmessungen. Für diese nanoskalige Strukturen sind außerdem Oberflächenzusammensetzung und Oberflächendefekte genauso wichtig wie die Strukturabmessungen, um die gewünschte Funktionalität zu erreichen. Letztendlich ist es daher notwendig beliebige Materialien mit der Präzision einzelner atomarer Lagen abzuscheiden und abzutragen. Die vorliegende Arbeit untersucht geeignete Fabrikations- und Charakterisierungsprozesse für die Ära der atomar genauen Materialstrukturierung mittels sogenannter Atomic Layer Deposition (ALD) und Atomic Layer Etching (ALE). Um die Herausforderungen atomar genauer Materialstrukturierung zu adressieren ist ein tiefgehendes Verständnis der Materialien und ihrer physikalisch-chemischen Wechselwirkungen von Nöten. In der vorliegenden Arbeit wird die Synergie verschiedener Materialien und Fabrikationsprozesse untersucht. Durch Anwendung von ALD für die Doppelstrukturierung mittels Spacer-Technik (spacer defined double patterning, SDDP) wird gezeigt wie sich Strukturen mit Dimensionen unterhalb von 10 nm herstellen lassen. Generell ist die Auflösung von SDDP durch das Fehlen geeigneter Nanofabrikationsprozesse für Strukturen unterhalb von 10 nm limitiert. Die Arbeit etabliert, dass thermische ALD eine konforme Abscheidung einer Titandioxid-Spacer-Schicht erlaubt, ohne dabei das darunterliegende Substrate zu beschädigen oder zu modifizieren. Zusammenfassen lässt sich sagen, dass die erste erfolgreiche Fabrikation von 7.5 nm breiten Titanoxidstrukturen mittels SDDP nur durch die Anwendung von Prozessen auf atomarem Maßstab ermöglicht wurde. Während ALD bereits zu einer produktiven Standardtechnologie geworden ist, erweist sich die Etablierung des korrespondieren Ätzprozesses, nämlich ALE, als ungleich schwieriger. Tatsächlich ist die kontrollierte Materialabtragung um jeweils eine Atomlage ein komplexes wissenschaftliches Problem. Dies gilt besonders für direktionales Ätzen. Ein Hauptziel der Arbeit besteht in der Entwicklung von Methoden, die es erlauben existierende Plasmaätzanlagen für ALE zu verwenden. In diesem Zusammenhand etabliert und evaluiert diese Arbeit einen zyklischen Prozess basierend auf Fluorcarbonen (FC) für ALE von Siliziumdioxid. Es werden die beteiligten Reaktionsmechanismen charakterisiert und der Einfluss der Prozessparameter evaluiert. Mittels eines zyklischen FC- und Argon-Plasmas ist es möglich Siliciumdioxid atomar genau in einer minimal modifizierten, konventionellen Plasmaätzanlage zu ätzen. Plasma-basiertes ALE erlaubt direktionales Ätzen, das für tiefe, schmale Strukturen erforderlich ist. Zum ersten Mal werden hier sowohl seitenverhältnisunabhängiges Ätzen als auch hohe Zuverlässigkeit beim Strukturtransfer mittels FC-basiertem ALE erreicht. Das Resultat wird durch eine detaillierte Untersuchung des Einflusses der Plasmaparameter auf das Ätzverhalten von Siliziumdioxid und Anwendung der gewonnenen Informationen auf ein selbstlimitierendes Verhalten ermöglicht. Zusammengefasst demonstriert die vorliegende Arbeit wie neue Technologieknoten, die Teil des zunehmenden Trends zu atomar genauer Halbleiterprozessierung sind, durch ALD und ALE ermöglicht werden

Plasma Physics and Chemistry for Nanomaterial and Device Fabrication

University of Minnesota Ph.D. dissertation.May 2018. Major: Mechanical Engineering. Advisor: Uwe Kortshagen. 1 computer file (PDF); viii, 123 pages.This dissertation thesis revolves around one specific type of plasma: low pressure glow discharges. In the first half we will focus on particle dynamics visualized by laser light scattering in a silane-containing dusty plasma. A better understanding of par- ticle dynamics in dusty plasmas can be beneficial to both the intended synthesis of nanoparticles and the mitigation of nanoparticle contamination issues. Three distinct types of spatiotemporal behavior are observed for the dust particles, depending on the specific plasma power and pressure. The changing balance between the ion drag force and the electrostatic forces is hypothesized to be the dominant mechanism that determines particle dynamics in our case. It is also hypothesized that the dependence of particle dynamics on plasma power and pressure might be attributed to the generation and growth rate of dust particles. Based on our experimental results, the combination of laser light scattering and plasma emission proves to be an effective method for observing dust particles between tens of nanometers to a few hundreds of nanometers. In the second half we will instead focus on the application of a magneti- cally enhanced glow discharge, namely magnetron sputtering, as a critical de- position technique for the fabrication of anisotropic plasmonic nanostructures. Upon light irradiation at the resonance frequency, plasmonic nanostructures can exhibit interesting near-field enhancement and far-field extinction, arising from the resonant oscillation of conduction electrons in the nanostructures. Specifically, we fabricated plasmonic nanocups and nanorods from alternative low-cost materials such as copper, aluminum and titanium nitride, rather than from expensive noble metals such as gold and silver. The copper and alu- minum nanocups exhibit main plasmon resonances in the near-infrared region, potentially suitable for biological and window coating applications. The copper nanorods exhibit two plasmon resonance peaks as expected, corresponding to electron oscillations in the transverse and longitudinal directions, respectively. Two sputtering systems at the University of Minnesota Nano Fabrication Cen- ter (NFC) are used in this study. Due to certain limitations of the NFC systems we encountered during preliminary attempts at titanium nitride fabrication, we also constructed a custom-built angle sputtering system with a tiltable heated stage, introduced in detail in the appendix

Flexible and substrate-free optoelectronic devices based on III-V semiconductor nanowires

III-V nanowires have been the subject of intense research interest for the past 20 years, as their unique optical and electronic properties, which arise from their nanoscale dimensions and composition, make them particularly suited for high-performance opto-electronic devices. Since epitaxial growth is on expensive, brittle, crystalline substrates, the field of flexible devices has been little explored in the context of III-V nanowires. In order to fully exploit these properties and move away from conventional wafer based electronics to flexible electronics, hybrid devices consisting of organic and inorganic components must be developed to harness the benefits from both materials systems. Embedding high performance vertically aligned III-V nanowires in a flexible matrix enables applications where there is a need for substrate-free, flexible devices. The work in this thesis looks to address this by (1) developing a repeatable method of producing nanowire-polymer thin films and (2) demonstrating how these thin films could be fabricated into different opto-electronic devices. The thin films are made by encapsulating the nanowires in Parylene C, which are then be peeled off from the growth substrate, thus retaining the vertical alignment of the nanowires. These thin films are used to fabricate a THz modulator and a solar cell. Single and multi-layer THz modulators are fabricated from nanowire-Parylene C thin films laminated together. 1,2,4,8, and 14-layer modulators are compared, with the 14-layer modulator displaying the best performance. A high switching speed (<5 ps), modulation depth (-8 dB), extinction (13%) and dynamic range (-9 dB) and broad bandwidth operation (0.1 THz–4 THz) are obtained. This surpasses the performance of several devices in the literature and presents the first THz modulator which combines a large modulation depth, broad bandwidth, picosecond time resolution for THz intensity and phase modulation, which makes it an ideal candidate for ultrafast THz communication. In addition to the THz work, the fabrication process towards a flexible solar cell is also developed. This consists of optimising the dry etching, and annealing-free contacting processes to give nanowire devices that show good ohmic IV characteristics. Following this work, a proof-of-concept Schottky barrier solar cell is fabricated using the knowledge gleaned from this development work. This preliminary device gives a conversion efficiency of 0.02% and a fill factor of 0.3, with scope for device performance improvement by using nanowires that are grown and optimised specifically for solar cell operationEPSRC - Photonics CD

Near-surface Nitrogen Vacancy Centers in Diamond

The nitrogen-vacancy (NV) center is a point defect in diamond and has been championed as a promising solid-state "artificial atom." NV center properties such as its bright luminescence, room-temperature optical readout of spin states, and long spin decoherence lifetime make it an excellent system for applications in quantum information processing, high sensitivity magnetometry, and biotagging. In all applications, near-surface NVs are desirable. However, it has been found that the favorable properties of the NV center are significantly diminished as the NV center nears the surface. This dissertation presents efforts in understanding the effect of the surface on the luminescence of NV centers less than a wavelength of light from the surface. We use plasma assisted etching to, independently, change the surface termination and bring the NV closer to the surface. We find that treating the surface with CF4 plasma results in a deposited polymerous fluorocarbon which helps stabilize nearby NVs. We propose using a downstream etcher to bring NVs closer to the surface, while minimizing damage and maintaining NV luminescence. Finally, we enhance emission of these near-surface NVs by coupling them into a hybrid diamond plasmonic cavity. The fabricated devices result in a measured Q of 170, higher than other previously fabricated diamond plasmonic devices.Engineering and Applied Science

Laser trapping microchip for biotechnological applications: design and development

This work presents a novel approach towards integrated dual-beam optical trapping achieved using planar lightwave circuit (PLC) technology. Three fabrication technologies sol-gel, photolithography and reactive ion etching were combined to fabricate a Laser Trapping Microchip (LTM) allowing one-dimensional manipulation of transparent micrometer-size spherical objects. Detailed steps of the LTM development are described, beginning with a theoretical approach and numerical simulations through the design and synthesis of a suitable photopatternable sol-gel material, culminating in the fabrication process and experimental confirmation of the trapping properties of the device. The proof of concept of this unique device was achieved by demonstrating its optical trapping abilities using micrometer size polystyrene beads with diameters in the range between 4 pm and 10 pm and the refractive index of 1 59. The LTM device possesses many advantages over currently existing dual-beam laser trapping systems such as small overall dimensions (~15 x 30 x 0 5 mm), low power optical power consumption (<15mW), improved stability of the optical trap due to precise alignment of the optical paths and a relatively easy fabrication process. For these reasons there are many potential applications of the LTM device in biotechnology, microfluidics and other sciences making it an attractive device for commercial use

Modélisation fluide du transport et des instabilités dans une source plasma froid magnétisé

Il est bien connu que les plasmas froids magnétisés dans des dispositifs tels que les propulseurs Hall et les sources d'ions montrent souvent l'émergence d'instabilités qui peuvent provoquer des phénomènes de transport anormaux et affecter fortement le fonctionnement du dispositif. Dans cette thèse, nous étudions les possibilités de simuler ces instabilités de manière auto-cohérente par la modélisation fluide. Cela n'a jamais été fait auparavant pour ces conditions de plasma froid, mais cela présente un grand intérêt potentiel pour l'ingénierie. Nous avons utilisé un code fluide quasi-neutre développé au laboratoire LAPLACE, appelé MAGNIS (MAGnetized Ion Source), qui résout un ensemble d'équations fluides pour les électrons et les ions dans un domaine 2D perpendiculaire au champ magnétique. On a constaté que dans de nombreux cas d'intérêt pratique, les simulations MAGNIS produisent des instabilités et des fluctuations du plasma. Un premier objectif de cette thèse est de comprendre l'origine de ces instabilités observées dans MAGNIS et de s'assurer qu'elles sont un résultat physique et non un artefact numérique. Pour ce faire, nous avons effectué une analyse de stabilité linéaire basée sur des relations de dispersion, dont les taux de croissance et les fréquences qui en sont issus analyse ont été comparés avec succès à ceux mesurés dans les simulations de MAGNIS pour des configurations simples et forcés à rester dans un régime linéaire. Nous avons ensuite identifié les principaux modes et mécanismes de ces instabilités (induits par les champs électrique et magnétique, le gradient de densité et l'inertie), connus de la littérature, susceptibles de se produire dans ces simulations de fluides. Par la suite, nous avons simulé l'évolution non-linéaire et la saturation des instabilités et quantifié le transport anormal généré dans différents cas relatifs aux sources d'ions en fonction de divers paramètres clés du système (champs électriques et magnétiques et température des électrons). Enfin, nous avons mis en évidence plusieurs limitations de MAGNIS, et plus généralement de modèles fluides, dues aux approximations physiques (quasi-neutralité, absence d'effets cinétiques). Nous avons montré que les modes fluides sont parfois les plus instables à des échelles infiniment petites où la théorie n'est plus valable et ne peuvent donc être résolues numériquement. Nous avons proposé différentes manières de remédier à ce problème par l'introduction de termes diffusifs inspirés de la physique à petite échelle (non-neutralité, rayon de Larmor), que nous avons ensuite testés dans MAGNIS.It is well known from experiments that magnetized low-temperature plasmas in devices such as Hall thrusters and ion sources often show the emergence of instabilities that can cause anomalous transport phenomena and strongly affect the device operation. In this thesis we investigate the possibilities to simulate these instabilities self-consistently by fluid modeling. This is of great potential interest for engineering. We used a quasineutral fluid code developed at the LAPLACE laboratory, called MAGNIS (MAGnetized Ion Source), solving a set of fluid equations for electrons and ions in a 2D domain perpendicular to the magnetic field lines. It was found that in many cases of practical interest, MAGNIS simulations show plasma instabilities and fluctuations. A first goal of this thesis is to understand the origin of the instabilities observed in MAGNIS and make sure that they are a physical result and not numerical artifacts. For this purpose, we carried out a detailed linear stability analysis based on dispersion relations, from which analytical growth rates and frequencies were successfully compared with those measured in MAGNIS simulations for simple configurations forced to remain in a linear regime. We then identified these linear unstable modes and their responsible mechanisms (involving parameters such as the density gradient, electric and magnetic fields and inertia), known from the literature, that are likely to occur in these fluid simulations. Subsequently, we simulated the nonlinear evolution and saturation of the instabilities and quantified the anomalous transport generated in different cases relevant to ion sources, depending on various key parameters of the system (electric and magnetic fields and electron temperature). Finally, we highlighted several limitations of MAGNIS, and more generally of fluid models, due to the physical approximations made (quasineutrality, absence of kinetic effects). We showed that the fluid modes are sometimes most unstable at infinitely small scales for which the theory is no longer valid and which cannot be resolved numerically. We proposed, and tested in MAGNIS, ways to overcome this problem by introducing effective diffusion terms representing small scale processes (non-neutrality, Larmor radius)

ICP Etching of Silicon for Micro and Nanoscale Devices

The physical structuring of silicon is one of the cornerstones of modern microelectronics and integrated circuits. Typical structuring of silicon requires generating a plasma to chemically or physically etch silicon. Although many tools have been created to do this, the most finely honed tool is the Inductively Couple Plasma Reactive Ion Etcher. This tool has the ability to finesse structures from silicon unachievable on other machines. Extracting structures such as high aspect ratio silicon nanowires requires more than just this tool, however. It requires etch masks which can adequately protect the silicon without interacting with the etching plasma and highly tuned etch chemistry able to protect the silicon structures during the etching process. In the work presented here, three highly tuned etches for silicon, and its oxide, will be described in detail. The etches presented utilize a type of etch chemistry which provides passivation while simultaneously etching, thus permitting silicon structures previously unattainable. To cover the range of applications, one etch is tuned for deep reactive ion etching of high aspect ratio micro-structures in silicon, while another is tuned for high aspect ratio nanoscale structures. The third etch described is tuned for creating structures in silicon dioxide. Following the description of these etches, two etch masks for silicon will be described. The first mask will detail a highly selective etch mask uniquely capable of protecting silicon for both etches described while being compatible with mainstream semiconductor fabrication facilities. This mask is aluminum oxide. The second mask detailed permits for a completely dry lithography on the micro and nanoscale, FIB implanted Ga etch masks. The third chapter will describe the fabrication and in situ electrical testing of silicon nanowires and nanopillars created using the methods previously described. A unique method for contacting these nanowires is also described which has enabled investigation into the world of nanoelectronics. The fourth and final chapter will detail the design and construction of high magnetic fields and integrated planar microcoils, work which was enabled by the etching detailed here. This research was directed towards creation of a portable NMR machine.</p