The instability under bias voltage stress and low mobility of hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT), produced by plasma enhanced chemical vapor deposition (PECVD) technique, are the main problems impeding the implementation of active matrix arrays for light emitting diode display panels and their peripheral circuitry. Replacing a-Si:H by hydrogenated nanocrystalline silicon film (nc-Si:H) seems a solution due to its higher mobility and better stability. Therefore nc-Si:H TFT was produced and investigated in this thesis. All TFT layers (doped nc-Si:H, intrinsic nc-Si:H and insulator films) were produced separately, characterized by optical (UV-visible and FTIR spectroscopies, XRD) and electrical (current-voltage, I-V) methods, and optimized for TFT application. Afterwards the non self-aligned bottom-gate TFT structure was fabricated by the photolithographic method using 2-mask set. The n+ nc-Si:H films, used for TFT drain/source ohmic contacts, were produced at high H2 dilution and at several RF power densities (PRF). The change of their lateral resistivity (rho) was measured by reducing the film thickness via reactive ion etching. The rho values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The optimum PRF for the lowest incubation layer was determined. Among the deposition parameters only increased NH3/SiH4 flow rate ratio improved the insulating properties of the amorphous silicon nitride (a-SiNx:H) films, chosen as the TFT gate dielectric. The electrical characteristics of two TFTs with a-SiNx:H having low leakage current, fabricated at different NH3/SiH4 ratios (~19 and ~28) were compared and discussed. The properties (such as crystallinity, large area uniformity, etc.) of the nc-Si:H film as TFT channel layer, were found to depend on PRF. For the films deposited at the center of the PECVD electrode the change from an amorphous dominant structure to a nanocrystalline phase took place with increasing PRF, whereas those at the edge had always nanocrystalline nature, independent of PRF. The two different TFTs produced at the center of the electrode with a-Si:H and nc-Si:H grown at low and high PRF, respectively, were compared through their I-V characteristics and electrical stability under the gate bias voltage stress. Finally, nc-Si:H TFT structure, produced and optimized in this work, was analyzed through gate-insulator-drain/source capacitor by capacitance-voltage (C-V) measurements within 106-10-2 Hz frequency (F) range. The inversion regime was detected at low F without any external charge injection. Besides, ac hopping conductivity in the nc-Si:H bulk was extracted from the fitting results of the C-F curves.

Kohlenstoffnanoröhren besitzen eine Reihe von einzigartigen strukturellen, mechanischen und elektronischen Eigenschaften. Sie können in Abhängigkeit von der Chiralität metallisches oder halbleitendes Verhalten zeigen, hohe mechanische, thermische und chemische Stabilität aufweisen, können chemisch funktionalisiert werden und sind hervorragende Elektronenemitter. Vor dem Hintergrund dieser vielversprechenden Eigenschaften wurde schnell die Frage von möglichen technischen Anwendungen von Kohlenstoffnanoröhren gestellt. Vor einer umfassenden kommerziellen Umsetzung sind allerdings noch grundlegende Untersuchungen, sowohl zu den Eigenschaften als auch zu einer gezielten Herstellung und Manipulation, erforderlich. Der Mechanismus des gerichteten Wachstums der Kohlenstoffnanoröhren ist äußerst komplex, weshalb er bis heute nicht völlig aufgeklärt werden konnte. Der Grund liegt in der Vielfalt der möglichen Reaktionen zwischen den Molekülen in der Gasphase, der Wechselwirkung zwischen Gasphase und verwendeten Unterlagen und den Reaktionsmechanismen auf diesen Substratoberflächen. Bislang fehlt es an einem einheitlichen Verständnis des Entstehungsprozesses von Kohlenstoffnanoröhren bzw. –nanostrukturen. Der Schwerpunkt dieser Arbeit liegt in der Abscheidung von Kohlenstoffnanostrukturen mittels plasmaaktivierter und hitzdrahtgestützter chemischen Gasphasenabscheidung -„Plasma enhanced hot filament chemical vapor deposition“ (PE-HF-CVD). Es sollen Abscheidungsbedingungen für die Synthese von unterschiedlichen Kohlenstoffnanostrukturen gefunden und optimiert werden. Die Darstellung und Charakterisierung von „phasenreinen“, mehrwandigen, tubularen Röhren auf unterschiedlichen metallbeschichteten Substraten steht im Vordergrund der Arbeit. Das Interesse besteht in einer Abscheidung bei niedrigen Substrattemperaturen, damit temperaturempfindliche Werkstoffe wie z.B. Glas, als Substratmaterialien eingesetzt werden können. Mittels der PE-HF-CVD Methode, die als vielversprechende Technologie zur Darstellung gerichteter Kohlenstoffnanoröhren gilt, sollen Erkenntnisse zum Einfluss einzelner Abscheidungsparameter auf den Wachstumsprozess von Nanoröhren gewonnen werden, wozu auch die plasmadiagnostische Langmuirsondentechnik und die optische Emissionsspektroskopie (OES) eingesetzt werden. Dadurch soll der Zusammenhang zwischen inneren Plasmaparametern und Wachstumsprozessen der Kohlenstoffnanoröhren oder –fasern definiert werden, um eine Prozesskontrolle während der Abscheidungsphase zu ermöglichen.

A novel CVD copper process is described using two new copper CVD precursors, KI3 and KI5, for the fabrication of IC or TSV (Through Silicon Via) copper interconnects. The highly conformal CVD copper can provide seed layers for subsequent copper electroplating or can be used to directly fabricate the interconnect in one step. These new precursors are thermally stable yet chemically reactive under CVD conditions, growing copper films of exceptionally high purity at high growth rates. Their thermal stability can allow for elevated evaporation temperatures to generate the high precursor vapor pressures needed for deep penetration into high aspect ratio TSV vias. Using formic acid vapor as a reducing gas with KI5, copper films of > 99.99 atomic % purity were grown at 250°C on titanium nitride at a growth rate of > 1500 Å/min. Using tantalum nitride coated TSV type wafers, ~ 1700 Å of highly conformal copper was grown at 225°C into 32 μm × 5 μm trenches with good adhesion. With ruthenium barriers we were able to grow copper at 125°C at a rate of 20 Å/min to give a continuous ~ 300 Å copper film. In this respect, rapid low temperature CVD copper growth offers an alternative to the long cycle times associated with copper ALD which can contribute to copper agglomeration occurring. © 2008 Elsevier B.V.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Silicon carbide (SiC) is one of the hardest known materials and is also, by good fortune, a wide bandgap semiconductor. While the application of SiC for high-temperature and high-power electronics is fairly well known, its utility as a highly robust, chemically-inert material for microelectrical mechanical systems (MEMS) is only beginning to be well recognized. SiC can be grown on both native SiC substrates or on Si using heteroepitaxial growth methods which affords the possibility to use Si micromachining methods to fabricate advanced SiC MEMS devices. The control of film stress in heteroepitaxial silicon carbide films grown on polysilicon-on-oxide substrates has been investigated. It is known that the size and structure of grains within polycrystalline films play an important role in determining the magnitude and type of stress present in a film, i.e. tensile or compressive. Silicon carbide grown on LPCVD polysilicon seed-films exhibited a highly-textured grain structure and displayed either a positive or negative stress gradient depending on the initial thickness of the polysilicon seed-layer. In addition a high-quality (111) oriented 3C-SiC on (111)Si heteroepitaxial process has been developed and is reported. SiC MEMS structures, both polycrystalline (i.e., poly-3C-SiC) and monocrystalline (i.e., 3C-SiC) were realized using micromachining methods. These structures were used to extract the stress properties of the films, with a particular focus on separating the gradient and uniform stress components.

Silicon carbide, SiC, is a semiconductor material which has many diverse uses in many of today's leading technologies. The wide band-gap aspect of the material has been utilized to create power and high frequency electronics, its physical hardness enables its use for MEMS devices, and the biological compatibility make perfect for utilization in medical applications. SiC is not a chemical compound normally found in nature and must be artificially generated. One of the methods used for the creation of single crystal, high quality SiC material is provided through the use of a chemical vapor deposition reactor. The University of South Florida currently has a horizontal hot-wallLPCVD reactor used by Dr. S. E. Saddow and his group to grow epitaxial SiC material for research grants by ONR and ARL.These agencies have commissioned the construction of a second LPCVD reactor for the primary purpose of growing 3C-SiC, a specific SiC crystal polytype, and this work describes the fabrication of the new reactor, MF2. This reactor was designed using the first reactor, MF1, as a template, but the design was modified to better facilitate single crystalline growth. The environment of the reactor is a very important consideration for crystal growth, and slight variations can cause critical defect incorporation into the crystal lattice. Many conditioning runs were required to facilitate the epitaxial growth of the different polytypes of SiC, and constant switching of the primary hot-zone required for the growth of hexagonal 4H-SiC and 6H-SiC to the hot zone required for 3C-SiC consumed precious resources and time. The new reactor uses a single primary control to monitor the three most important environmental concerns; hot-zone temperature, gaseous flow, and chamber pressure. The new reactor has been designed to use 100 mm Si substrates instead of the 50mm Si substrate size currently in use by MF1. The construction, testing, and 3C-SiC epitaxial growth on Si substrate capability of a 200 mm 3C-SiC hot-wall LPCVD reactor are demonstrated through this work.

The first part of this dissertation is an introduction describing a brief historical background of carbon nanotubes (CNTs) and their pseudo 1D structure responsible for many exotic electronic properties. The second part describes our experimental setup. The third part is about the growing of Multi-Walled Carbon Nanotubes (MWCNTs) by the chemical vapor deposition (CVD) method. Then the fourth part demonstrates a simple but reliable method to make firm contact junctions between MWCNTs and metals such as tungsten (W). The novel point of our method consists, after making a mechanical preliminary contact at a selected MWCNT, in applying a series of voltage pulses across the contact. Thin oxide layers that may form between the MWCNT and the W wire, are removed in steps by the resistive heating and electron impact during the application of each voltage pulse. Furthermore, this simple process of contact welding in steps does not bring about any permanent change in the electronic transport properties of the MWCNTs. The fifth part discusses our bending experiments. We apply a uniform and continuous bending to a selected MWCNT at room and liquid nitrogen temperatures to study the strain effect on the electrical transport in the MWCNT. There are a few published experimental works related to the bending deformation; however, this is the first study of electronic transport properties in continuous bending and releasing deformations. We observed a saturation behavior with the MWCNT and also found the bending deformation causing an anomalous change in the saturation behavior. In the sixth part we depict some interesting phenomena due to the stretching deformation of MWCNT, where we were able to propose a simple model for electron localization induced by the deformation. The last part deals with the formation of the "X-junction" between two MWCNTs. A strong X-junction can be formed simply by means of the e-beam inside the Scanning Electron Microscope (SEM). The X-junctions may form the basic elements of nano-electronic circuits such as various metal-insulator junctions, quantum dots, and similar devices. / text

The significance of the radioxenon memory effect in the context of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty is introduced as motivation for the project. Existing work regarding xenon memory effect reduction and thin film diffusion barriers is surveyed. Experimental techniques for radioxenon production and exposure, as well as for thin film deposition on plastic by plasma enhanced chemical vapor deposition (PECVD), are detailed. A deposition rate of 76.5 nm min⁻¹ of SiO₂ is measured for specific PECVD parameters. Relative activity calculations show agreement within 5% between identically exposed samples counted on parallel detectors. Memory effect reductions of up to 59±1.8% for 900 nm SiO₂ films produced by plasma enhanced chemical vapor deposition and of up to 77±3.7% for 50 nm Al₂O₃ films produced by atomic layer deposition are shown. Future work is suggested for production of more effective diffusion barriers and expansion to testing in operational monitoring stations. / text

Οι νανοσωλήνες άνθρακα (CNTs) εξακολουθούν να προσελκύουν το ενδιαφέρον πολλών ερευνητικών ομάδων λόγω των ασυνήθιστων μηχανικών, δομικών και ηλεκτρονικών τους ιδιοτήτων, που τους καθιστούν σοβαρούς υποψήφιους για μια πληθώρα εφαρμογών. Συνεπώς, έχουν αναφερθεί διάφορες τεχνικές, που αποσκοπούν στη μαζική παραγωγή νανοσωλήνων άνθρακα. Ο βασικός στόχος της παρούσας μελέτης ήταν να εξερευνηθεί η επίδραση καταλυτικών και λειτουργικών παραμέτρων στο ρυθμό της ανάπτυξης και την ποιότητα των παραγόμενων νανοσωλήνων άνθρακα μέσω της διεργασίας της χημικής εναπόθεσης ατμών (CVD) αιθυλενίου. Τα πειράματα εναπόθεσης διεξήχθησαν σε θερμοβαρυμετρικό αντιδραστήρα, που επιτρέπει τη συνεχή καταγραφή της μεταβολής του βάρους του δείγματος με τον χρόνο. Τα προϊόντα της αντίδρασης αποτελούνταν κυρίως από πολυφλοιικούς νανοσωλήνες άνθρακα (MWCNTs) και χαρακτηρίστηκαν με ηλεκτρονική μικροσκοπία σάρωσης (SEM) και Raman φασματοσκοπία. Υιοθετήθηκαν επίσης η ηλεκτρονική μικροσκοπία διέλευσης (ΤΕΜ) και η θερμοβαρυμετρική ανάλυση (ΤGA). Μια σειρά από μονομεταλλικούς καταλύτες Fe2O3/Al2O3, παρασκευασμένοι με διαφορετικές μεθόδους, εξετάστηκαν υπό συνθήκες ανάπτυξης CNTs. Η ελεγχόμενη εκρηκτική καύση (CEB) των πρόδρομων ενώσεων βρέθηκε ότι είναι η πιο αποδοτική μέθοδος για την παρασκευή του μονομεταλλικού καταλύτη σε σχέση με το ρυθμό ανάπτυξης και την απόδοση σε CNTs. Το αποτέλεσμα αυτό αποδόθηκε στην παρουσία σωματιδίων αιματίτη μικρής διαμέτρου στον καταλύτη. Η παρουσία του υδρογόνου στην αέρια τροφοδοσία της αντίδρασης επίσης αποδείχθηκε ότι προάγει το ρυθμό παραγωγής των MWCNTs. Η απόδοση και η ποιότητα των ΜWCNTs εξαρτώνται από τη συγκέντρωση της πηγής του άνθρακα (αιθυλένιο) στο ρεύμα της τροφοδοσίας καθώς και από τη θερμοκρασία της αντίδρασης. Υπό τις παρούσες πειραματικές συνθήκες, η βέλτιστη θερμοκρασία αντίδρασης βρέθηκε ότι είναι οι 650 0C. Αποδείχθηκε επίσης ότι η CVD του αιθυλενίου παράγει περισσότερους νανοσωλήνες άνθρακα από τη CVD του ακετυλενίου, σε όμοιες πειραματικές συνθήκες. Πολυφλοιικοί νανοσωλήνες άνθρακα αναπτύχθηκαν επίσης σε μια σειρά από καταλύτες Χ% κβ Fe2O3/Al2O3 με CVD αιθυλενίου στους 650 0C. Οι παραπάνω καταλύτες με συγκέντρωση οξειδίου σιδήρου που κυμαινόταν από 0 ως 100 %, παρασκευάστηκαν με ελεγχόμενη εκρηκτική καύση των πρόδρομων νιτρικών ενώσεων τους. Τα αποτελέσματα έδειξαν ότι η απόδοση και η ποιότητα των παραγόμενων νανοσωλήνων άνθρακα εξαρτώνται σε μεγάλο βαθμό από τη συγκέντρωση του Fe2O3. H βέλτιστη φόρτιση του οξειδίου του σιδήρου βρέθηκε ότι είναι η 75% κβ, η οποία οδήγησε σε δομή καταλύτη που απέφερε την μεγαλύτερη απόδοση (~2000 %), δηλαδή το βάρος των εναποτιθέμενων MWCNTs ήταν 20 φορές μεγαλύτερο από το βάρος του αρχικού καταλύτη. Το αποτέλεσμα αυτό αποδόθηκε στη δημιουργία μεγάλου αριθμού ενεργών κέντρων και στη μεγάλη διασπορά της φάσης του Fe2O3. Μια σειρά από διμεταλλικούς καταλύτες Μ-Fe2O3/Al2O3 (Μ: Ru, Ni, Co, Mo) παρασκευάστηκαν με διαφορετικούς μεθόδους και εξετάστηκαν υπό συνθήκες CVD αιθυλενίου. Η ελεγχόμενη εκρηκτική καύση των πρόδρομων ενώσεων τους βρέθηκε ότι είναι η πιο αποτελεσματική μέθοδος για την παρασκευή του Ni-Fe2O3/Al2O3 και του Co-Fe2O3/Al2O3, ενώ η μέθοδος της συγκαθίζησης για την παρασκευή του Ru-Fe2O3/Al2O3 και του Μο-Fe2O3/Al2O3. Κατά τη μελέτη του διμεταλλικού καταλύτη Ru-Fe2O3/Al2O3, παρασκευασμένου με τη μέθοδο της συγκαθίζησης, βρέθηκε ότι η υψηλή του απόδοση σε MWCNTs οφείλεται στη μεγάλη διασπορά της φάσης του Fe2O3, που επιφέρει η παρουσία του ρουθινίου και στην χαμηλή συγκέντρωση της φάσης του RuO2. H ποσότητα και η ποιότητα των παραγόμενων MWCNTs εξαρτώνται από τη συγκέντρωση του αιθυλενίου στη τροφοδοσία και από τη θερμοκρασία της CVD διεργασίας. Η βέλτιστη συγκέντρωση βρέθηκε ότι είναι η 20% και η βέλτιστη θερμοκρασία οι 650 0C. Ακόμα, μεταξύ διάφορων υποστρωμάτων που εξετάστηκαν, βρέθηκε ότι το πιο αποδοτικό είναι η αλούμινα, η οποία προέρχεται από το ένυδρο νιτρικό αλουμίνιο. Επίσης, εξερευνήθηκε η επίδραση του λόγου Fe/Ni της δομής του διμεταλλικού καταλύτη Ni-Fe2O3/Al2O3 , παρασκευασμένου με τη CEB μέθοδο, στο ρυθμό της ανάπτυξης των MWCNTs μέσω της CVD του αιθυλενίου. Βρέθηκε ότι για φόρτιση σε μέταλλο ίση με 52.5 %, ο βέλτιστος λόγος ήταν Fe/Ni = 6, ο οποίος οδήγησε στην εντυπωσιακή απόδοση του 3600 % σε ΜWCNTs. Αυτό αποδόθηκε στο σχηματισμό χημικής ένωσης μεταξύ των στοιχείων Ni, Fe, Al και O και στο σχηματισμό πολλών νανοκρυσταλλιτών Fe2O3, όπως τεκμηριώθηκε από την ανάλυση TEM. Επίσης, αποδείχθηκε ότι η CVD του αιθυλενίου σε αυτόν τον καταλύτη είναι πιο αποδοτική από τη CVD του ακετυλενίου. Ένας φασματογράφος μάζας χρησιμοποιήθηκε για να καθοριστούν οι χημικές αντιδράσεις που λαμβάνουν χώρα κατά τη CVD του αιθυλενίου στον συγκεκριμένο διμεταλλικό καταλύτη. Βρέθηκε ότι οι ρυθμοί της διάσπασης του αιθυλενίου και της παραγωγής υδρογόνου είναι πολύ υψηλοί στο αρχικό στάδιο της εναπόθεσης, ενώ υδρατμοί παράγονται από την αντίδραση του υδρογόνου με τα μεταλλικά οξείδια. / Since their discovery in 1991, Carbon Nano-Tubes (CNTs) continue to draw significant attention due to their various potential applications, deriving from their extraordinary structural, electronic and mechanical properties. Thus, several methods of production of CNTs have been reported. The main goal of this research was the investigation of the influence of catalytic and operational parameters on the rate of growth and quality of CNTs via the process of Chemical Vapor Deposition (CVD) of ethylene. Deposition experiments were carried out in a thermogravimetric hot-wall reactor , which enables continuous monitoring of the evolution of carbon mass with time. The products of the deposition comprised mainly Multi-Wall Carbon Nano-Tubes (MWCNTs) and they were characterized using Scanning Electron Microscopy and Raman spectroscopy. Transmission Electron Microscopy and Thermo-Gravimetric Analysis were also employed. A series of Fe2O3/Al2O3 catalysts prepared by different methods were investigated under conditions of synthesis of CNTs. Controlled explosive burning (CEB) of precursor compounds was found to be the most effective method of preparation of the catalyst with respect to rate of deposition and yield of CNTs. This result has been attributed to the presence of hematite particles of small diameter on the catalyst. The presence of hydrogen in the gas feed mixture, even at small concentration, proved to be beneficial for the rate of production of MWCNTs. Yield and quality of MWCNTs depend on the concentration of the carbon source (ethylene) in the feed mixture and on temperature of deposition. Under the present experimental conditions, the optimal reaction temperature was proved to be 650 0C. It was also found that ethylene CVD process is more productive than acetylene CVD process, under identical experimental conditions. MWCNTs were also grown on a series of X % wt Fe2O3/Al2O3 catalysts by thermal cracking of ethylene at 650 0C. The above catalysts with composition ranging from 0 to 100 % wt Fe2O3 were prepared by controlled explosive burning (CEB) of their nitrate precursors. Results show that the final yield and quality of the MWCNTs are highly dependent on the iron oxide concentration of the catalyst. The optimal iron oxide loading was found to be 75%wt, which led to a yield of ~2000 % relative to the initial weight of the catalyst. This result was attributed to the formation of large number of active sites for CNTs growth as well as to the high dispersion of the Fe2O3 phase. A series of bimetallic catalysts M-Fe2O3/Al2O3 (M: Ru, Ni, Co, Mo), were also prepared by different methods and investigated under conditions of CVD reaction of ethylene. Controlled explosive burning (CEB) of precursor compounds was found to be the most effective method of preparation of the catalysts Ni-Fe2O3/Al2O3 and Co-Fe2O3/Al2O3 with respect to rate of deposition and yield of CNTs. Co-precipitation of nitrate precursors (CP-W(H)) was the most effective method of preparation of the catalysts Ru-Fe2O3/Al2O3 and Mo-Fe2O3/Al2O3. During the study of the Ru-Fe2O3/Al2O3 catalyst, prepared by CP-W(H) method, its high catalytic activity ( ~2600% MWCNTs yield) was attributed to the high dispersion of Fe2O3 particles, due to the presence of ruthenium, and the low concentration of RuO2 phase. Yield and quality of MWCNTs depend on the concentration of ethylene in the feed mixture and on temperature of CVD reaction. Under the present experimental conditions, the optimal concentration of ethylene and reaction temperature was found to be 20% and 650 0C, respectively. Furthermore, the most effective substrate, among others tested, was proved to be the aloumina deriving from aluminum nitrate. The influence of the ratio Fe/Ni in the structure of Ni-Fe2O3/Al2O3 catalyst, prepared by CEB method, on rate of growth of MWCNTs was investigated. It was found that the optimal value was Fe/Ni = 6 for 52.5 % metal loading, which led to the impressive yield of ~3600% . This was attributed to the generation of a chemical compound comprising Fe, Ni, Al and O, which in turn induced the formation of Fe2O3 nanocrystallites, as established by TEM analysis. Furthermore, it was evidenced that CVD of ethylene is more efficient process than CVD of acetylene. A mass spectrometer was also employed as a way to determine the chemical reactions that take place during carbon deposition in this bimetallic catalyst. It was found that ethylene decomposition and hydrogen production rates are high at the first stages of deposition, while H2O(g) is produced due to the reaction of hydrogen with the metal oxides.

<p>The overall aim of this project is to study the heat transfer inside the reaction chamber of the Hot-Wire Chemical Vapor Deposition (HWCVD) system with a commercial software package FLUENT6.3 / it is one of the most popular Computational Fluid Dynamics solvers for complex flows ranging from incompressible to mildly compressible to even highly compressible flows. The wealth of physical models in FLUENT allows us to accurately predict laminar and turbulent flows, various modes of heat transfer, chemical reactions, multiphase flows and other phenomena with complete mesh flexibility and solution-based mesh adaptation. In this study the 3-D HWCVD geometry was measured and created in GAMBIT which then generates a mesh model of the reaction chamber for the calculation in FLUENT. The gas flow in this study was characterized as the steady and incompressible fluid flow due to the small Mach number and assumptions made to simplify the complexity of the physical geometry. This thesis illustrates the setups and solutions of the 3-D geometry and the chemically reacting laminar and turbulent gas flow, wall surface reaction and heat transfer in the HWCVD deposition chamber.</p>