UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Subject: search.filters.subject.ALD

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    REACTION NETWORK ANALYSIS FOR THIN FILM DEPOSITION PROCESSES
    (2016) Ramakrishnasubramanian, Krishnaprasath; Adomaitis, Raymond; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Understanding the growth of thin films produced by Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD) has been one of the most important challenge for surface chemists over the last two to three decades. There has been a lack of complete understanding of the surface chemistry behind these systems due to the dearth of experimental reaction kinetics data available. The data that do exist are generally derived through quantum computations. Thus, it becomes ever so important to develop a deposition model which not only predicts the bulk film chemistry but also explains its self-limiting nature and growth surface stability without the use of reaction rate data. The reaction network analysis tools developed in this thesis are based on a reaction factorization approach that aims to decouple the reaction rates by accounting for the chemical species surface balance dynamic equations. This process eliminates the redundant dynamic modes and identifies conserved modes as reaction invariants. The analysis of these invariants is carried out using a Species-Reaction (S-R) graph approach which also serves to simplify the representation of the complex reaction network. The S-R graph is self explanatory and consistent for all systems. The invariants can be easily extracted from the S-R graph by following a set of straightforward rules and this is demonstrated for the CVD of gallium nitride and the ALD of gallium arsenide. We propose that understanding invariants through these S-R graphs not only provides us with the physical significance of conserved modes but also give us a better insight into the deposition mechanism.
  • Thumbnail Image
    Item
    ATOMIC LAYER DEPOSITION OF SOLID ELECTROLYTES FOR BEYOND LITHIUM-ION BATTERIES
    (2015) Kozen, Alexander; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis outlines methodology and development of an atomic layer deposition (ALD) process for the well-known solid-state electrolyte lithium phosphorous oxynitride (LiPON). I have developed a quaternary ALD LiPON process through a novel stepwise additive development procedure. ALD process kinetics and chemistry were investigated using in-operando¬ spectroscopic ellipsometry and in-situ x-ray photoelectron spectroscopy (XPS). ALD LiPON exhibits a tunable ionic conductivity proportional to N content, with the highest conductivity of 6.5x10-7 S/cm at 16.3% N. Two applications of ALD LiPON are investigated: ALD LiPON films as a protection layer for next-generation lithium metal anodes in the lithium sulfur battery system, and as solid electrolytes in 3D thin film batteries with discussion towards development of an all ALD 3D battery. Lithium metal is considered the “holy grail” of battery anodes for beyond Li-ion technologies, however, the high reactivity of Li metal has until now prevented its commercial use. Here, ALD protection layers are applied directly to the Li anode to prevent chemical breakdown of the liquid electrolytes while allowing ion transport through the protection layer. Protection of lithium metal is investigated with two materials: low ionic conductivity ALD Al2O3, demonstrating a 60% capacity improvement in Li-S batteries by protecting the Li anode from sulfur corrosion during cycling, and high ionic conductivity ALD LiPON, demonstrating a 600% improvement in Li-S battery capacity over unprotected anodes. Interestingly, ALD LiPON also forms a self-healing protection layer on the anode surface preventing deleterious Li dendrite formation during high rate cycling. Solid Li-based inorganic electrolytes offer two profound advantages for energy storage in 3-D solid state batteries: enhanced safety, and high power and energy density. Until now, conventional solid electrolyte deposition techniques have faced hurdles to successfully fabricate devices on challenging high aspect ratio structures, required for improvements in both device energy and power density. In this thesis, I demonstrate fabrication of ALD heterostructures suitable for use in 3D solid batteries, and although this work is incomplete I discuss progress towards future use of ALD LiPON solid electrolytes in all ALD solid-state 3D batteries.
  • Thumbnail Image
    Item
    Combinatorial Experiments Using a Spatially Programmable Chemical Vapor Deposition System
    (2007-05-02) Sreenvivasan, Ramaswamy; Adomaitis, Raymond; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A CVD reactor concept featuring a segmented design allows individual regions of a wafer to be exposed to different precursor concentrations simultaneously during a run resulting in different thickness profiles on the wafer and a thickness gradient at the boundaries between segment regions. Different recipes were cycled through each of the segments in a sequence of deposition experiments to develop a model relating precursor concentration to film thickness in each segment region. As a demonstration of spatial programmability, the system was re-programmed using this model to produce uniform thickness amongst the segments; inter-segment uniformity approaching 0.48 % (thickness standard deviation) was demonstrated. In a subsequent study, segmented CVD reactor designs enabling spatial control of across-wafer gas phase composition were evaluated for depositing graded films suitable for combinatorial studies. Specifically two reactor designs were evaluated with experiments and response surface model (RSM) based analysis to quantify the reactor performance in terms of film thickness uniformity, sensitivity to adjustable reactor operating conditions, range of thickness over which uniformity could be achieved and each reactor's ability to control the thickness gradient across the wafer surface. Design features distinguishing the two reactor systems and their influence on gradient control versus deposition rate performance are summarized. Response Surface (RS) models relating wafer state properties to process recipes are shown to be effective tools to quantify, qualify and compare different reactor designs.
  • Thumbnail Image
    Item
    SENSOR BASED ATOMIC LAYER DEPOSITION FOR RAPID PROCESS LEARNING AND ENHANCED MANUFACURABILITY
    (2006-03-16) Lei, Wei; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the search for sensor based atomic layer deposition (ALD) process to accelerate process learning and enhance manufacturability, we have explored new reactor designs and applied in-situ process sensing to W and HfO2 ALD processes. A novel wafer scale ALD reactor, which features fast gas switching, good process sensing compatibility and significant similarity to the real manufacturing environment, is constructed. The reactor has a unique movable reactor cap design that allows two possible operation modes: (1) steady-state flow with alternating gas species; or (2) fill-and-pump-out cycling of each gas, accelerating the pump-out by lifting the cap to employ the large chamber volume as ballast. Downstream quadrupole mass spectrometry (QMS) sampling is applied for in-situ process sensing of tungsten ALD process. The QMS reveals essential surface reaction dynamics through real-time signals associated with byproduct generation as well as precursor introduction and depletion for each ALD half cycle, which are then used for process learning and optimization. More subtle interactions such as imperfect surface saturation and reactant dose interaction are also directly observed by QMS, indicating that ALD process is more complicated than the suggested layer-by-layer growth. By integrating in real-time the byproduct QMS signals over each exposure and plotting it against process cycle number, the deposition kinetics on the wafer is directly measured. For continuous ALD runs, the total integrated byproduct QMS signal in each ALD run is also linear to ALD film thickness, and therefore can be used for ALD film thickness metrology. The in-situ process sensing is also applied to HfO2 ALD process that is carried out in a furnace type ALD reactor. Precursor dose end-point control is applied to precisely control the precursor dose in each half cycle. Multiple process sensors, including quartz crystal microbalance (QCM) and QMS are used to provide real time process information. The sensing results confirm the proposed surface reaction path and once again reveal the complexity of ALD processes.