Browsing by Author "Gregory Parsons, Committee Member"

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Atomic Layer Deposition on Fiber Forming Polymers and Nonwoven Fiber Structures.
(2010-03-22) Spagnola, Joseph; Mark Johnson, Committee Chair; Gregory Parsons, Committee Member; Ronald Scattergood, Committee Member; Jon-Paul Maria, Committee Member
Electrospinning Yarn Formation and Coating.
(2010-11-22) Sahbaee Bagherzadeh, Arash; William Oxenham, Committee Chair; Behnam Pourdeyhimi, Committee Chair; Saad Khan, Committee Member; Gregory Parsons, Committee Member; Richard Spontak, Committee Member
Formation of Low-Resistivity Germanosilicide Contacts to Phosporous Doped Silicon-Germanium Alloy Source/Drain Junctions for Nanoscale CMOS
(2003-12-30) Mo, Hongxiang; Douglas Barlage, Committee Member; Gregory Parsons, Committee Member; Mehmet Ozturk, Committee Chair; Veena Misra, Committee Member
Conventional source/drain junction and contact formation processes can not meet the stringent requirements of future nanoscale complimentary metal oxide silicon (CMOS) technologies. The selective Si[subscript 1-x]Ge[subscript x] source/drain technology was proposed in this laboratory as an alternative to conventional junction and contact schemes. The technology is based on selective chemical vapor deposition of in-situ boron or phosphorus doped Si[subscript 1-x]Ge[subscript x] in source/drain areas. The fact that the dopant atoms occupy substitutional sites during growth make the high temperature activation anneals unnecessary virtually eliminating dopant diffusion to yield abrupt doping profiles. Furthermore, the smaller band gap of Si[subscript 1-xGe[subscript x] results in a smaller Schottky barrier height, which can translate into significant reductions in contact resistivity due to the exponential dependence of contact resistivity on barrier height. This study is focused on formation of self-aligned germanosilicide contacts to phosphorous-doped Si[subscript 1-x]Ge[subscript x] alloys. The experimental results obtained in this study indicate that self-aligned nickel germanosilicide (NiSi[subscript 1-x]Ge[subscript x]) contacts can be formed on Si[subscript 1-x]Ge[subscript x] layers at temperatures as low as 350°C. Contacts can yield a contact resistivity of 1E-8 ohm-cm² with no sign of germanosilicide induced leakage. However, above a threshold temperature determined by the Ge concentration in the alloy, the NiSi[subscript 1-x]Ge[subscript x]/Si[subscript 1-x]Ge[subscript x] interface begins to roughen, which affects the junction leakage. For phosphorus doped layers considered in this study, the threshold temperature was around 500°C, which is roughly 100°C higher than the threshold temperature for NiSi[subscript 1-x]Ge[subscript x contacts formed on boron doped Si[subscript 1-x] Ge[subscript x] layers with a Ge percentage of ~ 50%. Nickel and zirconium germanosilicides were also considered as contact candidates but they were found to result in a contact resistivity near 1E-7 ohm-cm².
Formation of Metal Silicide and Metal Germanosilicide Contacts to Si[subscript 1-x]subscript Ge[subscript x] Alloys
(2004-04-20) Burnette, James E. Jr.; Dale Sayers, Committee Member; Robert Nemanich, Committee Member; Gregory Parsons, Committee Member; David Aspnes, Committee Member
The goals of this research were to study the phase stability and formation of Ti-Si[subscript 1-x]Ge[subscript x] and Co-Si[subscript 1-x]Ge[subscript x] thin film reactions. The Ti-Si[subscript 1-x]Ge[subscript x] and Co-Si[subscript 1-x]Ge[subscript x] solid phase reactions result in the formation of precipitates within the grain boundaries of the films thus formed. The precipitates are either Ge or a Si-Ge compound, depending on the type of metal used in the reaction. The formation of Ti(Si[subscript 1-y]Ge[subscript y])₂ thin films on Si[subscript 1-x]Ge[subscript x] has been examined. It has been found that the generation of Ge-rich Si-Ge precipitates which form in the Ti-Si[subscript 1-x]Ge[subscript x] solid phase reaction could be reduced or eliminated by the insertion of an amorphous Si layer before the metallization step. A Gibbs free energy model, which was parameterized in terms of Ge concentration by atomic percentage was used to determine stability between the Ti(Si[subscript 1-y]Ge[subscript y])₂ layer and the Si[subscript 1-x] Ge[subscript x] substrate. The films in this study were characterized using x-ray diffraction (XRD) to investigate phase formation, stability, and the composition of the Ti(Si[subscript 1-y]Ge[subscript y])₂ layer. Scanning electron microscopy (SEM) was used to determine the surface morphology and phase stability. It was found that amorphous Si layers of a certain thickness could prevent precipitate formation, depending on the composition of the underlying Si[subscript 1-x] Ge[subscript x] layer. The formation of CoSi₂ on Si[subscript 1-x]Ge[subscript x] was also examined. The solid phase reaction of Co and Si[subscript 1-x]Ge[subscript x] results in the formation of a poly-crystalline CoSi₂ layer, and the occurrence of a Ge precipitate. The TIME (Titanium Interlayer Mediated Epitaxy) process has been used in the formation of epitaxial CoSi₂ on Si (100). A Ti layer of varying thicknesses, which serves as a barrier to retard the diffusion of Co atoms was deposited on a c-Si/Si[subscript 1-x]Ge[subscript x] substrate pseudomorphically strained to Si (100), before the final Co metallization step. The films in this study were characterized using x-ray absorption fine structure (XAFS) to determine the short-range crystalline order, XRD to determine phase formation and long-range crystalline order, Auger electron spectroscopy (AES) to determine surface chemistry, and SEM to determine the surface morphology. This work shows that the formation of epitaxial CoSi₂ on Si[subscript1-x]Ge[subscript x] can be achieved, depending on the thickness of the diffusion barrier. In addition, the optimal diffusion barrier thickness has been determined for the Co layer thickness used in these studies.
Free Meniscus Coating Using Compressed Carbon Dioxide
(2003-07-16) Novick, Brian Jeffery; Gregory Parsons, Committee Member; Ruben Carbonell, Committee Co-Chair; Jan Genzer, Committee Member; Joseph DeSimone, Committee Co-Chair; Orlin Velev, Committee Member; Peter Kilpatrick, Committee Member
This thesis investigates the use of compressed carbon dioxide as a replacement solvent for web based coating processes including the free meniscus based devices. We use theory, such as Tallmadge's Four Force Inertial Theory, to show why carbon dioxide based free meniscus coaters are advantageous over normal coating processes. We show theoretically that thinner films can be formed at faster rates, that important deposition forces can be controlled, that there is better penetration into porous materials, that there are less capillary forces, that films may have increased uniformity, and that there is better process control. This research also details how coatings can be applied by using a novel high pressure free meniscus coater (hFMC) to deposit thin films of important perfluorpolyether lubricants for microelectronics. The coater was designed as part of this thesis. We have investigated what substrates can be coated by showing that compressed gaseous carbon dioxide induces the wetting of low enery surfaces by low Mw coating precursors. We have shown that the hFMC device can be used to take advantage of the induced wetting. Biocompatible precursors have been coated onto porous PTFE and polymerized at high pressure. The coating process results in porous PTFE with significantly different properties than uncoated samples. We have also investigated what materials can be coated from carbon dioxide by studying the rheological effects of carbon dioxide on coating precursors. We find that changing the backbone structure, end groups, or side groups on the precursor affect the mixture viscosity. The results of this investigation open up new potential applications of this environmentally benign coating process.
Interfacing Epitaxial Oxides to Gallium Nitride
(2008-08-19) Losego, Mark Daniel; Jon-Paul Maria, Committee Chair; Mark Johnson, Committee Member; Zlatko Sitar, Committee Member; Gregory Parsons, Committee Member
Molecular beam epitaxy (MBE) is lauded for its ability to control thin film material structures at the atomic level. Controlling the chemistry and structure of epitaxial interfaces at the atomic level can improve performance of microelectronics and cultivate the development of novel device structures. This thesis explores the utility of MBE for designing interfaces between oxide epilayers and the wide band gap semiconductor gallium nitride (GaN). The allure of wide gap semiconductor microelectronics (like GaN, 3.4 eV) is their ability to operate at higher frequencies, higher powers, and higher temperatures than current semiconductor platforms. Heterostructures between ferroelectric oxides and GaN are also of interest for studying the interaction between GaN's fixed polarization and the ferroelectric's switchable polarization. Two major obstacles to successful integration of oxides with GaN are: (1) interfacial trap states; and (2) small electronic band offsets across the oxide / nitride interface due to the semiconductor's large band gap. For this thesis, epitaxial rocksalt oxide interfacial layers (˜8 eV band gap) are investigated as possible solutions to overcoming the challenges facing oxide integration with GaN. The cubic close-packed structure of rocksalt oxides forms a suitable epitaxial interface with the hexagonal close-packed wurtzite lattice of GaN. Three rocksalt oxide compounds are investigated in this thesis: MgO, CaO, and YbO. All are found to have a (111) MO || (0001) GaN; <1`10> MO || <11`20> GaN epitaxial relationship. Development of the epilayer microstructure is dominated by the high-energy polar growth surface (drives 3D nucleation) and the interfacial symmetry, which permits the formation of twin boundaries. Using STEM, strain relief for these ionicly bonded epilayers is observed to occur through disorder within the initial monolayer of growth. All rocksalt oxides demonstrate chemical stability with GaN to >1000°C. Concurrent MBE deposition of MgO and CaO is known to form complete solid solutions. By controlling the composition of these alloys, the oxide's lattice parameter can be engineered to match GaN and reduce interfacial state density. Compositional control is a universal challenge to oxide MBE, and the MgO-CaO system (MCO) is further complicated by magnesium's high volatility and the lack of a thermodynamically stable phase. Through a detailed investigation of MgO's deposition rate and subsequent impact on MCO composition, the process space for achieving lattice-matched compositions to GaN are fully mapped. Lattice-matched compositions are demonstrated to have the narrowest off-axis rocking curve widths ever reported for an epitaxial oxide deposited directly on GaN (0.7° in f-circle for 200 reflection). Epitaxial deposition of the ferroelectric (Ba,Sr)TiO3 by hot RF sputtering on GaN surfaces is also demonstrated. Simple MOS capacitors are fabricated from epitaxial rocksalt oxides and (Ba,Sr)TiO3 layers deposited on n-GaN substrates. Current-voltage measurements reveal that BST epilayers have 5 orders of magnitude higher current leakage than rocksalt epilayers. This higher leakage is attributed to the smaller band offset expected at this interface; modeling confirms that electronic transport occurs by Schottky emission. In contrast, current transport across the rocksalt oxide ⁄ GaN interface occurs by Frenkel-Poole emission and can be reduced with pre-deposition surface treatments. Finally, through this work, it is realized that the integration of oxides with III-nitrides requires an appreciation of many different fields of research including materials science, surface science, and electrical engineering. By recognizing the importance that each of these fields play in designing oxide ⁄ III-nitride interfaces, this thesis has the opportunity to explore other related phenomena including accessing metastable phases through MBE (ytterbium monoxide), spinodal decomposition in metastable alloys (MCO), how polar surfaces grown by MBE compensate their bound surface charge, room temperature epitaxy, and the use of surface modification to achieve selective epitaxial deposition (SeEDed growth).
Issues in Patterning Self-Assembled Monolayers by Molecular Replacement: Comparison of Adventitious and Directed Replacement of One Molecule in a SAM with Another.
(2010-12-20) Tucker, Eric; Christopher Gorman, Committee Chair; David Muddiman, Committee Member; Edmond Bowden, Committee Member; Gregory Parsons, Committee Member
Lanthanide-based Oxides and Silicates for High-K Gate Dielectric Applications
(2007-07-27) Jur, Jesse Stephen; Angus Kingon, Committee Chair; Gregory Parsons, Committee Member; Jon-Paul Maria, Committee Member; Mark Johnson, Committee Member
The ability to improve performance of the high-end metal oxide semiconductor field effect transistor (MOSFET) is highly reliant on the dimensional scaling of such a device. In scaling, a decrease in dielectric thickness results in high leakage current between the electrode and the substrate by way of direct tunneling through the gate dielectric. Observation of a high leakage current when the standard gate dielectric, SiO2, is decreased below a thickness of 1.5 nm requires engineering of a replacement dielectric that is much more scalable. This high- dielectric allows for a physically thicker oxide, reducing leakage current. Integration of select lanthanide-based oxides and silicates, in particular lanthanum oxide and silicate, into MOS gate stack devices is examined. The quality of the high-K dielectrics is monitored electrically to determine properties such as equivalent oxide thickness, leakage current density and defect densities. In addition, analytical characterization of the dielectric and the gate stack is provided to examine the materialistic significance to the change of the electrical properties of the devices. It is shown that optimization of low-temperature processing can result in MOS devices with an equivalent oxide thickness (EOT) as low 5 Å and a leakage current density of 5.0 A⁄cm2. High-temperature processing, consistent with a MOSFET source-drain activation anneal, yields MOS devices with an EOT as low as 1.1 nm after optimization of the TaN/W electrode properties. The decrease in the device effective work function (phi_M,eff) observed in these samples is examined in detail. First, as a La2O3 capping layer on HfSiO(N), the shift yields ideal-phi_M,eff values for nMOSFET deices (4.0 eV) that were previously inaccessible. Other lanthanide oxides (Dy, Ho and Yb) used as capping layers show similar effects. It is also shown that tuning of phi_M,eff can be realized by controlling the extent of lanthanide-silicate formation. This research, conducted in conjunction with SEMATECH and the SRC, represents a significant technological advancement in realizing 45 and sub-45 nm MOSFET device nodes.
Molecular Electronic Memories
(2006-03-27) Amsinck, Christian Johannes; Paul Franzon, Committee Chair; Veena Misra, Committee Member; John Muth, Committee Member; Gregory Parsons, Committee Member
The feasibility of building large memories using molecular electronic devices with bistable conductance-state memory has been investigated. A novel fabrication method for twoterminal molecular memory devices that is integrateable into large-scale arrays while avoiding top-contact evaporation on a molecular monolayer has been developed. A sacrificial layer underneath the top contact metal is wet-etched to create free-standing cantilevers in aqueous solution and a self-assembled monolayer is formed on the underside of the cantilever. Subsequent atmospheric drying causes the freestanding structure to become permanently adhered to the substrate, resulting in a two-terminal molecular structure. This device has been investigated with alkanethiol monolayers as a proof-ofconcept, and the expected decrease in current with increasing chain length is observed. The measured current density in control devices without molecules is also consistent with models of loaded cantilevers. Previously characterized molecules exhibiting memory behavior were also investigated and demonstrated bistable memory effects similar to earlier observations. The scalability of such bistable molecular memory devices was analyzed from a circuits perspective, and the impact of different system parameters was quantified. It is necessary to build large arrays with at least several hundred molecular memory cells along each dimension, in order to prevent peripheral circuitry from dominating the area. It is quantitatively shown how this requirement constrains the minimum allowable forward⁄reverse-bias rectification ratio of the molecular devices, as well as the minimal on⁄off ratio of the two molecular conductance states. The parasitic wiring impedance is negligible in the case of metallic interconnect, but the impedance of currently available molecular wires makes large-scale all-molecular arrays infeasible.
Optimization of Metal Gate Electrode Stacks for Work Function Tuning
(2007-08-22) Lee, JaeHoon; Doug Barlage, Committee Member; Veena Misra, Committee Chair; Carlton Osburn, Committee Member; Gregory Parsons, Committee Member
Processing Science of Barium Titanate
(2009-04-22) Aygun, Seymen Murat; Gregory Parsons, Committee Member; Zlatko Sitar, Committee Member; Jon-Paul Maria, Committee Chair; Yuntian Zhu, Committee Member
Barium titanate and barium strontium titanate thin films were deposited on base metal foils via chemical solution deposition and radio frequency magnetron sputtering. The films were processed at elevated temperatures for densification and crystallization. Two unifying research goals underpin all experiments: 1) To improve our fundamental understanding of complex oxide processing science, and 2) to translate those improvements into materials with superior structural and electrical properties. The relationships linking dielectric response, grain size, and thermal budget for sputtered barium strontium titanate were illustrated. (Ba0.6Sr0.4)TiO3 films were sputtered on nickel foils at temperatures ranging between 100-400 Ã‚Â°C. After the top electrode deposition, the films were co-fired at 900 Ã‚Â°C for densification and crystallization. The dielectric properties were observed to improve with increasing sputter temperature reaching a permittivity of 1800, a tunability of 10:1, and a loss tangent of less than 0.015 for the sample sputtered at 400 Ã‚Â°C. The data can be understood using a brick wall model incorporating a high permittivity grain interior with low permittivity grain boundary. However, this high permittivity value was achieved at a grain size of 80 nm, which is typically associated with strong suppression of the dielectric response. These results clearly show that conventional models that parameterize permittivity with crystal diameter or film thickness alone are insufficiently sophisticated. Better models are needed that incorporate the influence of microstructure and crystal structure. This thesis next explores the ability to tune microstructure and properties of chemically solution deposited BaTiO3 thin films by modulation of heat treatment thermal profiles and firing atmosphere composition. Barium titanate films were deposited on copper foils using hybrid-chelate chemistries. An in-situ gas analysis process was developed to probe the organic removal and the barium titanate phase formation. The exhaust gases emitted during the firing of barium titanate films were monitored using a residual gas analyzer (RGA) to investigate the effects of ramp rate and oxygen partial pressure. The dielectric properties including capacitor yield were correlated to the RGA data and microstructure. This information was used to tailor a thermal profile to obtain the optimum dielectric response. A ramp rate of 20 Ã‚Â°C/min and a pO2 of 10-13 atm resulted in a permittivity of 1500, a loss tangent of 0.035 and a 90 % capacitor yield in 0.5 mm dot capacitors. Yield values above 90% represent a significant advantage over preexisting reports and can be attributed to an improved ability to control final porosity. Finally, the dramatic enhancement in film density was demonstrated by understanding the processing science relationships between organic removal, crystallization, and densification in chemical solution deposition. The in situ gas analysis was used to develop an each-layer-fired approach that provides for effective organic removal, thus pore elimination, larger grain sizes, and superior densification. The combination of large grain size and high density enabled reproducing bulk-like dielectric properties in a thin film. A room temperature permittivity of 3000, a 5 ÃŽÂ¼F/cm2 capacitance density, and a dielectric tunability of 15:1 were achieved. By combining the data sets generated in this thesis with those of comparable literature reports, we were able to broadly rationalize scaling effects in polycrystalline thin films. We show that the same models successfully applied to bulk ceramic systems are appropriate for thin films, and that models involving parasitic interfacial layers are not needed. Developing better models for scaling effects were made possible solely by advancing our ability to synthesize materials thus eliminating artifacts and extrinsic effects.
Spin Coating and Photolithography Using Liquid and Supercritical Carbon Dioxide
(2002-10-04) Hoggan, Erik Nebeker; Joseph DeSimone, Committee Co-Chair; Peter Kilpatrick, Committee Member; Gregory Parsons, Committee Member; Ruben Carbonell, Committee Co-Chair; Christine Grant, Committee Member
This thesis details work on the utilization of dense phase carbon dioxide (CO2) in semiconductor processing. In particular, work is presented on the formulation of CO2 soluble photoresists and the spin coating of those photoresists using only liquid CO2 as a solvent. As part of this spin coating work, a novel high-pressure CO2 spin coater was designed and constructed, and the theoretical equations governing its performance were derived. Also discussed in this thesis are 248 and 193 nm exposures of these CO2 spun films and subsequent development in supercritical CO2. Resist stripping was also performed in CO2. In short, this thesis details the first steps towards a complete replacement of all aqueous and organic solvents in the conventional photolithographic processes of spin coating, developing, and resist stripping. This change not only confers significant environmental advantages, but opens up many new avenues in resist chemistry and promises improvements in large scale film uniformity, elimination of feature collapse, elimination of extraneous processing steps, and improved control of the lithographic process.