Browsing by Author "Gregory N. Parsons, Committee Chair"
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- The Atomic Layer Deposition of Noble Metals for Microelectronics Applications(2006-12-07) Park, Kie Jin; Gregory N. Parsons, Committee ChairThe purpose of this research has been to explore noble metals prepared using thermal atomic layer deposition (ALD) for gate electrode applications in CMOS technology. ALD Ruthenium and Rhodium metal films have been focused due to their high work function, low resistivity of their oxidation forms. Study includes 1) ALD Ru process, 2) ALD Ru nucleation behaviors, 3) area-selective ALD Ru process, 4) ALD Ru work function modification, 5) ALD Rh process and work function. For item 1), ALD Ru films were formed using ruthenocene and oxygen as precursors. ALD window was discovered within 310 to 340°C from ALD Ru growth rate dependence on deposition temperature. Self-limiting reaction behavior was shown from growth rate versus precursor dose time. ALD Ru resistivity was measured to about 20˜30μΩcm and Auger spectroscopy result was consistent with metallic Ru. Foe item 2), ALD Ru was deposited on chemical SiO2, thermal SiO2, and H-terminated Si surfaces. From thickness vs. ALD cycle, growth rates of Ru on those substrates were similar while as initial nucleation periods were different. Contact angle values of initial substrates showed hydrophilicity was related to the incubation time difference between substrates. ALD Ru Nucleation behavior was investigated on H-terminated Si during incubation period and growth model was proposed. For item 3), extending ALD Ru nucleation study, area-selective ALD Ru process was demonstrated. Octadecyltrichlorosilane was used to make surface very hydrophobic inhibiting nucleation. Metal-oxide-semiconductor (MOS) capacitor was fabricated using selective deposition process and spectroscopic (XPS) and electrical (capacitance-voltage) measurements of the capacitor confirmed the viability of selective deposition. For item 4), ALD Ru work functions on SiO2 and HfO2 was measured and it turned out that Ru work functions on high-k dielectrics are smaller than on SiO2 possibly due to dipole formation at metal/dielectric interface. Organic self-assembled monolayers were applied on high-k dielectric surfaces prior to ALD Ru deposition to modify the dipole at the interface. ALD Ru work functions increased with amine-terminated self-assembled monolayer and decreased with vinyl-terminated monolayer. For item 5), ALD Rh has rarely been studied even though Rh is a candidate material for PMOS gate electrode. We investigated and developed successful ALD Rh process using Rhodium acetylacetonate and oxygen as precursors. ALD window was found at 280 to 310°C. It was shown that ALD Rh resistivity decreased with deposition temperature having minimum (˜10mμΩcm) at 300°C. XPS result was consistent with metallic Rh.
- Deposition of Metal and Metal Oxide Thin Films from Metal Organic Precursors in Supercritical Carbon Dioxide Solution(2005-04-22) Barua, Dipak; Ruben G. Carbonell, Committee Member; Gregory N. Parsons, Committee Chair; Carlton Osburn, Committee MemberThin films of metals and metal-oxides are deposited in batch (Chemical Fluid Deposition) and cyclic (Atomic Layer Deposition) processes from metal organic precursors in supercritical carbon dioxide solutions. New materials have been introduced in the deposition processes. Deposited films are analyzed in details in order to evaluate their quality and chemical composition. Analyzing techniques, X-ray photoelectron spectroscopy (XPS), ellipsometry, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and auger electron spectroscopy (AES) are adopted to characterize the films. Capacitance-voltage measurements are performed to prove the device quality deposition of metal oxide films. The process establishes a new approach in metal oxide deposition, and controllable growth of metal and metal oxide films in supercritical carbon dioxide.
- Fabrication and Characterization of Electrical Contacts for Charge Transport Study in Molecular Electronics.(2006-09-29) Chu, Changwoong; Veena Misra, Committee Member; Orlin D. Velev, Committee Member; Gregory N. Parsons, Committee Chair; Christine S. Grant, Committee MemberNanoscale imprint lithography (NIL) is investigated in the view point of the ability to form nanoscale feature. NIL at room temperature is proposed and demonstrated on thermoplastic substrate that has a restriction of heating. Anisotropic oxygen-based plasma etch performance is evaluated to remove the residual resist at the bottom of impressed pattern and to achieve the thinner patterns with various etching molecules. The patterning fidelity in nano-imprint lithography including the ability of polymer deformation is studied, and based on the results a mechanism for the polymeric behavior of imprinted resist is discussed. A procedure using geometrical shadowing in common metal-evaporation tools to form nanoscale metal electrodes with controlled width-to-pitch ratios is demonstrated and characterized for feature sizes near 50 nm. Successive formation of metallic bridge with the metallic nanoparticle for the conductance study and the electrical characterization are described. From the results of electrical conduction, we estimate the contact area (~20.1 nm2) and the number of molecules between nanoparticle and surface-bound molecules, and then calculate the resistances of single molecules, contact resistance, the tunneling probabilities in contacts. The electrical characterization of the conjugated molecules has been accomplished using the same nanoscale test-bed in terms of surface bound head groups. As a new approach for the interconnecting elementary molecular devices, Au nanoparticle dimer bridged by conjugated molecule is assembled on the nanoscale electrode gap. Oligo Phenylacetylene-bridged gold nanoparticle dimer was prepared for the demonstration. Resistance measured at low bias regime is 2.2 ± 0.64 GΩ at room temperature, which is comparable with the single molecule conduction. The selective adsorption of SAM on Au plates by means of electron supply is proposed to develop the pliable manipulation of self-assembling molecular elementary devices. The method is applied to the two metal patterns, which is an electrical test-bed for the molecular resistors. The electrical characterization is in good agreement with the selective formation of molecular layer on metal.
- A Holistic Investigation of Alternative Gate Stack Materials for Future CMOS Applications(2007-05-04) Terry, David Bartholomew; Gregory N. Parsons, Committee ChairHigh dielectric constant (high-k) insulators metal gate electrodes are important for advanced MOS devices to limit gate leakage by increasing gate capacitance with ultimately thicker films and eliminate poly-depletion & dopant diffusion, respectively. Reactions between dielectric⁄substrate and gate electrode⁄dielectric during deposition or post-deposition processing lead to an increase in interfacial layer formation, and the mechanisms that control the changes need to be well understood. We investigate yttrium-based and hafnium-based high-k dielectrics and ruthenium-based gate electrodes formed by various processing methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD) on Si(100). Characterization techniques include IR, XPS, TEM, EELS, AES, and IV and CV electrical analysis. During deposition and post-deposition treatments the interfaces have some extent of interfacial layer formation. The extent of the intermixing depends on substrate surface preparation, process conditions, and annealing conditions. The transition metal alluminate dielectrics show evidence on flatband voltage tuning via charge compensation. Also, the ruthenium gate electrodes show that process condition can have a direct effect the electronic and chemical properties of MOS structures such as in-situ versus ex-situ capacitor fabrication and the role of subsurface adsorbed oxygen in ruthenium.
- Interface reactions during processing of chemical vapor deposited yttrium oxide high-k dielectrics(2002-11-28) Niu, Dong; H. Henry Lamb, Committee Member; Gerald Lucovsky, Committee Member; Veena Misra, Committee Member; Gregory N. Parsons, Committee ChairHigh dielectric constant (high-k) insulators are important for advanced MOS devices to limit gate leakage and increase gate capacitance. Reactions between high-k's and the substrate during deposition or post-deposition processing lead to an increase in the equivalent oxide thickness, and the mechanisms that control the changes need to be well understood. We investigate yttrium-based high-k dielectrics formed by oxygen plasma assisted CVD on Si(100), using two different yttrium diketonate precursors. Characterization techniques include IR, XPS, TEM, EELS, AES, and IV and CV electrical analysis. During deposition and post-deposition anneals a thin Y-O-Si (silicate)/SiO₂ structure due to intermixing of Y, O and Si and substrate oxidation is formed at the interface, between the Y₂O₃ and silicon. The extent of the intermixing depends on substrate surface preparation, process conditions, and annealing conditions. As-deposited Y₂O₃ films show evidence for O-H bond due to water absorption. With in-situ deposited Si capping layers, water pickup is significantly reduced, and interfacial SiO₂ layer after annealing is less than 5 Å. Analysis of reaction mechanisms suggests that Si diffusion is attributed to silicate formation, and water absorption, catalytic dissociation of residual O₂, and O₂ plasma may account for SiO₂ formation. Nitridation of chemical vapor deposited yttrium oxide using N₂ plasma during deposition and post-deposition treatments is investigated. The use of N₂ instead of O₂ during deposition minimizes the substrate oxidation. Similar activation energies for post-deposition anneals of O₂ and N₂ films indicate substrate oxidation processes are likely the same. Bulk properties including chemical bonding, concentration and distribution of N are also studied for as-deposited and annealed films.
- Nanoscale Assembly for Molecular Electronics and In Situ Characterization during Atomic Layer Deposition(2009-08-03) Na, Jeong-Seok; Gregory N. Parsons, Committee ChairThe work in this dissertation consists of a two-part study concerning molecular-based electronics and atomic layer deposition (ALD). As conventional “top-down†silicon-based technology approaches its expected physical and technical limits, researchers have paid considerable attention to “bottom-up†approaches including molecular-based electronics that self assembles molecular components and ALD techniques that deposit thin films with atomic layer control. Reliable fabrication of molecular-based devices and a lack of understanding of the conduction mechanisms through individual molecules still remain critical issues in molecular-based electronics. Nanoparticle/molecule(s)/nanoparticle assemblies of “dimers†and “trimers†, consisting of two and three nanoparticles bridged by oligomeric ethynylene phenylene molecules (OPEs), respectively, are successfully synthesized by coworkers and applied to contact nanogap electrodes (< 70 nm) fabricated by an angled metal evaporation technique. We demonstrate successful trapping of nanoparticle dimers across nanogap electrodes by dielectrophoresis at 2 VAC, 1 MHz, and 60 s. The structures can be maintained electrically connected for long periods of time, enabling time- and temperature-dependent current-voltage (I-V) characterization. Conduction mechanisms through independent molecules are investigated by temperature dependent I-V measurements. An Arrhenius plot of log (I) versus 1/T exhibits a change of slope at ~1.5 V, indicating the transition from direct tunneling to Fowlerï€ÂNordheim tunneling. Monitoring of the conductance is also performed in real-time during trapping as well as during other modification and exposure sequences after trapping over short-term and long-term time scales. The real-time monitoring of conductance through dimer structures during trapping offers immediate detection of a specific fault which is ascribed to a loss of active molecules and fusing of the nanoparticles in the junction occurring mostly at a high applied voltage (≥3 VAC). After successful trapping, the sample exposure to air reveals a small rapid decrease in current, followed by a slower exponential increase, and eventual current saturation. This work also reports on the dependence of electron transport on molecular length (2 to 4.7 nm) and structure (linear-type in dimers and Y-type in trimers). The extracted electronic decay constant of ~0.12/Ã… and effective contact resistance of ~4 Megaohmï — indicate a strong electronic coupling between the chain ends, facilitating electron transport over long distances. A three terminal molecular transistor is also demonstrated with trimers trapped across nanogap electrodes. The source-drain current is modulated within a factor of 2 with a gate bias voltage of -2 to +2 V. A subthreshold slope of ~110 mV/decade is obtained. Finally, we report on both fundamental understanding and application of atomic layer deposition. First, in situ analysis tools such as quartz crystal microbalance and electrical conductance measurements are combined to reveal direct links between surface reactions, charge transfer, and dopant incorporation during ZnO and ZnO:Al ALD. Second, the ability of ALD to form uniform and conformal coating onto complex nanostructures is explored to improve the ambient stability of single molecules/nanoparticle assemblies using Al2O3 ALD as an encapsulation layer. In addition, the ability to shield the surface polarity of ZnO nanostructures using Al2O3 + ZnO ALD, leading to hierarchical morphology evolution from one-dimensional ZnO nanorods to three-dimensional ZnO nanosheets with branched nanorods during hydrothermal growth is investigated.
- Nanoscale Engineering Materials with Supercritical Fluid and Atomic Layer Deposition(2009-08-04) Peng, Qing; Gregory N. Parsons, Committee Chair; Jan Genzer, Committee Member; Ruben G. Carbonell, Committee Member; Saad A. Khan, Committee MemberWith the development of material science and technology, modification of substrates, which have random geometry and high aspect ratio three dimensional (3D) complex structures, with desired functional, reactive and stable coatings becomes important and challenging. The ability to fabricate mono- or multi-layers of functional materials with precisely controlled dimensions, finely tuned composition and molecular structures, attracts significant interests in materials science and is the key to construct such devices and structures at nano- and micro- scale with desired properties. In this study, supercritical carbon dioxide (scCO2) has been studied as an alternative route for modifying substrates due to the unique gas-like (low viscosity, high diffusivity and zero surface tension) and liquid-like properties (high density). 1) The reaction kinetics of metal oxides thin film deposition from pyrolysis of metal organics in scCO2 was studied in detail. This method was demonstrated as a powerful technique to coat oxides, including Al2O3, Ga2O3 and others, into 3D high aspect ratio complex structure of carbon nanotubes (CNTs) forest. 2) The low temperature scCO2 based hydrogenolysis process was developed as a useful way to functionalize aligned CNTs forest with dense Nickel nanoparticles. On the second part of this work, atomic layer deposition (ALD) /molecular layer deposition (MLD), as a vapor phase, stepwise and self-limiting vacuum based deposition process, was demonstrated as a powerful way to form highly conformal and uniform film onto substrates, even into highly complex 3D complex structures. In this study, 4) Metal oxide ALD is applied onto 3D electrospun polymer microfiber mats template to illustrate an effective and robust strategy to fabricate long and uniform metal oxide microtubes with precisely controllable wall thickness. Designer tubes of various sizes and different materials were demonstrated by using this method. 5) By further extending this technique, complex coaxial Al2O3/ZnO/Al2O3 multilayed microtubular structure is fabricated, which provides an unique platform to study the solid state reaction and diffusion process (Kirkendall Effect) between Al2O3 shells and the confined middle ZnO layers by annealing the samples at 700 ËšC. 6) The extension of ALD-MLD process of polyamides, zinc hybrid, aminosilane self assembly monolayers were studied by various techniques to illustrate the surface reaction mechanism.
- Reactions of High-k Gate Dielectrics: Studies in Hafnium, Zirconium, Yttrium, and Lanthanum-based Dielectrics and in-situ Infrared Results for Hafnium Dioxide Atomic Layer Deposition(2006-05-08) Kelly, Michael Jason; David F. Ollis, Committee Member; Gregory N. Parsons, Committee Chair; H. Henry Lamb, Committee Member; Veena Misra, Committee MemberAccording to the International Technology Roadmap for Semiconductors (2004) integrating a high dielectric constant (high-k) material into the gate stack will be necessary within the next two years (i.e., by 2007) to maintain the rate of scaling that has come to characterize the microelectronics industry. This work presents results for Y-, Zr-, Hf-, and La-based high-k gate dielectrics prepared by ex-situ oxidation of sputtered thin metal films and for HfO2 prepared by atomic layer deposition (ALD). The kinetics of substrate consumption during formation of yttrium silicate thin films were studied. We find results consistent with high-k dielectric formation by a two-step process in which yttrium metal reacts with the silicon substrate to form a metal silicide which is then oxidized to form the yttrium silicate dielectric. In other experiments, we show flatband voltage shifts of -0.2 and 0.95V in devices containing Zr-based dielectrics formed by oxidation of 8Å of Zr metal on Si at 600°C in N2O for 15 and 300s, respectively. Silicon oxidized in the same environment does not show this shift. The fixed charge scales with EOT for these films and is consistent with charge generation due to disruption of the SiO2 network by metal ions. Zr-based dielectrics exhibit this effect more strongly than Hf-based dielectrics. We show that La-based dielectrics absorb atmospheric H2O and CO2, and that reactions between these materials and deposited silicon electrodes are accelerated when H2O or other OH species are present at the interface. We show that the electrical properties of gate stacks having Ru and RuO2 electrodes in contact with PVD Y-silicate are more stable during thermal anneal than similar gate stacks having PVD ZrO2 or CVD Al2O3 dielectrics. For this work, we configured a Fourier transform infrared spectrometer for in-situ attenuated total reflection measurements and investigated ALD deposition of HfO2. We report the direct reaction of tetrakis(diethylamino) hafnium (TDEAHf) with SiH groups on HF-last Si. Island growth of HfO2 occurs, and SiH features are still present and shrinking after 200 cycles. To the best of our knowledge, these are the first in-situ FTIR results presented for atomic layer deposition using TDEAHf/H2O chemistry.
