<p>CASTRO, SUSANA PATRICIA. Characterization of the Boron Doping Process UsingBoron Nitride Solid Source DiffusionThe purpose of this research has been to develop an optimum process for the borondoping of implants and polysilicon gates of metal-oxide-semiconductor (MOS) devices.An experimental design was constructed to determine the effects of diffusiontemperature, time, and ambient on characteristics of the doping process. A temperaturerange of 800 to 1000 degrees Celsius was studied with a diffusion time between 10 and60 minutes. Two diffusion ambients were used for doping processes, a pure nitrogenambient and a nitrogen-oxygen gaseous mixture. Device wafers were fabricated, and thetesting of MOS capacitors and van der Pauw test structures was performed to determinethe effect of diffusion conditions on flatband voltage and poly gate doping. Materialscharacterization techniques were used on monitor wafers for each diffusion process todetermine the wafer structure formed for each process and evaluate the effectiveness ofthe deglaze etch. The processes that resulted in the best device characteristics withoutsuffering from significant poly depletion effects and flatband voltage shifts were wafersdoped at 800 degrees Celsius in a pure nitrogen atmosphere for 20 minutes and 45minutes. The presence of oxygen in the atmosphere caused the depletion of boron fromthe Si wafer surface. The formation of the Si-B phase only occurred on devices processedat 1000 degrees Celsius. The deglaze process used in this experiment did not fullyremove this layer, and thus all devices doped at this temperature were seriously degraded.<P>

<p>The characteristics of clean n-type GaN surfaces and the interface between this surface and Pt, Au and Ag, have been investigated. Gallium-terminated (0001) surfaces of GaN, free of carbon and oxygen within the detection limits of XPS have been achieved by annealing in ammonia at 860°C for 15 minutes. Additional, in-situ surface analysis indicated a flat, stoichometric, and unreconstructed surface free of other contaminants. The electron affinity of this surface was 3.1 ± 0.2 eV. The valence band maximum was located 3.0 ± 0.1 eV below the Fermi level, indicating the presence of a surface state near the valence band maximum. Individual layers of Pt, Au or Ag were deposited in-situ on the cleaned surface and the interfaces characterized using XPS, UPS, LEED and TEM. All as-deposited metal/GaN interfaces were abrupt and unreacted; the Pt and Au were deposited epitaxially. The Schottky barrier heights obtained from photoemission measurements were 1.2, 0.9 and 0.5 ± 0.2 eV for Pt, Au and Ag, respectively. Values of the metal work function from UPS results were 5.7, 5.3 and 4.4 ± 0.2 eV for Pt, Au and Ag, respectively. Schottky barrier heights determined via ex-situ current-voltage measurements were 1.15, 0.88 and 0.56 ± 0.05 eV for Pt, Au and Ag, respectively. Capacitance-voltage measurements yielded barrier heights of 1.25 and 0.96 ± 0.05 eV, for Pt and Au, respectively. These results indicate that the Fermi level of the cleaned surface is not pinned. Upon annealing the aforementioned contacts from 400 to 800°C for 3 minutes each. The rectifying behavior of the Pt and Au contacts degraded as a function of temperature during annealing at 400, 600 and 800°C for 3 minutes each until they became ohmic. This was correlated with TEM of the annealed interfaces, which displayed increased chemical reaction and roughening as a function of temperature. <P>

<p>The surface morphology and atomic structure of nitrogen doped, n-type 6H-SiC(0001)Si wafers before and after various surface preparation techniques were investigated. As-received wafers were exposed to in-situ cleaning with or without excess silicon to obtain either a (rt3 x rt3)R30&#176 or a (3 x 3) reconstructed surface. The resulting surfaces were characterized using reflection high-energy electron diffraction, photo-electron emission microscopy, and atomic force microscopy. An atomically clean, reconstructed surface was obtained via thermal annealing at 950ºC. Cleaning with excess silicon resulted in the formation of silicon islands on the surface. The surface morphology of hydrogen etched wafers depended upon their doping concentrations. Wafers with doping concentrations of greater than or equal 2.5 x 10E18 and less than 7 x 10E17 (ND-NA)/cm3 were investigated with the former exhibiting more surface features. The microstructure of all the samples showed regions with full and half unit cell high steps. An atomically clean, ordered, stepped surface was achieved via annealing at 1030 degrees Celcius. Chemical vapor cleaning resulted in the formation of silicon islands. The initial growth of AlN and GaN thin films on the cleaned, hydrogen etched 6H-SiC(0001) substrates were investigated using PEEM and AFM. The AlN films nucleated immediately and coalesced, except in the areas of the substrate surface which contained half unit cell height steps where pits were observed. The GaN films grown at 800ºC for 2.5 minutes exhibited nucleation and three-dimensional growth along the steps. The GaN films deposited at 700&#176 C for 2 minutes grew three-dimensionally with coalescence of the film dependent upon the step structure. Almost complete coalescence occurred in regions with unit cell high steps and incomplete coalesce occurred in regions with half unit cell height steps. Films of AlN grown for 30 minutes via GSMBE on hydrogen etched surfaces exhibited two-dimensional growth and had an RMS roughness value of 4 &Aring. Films grown at 1000 &#176 C exhibited an SK growth mode and had rocking curve FWHM of 150-200 arcsecs. MOCVD grown films on hydrogen etched wafers had an RMS roughness value of 4 &Aring and a XRD rocking curve FWHM of approximately 260 acrsecs. <P>

<p>The purpose of this research has been to use off-line characterization techniques to establish material-specific properties of gate-stack constituents (i.e., high-k dielectric stacks and electrodes) and complete gate-stack structures. Hence, the characterization methodologies were established to evaluate high-k dielectrics at various processing levels, which, in part, determine the final characteristics of an advanced gate-stack device. Material systems that were investigated include: Al-O, Hf-Si-O, Zr-Si-O, Ti-O, Ta-O and Sr-Ti-O. Various physical and electrical characterization techniques were used to establish fundamental understandings of the materials selected, thin-film growth/deposition processes, and gate-stack structures. General conclusions for stable and unstable gate-dielectric materials have been establishedregarding the presence of a problematic interfacial layer at the Si/dielectric interface, graded dielectric layers, and the stability of gate electrodes on high-k dielectrics.The nanometer-scale chemistry of a gate-stack capacitor whose expected structure is Si/SiOxNy/Ta2O5/TiN/Al was studied by high-resolution electron-energy-loss spectroscopy in a scanning transmission electron microscope. Elemental profiles with near-atomic-level resolution for Si, Ti, N, Al, and O demonstrate that the device structure deviates drastically from the expectation and is chemically complex.It is concluded that the graded distribution of certain elements across the gate-stack capacitor completely precludes a band-structure model that assumes abrupt interfaces and chemically discrete layers. This study impacted on subsequent interpretations of flatband voltage extractions and electrical degradation following backside metallization/postmetallization annealing for capacitors whose dielectric-stack was based on Ta-O.Detailed and extensive electrical characterizations of Pt/SiOx/Sr-Ti-O/Si MOS capacitors were carried out to investigate reliability issues in a bi-layer gate dielectric. Based on these studies, models are proposed to describe the carrier transport and dielectric degradation for a Sr-Ti-O capacitor. It is concluded that conduction is dominated by Frenkel-Poole emission from mid-gap trap levels. The trap barrier height is estimated to be 1.51eV. A model based on the atomic and electronic structure of oxygen vacancies can account for the reported leakage-current characteristics. In addition, it is tentatively proposed that anode-hole injection and hole trapping control the dielectric degradation under gate injection.<P>

<p>Characterization of nitride films on 6H-SiC (0001) wafers via x-ray, TEM, and AFM was accomplished on standard GaN thin films with AlN or AlGaN buffer layers. TEM sample thinning capability was improved through the use of Nomarski in an optical microscope to gauge the thickness of the sample during preparation. TEM analysis was then completed of Au and Pt films deposited on chemical vapor cleaned GaN with annealed up to 800°C. Chemical reactions were detected in x-ray measurements of the 800°C Pt samples and GaN/metal interface roughening were confirmed by TEM images in both metals. Interface roughening is attributed to the chemical reactions and interfacial stresses greater than the yield stress of the metal created during heat treatments by the difference in the thermal expansion coefficients of the GaN and the metals. The GaN rocking curves were found to track very closely to the values of the underlying substrate and changes in buffer layer growth temperatures were found to change the screw and edge dislocation populations of subsequent GaN layers. GaN grown on 1030°C AlN buffer layers showed the lowest edge dislocation populations when compared against buffers grown in the range of 1010-1220°C, even though the 1220°C AlN was much smoother. AlGaN buffer layers provided more edge dislocation reduction, with a 1090°C Al0.2Ga0.8N layer yielding the best GaN rocking curve values found in this work. GaN films with AlN buffer layers grown on hydrogen etched SiC substrates did not show rocking curve improvement when compared against samples with unetched substrates. The AlN layers showed extremely narrow, substrate limited, on-axis rocking curve values, but it is not clear as to whether additional defects are present that may broaden the off-axis rocking curves, causing the poorer results seen in the GaN films. Reciprocal space maps of uncoalesced, maskless pendeo epitaxy samples revealed that the wing regions are shielded from poor substrate material when compared against the seed material. The wing regions also have lower strain and rocking curve widths than the corresponding seed material.<P>

<p>LOESING, RAINER, Development of High Resolution Depth Profiling Of Ultra Shallow Dopant Implants with SIMS (under the direction of Phillip E. Russell. Secondary Ion Mass Spectrometry (SIMS) is considered a reliable technique for precise and accurate dopant depth profiling in Si with respect to junction depth and implanted dose. The junction depths of source drain extension structures are predicted to be between 19-33nm for the 0.1µm MOSFET generation. Accurate high depth resolution analysis of these ultra-shallow junctions by SIMS can only be provided if atomic mixing caused by energetic primary ion bombardment is minimized and extensive beam induced crater bottom roughening is avoided. For quantitative measurements, the influence of primary ion implantation, sputter rate changes and beam induced crater bottom roughness on secondary ion intensities has to be known. In this work SIMS was used to develop techniques for the accurate analysis of ultra shallow B, P and As implants in Si.Low energy O2+ primary ion bombardment was found to give the highest depth resolution for the analysis of B and P in Si, while low energy Cs+ and CsC6- primary ion bombardment resulted in the highest depth resolution for the analysis of As in Si. To obtain a more accurate profile shape and depth scale it was found to be essential to limit beam induced crater bottom roughness by means of sample rotation, variations of primary ion angle of incidence or change in sample chamber vacuum conditions. Beam induced crater bottom roughness was investigated for low energy O2+, Cs+ and CsC6- ion bombardment using atomic force microscopy (AFM) and optical profilometer (OP) measurements. OP was found to be a valuable tool for investigating small changes in sputter rate in the initial stages of a SIMS depth profile. It was shown that dose measurements of ultra shallow implants can be improved by using a correction procedure based on bulk doped standards. SIMS was proven to be a valuable tool for the characterization of ultra shallow implants in Si, but careful consideration of analysis conditions and SIMS artifacts is required for accurate analysis.<P>

<p>Free-standing single crystals of bulk GaN were grown via unseeded vapor phase transport at 1130C on hexagonal BN surfaces via direct reaction of Ga with ammonia. The temperature and stability of the Ga source were critical in terms of uniform nucleation and growth. The source temperature was maintained at 1260C to minimize a rapid reaction leading to the formation of GaN and the subsequent decomposition beneath the surface and consequent spattering of Ga. A maximum crystal growth temperature of 1130C was determined in which the GaN growth kinetics were much greater than decomposition. The number of nucleation events was reduced and the crystal size increased by a novel nucleation technique wherein ammonia was introduced at high temperatures. The resulting crystals were either needles or platelets depending on the process variables employed. Low V/III ratios achieved via ammonia flow rates 75sccm and/or ammonia total pressures 430Torr favored lateral growth. The average lateral growth rate for the platelets was ~50micron/hr; the average vertical growth rate for the needles was ~500micron/hr. Growth rates in all other directions for each of these two morphologies were very low. Seeded growth of both needle and platelet crystals was also achieved; however, the growth rate decreased at longer times and higher pressures due to reaction with hydrogen from the increased decomposition of ammonia. Nitrogen dilution of ammonia reduced the amount of hydrogen generated as a result of ammonia decomposition and increased the kinetic barrier to desorption of reactants from the GaN surface and then alleviated the enhanced decomposition of GaN crystals. A 2mm x 1.5mm needle and a 2.3mm x 1.8mm x 0.3mm platelet of GaN were grown with minimal decomposition in a 66.7% ammonia + 33.3% nitrogen gas mixture. Excellent crystalline quality was confirmed by Raman spectroscopy and Photoluminescence.Crystal growth using a Ga- 5at%Al source was conducted in an attempt to increase growth rate and inhibit decomposition. No notable change in growth rate was observed and hollow crystals were formed, indicating that Al promotes vertical growth under otherwise similar conditions for GaN growth. In addition, fine-grained AlN was formed within the binary Ga-Al source, thus, the supply of Al was progressively reduced. Nucleation control via addition of Si resulted in a slightly reduced number of larger crystals. X-ray Photoelectron Spectroscopy suggested that amorphous silicon nitride was formed on the BN substrate and nucleation rate was slightly reduced. Silicon was not detected within the sensitivity of Energy Dispersive Spectroscopy. Raman spectroscopy revealed insignificant amount of Si present in the crystal. Smoother surface morphology of the crystals grown in the presence of Si was observed by Scanning Electron Microscopy.<P>

<p>The purpose of the research presented herein has been to determine the underlyingmechanisms of and to optimize the growth parameters for the growth of smooth surfaceson InGaN and GaN thin films via metalorganic vapor phase epitaxy. Relationshipsamong dislocation density, film thickness, flow rates of the reactants, kinetic growthregime, and thermodynamic growth mode with the surface morphology and surfaceroughness were determined. The two chief parameters affecting template surface roughness in both growth ofGaN above 1000ºC were determined to be temperature and layer thickness. An optimumtemperature of 1020ºC was found for the former process, below which the islands formedin the growth on AlN buffer layers did not coalesce properly, and above which a hillockgrowth instability was pervasive on the surface. Increasing the GaN film depositiontemperature to 1100°C for GaN film deposition via PE enhanced sidewall growth;however, surface roughness was increased on the (0001) growth plane through theformation of hillocks. Template thickness above 2.5 microns had the lowest root mean squaresurface roughness of 0.48nm over 100 square microns. This was attributed to reductions indislocation density, as measured by corresponding 50% reductions in symmetric andasymmetric full width half maximum values of X-ray rocking curves. GaN films were grown at 780ºC to remove the influence of indium incorporationon the surface roughness. V-defects covered the surface at a density of 2E9 per square centimeter andwere linked with a boundary dragging effect. Growth parameters that affect Inincorporation into the InGaN films were investigated and measured using roomtemperature photoluminescence, x-ray diffraction, and x-ray photoelectron spectroscopy.Temperature and growth rate had the greatest effect on incorporation over the range of760 to 820ºC and 25 and 180nm/hr, respectively, through kinetically limiting InNdecomposition. Additions of In into the GaN film produced hillock islands that wereattributed to a strain relief mechanism. The V-defects were also observed in InGaN films;however, their formation was suppressed below a nominal thickness of 25nm<P>

<p>JONSEN, DANIEL EVERETT. Experimental and Computational Studies of Carbon Sputtering with Application to Deposition of Tetrahedrally Bonded Amorphous Carbon Films. (Under the direction of Dr. Jerome J. Cuomo.) <p>In this work, amorphous carbon films are deposited on various substrates by ion beam sputtering of a graphite target. In addition, computational studies of the carbon sputtering process are performed using a molecular dynamics simulation program. In both cases, several process parameters are varied with the intent to find the optimum conditions for the sputter deposition of amorphous carbon films of high sp content amorphous carbon films.<P>

<p>The goals of this thesis were to synthesize nanocrystalline Zn, to study the mechanical properties of bulk nanocrystalline Zn and try to reveal the deformation mechanisms in nanocrystalline materials. Nanocrystalline Zn powder has been synthesized by a cryomilling method. The average grain size decreased exponentially with the cryomilling time and reached a minimum average grain size of around 17nm. Large numbers of small grains (2~6nm) have been found in the very early stages of cryomilling. Dynamic recrystallization (DRX) was used to explain the observed phenomena. Differential scanning calorimetry (DSC), x-ray diffraction and transmission electron microscopy (TEM) were used to study the structural changes and grain size distribution with milling time and subsequent annealing. Maxima in both stored enthalpy (for the low temperature DSC peak) and lattice strain on the Zn basal planes were observed at the same milling time. Dislocation density on the basal planes is proposed as a major source for lattice strain and the measured stored enthalpy. The released enthalpy that might be due to grain growth is very small. These cryomilled nanocrystalline Zn powders were consolidated into disks with a density of nearly theoretical density by uniaxial compression at room temperature. Cyclic variation of microhardness with milling time has been observed in cryomilled nanocrystalline Zn. Evidence from transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) suggests that the variation of dislocation density and grain size distributions determine the hardness behavior. A model, based on a kinetic reaction-rate model for cyclic amorphous-to-crystalline phase transformations observed during ball milling, simulates the experimental results very well. The model confirms the effect of DRX on modulated cyclic variation of microhardness. Dislocation strain hardening and recrystallization effects are superposed linearly with the intrinsic grain boundary hardening during the simulation. A dislocation density on the order of 10/sup 16/m /sup -2/ is predicted to be necessary to trigger DRX from the model. This prediction is evidenced by HRTEM observation of dislocation density on the same order and consistent with the estimation from thermodynamic calculation. The activation energy for rate controlling step in DRX estimated from the model is around 50 kJ/mol. This estimation indicates that a grain boundary diffusion controlled mechanism could dominate in DRX. Ductility of cryomilled nanocrystalline Zn has been studied by MDBT. The yield strength obtained from MDBT shows modulated cyclic variations with cryomilling time. Three times yield strength is consistent with the microhardness values for the same Zn samples. Ductility of CM2h and CM4h samples are much better than other cryomilled samples as indicated by a much larger ratio of normalized displacement than other cryomilled nanocrystalline Zn samples. However, the ductility of all cryomilled Zn samples is poor or very limited. The poor ductility of cryomilled Zn is presumably due to the remaining flaws as a result of incomplete bonding between particles. The Young?s modulus measured from MDBT barely changes for all tested samples. Bulk (spherical balls) ultra-fine-grained (UFG) or nanostructured Zn via in situ consolidation of powders are produced by mechanical attrition at room temperature. The size of these spherical balls increased with the increase of ball milling time. The grain size decreased rapidly to around 80nm after 1h of ball milling and then increased to around 240nm at 3h. The grain size decreased gradually thereafter with the increase of milling time. An average gain size of around 23nm was achieved for Zn bulk samples ball milled for 25h. In situ consolidation of metal powders during mechanical attrition may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination. The hardness, yield stress measured from MDBT, and tensile tests are consistent with one another. The hardness increased almost linearly with the decrease of grain size. The positive Hall-Petch slope is much smaller compared to the slope for coarse-grained Zn. Except for BM1h Zn sample, all other samples possess good ductility as evidenced from miniaturized disk bend test (MDBT) results and from the observations of fracture surfaces studied by FESEM. A bulged hat shape sample is usually obtained after MDBT test. The Young?s modulus almost keeps the same as for conventional coarse-grained Zn. The low temperature ball milling proves to be more efficient in reducing the grain size. A maximum elongation of around 110% is achieved for UFG Zn (around 240nm) under uniaxial tension test, which discloses a superplastic deformation in UFG Zn at room temperature. The elongation of room temperature ball milled Zn decreases with the decrease of grain size. Around 20% elongation is observed for Zn with an average grain size of around 23nm. Tension tests at elevated temperature result in a reduction of yield stress. The significant drop of yield stress at 200 centigrade degree or above may be due to recovery or recrystallization as evidenced from FESEM images. A strain rate sensitivity value of around 0.14 is usually found for Zn tested at 20 centigrade degree - 40 centigrade degree. <P>