Metal Organic Chemical Vapor Deposition And Atomic Layer Deposition Of Strontium Oxide Films On Silicon Surfaces

Epitaxial oxide films like strontium titanate (SrTiO3) grown on silicon have a wide range of potential applications, including high k-dielectric devices, ferroelectrics, optoelectronics, and buffer layers for the heteroepitaxy of III-V semiconductor as well other pervoskites and high-Tc superconductors. The crystalline structure of SrTiO3 consists of alternating sublayers of SrO and TiO2. The epitaxy of SrTiO3 on Si(100) must be initiated with the nucleation of the SrO sublayer first. This thesis presents the methodology used for growing SrO on Si(100) surfaces via metal organic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). Sr(2,2,6,6-tetramethyl-3,5-heptanedionate) 2 [Sr(thd)2] is the beta-diketonate precursor used to conduct these film growth studies, but the use of this class of metal organic sources comes with several challenges. First, their thermal properties change with atmospheric exposure. Second, successful control of vapor delivery is challenging because beta-diketonates have low vapor pressures and their decomposition temperature is close to their vaporization temperature. Additionally, film growth results are difficult to reproduce because these compounds degrade with time. To overcome these challenges, we developed a Sr(thd)2 delivery scheme using a novel source vaporizer that successfully controls the vaporization and vapor transport to the growth surface under steady vapor pressure while preventing the decomposition of the solid source. This vaporization scheme has been able to grow SrO films on Si(100) with high uniformity and low carbon contamination, as shown with ex-situ Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The MOCVD experiments provided enough evidence to encourage ALD investigations which incorporated the integration of the controlled vaporization with a ultra high vacuum (UHV) reaction chamber that provided the ability to conduct growth experiments on functionalized Si(100) surfaces. The ability to tune the chemistry on the Si(100)-2x1 surface can aid in guiding surface reactions of the metal organic precursor with the growth surface. Our goal has been to hydroxyl terminate the Si(100)-2x1 surface in order to nucleate SrO monolayers. Following the desorption of a protective chemical oxide layer, dissociative chemisorption of H2O is carried out in UHV to hydroxyl terminated Si(100)-2x1. Metal oxide growth can be correlated to the concentration of hydroxyl groups on the silicon surface due to the facilitation of ligand exchange from the surface. Furthermore, hydroxyl-terminated surfaces initiate two-dimensional nucleation of the metal oxide while avoiding incubation periods common to the ALD of metal oxide. In-situ AES and low energy electron diffraction LEED were used to investigate the crystalline quality of the nucleated monolayers and the epitaxial orientation of SrO films on Si(100)-2x1 surfaces. The results of the ALD experiments were, unfortunately, inconsistent. Nonetheless, the focus of this thesis is to show the methodology for developing growth protocols that can be used in ALD reactions on functionalized Si(100)-2x1 surfaces for the epitaxy of metal oxides.

Offering thorough coverage of atomic layer deposition (ALD), this book moves from basic chemistry of ALD and modeling of processes to examine ALD in memory, logic devices and machines. Reviews history, operating principles and ALD processes for each device.

A versatile home-made atomic layer deposition (ALD) reactor was designed and built in our lab. This reactor can be used to deposit metal oxides on both wafer substrates and porous inorganic particles. Also, a simple procedure for selective ALD has been developed for the processing of silicon wafers in order to facilitate the spatially resolved growth of thin solid films on their surfaces. Specifically, a combination of silylation and UV/ozonolysis was tested as a way to control the concentration of the surface hydroxo groups required for subsequent atomic layer deposition (ALD) of metals or oxides. Water contact angle measurements were used to evaluate the hydrophilicity/hydrophobicity of the surface, a proxy for OH surface coverage, and to optimize the UV/ozonolysis treatment. Silylation with silanes was found to be an efficient way to block the hydroxo sites and to passivate the underlying surface, and UV/O 3 treatments were shown to effectively remove the silylation layer and to regain the surface reactivity. Both O3 and 185 nm UV radiation were determined necessary for the removal of the silylation layer, and additional 254 nm radiation was found to enhance the process. Attenuated total reflection-infrared absorption spectroscopy was employed to assess the success of the silylation and UV/O 3 removal steps, and atomic force microscopy data provided evidence for the retention of the original smoothness of the surface. Selective growth of HfO2 films via TDMAHf + H2 O ALD was seen only on the UV/O3 treated surfaces; total inhibition of the deposition was observed on the untreated silylated surfaces. We believe that the silylation-UV/O 3 procedure advanced here could be easily implemented for the patterning of surfaces in many microelectronic applications.

Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS)* at Purdue University in 1957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dis semination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the though that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all concerned if the printing and distribution of the volumes were handled by an international publishing house to assure improved service and broader dissemi nation. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Corporation of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 37 (thesis year 1992) a total of 12,549 thesis titles from 25 Canadian and 153 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this impor tant annual reference work. While Volume 37 reports theses submitted in 1992, on occasion, certain uni versities do report theses submitted in previous years but not reported at the time.

In this dissertation, key aspects of the surface chemistry associated with atomic layer deposition (ALD) are discussed. ALD is a novel and promising film deposition technique that can deliver precise thickness control at the angstrom or monolayer level; the self-limiting aspect of ALD makes it a unique method that can lead to excellent step coverage and conformal deposition on high aspect ratio structures. In spite of its central role in efficient film deposition processes, little is known about the mechanisms of the chemical reactions involved. Even the most basic information, such as the initial surface reactions, is in many instances unknown. There is a limited knowledge on the surface chemistry (e.g., substrate, precursor's reactivity) effects for the growth of the films. Reactivity in ALD is controlled by the nature of the substrate, where specific nucleation sites are often responsible for the initial deposition and where a change in chemistry may take place as the first layer of the growing film is formed. The precursor's reactivity towards the surface being used and its properties are fundamental aspects in an ALD process. The majority of the experiments discussed in this dissertation are devoted to the elucidation of the reaction mechanisms of the thin films. The experiments are carried out using in-situ Fourier transform infrared spectroscopy (FTIR) in order to examine the chemical composition of surface adsorbates. The use of in-situ characterization techniques is crucial for better control and understanding of thin film deposition. Knowledge of the surface chemistry underpinning the ALD processes is essential in order to design precursors in a rational way that will lead to successful film growth.

Along with the unceasing development of the surface and material science, modification of substrates surfaces in nanoscale, to fabricate the functional materials with precisely controlled dimensions, refined composition and desired properties becomes crucial. In this report, atomic layer deposition (ALD), a vapor phase, sequential and self-limiting deposition process, has been used as an alternative strategy to modify the surface of materials and fabricates nanometer or micrometer level of functional materials with precise control. In the first part of this dissertation, ALD was used to modify the surface of the shape-engineered nanocrystals (SENCs), which enhanced the thermal stability of the SENCs from 300?C to 700?C and enhanced the catalytic activities of the nanocrystals as well. We also proposed a new reaction mechanism of metal-organic precursor with oxide surface, in which the conventional layered ALD growth does not happen but the oxide surface was modified via controlled metal doping. In the second part of this dissertation, ALD precursors were used to reacting with liquid substrates to fabricate freestanding solid thin films. Benefits from the unique reaction mechanism of the ALD metal-organic precursors, the thickness and the compositions of the fabricated films can be controlled. The fundamental of gas-liquid reaction has been discussed in this study. In the third part of this dissertation, area-selective ALD (AS-ALD) has been reported using carboxylic acid self-assembled monolayer as a growth inhibitor. Excellent selectivity of AS-ALD has been achieved by using this method, which could potentially be used in microfabrication as a substitution step for photolithography.

In the first part of this work, thin films of Al2O3 deposited via atomic layer deposition (ALD) are demonstrated to improve the thermal stability of cellulose nanocrystal (CNC) aerogels. ALD is a chemical vapor deposition (CVD) like method in which sequential precursor exposures and self-limited surface reactions produce a conformal thin film with precise thickness control. The conformal nature of ALD is well suited to coating the porous microstructure of aerogels. SEM micrographs of coating thickness depth profiles are shown to agree with trends predicted by precursor penetration models. Thermogravimetric analysis shows samples coated with ALD Al2O3 have increased decomposition temperatures. In the second part of this work, ALD zinc tin oxide (ZTO) is used to demonstrate a technique for measuring the substrate inhibited growth in multicomponent and laminate ALD systems. The thickness control of ALD makes it attractive for multicomponent and laminate systems. However, the surface reactions of ALD mean that the first few cycles, while the film nucleates, may have a different growth per cycle (GPC) than when the film is growing on itself in a bulk growth regime. A model for the substrate inhibited ALD of ZTO is derived from two complementary sets of laminates. The thickness and composition predictions of our model are tested against the bulk GPC of ZnO and SnO2. In the final part of this work, prompt inorganic condensation (PIC) is explored as a potentially more environmentally friendly alternative to ALD for planar thin film applications. Whereas ALD requires expensive vacuum systems and has low precursor utilization, solution based methods, such as PIC, allow atmospheric processing and precursor recycling. The water based PIC solutions use nitrate counter ions which evaporate at low temperatures. Combined with the low energy required to convert the hydroxide precursor clusters into an oxide film makes PIC a promising low temperature route to dense solution processed thin films. The dielectric performance of PIC Al2O3 is shown to be comparable to ALD Al2O3 films on Si though a large interfacial SiO2 layer is found to be dominating the behavior of the PIC films. This interfacial layer is shown to form very quickly (≤ 2 min) at low temperatures (≤ 50°C). This low temperature interfacial oxide growth could be a benefit in passivating solar cells.