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.