(646d) Surface Chemistry for the Growth of Epitaxial Oxide Layers on Si(001)-2x1

The growth of nanometer thin epitaxial oxide layers on semiconductor substrates is of interest for new materials including heteroepitaxy layers and high permittivity dielectrics. Literature reports have demonstrated that high quality epitaxial interfaces can be achieved for SrTiO3 (STO) grown on Si(001)-2x1 by molecular beam epitaxy methods. It would be advantageous if these materials could be grown by chemical means such as MOCVD or ALD; such methods could open new process windows or lead to new applications for these materials. In order to grow epitaxial STO layers, it is necessary to template the Si(001)-2x1 surface with a SrO monolayer. The template layer prevents silicon oxidation and preserves the crystalline order for subsequent STO growth. This paper presents a methodology for the chemical growth of the SrO template layer and discusses the surface chemistry and precursor chemistry issues. Growth is initiated by the desorption of a SiO2 chemical oxide in UHV to prepare a clean Si(001)-2x1 surface. The Si(001)-2x1 surface is subsequently reacted with H2O to prepare a 1/2 ML hydroxyl-terminated surface. These hydroxyl sites are hypothesized to be reactive sites for the alkaline earth metal organic precursor, Sr(tmhd)2. AES and LEED data show evidence for a successful reaction and 2x1 order is maintained for at least the first reaction cycle. Further ALD style reaction cycles to increase the surface coverage lead to undesirable carbon buildup on the surface and the loss of crystalline order by LEED data. In contrast, co-dosing Sr(dpm)2 with H2O does not increase the carbon signal, and therefore the carbon is not intrinsic to the surface reaction. Single molecule resolution UHV-STM studies combined with DFT quantum chemistry models of silicon clusters show that the free precursor ligand (tmhdH) adsorbs with near unity sticking probability on the Si(001)-2x1 surface. Multiple adsorbate configurations are observed for this multifunctional molecule, and these structures are assigned based on a combination of STM and DFT data. Temperature programmed desorption studies of tmhdH show no desorption products other than hydrogen, and decomposition of tmhdH leads to surface carbon. The results suggest that free ligand may cause carbon deposition during growth, and this motivates study of the vaporization chemistry. A novel solid source vaporizer has been implemented for this work, and the vaporization chemistry will be discussed in the context of the surface chemistry and growth reaction.