Characterization of the interface of high-k praseodymium oxide thin films on silicon surfaces

The goal of this project has been to investigate, at the atomic scale and from the very early stage, the growth of praseodymium oxide on silicon (111) and (001) oriented substrates. The study focuses on characterizing the structural, chemical, and electronic properties of Pr2O3 deposited on both Si(111) and Si(001) substrates, with emphasis on the latter, which is of more technological importance. This rare-earth oxide has been considered recently as a good "high-k'' candidate to substitute SiO2 as a gate oxide in CMOS transistors for further down scaling of devices. In this process, surfaces and interfaces begin to dominate the silicon device performances, due to the large surface to volume ratio. While the surfaces and interfaces are of increasing importance for electronic devices, such low-dimensional structures are difficult to study. In this context, brilliant synchrotron radiation is a valuable tool, which we employed here for X-ray diffraction and photoelectron spectroscopy analysis. The obtained results are complemented by other surface science techniques such as scanning tunneling microscopy, Auger electron spectroscopy, and low energy electron diffraction. It is found that an epitaxial hexagonal Pr2O3 layer can be grown on the (111) surface. On the (001) surface, an ultra thin layer of cubic Pr2O3 is covered by Pr-silicate upon further growth. Since the atomically clean surfaces are the starting point for the growth, they have been characterized as well. In particular, the atomic structure of the Si(001)-2x1 reconstructed surface has been analyzed.