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Keywords:
high-index Si surface; in situ measurement; oxidation; scanning tunneling microscopy (STM)
Abstract
Thermal oxidation of Si(l 13) in a monolayer regime was investigated using high-temperature scanning tunneling microscopy (STM). Dynamic processes during thermal oxidation were examined in three oxidation modes - oxidation, etching, and transition modes - in the third of which both oxidation and etching occur. A precise temperature-pressure growth mode diagram was obtained via careful measurements for Si(l 13). and the results were compared with those for Si(lll) in the present work and Si(001) in the literature. Initial oxidation processes were identified based on high-resolution STM images.
Introduction
High-index silicon surfaces have drawn considerable interest for their usefulness in three-dimensional metal oxide semiconductor field-effect transistors (MOSFETs) [1]. Here, formation processes of ultrathin SÍO2 at the interface are considered to be quite important in determining its dielectric properties. To study procedures to fabricate gate dielectrics, it will be necessary to understand thermal oxidation on silicon surfaces as well as metal-induced oxidation and silicidation [2]. Nevertheless, dynamic processes in oxidation have been studied scarcely so far. especially for high-index silicon surfaces. The study of the oxides grown on high-index silicon surfaces is of great significance because the corners of the Fin-type FETs should have such surfaces, where the electric field is enhanced, which significantly affects the device performance [3].
Recently, the observation of oxidation at the atomic level in both real time and real space has been recognized as an important experimental challenge toward elucidating the dynamic processes in oxidation. For example, the formation processes of iron oxide nanoparticles have been studied in detail using stateof-the-art X-ray scattering methods [4]. As a complementary method, variable-temperature scanning tunneling microscopy (VT-STM) has been used as the ideal tool to investigate reaction dynamics on surfaces. In our previous studies, we applied our VT-STM to investigate hydrogen diffusion [5] and titanium silicide formation [6] on Si(001).
In our previous studies of oxidation on Si( 113). we investigated the electronic states of the Si 2p and O Is core levels in detail during thermal oxidation using high-resolution X-ray photoelectron spectroscopy with synchrotron radiation [7-9]. Using a state-of-the-art wet oxidation procedure, we also reduced the interface trap density (Dit) at the SiCU/Si interface on the Si(l 13) substrate dramatically,...