Oxidation of the Si(111) (7×7) surface: Electron energy loss spectroscopy, low-energy electron diffraction, and Auger electron spectroscopy studies

Abstract

High-resolution vibrational/electronic-transition electron energy loss spectroscopy, low-energy electron diffraction, and Auger electron spectroscopy have been used to study the oxidation of the Si(111) (7×7) surface at 300 K. From the initial stage (O2 exposure ∼1 L, fractional oxygen coverage θ∼0.2), an Si–Si bond breaking occurs, and atomic oxygen is adsorbed in the bridge site (between the first and second layers of Si substrate) as well as in the on-top site. Some molecular species (superoxide-like species) are also existent. With the increase in O2 exposure up to 100 L where θ∼1.5 is reached, the number of the Si–O–Si species in the selvedge region of Si substrate is greatly increased. By heating the surface pre-exposed to 1–100 L O2 at 850 K, the superoxide-like species are removed and the number of oxygen atoms in the on-top sites is decreased. With the increase in O2 exposure (0→100 L) and by heating (300→850 K), the bond angle of the Si–O–Si species is increased towards that of the vitreous SiO2. The Si oxide which is totally characteristic of vitreous SiO2 is not formed by exposing the Si(111) surface kept at 700 K to 10 000 L (10−5 Torr×103 s) oxygen. The effect of residual water–vapor adsorption has been carefully examined and minimized.