Acta Phys. -Chim. Sin. ›› 2010, Vol. 26 ›› Issue (11): 3030-3034.

• PHOTOCHEMISTRY AND SPECTROSCOPY •

XPS Study of the Thickness Nanosize Effect for Ultrathin SiO2 on Si Substrate

ZHAO Zhi-Juan, LIU Fen, ZHAO Liang-Zhong

1. Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
• Received:2010-04-27 Revised:2010-08-02 Published:2010-10-29
• Contact: LIU Fen E-mail:fenliu@iccas.ac.cn
• Supported by:

The project was supported by the Special Research Foundation of Commonweal Profession for Quality Inspection, China (200710199).

Abstract:

X-ray photoelectron spectroscopy (XPS) was used to record the Si 2p and valence band spectra for a series of ultrathin SiO2 on Si substrate with the oxide thickness (d) ranging from 1.45 to 7.2 nm. The thicknesses of these samples were measured precisely in the international key comparison. The results show that the samples with the oxide thickness of d<2 nm have a lower Si 2p binding energy (EB ). This has been attributed to the extra-atomic relaxation provided by both the polarization of the neighboring atoms of SiO2 and charge transfer from atoms of the Si substrate to the core holes created by photoionization (the screening distance was about (2.5±0.6) nm). The EB of Si 2p increased when d>3 nm and in this case extra-atomic screening was provided by the polarization of the neighboring atoms of SiO2. The sample with a smaller d showed a higher EB for Si 2p. The valence band structure is also related to the thickness nanosize effect. The samples with d<2 nm show a higher relative peak intensity of the O 2p non-bonding electrons and lower peak intensities for the O 2p—Si 3p and O 2p—Si 3s bonding electrons from SiO2.

MSC2000:

• O647