Effect of residual oxygen on ionization processes of Si + and Si 2+ sputtered from Si(1 1 1)-7 × 7 surface

Abstract

The effect of residual oxygen impurity on ionization processes of Si + and Si 2+ has been studied quantitatively. In this study, ion sputtering experiments were carried out for a Si(1 1 1)-7 × 7 surface, irradiated with 9–11 keV Ar 0 and Kr 0 beam. Even if the oxygen concentration is less than the detection limit of Auger electron spectrometry, SiO + and SiO 2 + ions have been appreciably observed. Moreover, as the SiO + and SiO 2 + yields increases, the Si + yield is slightly enhanced, whereas the Si 2+ yield is significantly reduced. From the incidence angle dependence of secondary ion yields, it is confirmed that Si +* (Si + with a 2p hole) created in the shallow region from the surface exclusively contributes to Si 2+ formation. By assuming that the SiO + and SiO 2 + yields are proportional to the residual oxygen concentration, these observations are reasonably explained: The increase of Si + with the increase of residual oxygen is caused by a similar effect commonly observed for oxidized surfaces. The decrease of Si 2+ yield can be explained by the inter-atomic Auger transition between the residual oxygen impurity and Si +*, which efficiently interferes the Si 2+ formation process.