Effect of residual oxygen in Si(1 1 1)-7 × 7 surface on Si+ and Si2+ sputter yields

Effect of the residual oxygen impurity on the secondary ion yields in the sputtering from the Si(1 1 1)-7 × 7 surface bombarded by the 11 keV Ar0 neutral beam has been studied with use of a time-of-flight technique. Even if the oxygen concentration is much less than the detection limit of the present Auger electron spectrometer, not only Si+ and Si2+ ions but also SiO+ and SiO2+ ions have been significantly detected. As the oxygen ion yield, estimated from SiO+ and SiO2+ signals, increases, the Si+ yield is enhanced, whereas the Si2+ yield is reduced. The enhancement of the Si+ yield may be ascribed to the large electron affinity of O in comparison to that of Si, while the decrease in the Si2+ yield could be explained in terms of the inter-atomic Auger transition between O and one of the precursors for Si2+ (viz. an excited Si+ with a 2p hole, Si+∗), which efficiently interferes with the production of Si2+.