Transient sputtering of an amorphous Si surface under low energy O ₂⁺ ion bombardment

The transient sputtering of an amorphous Si surface with 500 eV O ₂⁺ ion bombardment at surface normal incidence was studied via the in-depth composition profiles for the incorporated oxygen and the sputtering yield change in Si, which were obtained from in situ medium energy ion scattering spectroscopy. As ion doses are increased, the Si surface is thickly oxidized, and the sputtering yield is rapidly reduced. At the initial stage of the sputtering, owing to an incorporation rate of oxygen higher than the sputtering rate of Si, the surface is gradually swelled by the ion dose of ∼1.5 × 10¹⁶ O₂⁺ ions/cm². A dynamic Monte Carlo calculation, which takes into account both swelling and diffusion effects, has also been carried out to understand the underlying mechanism of the transient processes. In particular, we calculated the sputtered depth as a function of ion dose, and the secondary ion mass spectroscopy depth profiling showed a transient shifting of 2.7 nm to the thicker depth.