Molecular dynamics simulations of sub-10 nm wavelength surface rippling by ion beams

Abstract

Molecular dynamics simulations have been carried out to examine the etching of Si by 200 eV ions at varying angles of incidence. The formation of a ripple-like morphology perpendicular to the direction of ion bombardment was observed as the bombarding angle was moved away from normal incidence to ∼50°. The wavelengths of these initial morphologies were on the order of 5 nm and fluctuated in shape over the course of bombardment. As the incidence angle was increased to 80° off-normal and above, a clear transition was observed to ripple formation parallel to the direction of ion bombardment. The ripples formed at 80° bombardment have a wavelength of ∼2.5 nm and show much greater stability than those at 50° and persist and grow in amplitude over the course of bombardment. We discuss the possible formation mechanisms of these ripples, including local micro-masking and interpretation in terms of the Bradley–Harper (Bradley and Harper 1988 J. Vac. Sci. Technol. A 6 2390) theory of sputtering-induced surface ripples.