Molecular dynamics simulations of sub-10 nm wavelength surface rippling by CF₃⁺ ion beams

Molecular dynamics simulations have been carried out to examine the etching of Si by 200 eV CF+3 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.