Ripple pattern formation on silicon surfaces by low-energy ion-beam erosion: Experiment and theory

Abstract

The topography evolution of Si surfaces during low-energy noble-gas ion-beam erosion (ion energy $\ensuremath{\leqslant}2000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) at room temperature has been studied. Depending on the ion-beam parameters, self-organized ripple patterns evolve on the surface with a wavelength $\ensuremath{\lambda}<100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Ripple patterns were found to occur at near-normal ion incidence angles (5\ifmmode^\circ\else\textdegree\fi{}--30\ifmmode^\circ\else\textdegree\fi{}) with the wave vector oriented parallel to the ion-beam direction. The ordering and homogeneity of these patterns increase with ion fluence, leading to very-well-ordered ripples. The ripple wavelength remains constant with ion fluence. Also, the influence of ion energy on the ripple wavelength is investigated. Additionally it is shown that the mass of the bombarding ion plays a decisive role in the ripple formation process. Ripple patterns evolve for ${\mathrm{Ar}}^{+},{\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ ions, while no ripples are observed using ${\mathrm{Ne}}^{+}$ ions. These results are discussed in the context of continuum theories and by using Monte Carlo simulations.