Nonuniversality due to inhomogeneous stress in semiconductor surface nanopatterning by low-energy ion-beam irradiation

Abstract

A lack of universality with respect to ion species has been recently established in nanostructuring of semiconductor surfaces by low-energy ion-beam bombardment. This variability affects basic properties of the pattern formation process, like the critical incidence angle for pattern formation, and has remained unaccounted for. Here, we show that nonuniform generation of stress across the damaged amorphous layer induced by the irradiation is a key factor behind the range of experimental observations, as the form of the stress field is controlled by the ion/target combination. This effect acts in synergy with the nontrivial evolution of the amorphous-crystalline interface. We reach these conclusions by contrasting a multiscale theoretical approach, which combines molecular dynamics and a continuum viscous flow model, with experiments using Xe + and Ar + ions on a Si(100) target. Our general approach can apply to a variety of semiconductor systems and conditions.

Ion damage overrides structural disorder in silicon surface nanopatterning by low-energy ion beam sputtering

“…In ref. [32], an equivalence between near-normal and grazing incidence conditions has been established for the bulk damage. Namely, the stress distribution under oblique incidence follows from that at a different condition (e.g.…”

“…Thus, the rearrangements induced by sustained IBS eventually govern its atomic structure, independently of its previous history. Within the ioninduced viscous flow theory for low-energy IBS [18,32,33], ripple formation is controlled by the relaxation of such a damaged surface layer, once it is formed. This is driven by the large ion-induced residual stress which occurs for the present range of energies, as predicted by Davis' model [18,26].…”

Stress vs sputtering effects in the propagation of surface ripples produced by ion-beam sputtering

“…From a physical viewpoint, stress generation coexists with sputtering in tailoring the resulting process. The former seems to be more relevant for ion-incidence angles close to the threshold angle for ripple formation [4]; the latter becomes relatively more important as the width of the amorphous layer (and hence the accumulated stress) is reduced, namely, at grazing incidence [5].…”

“…This important role for stress has been recently implemented into a continuum model for the evolution of the surface [2], which for Si irradiation has received experimental support with respect to e.g. the ion-energy dependence of the typical sizes of the patterns appearing [3,4]. From a physical viewpoint, stress generation coexists with sputtering in tailoring the resulting process.…”

“…Interestingly, one of the predictions of the ion-induced solid flow theory is that different states of stress involve different scenarios for pattern formation [4]. Namely, depending on the relative values of stress at the free and amorphous-crystalline (a-c) interfaces, the pattern formation process can occur in such a way that either: (i) Ripples form only for h > h c as for the experiments mentioned on Si; since this behavior cannot be predicted by the classical Bradley-Harper (BH) theory [11], this is termed a non-BH type scenario.…”