Ripple structure of crystalline layers in ion-beam-induced Si wafers

Abstract

Ion-beam-induced ripple formation in Si wafers was studied by two complementary surface sensitive techniques, namely atomic force microscopy (AFM) and depth-resolved x-ray grazing incidence diffraction (GID). The formation of ripple structure at high doses ͑ϳ7 Ã 10 17 ions/ cm 2 ͒, starting from initiation at low doses ͑ϳ1 Ã 10 17 ions/ cm 2 ͒ of ion beam, is evident from AFM, while that in the buried crystalline region below a partially crystalline top layer is evident from GID study. Such ripple structure of crystalline layers in a large area formed in the subsurface region of Si wafers is probed through a nondestructive technique. The GID technique reveals that these periodically modulated wavelike buried crystalline features become highly regular and strongly correlated as one increases the Ar ion-beam energy from 60 to 100 keV. The vertical density profile obtained from the analysis of a Vineyard profile shows that the density in the upper top part of ripples is decreased to about 15% of the crystalline density. The partially crystalline top layer at low dose transforms to a completely amorphous layer for high doses, and the top morphology was found to be conformal with the underlying crystalline ripple.The formation of periodic ripple or a wavelike pattern with a spatial periodicity varying from nm to µm range on obliquely ion-bombarded solid surfaces has become a topic of intense research in the context of fabrication of nanoscale textured materials, 1 such as templates for growing nanowire, nanorods, or nanodots. Ion-induced ripples are thought to be produced by interplay between a roughening process caused by the ion-beam erosion (sputtering) of surface and a smoothening process caused by thermal or ion-induced surface diffusion. [2][3][4] The balance between positive surface diffusion and negative surface tension develops instability along the projection of the ion beam and also perpendicular to it, leading to ripple formation in both directions. However, experimentally observed ripple structure has the direction for which the growth rate is largest and is generally along the projection of the ion beam, consistent with current theoretical models. [1][2][3] It is an established fact that monocrystalline semiconductors may be rendered amorphous, easily compared to crystalline metals under room-temperature keV energy heavy-ion (such as Ar) impact. 5 However, our conventional wisdom on ion-solid interaction does not answer the question whether the amorphous/crystalline interface underneath the top surface maintains its planarity when the semiconductor surface under oblique ion bombardment transforms its initial flat geometry to a corrugated one. This is a relevant question in accounting for the extent of the disordered zone responsible in the smoothening mechanism by viscous relaxation assumed in some recent models 6 of ripple formation in semiconductors. Interestingly, quite recently, 7 a cross-sectional transmission electron microscopy (XTEM) study on an obliquely incident (50-120) keV Ar + bombarded Si s...

Wavelength tunability of ion-bombardment-induced ripples on sapphire

“…Similar behavior of surface amorphization under ion bombardment has been noted in the study of ion sputtered Si and InP. 16,29 The key idea of the IVF model is that this thin layer can relax by a collective motion ("flow"), driven by surface tension.…”

THz radiation by amplitude-modulated self-focused Gaussian laser beam in ripple density plasma

“…This kind of density ripple can be created by different techniques (Hazra et al, 2004;Pai et al, 2005;Layer et al 2007;Liu et al, 2008). The laser propagates in the z-direction and polarized in the x-direction.…”

Investigations of ripple pattern formation on Germanium surfaces using 100-keV Ar+ ions

“…This is minimum at 75° incidence angle due to lesser ion interaction with the surface atoms and also a decrease in ion-induced diffusion. It is well reported in literature that low-energy ion beam irradiation leads to amorphization of surfaces due to creation of point defects through collision cascades, and further irradiation induces the restructuring of the amorphous layer in the form of nanostructures such as dots or ripples depending on the angle of incidence of the ion beam [32].…”