Swelling as a stabilizing mechanism in irradiated thin films

Abstract

Irradiation of semiconductor surfaces often leads to the spontaneous formation of rippled structures at certain irradiation angles. However, at high enough energies, in the keV range, these structures are sometimes observed to vanish for all angles, despite the absence of any identified, universally-stabilizing physical mechanisms in operation. Here, we examine the effect on pattern formation of radiation-induced swelling, which has been excluded from prior treatments of stress in irradiated films. After developing a suitable continuum model, we perform a linear stability analysis to determine its effect on stability. Under appropriate simplifying assumptions, we find swelling indeed to be stabilizing at all angles for wavenumbers typical of experimental observations. Therefore, this mechanism may account for the suppression of ripple formation observed at energies over 1 keV.

Swelling as a stabilizing mechanism in irradiated thin films: III. Effect on critical angle in a composite model

“…In the present work, we conclude an ongoing investigation [37,38] into the potential role of ion-induced swelling (IIS) in explaining the variety of observed phenomena. We develop a model in the so-called 'hydrodynamic' class, which has recently shown promise in reaching agreement between experiment and theory [34,36,45], that combines the effects of both APF and isotropic IIS, along with a proposed experimental method for estimating the relative strength of these two effects.…”

“…However, this mechanism has not typically been included in studies of ion-induced pattern formation. It was first suggested as a stabilizing mechanism in [37], and shown to be stabilizing at all angles of incidence in the limit of small swelling rates. That analysis was extended to arbitrary swelling rates in [38], where it was then suggested that swelling could potentially modify θ c in an ion-, target-, and energyspecific manner.…”

“…Indeed, within the gradual regime, such mechanisms as stress buildup and relaxation, surface diffusion, and viscous flow may occur [21][22][23][24][25][26][27][28][29][30][31][32][33]. Many other mechanisms have been suggested to act in this regime to influence pattern formation, such as effective body forces [34,35], anisotropic plastic flow (APF) [36], and isotropic swelling [37,38]. Because these mechanisms are slower, smaller in length-scale and active within the amorphous bulk, they may be more difficult to experimentally observe when compared with prompt-regime surface phenomena.…”

Ion-induced nanopatterning of silicon: Toward a predictive model

“…Recently, inspired by images of expanding bubbles in cross-sectional TEM images such as those found in the work of Chini et al, 33 Swenson and Norris studied the effect of ion induced swelling, an effect omitted from prior treatments of (purely shear) stress. 166 Under appropriate simplifying assumptions, these authors found that swelling could indeed be stabilizing at all angles for wavenumbers typically observed in experiments. This mechanism may therefore be useful in reconciling experiments with theory at ion energies above 1 keV.…”

Special issue on surfaces patterned by ion sputtering

“…The experimental results are compared with predictions based on analytical descriptions and binary collision simulations in the initial linear stages [9], and with a nonlinear partial differential equation in the nonlinear stage [10], respectively. The mechanisms acting during IBS are also explored theoretically in [11]. Specifically, the suppression of pattern formation for all incidence angles at high energies under suitable conditions in the keV range is studied here using a viscous flow model, suggesting the stabilization of the surface for large dwell times (defined as the ratio between the ion induced fluid thickness and the erosion rate).…”