Propagation of nanoscale ripples on ion-irradiated surfaces

Gnaser, Hubert; Reuscher, B.; Zeuner, A

doi:10.1016/j.nimb.2012.05.028

Cited by 25 publications

(11 citation statements)

References 40 publications

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“…In simulations, the traveling velocity υ r as well as the descending velocity υ ER was observed to remain almost unchanged during etching (0 < t < 120 s). Similar propagation velocities of parallel-mode ripples have been reported in IBS experiments as mentioned above using 30-keV Ga + beams: 70 θ i = 45°(λ r ≈ 400 nm, z r ≈ 150 nm]; 100 and υ r ≈ 77 nm/(10 17 ions cm −2 ) on SiO 2 at θ i = 52°(λ r ≈ 450 nm, z r ≈ 130 nm). 70,101 Note that the present υ r ≈ 5.5 nm/s corresponds to ≈ 1.3υ ER and to ≈ 55 nm/(10 17 ions cm −2 ).…”

Section: Effects Of Reduced Ion Reflection On Ripple Topography Ansupporting

confidence: 81%

“…of these time-varying top-and side-view images indicate that the surface features or ripples [characterized by four, three, two, and one wave crest(s)/trough(s) for r i = 1, 0.9, 0.85, and 0.8, respectively] move or travel laterally across the surface being etched in the direction of ion incidence (or in the x-direction), with the surfaces being moved vertically downward (or in the negative z-direction) through etching. The propagation of parallel-mode ripples in the ion incidence direction has so far been observed in several IBS experiments 70,[98][99][100][101] (although there is a recent exception), 102 which is opposite to the predictions of continuum models 71 and MC simulations 97,103-106 of the ion beam-induced ripple formation. This discrepancy may suggest that the ion-induced ripple formation and evolution and its topography and dynamics are largely affected by the ion reflection followed by re-impingement on feature surfaces, the effects of which have not been included in IBS models and simulations, 36,71,97 although they include surface processes such as ion-induced sputtering and surface diffusion of defects.…”

Section: Effects Of Reduced Ion Reflection On Ripple Topography Anmentioning

confidence: 91%

“…In plasma etching, the ion reflection was taken into account in continuum models and MC simulations for feature profile evolution, usually assuming specular reflection from feature sidewalls, to reproduce microtrenches formed at the corner of the feature bottom; 57-65 a few plasma beam and MC studies of Sawin et al suggested the importance of the effects of ion reflection on surface roughening and rippling; 5,25,[31][32][33] the ion reflection was also suggested as a possible explanation for the evolution of surface roughness during pulsed plasma etching. 28 In IBS, Hauffe suggested that the coarsening of terrace-like (or sawtooth-like) ripple structures is caused by reflected ions that re-impinge on the adjacent facets, 53 which was supported in several experiments [66][67][68][69] while not in some other experimental 70 and continuum model 71 studies; Bradley and Harper gave little more than comments on the effects of ion reflection on the ripple formation, in their pioneering theoretical study based on continuum equations; 40 a few classical molecular dynamics (MD) simulations were concerned with the step-edge sputter yields at high off-normal ion incidence arising from the ion reflection and re-impingement and with their effects on the ion surface channeling and ripple formation thereat. [54][55][56] We have investigated surface roughening and ripple formation during Si etching in Cl-based plasmas: 7,72-78 our MC-based three-dimensional atomic-scale cellular model (ASCeM-3D), mechanistically including the effects of ion reflection, simulated the roughening and rippling in response to ion incidence angle θ i .…”

Section: Introductionmentioning

confidence: 99%

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Origin of plasma-induced surface roughening and ripple formation during plasma etching: The crucial role of ion reflection

Hatsuse

Nakazaki

Tsuda

et al. 2018

Journal of Applied Physics

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Plasma-induced surface roughening and ripple formation has been studied based on Monte Carlo simulations of plasma-surface interactions and feature profile evolution during Si etching in Clbased plasmas, with emphasis being placed on the role and effects of ion reflection from microstructural feature surfaces on incidence. The simulation model included the effects of Cl + ion reflection (and/or its penetration into substrates) through calculating the momentum and energy conservation in successive two-body elastic collisions with substrate Si atoms every ion incidence. The "reflection coefficient r i " was then further introduced in the model (0 ≤ r i ≤ 1), representing the fraction of ions incident on surfaces with the reflection/penetration calculation scheme turned on. The coefficient r i is, in a sense, a measure of the reflection probability for impacts of an ion species onto Si surfaces relative to that for Cl + impacts. Simulations for ion incidence angles of θ i = 0°, 45°, and 75°onto substrate surfaces with incident energies in the range E i = 20−500 eV showed that as r i is slightly decreased from unity, the roughness decreases substantially, and the ripple formation fades away: the roughness remains at the low level of stochastic roughening during etching for decreased r i ≤ r i * ≈ 0.95−0.75 (the critical r i * tends to be lower at higher E i and θ i ) with no ripple structures at off-normal θ i . This elucidates that the ion reflection is indispensable in surface roughening and rippling during plasma etching, and their degree relies significantly on the reflectivity of ions. Simulations further showed that at intermediate off-normal θ i = 45°, the ripple wavelength increases significantly with decreasing r i , while the increase in amplitude is relatively less significant; thus, sawtooth-like ripple profiles pronounced for r i = 1 tend to be collapsed with decreasing r i . These effects of reduced ion reflection on plasma-induced surface roughening and ripple formation are discussed in terms of effectively enhanced smoothing due to neutral reactants, which competes with the roughening and rippling caused by ion bombardment. Published by AIP Publishing.

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Section: Effects Of Reduced Ion Reflection On Ripple Topography Ansupporting

confidence: 81%

Section: Effects Of Reduced Ion Reflection On Ripple Topography Anmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Origin of plasma-induced surface roughening and ripple formation during plasma etching: The crucial role of ion reflection

Hatsuse

Nakazaki

Tsuda

et al. 2018

Journal of Applied Physics

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“…For example, the CV model with the sinh approximation for the angle-dependent forward-directed mass transport predicts a transition from stability to instability at 45°ion incidence angle. Several experimental results show that pronounced parallel oriented ripple patterns already appear at angles between 30°and 45° [30][31][32][33][34]. Even Carter and Vishnyakov reported pronounced parallel oriented ripple patterns after 40 keV Ar and Xe ion irradiation of Si at 45° [35].…”

Section: Introductionmentioning

confidence: 99%

Surface instability and pattern formation by ion-induced erosion and mass redistribution

Hofsäß

2013

Appl. Phys. A

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The contribution of curvature dependent sputtering and mass redistribution to ion-induced self-organized formation of periodic surface nanopatterns is revisited. Ion incidence angle-dependent curvature coefficients and ripple wavelengths are calculated from 3-dimensional collision cascade data obtained from binary collision Monte Carlo simulations. Significant modifications concerning mass redistribution compared to the model of Carter and Vishnyakov and also models based on crater functions are introduced. Furthermore, I find that curvature-dependent erosion is the dominating contribution to pattern formation, except for very low-energy irradiation of a light matrix with heavy ions. The major modifications regarding mass redistribution and ion-induced viscous flow are related to the ion incidence angle-dependent thickness of the irradiated layer. A smaller modification concerns the relaxation of inward-directed mass redistribution. Ioninduced viscous flow in the surface layer also depends on the layer thickness and is thus strongly angle dependent. Simulation results are presented and compared to a variety of published experimental results. The simulations show that in most cases curvature-dependent erosion is the dominant contribution to surface instability and ripple pattern formation and also determines the pattern orientation transition. The simulations predict the occurrence of perpendicular ripple patterns at larger ion incidence angles, in agreement with experimental observations. Mass redistribution causes stabilization of the surface at near-normal ion incidence angles and dominates pattern formation only at very low ion energies.

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“…Experimental reports on ripple motion are comparatively few (e.g., Refs. [62,[66][67][68], reviewed, e.g., in Refs. [25,69]), there being even less where the direction of motion is correlated with the dominance of nonlinear effects and/or the stress distribution in the irradiated layer.…”

Section: B One-dimensional Systemsmentioning

confidence: 99%

Stress-driven nonlinear dynamics of ion-induced surface nanopatterns

2019

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For many solid targets, like semiconductors, that become amorphous under irradiation by energetic ions, the outermost surface layer displays formation of asymmetric nanoscale ripples in macroscopic timescales. In contrast to the well-known macroscopic case of an incompressible thin fluid film spreading down an incline, in which the morphological instability is controlled by gravity, here we prove that residual stress induced by the ions is responsible for pattern formation and accounts for its long-time dynamics, even in absence of sputtering effects. Using a continuum framework, we derive closed nonlinear evolution equations for the depth of the irradiated layer. This description includes novel terms associated with the spatial distribution of damage that builds up through sustained bombardment, thus extending to the nanoscale classic models of macroscopic fluidflow systems, and providing detailed information on the pressure and velocity fields within the irradiated layer. Numerical simulations reproduce the main dynamical features of surface nanopatterning under the assumed conditions, elucidating the ensuing nonlinear properties on ripple amplification and transport.

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Propagation of nanoscale ripples on ion-irradiated surfaces

Cited by 25 publications

References 40 publications

Origin of plasma-induced surface roughening and ripple formation during plasma etching: The crucial role of ion reflection

Origin of plasma-induced surface roughening and ripple formation during plasma etching: The crucial role of ion reflection

Surface instability and pattern formation by ion-induced erosion and mass redistribution

Stress-driven nonlinear dynamics of ion-induced surface nanopatterns

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