Order enhancement and coarsening of self-organized silicon nanodot patterns induced by ion-beam sputtering

Abstract

The temporal evolution of the characteristic wavelength ͑͒ and ordering range ͑͒ of self-organized nanodot patterns induced during Ar + ion beam sputtering on Si͑001͒ and Si͑111͒ surfaces is studied by atomic force microscopy and grazing incidence x-ray diffraction. The patterns exhibit initial coarsening of ͑up to 54-60 nm͒ and increase in ͑up to 400-500 nm͒ after which both features stabilize. The pattern formation is only weakly controlled by the crystallographic surface orientation, Si͑111͒ surfaces showing a faster evolution into a proper stationary state. This trend is attributed to a higher sputtering rate at this orientation, as confirme by theoretical simulations. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2398916͔The current road to miniaturization demands for lowcost and large-scale compatible nanopatterning methods with reproducible and controllable features, achievement of high in-plane ordering being a crucial issue, e.g., for ͑opto͒elec-tronic devices.1 Ion beam sputtering ͑IBS͒ is a promising technique since it induces self-organized regular patterns over large areas ͑several cm 2 ͒ onto metal, semiconductor, and insulator surfaces after a few minutes of irradiation.2 In particular, ripple 3 and nanodot 4 morphologies can be produced onto amorphous materials or crystalline surfaces that amorphize upon ion bombardment. Theoretically, pattern formation by IBS can be understood as the interplay between the ͑unstable͒ dependence of the sputtering yield on surface curvature and stabilizing surface relaxation mechanisms such as surface diffusion. 5Complete understanding and control of the physical mechanisms involved in pattern formation by IBS is still lacking, issues such as crystallinity, in-plane correlation, and order remaining to be understood. Here, we study the time evolution of the quality of nanodot patterns induced by IBS onto the relevant Si͑001͒ and Si͑111͒ surfaces, in terms of in-plane order and correlation. Our results indicate that the pattern dynamics is qualitatively independent of the surface orientation, together with the occurrence of coarsening of the characteristic wavelength and simultaneous improvement of the short-range hexagonal order ͑as described by the correlation length ͒. Both features stabilize for long enough times, the Si͑111͒ surface reaching earlier a proper stationary state as a result of its faster dynamics. We correlate this fact with the increased sputtering rate ͑SR͒ measured onto this orientation, which is confirme through comparison with theoretical models of IBS pattern formation.Si͑001͒ and Si͑111͒ samples ͑p type, 0.3-1 ⍀ cm͒ were sputtered at normal incidence as described in Ref. 6. The SR was determined experimentally in all the processed samples by partially masking them during the sputtering process and measuring the resulting step edge height with a profilomete . It was observed that the SR was ϳ10% higher for Si͑111͒ than for Si͑001͒. The resulting surface topography was imaged by atomic force microscopy ͑AFM͒ with a Nanoscope IIIa equipm...

Universal non-equilibrium phenomena at submicrometric surfaces and interfaces

“…for 4 h., which is favorably compared in panel (a) of the same figure with the result provided by numerical integration of equation (9). The main stages of evolution are similar to those described for the KS equation (5), with the difference that now there is coarsening of the main pattern wavelength at intermediate times (not shown in the figure, see also [56]) and the dot pattern shows short-range hexagonal ordering, as evidenced by the height autocorrelation shown in figures 6(a) and (b). The wavelength coarsening prior to the stationary state can be perhaps more easily visualized under oblique incidence conditions, when the pattern has a rippled shape.…”

Observation and Modeling of Interrupted Pattern Coarsening: Surface Nanostructuring by Ion Erosion

“…This is also reflected in the PSD curves where the power-law regime at low-k values is broader for the sample bombarded at high flux values (È 3 ) confirming its faster dynamics. The result that the asymptotic morphologies are not affected by the dynamics contrasts with the trend obtained in [31], where a higher erosion rate and a thermal relaxation mechanism led to slightly smaller ' f values and a less defined pattern order for different crystallographic orientations. The observed discrepancy may be explained taking into account the different target temperature reached during irradiation.…”

“…The observed discrepancy may be explained taking into account the different target temperature reached during irradiation. In particular, from the measurement of the etched depth after irradiation, it is noted that the estimated flux employed in [31] was nearly 3 times the maximum value used here, which might have raised the target temperature enhancing thermally activated surface diffusion. In summary, for the specific case of IBS nanostructuring, we have been able to describe the full dynamics of an experiment by a single continuum equation.…”

Nanostructures on fused silica surfaces produced by ion beam sputtering with Al co-deposition

“…The coarsening of the patterns on the Si surface is due to the simultaneous Al deposition during IBS. Such coarsening is different from previously reported coarsening with increasing sputtering time [7,9,12,[63][64][65]. Although some theoretical work has explained the coarsening based on numerical models [66,67], a model and simulation that can accurately predict the coarsening due to the impurity co-deposition remains unavailable at this time.…”