Yuji Kataoka oral presentation (FN1-Mon4-2-4)
Influence of the amorphous/crystalline interface on ion-beam-induced surface roughening of Si(001)
Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, 243-0197 Atsugi, Japan
Ion beam bombardment is a well-establish technique for controlling the physical and chemical states of a solid surface. In particular, oxygen ion bombardment at high fluences forms a synthetic oxide layer on a solid surface. The oxidation technique is commonly used to enhance the fraction of positively charged ions emitted from the bombarded surface in secondary ion mass spectrometry (SIMS). The bombardment conditions are, however, limited to near-normal incidence because oblique incidence causes the surface roughening. Patterns consisting of a series of ripples are known to be formed under oblique bombardment. Various theories based on Sigmund's model have been proposed and extended with the observations of surface morphology changes using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experimental results previously reported are not entirely explained by the theoretical models. On the other hand, another interesting and recent model concerning the pattern dynamics has been proposed. The model suggests that the amorphous/crystalline (a/c) interface may play a relevant role in the ripple formation. The formation of ripples at top surface is a consequence of mass rearrangement at the a/c interface induced by incompressible solid flow inside the amorphous layer.
In this study, the dependence of the a/c interface on the ripple formation was investigated using crystal truncation rod (CTR) scattering with synchrotron x-ray. The CTR scattering can provide information on the lattice boundary at crystal surface and also on the interface boundary on an atomic scale. The surfaces of Si(001) were bombarded with 5 keV O2+ at impact angles of 0° and 60° with respect to the surface normal. The O2+ beam was raster scanned over an area of 1000 × 1000 μm2 in the (x0, y0) plane normal to the beam axis. The beam current was 1 μA. 30Si+ ions were detected, and the variations of the signals were monitored during the bombardment. The bombardment was stopped before the signals of 30Si+ were changed due to the surface roughening. The CTR scattering measurements were performed on the beam bombarded area. The Si(11L) CTR on SiOx/Si(001) interface was explored with a x-ray wavelength of 1.16 Å. The intensity distributions of the CTR suggested that the oblique incidence forms a complicated interface layer consisting of amorphous and crystalline silicon and the interface layer leads to the surface roughening.
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