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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P280
High resolution grazing incidence diffraction on lateral nanostructures created
by focused ion beam implantation on semiconductor surfaces
Joerg Grenzer 1 , Lothar Bischoff 1 , Ullrich Pietsch 2
1 Forschungszentrum Rossendorf e.V., Institute of Ion Beam Physics and Materials
Research, P.O.Box 51 01 19, D-01314 Dresden – 2 Institute of Physics, University of
Siegen, Walter Flex 3, 57078 Siegen
Ion beam implantation is one of the major technologies in the semiconductor industry.
Although there have been a lot of technological applications, there is relatively little
known about the structural changes of semiconductors after ion beam implantation at
low doses. The focused ion beam implantation technique opens a way to manipulate
the device structure locally, on a length scale of a few 10 nm. Of particular interest is
the creation of lateral nanostructures by writing any pattern directly into the substrate.
We report on the strain and defect analysis of two dimensional dot lattice structures
that were produced in GaAs and Si (001) substrates using a 10 14 cm −2 dose Ga +
focused ion beam at an energy of 25 keV. The spot size of the focused ion beam was
below 50 nm. The structural analysis of the samples was performed utilizing the method
of high resolution X-ray grazing-incidence diffraction at the ID01 and ID10 beam lines
of the ESRF.
X-ray grazing incidence diffraction is a scattering method which combines in-plane
Bragg diffraction and out-of plane reflectivity under the condition of X-ray total external
reflection from crystalline surfaces. The formation of an evanescent wave propagating
parallel but close to the sample surface opens the possibility to probe crystalline
surface structures. Moreover, it is possible to change the X-ray penetration depth by
tuning the incidence angle in the vicinity of the critical angle αc (the angle at which
the X-ray wave starts to penetrate the sample). The use of a laterally periodic wire
structure generated on cubic materials makes possible a separate analysis of strain
and damage profiles by measuring two symmetry-equivalent in-plane Bragg reflections.
Additionally, periodic structure allows us to measure very low strain fields.
We performed a detailed structural analysis of the implanted nanostructures that have
a small modulation of the lattice constant only and do not possess any measurable
density contrast. Therefore, such studies, operating at the resolution limit, are only
possible using very high brilliant beam lines at 3rd generation synchrotrons.