L.J.M. Selen

Strain measurements in ultra-thin buried films (<50 Å) with RBS ion channeling

A method has been developed to measure strain in ultra-thin (<50 A) buried films. The presence of the film leads to a step in the yield of the host crystal in a channeled RBS spectrum for off-normal crystal axes. The size of this step depends on the flux distributions in the channel, which in turn depend on the angle ψ between the incoming beam and the crystal axis. Two maxima in the step size appear as a function of the angle ψ. Monte Carlo (MC) simulations have been used to interpret the experiments.

Channeling on boron clusters in silicon

Low energy ion implantation at high doses of boron (>1015 cm−2) in Si is necessary for the fabrication of ultrashallow junctions but can result in the undesirable presence of boron clusters. Values for the dimensions of the lattice distortions in the implanted Si are obtained by comparing the enhanced dechanneling and the direct scattering peak in the region with clusters in a channeled Rutherford backscattering spectrometry spectrum to those from Monte Carlo calculations on a curved crystal structure. Values of about 0.17 and 65 nm are found for the maximum deformation and the length of the distortions in the crystal, respectively, which implies that the lattice distortions extend significantly outside the layer in which the B clusters are supposed to be present.

Planar ion-channeling measurements on buried nano-films

Planar MeV ion-channeling measurements on 2.2 nm thick Si1-xGex nano-films buried in Si are presented. The presence of the nano-film leads to a step in the yield of the host crystal in a {0 1 1} planar channeled RBS spectrum. In previous work we showed that with the help of Monte Carlo (MC) simulations the step height in axial channeling measurements provides useful information on the tetragonal distortion in buried nano-films. Since the step height is larger for planar channeling measurements, we extend this method to planar channeling in the present work. The measurements show that the flux distribution of channeled ions is not in statistical equilibrium, but still oscillates at the depth of the buried films (about 280 nm), This is confirmed by simulations performed with the MC simulation code FLUX and a qualitative understanding is obtained for the observed phenomena. The accuracy of the calculated step height curves appears much more sensitive to the choice of ion-atom potential than those from axial channeling, which can be attributed to the non-equilibrium distribution of channeled ions between the planes. Consequently, from planar channeling measurements, the tetragonal distortion can be determined with about the same accuracy as from axial channeling measurements in spite of the higher steps

Planar MeV ion channeling on strained buried nanofilms

Planar MeV ion channeling experiments have been used to characterize a buried Si1-xGex film with a thickness of 2.2 nm in a silicon host crystal. The tetragonal deformation in the film shows up as a translation of the {011} planes across the film, which was measured as a step in the yield of the planar channeled Rutherford backscattering spectra. The flux distribution between the planes acts as a probe for the position of the planes. The angular dependence of the step height has been measured for different incident ion energies and interpreted with Monte Carlo calculations. Simulations only resemble the measured spectra when the Hartree-Fock potential is used for the ion-atom interaction. The translation of the planes can be measured with an accuracy of approximately 10%, which is comparable to results obtained with axial channeling experiments

Transmitted ion energy loss distributions to detect cluster formation in silicon

Abstract The energy loss distribution of ions transmitted through a 5.7±0.2 μm thick Si crystal was measured and simulated with the Monte Carlo channeling simulation code FLUX . A general resemblance between the measured and simulated energy loss distributions was obtained after incorporation of an energy dependent energy loss in the simulation program. The energy loss calculations are used to investigate the feasibility to detect the presence of light element dopant clusters in a host crystal from the shape of the energy loss distribution, with transmission ion channeling. A curved crystal structure is used as a model for a region in the host crystal with clusters. The presence of the curvature does have a large influence on the transmitted energy distribution, which offers the possibility to determine the presence of dopant clusters in a host crystal with transmission ion channeling.

Ion-channeling analysis of boron clusters in silicon

We have measured axially channeled Rutherford backscattering spectra of Si1−xGex nanofilms in silicon(001). A step in the yield of the host crystal was found for off-normal axes at the depth of the nanofilm. The step was measured as a function of the angle between the incoming beam and the [011] axis and shows two maxima. It is found that Monte Carlo simulations assuming tetragonal distortion reproduce the experimental results. A universal curve was derived which enables determination of the tetragonal distortion from ion-channeling experiments, for a given film thickness. The results are compared with XRD measurements.