Atomic Registry at the Pt-Si Interface Studied by Transmission Channeling RBS

ABSTRACTTransmission channeling Rutherford scattering of MeV ions is one of the only techniques which can probe the atomic registry at a “buried” internal interface between a thin film and single-crystal substrate. Interfacial intermixing, dislocations, and reconstruction can be observed at concentrations above ∼ 3×1015 atoms/cm. The physical basis for this measurement is the “flux-peaking” effect, which is well known in conventional ion channeling as a method to determine the lattice location of dilute impurities. Transmission channeling is conceptually similar, but the scattering arises from the interface at the exit side of a thin single crystal sample rather than from a volume effect.In this work, we apply transmission channeling to measure the low temperature intermixing between Pt and Si. In a previous study, we suggested that a disordered interface forms prior to crystalline suicide formation. The present results are a quantitative measurement of the area density of Si which intermixes with Pt at 150°C. Experiments are performed using 80A Pt layers e-béam deposited onto 1–2μm thick single crystals of Si(100) and (111) following various interfacial cleaning procedures. We find that >1×1016 Si atoms/cm2 are displaced from their lattice sites after Pt deposition, increasing to ∼2×1016/cm2 upon annealing to 150°C. The room temperature intermixing of >6 monolayers of Si is large, but not inconsistent with existing studies of the Pt - Si reaction. The transmission channeling measurement includes any Si segregated at grain boundaries or the free surface as well as the interface. No systematic differences are observed as a function of substrate orientation or cleaning procedure.