Self-Assembled Manganese And Manganese Silicide Nanostructures On Si Restructured Surfaces

Self-assembled nanostructures are of special significance in the next generation of electronic devices because the size limit of lithographic methods in the convetional microelectronics progress. The epitaxial growth of silicide nanostructures are eminently silicon compatible, so the nanostructures can be used as Ohmic or Schottky barrier contacts and as low resistive interconnections. Based on previous research, in this dissertation, the epitaxial growth of manganese and its silicides on Si(100)-2×1 restructured surfaces as well as on Si(111)-7×7 restructure surfaces was studied by ultra high vacuum scanning tunneling microscope. The main result of our work are summarized as follows:(1) Reactive epitaxial growth of manganese and manganese silicide on Si(100)-2×1 surfacesEpitaxial growth of manganese and manganese silicide on Si(100)-2×1 reconstructed surface at different temperatures was studied using ultra high vacuum molecular beam epitaxial-scanning tunneling microscopy system(UHVMBE-STM). The results showed that when the temperature of substrate was controlled from room temperature(RT) to 135℃in the growing progress, the products were manganese nanoclusters which were almost in the same size; when the substrate temperature was elevated to 210℃, manganese began to react with Si, and there were manganese silicide nanowires on the substrate; when it was up to 330℃, the nanowires on the substrate were totally replaced by stick-like manganese silicide and three-dimensional(3D) irregularly-shaped silicide islands. Along with the deposited temperature increasing, the relationship between the nucleation density of the products and the deposition temperature was well in accorded with that the classical nucleation theory of the two-dimensional (2D) island growth.When the coverage of Mn reached to 3ML, and the annealing temperature up to 540℃, the produced islands contain two kinds, the one is the irregular island, and the other is the flat island, this may be because that at this temperature Mn atoms reacted with Si atoms on the top surface and the product may be Mn5Si3 and MnSi. (2) Scanning tunneling microscopy study of manganese silicide thin films grown on Si(111)-7×7 surfaces by solid-phase epitaxy methodAnnealing of manganese thin films deposited on Si(111)-7×7 surfaces at a temperature range between 300℃and 650℃have studied in situ with a ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The deposited Mn atoms form an ordered nanocluster array on the Si(111) surface at room temperature. When the sample was annealed at 300℃, the Mn nanoclusters increased in size and the nanocluster array became disordered. When the annealing temperature reaches about 400℃, Mn begin to react with Si and the products consist of three-dimensional (3D) and tabular islands. The tabular islands are MnSi compound and the 3D islands are considered to be Mn-rich silicides. The MnSi tabular islands are the only product when the sample was annealed at 500℃. As the annealing temperature reached 650℃, the MnSi tabular islands transferred into large 3D islands which are likely to be Si-rich manganese silicides and the destroyed substrate surface recovered 7×7 structure through recrystallization.