Ion implantation and ion beam synthesis
For example, at conventional low- and medium-fluence (< 1016 ions/cm-2) ion implantation in microelectronics the concentration of introduced dopands is usually below the solubility limit of them in silicon. At certain annealing temperatures the impurity atoms are solved in Si and located on crystal lattice sites or, as a small part, remain as soluted interstitial atoms.
At ion beam synthesis (IBS) high-fluence (> 1016 ions/cm-2) ion implantation leads to a far-from-equilibrium state (supersaturated solid) which relaxes towards thermodynamic equilibrium during subsequent annealing by phase separation through precipitation and ripening (Ostwald-Ripening) of nanoclusters (NC) (see figure). Tailoring of the size and size distribution of NCs can be achieved by a control of implantation parameters (ion energy, flux and fluence, sample temperature) and annealing parameters (temperature, time, ambient conditions etc,). Phase separation of ion implanted, immiscible impurity atoms from the surrounding matrix, i.e. the formation of NCs, can also occur during the implantation process if the impurity atoms are sufficiently mobile due to collisional ion mixing; otherwise a subsequent annealing is always necessary.
The IBS of semiconducting NCs has attracted much interest due to their compatibility with CMOS technology and due to unique physical properties of charge storage in NCs. A great effort is devoted to their applications in new microelectronic devices, e.g. charge storing Si- and Ge-NCs in non-volatile memory circuits.
The figure shows cross-section views of the layer of phase separated Si in a 10 nm thick SiO2 layerimplanted with 1 keV Si+ ions. Cross-sectional transmission electron microscopy (XTEM) images for (a)