Structural and Electron Transport Properties of Ultrathin SiO2 Films with Embedded Metal Nanoclusters Grown on Si

During the last decade, much attention has been focused on the investigation of the semiconductor and metal nanocrystals (NCs) embedded in the dielectric matrices. The interest was generated by the promising applications of the nanocomposite structures in nanoelectronics. Particularly, the semiconductor or metal NCs embedded in the dielectric layer of a metal–insulator–semiconductor field-effect transistor (MOSFET) may replace the SiNx floating gates in the nonvolatile memory devices, allowing for thinner injection oxides, and subsequently, smaller operating voltages, longer retention times, and faster write/erase speeds (Tiwari et al., 1996). The performance of such memory devices strongly depends on the parameters of NCs arrays, such as their size, shape, spatial distribution, electronic band alignment, as well as on the possibility to make reproducibly the uniform tunnel transparent oxide films. The charge accumulation in the NCs can be limited by the single-electron effects such as Coulomb blockade provided that the cluster has a sufficiently small size, which, in principle, allows for the single electron memory devices (Yano et al., 1994; Guo et al., 1997). Up to the present time, the thin film nanocomposite structures have been studied extensively (Ruffino et al., 2007). The most popular methods to fabricate NCs in the dielectric matrices include low-energy ion implantation with subsequent annealing (Bonafos et al., 2000), the deposition of the non-stoichiometric oxide layers also followed by the annealing (Tiwari et al., 2000), and the deposition of the multilayered oxide/NC structures (Ruffino & Grimaldi, 2007). The main disadvantage of the ion implantation is a considerable thickness of the layer where the NCs are nucleating, and also a rather large dispersion in the NCs’ sizes. The latter fact is a direct consequence of the NCs’ nucleation by Ostwald ripening. The largest NCs with the minimum density are concentrated at the mean projected ion path, while the smaller NCs with higher density are nucleated in the tails of the implanted ions depth distribution. Recent attempts to improve the ion implantation technique to address the above problems are concerned mainly about the reduction of the ion energy down to ~ 1