Percolation of Electron Tunneling between Si Nanocrystals Synthesized in Thin SiO2 Films by Ion Implantation

The controlled fabrication of a narrow layer of Si nanocrystals (NCs) in thin SiO2 films for multi-dot non-volatile memories (NC memory) is still a considerable materials issue, which will be addressed in this contribution. The synthesis of NCs by Si+ implantation of SiO2 followed by a thermal treatment aims at an optimum NC density. A NC density being as high as possible is required in order to achieve a substantial threshold voltage shift of the MOS transistor. On the other hand, the advantages of the NC memory, as good scalability and data retention, are lost at too high NC densities. Then NC’s charge can spread over neighboring NCs by direct e- tunneling, i.e. due to electrical in-plane percolation paths. One single oxide defect could discharge several electrically percolated NCs.
This contribution is devoted to the trade-off between these two optimization routes. The Si NC formation by nucleation, growth and Ostwald ripening in low-energy Si+ implanted SiO2 is predicted by kinetic lattice Monte Carlo simulations. On the basis of these simulations, the dependence of the Si NC density, the distribution of the NC spacing as well as the threshold for extended electron tunneling paths are predicted. Thus, process conditions could be identified, where NCs align in narrow layer at high density but are sufficiently electrically isolated.