Nanocluster Synthesis by High-Fluence Ion Implantation in Thin Films Studied by MC Simulations

The nanocluster (NC) formation by phase separation of implanted impurity atoms from the host matrix has been studied. The deposition of impurity atoms by high fluence Si+ implantation into SiO2 was simulated using the computer code TRIDYN including dynamic target changes due to by sputtering, ion mixing and swelling. The depth profiles differ considerably from that predicted by the TRIM code. The TRIDYN profiles were used as input for kinetic lattice Monte-Carlo simulations of phase separation. The interaction of the Si atoms in the SiO2 layer is approximated by the nearest-neighbor Ising Hamiltonian, while the time evolution of the system is governed by the importance sampling of configurations according the Metropolis algorithm. The simulations show that NC formation proceeds via (i) nucleation and growth at low impurity concentrations, and via (ii) spinodal decomposition and interface minimization at high concentrations. Due to the small distance between the NCs and the SiO2/Si interface, Si atoms condense steadily onto the substrate and a zone denuded by NCs is formed at the interface. As the mass conservation is violated for impurity atoms within the SiO2, the description of the NC coarsening by the Lifshitz-Slyozov-Wagner theory is not applicable. Rather, the evolution of the NCs is determined by the competition of coarsening and dissolution.