Computer modeling of single-layer nanocluster formation in a thin SiO_2 layer buried in Si by ion mixing and thermal phase decomposition

摘要

A single sheet of Si nanoclusters with an average diameter of about 2nm has been formed in a 30nm Si/7nm SiO2/Si layer stack by 50 and 60keV Si+ ion-beam mixing at room temperature and fluences between 8.510(15) and 2.610(16)ions/cm(2) and by subsequent thermal annealing at a temperature above 1000 degrees C. Computer modeling of the process is accomplished by TRIDYN dynamic ballistic simulation of ion mixing and subsequent lattice kinetic Monte Carlo simulation of the phase decomposition of substoichiometric silicon oxide into Si nanoclusters in a SiO2 matrix. The simulation algorithms are briefly described with special emphasis on the choice of governing parameters for the present system. In comparison to the experimental results, it is concluded that the predicted ion mixing profiles overestimate the interface broadening. This discrepancy is attributed to the neglect of chemical driving forces in connection with thermal-spike induced diffusion, which tends to reconstitute the Si/SiO2 interfaces. With a corresponding correction and a suitable number of Monte Carlo steps, the experimentally obtained areal densities and average diameters of the nanoclusters are successfully reproduced.