Transient nucleation and manipulation of nucleation sites in solid-state crystallization of a-Si films

Abstract

Solid-state nucleation of Si crystals in a-Si films is controlled by Si ion implantation prior to the isothermal annealing. The process of the nucleation includes a long transient period that causes the diminishing shape of the grain size distribution (GSD). The parameters appearing in the kinetic theory of transient nucleation are estimated from the GSD in a-Si. It is found that the ion implantation reduces the steady-state nucleation rate and elongates the time lag, while the growth rate is almost constant. The dependence of the above parameters is simulated based on the model of heterogeneous nucleation. It is qualitatively suggested that the suppression of the nucleation can be attributed to the modification of the interface to the SiO2 underlayer such as the changes in the self-diffusion or in the interfacial energy. When the nucleation rate is spatially controlled in the plane of the film, a small portion provides the artificial nucleation site. If the sites are periodically placed, the GSD shrinks to have a shape like log-normal. A model for the manipulated nucleation site explains the shape of the GSD, and how a single nucleus is selected to grow in the site.