Ion beam induced amorphous-crystalline phase transition in Si: quantitative approach

A point defect diffusion model for ion beam induced crystallization and amorphization at the amorphous/crystalline interface in Si is presented and shown to be successful in providing a quantitative explanation for the phase transition kinetics. The model takes into account a minimum set of the most plausible elementary processes of point defects in crystalline Si as well as the formation and dynamic annealing of disordered regions during ion bombardment. Two mechanisms for the phase transition are proposed and shown to lead to nearly identical mathematical formulations. The first mechanism assumes that the recombination of interstitial atoms at the phase boundary leads to crystallization, while the same process for vacancies causes the growth of the amorphous layer. Based on the second mechanism, the recombination of a Frenkel pair at the amorphous/crystalline interface produces the recrystallization of a small volume, whereas excess of the vacancies provokes the process of amorphization. Contribution to amorphization from disordered regions, vacancies, and divacancies at the phase boundary is also taken into account in the model. The defect processes are described by nonlinear differential equations. The defect reaction parameters are identified based on experimental data. The results indicate that the transition from amorphization to crystallization regime with increase in the substrate temperature is mainly due to strong reduction of vacancy concentration and a weak increase in the concentration of interstitial atoms. A number of experiments are simulated with the calculated parameters to test the developed model.