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

A point defect diffusion model for ion beam induced crystallization and amo rphization at the amorphous/crystalline interface in Si is presented and sh own 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 bom bardment. Two mechanisms for the phase transition are proposed and shown to lead to nearly identical mathematical formulations. The first mechanism as sumes that the recombination of interstitial atoms at the phase boundary le ads to crystallization, while the same process for vacancies causes the gro wth of the amorphous layer. Based on the second mechanism, the recombinatio n of a Frenkel pair at the amorphous/crystalline interface produces the rec rystallization 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 in to account in the model. The defect processes are described by nonlinear di fferential equations. The defect reaction parameters are identified based o n experimental data. The results indicate that the transition from amorphiz ation to crystallization regime with increase in the substrate temperature is mainly due to strong reduction of vacancy concentration and a weak incre ase in the concentration of interstitial atoms. A number of experiments are simulated with the calculated parameters to test the developed model. (C) 2000 Elsevier Science B.V. All rights reserved.