Role of Boron Atoms on Fluorine Diffusion under Various Stages of Annealing

Abstract

We demonstrate the role of boron atoms on fluorine diffusion through experiments on the preamorphized samples uniformly doped with boron under three stages of annealing. In the preannealing stage, during and after implantation at room temperature, fluorine diffusion is significantly retarded by the high background boron concentrations. Similarly, in the second stage of annealing, at 550°C, the substrate condition remains amorphous and the fluorine migration is suppressed in the presence of boron. We suggest that negatively charged fluorine atoms are trapped at dangling bonds positively charged by boron atoms by the Coulomb attractive force. In the third stage of annealing, at 800°C, fluorine atoms migrate anomalously and accumulate at the 0.8 projected range of fluorine only in the samples doped with boron. This result suggests that the background boron enhances fluorine migration by the dissolution of small defects or the prevention of the formation of small defects in the recrystallized region, resulting in fluorine accumulation at the damaged area associated with the implantations.