Role of point defects in the transient diffusion and clustering of implanted boron in silicon

Abstract

The influence of a supersaturation of point defects on the diffusion and clustering of boron in crystalline silicon is discussed. It is shown that, with suitable approximations, a generalized boron solubility can be derived which is an inverse function of the diffusion enhancement. This concept is applied to the problem of anomalous transient boron diffusion after medium dose implantation, where the observed boron profile consists of a relatively static peak and a mobile diffusion tail. The model predicts that diffusion starts first in the low concentration part of the boron profile, developing more slowly at higher concentrations as the point defect supersaturation relaxes towards equilibrium. Previous models have assumed that anomalous boron profile shapes arise from the spatial distribution of implant damage or channelled ions. The new model provides a more promising interpretation of recent experiments in which the damage profile has been separated from the boron-doping profile.