Effect of fluorine on boron thermal diffusion in the presence of point defects

With the increased interest in the use of fluorine co-implantation with boron for boron diffusion suppression in MOSFET devices, it is important to understand the mechanisms by which fluorine reduces boron diffusion. Mechanisms, such as B-F chemical reaction, vacancy-fluorine clusters and fluorine-interstitials interactions have been proposed in the literature. In this paper, a point defect injection is done to investigate the mechanism responsible for boron TED and thermal diffusion suppression in F+ and B+ implanted silicon. A 5 keV, 7 × 1012 cm−2 B+ implant into silicon is used which is typical for halo implants in n-MOS. Three F+ energies, 5, 50 and 185 keV, are used. It is followed by rapid thermal annealing at 900-1000 °C for different times in N2 for an inert anneal and O2 for injection of interstitial point defects from the surface. Fluorine profiles for samples implanted with 185 keV F+ and annealed in N2 show two fluorine peaks at ∼Rp and ∼Rp/2. Under interstitial injection, the Rp/2 peak decreases in size and for long anneal times is completely eliminated, supporting an earlier claim that the Rp/2 peak is due to vacancy-fluorine clusters. The amount of suppression of both boron TED and thermal diffusion at 900 and 1000 °C anneal is correlated to the amount of fluorine remaining after anneal.