Modeling Rapid Thermal Diffusion of Arsenic and Boron in Silicon

Abstract

Rapid thermal annealing (RTA) of high dose B and As implants is believed to produce large transients of point defects that may exist for the duration of the anneal (2–30s). Enhanced diffusion during RTA of boron implants >1015 cm−2is related to damage clusters at the peak of the range which can grow into cross‐grid dislocation networks. This process can create point defects through dislocation‐dislocation reactions and by nonconservative climb processes. Enhanced diffusion during RTA of high dose As implants is related to the amorphous Si surface layer formed during implantation. Regrowth of this layer into a defect‐free, crystalline layer is assumed to produce point defects which remain behind until they diffuse away. In the meantime, they contribute to enhanced As diffusion during the first 5–10s of the RTA cycle. Preamorphorization at low temperature eliminates this enhanced diffusion of As by eliminating the source of point defects presumed to be vacancies because of the associated defect removal in the implanted layer. Enhanced dopant diffusion has been modeled by overlaying an empirical transient point defect model on thermally assisted diffusion models associated with steady‐state furnace environments. A weighted exponential function was used to describe the transient process with a decay time of 4.4s.