  Modeling of the phosphorus radiation-enhanced diffusion in the course of
implantation of high-energy protons into an elevated-temperature silicon
substrate and during its treatment in a hydrogen-containing plasma with
addition of a diffusant has been carried out. It follows from the results
obtained that the radiation-enhanced diffusion occurs by means of formation,
migration, and dissociation of "impurity atom -- silicon self-interstitial"
pairs being in a local thermodynamic equilibrium with substitutionally
dissolved impurity atoms and nonequilibrium point defects generated due to
external irradiation. The resulting value of the average migration length of
nonequilibrium silicon self-interstitials decreases from 0.19 micrometer for
proton energy of 140 keV to 0.09 and 0.08 micrometer for energies of 110 and 80
keV, respectively. The decrease of the average migration length with the proton
energy can be due to the interaction of silicon self-interstitials with the
vacancies generated at the surface or with the defects formed in the phosphorus
implanted region. Based on the pair diffusion mechanism, a theoretical
investigation of the form of impurity profiles that can be created in thin
silicon layers due to the radiation-enhanced diffusion was carried out. It is
shown that depletion of the uniformly doped silicon layer occurs during plasma
treatment except for the silicon -- insulator interface where a narrow region
with a high impurity concentration is formed. The results of calculations give
a clear evidence in favor of further investigation of various doping processes
based on the radiation-enhanced diffusion, especially the processes of plasma
doping, to develop a cheap method for the formation of strictly assigned
impurity distributions in the local semiconductor domains.
