An extended "five-stream" model for diffusion of donor and acceptor dopants in Si during the production of ultrashallow π-v junctions

Abstract

The ultrashallow p-n junctions (USJ) in modern VLSI technology are produced by low-energy high-dose ion implantation of donor or acceptor atoms into a Si waver with subsequent rapid thermal annealing (RTA) for healing the lattice defects and electrical activation of the dopants. During RTA, the phenomenon of transient enhanced diffusion (TED) is observed, which hinders obtaining the optimal concentration profile of the dopants and thus the required current-voltage characteristics of USJ. Solving the intricate problem of TED suppression is impossible without mathematical modeling of this complex phenomenon. However, modern software packages such as SUPREM-4 (Silvaco Data Systems), which employ the so-called "five-stream" approach, encounter severe difficulties in predicting TED. In this work, an extended "five-stream" model for diffusion of implanted dopants in monocrystalline Si during RTA is developed taking into account all the possible charge states of both point defects (vacancies and self-interstitials) and diffusing pairs ("dopant atom-vacancy" and "dopant atom-silicon self-interstitial"). The sink/source terms describing reactions between differently charged pairs and point defects are derived. New initial conditions are formulated basing on the experimental concentration profiles of dopants determined by the second-ion mass spectrometry and the profiles of "net" vacancies and self-interstitials after implantation, which are obtained by Monte-Carlo simulation.