CRITICAL ANGLES AND LOW-ENERGY LIMITS TO ION CHANNELING IN SILICON

Channeling theory is reviewed and some improvements are presented. Sev eral models for the calculation of critical approach distances, critic al angles, and minimum energies for channeling are compared. While the influence of the choice of the interatomic potential is small, existi ng models of the critical approach distance yield rather different res ults particularly in the case of planar channeling. An improved model is proposed based on binary collision simulations. A low-energy limit to ion channeling along a given axis or plane is defined by equating t he critical approach distance with the channel radius. Minimum energie s for channeling and critical angles as a function of energy are prese nted for B, P, and As in Si along the major channels. In the case of B in Si from these data channeling maps are constructed and compared wi th channeling maps obtained from binary collision simulations. The pre dicted minimum energies for channeling are shown to agree well with a large number of experimental data obtained by SIMS, thermal wave, and backscattering yield measurements. Finally, the relevance of the criti cal angles and of calculated channeled fractions to ion implantation i s discussed.