A study of ultra-shallow implanted dopant profiles in silicon using BC and MD simulations

Abstract

The validity of the binary collision approximation for the calculation of low-energy implanted dopant profiles is investigated using IMSIL in its binary collision (BC) mode and in a newly added molecular dynamics (MD) mode. The MD mode takes only ion-target atom interactions into account, and considers lattice vibrations and electronic stopping in the same way as the BC mode. Good agreement is found between predictions of the new MD code and the results of recent round robin simulations for 200 eV B in Si. This is also true for the BC simulations if the time integral is taken into account in the calculation of the turning points of the trajectories. In contrast to common belief, it is not necessary to use a special treatment of “simultaneous collisions”. Simulations of B implantations into Si parallel to the [110] or [100] direction or tilted by 9° with respect to the [100] direction show that the binary collision approximation may be used at least down to implantation energies of 200 eV and that the errors are still moderate at 50 eV. Moreover, it is found that profiles of B implanted near the [100] direction do not depend on the tilt angle around 200 eV and below.