An efficient molecular dynamics scheme for predicting dopant implant profiles in semiconductors

We present a highly efficient molecular dynamics scheme for calculating the concentration profile of dopants implanted in group-IV alloy, and III-V zi nc blende structure materials. Our program incorporates methods for reducin g computational overhead, plus a rare event algorithm to give statistical a ccuracy over several orders of magnitude change in the dopant concentration . The code uses a molecular dynamics (MD) model, instead of the binary coll ision approximation (BCA) used in implant simulators such as TRIM and Marlo we, to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and screened Coulomb potentials. Inelastic energy loss is accounted for using a Firsov model, and electronic stopping is described by a Brandt-Kitagawa model which contains the single adjustabl e parameter for the entire scheme. Thus, the program is easily extensible t o new ion-target combinations with the minimum of tuning, and is predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy, large angle implants, a nd for situations where a predictive capability is required with the minimu m of experimental validation. We give examples of using our code to calcula te concentration profiles and 2D 'point response' profiles of dopants in cr ystalline silicon, silicon-germanium blends, and gallium-arsenide. We can p redict the experimental profile over five orders of magnitude for [100] and [110] channeling and for non-channeling implants at energies up to hundred s of keV. (C) 1999 Published by Elsevier Science B.V. All rights reserved.