Dislocation formation in silicon implanted at different temperatures

The formation of pre-amorphization damage, i.e. dislocations formed by the agglomeration of silicon interstitials, requires a minimum amount of implant damage. The amount of damage can be altered by changing the implant temperature or current density, which can influence dislocation formation. We studied this using cross-sectional transmission electron microscopy for boron and indium implants at kiloelectronvolt and megaelectronvolt energies respectively. Dislocation formation for boron implants, where only simple cascade densities are generated, does not depend on implant temperature or current density. For 1 MeV indium implants, where the implant damage consists mainly of amorphous zones, an increase in critical dose for dislocation formation by a factor of approximately 3 is observed if the implant temperature is raised. This is attributed to the interaction of point defects with the amorphous zones during the elevated temperature implant. Implants of 150 keV indium at room temperature result in complete amorphization before the critical amount of crystal damage is reached. Here, end-of-range loops (EOR-loops) from after annealing. Increasing the implant temperature suppresses amorphization, and pre-amorphization damage is observed if a critical amount of crystal damage has been generated. EOR-loop formation results from the agglomeration of silicon interstitials from the amorphous-crystalline transition region. If the number of interstitials in this region is lowered by carrying out the implant at low temperature, EOR-loop formation can be suppressed. This is shown by comparing amorphizing germanium implants done at room and liquid nitrogen temperatures

An Efficient Molecular Dynamics Scheme for the Calculation of Dopant Profiles due to Ion Implantation

We present a highly efficient molecular dynamics scheme for calculating the concentration depth profile of dopants in ion irradiated materials. The scheme incorporates several methods for reducing the computational overhead, plus a rare event algorithm that allows statistically reliable results to be obtained over a range of several orders of magnitude in the dopant concentration. We give examples of using this scheme for calculating concentration profiles of dopants in crystalline silicon. Here we can predict the experimental profile over five orders of magnitude for both channeling and non-channeling implants at energies up to 100s of keV. The scheme has advantages over binary collision approximation (BCA) simulations, in that it does not rely on a large set of empirically fitted parameters. Although our scheme has a greater computational overhead than the BCA, it is far superior in the low ion energy regime, where the BCA scheme becomes invalid.Comment: 17 pages, 21 figures, 2 tables. See: http://bifrost.lanl.gov/~reed