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) form 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.