Profiling Shallow As Implants with Low-energy Cs Bombardment on a Modified Cameca IMS-4f

Abstract

The inability to decouple primary ion beam energy and incidence angle in Cameca-type magnetic sector SIMS instruments makes profiling shallow As implants (≥20 keV), using typical Cs + bombardment conditions and negative secondary ion detection, problematic. A Cameca IMS-4f has been modified to lower the Cs+ primary beam impact energy by concomitant decreases in primary ion beam energy and sample potential. Evaluation of the instrument's performance after modification shows about a 35% improvement in depth resolution as defined by the decay length, λ, of a 20 keV As implant profile. This is accompanied by a decrease in useful yield, resulting from the lower sample potential, of about a factor of eight. Comparison of Cameca IMSD-4f data from a 5 keV As implant with data obtained on a quadrupol-based instrument suggests that the Cameca's fixed incidence angle at low energy is the limiting factor to further improvements in depth resolution. Nevertheless, the ease and relatively low cost of modification makes this an attractive approach to increasing the range and flexibility of existing Cameca SIMS instruments.