Reducing arsenic to germanium cross contamination with isotopically enriched SDS 72GeF4

Pre-amorphization (PA) implants are becoming increasingly popular in CMOS processing as junction depths decrease. As an isoelectric species, germanium has demonstrated a capability for performing such implants into silicon. The gaseous vapor of liquid GeF₄ is a common source of germanium for ion beams. The isotope with the atomic mass 74 is usually chosen for implantation because of its high natural abundance. However, cross contamination issues exist with similar mass dopants such as arsenic. The use of isotopically enriched ⁷²Ge to more than 50% abundance improves the available beam current and reduces potential cross contamination. The use of the isotopically enriched ⁷²Ge safe delivery system (SDS) source has been evaluated in a high current implanter. The mass resolution of this high current implanter is demonstrated. The surface and energetic cross contamination levels using both natural abundance GeF₄ and a SDS GeF₄ enriched source are compared using SIMS. The effectiveness of a between species purge, when using different implants, to reduce the energetic arsenic contaminant is presented