Deactivation Induced Within Wafer Nonuniformity During Nonmelt Laser Annealing of Arsenic and Phosphorus Implanted Silicon

In the setup for nonmelt laser spike anneal (LSA), the wafer is mounted with the front-side facing the laser beam and backside facing the heated hotplate. When arsenic or phosphorus-implanted silicon is subjected to LSA, sheet resistance degradation, indicative of dopant deactivation, is observed when the post-LSA thermal budget provided by the heated chuck (hotplate) is increased. This additional thermal budget is associated with the chuck temperature and duration a wafer is left on the chuck after LSA. The deactivation is believed to occur due to the ineffective removal of implantation damage by LSA, giving rise to the release of point defects during the post-LSA thermal cycle that aids inactive clusters formation. The observed phenomena severely degrades the within wafer uniformity since LSA is a localized heating process that relies on scanning the laser beam across the whole wafer. As such, different portions of the implanted silicon wafer will remain on the hotplate for varying durations depending on when the laser beam scans through a particular spot. By adopting a dual step source/drain anneal scheme that incorporates a spike rapid thermal annealing condition sufficient to anneal out the implantation damage prior to LSA, the within wafer nonuniformity issue can be rectified.