Alternating Reversed Scanning Sequence for Improved Within-Wafer Uniformity During Nonmelt Laser Annealing of Arsenic-Implanted Silicon

Beyond the 45-nm technology node, nonmelt laser thermal annealing (LTA) is a potential candidate to replace the spike rapid thermal annealing (RTA) for the formation of ultrashallow and highly activated source/drain extension junctions. However, one major drawback of LTA is that it is ineffective in the removal of implantation-induced damage. As such, arsenic deactivation, as a result of cluster formation due to the release of excess interstitials from the end-of-range (EOR) region, is observed when a post-LTA thermal budget is applied. Since conventional LTA comprises localized heating using a laser beam scanning the wafer front-side in a nonalternating sequence, different portions of the wafer will experience varying post-LTA thermal budget from the hotplate, depending on when the laser beam scans through it. Because dopant deactivation increases as the post-LTA thermal budget increases, severe degradation of the within-wafer uniformity is observed. To address this problem, a multiple-pulse, alternating reversed laser scanning technique is implemented to average out the differences in post-LTA thermal budget across the wafer between each pulse. Using such a scheme, the variations in subsequent dopant deactivation across the wafer is reduced and significant uniformity improvement of up to 50% is observed.