Study of ultra-shallow p+n junctions formed by excimer laser annealing

Excellent ultra-shallow p+n junctions have been formed by thermally treating the BF2+-implanted Si samples by excimer laser annealing (ELA) at 300–400 mJ cm−2 with post low-temperature long-time furnace annealing (FA) at 600 °C. A junction with a leakage current density lower than 20 nA cm−2 and a sheet resistance smaller than 200 Ω □−1 can be well achieved. No considerable dopant diffusion is observed by using this low-thermal-budget annealing process. However, by simply using the ELA treatment at 300–400 mJ cm−2, the resultant junction shows a leakage current density as high as 104 nA cm−2 and a peripheral leakage current density of 103 nA cm−1. The large junction leakage is primarily due to the leakage current generated within the junction region near the local-oxidation-of-silicon (LOCOS) edge, and which is substantially caused by the ELA treatment. The large peripheral junction leakage current density can be significantly reduced to be about 0.2 nA cm−1 after a post low-temperature FA treatment at 600 °C. As a result, the scheme that employs ELA treatment with post low-temperature FA treatment would be efficient for forming excellent ultra-shallow p+n junctions at low thermal budget.