Activation of shallow, high-dose BF+2 implants into silicon by rapid thermal processing

Rapid thermal processing has been used to activate shallow p+ layers (∼0.1–0.15 μm) following BF+2 implantation (49 keV, 2–6×1015 cm−2) into amorphized silicon. For doses of 2×1015 cm−2, the shallow as-implanted boron profile was preserved, unlike the case of furnace annealing (900 °C, 30 min). Sheet resistance of 85 Ω/sq following rapid annealing was close to that calculated assuming 100% activation of dopants in their as-implanted distribution. At 6×1015 cm−2 dose, however, these same rapid annealing conditions (10–15 sec exposure to a 1250 °C heater) produce considerable dopant redistribution (≳2000 Å) with peak carrier concentration of ∼1020 cc−1, which is far below the as-implanted value of ∼1021 cc−1. A two-step anneal is described which permits shallow junctions of ∼1500 Å to be obtained for the 6×1015 cm−2 dose implants; however, maximum carrier concentration was still ≲1020 cc−1. The present data suggests that the concentration limit for activation of implanted boron encountered when furnace annealing is applicable even when annealing is carried out on a much shorter time scale of 10 sec versus 30 min.