Formation of ultrashallow p+-n junctions by low-energy boron implantation using a modified ion implanter

A conventional ion implanter (Varian Extrion Series 400 implanter) has been modified for the purpose of implanting at ultralow energies (0.5–5 keV). A 35 keV ion beam is decelerated to the desired energy just prior to impacting the substrate, thereby minimizing beam expansion and beam current reduction. The deceleration lens was designed to minimize the variation in energies and incident angles of implanted ions at the target. Computer simulation of the deceleration system indicated that less than a 2° variation in incident angles and a 50 eV variation in ion energies could be expected for 1 keV 11B implantation. Secondary-ion mass spectrometry revealed essentially identical as-implanted boron profiles for 1.35 keV 11B implanted with the modified system and 6 keV BF2 implanted without the modification, indicating successful deceleration. The modified implanter was used to form ultrashallow p+-n junctions via 1 keV 11B implantation coupled with rapid thermal annealing. Results indicate that ultralow-energy B implantation can be used to create junction depths as shallow as 50 nm.