Exploring the sheet resistance variation with various beam current densities in low-energy ion implantation

The effect of ion beam current density, varied from 0.2 to 0.5 mA/cm2, on electrical characteristics of the shallow junction is investigated. Given an implant energy at 10 keV and a constant phosphorus ion dose of 2.25 x 1015 cm-2, the sheet resistance of the implanted Si after rapid thermal annealing (RTA) increases (from 66 to 70 Ω/sq) with increasing beam current density. To investigate the sheet resistance variation, thermal wave, cross-sectional transmission electron microscopy and secondary ion mass spectrometry (SIMS) are conducted. These analyses identify that dose rate and dose shift are the factors relating to the sheet resistance variation. SIMS depth profiles of phosphorous, before and after RTA annealing, reveal that implantation with higher beam current density leads to a smaller integrated dose. It is also found that dose rate induced crystal damage has no effect on the sheet resistance variation. The cause of dose shift is explored and it should arise from the neutralized ion species which are not detected by the Faraday cup