The effect of plasma exposure and annealing atmosphere on shallow junction formation using plasma source ion implantation

The effect of recoil-implantation and out-diffusion in plasma source ion implantation (PSII) on ultra-shallow p+/n junction formation has been studied. Because the wafer is directly exposed to plasma, diborane radicals in the plasma can be adsorbed on the wafer surface. The amount of recoil-implanted boron as an additive dose was measured. In the annealing process, increasing the nitrogen pressure from vacuum to 360 torr, decreased the boron out-diffusion. In addition, increasing the annealing time rendered the boron out- and in-diffusion severe. Considering recoil implantation, the wafers were implanted with a dose of 1.98×1015 atoms/cm2. The as-implanted wafers were subsequently spike-annealed at 1000 °C in nitrogen ambient. With implant energy of 0.5 and 1 keV, ultra-shallow junction depths of 360 and 380 Å, respectively, could be acquired. In addition, sheet resistance of 420 and 373 Ω/□ were obtained, respectively. This junction depth and sheet resistance prepared by PSII was found to satisfy next-generation memory-device doping technology.