According to the 1999 International Technology Roadmap for Semiconductors the source/drain extension junction will be in the range of a few tens of nanometers for the up-coming 130 nm and 100 nm nodes. Although the junctions have to become shallower, a decreasing sheet resistance is also required. This paper summarizes the latest results for ultra-low energy implants employing conventional beamline systems. The formation of ultra-shallow junctions is influenced by several important factors, among these arc: Species, dose, and energy of the implant; a controlled gaseous ambient; and a controlled and reproducible thermal budget during rapid thermal annealing. All the data are analyzed and discussed with respect to the junction depth versus sheet resistance figure. The results indicate that BF2 produces shallower junctions with lower sheet resistance than energy-equivalent boron implants. This is shown to result from both a more efficient annealed dopant profile (i.e. more 'box-shaped') and a higher electrical activation. Other parameters that improve the R_s vs. X_J curve (i.e. move the curve "south-west") are limited gaseous concentration processing for oxygen and faster ramp-up and cool-down rates due to reduced diffusion.
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