In silicon technology it is thought that an electrically activated, ultra-shallow doping layer will be necessary in the future. The thickness of dopant extension layers under the source and drain electrode is predicted to reach 10nm in the year 2014. Boron is widely used as p-type dopant in silicon-device technology. Ion implantation is a useful method for the controlled introduction of impurities into a solid; however, defects are also introduced. High-temperature annealing after ion implantation recovers the crystallization of silicon and activates the implanted dopant. However, diffusion of the dopant occurs during the annealing, and it is difficult to keep the ultra-shallow dopant profile because boron is the fast diffuser in Si.
In this study, ultra-low-energy ion implantation below 100eV, which was close to the displacement energy of the solid, was examined to reduce the damage during implantation process. Boron ion of energy ranging between 30 and 500 eV, was implanted into intrinsic Si substrate (resistivity is > 10000 ohm cm) at temperatures ranging from RT to 1073K. Sheet resistance after boron implantation at the energy of 200 eV decreases from 100 k ohm to 4 k ohm with increasing the substrate temperature. The lowest sheet resistance of 2.8 k ohm was achieved at the ion energy of 300 eV and the substrate temperatures of 1073K. Junction depth of boron-doped layers was below 8 nm by the analysis of secondary ion mass spectroscopy.
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