Two-dimensional effects on ultralow energy B implants in Si

A systematic work has been carried out in order to optimize sample preparation and scanning capacitance microscopy (SCM) on double beveled samples. The method allowed us to enhance depth and lateral resolution and it has been applied to characterize two-dimensional profiles of ultralow energy B implants in Si after diffusion. Implants have been performed into patterned wafers with different stripe widths ranging from 0.5 to 5 microns. B transient enhanced diffusion is strongly reduced with decreasing feature size below about 2 microns. This effect has been related to the high interstitial diffusivity with respect to B. It is even enlarged for lateral diffusion due to the interstitial recombination under the SiO2 mask at the Si/SiO2 interface. The implications for the formation of ultrashallow junctions in device structures are also discussed.