Two-dimensional profiles of ultralow-energy B implants in Si after diffusion have been studied in detail by scanning capacitance microscopy in connection with a double beveling technique to enhance depth and lateral resolution. Implants have been made into patterned wafers with different feature sizes ranging from 0.8 to 5 μm. It is demonstrated that the B transient enhanced diffusion is strongly reduced with decreasing feature size below about 2 μm. This effect is related to the increasing effect of interstitial lateral out-diffusion under the SiO2 mask. The implication for the formation of ultrashallow junctions in device structures is discussed.