Ultrashallow boron-doped junctions in silicon have been investigated using secondary-ion mass spectroscopy and four-point probe technique. The junctions were obtained by implanting B+ ions into n-type Si(100) at 200 eV to doses of 1.5 x 10(14) and 6 x 10(14) cm-2 and at substrate temperatures in the range 30-900-degrees-C during B implantation. Both post-implantation in situ annealing by electron bombardment heating and rapid thermal annealing in a separate system were employed. The results show that sub 20 nm p+ n junctions are obtained without the need for further processes such as preamorphization and high-temperature annealing.