Boron was implanted into n-type Si at energies from 500 eV to 1 keV and doses near 1 E14 cm-2and 1E51 cm−2. Electrical activation was achieved by rapid thermal annealing (RTA) in nominally pure N−2and 0.1% 02 with the fastest available heating rates of up to 150 °C/s, cooling rates up to 80 °C/s, and included “spike” anneals with minimum dwell time at peak temperature. Measurements of sheet resistance, Hall coefficient, and secondary ion mass spectroscopy profiling were used to determine dopant activation and diffusion. Surface oxidation was studied by film thickness ellipsometry. Analyses of electrical transport measurements are used to relate junction depths to sheet resistance and their dependence on annealing temperature and time. For spike annealing, junction leakage and adequate activation limits the minimum practical temperature while diffusion limits the maximum practical temperature for formation of shallow junctions.